Operator 1 chapter 5 sedimentation and floatation

Water information that is important

1.000 specific gravity at 4 degrees C or 39 F Weights 8.34 pounds per gallon

Start up procedures for SD units

Always thoroughly inspect entire unit before allowing wastewater to enter -remove all debris and tools form unit -follow wastewater and solids paths through unit be sure to understand how the unit works and what happens when all valves or witches are open or closed -lubricate equipment -allow unit to run for2 hours Observe operation fo unit, check proper alignment and clearance -keep bolts tight -fill unit with water -allow unit to fill and effluent to flow over effluent weirs -inspect tank and pipes for leaks repair any, if unit has not been tested for leaks, allow unit to sit 24 hours without any influent if water level drops more than inch, find leak and repair it -make sure no pipes are plugged Operate values to be sure they operate freely and watertight -divert wastewater to the unit, leave dome vent open until gas production starts, teh vent must be open to atmosphere to prevent gases from accumulating in confined spaces, time for gas production to start will depend on temp of sludge under digestion, the warmer the sludge shorter time for gas to form, gas will start being produced after approximately 3 weeks -chlorinate final effluent -add lime to digestion unit if pH is below 7 sample supernatant by lowering an adjustable overflow tube in scum pit and measuring pH if pH is closely controlled these units may be started without seeding with digested sludge, lime should be adde don very first day during start up and dialysis until pH remains above 7 recommended lime doses on page 149

Shutdown procedures for clarifiers

Annually during low flow each clarifier should be shut down for inspection, this prevents serious problems and filaures in future - divert flow to other clarifiers and close the influent and effluent control gates of clarifier being shut down -pump all remaining sludge to digester or to a solids handling system - dewater clarifier by draining remaining wastewater to headwords or pumping remaining wastewater to other claviers -hose down the walls floor and equipment inside clarifier -inspect clarifier with start up procedures -Repair or replace broken equipment -repaint metal surfaces that ahve lost their protective coating or are showing signs of corrosion

Safety in clarifer gases

Any enclosed area like wet well for pump, may contain dangerous gases if ventilation is not proper Hydrogen sulfide chlorine carbon dioxide carbon monoxide gasoline and petroleum products and methane are all possible to find

Solids in clarifier

Are scrapped to one end in rectangular clarifiers and middle in circular clarifiers into a sump From sump, solidsa re pumped into sludge handling or disposal system Include sludge digestion, vacuum filtration, filter presses, incineration, land disposal, lagoons, and burial

Combined sedimentation digestion unit flow

Bar screen Primary settling - effluent to treatment system oxidation ponds or land treatment Sludge digestion Digested solids to drying beds Anitary landfill

Sludge volume index

Calculation that indicates the tendency of activated sludge solids or thicken or become concentrated during the sedimentation thickening process SVI is calculated in following manner Allow mixed liquor sample from aeration basin to settle for 30 minutes Determine suspended solids concentration for sample of mixed liquor Calculate SVI by dividing measured or observed wet volume in milliliter per liter, of settled sludge b the dry weight concentration of MLSS in grams / liter

4. Quality of supernantant return from digester check item

Check it

Rectangular clarifiers start up procedure

Check tank hoppers channels control gates weirs bearings grease lines and drive alignment Sludge collectors differ in rectangular clarifiers compared to circular Wooden crosspieces or flights are laid across the tank and each end is attached to endless chain along both sides of tank Chains attached to cross peices connect together to for collector mechanism Driven.by connecting shaft and sprockets taht drag crosspieces along rails imbedded in the floor fo tank Each flight has metal wearing shoes Make sure that chain on one sides is not one or two links longer or shorter than the chain on opposite side if this occurs wooden flights will ran at angle across tank This can cause sludge to pile higher on trailing side or cause flights to hang up with resultant severe damage to flights

Avoiding falls

Clean up oil and grease slicks on walkways promptly Walking not running when near open tanks Avoid clutter pick up and store hoses ropes cables tools buckets and lumber Not sitting on climbing through or hanging over gaurd rails or handrails Providing gratings deck covers or safety chains on or around openings to pits below floor level

Bulking

Clouds of billowing sludge that occur throughout secondary clarifier and sludge thickeners when the sludge does not settle properly In activated sludge process, bulking is usually caused by filamentous bacteria or bound water

Carbon monoxide

Colorless odorless nonirritating flammable explosive usually around gas engines or leaky gas systems in poor ventilated places Interferes with blood ability to carry oxygen kills by oxygen depreiveation

Plant operation layout key points

Control gates must be suitable located in order to isolate each clarifier Baffles weirs or skirts should be capabale of controlling clarifier inlet velocities Collector mechanisms and drive units must ahve protective devices such as. Shear pins clutches stall alarms and on off switches Make sure suction type mechanisms for removing sludge have provisions for removal from center floor fo clarifer in case the suction mechanism fails and also for draining clarifer Surface skimmer for scum removal provided Scum box should e located with consideration given direction of prevailing winds and to removal of any accumulated flaotables on water surface Hose bibs high pressure water faucets should be conveniently located with respect to scum boxes launders weirs clarifer center columns for easy washdown Sampling equipment should be easiely accessable Clarifer flow adn lvel controllers must be properly located for operational propose Grease or scum weirs must be at proper depth for scum control and removal of floating material from the water surface

Skimmed solids

Disposal of these are varied by plant Some bury it with material cleaned off bar screen, others incinerate it or pump it into digester Even though pumping skimmed solids to a digester is not considered good practice because skimming can cause operational problems, it is common practice

Cleaning mechanically cleaned tanks

Do not need to be shut down for cleaning, doing so can cause septic conditions rapidly If sludge is not removed at reusable intervals Can vary from 30 minutes to 8 hours depending conditions, for when sludge must be removed

Clarifier efficiency formula

Efficiency (%) = in-out/in X100

Methane

Explosive odorless and may cause asphyxiation

Sedimentation and flotation unit

Found after the grit channel, Called settling tanks, sedimentation tank, clarifier Most common name is primary clarifier since it helps to clarify or clear up the wastewater Function is to remove setteable and floatable solids Other types of treatment following primary clarifier convert more solids into settleable form Secondary clarifiers found later in the system are considered part of other types of processes, but functions the same as the primary clarifier

Hydrogen sulfide

H2S causes rotten egg odor Can quickly dull sense of smell Readily combined with oxygen to form sulfuric acid, which dissolves concrete If you breathe it in can irritate respiratory system bronchitis pulmonary edema These effects occur due to alkali sulfide when fans comes into contact with moist tissue extremely toxic flammable and explosive when mixed with right amount of air

Hydrostatic system

In hydrostatic sludge removal system Surface of water in clarifier is higher than the surface of the water in teh sludge well or hopper This difference in pressure head forces sludge from teh bottom fo clarifier to flow through pipes into sludge well or hopper

Abnormal conditions for SD system

Inflows are higher than desig flows due to stormwater inflow and infiltration Solids loadings are high due to seasonal or industrial discharges Toxic substances or high or low pH liquids are relased into collection system With a single combined sedimentation digestion unit there is little an operator can do in terms of adjusting valves or directing flows, if they occur occasionally and upset unit, provision should be made to construct emergency pond to hold abnormal flows until tehy an be treated

Equipment and process failures caused by operator errors

Insufficient frequency or time for removing sludge Poor equipment maintenance and housekeeping Insufficient knowledge of equipment or treatment processes related to - laboratory analysis -clarifier loadings like Flows million gallons per day Detention time Hr Surface loading Gallons per day / square feet Solids in pounds of solids/day.square feet (secondary clarifier Solids balance in lbs in to lbs out by day Inability to recognize a mechanical or electrical problem Not restarting a drive mechanism that tripped out during a momentary power failure such as thunderstorm

Maintenance of SD unit

Lubricate all equipment in accordance -if any tools or other objects fall into clarifer stop rotation and remove tool or object -if scraper mechanism stops moving, determines the cause and remove it before attempting to start mechanism again do not tamper with overload switch adjustments in an attempt to force machine to operate agaisnt the overload

Role of operator in clarifier performance

Make sure that accumulated settled soldisa re removed from bottom fo clarifier before septicity and gasification take place Surface flat tables like oil and grease are continuously and regularly skimmed and removed from water to prevent flaotalbes from reaching downstream secondary treatment and disinfection processes

Gasoline

May cause fires ro explosions displace oxygen as well

MPN

Most probably number of coliform group organisms per unit volume of sample water expressed as a density or population of organisms per 100 milliliter of sample water

Carbon dioxide

Odorless stastesless can displace oxygen choking you Concentration of 10 percent or 100000 ppm can produce unconsciousness and oxygen deficiency

Troubleshooting plant clarifer problems

Page 121-128

Trickling filter clarifiers

Produce filter sloughings from biological action in filter Material is generally quite high in biochemical oxygen demand and lowers effluent quality

Conclusive method for measuring efficiency of clarifiers

Proper analysis of samples Frequency of testing and expected ranges vary by plant Strength of wastewater freshness characteristics of water supply weraher and industrial wastes all service to affect common ranges of test results

Return sludge rates

Range from 10-50 percent of plant inflow Can reach 100 if activated sludge process was upset, but running sludge rate return too hgih can result in turbulance inside tank upsetting sludge blanket

Sludge volume index formula

SVI (mL/gram) = settled sludge volume/sample volume (Ml/L)/ suspended solids concentration (Mg/L) X 1000mg/1gram

Representative sample

Sample portion of material water or wastestream that is nearly identical in content and consistency as possible tot that of larger body being sampled

Secondary tanks vs primary tanks

Secondary tanks following trickling filters can be either circular or rectangular and have sludge collector mechanisms similar to primary clarifers About same detention time for secondary clarifiers but surface loading and weir overflow rates are generally lower due to les dense characteristics of secondary sludges Detention time is 2-3 hours Surface loading is 800-1200 gallons per day per square feet Weir overflow is 5000 to 15000 gallons per day per lineal foot of weir

Launders

Sedimentation tank effluent troughs consisting of overflow weir plates

Pumps used to pump trickling filter sludges

Similar to raw sludge pumps and may be piston progressive cavity or centrifugal type pumps

Toxic

Substance that is poisonous to living rongaism Can be classified in terms of physiological actionlike irritants asphyxiants systemic poisons and anethsetics and narcotics Irritants are corrosive substances that attack the mucus membrane surfaces of the body Asphyxiates affect breathing

Surface loading formula

Surface loading (gallons per day/ square ft) = flow in gallons per day /square area (square ft) Or metic Surface loading in (cubic meters per day/square meters) = flow in cubic meters per day / square area square meters

Surface loading rate formula

Surface loading (gallons per day/square feet)= flow (gallons per day)/surface area (square Feet)

Strains adn overexertion prevention

Use proper tools ro equipment to Move stuck or reluctant valves or lift heavy objects

Procedure to place additional clarifers on line or off line

When placing clarifier on line open inlet gate to clarifier -Operate the sludge collector skimmer and pumps with normal daily operating procedures -When taking clarifier off line, divert wastewater begin treated to other clarifers by closing inlet gate -Collect sludge on bottom of clarifier and pump the sludge from hopper if it is thick enough to pump, thickness of sludge can be determined by the sound fo sludge pump, and use of thickness measuring sensors or observation of sludge through sight glass -the skimmer and sludge collector mechanisms may be left on or turned off depending on conditions of tank contents with regard to sludge left in clarifer or scum on water surface This procedures assumes clarifers have only been off or on line for less than 2 days If clarifer taken off line, it is assumed to be back on in 2 days Number of secondary clarifiers on line stay constant while primary fluctuate, but secondary can change with increases or decreases in seasonal flow During extreme cold, make sure that clarifiers that arent covered do not freeze when off line you may be better off leaving them on the line so they will not freeze

Mathematical methods vs lab

You can check detention time weir overflow rate surface loading rate and solids loading with math, but lab analysis is more reliable and realistic

General maintenance for clarifiers

-Maintain a record and file system for future reference. This should obtain sheets to write down description and date for all repairs and regular maintenance activities like lubrication should include operating instruction manuals brochures names and addresses and numbers of manufacturers sometimes found on computer - always lubricate equipment at intervals recommended and use proper lubricants - clean all equipment and structures regularly, remove floating material and algae from inlet baffles and effluent weirs and launders keeping scum removal equipment clean adn properly adjusted help prevent odors -inspect and corrrect all peculiar noises leaks pressure adn cause gauge irregularities belts electrical systems and safety devices -when sedimentation tank must be drained for inspection or repairs, keep wooden flights moist by periodic sprinkling with hose to prevent cracking or warping -keep weirs level this helps prevent short circuiting which reduces the efficiency of clarifier

Operational suggestion imhoff tank

-general ther is no mechanical sludge scraping device for removing settled solids from floor of settling areas tehy accumulate before passing through slot to digestion area it may be necessary to push accumulation through slot with squeegee or similar device attached to long pole dragging a chain on floor and allowing it pas. Through slot is another method for removing sludge accumulation - scum fromsedimentaion area is collected with hand tools and placed in separate container for disposal Scum may also be transferred to gas venting area where it will work down into digestion compartment scum in gas vent should be soft and broken up by soaking periodically with water or punch in holes into it and mixing it with liquid portion fo digestion compartment -some tanks have piping and valuing to reverse direction of flow fro one end toward other end Flow should be reversed periodically for maintain an even sludge depth in digestion compartment sludge level in digeison area must be lower tha slot in floor of settlinga rea to prevent plugging of slot line of gas bubbles directly over the slot indicates sludge level in teh digestion chamber is too high -explanation of sludge digestion in volume 2 chap 12 is there Neither sludge mixing or heating devices are used in imhoff tank sludge loading rates withdrawal rates lab tests and visual appearance of sludge are similar to waht they are in unheated digested Process is working fi slduge in digestion area is relatively odorless or has musty smell and is black or very dark in color

Ways to determine thick or thin sludge without lab

-sound fo sludge pump will usually have different sound from thick apposed to thin - pressure gauge readings, pressure is higher on discharge side fo pump and vacuum will e greater on inlet (suction ) side of pump when sludge is thick -sludge density gauge readings -visual observation fo small quantity of sludge -use a sight glass in sludge line to observe sludge as it flows in pump

5. Influent check item

A change in composition or temperature B change in flow rate An increase in flow rate can cause hydraulic overload. This can be determined b calculating teh detention time weir overflow rate adn surface loading rate If tank is hydraulically underloaded effluent could be recirculated back to primarily clarifer to reduce length of detention time

2.. collector mechanism check item

A circular clarifier 1.Drive motor 2. Shear pin 3 overload switch 4 skimmer dump arm. Aoperation B rubber squeegee 5 scum trough 6 scum box B rectangular clarifier 1 drive motor 2 shear pin 3 clutch and drive gear 4 flights 5 scum trough 6 skimmer operation 7 cross collector 8 inlet line or slot 9 target baffle

6. Jerking or jumping collector mechanism check item

A sludge blanket to deep Pump out sludge if mechanism is all right B drive unit may have bad sprocket or defective chain link C broken flight or rock or stick jammed between flight or squeegee blade and floor or tank If B or C occur, tank must be dewatered never attempt to back up or help pull collector mechanism because severe equipment damage will result

1. Sludge pump check item

A. Piston pumps 1. Ball check seating 2 shear pin 3. Pack adjustment 4 drive belts 5 high pressure switch 6 pumping time B. Postiive displacement scru screw pumps 1. Pump gas bound 2.rotor plugged 3 drive belt 4 packing adjustment 5 packing time C centrifugal pumps 1 pump gas bound 2 packing adjustment 3 impeller plugged 4 pumping time D air injector 1 air supply 2 foot valves 3 sludge valves 4 electrodes 5 pumping time

OSHA

Act regulates design construction operation and maintenance of indsutarl workers and plants and wastewater treatment plants Act does not apply directly to municipalities unless states have approved plans and jurisdiction plans Contract operators and private facilities do not fall under osha either

Most common biological processes

Activated sludge process Trickling filters Rotating biological contactors

Actual vs theoretical detention time

Actual detention time is often less tahn detention time calculated using formal and can be measured by use of dyes tracers or floats

When does floatation occur in process

After primary clarifier, the solids are skimmed in secondary clarifier

Pressure floatation

Air is forced into water in pressure chamber where air becomes dissolved in liquid the pressure is then relased from wastewater and water is returned to atmospheric pressure because of cahnge in pressure, the dissolve dair is relased from solution in form of tiny air bubbles these air bubbles carry solids to surface for skimming

Cleaning weirs and troughs

Algae can be probed in weirs and effluent troughs Chlorine can be added between baffle adn weir to control algae, its unsafe to enter weir or trough or unreachable with brush on pole to remove algae Chlorine solution pipe can be completely looped around the clarifier using a 3/4 inch pvc pipe with 1/8 inch holes drilled where v notch is lowest Can also add chlorine at the high point of trough opposite the effluent discharge gate or place chlorine tables int th trough at several spots a day Adding chlorine in trough controls algae in the trough using a fire hose or high pressure water jet to remove algae from weirs and troughs also can be effective

Sedimentation digestion unit parts and purpose

Bar screen- filter course material Flame check-parents flame from traveling down gas outlet pipe to top of digester compartment where flame could cause explosion Gear motor- provides power to turn scraper baldes in bottom fo both clarifier and digester Clarifier arm and blades- scraps settled solids to center hole where sludge enters the digester Clarifier compartment- provides storage space for wastewater being treated and allows heavy solids to settle to bottom ad light solids to float to the surface Digester arm and baldes- scraps digested sludge on digester bottom to the sludge withdrawal pipe Effluent launder or effluent trough- conveys settled wastewater away from clarifier Scum breaker arm and stationary pickets- breaks up scum accumulation in top of digester compartment Digester compartmetn- provides storage space for sludge allow digestion to occur and separation of liquids and solids for disposal Sampling outlet- allows withdrawal of digester sludge for laboratory testing Sludge withdrawal- allows digested sludge to be removed from digester

Starting sludge collectors

Be careful if it has not been operated in several weeks Wearing hoes on flights may have started rusting where they are sitting on rails Lift each individual flight off rail to be certain it is free and apply grease or sae 90 gear oil to shoe and ail If precautions arent taken, flight wearing shoes could stick to the rails and whole collector system could be pulled down to the floor fo tank, before the collectors are started in new tank, each flight should be checked for clearance of one to two inches between wall and end fo flight If they are too long, they may rub tank walls and break Same safety precautions

Safety with sd units

Be careful when removing debris from open tanks, secur efirm footing so you do not slip and fall do not lift more than you can handle -be sure all moving machinery parts have covers and guards - be aware of the fact that digester gas is very toxic and poisonous when mixed with air this gas can burn or explode everyone msut strictly observe the following rules A. Post danger sign near gas dome indicating no smoking or open flames B- keep all lighted cigars cigarettes pipes or any open fire away form digester or it's gas at all times C- do not inhale digester gas D- do not enter the settling or digesterion compartments unless empty of all sludge adn forced ventilation has cleared atmospheric hazards and comply with federal state OSHA confined space laws E-remove all oil and grease spills and other slippery matter surfaces

Dealing with shock loads from toxic wastes

Best treated and controlled by addition of proper chemicals such as coagulants or chlorine at plant headwords at preliminary treatment area Increased recirculating rates awith trickling filters can dilute toxic wastes

Chlorine

CL2 very irritating to eyes skin and mucous membrneas Cause death by suffocation and formation fo acid in lungs Acts as asphyxia this causing cramps in muscles like larynx choking Well of mucous membranes nausea vomiting anxiety and syncope loss of consciousness and fainting Proper breathing equipment is needed when working with chlorine

Coagulant

Chemical that causes very fine particles to clump together into large particles This makes it easier to separate solids from liquids by settling skimming draining or filtering

Safety checks

Clarifer msut be equipped with adequate access by stairs ladders ramps catwalks and bridges with railings that meet all state and OSHA requirements Catwalks and bridges have floor plates or grates firmly secured adn equipped with toe boards and non-skid surfaces Adequate lighting must be provided on clarifer Launders channels and effluent pipelines that carry from flow from clarifer to another conduit channel or structure must have safety grates over entrance to prevent accidental injury or entry into system In circular clarifer turntables adjustable inlet deflection baffles and return sludge control valves must have safe access without requiring operator to leave a bridge or catwalk Adequate gaurds must be placed over chain drives belts and other moving parts Safety hooks poles or floats should be stationed at strategic locations near every basin to reduce anyone who falls Do not allow any pipes or conduits to cross top of cakewalks or bridge s Adequate offset of drive units motors and other equipment must be provided to allow unobstructed access to all areas

Floatation process

Colloids and emulsions are suspended solids taht neither settle nor float to surface and remain inn liquid and passes through clarifier unresolved Floatation process gets out these suspended solids that are hard to reach Done by pumping air into mixture to cause the suspended material to float to the surface where it can be skimmed off Particles can be flocculated with air or chemcial coagulants which force or carry liquid surface by minute air bubbles, most air bubbles ar released at liquid surface particles in form fo scum or foam are removed by skimming Done by vacuum floatation or pressure flotation Process is based upon release of gas bubbles in liquid suspension under conditions in which the bubbles and solids will associate with eachother to form combination with lower specific gravit than the surrounding liquid They must stay together long enough for the combination tor ise to surface and be removed by skimming

Package treatment plant

Combined sedimentation and digestion unit is Called this Plant influent passes through flowmeter to record flow Bar screen is first treatment unit of package Coarse solids are removed Then water enters clarifier near surface in center and the circular influent well directs flow and solids toward the toward bottom of clarifier Settled wastewater slowly flows through clarifier and leaves over effluent weir around outside of clarifier Effluent leaves the unit by effluent trough launder and usually received additional treatment in secondary package plant pond or land treatment disposal system Solids settling to bottom for clarifier tray are scraped to center of unit slot in center of tray allows solids to flow into digestion compartment below the slot is a deluge seal or bott that prevents gas from digestion and digested sludge from floating up into clarifier in digester, sludge undergoes anaerobic decomposition Digested sludge is removed from bottom of digester by pumping or by gravity flow to drying beds Scum is skimmed from surface of clarifer into scum trough Scum flows from trough to scum pit a submersible pump moves the scum to digestion compartment Supernatant is removed from digester by lowering an adjustable overflow tube and allowing liquid to flow into scum pit, again the submersible pump moves supernatant to the clarifer influent well and supernatant flows through clarifier Gas from digestion process rises to top of digester in as tiny bubbles the tray bottom of clarifier slopes upward to the outside, this slope helps move sludge to center slot and allow gas to accumulate along the outside edge of digestion portion of the unit Gas is collected in gas dome and usually burned by waste gas burner sufficient gas is not produce to serve as reliable source of energy for power or heating so its not

Composite (proportional) sample

Composite sample is collection of individual samples obtained at regular intervals, usually every one or two hours during 24 hour span Each individual sample is Combined with the others in proportion to their rate of flow when the sample was collected Equal volume individual samples also may be collected at intervals after a specific volume fo flow passes the sampling point or after equal time intervals and still be referred to as composite sample Resulting mixture forms a representative sample and is analyzed to determine the average conditions during the sampling period

Septicity

Condition which organic matter decomposes to form foul smelling products associated with absence of free oxygen If severe the water produced hydrogen sulfide turns black contains no oxygena nd wastewater has high oxygen demand

Normal operation of SD unit

Consists of inspecting unit on daily basis observe flow Daily -remove debrisa nd solids from bar screen and properly dispose fo them by burial hose downs clean and walls -hose down baffles weirs scum trough scum pit to remove any grease scum or floating debris, accumulations are unsightly ad usually /produce odors and flies if not immediately removed -measure pH in digester if low add lime, if constant may be measured 2-3 times a wee -withdraw supernatant once or twice a day, analysis and interpretation of lab results of suspended solids and settleable solids in the effluent can indicate frequency of supernatant withdrawal solids in effluent Amy indicate supernatant should be removed more frequently - after supernatant withdrawal from scum pit, pump the clear supernatant to clarifier, when most supernatant has been pumpe dout of pit, only scum will remain, pump scum to digester, do not allow submersible scum pump to run dry because pump motor will be damaged, pump scum frequently enought o prevent odors or flies If supernatatnt is high in solids, return supernatant to digester, prevent supernatant solids from flowing out with clarifier unit, solids may be in supernatant during initial stat up, under these conditions, supernatant. May be pumped t dryin beds until digester solids in supernantant din I ate digested solids should be removed from digestion compartment - digested sludge should be withdrawn from digester when solids start appearing in supernantant this will occur several months after start up and regularly during normal operation frequency of digested slug remove algae will depend on solids loading of unit design capacity and effectiveness of digestion process in unit Scraper mechanism on bottom fo digester will help to prevent sludge coming during sludge withdrawal withdraw sludge slowly so sand and other grit on bottom of digestion unit will be removed too do not remove sludge so fast taht calrifer effluent will stop flowing over effluent wieirs, if digested sludge is allowed to flow out too quick, sludge directly above the sludge withdrawal pipe will flow out, a cone will develop in sludge and supernatant will flow out rather than allowing remaining digested sludge to flow toward withdrawal pipe Always a leave some digested sludge remaingi in digestion compartmetn As sloon as sludge starts to run thin, stop removing sludge If cone developes try removing some supernatant to scum pit when done removing digested sludge, wash out line with plant effluent, ]shut valve by digestion compartmetn and leave the remainder of line open so gas produced from digestion will not cause pressure build up which damages pipes and valves. Digested sludge is sent to sand drying beds after sludge is dried it is removed to landfill. Do not smoke around drying beds while digested sludge is applied methane gas can mix with air to form explosive conditions if odors develop using masking agent -in colder climates contents of digester may be heated in order to obtain better and faster digestion, try to maintain temperature of digester contents betweeen 80-95 F closer to 90 faster the digestion -gas production wil not start until solids digestion starts in digester, gas line should be equipped with moisture trap and flame arrested, and connected to waste gas burner. Be sure gas line is clear, scum and indigestible material can prevent gas from flowing from digestion compartmetn if neccesary remove the scum and debris once methane is produced, waste gas should be burned

Combined sedimentation unit

Consists of small clarifer constructed over a sludge digester Treatemaent units have been designed and constructed to serve small populations such as schools campgrounds and subdividsions usually they are installed instead of imhoff tanks or septic tank systems Efficiencies are similar to primary clarifiers with approximately 65 percent of suspended solids and 35 percent of BOD removed from influent

Gasification

Conversion of soluble and suspended organic mateirals into gas during aerobic or anaerobic decomposition In clarifiers it resulting gas bubbles can become attached to settled sludge and cause large clumps of sludge to rise and float on water surface in anaerobic sludge digesters this gas is collected for fuel or disposed fo using waste gas burner

Charcteristics and appearance of secondary settling tank sludge

Darker in color, but not gray or black, will tur black if allowed in secondary clarifer for too long Sludge pumping rates should be increased or time of pumping lengthened or made more frequent to combat this Sludge particle sizes may be very irregular with generally good settling characteristics setting wise. Sludge mat appear to be fluffy humus type material and usually ahve little or no odor if sludge removal occurs at regualr intervals Dispose of sludge collected in final settling tanks depends on particular plant design Sometimes sludge can be transfered to primary settling tank to be settled with primary sludge and othertimes its directly transferred to digestion system

Sampling and analysis for SD units

Depend on NPDES national pollutant discharge elimination system permit requirements avaliable time and capability of facility to make operational changes on basis of interpretation of test results typical test their purpose and expected ranges of tests results are listed in table s5.4

Sedimentation and flotation units

Designed ot pyscially remove solids that settle easily at bottom ro float on top Sedimentation is principle basis of design in units Primary clarifers Secondary clarifiers Combined sedimentation digestion units Floatation units Imhoff tanks

Detention time formula

Detention time (hours) = Tank volume (cubic Ft) X 7.48 (gallons/cubic ft) X 24 (hours/day) / Flow (gallons per day)

Dealing with abnormal conditions

Development and enforcement of sewer use ordinance and industrial pretreatment facility inspection program are effective long term approaches to fixing problem with toxic wastes Installing monitoring devices instrumentation control structures and chemcial feed systems will also provide operator with helpful tools to maintain clarifer performance under abnormal conditions

Tests frequency location common ranges for primary clarifiers

Dissolved oxygen-daily-effluent-0-2mg/l Setteable solids- daily-influent effluent- 5-15mg/l .3-3mg/l PH-daily-influent-6.5-8.0 Temperature- daily-influent effluent - 50-85 F 10-30C Bod- weekly minimum-influent effluent-150-400 mg/l 50-150mg/l Suspended solids-weekly minimum- influent effluent- 150-400 mg/l 50-150mg/l When discharge requirements permit primary treatment these may also be important Chlorine residual- daily- plant effluent -.5 to 3.0 mg/l depending on requirements Coliform group bacteria- weekly- effluent- 5000,2000000 per 100 ml depends on requirements

Electric shock

Do not use water for cleaing electical panels electic motors or other electical equipment Use rubber floor mats in front fo electical panels Do not work on electical equipment unless you are qualified electrician and authorized to do so

Maintenance checks

Drive mechanisms lubrications points locations ro changing oil in gear boxes and turntables are accessable Weirs launders and contorl boxes must be accessible for cleaning painting and other jobs Sludge pumps must be located and capable of backflusing pipelines or pumping down clarifiers Provisions should be made to connect and locate for portable pumps to dewater clarifer if clarifers are not connected to plant drainage system Influent and effluent pipelines conduits or channels must be installed so taht each end can be isolated and dewatered by Gravity drain or portable pump Sludge and scum lines to pump suctions must be kept as short as possible and free fo fittings 90 degree bends and reducers cleanouts are required on sludge and scum lines to provide access for cleaning equipment sucha s sewer rods and high velocity cleaners cleanout should be installed in lines at locations that allow the lines to be worked on while clarifer remains in service Auxiliary service lines water air electical instrumentation sample and chemcial feed should be studied,These lines have isolation valves at appropriate locations and should be accessable for repairs when necessary conduits for instrumentation electical wiring adn cables should be equippe with pull boxes that are watertight sample lines should have cleanouts and valuing to allow periodic flushing of lines air lines must be equipped with condensate drains at all low points including. Ends of line Covered clarifers should contain lightweight openings to provide easy access to scum channels skimmers launders and drive mechanism units

Collecting scum

Floating material may leave clarifier in effluent if method is not holding it back, a baffle is generally provided at some point in tank, parimary clarifers often ahve scum collections area where scum is skimmed off by some mechanical method, usually skimming arm or paddle wheel Using hand tools like skimming dipper attached to broom handle Frequently check scum trough to be sure its working properly clean box with brush and hot water scum may be disposed by burning or burial

Floating sludge on clarifier surface problem

Floating sludge may results form sludge not passing from bottom fo clarifier around sludge seal and into sludge digester, - try withdrawing more supernatant so sludge can flow into digester -shut off sludge scraper. Check the sludge seal by feeling witha pole or rod to remove any screenings or other objects thtat might plug it -pump less cum or supernatant into the digester, excessive pumping may forcing sludge out of digestion compartment

Factor most influencing clarifier performance

Flow into the plant Both surface loading and detention time are directly related to flow Both surface loading and detention time vary widely throughout the day due to the hourly changes in plant inflow resulting from activities of the people and industries i the community Most clarifiers produce fairly consistent removals of biochemical oxygen demand and suspended solids

Rate for settling of particles of wastewater

For specific gravity of 1.05 or 5% greater than water, speeds of 1 to 2 feet per minute are ideal and much slower than grit channel velocities which are around 1 ft per second.

Flocculation

Gathering together of fine particles after coagulation to form larger particles by process of gentle mixing this clumping together makes it easier to separate the solids form water

Operational strategy for clarifers

Have good preventative maintenance program Closely monitor operating conditions Respond to any lab results that indicate problems are developing Plants with 4 or more clarifiers can improve their performance by diverting flows or fewer clearifers under certain circumstances During low flow periods from midnight until 6AM fewer clarifiers need to be on in process flow line Try not to allow unfavorable detention times like less than half an hour or longer than three hours, to last longer than four to six hours without palcing more or fewer clarifiers in line Prevent detention times in primary clarifers from becoming too long in order to keep water flowing to aerobic biological treatment processes

Retention time of sludge

How fast sludge remains inside tank, mechanisms for activated sludge removal are usually rapid to reduce sludge retention time in clarifiers and several of the mechanisms have valves or adjustable rings to contorl return sludge rates with different collection points in clarifer mechanism Flows can be regulated from each pipe removing activated sludge from clarifier to control activated sludge process Reason for ability to regulate each pipe is different activated sludge densities will develop different settling patterns in particular clarifers as they have varying sludge index volumes An SVI of 100 causes sludge tos entitle near tank inlet, thus requiring most of sludge to removed from center or inner quarter of tank floor area SVI of 500cause solids settling curve to take on shape of bowl, under this condition then sludge gathers at outside of clarifer and requires higher return flow rates to pump Outside sludge return nozzles and pipes must handle much larger clarifier bottom area Operator must adjust return flow rates from individual pipes to remove solids from tank areas where the activated sludge is ettling by reducing the return sludge flows from areas where the activated sludge not settling

Storm flow infiltration problem

If its frequent problem, sealing of sanitary sewers or use fo flow equalization basin may improve the quality of clarifier effluent There may not be much taht can be done to prevent development of septic wastewater in a collection stem They naturally happen during hot weather when wastewater travel times in collection streams to treatment plant become too long Chemical teamten with chlorine or hydrogen peroxide added at a pump station may improve the condition of septic wastewater and protect structures from corrosion damage

Detention time problem correction

If its too low, or lab tests indicate poor removal of solids, then additional tanks should be put into operation Flows fluctuate considerably between day and night and any calculated detention time is for a specific flow

Safety during start up procedures

If working down I tank wear hard hat Keep hands away from moving equipment When working on equipment be sure to tag and use a lock out device on main circuit breaker and influent contorl gates to prevent equipment from starting unexpectedgly and causing equipment damage or injury keep key for lock out in pocket

Test typical results and purpose

Inflow- depends on population served may range from 80-130 gallons per day- determine hydraulic loading on facility identify flow trends and when facility is approaching design capacity Clarifier tests Suspended solids 100-300 mg/l influent 50-100 effluent- indicates efficiency Settleable solids- influent 50-100 mlL effluent 5-15 ml/l efficiency indciator BOD influent 150-300 mg/L effluent 100-200 mgL Digestion tests Temp- depends on location season and whether sludge heated- forecasts digestion rates which depend on temp of digested sludge PH- 7-7.8 determines if effective digestion is taking place too low a pH value indicates poor digestion Quantity of sludge withdrawn- depends on population detention time in digester and temp- determines effectiveness of clarifier in removing solid and effectiveness of digester in reducing solids Effluent Chlorine residual- depends on NPDES permit requirements- determines if sufficient chlorine is applie dto effluent to achieve adequate disinfection

Circular clarifier parts and purpose

Influent control gate- throttles or stops flow to sedimentation basin or clarifier Influent channel or pipe- transports wastewater to the clarifier Effluent weir- ensures equal flow over all weirs Designed for small surface elevation water level adjustments in the clarifier provided the plate is designed for vertical movement. (Up down) Influent well- receives the flow from the influent pipe, reduces flow velocities, and distributes flow evenly across the upper portion of clarifier contents A small circular compartment in the top center of the clarifier Effluent trough launder- collects the settled wastewater flowing over the weirs adn conveys it from the clarifier Scum skimmer arm- skims or collects floating material from the surface of the wastewater and moves it to the scum trough. Scum trough- recieves floating mateirals scraped from teh surface by scum skimming arm Scum pipe- allows the collected scum to flow from skimmer box to a scum tank or a pump Drive unit- causes the collector to rotate a power unit that is connected to the vertical drive cage and causes the collector to rotate Vertical drive cage- transmits power from drive unit to sludge collector mechanism Sludge collector mechanism- drags settled solids across clarifier bottom to a sludge collection pit or sump a mechanism that rotates around teh bottom of the clarifier and consists of squeegee type scrappers Baldes and scraper squeegees- scraps sludge from bottom of clarifier to sump Sump- collects the sludge before withdrawal Sludge withdrawal pipe- removes the sludge from clarifier usually connects to sludge pump

Rectangular sedimentation basin parts and purpose

Influent control gate- throttles or stops flow to sedimentation basin or clarifier Influent channel or pipe- transports wastewater to the clarifier Target baffle or deflector plate- spread the wastewater evenly across the width of the clarifier for even distribution and prevents short circuiting Effluent weir- ensures equal flow over all weirs Designed for small surface elevation water level adjustments in the clarifier provided the plate is designed for vertical movement. (Up down) Effluent trough launder- collected settled waterwater flowing over the weirs and conveys it from sedimentation basin Main sludge collector- drags settled solids to the sump, a continous chain with crosspieces flights or scrapers are attached Sprocket- supports chains adjusts tension or forces the chain to move, a wheel with teeth around the outside that fit into chain link Angle track- provides a track on which main collector crosspieces ride Sludge collector drive- provides power that causes main and cross collector units to move Cross collector- drags sludge to deep end fo sump for removal by pumping also preventing bridging of sludge into sump Sump- recieves settled sludge from the floor of the sedimentation basin stores sludge in sufficient quantity to avoid frequent (less than once an hour) removal by pumping but of sufficient volume to maintain sludge thickness and to exclude water in the sedimentation basin from being pumped out during pump cycle Sludge withdrawal pump- removes sludge from the sump Wearing shoe- prevents wear on the scraper crosspieces, usually a piece of iron attached close to outer ends of scraper Scum skimmer or collector- skims or collects floating material from surface of the wastewater and moves it to the scum trough Scum trough- recieves the floating material from the scum skimmer for removal Scum baffle- extends above the water surface and prevents the floating material form reaching the effluent trough

Start up procedure for clarifier

Inspect tank carefully as outlined Circular clarifiers Check these items Control gases for proper operation Clarifier tank for sand and debris Collector drive mechanism for lubrication oil level drive alignment and complete assembly Gaskets gears drive chain sprockets and drive motor usually single speed for proper installation and rotation Squeegee blades on collector plow for proper distance from the floor of tank All other mechanical items below waterline for proper installation and operation Tank sumps or hoppers and return lines for debris and obstructions Tank structure for corrosion cracks and other indications fo structural failure Scraping action of baldes should contorl entire area from the topside wall to sludge hopper Improper movements can be caused by drive unit, squeegees that ahve too much drag, or uneven clarifier floor If unit is water lubricated ensure enough water is in the center bearing Test stall alarm if it comes with one to see if machanism stops when overloaded Time period it takes for plows to make one complete revolution around tank and record the time for later reference Checks dn record amperage that motor draws let unit operate for several hours and monitor

Daily operation and maintenance

Inspection- make several daily inspections with a. Stop look listen and think routine Cleanup- using water under pressure wash off accumulations of solid particles grease slime and other material from walkways Lubrications- grease all moving equipment and check oil levels in motors Preventative maintenance- follow manufactures specifications - flights- examine bolts for looseness corrosion and excessive wear on those parts inspected above waterline Chain and sprocket- check for wear because .05 inch wear on each of the 240 link pins will cause about one foot of extra slack Recordkeeping- write in your notebook any unusual observations and ransfer these notes to plant record sheet Sampling and lab analysis- Sludge and scum pumping-

Only accurate measurement of sludge density

Lab test total solids test Many operators use centrifuge test as well

Lineal

Length of one direction of a line

Retention time

Length of time water sludge or solids are retained or held in clarifier or sedimentation tank

Instrumentation to monitor secondary clarifiers

Levels fo sludge blanket in clarifier Concentration of suspended solids in clarifer effluent Control and pacing of return sludge flows Level of turbidity in clarifer effluent Concentration of dissolved oxygen in clarifer effluent Level of pH Lab tests should be done to support what instruments say Also test for Biochemcial oxygen demand and ammonia nitrogen measurements

Emulsion

Liquid mixture fo two or more liquid substance not normally dissolve dinto one another But one liquid held in suspension in the other, usually contains globules of one or more substance and those usually are grease oil fat or resinous substances This material also exerts high oxygen demand

Emulsion

Liquid mixture of two or more liquid substances not normally dissolved into one another one liquid is held in suspension in the other

Weir weer diameter

Many circular clarifiers ahve circular weir within outside of edge of the clarifier all the water leaving the clarifier flows over this weir Diameter of the weir is length of a line from one edge of a weir to the opposite edge and passing through the center of the circle formed by the weir

Primarily clarifiers

Meant to remove settleable and floatable material as possible Removal of organic setteable solids is important as they cause high demand for oxygen BOD i recieving waters and subsequent biological treatments

Density

Measure of how heavy a substance is for its size Expressed in grams per cubic centimeter or pound per cubic foot Density of water is 1 gram per cubic centimeter or 62.4 pounds per cubit foot

Adding lime to water

Mix in barrel until milky Use rubber gloves and eye/face protection lime is moderately caustic irritant to all exposed surfaces of the body. Pour mixture into scum pit and then pump into digestion unit usuing submersible pump Allow water to flow from influent to clarifer to scum pit or washdown hose may be used to add water to scum pit Pump out scum pit and wash down tor move any remaining lime in digestion unit then stop when pH is 7 You can also use anhydrous ammonia to rise oH but handle carefully cause it is hazardous and must use respiratory eye and skim protection if ammonia hazard is in concentration above federal or local standards TLV is 25 with inhalation limit of 50 ppm per hour

Surface loading

One of the guidelines for the design fo settling tanks and clarifiers in treatment plants used by predators to determine if tanks and clarifiers are hydraulically over or underloaded also called overflow rate

Why clarifiers fail

Operator errors Equipment failures Excessive hydraulic loadings shock loads

Typical solids loadings

Primarily clarifers- usually not design consideration Secondary clarifers- 12-30 lbs per day. Per square ft Dissolved air flotation - 5-40 lbs per day per square ft Sludge thickening- 5-20 lbs per day per square ft

Lesson 2

Principles of operation of various types of units

Clarifier problems and response to poor clarifier performance

Problems -floating chunks of sludge 12345 -large amounts fo floating scum 2.3 2.4 2.5 -loss of solids over the effluent of weirs 12345 2.7 2.8 -removal efficiencies are low 5 6A -pH is low and there are odors 123456 -sludge blanket is deep but pump sludge is thin 3 2.1 2.2 2.3 2.6 -sludge collector mechanism jerks or jumps 6 -sludge collector mechanism will not operate, drive motor thermal overloads, or overload protective switches keep tripping Check items are on page 6

Sludge gasification

Process in which soluble and suspended organic matter are converted into gas by anaerobic decomposition the resulting gas bubbles can become attached to settled sludge and cause large clumps fo sludge to rise and float on water surface

Drowning prevention

Put handrails and proper walkways by open tanks Cover open pits with grating sand ect plates Have approve dlife preservers and life lines handy to thro to anyone who may fall in Use the buddy system when working around water surface

Imhoff tanks

Rarely constructed today, may be used to serve very small community Consists of whole plant Combines sedimentation and sludge digestion in same unit there is to compartment where sedimenetation occurs and bottom for digestion of settled particles Two compartments are separate by flow tih slot designed to allow settling particles to pass thorugh to digestion compartmetn Wastewater flows slowly through upper tank as in any other standard rectangular sedimentation tank settling solids pass through slot to bottom sludge digestion tank Anaerobic digestion of solids is same as in separate digester Gas bubbles form and rise to surface they carry solid particles with them, slot is designed to prevent solids from passing back into upper sedimentation area as result of gasification Same calculations are used for clarifier for imhoff tank to determine loading rates Typically they are Detention time- 1-4 hours Surface settling rate- 600-1200 gallons per day per square ft Weir overflow rate-10,000 to 20000 gpd/ft BOd removal 25-35 percent Digestion area Digestion capacity 1 to 3 cubic ft per person Sludge storage time 3-12 months

Hydraulic loading

Refers to lows MGD or meters per day, to a treatment plant or treated process Detention times surface loadings and weir overflow rates are directly influenced by flows

Sampling

Sample influent and effluent from clarifier Samples should represent true nature of wastewater or stream sampled Levels can vary throughout day week or year but you must determine these variations in order to understand understand how to best use clarifier Test results can determine number of clarifer units needed in operation

Flights

Scraper boards made form redwood or other rot resistant woods or plastics used to collect and move settled sludge or floating scum

Secondary clarifer tanks with activated sludge clarifiers

Secondary clarifers after active sludge processes are designed to handle large volumes of sludge and are more conservative in design because sludge tends to be less dense Detention time 2-3 hours Surface loading 300-1200 gallons per day per square ft Weir overflow 5000-15000 gallons per day per lineal feet of weir Solids loading 24-30 lbs per day per square feet Purpose is identical, but particles settled received aeration rather than trickling filter, most plants that use activated sludge process are equipped with mechanisms to return activated sludge back to aeration tank and remove it quickly to do so Sludge volume in secondary tank will be treated from activated sludge process than trickling filter process Sludge removal mechanism tend to differ from most primary clarifers mechanisms, especially with circular clarifers They have continous sludge removal by hydrostatic systems with sludge pumped back into aeration tanks by large capacity pumps Usually these pumps are centrifugal type with variable speed controls or are large air - lift type

Most important clarifier operators regulate

Secondary clarifiers in sludge activation process, most critical require most attention from operator

Water quality indicated and expected removal efficiency

Setteable solids 95-99 Suspended solids 40-60 Total solids- 10-15 Biochemical oxygen demand 20-50 Bacteria 25-75

Factors influencing designs and performance of clarifiers

Settling charcteristics fo suspended particles in water are most important considerations Engineers must consider speed at which particles will settle in order to determine correct dimensions for tank Tendency of particle to float and rate of downard travel (settling ) are dependent on weight of particle in relation to weight of equal volume of water, or specific gravity of particle The particle size and shape, temperature of liquid also impact this Organic setteable solids are seldom more than 1 to 5 Percent heavier than water therefore their settling rates are slow

Settling tanks on velocity

Settling tanks decrease the velocity of wastewater far below the velocity of a collection sewer, and even slower than a grit channel, which takes out the biggest grit and heavy materials in water.

Processing waste activated sludge

Should be done by liquid solids separation process other than clarifier Usually processed by separate gravity or flotation sludge thickerns in order to concentrate the sludge to 3 to 4.5 percent solids before pumping solids to digester or dewatering system Returning waste activated sludge to primary clarifier causes a build up of raw sludge, this additional volume or aw sludge are pumped into digester, and this increases supernatant carrying digester solids back to headworks of the plant, increasing solids volume in water, continuously until cycle is broken, and this is why excess sludge is processed separate

Plans and specification of plant

Should be reviewed by operators so they Become familiar with plant Learn waht will be constructed d Offer suggestions to how the plant can be better easier designed or more effective in operation and maintenance

Withdrawal pumping rates

Slow to prevent pulling too much water with sludge Take samples frequently and examine them while sludge is pumped for excess water If sludge goes thin stop pumping

Sludge septicity symptom

Sludge gasification occurs, causing large clumps of sludge to float on water surface Septic sludge is genrally odorous and acidic

Package treatment plant

Small plant often fabricated at the manufacturers factory hauled to site and installed as one facility the package may be either a small primary or secondary treatment plant

Molecule

Smallest division fo compounds that still retains or exhibits all properties of substances

Solids loading formula and solids applied formula

Solids applied (pounds / day) = Flow (million gallons per day) Solids (mg/l) 8.34 (lbs/gallon) Solids loading lbs per day per square feet= solids applied /surface area square ft

3. Pipes and sludge sump check item

Sometimes pipes ro sumps may be cleansed by back flushing

Conditions effect sludge concentration

Specific gravity Size Shape of particles Temperature of wastewater Turbulence in tank

Wastewater solids information

Specific gravity of 1.05 will weight 8.76 pounds per gallon

Activated sludge process

Speeds up decomposition fo wastes in wastewater being treated Activated sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated, after time in aeration tank, sludge is activated adna llowed tos ettle out by sedimentaitona nd is disposed of or reused in aeration tank as needed. Remaining wastewater then undergoes treatment

Masking agents

Substances used to cover up or disguise unpleasant odors can be dripped into wastewater sprayed into air or evaporated using heat with unpleasant fumes or odors and then disrahcgged into air by blowers to make bad small gone

Lab testing for imhoff tank

Suggested analysis with haul range and typical removal percent Settleable solids - 3-10ml/l 75-90 percent Suspended solids- 200-400mg/l 45-65 PH 6.7-7.3 Alkalinity- 1-300mg/l Bod- 200-500mg/l 25-35 Digestion area PH 6.7-7.3 Alkalinity 1000-3000mg/l Volatile acids 100-500mg/l

Factors that impact settling characteristics of particles in clarifer

Temperature Short circuits Detention time Weir overflow rate Surface loading rate Solids loading

Solids loading in settling impact

Term solids loading used to indicate amount of solids that can be removed daily by clarifier for each square foot. Of clarifier liquid surface area If solids loading increases above design values, you can expect an increase in effluent solids, tank isnt big enough to remove solids present Can be applied to secondary clarifiers and gravity or flotation sludge thickeners loading rates are expressed in pounds per day per square foot and depend on nature fo solids and treatment requirements Must know Flow in million gallons per day Suspended solids concentration in mg/l Liquid surface area in square feet

Ideal sludge to pump

Thick as possible, least amount of water is desirable Amount of sludge solids in water affect volume fo sludge pumped and digester operation A good thick primary sludge will contain 4-8 percent dry solids as indicated by total solids test in laborator

Surface settling rate or surface loading rate impact on settling

This rate is expressed in terms fo gallons per day per square foot of tank surface area Operators and designers have indicated that surface loading rate has a direct relationship to setteable solids removal effciency in tank Suggest loading rate varies from 300-1200 gallons per day per square foot of tank surface area Depending on nature of solids and treatment requirements. Low loading rates are frequently used in small plants in cold climates Warm regions low rates may cause excessive detention, which could lead to septicity Calculating surface loading rate requires knowing flow in god and square feet fo liquid surface area Low surface loading rates increase detention, or mean water travels slower in flowing into tank

Detention time

Time required to fill tank at a given flow or theoretical time required for given flow fo wastewater to pass through a tank

Activated sludge plants and toxic waste

Toxic wastes can be reduced through increased aeration rates with strip (drive out) toxicants out of mixed liquor usually this procedure is ineffective because te toxic wastes has already passed through plant before impact discovered Reduction or complete halting of solids wasting rate may help if some resistant bacteria have survived Change the mode of operation to contact stabilization or step aeration exposing only small portion fo the organism population to toxic wastes If all bacteria have been destroyed or if tocicant is bound in the sludge, get rid of the solids do not dispose of toxic solids in digester, they may be disposed fo in an approved sanitary landfill, provided you recieve permission from regulatory authorities

Abnormal conditions influencing clarifier performance

Toxic wastes from industrial spills or dumps Storm flows and hydraulic overloads Septicity from collection system problems Not much an operator can do aboutthese factors Corrective action should be taken however, and if a toxic waste dump is suspected or identifies as cause fo plant problem, immediate action should be taken to identify source and prevent future dumps

Sloughing

Trickling filter slimes that have been washed off the filter media They are generally quite high in biochemical oxygen demand and will lower effluent quality unless removed

Clarifier efficiency factors

Types of solids in wastewater especially if significant amount are industrial waste Age (time in collection system) of wastewater when it reaches plant older water becomes stale ro septic solids do not settle properly because gas bubbles cling on the particles and tend to hold them in suspension Rate of wasteawtaer flow as compared to design flow this is called hydraulic loading Mechiac conditions and cleanliness of the clarifier Proper sludge withdrawal fi sludge is allowed to remai in tank, it tends to gasify and entire sludge blanket depth may rise to water surface in clarifer Suspended solids that are returned to primary clarifier from other treatment processes may not settle completely, sources fo these solids include waste activated sludge digester supernatant and sludge dewatering facilities centrate from centrifuges and filtrate from filters

Ph in clarifier

Typically not affected significantly by clarifier

Milimicron

Unit of length to one thousandth of a micron 10-6 millimeters or 10-9 meters correctly called nano meters

Shut down procedures

Unit should be shut down annually for inspection maintenance and repair If there is only one unit for treating wastewater, standby emergency pond should be available to contain wastewater schedule shutdowns during periods of expected low flows -divert flow to other units or standby pond -drain clarifier and digester to drying beds Wash down inside of unit Inspect the facility be sure facility is adequately ventilated and test for oxygen enrichment or deficiency, combustible gases, and toci gases appropriate confined space procedures should be implemented to accomplish entry/work in a combined sedimentation digestion unit, look for corrosion dame unpainted surfaces worn pats cracks and leaks -make neccesary repairs -follow start up procedure

Septic tanks

Used mostly for treating wastewater from individual homes or from smal populations like camps where sewers have not been provided Tehy operate like imhoff tank except there is no separate digestion compartment Detention time is long like 12-24hours and most setteable solids will remain in tank, tehy must be pumped out and disposed of periodically to prevent th tank from filling Part of solids in septic tank are liquified and sicharged with wastewater into subsurface soil leaching system Conditions are not favorable for rapid gasification and most waste stabilization occurs in soil Septic tank effluent is disposed of in underground perforated pipes called leach lines and sampling effluent may be impossible Ability of soil to leach the septic tank effluent is critical factor in subsurface waste disposal One method of operating septic tank effluent leaching systems is to apply effluent to half of system while other half rests, monthly, switch flow from one half to other half, this procedure gives leaching system chance to recover its percolation ability

Secondary clarifers

Usually located after biological process in flow pattern fo treatment plant Purpose of them is to remove new converted solids produced by biological treatment Sometimes chemical process or used in place of biological proces of this is more common

Freeboard

Vertical distance from normal water surface to top of confining wall Verticlea distance from the sand surface to underside of trough in sand filter This distance is also called available expansion

Colloids

Very small fine divide solids that do not dissolve that remain dispersed in liquid for long time due to their small size and electrical charge Usually less than 200 millimicrons in size and genrally will not settle readily Organic colloids have high oxygen demand so their removal is desirable

Colloids

Very small finely divided particles that do not dissolve, that remain dispersed in liquid for long time due to their small size and electric charge, when most fo the particles in water have negative electrical charge, they tend to repel eachother, thsi repulsion prevents particles from clumping together becoming heavier and settling out

Vacuum floatation

Wastewater is aerated from. Short time in tank where it becomes saturated with dissolved ai the air supply is then cut off and large air bubbles pass to surface into atmosphere The water flows to vacuum chamber which pulls out dissolved air in form of tiny air bubbles bubbles then float the solids to the top

Weir overflow rate settling impact

Wastewater leaves clarifer by flowing over weirs into effluent troughs Number of lineal feet of weir in relation to flow is important to prevent short circuits or high velocity near the weir or launder which might pull settling solids into effluent Weir overflow rate is number of gallons of wastewater that flow over one lineal foot of weir per day Most designs recommend about 10000 to 20000 gallons per day per lineal foot Higher weir overflow rates have been used for materials with high settling rate or for intermediate treatment Secondary clarifiers adn high effluent quality requirements generally need lower weir overflow rates than would be acceptable for primary clarifers Primary get most weir overflow rate, after this its less for rest of plant Need to know flow in gallons per day and lineal feet of weir

Temeperature impact on settling

Water expands as temperature increases Below 4 C opposite is true and water compresses As water temp increases, settling rate increases Molecules of water react to temperature changes moving closer or farther apart and change liquid density High temp means lower density of water means particles settle fatster

Detention time impact settling

Water needs to remain in water long enough to settle, if tank is too small for quantity of flow settling rate of particles, too many will exit in effluent Detention time to setting rate of particles is important Most engineers design settling tanks for about 2 3 hours of detention time, this si flexible and dependent on many circumstances Detention time can be calculated by knowing quantity of flow per day Tank dimensions or volume

Short circuit impact on settling

Water should be dispersed evenly across the tank, otherwise cross section fo tank and flow at same velocity in all areas toward discharge end When velocity is greater in some sections tahn others, short circuit happens High velocity areas decrease detention time fo wastewater, and particles may not have enough time to reach the bottom and settle out.additionally the higher velocity present when a short circuit occurs keeps particles in suspension preventing them from settling. If velocity is too low, septic conditions occur that are not ideal. Weir plates, baffles, port openings, and proper design of inlet channel can prevent short circuits Can also be caused by turbulance and stratification of density layers due to temperature or salinity Temperature layers can cause short circuiting whe warm influent flows across top of cold water in settling tank, or cold influent flows under warm water in settling tank creating currents

Specific gravity

Weight of a particles substance or chemcial solution in relation to weight of equal volume of water Water ahs specie gravity of 1.000 at 4 C 39 F Usually wastewater particles ave specific gravity .5 to 2.5 specific gravity less than 1 float more sink Same thing for gas in relation to equals volume fo air in wastewater particles Chlorine gas specific gravity is 2.5

Length of weir formula

Weir length (ft)=pie X diameter of clarifier

Weir overflow rate formula

Weir overflow (gallons per day/square ft= flow (gallons per day) / length of weir Ft

Operational strategy

With only one unit, operator must try to treat entire flow, if inflows do not exceed design capacity, problems should not develop -follow normal operational procedure -collect and analyze samples on reagulra basis -plot results of tests and look for trends -make any neccesary adjustments -maintain al equipment according to scheudle

Removing supernatant

Withdrawn from digestion compartmetn by lowering sleeve on overflow tube in scum box, when top for leeve si below water surface in clarifer, supernatant will flow out digestion compartment removal of Supernatant provides space in digester for sludge being scrapped from bottom tray Lower the sleeve so approximately one half inch fo wate rwil flow vote rtop fo sleeve for 15-30 minutes twice a day