Operator 1 chapter 6 Trickling filters

If filter is left out of service for several days or longer, follow steps

-close filter underrain outlet gate to prevent flow from other units from entering underdrain tunnel -drain or pump down underdrain channel to prevent odors and insects from developing in captured stagnant wastewater -hose down distributor arms side walls vent ducts and underdrain tunnels -remove any grit or debris from Amin underdrain collection channel inspect underdrains and remove any debris i order to prevent stoppages - check oil level inn distributor turn table to proper level and possible presence of water -inspect turntable seal -consider remova of material biomass from media if growths are very heavy if not removed excessive growths may. Cause ponding when filters are restarted after drying teh material con be removed by use of leaf rake most of remaining material will be flushed out when unit is put back into service Steps take small amounts of time but can prevent unnecessary mistakes or prevent plant effluent from violating discharge requirements

Removing filter flies

-increase recirculation rate, continous hydraulic loading of 200 gallons per day per square ft or mor will keep filter fly larvae washed out of rock filter media Synthetic media will require higher hydraulic loadings or use of weekly flushing by turning on all filter pumps -keep orifices openings clear including end gates of distributor arms these grates can be opened slightly to obtain a flushing action on walls - apply approved insecticides with caution to filter walls and other plant structures - flood filter for 24 hours at intervals frequent enough to prevention completion of life cycle this cycle is short as seven days in hot weather adn poor effleunt wil result form practice so use it carefully monitored -Dose with about 1 mg/l chlorine for few hours each week chlorine will cause some slime layer to slough off too much chlorine wil remove too much of slime layer reducing BOD removal and lowering the effluent quality of plant - shrubbery weeds and tall grass provide natural sanctuary to filter flies good grounds maintenance and cleanup practices will help to minimize fly problems

Step by step procedures for shut down trickling filter

-inspect plant to be sure no abnormal conditions are present to affect effectiveness of other operating areas and process units -if filter to be take out of service has filter influent and recirculation pumps that supply only the filter being shut down, reduce pump speed to minimum range, reducing speed of pump will tend to relieve part of the surge created by remaining process units wen filter is shut down and due to reduced laod when pump started agin the life of variable speed pumps using belt drives is extended - stop influent flow feed and recirculation pumps for filter allow distributor arms to stop moving secure the arms and open the end gates. Restart the pump in order to flush the arms for few minutes do not try to open the gates or stop the arms when arms are still moving -stop the finluent flow feed and recirculation pumps for the filter and close the pump discharge valves, tag and lock out pump motor starters the filter distributor will stop rotating soon because no water is flowing out the outlet orifices Never attempt to stop rotating distributor by standing in front or grabbing with hands -check remaining plant parts for proper operation particularly wet wells and distribution or diversion structures between the other filters and clarifiers for normal water levels and position of flow control valves -Once the distributor arms has stopped rotating remove debris and rags from distributor arm orifice plates also remove the top fo media any debris and rags that could have been dumped during flushing of distributor arms

Shutdown of filter planning and considerations

-what is incoming flow could shutdown be better scheduled at time such as during low flow when operators are available to work -how will shutdown affect rest of plant, when the process or equipment is placed back on line after shutdown will it cause development of hydraulic surge which overload other processes like clarifers or chlorinators -if filter media is to be shut down for maintenance, are necessary tools and other items like funnels buckets lubricants available - are there any other. Tasks that should be performed while the unit is off the line, for example, does one of the recirculation pumps need repacking?

Industrial discharges solution

1. If toxic chemcial is known, neutralizing agent may be added to influent chlorine is used to counteract cyanide If high pH is detected excess of 9 then lower pH by adding an acid such as acetic or sulfuric if below 6, add caustic soda like sodium hydroxide if pH is not properly adjsuted you could produce toxic hydrogen cyanide or cyanogen chloride overcholriantion may destroy entire biological process always wear appropraite safety gear 2. Operate plant filters in series with high recirculation rebate in order to dilute influent and bring pH toward neutral the first filter may slough and lose its biological culture from the media but you may save biological growths in second filter If filters are operated in parallel the toxic flow may strip media in both filters or growths 3. Store toxic waste in collection system until its diluted by other water and gradually released during high flows 4. Locate industry responsible for toxic discharge and require the industry to start a source control program be sure your sewer use ordinances are inforced 5. Restrict toxic industrial discharges. Allow releases to occur slowly rather than in sludges or large batches also allow discharges to be released when plant can handle toxic wastes another type of restriction on very toxic agents is to allow discharges to the collection system only when tested neutralized and plant flows are sufficient to dilute discharge

Plant operation plan to control high flows from stormwater inflow and groundawater infiltration

1.Reduce or stop filter recycle or recirculation flows A-recycling flows to a filter are for dilution Dissolved oxygen increase and maintained hydraulic laod on filter media B-reduction in recycle flows in some plant designs also will reduce the hydraulic loadings on teh secondary clarifiers thus providing for better removal of solids sloughed from filter resulting from hgih flows 2. Place filters i parallel operation since stormwater has diluted the inflow, the DO will be higher in the inflow, loading each filter equally half of total flow to each filter, instead of forcing the total flow across each filter will reduce sloughing and keep each filter functioning 3. Keep the influent screening equipment operating and check often, especially if collection stem is combined sanitary and stormwater system which may have leaves and other debris in flow 4. Increase postchlorination rates to match flows in order to ensure proper disinfection 5. Use collection system as a storage reservoir by thrilling plant influent gate or by changing pumping elevations of pumping start and stop cycles A. This should only b down when lowest manhole elevation In the system is known and the maximum water level can be held at least 2 feet below manhole rim elevation to prevent system overflow B. Beware of pump problems developing when teh wet well water level is higher than normal highs ater levels reduce head a pump must work against, which results in a higher pumped flow which calls for an oversized pump motor 6. Use chemcials on influent to reduce solids and BOD laod by causing chemcial precipitation in primary clarifiers 7. Inspect collection system for major defects and develop programs to reduce inflow and infiltration 8. Reduce pumping of digester supernatant back to headworks in order to keep hydraulic loading as low as possible 9. Reduce pumping of sludge to anaerobic digesters because the sludge temperature will be lower than usual due to lower temperatures of the storm waters

Typical trickling filter plant lab results

6.31 page 181 of book

High flows due to stormwater inflow and groundwater infiltration solutions

A. If collection system is clean from good maintenance or from recent storms, the high flows usually dilute the solids and BOD and possibly reduce influent and solids loadings to below the ADWF loading B. If A above is true, then influent could have a higher than normal Dissolved Oxygen

Response to poor trickling filter effluent performance

Ability to make corrections depend on alertness and ingenuity as well as design of collection system and treatmetnplant Check influent flow and characteristics, state health of microorganisms population and operation of filter Several operational procedures can be done to correct deficiencies in plant performance

Maximum efficiency of filter and climate considerations on filter

Accomplished when slime growths on filter media are aerobic Done by proper design of wastewater collection system, proper operation of primary clarifiers Or by pretreatment of wastewater by aeration or addition of recycled filter effluent The supply of slimes may be improved by increased air or water recirculation Thin slime growth may be aerobic on surface but anaerobic next to media, trickling filter media of rock or slag can accumulate slimes only on outside surface but manufactured media provide considerably more surface area per unit of dead space Temp on water and climate also affect filter operation with temp of wastewater being more important Of course temp will vary constantly within limits, activity of organisms increases as temperature rises, therefore higher loadings and greater efficiency is possible in warmer climates if aerobic conditions can be reasonably Maintained on filter

Increasing efficiency of filter and sloughing importance

Add recirculation Filter effluent is recycleda nd brought into contact with biological film once more Increase contact time of water on the media and helps to seed lower portions fo filter with active organisms Due to increased flow rate per unit of area, higher flows tend to cause more continous and uniform sloughing of excess or aged growths, Uniform continous sloughing of growths is important because it provides more agressive surface of new growths to treat wastewater Sloughing prevents ponding and improves ventilation through filter Increased hydraulic loadings also decrease opportunity for small and filter fly breeding thickness of biological growth has beenobserved to directly relate to organic strength of wastewater higher BOD thicker layer of film By use fo recirculation, strength of wastewater applied to filter can be diluted thushelping prevent excessive build up

Nitrification

Aerobic process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen usually nitrate The second stage of Biochemical oxygen demand is sometimes referred to as nitrogenous BOD. Where first stage of BOD is referred to as carbonaceous BOD

Daily operation of filter

After media has slime growth, very little routine operational control is required Check items daily -any indication of ponding -filter flies -odors -plugged orifices -roughness or vibration of distributor arms -leaking past the distributor turntable seal -splash beyond the filter media -cleanup of slimes not on media

Suspended solids problem

An effluent that is high in suspended solids may be expected to affect all other test results ordinarily problem is due to four principle factors -heavy sloughing from filters Heavy sloughing may be seasonal weather changes, period of heavy organic loading on filters, or corrective action taken to overcome ponding filter flies or other problems -high hydraulic loading or short circuiting through secondary or Final clarifier Will carry light solids from filters over weirs if plant receiving more flow than designed to handle, you may adjust recirculation rates or flow pattern -shock loading caused by toxic wastes or hydraulic or organic overloads BOD - gasification (denitrification) caused by septic sludge in secondary clarifier

Trickling filters work on

Any organic waste taht can be treated by other aerobic biological processes can be treated by trickling filter This includes addition to domestic wastewater, wastewater from food processing textile carbonated beverage and even dairy adn fermentation industries as well as pharmaceutical processes Industrial wastewater taht cannot be treated are those that contain excessive concentrations of toxic materials such as pesticide residues heavy metals and highly acidic or alkaline wastes that harm organisms on filter media

Hydraulic loading

Applied to filter is total volume fo liquid including recirculating expressed as gallons per day per square foot of filter surface area

Shock load

Arrival at a plant of a waste taht is toxic to organisms in sufficient quantity or strength to cause operating problems Possible problems include odors and sloughing off of the growth or slime on trickling filter media Organic or hydraulic overloads also can cause a shock load

Maintenance of bearings

Bearings have water seal to prevent uneaten distribution of wastewater over the media and protect bearings when they located in the base Mercury seals must be removed if they are present as tehy are hazardous Be sure to monitor oil level carefully must be checked weekly Drain out pint of oil into clean container adn fi oil is clean and free of water return to unit and if dirty refill with mixture of 1/4 oil 3/4 solvent like kerosene Water in oil will appear at bottom of oil in container if water found in oil sealing fluid is low or the gasket must be replaced in mechanical seals

Plans and specifications sshould be reviewed by operators because

Become familiar with proposed plant Learn waht will be constructed Offer suggestions on how plant can be designed for easier and more effective operation and maintenance Areas influencing how plant will be operated include 1.Site A access to filter consider roads for maintenance equipment and walkways B overhead clearance determine locations and distances to electical power and telephone lines C trees and shrubs near filter as leaves will plug filter D location of hose bibs at convienent spots 2. Trickling filter structure A access to turntable seals and also oil drain fill and level plugs B layout of underdrain grills channels and channel slopes with access to space provided for flushing out solids carrying them away and proper ventilation C location of valves and gates and provisions made to allow flooding of filter media and dewatering of effleunt control boxes and underdrain collector channels with valves located between bobserfation and sampling manholes D access to effleunt boxes E center column support which is wide enough for timbers and tacks to be used to raise distributor from turntable for race maintenance F covere trickling filters 1 operator cannot see if arms are moving under the cover some types fo devices that cause a light to flash when arm passes a certain point should be placed on end of one of the arms then operator can determine speed of roatation of distributor arm 2. Filter is completely covered a forced air ventilation system will be needed. If odors cause complaints use odor scrubbing device as needed and odor scrubbing fans Proper mateirals must be used to avoid corrosion of roof strucutre Walls should extend minimum of 4-5 feet aboce surface of trickling filter media Vents should be designed to prevent staining spraying of outside of filter tower they should also be designed to close if forced ventilation is used Equipment- distributors Adjsutibel orfiices palates should be installed on both and leading and derailing edges of distributor arms Safety stops installed dto present end gate handle from catching in the media during flushing of distributor arm Turnbuckle on guy rods msut ahve sufficnet thread length to make necessary adjustments Valves-valvees must seat properly against design heads to prevent leakage back into channel during dewatering process A protective coating must be applied to all gates and frames Stop nuts must be installed on vll valve stems

Substitutions for BOD

Can use COD or SBOD in mg/l in place of BOD

Industries impacting biological treatments

Canneries meat packing houses or metal plating processes may require operator to change recirculation rates or mode of filter operation sequence If BOD rises, then recirculation should be increased

Pre start of filter

Check carefully before new one is started or placed in service again New plants are seldom started up without some unexpected frustrating problems Filter bearings come in special grease to prevent damage during transportation Packing grease must be removed and replaced with proper grease before start up If possible arrange to be present when new equipment is serviced, see correct oil and amount of oil to use in reservoirs Most contractors use motor oil in everything Record amount and type of oil After oil installed in distributor check arms fo reven adjustment and level Rotate unit by hand and observe smooth turning any vibration or roughness should be corrected before starting it If distributor has adjustable orifices get design specs and rule adn check out orifice settings file specification sheet for future reference In trickling filter plant with fixed spray nozzle each nozzle should be checked to ensure that it is free of foreign objects To prevent damage to pumps craw into underdrain system of filter adn remove debris like rocks wood other debris check painted surfaces for damaged areas touch them up before they get wet to prevent corrosion and further damage Few nicks on distributor arm can seriously affect the life of original protective coatings Check all valves for smooth operation On sliding gate valves, see gates seat properly There are adjustable wedges and stops on this type fo valve with valve adjusted set the lock nut on stem to prevent jamming or losing gate too quickly or tightly This can allow years of trouble free valve operation Have correct manual for each piece of equipment Read them carefully follow recommendations Remove any trash on or in media

Poor effluent quality problem

Check organic load on filter when treated effluent quality poor Measure both soluble and total BOD in final effleunt results will indicate if poor effluent is caused by BOD associated with escaping solids (high total BOD) or poor effluent results from trickling filter BOD removal capacity being exceeded high soluble BOD

Biomass

Clump of organic material consisting of living organisms feeding on wastes in wastewater dead organisms and other debris also see zoogleal film and zoogleal mass

Zoogleal film

Complex population of organisms that form a slime growth on the filter media and break down the organic matter in wastewater these slimes consist of living organisms feeding on wastes in wastewater dead organisms silt and other dibris Also referred to as slime growth

Fixed spray nozzle

Con shaped spray nozzle used to distribute water over filter media similar to lawn sprinkling system a deflector or steel ball is mounted within cone to spread flow fo water through the cone causing a spray action

Ponding

Conditions occurring on trickling filters where the hollow spaces Voids become plugged to extent that water passage through the filter is inadequate ponding may be result of excessive slime growths trash or media breakdown

Plant inflow problem

Considered abnormal when there are high flow rates, extreme levels fo suspended solids, or biochemcial oxygen demand, or inflows of septic influent High flow rates greater than 2.5 times the average dry weather flow, usually result from four sources -Stormwater inflow and groundwater infiltration Operator knows about this one -broken collection system pipe that permits excess inflow from groundwater or creek or stream -clearance of main line sewer stoppage and teh release of the backed-up wastewater -industrial discharges These three operator may not immediately know They all cause excess flow that can meet or exceed hydraulic capacity Conditions 3 and 4 impose other loads that the operator must also consider these loads include heavy solids adn BOD septicity and in case of industrial discharge, toxic material or load may case harm to biological treatment process

What type of hydraulic and organic loading is best on filter

Constant hydraulic loading on each trickling filter by adjusting recirculation rate Also adjusted to maintain dissolved oxygen from 3-6 mg/l in rock media and 4-8 mg/l in synthetic media Organic loadings should be calculated weekly basis and compared with plant effluent suspended solids and BOD if plant effleunt BOD or suspended solids changing look for change in hydraulic or organic loadings

Recirculation application

Constant or intermittent And at steady or fluctuating rate Sometimes recirculation only done during low flow, to keep rotary distributors in motion, prevent drying of filter growths or prevent freeing Can be used to reduce strength of wastewater applied to filter, steady recirculation rates for two or three hours of each week requires more energy, but tends to even out the highs and lows of organic loading This high rate will cause sloughing on regular basis rather tahn allowing slime growths to build up and slough under uncontrolled conditions

Classification of filters

Depending on hydraulic or organic loadings applied Filters are Standard rate high rate or roughing filters Further distinguished as Single stage, two stage, and series or parallel to indicate flow pattern of plant

Fixed nozzles maintenance

Distribution piping system is buried under the media and feeds into riser pipes spaced evenly across filter bed. Each riser pipe is equippe with spray head called nozzle at tp rise pipe above filter bed media nozzles are designed to handle high flows at low pressures and to pas some debris that would be in wastewater in order to prevent plugging. Riser pipes and nozzles are spaced evenly just like lawn irrigation system in order to provide equal distribution of wastewater on filter media Fixed nozzles must be observed frequently to detmerine that each is putting out desired spray patterns nd evenly covering media Nozzles can be come plugged and flow restricted, causing poor spray patterns system should be shut down, usually by closing valve on feed distribution pipe to clogged nozzles. On faulty nozzle the ball is removed adn rags or debris are removed from cone and deflector prper cleaning may require turning system on blowing air through riser pipe to remove stoppage and then reassembling nozzle Screen may be installed ahead of filter pimps or siphon if plugins is frequent

BOD problems

Effluent BOD will generally go up or down along with suspended solids This si not always true Water reaching plant in aerobic condition will reduce organic load and odors and consequently the effluent will be lower aeration has been used by force mains with some degrees of success when applied properly Recirculation rate and flow patterns will affect effleunt quality these can be varied experimentally keeping in mind that too low recirculation leads to filter flies and ponding while too high can cause excessive sloughing or hydraulic overload the clarifiers Biological systems respond to changes in environment and reach balance over time if you cahnge operation give plant couple weeks to reac equilibrium state to see if it fixed problem

Organic loading

Expressed as pounds of BOD applied per day per 1000 cubic feet of filter media Recirculation adds additional organic loading on filter however, added loadings is omitted in most calculations because it was included in influent laod

Trickling filter/solids contact process

Final effluent from trickling filter passes through aerated solids contact tank similar to activated sludge aeration tanks and then through secondary clarifiers with flocculator center wells. Sludge from secondary clarifier is mixed with trickling filter effluent adn mixture flows through aeration solids contact tank Aerated solids contact time detention time is one hour or less based on total flow including recycle or return sludge flow Solids retention time is less than 2 days Mixed liquor suspended solids can range from 1000-2500 mg/L and have little effect on final effluent suspended solids Benefits is more forgiving and less suspectable to shock loads but does require greater operator attention tahn the conventional trickling filter process Sludge blanket should be less than .5 ft to ensure fresh aerobic conditions

BOD applied formula

Flow (million gallons per day) X BOD(mg/l)X8.34(pounds per gallon)

Flow and dosing tanks

Flow is usually intermittent and is controlled by automatic siphons that regulate the flow from dosing tanks Dosing tanks and siphons should be constructed to facilitate cleaning and reduce problems caused by corrosion Attempt to record time required to fill and sicharge the dosing chamber if this time becomes shorter, this could indicate grease and solids are accumulating in siphon and pipes and should be removed

Protozoa

Group of motile microscopic organisms usually singled cell and aerobic that sometimes cluster into colonies and generally consume bacteria as an energy source

Safety in plan and specifications

Guardrails msut be located where necessary Be sure switches for turning off pumps to distributor arms are located so taht distributor arm can be stopped quickly if neccessary Look for ares where splashing water could cause a slippery surface and suggest corrective changes Install 115-120 volt receptacles at appropraite locations to permit use of drop lights when inspecting vents and underdrains

Underdrain system

Has sloping bottom Leads to a center channel that collects filter effluent the underdrain system supports the media and permits air flow common mateirals and methods for constructing underdrain systems include use fo spaced redwood stringers and prefabricated blocks constructed of concreate vitrified clay or other suitable material

High flows due to borken collection system pipe solutions

High flows consists of clear water from a creak or stream above broken pipe or from groundwater infiltration 1. Operate the plant using the same procedures as outlined under condition one 2. Have broken pipe repaired as soon as possible

Settleable solids problem

High in effluent mean solids ar being carried over clarifier weir Thsi also means suspended solids will be high, correct clarifer to fix problem

Roughing filter

Highly loaded filters commonly combined with other biological treatment processes like activated sludge, rotating biological contactors, RBCs, ponds, toa chieve higher levels of BOD removal

Hydraulic loading formula

Hydraulic loading (gallons per day/square feet)= flow gallons per day / surface area square feet of trickling filter

Screening problems impacting filter

If communitor screening equipment fails you must clean bypass bar rack to remove much of debris as possible frequent skimming of primary clarifer can help protect the trickling filter as well Frequency of flushing distributor arms should be increased to daily t keep them clean also distributor orifices should be cleaned more frequently to ensure an even application of wastewater to the media surface recirculation and influent feed pumps should also be checked for proper flows and discharge pressures because pump impellers may become plugged or loaded iwth debris thus reducing flows and requiring shutdown of pumps for cleaning

How to control abnormal flow

In filter plant you can Increase number of filters in operation adjusts loading rates as result, filter should have active slime growths on media Reduce or stop filter recycle or recirculation rates adjusts Dissolved oxygen and dilution Operate filters in parallel operations rather than series operation W

Fixing ponding

Increasing hydraulic loading is likely to flush off some fo heavier portions of biological film and Amy slowly cure this condition, this can be achieved by increasing the recirculation rate or adjusting orifices on distributor assembly so that is distributes flow more evenly Minor ponding which may occur from time to time, can be elmeinted by several method like -spray filter surface with high pressure water stream, sometimes stopping rotary distrubotr over ponded area wil flow growth from oids one way to do this is to shut off the flow momentarily wait for distributor to stop, move the distributor to problem area, and then restart the flow while keeping distributor over ponded area -hand turn or stir filter surface with rake fork or bar removing accumulation of leaves and debris -dose filter with chlorine at about 5 mg/l for several hours if done during periods of low flow, amount of chlorine used is held to minimum -if possible to flood filter, keeping media submerged for 24 hours will cause growth to slough somewhat, keep surface of media covered by do not let water rise high enough to get into distributor bearings, under these conditions growths tend to become anaerobic and loosen or liquify, after holding period carefully release wastewater in order to avoid NPDES effluent discharge requirement violation -shut off flow to filter for several hours the growth will dry and cna be removed by used of leaf rake most of remaining material will be flushed out when unit put back in service Last two options are drastic measures and first 3 affect effleunt the least Chlorine should be added if last two are used

Loadings and efficiency of trickling filter depends on

Influent characteristics like inflow and biochemical oxygen demand and required quality of effluent to receiving waters like dissolved oxygen and solids To calculate efficiency remember that frequency of each test and expected ranges will vary from plant to pant with strength of wastewater (BOD) freshness characteristics of water supply weather and industrial wastes all affect common range of various test results

Part and purpose of trickling filter

Inlet pipe- conveys wastewater to be treated to trickling filter Distributor base- supports rotating distributor arms Distributor bearings- allow distributor arms to rotate Distributor arms- convey wastwatre to outlet orifices located along arms Outlet orifice- controls flow to filter media adjustable to provide even distribution of wastewater to each square foot of filter media Speed-retarder orifice- regulates speed of distributor arms Splash plates- distribute flow from orifices evenly over filter media Arm dump gate- drains distributor arm and contorls filter flies along filter retaining wall also used fro flushing distributor arms to remove accumulated debris that might block outlet orifices Filter media- provide large surface for biological slime growth to develop Supporting grill- keeps filter media in place and out of underdrain system. Underdrain system- collects treated wastewater from under filter media and conveys it to underdrain channel also permits air flow through media Underdrain channel- drains filter effluent to outlet box Outlet box- collects filter effluent before it flows to next process Outlet valve- regulates flow of filter effluent from outlet box into outlet pipe closed when filter is to be flooded Outlet pipe- conveys filter effluent to next treatment process Retaining wall- holds filter media in place Ventilation prot- allows air to flow through media Stay rod- supports distributor arms Turnbuckle on stay rod- permits adjusting and leveling of distributor arm in order to produce even distribution of water over media Center well- provides for higher water head to maintain equal flow to distributor arms usually a head of 18 to 24 inches is maintained on the orifices Splitter box- divides flow to trickling filters for recircualtion or to secondary clarifiers Auxiliary equipment Recirculating pump- returns or recirculates flows to trickling filters

Clarifers and filters operation

Interconnected If recirculation pattern permits, good idea is return filter effluent to primary filter Effective odor contorl emasure because it adds oxygen to incoming wastewater that is often septic Increasing recirculation rate will increase hydraulic loading on clarifer so make sure it stays in limits If loading too low goes septic If too high or excessive then may wash solids out of clarifer Hydraulic loading on clarifers should not be greater than 900-1200 gallons per day per sqaure foot on average conditions and and less than 2000-3000 gallons per day per square foot for peak conditions

Roughing filters

Is actually a high rate filter receiving a very high organic loading Any filter receiving organic loading of 100-over 300 lbs of BOD per day per 1000 square feet of media volume is considered to be in this class This type of filter is used primarily to reduce organic load on subsequent oxidation processes such as a second stage filter or activated sludge process Many times they are used in plants that receive strong organic industrial wastes They are also used where an intermediate 50-70 percent BOD removal degree of treatment is satisfactory Most roughing filters ahve provisions for recirculation Basically same operation as high rate filters with recirculation overall BOD reductions are much lower than high rate filters, but reductions per unit volume fo filter Media are greater

Trickling filters are

Large diameter shallow cylindrical structures with stone and having an overhead distributor When natural media like stones used, trickling filter is usually cylindrical with shallow bed When synthetic media like plastics are used, filter could be cylindrical or rectangular with much deeper bed Synthetic media filters are often called filter towers or biofilter towers

Grit affecting filter

Large volume of grit will seldom reach filters unless a primary clarifer is bypassed or excessively overloaded with flow when parimary clarifer is excessively hydraulically overloaded the grit will be deposited in the under-drain which will allow septic dams and conditions to develop and produce odors Grit also can increase ponding on filter by filling the small voids between media and reducing the downward flow of water when this occurs the filter is taken out of service flooded drained and media washed off with water from a hose under pressure and underdrain cleaned

Principles of operation

Maintenance of good growth of organisms on filter media is crucial to operation

Recirculation during low inflow

May help keep slime growths wet minimize fly fly development wash off excessive growths reduce or stop recirculation during high flow periods, to avoid clarifer problems Recirculation of final clarifer effluent dilutes influent wastewater and recirculation improves slime development on media proper recirculation rates help contorl snail populations on media

Trickling filters biological oxidation beds and rotating biological contactors three basic parts

Media (retaining structure) Underdrain system Distribution system

Typical loading rates high rate filters

Media rock- 3-5 ft depth, growth sloughs continously Hydraulic loading -100-1000 gallons per day per sqaure foot or .07 to .7 gallons per minute per square foot Organic loading BOD - 25-100 lbs per day per 1000 cubic ft Media synthetic - 15-30 ft depth growth sloughs continously Hydraulic loading- 350-2100 gallons per day per square foot or .2 to 1.5 gallons per minute per square foot Organic BOD loading- 50-300 lbs BOD per day per 1000 cubic ft

Typical loading rates standard rate filter

Media rock- 6-8 ft depth grwothing slows periodically Hydraulic loading- 25-100 gallons per day per sqaure foot or .02 to .07 gallons per minute per sqaure foot Organic BOD loading - 5-25 lbs BOD per day per 1000 cubic ft.

Roughing filter typical loading rate

Media synthetic- 15-30 ft depth growth sloughs continously Hydraulic loading- 1400 to 4200 gallons per day per sqaure foot 1.0 to 3.0 gallons per minute per sqaure foot Organic BOD loading- 100 to over 300 lbs BOD per day per 1000 cubic ft

Lab tests should be done to observe these

Most samples should be analyzed to determine the temperature pH dissolved oxygen BOD COD and setteable solids Effluent sample should be analyzed for chlorine residuals adn most probable number of coliform group organisms in addition to usually water qualtidy indicators

Odors correction

No odors should be present as trickling filters are aerobic process Unles sodor producing compounds are prsent in water in high concentrations Presence of foul odors indicate anaerobic conditions are predominate If surface of slime growth is aerobic then odors should be minor, corrective measures should be taken immeditealy if foul odors develop handle problem this way -do everything possible such as prechlorination or preservation to maintain aerobic conditions in sewer collection system and primary treatment units -check ventilation in filter heavy biological growths or obstructions in underdrain system will interfere with proper ventilation examine the ventilation facilities such as draft tube or other inlet for stoppages if necessary force air into underdrain using mechanical equipment like fans or compressors, natural ventilation through a filter will occur if vents are open and difference between air temperature and filter temperature is greater than 3 degrees farenhiet -increase recirculation rate to provide more oxygen to filter bed and increase sloughing - keep wastewater splash from distributor away from exposed structures grass or other surfaces if slime growths appear on sidewalks, inside walls of filter or distributor splash plates remove them immediatealy -in some cases during hot weather odors will be noticeable from filters in good condition, if these odors are serious problem like to neighbors use masking agents

Fixed nozzle distribution system

Not as common as rotary type but is commonly found only in small plants Disadvantages of fixed nozzle are difficult access for nozzle cleaning and high pumping requirements to maintain good hydraulic flow of distribution Nozzles are located on surface of filter like lawn sprinkler system Each fixed nozzle consists of circular orifice with an inverted cone shaped deflector mounted above the center deflector breaks the flow into spray Some have steel ball in inverted cone Fixed nozzle system requires complex elaborate pipin systems o ensure even distribution of water and nozzles extend six to twelve inches above the media and are shaped so taht an overlapping spray pattern exists at the start of dosing when the head in the dosing tank is the greatest Pattern is carefully worked out to provide a relatively even distibution of wastewater

Filter staging

Number of filters is determined more by plant design tahn operation smaller plants where flow is fairly low, strength of rat wastewater is average and effluent quality limits are not too strict, a single stage plant (one filter) is often sufficient and most economical slightly slightly overloaded plants with addition of some recirculation capability can sometimes improve the effluent quality enough to meet receiving water standards and NPDES permit requirements without necessity of adding more stages

Fixed nozzle filter placed in service

Observe spray pattern Usually some debris will show up to plug some nozzles amount depending on how thoroughly plant is checked out prior to start up Be sure to keep nozzle clear as water is distributed over all filter media regualr care is required to keep fixed nozzles working

Operational strategy for trickling filters

One of most trouble free types of secondary treatment Process requires les operating attention and control than other types Difficulty due to shock loads are less frequent when recirculation used and recovery is faster Filter can act like sponge and treat great amounts of BOD for shor time periods without severe upset Recirculation can be sud to maintain constant load on filter and thus produce better quality effleunt when shock loads happen creating more turbidity in trickler effluent

Dissolved oxygen problem

One principle functions of trickling filter plant is to stabilize oxygen demaidnng substances in water being treated Addition of dissolved oxygen to water helps achieve this When suspended solids and BOD tests are in range then DO is in range, increased recirculation will increase the DO in plants with very low inflows excessive detention time in clarifiers may cause a problem with low DO in effluent If this is case remember that any agitation of effluent wil cause it to pick up dissolved oxygen, if elevation is available then staircase type effleunt discharge will help otherwise you can aerate effleunt using compressed air or paddle type aerators Sometimes low DO results in rising sludge (denitrification) the sludge blanket in secondary clarifier should be lower to les than .5 foot by increasing sludge pumping rate

Orifice

Opening hole in a plate wall or partition An orifice flange or plate placed in a pipe consists of slot or calibrated circular hole smaller than the pipe diameter. Difference in pressure in pipe above and at the orifice may be used to determine the flow in the pipe

Industrial discharges procedures

Operate plant using same procedures as condition one due to high flows with high solids loadings Also do same procedures as outlined in condition 3 as high flows and toxic material in plant influent a toxic material often can be detected if the industry notifies plany or if the influent sampling equipment monitors for specific chemical and sends out an alarm typical toxic conditions include an excessively high or low pH or presence of excess amounts of ammonia heavy metals or hydrocarbons unfortunately in most plants the influent is not monitored continously for high or low pH or specific toxic amtierla that causes the problem. Often operator does not know something toxic is in water until biological processes are not functioning and solids content in plant is too high few days after it hits

Standard rate filter

Operates with hydraulic loading range of 25-100 gallons per day per square foot or 1 to 4 million gallons per day per acre An organic BOD loading of 5-25 pounds of bod per day per 1000 cubic foot Filter media is usually rock with depth of 6-8 feet Application of filter by rotating distributor Many standard rate filters are equipped to provide some recirculation during low flow periods Filter growth is often heavy and in addition and Protozoa many types of worms snails and insect larvae can be found Growths slough at intervals noticeably in spring and fall Effluent from these filters are standard rate filter usually quite stable with BOD as low as 20-5 mg/L

Organic loading formula

Organic loading in (pounds of BOD/day/1000 cubic feet= Bod applied (pounds per day)/ volume of media in cubic feet NOTE* volume of media value is divided by 1000 so 8000 would actually be 8.000

Typical loading rates in metric units

Page 200 6.73

Troubleshooting trickling filter

Pages 191-194

Check distribution of water over filter

Pans of same size are placed level with rock surface at several points along radius of circular filter and should be same amount across whole area when test done Should all be about the same within 5% of eachother If distribution is not uniform then orifices and stay rod turnbuckles must be adjusted

How trickling filter works

Passing wastewater through filter causes development of gelatinous coating of bacteria Protozoa and other organisms that absorb and use much of the suspended colloidal and dissolved organic matter from watwater as it passes over growth in a rather thin film Part of this material is used as food for production fo new cells while other portions are oxidized to carbon dioxide and water Partially decomposed organic matter together with excessive and dead film si continuously or periodically washed or sloughed off and passes from filter with effluent

Sloughing problem

Periodic uncontrolled sloughing of biological slime growths from filter media Increasing recirculation pumping rate to the filter on weekly basis may help to induce controlled sloughing rather than allow slime growths to build up During flushing process slow down rotation fo distributor arms by adding more speed retarder orifices to rpoduce slower rotation and thus cause a longer flush that penetrates deeper into filter media

Force main

Pipe that carries water under pressure from the discharge side of a pump to point of gravity flow downstream

Main indicator of effectiveness of trickling filter

Plant effleunt If quality of plant effleunt drop, like Incease in effleunt BOD or suspense dolids then changes must be made in operation like changing recirculation rates and change in the operation of filters from parallel to series operation Vice certainly Use trend chart to note changes in plant effluent Determine what you consider ar emits important operational factors for plant like plant influent flow and effluent suspended solids

Budget considerations

Power costs are large item in plant budget Use lowest recirculation rates taht will yield good results Be careful not to cause ponding reduced BOD removal efficiency or other problems that happen when recirculation rates are too low Also reduced hydraulic loadings mean better settling in clarifers This results in less chlorine usage in plants that disinfect final effluent since organic matter exerts high chlorine demand if filter effluent rather than secondary clarifier effluent is recirculated te hydraulic loading on secondary clarifer is not affected

Primary vs secondary treatment

Primary = removal of setteable solids and floatable solids (scum) Secondary= suspended solids or dissolved solids which exert a strong oxygen demand on the recieving waters

Test fluctuations

Primary effluent tests may vary by plant due to variations in recirculation patterns and activities of those discharged wastes into collections ystem Settleable solids test of effluent is usually required by regulatory agencies Setteable solids will be as low as unreadable so record trace or less than .1 ml/l Tests of trickling filter effluent for dissolved oxygen settleable solids and clarity are sometimes useful in evaluteing problems when they occur Frequency of testing may vary widely from shown on table

Secondary treatment

Process to convert dissolved or suspended materials into form more readily separated from water being treated usually process follows primary treatment by sedimentation process commonly is type fo biological treatment followed by secondary clarifiers taht allow solids tos etttle out fo water being treated

Response to abnormal conditions

Proper planning needed

Media purpose

Provide large surface area upon which biological slime growth like zoogleal film can grow Containing living organisms taht break down the organic material Could be made of rock slag coal bricks redwood blocks molded plastic Must be sizesa nd stacked in way to provide empty spaces for air to ventilate the filter and keep conditions aerobic For rock sizes are 2 to 4 inches or 5 to 10 centimeters Media must be uniform in size to allow ventilation, but exact size isnt too critical Media depth ranges from 3-8 feet for rock media and 15 to 30 ft in synthetic media

Loading

Quantity of material applied to device at one time

Difference in trickling filter and rotating biological contractor

RBC treats wastewater with similar methods to filter except instead of applying water over media, media is rotated through wastewater being treated Structures in both filters and contactors may be covered and forced air ventilated for odor control and prevention of freezing in cold weather

Computing BOD ignore the

Recirculated effluent, where recirculation is used

Clarity problem

Related primary to amount size shape and characteristics of suspended solids in effleunt Industrial or food processing wastes may cause discoloration Trickling filter effluent tends to be slightly turbid Excessive turbidity can interfere with disinfection

Oxidation decomposition process

Requires contious supply of dissolved oxygen to operate Biological film needs dissolved oxygen Can be absorbed from air circulating through filter voids or adequate ventilation of filter provided Voids in filter media must be kept open Clogged spaces create problems including ponding and a reduction i overall filter efficiency Synthetic material provide 95% of total filter volume thus providing space for biological slimes to slough and pass through While rock media provides 35% total void space Plastic media trickling filters can be loaded much higher rates than those of rock media

High rate filters

Result of trying to reduce costs associated with standard rate filters and attempt to treat increased waste loads with same facility Same BOD reductions can be obtained with higher design loadings Usually ahve rock media depth of 3-5 feet or synthetic media with depth of 15-30 feet Recommended loading ranges from 100-1000 gallons per day per square foot for rock and 350-2100gallons per day per square foot for synthetic media 25-100 pounds of BOD per day per 1000 square ft rock 50-300 pounds of bod per day per 1000 square feet synthetic Filters designed to receive wastewater continously and practically all high rate installations use recirculation loadings may be higher for synthetic media Due to heavier flow of water over media, uniform sloughing of filter growths occurs with high rate filters this material is somewhat lighter tahn standard unit rate and more difficult to settle Effluents with BOD as low as 20-50 mg/L

Ponding

Results from loss of open area in filter, if voids are filled, flow tends to collect on surface in ponds, ponding can be caused by excessive organic loading without a corresponding high recirculation rate, perhaps the most common source of ponding is from lack of good primary clarification prior to filter Another cause of ponding is use fo media that are too small or not sufficiently uniform in size In nonuniform media, smaller pieces fit between larger ones and thus make it easier for slimes to plug filter, fi this condition exists, replacement fo media is most satisfactory solution other causes of ponding can be include poor or improper media permitting cementing or breakup, accumulation of fires or trash in filter voids, high organic growth rate followed by a shock load and rapid uncontrolled sloughing, or excessive growth fo is ect larvae or snails accumulating in voids

Recirculation

Return of part of the effluent from treatment process to incomeing flow

Tricking filter media

Rocks or other durable materials that make up body of the filter either directly or after passing through clarifier

Distribution system

Rotary type distributor that consists of two or more horizontal pipes supported a few inches above the filter media by a central column Water is fed from column through horizontal pipes and distributed over media through orifices located along one side of pipe Distributor arms or pipes on trickling filter rotate due to force fo wastewater flowing out f orifices

Distributor

Rotating mechiasm that distributes wastewater evenly over surface of trickling filter or other process unit similar to fixed spray nozzle

PH problem in effleunt

Should move from whatever value found in influent toward neutral Starts off acidic and move up to 7 or greater PH changes caused by industrial waste dumps or other unusual wastes entering plant, pH should remain normal as long as suspended solids and BOD are within limits reasonable An effective industrial waste monitoring and regulation program will decrease probability of harmful industrial discharges If pH varies beyond range of 7-9 then corrective action chemical neutralization must be added

Safety with trickling filters

Shut off flow to filter and allow distributor to stop rotating before starting work on it Force of arms is about equivalent to good side truck Slime growth on filter is slippery, rubber boots with deeply ridges soles can help footing Use plastic grating over synthetic media filters to walk across anda ccess bottom of distributor for repairs

Humus sludge

Sloughed particles of biomass from trickling filter media that are removed from water begging treated in secondary clarifiers

Microorganisms

Small organisms only seen through microscope

Placing filter in service

Start during late April through early june This procedure will produce most slime growth during shortest period of time Problems avoided will include wet weather flows in spring odors in summer and dormant bacteria in winter Start wastewater flow to filters observe rotating arms carefully for smooth operation speed of rotation and even distrubiton of water over media Time of speed for otation record flow rate and log them for future reference Starting up recirculation can be tricky as the pump may run out of water before the return from teh filter has begun You mat have ot block channels launders in clarifier and build upetra water before starting the pump conversely shutting off recirculation will result in surge of water because pump is no longer removing water but water is still returning from filter Slime growth occurs after several days on filter media During this period low efficiencies of waste removal may be expected Time of tear weather conditions and strength of wastewater all influence slime growth time for development Growth may be accelerated by recirculating wastewater prior to treating the main wastewater flow stream Waste activated sludge may also be added to recirculated flow to encourage slime growth development During this period, unstable effluent will be produced this effluent will exert a pollutional load on receiving waters heavy chlorination is used during this time of slime growth to reduce pollution load In areas that can affect fish chlorine use may be restricted, if older plant is being phased out it may be possible to load new facilities lightly or intermittently until full slime growth is done

Masking agents

Substances used to cover up ro disguise unpleasant odors

Shortcoming of BOD test

Test is difficult to use as daily operational tool unless influent BOd remains fairly constant If industry dumped water with high BOD you could not measure the BOD and you must base your operational adjustments on experience and probably BOD Use chemical oxygen demand test to estimate rapid changes in influent laod for contorl purposes COD test procedure will produce rustles in about 4 hours

Filter flies

Tiny gnat size filter fly psycho da is primary nuisance insect connected with filter operations Occasionally found in great numbers and can be extremely difficult problem to plant operating personnel Found most frequently in low rate filters

Trickling filter

Treatment process in which wastewater trickling over media enables formation of slimes or biomass which contain organisms that feed upon and remove wastes from water being treated

Nutrients problem

Trickling filter bacteria need adequate nutrients to grow Nitrogen and phosphorus Usually nutrients are present in wastewater Industrial wastewaters are often nutrient deficient like food processing wastes When industrial water dominates system, then composition of influent should be analyzed to ensure that each incoming 100 pounds of BOD there are five pounds of ammonia nitrogen and one pound of orthophosphate Nutrients can be added to achieve good treatment

Two stage filter plants

Two filters are operated in series, sometimes a secondary clarifier is installed between the two filters recirculation is almost universally practiced at two stage plants with many different arrangements being possible Choice of recirculation scheme is based on consideration fo which arrangement produces best effluent under the particular conditions of wastewater strength and other characteristics

Daily operating procedure

Use lowest recirculation rate that will produce good results but not cause ponding or other problems This conserves energy and minimize operating costs Must maintain routine observation of proces units Analysis of plant inflows to obtain wastewater characteristics and determination of water quality of plant effluent An alert operator will note changes in process units by observing various physical factors like flow rate or height over weirs launder levels amount of scum on clarifier and appearance of effleunt Rotation of filter distributor arms, spray patterns, and color fo media and odors, which indicate a change in biological treatment system, changes in any of these factors require investigation to identify the cause adn detmerine necessary corrective action Measure and record all important process factors Inflows measured by flowmeter Flows produce daily patterns on recording chart during dry weather Laboratory analysis of samples from various process stages including plant influent effleunt and secondary clarifer effleunt will indicate wter quality changes taking place in plant

Chlorine demand problem

Usually caused by primary excessive solids in effleunt This causes difficulty in maintaining residual chlorine in effleunt Remove suspended solids to fix this Loss of ammonia and inability to form chloramines may also result in increased chlorine demands and poor coliform reduction

High flows due to clearance of main line sewer stoppages solutions

Usually caused by surge or slug of high flows results from stoppage is cleared Influent is septic odorous and probably high solids and BOD load 1. Increase prechlorinationrates in order to control odors and reduce influent BOD load 2. Store the relased surge in collection system and allow it to flow slow into plant 3. Place filters in series operation apply initial loading to first filter and have it perform as roughing filter to reduce the shock load on next filter 4. Increase the recycle rates to both filters in order to increase dilution of influent to the filter, increase dissolved oxygen content of water applied to the filter 5. Increase postchlorination rates to maintain effective disinfection 6. Frequently skim the surface of primary clarifer to keep grease and other floatable off filter media and out of the orifices on the distributor arms 7. Frequently pump sludge from the bottom of the primary clarifier to reduce solids load to the filters 8. Stop recycle flows of supernatant or other heavy solids back to the plant influent or to the primary clarifier these flows would complicate the filter problems 9. Feed chemcials into plant influent 10. Arrange collection system maintenance crews to inform plant when system stoppage is cleared and expected to hit the plant

Underdrain maintenance

Usually cleanouts or flusher branches are located on the head end of each line or channel for flushgin to remove sludge deposits or debris from underdrain system if flushing will not clear line and agency or city's collection system has high velocity cleaner for cleaning sewer lines, use that to clean underdrain You may wish to schedule cleaning procedure every 3-6 months Clean underdrain system provides for fast carry off of filter bed effleunt promotes unrestricted air flow for media ventilation and reduces problems caused by odors septic conditions adn ponding

Colloids

Very small finely divided solids that are particles taht do not dissolve that email dispersed in a liquid for a long time due to their small size and electrical charge. When most of the particles in water have negative electrical charge they tend to repel each other this repulsion prevents particles from clumping together becoming heavier and settling out

Volume of media formula

Volume of media/1000 in cubic Feet= surface area (square feet) X depth (Ft) So if answer is 7,850 actual answer should be 7.85

Series operation

Wastewater being treated flows through one treatment unit then lows through another treatment unit

Parallel operation

Wastewater being treated is split and portion flows to one treatment unit while remainder flows to another similar treatment unit also see series operation

Cold weather problem

Water sprayed from distributor nozzles or exposed in thin layers on media may freeze adn buildup ice on filter Solve problem by -decrees amount of recirculation because influent is usually warmer than recycled flows provided sufficient flow is maintained Operate two stage filters in parallel rather than in series Adjust or remove orifices and splash plates to reduce spray effect Construct wind screens covers canopies to reduce heat losses Break up adn remove larger ares of ice building Partially open end gates to provide as tream rather tahn spray along retaining wall Add hot water or steam to filter influent if necessary Filter unit efficiency is reduced during periods fo icing, it is important to keep unit running removing it form service will lead to additional maintenance problems and damage effluent quality Structural damage can occur as well and ice forming and moisture may condense in the oil and damage bearings

Secondary clarifer impact on filter

When a secondary clarifier is out of service solids in the treated effleunt will increase and will accumulate in chlorine contact basin operate filters in series, apply normal recirculation flows to first filter and do not recirculate to the second filter, apply normal flow as evenly as possible to second filter this procedure should minimize sloughing from the media on second filter for a while and, hopefully, until secondary clarifier is back in service A simple device containing a coarse hardware cloth screen or similar device could be installed din underdrain channel or outlet box to catch the sloughing the screen would be removed and cleaned frequently

Coliform count

When bacterial count requirement msut be met, excessive solids in effleunt are serious problem Even with high chlorine residuals, sporadic reuslts occur because some particles are not penetrated completely by chlorine Some type of water treatment plant technique like coagulation and settling or sand or diatomaceous earth filters may be used to further treat solids in water. Good disinfection is achieved if previous treatment processes do their job however notification and denitrifciaton are also very common cause of poor coliform reduction, some plants either taken treatment units off line to reduce nitrificaiton or added about one mg?L ammonia prior to chlorination to form chloramines to improve disinfection

Primary clarifer impact filter

When its out of service in filter plant, operate filters in series, use the first filter as a roughing filter to remove the large pieces of suspended wastes, the first filter can perform satisfactorily this way for several weeks, but require a cleanup of filter afterward this procedure should keep second filter healthy and leave only one filter to clean

Chlorinator impact filter

When one chlorinator is not working, bring another chlorinator on line, if one is available and no other chlorinator is available, reduce hydraulic load on secondary clarifiers as much as possible to obtain the best solids removal, if you do not ahve a standby chlorinator develop emergency procedures now to chlorinate your effluent when the chlorinator is not working some smaller plants use sodium hypochlorite as a standby disinfectant.

Distributor arms

Work only after arms stoppe dmvoing Unless using pressure hose for cleaning and stand outside filter wall Arms must be flushed weeekly but opening the end dump gates one at time clean debris off of surface each day Clean orifices as needed Install coarse hardware cloth or screen to prevent considerable plugging present Screens are better If jumpy vibrate or slow down with same amount of water passing through it, the bearings and races are probably damaged and will require replacement Oil check each week Adjust turnbuckle occasionally on guy rods to keep rotating distributor arms at proper level to provide even flow over all media Speed of roatation of distributor should not be excessive Speed controlled by regulation of flow through orifices if it rotates too fast, it may damage bearings races on turntable To reduce speed of rotation, provision usually is made on front of each arm for orifices which are easily installed. The force of water flowing out of these orifices cancel some of thrust of regular orifices, if too slow increase flow Slime should be removed from the plates as slime growth can through off uniform distribution