Chapter 5

Factors operators can use to calculate when the filtration cycle will be completed?

1. Effluent turbidity level 2.Elapsed run time 3. Head loss

Which factors are important filter process control guidelines?

1. Filter effluent water quality (turbidity) 2. Filter influent water quality (turbidity) 3. Filter performance

Which factors are indicators of abnormal filtration conditions?

1. Filter turbidity breakthrough 2. Filters that will not come clean during backwash 3. Media boils during backwash 4. Mud balls in filter media 5. Rapid changes in head loss buildup in the filter

Factors that an operator should investigate when troubleshooting a filtration process

1. Filtration process changes 2. Process problems 3. Filter effluent quality changes 4. Sedimentation process effluent quality changes 5. Source water quality changes

What problem is created by too high backwash rate?

There could be excessive loss of filter media and media disturbance

Under which conditions may clean filters be put into service?

1. A dirty filter is removed for back washing 2. To decrease filtration rates 3. To increase plant production as a result of increased demand for water

Which types of impurities are removed by filtration?

1. BOD 2. Biological forms 3. Colloids 4. Floc 5. Suspended particles

Which process calculations are operators expected to perform in the routine operation of the filtration process?

1. Backwash rate 2. Filtration Rate 3. Percent of water production used to back wash filter 4.Unit Filter Run Volume

Which tasks should an operator perform when checking a filter as part of starting up or shutting down the filtration process?

1. Be sure filter media and wash water troughs are clean of all debris as leaves, twigs, and tools 2. Check and be sure all access covers and walkways gratings are in place 3. Check source of backwash water to ensure it is ready to go 4. Make sure process monitoring equipment such as head loss and turbidity system are operational

Which tasks are typical routine maintenance functions?

1. Checking pumps and motors for leaks, unusual noise and vibrations, or overheating 2. Ensuring good ventilation in equipment work areas 3. Inspecting for alignment of shafts and coupling 4. Keeping electric motors free of dirt, moisture and pests 5. Maintaining proper lubrication

Filter removal of TURBIDITY depends on what factors?

1. Chemical characteristics of the water being treated 2. Filter type and operation 3. Nature of suspension 4. Types and degree of pre-treatment

Abrupt changes in which water quality indicators are warnings to operators of abnormal process conditions?

1. Chlorine demand 2. Color 3. pH and alkalinity 4. TON 5. Turbidiy

Which safety precautions should be followed when working with mechanical equipment

1. Clean up all lubricant and chemical spills 2. Do not wear loose clothing around rotating equipment 3. Keep hands clear of equipment 4. Use protective gloves on rotating equipment \

Short filter runs may result from which factors?

1. Clogging of the filter under drain system 2. Excessively high filtration rates 3. Excessive mud ball formation in the filter media 4. Filter aid overdosing 5. Increased solids loading

Which water treatment technologies are recognized by the SWTR

1. Conventional filtration 2. Diatomaceous filtration 3. Direct filtration 4. Slow sand

What types of filter control system are commonly used in gravity filtration installations?

1. Declining rate 2. Rate-of-flow 3. Self-backwash 4. Split-flow

Which factors can be used to develop process guidelines to assist operators in evaluating normal process conditions and in recognizing abnormal conditions?

1. Design considerations 2. Trial and experience 3. Water quality conditions 4. Water quality standards

What are the specific classifications of filter types used in water treatment today?

1. Diatomaceous earth filtration 2. Gravity filtration 3. Pressure filtration 4. Slow sand filtration

What are different types of gravity filtration systems used to treat water?

1. Dual media 2. Mixed media 3. Single media

Which characteristics are used to classify types of filter media?

1. Effective size 2. Hardness 3. Specific gravity 4. Uniformity coefficient

Particle counters can be used to perform which tasks?

1. To evaluate and compare the performance of different arrangements of filter media 2. To evalaute and compare the performance of different types of filter media 3. To measure effectiveness of polymer addition and polymer dose points to improve filter performance 4. To optimize filter startup rate 5. To optimize filter-to-waste period minimization

filter clogging

A buildup of head loss across the filter media until it reaches some predetermined design limit

breakthrough

A crack or break in a filter bed allowing floc or particulate matter to pass through a filter causing increased filter effluent turbidity

What is a desirable characteristics for filter media

A deeper filter bed with a larger media size

Direct filtration

A method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration.

Surface Water Treatment Rule

A set of treatment technique requirements that apply to all water system using surface water

Slurry

A watery mixture or suspension of insoluble matter

What backwash process adjustments would you make to solve such problems as media boils, media loss, or incomplete cleaning of media

Adjust the backwash flow rates, surface wash flow rate, or duration

Turbidity meter

An instrument for measuring and comparing the turbidity of liquids by passing light through them and determining how much light is reflected by the particles in the liquid. The normal measuring range is 0 to 100 and is expressed as Nephelometric Turbidity Units (NTUs).

What problems can develop from improper backwash rates

An insufficient backwash rates may not completely remove trapped solids from the filter media

Why is flow control critical for accurate and repeatable particle counter performance?

Because all particle count data must be based on sample volume

How do filter control systems regulate flow rates throughout the filter?

By maintaining an adequate head above the media surface

In the filtration process, how is filter efficiency measured?

By overall reduction in turbidity

What should you not check for after starting any piece of equipment?

Check for excessive noise and vibration, over heating, and leakage

What would you look for in evaluating the filter media condition after a back wash cycle?

Cracking, media loss, and mud balls

How could you adjust the filter operation if increases in source water turbidity and resultant increases in coagulant feed rates impose a greater loss on the plants active filters

Decrease filtration rates

Name a type of filtration that can be used to meet the requirements of the SWTR

Diatomaceous earth filtration

Which item is an indicator of an upset or failure in the filtration process or pretreatment process?

Excessive media loss

Depending on the amount of DO in the water being treated and the filtration rate, the filter will exhibit high head loss or clog after a given time period

False

Filter Backwash Recycling Rule requires that recycled filter back wash water be returned downstream of all treatment processes

False

Filtration is the first and most important step in the solids removal process

False

Particle counters can tell the difference between a particle of clay and a microorganism

False

The startup or shutdown of the filtration process is not a routine operating procedure in most water treatment plants

False

Usually higher backwash rates are required at low temperatures and with smaller media

False

In all gravity filtration systems the water level or pressure (head) below the media forces the water through the filter media

False; above the media

How frequently should the performance of the filtration process be evaluated?

Influent, every 2 hours; effluent, continuously

Why is diatomaceous earth filtration used in some water treatment applications and not in others

Limited use in larger treatment plants due to hydraulic flow, sludge disposal, and other operational conditions

Mud ball

Material round in shape that forms in filters and gradually increases in size when not removed by the back washing process

How can particle counters be used to monitor filter performance?

Measure effects of filter flow rate

What is an efficient means of handling filter backwash waters?

Recycle the water to the beginning of the plant

Problem caused by air-bound filters

The air prevents water from passing through the filter and causes shortened filter runs

submergence

The distance between the water surface and the media surface in a filter.

How does the declining-rate filter control system work?

The flow rate varies with head loss and each filter operates at the same, but variable, water surface level

Adsorption

The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another material.

How does the self-backwash filter control system work?

The influent flow to each filter is divided by a weir and the water surface level in each filter varies according to head loss, but the flow rate remains constant for each

Backwashing

The process of reversing the flow of water back through the filter media to remove the entrapped solids.

Advantage of the conventional filtration process

The system provides a great amount of flexibility and reliability in plant operation

Why must adequate clearance be allowed between the top of the filter media and the bottom of the wash trough?

To prevent the filter media from being carried out over the wash troughs during backwash

What is the primary purpose of the filtration process?

To remove particulate impurities and floc from water being treated

Why is activated carbon used along with other types of filter media?

To remove tastes, odors, and organic substances

Filter production rates are the measures of the amount of water that can be processed through an individual filter module in a given time period

True

Significant changes in source water turbidity levels, either increases or decreases, require immediate verification of the effectiveness of the filtration process in removing suspended solids and floc

True

The relative importance of removal mechanisms within a filter depends largely on the name of the water being treated, degree of pre-treatment, and filter characteristics

True

Which instrument would you use to monitor a filtration process?

Turbidity meter

diatomaceous earth

a soft, fine, porous deposit that is composed mainly of the skeletons of diatoms

Conventional filtration

filtration that is preceded by coagulation, flocculation and sedimentation.

Head loss

the head, pressure or energy lost by water flowing in a pipe or channel as a result of turbulence caused by the velocity of the flowing water and the roughness of he pipe, channel walls or restrictions caused by fittings.

Piezometer

used to measure hydraulic head