waste water ch12
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The sludge digester can either be an anaerobic or aerobic treatment system.
The pressure relief valve and the vacuum relief valve both are attached to a common pipe, but each works independently.
A properly operated floating cover can effectively controlthe scum blanket in a digester
Activated sludge will be destroyed in the digester to the same extent as raw sludge.
The neutralizing of a sour digester will bring the pH to asuitable level and also will cure the cause of the upset
The volatile acid/alkalinity relationship is an indication ofthe buffer capacity of the digester contents
Corrective action should be taken whenever trends orchanges in digester performance start in the wrong direction.
Aerobic sludge digestion tends to produce more noxiousodors than anaerobic sludge digestion
When the liquid in an aerobic digester becomes too warm,offensive odors may develop and the process effiuent willhave a very poor quality
Waste aerobic sludge from the secondary clarifier can providethe seed sludge to start the aerobic digestion process
Wet sludge can be spread on land to reclaim the land or on farm land and ploughed in as a soil conditioner and fertilizer.
What are raw sludge and scum?
Settled sludge solids that are removed from the bottomand the floating scum removed from the top of the clarifiers
What is the most common condition of imbalance in ananaerobic digester?
Excess acid formation (fermentation)
What is the purpose of a water seal on an anaerobic sludge digester?
Prevents air from entering the digester or digester gasfrom escaping
Why must water be trapped at low points in a digester gas system and removed?
To prevent restricting gas flow and causing damage to equipment
Why is it considered hazardous to start a digester when it is only partially full?
Because of explosive conditions created by the mixtureof air and methane in partially full digesters
How can an operator obtain a thick sludge to pump to the digester?
Hold a blanket of sludge as long as possible in the primaryclarifier
Why should the temperature in a digester not be changed by more than 1 °F or 0.5°C per day?
To allow the organisms time to adjust to the temperaturechange
Why is an aerobic digester commonly used?
To avoid the problems encountered when a waste aerobicactivated sludge with low solids content is placed inan anaerobic digester
What are bio solids?
A primarily organic solid product produced by waste water treatment processes that can be beneficially recycled
For successful operation of the anaerobic sludge digestion process, operators must perform which tasks?
- Keep careful records and use laboratory analyses to follow the process continually
- Know the facilities thoroughly so they can attain maximum flexibility of operation
- Maintain the facilities in the best possible condition at all times
- Understand the theory of the process so they know whatthey are basically trying to do
Why should a sludge line never be isolated by closing the valves on each end for several days?
Valves may become blocked by rags or other material
Which important objectives are accomplished in a well mixed digester?
- Inoculation of the raw sludge immediately with microorganisms
- Maintenance of homogeneous (similar) contents throughout the tank, including even distribution of food, organisms, alkalinity, heat, and waste bacterial products
- Prevention of scum blanket formation
- Removal of excess heat within the contents of the digester
- Use of as much of the total contents of the digester as possible and minimization of the buildup of grit and inert solids on the bottom
Why should the floating cover on a digester be inspected frequently (daily)? To prevent the cover from becoming
Which operational actions can cause a digester to become sour?
- Addition of excess food
- Excess water supplied, which dilutes the alkaline buffer
- Improper temperature changes
- Overdrawing of digested sludge
- Poor mixing
How can the recovery of a sour digester be accelerated?
- By neutralizing the acids with a caustic material such as anhydrous ammonia, soda ash, or lime
- By transferring alkalinity in the form of digested sludgefrom the secondary digester
Which steps should an operator take to prevent digester foaming?
- Do not over drain sludge from the digester
- Exercise caution when breaking up scum blankets
- Feed sludge at regular, short intervals
- Keep the contents of the digester well mixed from bottom to top at all times
- Maintain a constant temperature in the digester
Which items may unbalance the volatile acid/alkalinity relationship in a digester?
- A shock load produced by a storm flushing out the collection system
- Excessive feeding of raw sludge to the digester
- Removal of digested sludge
What does high solids content in the supernatant usually indicate?
- Too much digested sludge is being withdrawn from the digester
- Too much seed sludge is being withdrawn &om the digester
Which informative operational data could be plotted against time to illustrate changes or trends in digester performance?
- Carbon dioxide content of the digester gas
- Digester loading
- Gas production
- Volatile acid/alkalinity relationship
What should be done if the volatile acid! alkalinity relationship starts to increase?
Try to pump a thicker sludge
Which items are possible methods of controlling toxic materials in digesters?
- Add a chemical that will cause the toxic material to precipitate out of solution or form an insoluble compound
- Add a chemical that will neutralize the toxic material
- Dilute the toxic material below its toxic level
- Remove the toxic material from the waste at the source
Which items are important safety precautions when cleaning a digester?
- Always use a bucket and rope to lower tools and equipment
- Always use explosion-proof motors and electrical equipment when working near openings in the digester
- Before entering the digester, always test the atmosphere for oxygen content, flammable/explosive gases, and toxic gases Provide adequate ventilation at all times Rope off or barricade the area to prevent unauthorizedpersonnel from entering the area or the digester
Successful operation of aerobic digesters requires operators to measure and record what information?
Pounds of solids transferred and volatile contentVolume of raw and secondary sludges transferred to the aerobic digesterVolume of supernatant liquor withdrawn from the lastdigestion tank
Which problems could occur if "green" (partially digested)sludge is accidentally drawn to a sand drying bed?
- Odors will be produced
- Water held will provide an excellent breeding ground for nuisance insects
- Water will not drain rapidly
Which precautions must be practiced when disposing of sludge by withdrawal to land?
- Access to the land during wet weather must be provided
- Domestic water wells must not be located on the land receiving the sludge
- Never apply partially digested (green) sludge or scum
- Residential areas must not be located near land disposal sites
- Root crop vegetables must not be grown on the land
Which items must be monitored during the use of bio solids on agricultural land?
When examining the plans for sludge digestion and solids handling facilities, which items should operators check?
- Check for adequate backup or standby raw sludge pumps
- Check for combustible gas analyzers and their location in galleries or closed areas
- Check for location, size, and type of sampling ports
- Check the location and sufficiency of power outlets and wash water faucets
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