Sludge Digestion Flashcards
What is the purpose of sludge digestion?
To lower the volatile and pathogenic content and overall volume of sludge
What are the byproducts of anaerobic sludge digestion?
Methane
Water
Stabilized sludge
How do you ensure good sludge digestion?
Regular feed rate
Constant temperature
Appropriate nutritional content of food
What are the two bacteria types needed for anaerobic digestion?
Acid forming saprophytes and methane fermenters
Describe the anaerobic digestion process
Organic materials are converted to volatile acid by the acid fermenters (no waste stabilization occurs during this phase)
The volatile acids are then converted to methane gas by methane fermenters (waste stabilization occurs here)
What is the appropriate volatile acid/alkalinity ratio in an anaerobic digester?
.1
What conditions are needed for methane fermenters to grow?
Ph 6.6-7.6
Anaerobic
What are the purposes of mixing an anaerobic digester?
Distribute raw sludge
Bring microorganisms into contact with food
Distribute alkalinity
Distribute heat
Minimize settling of grit and inert solids
What are the different temperature zones in anaerobic digestion?
Psychrophilic (50-68 def F)
Mesophilic (68-113 deg F)
Thermophilic (120-135 deg F)
How long does psychrophilic digestion take?
50-180 days
How long does mesophilic digestion take?
5-50 days
How long does thermophilic digestion take?
5-12 days
What is a rule of thumb when changing digester temperature?
No more than one degree per day
What is an appropriate amount of volatile solids reduction after digestion?
50%
What components of gas will dominate at anaerobic digester startup?
CO2, ammonia, and sulfur
At what percentage of methane is digester gas burnable?
56%
At what percentage methane is burnable digester gas usable as fuel?
60%
At what mixture is oxygen and digester gas explosive?
5-15%
What are common causes of foaming in an anaerobic digester?
Acid regression/insufficient digestion
Rapid temperature changes
Thick sludge blanket being broken up
Overfeeding
How do you neutralize a sour digester?
Add anhydrous ammonia, lime, soda ash
1lb of lime for every 1000 gallons of sludge
Equivalent mg/l of lime to volatile acids
What is struvite?
The scale formed by ammonia, phosphorous, and magnesium. Almost as hard as concrete.
What is aerobic sludge digestion?
The conversion of organic sludge solids to odorless end products of carbon dioxide and water by aerobic microorganisms
Describe appropriate operating parameters for aerobic digestion
High MLSS (10000-15000)
Long detention time
As thick of sludge as possible
