Biodegradable Solid Waste and Sludge Treatment Processes Flashcards
What are the stages of wastewater treatment?
- Preliminary treatment
- Primary treatment
- Secondary treatment
- Tertiary treatment
- Sludge treatment
What happens in the secondary treatment?
Removes soluble organic contaminants in the wastewater and biological treatment
What’s involved in the primary treatment?
- Primary clarifyer
- Flotation
What is a significant by-product of anaerobic degradation of biodegradable materials, and why is it important?
Generates methane (CH4), which contributes to climate change but can be captured and used as a renewable energy source
What are the applications of anaerobic degradation in waste management?
Crucial for:
- Landfill processes
- The principal treatment for sewage sludge
- The treatment of other biodegradable wastes such as food waste and livestock manure
What is the result of anaerobic degradation regarding the residual material?
The residual material from anaerobic degradation is stabilized and can be used as a fertilizer or soil conditioner when spread on land
How does secondary treatment in wastewater management function?
- Provides oxygen for bacteria to reproduce
- Captures residual gas
- Increases pathogen removal without heating or mixing
What percentage of sewage sludge produced in the UK is treated by anaerobic digestion?
80%
What is the total production of sewage sludge in the UK, and how is it managed?
1.4 million tonnes of dry solids (DS) of sewage sludge annually, with almost 100% applied to land after treatment
What are the benefits of sewage sludge treatment?
- Increases stability of matter
- Reduces odour
- Reduces vector attraction
- Reduces or eliminates pathogen content
- Improves physical properties as a product for land application
What is hydraulic retention time?
The average amount of time that liquid and soluble compounds stay in a reactor or tank
What is the formula for HRT?
Reactor volume/flow rate
What is the HRT for primary stage?
12 days
Main advantage of biogas being produced during sludge anaerobic digestion?
Energy production
What is the typical residence time in a digester for sludge?
Days
What role do enzymes play in the digestion process?
Catalyse biochemical reactions
What is the initial step in the biochemistry of anaerobic decomposition and how does it occur?
The initial step is hydrolysis, which is facilitated by extracellular enzymes that break down complex organic compounds
What occurs during the fermentation stage of anaerobic decomposition?
Volatile acids are produced through acidogenic reactions. One key product is acetate, which can subsequently be converted to methane (CH4) by methanogenic bacteria.
What is acetogenesis in anaerobic decomposition?
Acetogenesis involves Obligatory Hydrogen Producing Acetogenic bacteria, which play a key role in the bioconversion processes leading to methane production
How is ammonia related to anaerobic decomposition?
In anaerobic decomposition, ammonia can be degraded from complex polymers, contributing to the breakdown and stabilization of organic material
What are methanogenesis reactions?
Methanogenesis reactions involve the liberation of methane from acetate by specialized bacteria and the oxidation of hydrogen (H2) using carbon dioxide (CO2) as an electron acceptor.
How much more methane created from acetate than from CO3 reduction?
x2
Why is the growth of fermentative bacteria encouraged in anaerobic decomposition?
The growth of fermentative bacteria is encouraged to produce hydrogen, which is a critical intermediate in the process of methane generation through subsequent biochemical reactions.
What is the primary feedstock used in compost production?
- Green waste
- Sewage sludge
- Municipal solid waste (MSW)
What are the main composting processes used in producing organic fertilizers?
- A Windrow Composting Process
- An Invessel Composting Process
What type of decomposition is utilized in compost production, and what does it involve?
Compost production utilizes autothermophilic aerobic decomposition, which involves stacking solid substrates that undergo biological degradation with controlled aeration.
How is waste managed during the composting process?
Waste is aerated and mixed several times to ensure proper decomposition and nutrient distribution. This process also helps to generate heat necessary for the degradation process.
How is heat generated during degradation process?
Mesophilic activity
What is the final step in compost production and what does it involve?
The final step is the screening of the final product to ensure its quality before it is marketed as a soil conditioner
What is the optimal nitrogen to carbon (N/C) ratio for composting?
1:25 to 1:30
What is the ideal particle size for agitated composting systems?
12.5 mm
What should the free air space percentage be in a composting system?
30%
What is the optimal temperature for composting?
55˚C
What are the dimensions for an effective compost heap?
1.5 m high and 2.5 wide
How many stages are there in the microbial succession of composting and what are they?
- 4 stage microbial succession
- Mesophilic
- Thermophilic
- Cooling
- Maturation/curing
At what temperature does mesophilic activity decline in composting, and which microbial population takes over?
Mesophilic activity declines at temperatures above 40 degrees Celsius, after which thermophilic bacteria take over.
How does the population of microbes vary with temperature in composting?
Mesophilic populations are higher at 40 degrees Celsius and below, while thermophilic populations are higher between 40 and 70 degrees Celsius
What indicates that a compost pile is functioning properly in terms of microbial activity?
An increasing diameter of the pile, indicating proper nutrient and food storage, along with rising temperatures, suggests thermophilic activity is functioning properly
What happens during the cooling and maturation phase of composting?
- Reaction rate slows as easily degradable substrates are depleted
- Heat loss occurs and the pile cools, allowing other bacteria and fungi to take over
- This supports the succession of higher organisms like nematodes and protozoa
What is a key chemical transformation that occurs during the maturation phase of composting?
Ammonia is converted into nitrate
Whats involved in the preliminary treatment?
- Screening
- Grit chamber
- Equalization tank
What is the HRT for secondary stage?
14 days
