Solid Waste And Sludge Treatment Flashcards
What does the anaerobic degradation of biodegradable materials produce?
Mehtane (CH4)
What does CH4 do?
Contribute to climate change
Can be captured for use as a renewable energy resource
What is anaerobic degradation of biodegradable materials good for?
Stabilising residual sludge from WW for spreading on land as fertiliser
Sewage sludge treatment has the 5 benefits of . . .
Increasing stability of biodegradable matter
Reducing odour and offensiveness
Reduces vector attraction
Reduces pathogen content
Improves physical properties as a product for land application
(TL;DR cleans, makes safe, makes useful)
How many stages are there in typical conventional anaerobic digesters?
Two
Primary and secondary
What is the main distinction between the primary and secondary phase of an anaerobic digester?
In primary phase sludge is heated and mixed. The main product is methane and heat
In the secondary secondary phase, there is no mixing or heating but instead increased sludge consolidation. Main product is digested sludge for fertiliser
What exactly goes on in the primary phase of anaerobic digestion?
Raw sludge goes in
12d long
Sludge is digested by mesophilic bacteria in a silo at 35°C
Methane is released in the reaction
Digested sludge moves into secondary phase
What exactly goes on in the secondary phase of anaerobic digestion?
Digested sludge is firstly dewatered
For 14 days:
Pathogen removal increases
No heating or mixing
Supernatant by product with high BOD extracted as a liquor to be treated more
Digested sludge extracted for use as fertiliser
What is the sciencey term for composting?
Autothermophilic aerobic decomposition
What roughly happens in composting?
Degredation of sewage sludge over several weeks by microbial succession
What happens to the heat generated by mesophilic activity during composting?
The heat gets conserved in heaps, increases temperature and can be extracted for commercial use or to be fed back into facility
What does composting produce?
Stabilised, dark brown residue which can be used as a soil conditioner
What are the (four) stages of composting?
Pre processing
1st stage high rate phase
2nd stage curing phase
Post processing
What is the nature of microbe activity in the 1st phase?
Mesophilic then thermophilic
What happens in the curing phase?
Cooling then maturation of compost product
