Sludge Treatment Process Flashcards
What is the purpose of sludge treatment
Increase stability of biodegradable matter, eliminate pathogen content, reduce odour and improve properties for land application
What is the primary stage of anaerobic digestion
heated up as pre-treatment to kill pathogens. Then it is mixed inside a sealed tank for 10 days or more and heated at mesophilic temperatures
what is secondary stage of anaerobic digestion
The sludge is left to remain in a tank without mixing or heating and the residual gas is captured. Then it proceeds to mechanical dewatering
what is one way of mechanical dewatering
Using a centrifuge
What are the four reactions occurring in anaerobic digestion and what microorganisms are causing them
hydrolysis by extracellular enzymes, fermentation by acid forming bacteria, acetogenesis by obligatory hydrogen producing acetogenic bacteria and methanogenesis by methanogens
What is composting
auto thermophilic aerobic digestion. The heaps of sludge and waste are degraded by microbes and the heat produced keeps the reaction continuing. Batch process.
Why is composting required for green waste
The tough organic material found in garden waste such as lignin and cellulose cannot be degraded anaerobically
Why is composting carried out in open air
It is cheaper. The reaction is self propagating and will require a constant supply of oxygen if performed in a sealed container, but attains greater control in a sealed environment
Why is bulk agent added to compost
Adds the necessary moisture, void space and carbon/nitrogen ratio for good composting
What are the four stages of composting
Mesophilic, thermophilic, cooling (fast rate phase lasts about 2 weeks)
maturation (about 2 months)
What microbes are used in composting first phase
mesophilic and thermophilic bacteria + fungi
What is produced from sludge treatment
Useful biogas such as methane, fertilisers and industrial chemical precursors.
