Biosolids Management (at 1.08.47 minute) Biosolids are the nutrient r i c h by-product of modern MSW treatment. Since the 1980s the management of these has been increasingly focused on recycling. Efforts to control the pollution at its source have dramatically improved the quality of wastewater coming into treatment plants and the quality of biosolids produced by these plants has
increased.
WATER Solids handling (at 1.10.10 minute)
A) Sludge thickening B) Sludge digestion C) Sludge dewatering
A) The first step is the sludge thickening process and the process is very similar to that
happening in clarifiers. This process takes solids concentration from 0.5% to 6%. In the gravity thickener we use gravity to settle the sludge out and make it thicker, so that it’s easier to treat in the rest of the solids handling facilities. When pressure is released the sludge floats to the top and we end up with 5% solids blanket at the top, which we scrape off and send to our solids handling facilities for digestion.
B) In the digesters we heat the sludge up and the micro-organisms start to break it down
and get rid of some of the volatile compounds. In that process it also destroys some of the pathogens. When we are finished the sludge is transformed into a useful product. But during that process we also generate some methane. That methane produced is used to run generators and those generators power part of the wastewater treatment plant. Waste heat is also generated which is used to heat the digestion process, so it’s a nice circle and a whole lot of the energy stored inside the sludge is used to make the whole process cheaper to operate.
•Most biodegradable organic material can be collected and used for anaerobic digestion
•The material is fed into a digester tank where it’s broken down by bacteria in the absence of oxygen.
•This produces biogas (a renewable natural gas), which is cleaned, compressed and sent to a
CHP (combined heat and power) plant.
•It also produced a “digestate” which can be used as a compost or fertiliser.
CHP plant (at 1.13.36 minute)
•With gas-fired CHP, biogas or natural gas is burned in a combustion chamber.
•This produces a flow of hot gas that drives a turbine, which is coupled to a generator producing electricity.
•The hot gas is then captured using a heat recovery boiler.
•The boiler provides space and water heating for local buildings.
•Excess low grade heat is also captured to drive a stream turbine -producing yet more electricity.
•Some of the heat could also drive an absorption chiller, producing cold air for air conditioning.