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Optimised biogas production at Malabar sewage treatment plant

Cowgill, Steven (2011) Optimised biogas production at Malabar sewage treatment plant. Masters by Coursework thesis, Murdoch University.

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Methane in biogas from anaerobic digestion of sewage sludge at Malabar Sewage Treatment Plant (STP) fuels a cogeneration system of rated capacity 2,975 kWE that helps meet the site’s electrical load of about 3,600 kWE. Low biogas flow rates limit the cogeneration system to peak loads of about 2,300 kWE in a rolling average of 1,900 kWE. Site operating costs are thus increased by the need to purchase up to 1,000 kWE of additional grid electricity at any given time.

This research investigated ways to increase the supply of biogas to the cogeneration system. A literature review of anaerobic digestion microbiology and high rate primary sewage treatment processes gave benchmark performance data against which Malabar STP digesters could be compared. Methods of increasing the biogas yield per unit mass of sewage sludge were evaluated for their likely benefit and risk at Malabar STP. The most viable of these were ultrasonic pretreatment of sludge, food waste co-digestion, and use of mechanical mixers in place of compressed biogas for sludge recirculation. These methods could increase existing steady state biogas flow rates by up to 40%.

It was concluded, however, that methods to increase biogas yield would be unnecessary at Malabar STP if Digester 3 was returned to active sludge digestion, and if the sludge in all digesters was maintained at a constant temperature of 35 oC ± 0.5 oC/d. Under these conditions some 10,300 m3/d of additional biogas would be produced, enabling the cogeneration system to operate at its rated capacity.

Item Type: Thesis (Masters by Coursework)
Murdoch Affiliation(s): School of Engineering and Energy
Supervisor(s): Jennings, Philip
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