This review indicates that although anaerobic treatment has the advantage of methane
energy production, release of effluent dissolved methane into the atmosphere results in
unwanted greenhouse gas (GHG) emissions. Reported concentrations of dissolved methane
are 8 – 40 mg/L, accounting for about half of the total methane production from the treatment
of low strength wastewaters. The dissolved fraction of the methane produced is affected by
several factors such as reactor type, influent organic concentration, hydraulic retention time
(HRT), solids retention time (SRT), temperature, influent sulfate concentration, and reactor
mixing conditions. In addition, oversaturation with methane is typical for reactors without
membranes or when operated at short HRT. If dissolved methane is not recovered, GHG
emissions from anaerobic treatment could be much greater than that from conventional activated
sludge treatment. The recovery of dissolved methane is essential in order to enhance energy production as
well as to reduce GHG emissions when anaerobically treating for low strength wastewater.
Keywords: Sewage treatment, anaerobic, AnMBR, dissolved methane, energy requirement, GHG emission, climate change.
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