Two different types of primary sewage sludge have been used as feedstock for production
of biogas through anaerobic digestion (AD): the one type was sludge from a typical primary
clarifier (PC), while the other type of sludge produced by a rotating belt filter, commonly called
microsieve (MS). Initially the main physicochemical characteristics of the sludges, such as total solids
(TS), volatile solids (VS), VS/TS, pH and carbon to nitrogen ratio (C/N) were determined, for MS:
37.86 0.08%, 83.00 0.41%, 0.83 0.00, 6.67 0.08 and 19.68 0.69, respectively, and for PC:
2.61 0.08%, 78.77 1.91%, 0.79 0.02, 6.61 0.10 and 14.46 1.23, respectively. Then, calculated
amounts of the sludges were inserted into airtight vials and were inoculated using anaerobic sludge.
The daily biogas production was measured over a period of 30 days. PC sludge maximized the daily
biogas production (44.20 mlbiogas/gvsd) 11 days after inoculation, while the MS sludge reach a peak
(37.74 mlbiogas/gvsd) 14 days after inoculation. The cumulative biogas production over the 30 days of
AD was in the same laver (442.29 mlbiogas/gvs for PC versus 434.73 mlbiogas/gvs for MS). However,
PC sludge indicated higher daily biogas production, compared to MS sludge, while the opposite
was observed for the period following the peak point. The Volatile Solids Reduction for PC and MS
sludges was recorded as 46.06% and 32.39%, respectively.

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