Abstract
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.
Highlights
Accepted: 3 December 2021Wastewater treatment plants (WWTPs) have been developed to treat wastewater to the desired standards, prior to discharge into the receiving environment
Due to the stringent laws associated with environmental protection from waste, and in this case wastewater, efforts have been targeted at finding novel and more efficient ways of meeting these requirements [1]
The WWTPs from which this study was conducted were in Chania city, which is on the northwestern part of the island (35.5138◦ N, 24.0180◦ E), as well as the WWTP in Rethymno city, which is located on the northern part of the Island (35.3644◦ N, 24.4822◦ E)
Summary
Accepted: 3 December 2021Wastewater treatment plants (WWTPs) have been developed to treat wastewater to the desired standards, prior to discharge into the receiving environment. Due to the stringent laws associated with environmental protection from waste, and in this case wastewater, efforts have been targeted at finding novel and more efficient ways of meeting these requirements [1]. WWTPs consume electrical energy during the process of treatment and due to the indefinite depletion of fossil fuel reserves, a lot of focus and effort has been placed on coming up with alternative renewable energy sources to help alleviate strain on the main source. Through the biological process of anaerobic digestion (AD) of sludge, it is well documented that environmental pollution can be controlled, but there is enormous potential for energy recovery [2], which may be enough even for the operation of energy self-sufficient WWTPs [3]
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