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The Role of Bulking Agent in Pile Methane and Carbon Dioxide Concentration during Wastewater Sludge Windrow Composting

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Abstract:

Wastewater sludge and wood chips were used as feedstock for the construction of two piles, Pile I (“PI”) and Pile II (“PII”), at a ratio of 1:1 and 1:2 v/v, respectively. Each pile was originally 1.3-m high, 2.0-m wide, and approximately 9.0-m long. A mechanical turner was used to turn the two windrows every 1 to 2 weeks. Three 500-mL-volume glass funnels were inverted and introduced into each pile: one in the core (named, respectively, “PIC” and “PIIC”), one at the top (“PIT” and “PIIT”), and one at the side (“PIS” and “PIIS”). Every 2 to 3 days, gas samples were collected using gas-tight syringes and analyzed in a gas chromatograph determining carbon dioxide (CO 2) and methane (CH 4) concentrations. An average gas concentration value between turnings was calculated and a two-way analysis of variance test was used to determine the significance of the differences between piles and pile location, followed by a Post Hoc Tukey test. During the thermophilic period, the mean CO 2 concentration in PIC was 103 mL/L, 65 mL/L in PIT, and 24 mL/L in PIS, whereas, for PII, these values were 102 mL/L, 59 mL/L, and 24 mL/L, respectively. The mean CH 4 concentration between turnings in PIC was 9.2 mL/L, 1.9 mL/L in PIT, and 0.9 mL/L in PIS, whereas, for PII, the corresponding values were 6.4 mL/L, 0.4 mL/L, and 0.1 mL/L. For methane, there were no significant differences between these mean values, not only between the same placement in different piles, but also between different placements and different piles. This is probably due to the relatively frequent turnings (10 turnings during a period of 100 days), which did not allow the development of more anaerobic pockets in PI than in PII, indicating that both piles had similar greenhouse gas impacts. Results for carbon dioxide were similar in both piles, with some differentiation appearing between the core and top placements compared to the side placement. Reduction of the decomposition rate further from the core and a typical windrow chimney effect (gases from the core flowing through the top) explain this similarity between placements. The similarity between piles can be explained by the similar amounts of easily decomposable organic matter found in both piles, indicating that the effect of the bulking agent ratio on the concentration of gases within the pile was not significant.

Keywords: aerobic; anaerobic; bulking agent; carbon dioxide (CO 2); emissions; greenhouse gases; methane (CH 4); wastewater sludge; wood chips

Document Type: Research Article

DOI: http://dx.doi.org/10.2175/106143007X221229

Publication date: January 1, 2009

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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