1. Wastewater transformations and fertilizer value when co-digesting differing ratios of swine manure and used cooking grease in low-cost digesters
- Author
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Lansing, Stephanie, Martin, Jay F., Botero, Raúl Botero, Nogueira da Silva, Tatiana, and Dias da Silva, Ederson
- Subjects
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ANAEROBIC digestion , *METHANE , *BIOGAS , *WASTEWATER treatment , *FERTILIZERS , *CHEMICAL oxygen demand , *PHOSPHORUS , *NITROGEN , *ENTEROBACTERIACEAE , *ESCHERICHIA coli - Abstract
Abstract: A nine-month co-digestion investigation was conducted in Costa Rica to optimize animal wastewater treatment, renewable energy production, and fertilizer creation using 12 Taiwanese-model, plug-flow digesters (250 L each) constructed of tubular polyethylene and PVC piping, operating without mechanical or heating components. The experiment tested three replications of four treatment groups: the control (T0), which contained only swine manure, and T2.5, T5, and T10, which contained 2.5%, 5%, and 10% used cooking grease (by volume) combined with swine manure. T2.5 had the greatest methane production (45 L d−1), a 124% increase from the control. No adverse effects were observed from co-digesting 2.5% grease in terms of organic matter removal, pathogen reduction, grease removal, and pH. Chemical oxygen demand (COD) was reduced 94.7% to 1.96 g L−1, fecal coliforms and Escherichia coli were reduced 99.2 and 97.1%, respectively, and grease removal was 99.9%. The average effluent pH (7.05) and alkalinity in T2.5 was within the optimal range for methanogens and increased significantly during the nine-month experiment, likely due to adaptation of the methanogenic organisms to the influent grease concentrations. Total nitrogen concentration decreased 34.0%, and NH4-N increased 97.1% during digestion in T2.5, with no significant differences between T2.5 and T0. There was less phosphorus reduction with co-digestion, with 181 mg g−1 of total phosphorus (TP) in T2.5 and only 90.6 mg g−1 of TP in T0, resulting in lower N:P ratios in the grease treatment groups due to the greater concentration of phosphorus in the effluent. [Copyright &y& Elsevier]
- Published
- 2010
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