Collection, analysis, and utilization of biogas generated by the anaerobic treatment of crab processing wastewater

Abstract

Energy recovery from the anaerobic treatment of crab processing wastewater was investigated. Biogas from two laboratory-scale, upflow anaerobic filters (Systems A and B) was collected and analyzed to determine percent by volume composition of methane (CH₄), carbon dioxide (CO₂), and hydrogen sulfide (H₂S). Biogas produced by System A (upflow anaerobic bed filter) produced biogas averaging 68, 28, and 1.5 % CH₄, CO₂, and HS, respectively. System A average gas production ranged from 6.3 to 15.8 liters per day (L/d) (6.6 to 10.0 L gas/L feed) for COD reductions ranging from 11,000 to 27,000 milligrams per day (mg/d) and COD loadings ranging from 16,700 to 43,600 mg/d. System B (upflow anaerobic packed filter) produced biogas averaging 68, 28, and 1.4 % CH₄, CO₂, and H₂S, respectively. System B average gas production ranged from 7.5 to 19.5 L/d (7.1 to 11.9 L gas/L feed) for COD reductions ranging from 11,700 to 28,700 mg/d and COD loadings ranging from 16,100 to 48,500 mg/d.

A pilot-scale biogas collection system was constructed to collect, treat (remove H₂S), store, and utilize the biogas produced by an anaerobic/aerobic crab processing wastewater treatment system treating between 15 and 30 gallons per day (gpd). Biogas was produced by a 190 gallon upflow anaerobic bed filter and a 190 gallon anaerobic clarifier operated in series. Preliminary results indicated biogas production rates comparable to maximum average gas production rates of the laboratory-scale systems at approximately 10 L gas/L feed. Biogas was stored in a 120 gallon tank at up to 12 pounds per square inch (psi) following removal of hydrogen sulfide. Biogas was then burned in a modified natural gas hot water heater to produce heated water for maintaining the anaerobic reactors at 35°C.