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Anaerobic biological treatment of frozen seafood wastewater

The effect of salinity was studied on the anaerobic treatment of raw, frozen seafood wastewater. A single‐stage of four organic loading rates (OLRs) ranging from 0.58 to 1.45 kg COD/m3.day and two stages of five OLRs in acidogenic reactors ranging from 0.29 to 2.31 kg chemical oxygen demand (COD)/m3.day were fed into laboratory‐scale bioreactors. The wastewater contained a COD of 1,735 mg/L with high salinity, sodium ion (Na+) and nitrogen (N) contents of 8.63 parts per thousand 5,071, and 165 mg/L, respectively. In the single‐stage operation, the COD and total volatile solids (TVS) removal reached maxima of 55 and 63%, respectively, at 0.58 kg COD/m3.day. In the two‐stage operation, the COD and TVS removal were 65 and 70% at the most appropriate OLR of 1.16 kg COD/m3.day. At this OLR, the highest CH4 content and CH4 yield obtained were not satisfactory at 26.62% and 71 L (reported at standard temperature and pressure)/kg COD removed, respectively. For both types of operation, the biogas did not contain sufficient methane (CH4) in all tests at all OLRs. The salts, Na+, and N at the levels in this study did not upset the organic removal efficiency but did adversely affect CH4 production. Two‐stage anaerobic operation could not prevent toxicity due to the characteristics of this wastewater.