Anaerobic treatment of fishery wastewater using a marine sediment inoculum

The effluent generated by the Chilean fishmeal industry during hydraulic unloading of fish from ships is high in organic load. After recycling and primary treatment to remove fats and proteins, the effluent contains 4-6 kg COD m(-3) and high salt content (an average of 1.85 kg SO4= m(-3) and 16.2 kg Clm(-3)). Marine sediments and fresh pig manure were assayed as anaerobic inocula to purify this saline effluent. The marine inoculum adapted better and faster at 37 degrees C, Showing a higher final methanogenic/sulphate-reducing bacteria ratio of 0.0025. Specific methanogenic activity at 37 degrees C was 0.065 kg CH4 COD (kg VSS day)(-1), corresponding to 1.3 kg COD (kg VSS)(-1) in 20 days. Methane production was inhibited at COD/SO4= ratios lower than 0.5. A 50% inhibition of the activity was found at 0.22 kg H2S m(-3), 53 kg Na(+)m(-3) and 10 kg SO4= m(-3) respectively; however, at the concentration range in the effluent neither was inhibitory. Kinetic parameters were obtained at 18 and 37 degrees C in mixed flow reactors. At those temperatures, mu(max) values were 0.267 and 0.479 days(-1), while K values for the Chen and Hashimoto model were 2.964 and 1.476, and the growth yield factor (Y) was 0.19 kg VSS (kg COD)(-1). The activation energies were estimated as 3.06 kJ mol(-1) for mu(max) and 27.51 kJ mol(-1) for K. showing that the saline wastewater treatment has a lower temperature dependence than the non-saline one. It was concluded that, under these conditions of high organic load, fishery effluent can be anaerobically treated. (C) 1997 Elsevier Science Ltd.