Anaerobic treatment of seafood processing waste waters in an industrial anaerobic pilot plant.

Abstract

Fish and shellfish canning industries produce waste waters whose characteristics depend upon the raw material processed which, in turn, varies throughout the year. Some production lines operate simultaneously, although it is possible to segregate or combine streams in order to optimise the treatment process. The main streams, produced in the cooking of mussel or tuna and in the manufacture of fish-meal, were treated individually or in combination at an industrial pilot plant, with an anaerobic central activity digester (CAD) of 15 m 3 , for two years. The most noticeable characteristics of wastes are their high organic load (COD 20 to 90 g/l) and the salinity (up to 14 g/l of Cl - ). Another problem is the high ammonia content, up to 4.5 g/l, produced after the degradation of proteins. A strategy for adapting sludges to the salinity and to the ammonia content was followed and specific methanogenic activities of 0.7 kg COD/kg VSS.d were achieved, with chloride, sodium and ammonia concentrations of up to 15.5, 9.7 and 3.5 g/l, respectively. COD reductions, applied OLR and HRT ranged between 70 and 90%, 5 to 6 kg COD/m 3 .d and 4.5 to 5 d, respectively. During the entire experimental period, nutrients addition was not necessary and pH remained neutral due to the high buffering capacity of the process (3 to 4 g CaCO 3 /l. Sudden changes in the influent composition did not affect the stability of the process, except when high suspended solids mixtures were treated. The biomass content in the digester varied around 11 g VSS/l and the mean specific methane production was 301 l/kg COD removed (15°C, 1 atm), with a biogas content of 60 to 65%. Hydrogen sulphide in biogas ranged from I to 4%. The mean anaerobic biodegradability was calculated for the main influents treated, being 84.9% for tuna-cooking effluents, 92.7% for mussel-cooking effluents, 79.4% for mixtures of tuna and mussel effluents and 71.4% for the tuna/mussel/fish-meal mixtures.