Anaerobic treatment of saline wastewaters under high sulphide and ammonia content

The anaerobic treatment of wastewaters from the seafood-processing industry was studied in a 15 m3 industrial pilot-plant. These effluents have a high organic content (10–60 g COD/litre), with protein percentages between 25 and 70%, and a salinity similar to sea water: sodium (5–12 g/l), chloride (8–19 g/l) and sulphate (0·6–2·7 g/l). This high concentration of salts, together with the production of sulphide and ammonia due to sulphate reduction and protein breakdown, respectively, produces important inhibitory/toxic effects on non-adapted biomass. A mixture of anaerobic sludges from the treatment of non-saline wastewaters was used as the inoculum. After an initial start-up procedure, where the acclimation of the biomass was the objective, 70–90% organic matter removal was achieved, operating at dissolved sulphide (DS), total ammonia (TA) and sodium concentrations in the ranges of 0·25–0·5 g S-DS/l, 1·0–3·0 g N-TA/l and 6–10 g/l, respectively. The adaptation of the biomass to the salinity and the antagonistic effects on sodium toxicity caused by the presence of other ions made it possible to operate at these high sodium concentrations. Due to the strong buffering capacity of the process, pH was maintained above 7·25, resulting in levels of free hydrogen sulphide (FS) that were lower than 100 mg S-FS/l, which were not high enough to produce inhibition effects on adapted sludges. However, the control of the influent protein content is necessary, since values higher than 200 mg N-FA/l of free ammonia (FA) were shown to be inhibitory for this process.