ANAEROBIC TREATMENT OF SALINE WASTEWATERS UNDER HIGH SULFIDE AND AMMONIA CONTENT

The anaerobic treatment of wastewaters from the seafood-processing ind ustry was studied in a 15 m(3) industrial pilot-plant. These effluents have a high organic content (10-60 g COD/litre), with protein percent ages 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 hi gh concentration of salts, together with the production of sulphide an d ammonia due to sulphate reduction and protein breakdown, respectivel y, produces important inhibitory/toxic effects on non-adapted biomass. A mixture of anaerobic sludges from the treatment of non-saline waste waters 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) tot al 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 adapt ation of the biomass to the salinity and the antagonistic effects on s odium toxicity caused by the presence of other ions made it possible t o operate at these high sodium concentrations. Due to the strong buffe ring capacity of the process, pH was maintained above 7 . 25, resultin g 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 a dapted 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.