Thermophilic anaerobic treatment of sulphur rich forest industry wastewater

Thermophilic anaerobic treatment of sulphur-rich paper mill wastewater (0.8 -3.1 gCOD/l, 340-850 mgSO(4)/l; COD:SO4 3.4-5.3) was studied in three labor atory-scale, upflow anaerobic sludge blanket (UASB) reactors and in bioassa ys. The reactors were inoculated with non-adapted thermophilic granular slu dge. In the bioassays, no inhibition of the inoculum was detected and about 62% COD removal (sulphide stripped) was obtained. About 70 to 80% of the r emoved COD was methanised. In the reactors, up to 60-74% COD removal (efflu ent sulphide stripped) was obtained at loading rates up to 10-30 kgCOD/m(3) d and hydraulic retention times down to 6 to 2 hours. The effluent total su lphide was up to 150-250 mg/l. Sulphide inhibition could not be confirmed f rom the reactor performances. The results from bioassays suggested that bot h the inoculum and sludge from the UASB reactor used acetate mainly for met hane production, while sulphide was produced from hydrogen or its precursor s.