The biological sulphate removal process

[摘要] ENGLISH ABSTRACT:South Africa is one of the world's major coal producers, resulting in the second highestforeign exchange earner for South Africa. However, the mining industry contributesnegatively to (ground) water pollution, due to the formation of acid mine drainage(AMD). AMD originates from the bacterial oxidation (Thiobacillus ferrooxidans) ofpyrite (FeS) and contains high levels of sulphate and metals. Sulphate rich waters can betreated applying the biological sulphate removal technology.This study concentrated on biologically removing sulphate from synthetic feed- and minewater, using the single-stage completely-mixed reactor system. The advantage of usingthis reactor system is that except for removing sulphate from about 2000 to less than200 mg/t', it can also partly biologically remove the formed sulphides. It was establishedthat both ethanol and sugar can be used, as the carbon and energy source, howeverethanol is more cost effective than sugar. Ethanol dosage and Hydraulic Retention Time(HRT) studies were undertaken to investigate at what concentration, the highest sulphateand sulphide removal rates were achieved. It was found that the highest sulphatereduction rates were obtained when using 1mf ethanol/f feed and that the removal rateswere dependent on the HRT: the lower the HRT, the higher the sulphate reduction rate.The highest sulphide oxidation rate was achieved at the HRT of 6 h. It was, furthermoreshown that the single stage completely-mixed reactor system could successfully be usedto remove sulphate from Schoongezicht mine effluent, not only removing the sulphate,but also most of the metals, thereby increasing the mine effluent pH from 2.5 to 7.The conclusion of this study was that a completely-mixed reactor system, as described inthis thesis, can successfully be applied to treating acid mine drainage using ethanol (1 m.eetanol/f feed water) as the carbon and energy source at a hydraulic retention time as lowas 4 hours. This technology has great potential for pilot- and full-scale treatment ofsulphate rich effluents such as acid mine drainage.

[发布机构] Stellenbosch University