The biological sulphate removal process

Greben, Harma (2001-12)

Thesis (MSc)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: South Africa is one of the world's major coal producers, resulting in the second highest foreign exchange earner for South Africa. However, the mining industry contributes negatively to (ground) water pollution, due to the formation of acid mine drainage (AMD). AMD originates from the bacterial oxidation (Thiobacillus ferrooxidans) of pyrite (FeS) and contains high levels of sulphate and metals. Sulphate rich waters can be treated applying the biological sulphate removal technology. This study concentrated on biologically removing sulphate from synthetic feed- and mine water, using the single-stage completely-mixed reactor system. The advantage of using this reactor system is that except for removing sulphate from about 2000 to less than 200 mg/t', it can also partly biologically remove the formed sulphides. It was established that both ethanol and sugar can be used, as the carbon and energy source, however ethanol is more cost effective than sugar. Ethanol dosage and Hydraulic Retention Time (HRT) studies were undertaken to investigate at what concentration, the highest sulphate and sulphide removal rates were achieved. It was found that the highest sulphate reduction rates were obtained when using 1mf ethanol/f feed and that the removal rates were 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, furthermore shown that the single stage completely-mixed reactor system could successfully be used to 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 in this thesis, can successfully be applied to treating acid mine drainage using ethanol (1 m.e etanol/f feed water) as the carbon and energy source at a hydraulic retention time as low as 4 hours. This technology has great potential for pilot- and full-scale treatment of sulphate rich effluents such as acid mine drainage.

AFRIKAANSE OPSOMMING: Suid Afrika is een van die vemaamste steenkool produseerders in die wereld, terwyl die uitvoer van steenkool die land se tweede hoogste verdiener is van buitelandse valuta. Ongelukkig dra hierdie industrie ook by tot die besoedeling van (grond) water, veral vanwee die vorrning van suur myn afloop. Bakteriese oksidasie (deur Thiobacillus ferrooxidansy van piried (FeS) is hoofsaaklik verandwoordelik vir die vorrning van suur myn afloop bevattende hoe konsentrasies van sulfaat en metale. . Die toepassing van biologiese sulfaatverwyderingsprosesse vir die behandeling van sulfaatryke waters is vroeer gedemonstreer. Die doel van hierdie studie was om 'n enkel-stadium reaktor met volledige vermenging te evalueer en te optimiseer om toegepas te word vir die biologiese verwydering van sulfaat vanuit sinteties bereide, sowel as mynwater. Hierdie reaktor is in staat om sulfaat te verwyder vanaf vlakke van ~ 2000 tot minder as 200 mg/P. 'n Verdere voordeel gepaard met die gebruik van hierdie reaktor is dat die sulfied wat gevorm word tydens sulfaatreduksie, gedeeltelik verwyder word deur die oksidasie daarvan na So. Die resultate wat behaal is in hierdie studie het aangedui dat beide etanol en suiker gebruik kan word as die koolstof en energiebron, terwyl etanol meer koste-effektief aangewend kon word. In teenstelling was metanol nie 'n geskikte koolstofbron vir sulfaatverwydering nie. Eksperimente is daarvolgens uitgevoer om toestande van optimum etanoldosering en hidroliese retensietyd (HRT) vir maksimum sulfaat- en sulfiedverwydering te bepaaJ. Die hoogste reduksie tempo's was verkry met 'n toediening van 1 mP etanol/f invloei, en die effektiwiteit van verwydering was afhanklik van HRT. Hoe laer die HRT, hoe hoer die tempo van sulfaatverwydering. Die beste sulfaatverwyderingstempo was behaal teen 'n HRT van 6 uur. Die resultate het verder aangetoon dat die enkel-stadium reaktor met volledige vermenging in staat was om sulfaat effektief te verwyder, en die pH te verhoog vanaf na 2.5 tot 7, in mynuitvloeisels van 'n plaaslike steenkoolmyn. Die gevolgtrekking uit hierdie werk is dat 'n volledig-gemengde reaktorstelsel, soos beskryf in die huidige studie, geskik is vir die suksesvolle behandeling van suur mynafloopwater met die gebruik van etanol (l mflP toevoerwater) as koolstof- en energiebron by 'n hidrouliese retensietyd tot so laag as 4 uur. Die tegnologie het groot toepassingspotensiaal vir volskaalse behandeling van sulfaatryke afloopwaters soos by. suur mynafloop.

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