Abstract
Where sulphate removal is targeted in the biological treatment of acid mine drainage wastewaters, a step additional to sulphate reduction is required to prevent the complete oxidation of sulphide back to sulphate. This linearisation of the biological sulphur cycle has presented a technological bottleneck, particularly in passive treatment operations. We report an investigation of sulphur production in floating sulphur biofilms as a means for addressing this problem. These 50 μm to 500 μm structures may be seen to form on the surface of sulphidic, organic waters and in which sulphide is partly oxidised to So and polysulphide. A Linear Flow Channel Reactor was developed in which the formation of the floating sulphur biofilm could be optimised and studied under controlled conditions. In this study the sulphide feed was sourced from a lignocellulose packed bed reactor treating a synthetic acid mine water (2 000 mg∙l -1 Na 2 SO 4 solution) and the Liner Flow Channel Reactors (surface area 1.1 m 2 and 2.2 m 2 ) were operated in a controlled environment chamber. The floating sulphur biofilm was harvested by settling to the bottom of the reactor where it remained largely unreacted until removed. It was shown that up to 88% of sulphide in the feed stream may be removed in this way and that this was achieved mainly by oxidation of sulphide to sulphur (including a polysulphide fraction). A mass balance accounting for the process showed that up to 66% of total sulphur species entering the system were recovered as So. Oxidation of sulphide to thiosulphate and sulphate was not found to be significant. A fraction of fine particulate sulphur is released into the stream on harvesting of the biofilm which does not readily settle in the reactor and may thus be lost to the mass balance account. The effects of temperature, loading rate and reactor surface area were investigated in optimising the performance of the reactor. Scale-up application studies in the use of the Linear Flow Channel Reactor in an acid mine drainage passive treatment environment have been undertaken in field studies. Keywords: floating sulphur biofilms, acid mine drainage, AMD passive treatment, linear flow channel reactor, sulphur biotechnology
Highlights
Environmental impacts of acid mine drainage (AMD) on public water systems may be widespread and South Africa presents a paradigm case where, following over a century of intensive gold and coal mining operations, water-scarce Witwatersrand and Mpumalanga areas are under threat (McCarthy, 2011)
Operation of the experimental 4-channel Liner Flow Channel Reactor (LFCR) (1.1 m2) was Figure 4 repeated over a number of 18-day runs and 8-day runs from which the data reported here were collected
Synthetic AMD from the Degrading Packed Bed Reactor (DPBR) was applied to the LFCR in these runs
Summary
Environmental impacts of acid mine drainage (AMD) on public water systems may be widespread and South Africa presents a paradigm case where, following over a century of intensive gold and coal mining operations, water-scarce Witwatersrand and Mpumalanga areas are under threat (McCarthy, 2011). Both large-volume and diffuse flows require treatment and biological processes offer potential advantages of low cost and low operational input requirements, where applied in passive treatment operations (Molwantwa et al, 2009). Linearisation of the biological sulphur cycle has presented a technology bottleneck, in the development of passive treatment operations, and a variety of processes have been considered for the effective removal of sulphur (Molwantwa et al, 2009)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
