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The VitaSOFT Process: A sustainable, long term treatment option for mining impacted water
Expanded Title:The VitaSOFT process was developed in response to further development requirements that were identified during the development and full scale demonstration of the Rhodes BioSURE® Process, a biological sulphate reducing process for the treatment of mine impacted water with a high sulphate concentration. A consequence of the exploitation of mineral resources is the generation of mine impacted water (MIW) where the commodities are associated with sulphide minerals. The BioSURE® Process was presented as a cost-effective and proven option for the treatment of MIW. The BioSURE® Process exploited the hydrolysis of organic material as a carbon source for biological sulphate reduction with accompanying sulphide production, metal precipitation and alkalinity generation. The process was successfully scaled up to a 10 Ml/d plant located at ERWAT’s Ancor WWTP in Springs, Gauteng, treating mine water from Grootvlei Mine utilizing primary sewage sludge (PSS) as an electron and carbon donor, with final sulphate concentrations of <250 mg/l. Integration of the plant with the Ancor WWTW for effluent polishing and access to PSS, as well as access to neutralised MIW from the high density sludge (HDS) process at Grootvlei made this a unique application of the technology. VitaOne8 identified that further work was required to implement the BioSURE Process elsewhere, in particular where the MIW has a high acidity, low pH, high concentrations of dissolved metals and a sulphate concentration in excess of 2000 mg/l. One of the disadvantages of the BioSURE Process was its reliance on PSS, which may not always be available, as well as on a continuous supply of iron hydroxide, and the associated disposal requirements for large amounts of iron sulphide sludge. This study addressed these shortcomings and developed a more robust process with broader and more flexible application potential: VitaSOFT. Maize silage was identified as an alternative carbon source, with advantages over PSS such as long shelf life, a higher percentage biodegradability, and lower nitrogen content. It was hypothesized that sufficient alkalinity could be generated in the biological sulphate reducing process to neutralize acidic MIW and precipitate contaminating metals as sulphides without the need for an upstream HDS process. Biological iron oxidation was suggested as a means to regenerate the iron hydroxide required for sulphide removal, so that a constant supply would not be required. Finally, it was suggested that the effluent of the biological sulphate reducing process could be softened and stabilised by removal of calcium carbonate as magnesium hydroxide, to decrease the salinity of the water in order to meet the final effluent standards for discharge. These hypotheses were tested first on bench scale and then in a 1 m3/d pilot plant at VitaOne8’s research and development facilities in Pretoria using synthetic MIW resembling that of the Western Basin of the Witwatersrand. It was demonstrated that maize silage was a valid alternative to PSS as a carbon source for biological sulphate reduction (BSR), which can be applied either as a supplementary carbon source where PSS is available, or as a primary source where there are no alternatives. The lower nitrogen content of silage compared with PSS resulted in a lower ammonia concentration in the BSR effluent. The implication of this is that there is no requirement for integration of the process with a WWTW, or for an alternative nitrification/denitrification step. An integarted biological sulphide oxidation reactor was introduced into the process. A substantial portion of the sulphide was removed biologically as elemental sulphur, minimising the requirement for iron hydroxide. Sufficient alkalinity was generated biogenically between the biological sulphate reducing and sulphide oxidizing processes to not only neutralize the incoming MIW, but also to precipitate all the calcium in the water as calcium carbonate without the need for lime addition. Lime was only be required for the removal of manganese and magnesium in a two stage process. The cost saving of lime and limestone is therefore two-fold; there is no requirement for an upstream HDS process, and less lime is required for desalination than would typically be required without the contribution of the biogenic alkalinity. Biological iron oxidation was successfully demonstrated as a viable means to regenerate iron hydroxide from iron sulphide. The validity of the new process was conclusively demonstrated. It differs significantly from the original patents by Rose et al., and the BioSURE process as applied at the Ancor site for Grootvlei mine, and a new patent was filed in July 2014, leading to a PCT Patent application in July 2015, as well as a full patent application in Argentina. Because the newly developed process differs sufficiently from the initial patents and original BioSURE Process, the decision was taken to change the name of the process to VitaSOFT, as acronym that refers to the four integrated biological processes.
Date Published:01/10/2016
Document Type:Research Report
Document Subjects:Mine water - Mine water treatment
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:2232/1/16
ISBN No:978-1-4312-0841-8
Authors:Joubert H; Pocock G
Project No:K 5/2232
Originator:WRC
Organizations:VitaOne8 (Pty) Ltd.
Document Size:2 533 KB
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