Abstract: Platinum group metal (PGM) refining processes produce large quantities of wastewater, which is contaminated with the compounds that make up the solvents/extractants mixtures used in the process. These compounds often include solvesso, β-hydroxyxime, amines, amides and methyl isobutyl ketone. A process to clean up PGM refinery wastewaters so that they could be re-used in the refining process would greatly contribute to continual water storage problems and to cost reduction for the industry. Based on the concept that organic compounds that are produced biologically can be destroyed biologically, the use of biological processes for the treatment of organic compounds in other types of waste stream has been favoured in recent years, owing to their low cost and environmental acceptability. This review examines the available biotechnologies and their effectiveness for treating compounds likely to be contained in precious metal extraction process wastewaters. The processes examined include: biofilters, fluidized bed reactors, trickle-bed bioreactors, bioscrubbers, two-phase partitioning bioreactors, membrane bioreactors and activated sludge. Although all processes examined showed adequate to excellent removal of organic compounds from various gaseous and fewer liquid waste streams, there was a variation in their effectiveness. Variations in performance of laboratory-scale biological processes are probably due to the inherent change in the microbial population composition due to selection pressure, environmental conditions and the time allowed for adaptation to the organic compounds. However, if these factors are disregarded, it can be established that activated sludge and membrane bioreactors are the most promising processes for use in the treatment of PGM refinery wastewaters.

Abstract: The use of nitrogen-based compounds as reagents in metal refining has led to high nitrogen compound concentrations in the waste-water generated. Some nitrogen compounds released into the environment are toxic to organisms and lead to eutrophication. Therefore, removal of nitrogen compounds from industrial wastewaters is a priority. A series of experiments was carried out using a synthetic metal refinery wastewater (MRWW) to assess the feasibility of biological ammonium removal from MRWW. A continuously stirred tank reactor, an airlift suspension reactor and a packed bed reactor were used under similar influent conditions with recirculation. Ammonium removal efficiencies over 85%, 90% and 99% were obtained, respectively, during the experimental period of 55 days.

Abstract: Eight field experiments were conducted at four sites in the UK in 2003 and 2004 to investigate the effects of sulphur (S) application on yield and malting quality of barley. Significant yield responses to S additions were obtained in five out of the eight experiments, with yield increases ranging from 0.2 to 1.2 t/ha (4.7-22.5%). At the two most S-deficient sites, S application significantly increased malt diastatic power, alpha-amylase activity, friability and homogeneity, and decreased (1 right arrow 3,1 right arrow 4)-β-glucan concentration in the wort, indicating an improved endosperm modification during malting. Sulphur applications also significantly increased the concentration of S-methylmethionine (the precursor of dimethylsulphide) in kilned malt, which could impact on beer flavour. When the supply of N was limiting, S applications decreased grain N concentration due to a dilution effect as a result of increased grain yield. In some cases, S applications resulted in decreased grain size. At sites non-deficient or marginally deficient in S, applications of S had little effect on grain or malting quality parameters. The need to maintain an adequate S supply to barley for both yield and malting quality was demonstrated.

Abstract: Aims: To compare Thiobacillus thioparus population dynamics in a control and a test activated sludge (AS) bioreactor, used for hydrogen sulfide (H2S) degradation. Methods and Results: Denaturing gradient gel electrophoresis (DGGE) was used to confirm the presence of T. thioparus, and real-time PCR was used to quantify the level of this bacterium in the AS samples. The DGGE analysis showed a band for T. thioparus in all samples, with the band being more prominent in the test sample with H2S diffusion. It also showed that although a change occurred in the diversity of the microbial population in the test sludge after 6 weeks of H2S diffusion, the microbial community structure of the test and control was still similar. Thiobacillus thioparus-specific PCR primers confirmed that 50% of the isolates from both the test and control bioreactors were T. thioparus. The thiobacilli population became more efficient at degrading the diffused H2S. This increase in efficiency was confirmed by a significant increase in the number of isolates from the test sludge compared with those from the control sludge, when they were grown in a thiosulfate-rich liquid medium. Conclusions: It was concluded that the use of AS process for H2S removal encourages the population of T. thioparus to increase even at times when the total biomass concentration shows a decrease. Significance and Impact of the Study: The research results give an insight into the dynamics of the microbial population in an AS pilot plant used in a dual role, to treat the wastewater and H2S.

Abstract: The effects of hydrogen sulfide (H2S) diffusion into activated sludge (AS) on odor and volatile organic compound (VOC) concentrations in offgas were studied over an 8-week period. Most VOCs detected in the offgas of both aeration tanks were aromatic hydrocarbons. The VOC concentrations generally decreased when H2S was introduced to the AS compared with the control, indicating a negative effect of H2S on VOC removal. Two volatile organic sulfur compounds present in the test AS offgas showed an increase followed by a decrease during H2S peak loads. Six VOCs and odor concentration increased during the introduction of an H2S peak; however no correlation was observed between H2S and odor concentration. The increase in odor concentration resulted from the increase in the concentration of six aromatic VOCs, which had their removal slowed down during a 100-ppmv H2S peak. Activated sludge diffusion provides effective H2S removal with minimal affect on odor emissions.

Abstract: The performance of activated sludge to be used on a dual-role to treat the wastewater and to serve as a bioscrubber to remove hydrogen sulphide (H2S) was evaluated. Trials were undertaken to compare four pilot plant designs (fine and coarse air diffusers in tall and short tanks) for effective H2S gas removal and wastewater treatment performance. Tank depth was not as important as bubble size for removal rate. However, tank depth was important in the configurations with coarse bubble diffusers, with tall tanks giving better H2S removal than short tanks. The fine bubble diffuser configurations achieved 94  100% H2S removal, compared with 83.9 – 99.8% for the coarse bubble configurations. The optimal pilot plant (fine bubble diffuser in short tanks) was tried in a field experiment (Bedford Wastewater Treatment Plant, UK), where 100% H2S and odour removal was achieved, but nitrification inhibition seemed to occur. Further studies using the same plant configuration in the Cranfield University Wastewater Treatment Plant showed no nitrification inhibition due to H2S diffusion when the plant was at steady state and the microbial biomass was well acclimatised. A significant increase in mixed liquor suspended solids and mixed liquor volatile suspended solids (MLVSS) occurred during H2S diffusion and the biomass in the test plant was able to cope with upsets in the process more efficiently than that in the control. Most of the H2S input to the process was oxidised to sulphate and intermediaries of sulphate oxidation. An increase in biomass sulphur occurred during high H2S peaks. Both MLVSS and phospholipid fatty acid profiling showed an increase in the viable biomass during H2S diffusion. Selective media, DGGE profile and real-time PCR showed an increase in the Thiobacillus thioparus population during H2S diffusion.