In most cases, data from petroleum industry wetland studies indicate that treatment wetlands are equally or more effective at removing pollutants from petroleum industry wastewaters than from other types of wastewater. In this study, we discussed the treatment efficiencies of oil-refinery industry wastewater by pilot-scale constructed wetland systems .The constructed wetland systems were one free water surface system filled with the sandy media and one subsurface flow system filled with the gravel media operated in parallel. Each system planted with Phragmites communis. The hydraulic retention time for the treatment wetland was controlled in turn at 0.96, 0.48, and 0.72 days. The experimental results showed that all of these contaminants could be reliably removed from wastewater by treatment wetland, especially the FWS. The effluents from the constructed wetland systems reusing and recovering were feasible.

Naphthenic acids (NAs) are carboxylic acids found in crude oil and petroleum products. The objectives of the research presented here were to: a) assess the occurrence and fate of NAs in crude oil and refinery wastewater streams; b) evaluate the biotransformation potential and inhibitory effects of NAs under nitrifying, denitrifying and methanogenic/fermentative conditions; c) investigate the factors affecting NA biotransformation under aerobic conditions and the microbes involved; and d) assess the toxicity of individual model NAs using quantitative structure-activity relationships (QSAR) and examine the effect of structure on NA biotransformation potential. NAs are ubiquitous in refinery wastewater streams and the desalter brine was found to be the main source of NAs in refinery wastewater. A commercial NA mixture was not biodegraded under nitrate-reducing or methanogenic/fermentative conditions. NAs were degraded under aerobic conditions by an NA-enriched culture; however, a residual fraction was not degraded under all conditions studied. The results indicated that NAs are not inherently recalcitrant and the residual fraction was due to the individual NA concentrations being below the minimum substrate concentrations at which they are no longer degraded. A fraction of the NA mixture was completely mineralized to carbon dioxide, with the remaining portion biotransformed to more oxidized intermediates. Overall, the results indicated that NAs were degraded under aerobic conditions; however, biological treatment of NA-bearing wastewater will not completely remove NA concentrations and thus, biological treatment must be combined with physical/chemical treatment to achieve complete NA removal.

South Africa is a water scarce country. The expansion of the industrial, mining, and agricultural sectors to meet the needs of South Africa’s growing population requires more water. There is therefore an urgent need to develop effective wastewater treatment processes in order to recover and reuse water. This dissertation presents the treatment of an acidic wastewater stream from a platinum refinery which at present is being disposed of by contract with a waste disposal company. The major concern in treating the acid effluent stream is the high concentration of sodium ions (18 200 mg/l) and chloride ions (104 900 mg/l). The precipitation process is used to treat wastewater, but ultimately it generates more secondary waste as a sludge. The other process that is used to treat wastewater is reverse osmosis (RO). RO is usually preferred in the last stage of the treatment because the process is more expensive as membranes need to be replaced regularly. The approach used in this research focuses on evaporating liquid, consequently concentrating the remaining solution until the ions in the solution crystallize. The liquid produced is recycled back into the platinum plant for reuse, and the remaining salt crystals are collected as the useful product. The proposed water treatment process produces dilute hydrochloric acid as the condensate and a crystallized sodium chloride rich residue. The refinery is currently disposing of around 20 000 l/day of wastewater to landfills. The proposed treatment process can recover half of the volume of the wastewater stream to the refinery, helping reduce the fresh water consumption of the process by 10 000 l/day. Furthermore, this will reduce the volume of wastewater going to disposal by a half, namely only 10 000 l/day will need to be disposed of. The amount of Cl that can be recovered is variable and depends on the quantity of chloride in the wastewater. In the two samples processed the recovery was between a 2,5 w% and 10,7 wt% aqueous HCl solution. This corresponds to a saving of between 250 to 1000 kg/day of HCl. As the concentration of the recovered solution is variable, the recycling process would need to monitor the composition of the recycled stream and make up the acid concentration to some fixed value for reuse in the prices. The production of a dilute hydrochloric acid stream should be particularly attractive to the platinum refinery as the operation of the refinery requires hydrochloric acid as a feed. Thus, by recycling the wastewater, the refinery would reduce the volume of wastewater to be disposed of thereby reducing the cost of disposal of the waste while simultaneously reducing the cost of buying fresh hydrochloric acid. The proposed recovery of liquid and recycling it back to the refinery, will also reduce the environmental impact of the refinery, and very importantly in a water scarce country, reduce the freshwater consumption of the process. / Physics / M. Sc. (Physics)