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14 July By Robyn Joubert
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Measuring odorous emissionsECOSERV sniffs out trouble zones at wastewater treatment works with custom-built flux chamber Southern Wastewater Treatment Works, Durban 's biggest industrial and domestic waste-water treatment plant, has embarked on an investigation to identify malodorous hot-spots in its facility in the South Durban industrial basin. “Odour is a major bone of contention in the basin area,” says ECOSERV consultant Robin Bissett. “Southern Wastewater Treatment Works has embarked upon a responsible management investigation to identify and quantify odorous sources within the treatment works with a view to assessing the feasibility of several mitigation options." Hiring ECOSERV to calculate hydrogen sulphide (H2S) emission rates and priority areas was the first step in Southern Wastewater Treatment Works' multi-million-rand endeavour. Working closely with University of KZN environmental engineering student Darren Wright, Robin settled on three methodologies to monitor hydrogen sulphide emission concentrations: passive sampling using Radiello Passive samplers; a continuous portable H2S analyzer and an ambient TRS analyser. “We had no idea of the expected concentrations we would be analyzing so we had to be sure to cover a wide range of concentration ranges,” says Robin. Robin commissioned sky light company Big Sky to build a flux chamber adapted from standard US EPA methodology. “The flux chamber is basically an enclosed cylindrical dome which floats on top of the sewage stream,” explains Robin. “It sucks air into an air-conditioned trailer which contains equipment to measure H2S emission concentrations.” The chamber can also be used in other contexts, for example to measure emissions rates of volatile organic compounds from liquid solvent storage tanks, or emissions from soil. “The flux sampler pulls samples through the instruments over a seven-day period to measure H2S emitted from the known circular area. Daily and hourly variations are recorded. We could then expand that figure to the total weir surface area and arrive at a total mass of H2S emitted per day.” This is the information that is required before scrubbers can be designed that can cope with the emission load. “The client has indicated that they intend to roof the priority areas and suck the air through scrubbers to absorb and trap odorous compounds.” Having almost completed the first emission rate survey, Robin is keen to use ECOSERV's new flux chamber to service other points at Southern Wastewater Treatment Works as well as at other facilities nationwide. “We would also encourage Southern Wastewater Treatment Works management to conduct medium- to long-term ambient fence line passive sampling to enable them to track improvements over time.” Robin, whose first post-graduate position was at Southern Wastewater Treatment Works, has enjoyed going back to his roots. “The client has expressed his trust in my capability to provide the level of accuracy that they require and this trust has not been misplaced. ”
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