Sewage Odour Control – The Singapore Experience

Odour nuisance has become a major environmental issue worldwide with increasing public demand for better control of odorous emissions from municipal wastewater treatment facilities, chicken farms, chemical plants and other industrial works. Odour annoyance affects the population directly and there is a trend that more and more people are becoming less tolerable with obnoxious odour emissions. Bad smell is often regarded as an indicator for possible health risks. In Singapore, much investment has been placed on the prevention of nuisance odour emissions from all the public-owned wastewater treatment plants and continuing research has been put into the development of better and more cost-effective odour control procedures. The local authorities have invested significantly in covering up their existing waste treatment process units and treating all captured sewage air by a variety of technologies such as chemical scrubbers and activated carbon towers. Recently, a new biotrickling filter technology was developed and trial tested at a local wastewater plant and results from the past 3 years of operation indicate an extremely cost-effective biological way of treating sewage odour. Singapore’s odour control experience from the use of the traditional chemical and activated carbon systems to this latest biotrickling filter technology is discussed and presented here. INTRODUCTION The nuisance impact of air pollutant emissions from water reclamation plants (WRPs) is a major issue of concern to the Singapore environment authority. Currently, all WRPs in Singapore have been covered to prevent odour emissions to ambient air. The covered odorous emissions are collected and treated by a variety of chemical scrubbers followed by activated carbon towers. Although chemical scrubbers provide high odour removal efficiencies, they are also costly in terms of recurrent chemical cost and dangerous in view of the need to handle vast quantities of chemical solutions. Due to inherent operation and maintenance issues related to fluctuating airflows, deterioration of chemical pumping and dosing systems etc, chemical scrubbers typically provide pollutant removal efficiencies in the range of 95 to 99%. In terms of odour, chemical scrubbers can reduce the overall odour by about 80 to 90% although significant chemical odour at the exhaust can often be detected if there is excessive dosing of chemicals. Over the last decade, research (1-3) has shown that a special blend of bio-culture of the genus Thiobacillus is effective in adsorbing odorous hydrogen sulphide, a principal component of sewage air. By immobilising the bacteria onto the surface of packing material in a biological reactor, it is possible to develop an efficient biotrickling filter for treatment of sewage air. When sewage air passes through the biotrickling filter, the biofilm of pollutant degrading microorganisms will aerobically degrade the absorbed pollutants. The technology has been experimented under lab conditions, field tested and is now commercially implemented under the brand name of AroBIOS by a spin-off university