Water & Wastewater Treatment Magazine
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32 | AUGUST 2018 | WWT | www.wwtonline.co.uk The Knowledge odour control Although capable of tackling the issues of odour, these solutions require capital investment and can be an expensive endeavour. Although tried and tested, the technologies mentioned above do come with some drawbacks such as limited lifespans, maintenance requirements and high initial set-up and running costs. Recently, an alternative approach has shown promise in helping to control odour issues and this is through the use of biological products. Q: What are the biologi- cal alternatives? A: Biological products come in either liquid or solid form and generally contain a blend of microorganisms along with preservatives and application specific chemicals. When considering the application of biological products towards odour control, two different methodologies are finding wider use within the industry. These are either through the use of atomisers or mist system techniques or via the direct dosing of bacteria into wastewater systems using an approach known as bioaugmentation. For each of these methods the dominant microbial agents are bacteria of the Bacillus genus, chosen due to their ease of manufacture, low pathogenicity and long-term stability (due to their ability to form spores). Q: What results can be achieved? A: Mist systems typically dose an absorbent agent around the affected area, be it small (a clarifier) or large (lagoon). The technology works via methods relating to adsorption, whereby the malodour is bound to or encapsulated by the agent and is either neutralised or masked from the receptors within the nose. The bacteria within these products then act to facilitate the degradation of In essence, the bacteria 'breathe' sulphate instead of oxygen, and instead of generating carbon dioxide they generate sulphide. The human nose can typically detect sulphide, mercaptan and dimethyl sulphide at concentrations in the low parts per billion, so even the generation of small amounts of these compounds can create nuisance odours. Q: What other types of solutions are available? A: Traditional treatments for malodours at a facility, whether urban or industrial, come in many different forms including: chemical additions; "capture-and- treat" technologies, which o en combine physical covering of plant with absorption and scrubber systems; or biological filtration. The use of chemicals centres around tackling either septicity or modifying pH to combat odours related to sulphides. Common techniques include the use of nitrate salts or ferric, and aeration. But great care should be taken when dosing such chemicals, as under-dosing may prove ineffective and over-dosing may cause problems further downstream. The implementation of capture-and-treat technologies can treat malodour via a few different mechanisms. By employing covers, a plant can prevent gaseous malodours from escaping by covering infrastructure such as anoxic selector tanks and primary effluent clarifiers. Malodours can then be removed via passage through chemical scrubbers for absorption into a liquid medium or through adsorption systems for immobilisation onto a solid support like activated carbon. Another method to remove odour is to use biological systems such as a filter or scrubber whereby gas comes into contact with microorganisms and a packing system to encourage degradation of the malodour. either captured malodorous compounds or the sources of these compounds. This method offers a fast acting and cost-effective primary and/or complementary approach to odour control. The direct dosing of different microbial species provides an opportunity to expand the metabolic potential of a system as well as impact the growth of sulphate-reducing bacteria through a range of mechanisms. These mechanisms may include the production of antimicrobial secondary metabolites or through direct competition for space and resources. Further to this, microbes are o en combined with a chemical agent such as sodium nitrate or percarbonate to promote either denitrification or aerobic metabolism within anaerobic zones, whereby the supplementation of additional microbes such as Bacillus aims to use up potential organic substrates capable of facilitating sulphate reduction. Ammonia issues may also benefit from bioaugmentation, with improvements in odour o en noted from slaughterhouse waste and slurries a er the addition of different Bacillus species, with the mechanism behind this likely passive ammonia uptake due to increased biomass production rather than enhanced nitrification. Q: What are the perfor- mance considerations for bioaugmentation? A: Although becoming more popular, not all bioaugmentation products are equal in performance. When considering dosing bacteria to a system it is important to take into account their residence time. The key to the activated sludge system is the ability to grow and retain biomass via flocculation and settlement. If a bioaugmentation product contains microbes that do not form biofilm or flocs then it is likely their residence time will be equal to the hydraulic retention time, rather than the longer solids retention time. It is this prolonged residence time that is needed for the additional microbes to acclimate and proliferate in order to make any significant difference within a system. Q&A SUMMARY Genesis Biosciences' spray and atomiser systems have been successfully deployed to combat malodour at a range of sites including landfills, piggeries and industrial WWTW. With over 23,000L of concentrates sold within the last year alone, the technology is proving to be a growing and sustained success with both fragranced and un- fragranced blends available for dosing. There are many different wastewater bioaugmenta- tion products available for a range of different problems; however, these products are o en poorly defined with little support- ing data. The tip of the bio- augmentation iceberg has only been scratched with the true potential of bio- logical products, especially those containing Bacillus, still to be realised for waste- water treatment. Taking to the challenge of providing better bioaugmentation products for wastewater applications, Genesis Biosciences is using cut- ting edge genomic and bioinformatic approaches to both screen and identify better candidate organ- isms for applications in the wastewater sector. Their aim is to develop a robust and rigorously tested product range that can be easily and cost ef- fectively applied to improve our wastewater quality.