Odour and out
BRE's Karim Ismail reports on Eco-Bio, a new process which is intended to tackle odour problems at source
As the summer intensifies, the number of odour complaints from WwTWs will be on the increase and odour treatment will move up the water industry's agenda. The Building Research Establishment Ltd (BRE) has been developing an innovative way of treating wastewaters, a way which would provide an alternative to the capital investment required by the industry to upgrade plants for sewage capacity, odour control and meeting discharge consent. The breakthrough comes from pioneering research and trials being conducted in the field of biocatalysis.
There are a number of odour control methods currently employed by the industry, mostly ranging from chemical dosing (calcium nitrate, potassium permanganate and ferric chloride) through to capital-intensive biofilters or tank covers.
An alternative method of odour control comes from the field of biocatalysis, a method which has gained wide acceptance in the pharmaceutical industry in North America. As the name suggests, it is a technique for accelerating microbiological activity. In the UK, BRE is promoting and using this technique, the Eco-Bio process, for the treatment of sewage and odours, landfill leachate, oily wastewaters, industrial effluents, and soil bio-remediation.
Raising the rates
The Eco-Bio process works by greatly increasing the metabolic rate, growth rate, and in-situ enzyme secretion efficiency of indigenous micro-organisms, thus increasing the degradation rate of contaminants. For example, the time taken to degrade crude oil spills to carbon dioxide and water is reduced from months to just days. Similarly, foul odours in sewage can be eliminated within three to six hours. This is done by adding a blend of secondary and tertiary micro-nutrients in powder and liquid form, consisting of minerals, vitamins, bio-stimulants and trace metals (collectively referred to as Dakarin), all extracted from natural plant matter. Unlike bio-augmentation processes there is no introduction of foreign bacteria or enzymes that have been externally conditioned. Also, unlike other nutrient supplements there is a much greater emphasis on providing fully bioavailable secondary and tertiary micronutrients such as vitamins and enzyme co-factors.
The Eco-Bio approach to odour treatment is based on eliminating the root cause of septicity in sewage. It works by eliminating the food sources and environmental conditions necessary for H2S and other nuisance odour production.
Mastery of the matrices
Dakarin is a highly effective odour treatment agent because of its multi-pronged approach to the problem. For H2S treatment, Dakarin catalyses the activity of sulphur-oxidising micro-organisms. These microbes promote the conversion of sulphides to sulphate and sulphur, which is a reversal of the bio-chemical reactions that generate H2S. Furthermore, H2S production usually occurs in anaerobic biofilms, for example the ones that coat the inner linings of sewage pipelines and septic tanks. These biofilms are naturally tough organic matrices. As long as they persist, the effects of any odour control agent can be considered only temporary. However, certain components in Dakarin are able to accelerate degradation of the organic matrix in the biofilm, thus removing the very environment in which anaerobic sulphide-generating bacteria produce H2S. This approach to odour control is very different to other methods and treats the problem at grass-roots level. Dakarin also contains organic forms of bio-available nitrate, which enable septicity control through efficient oxidation in anaerobic pathways.
In WwTWs there are many other potential sources of odour, thus making odour treatment more challenging. For example, mercaptans, ammonia, amines, partially digested organic matter, fats and oils, volatile organic compounds and organic matter high in BOD and COD - all these can generate odours. These are mostly associated with a variety of different industrial activities, which makes effective odour control strategies much more difficult and less predictable.
With Dakarin, however, through the central concept of enhancing the microbial bio-kinetics of treatment works, accelerated degradation of both organic and non-organic
compounds and fats means these pollutants can be effectively treated; thus may be improved both the odour levels and the final quality of the effluent from the plants. The
latter is evidenced by the recording of lower effluent BOD, COD, and ammonia concentrations in plants that use Dakarin. Trials have shown that problems with bulking sludge can also be eliminated, as Dakarin stimulates the biological degradation of fats, oils and grease, upon which substances thrive such filamentous micro-organisms as nocardia.
It should be noted that Dakarin is normally formulated in accordance with specific biological treatment objectives. For example, the formulation for odour control will be very different to the formulation for enhanced nitrification or hydrocarbon degradation. Therefore, Dakarin should not be considered an all-encompassing formulation for all applications.
The Eco-Bio process has been used at treatment works and pumping stations in the UK and Europe. Applications have been conducted on medium- and large-scale WwTWs in the UK to treat a variety of odour sources, including sulphur compounds, mercaptans, amines, FOG and organic matter, often in situations where alternative odour control agents failed to make their mark.
The treatment of sulphur compounds at a 70,000m3/day plant in the UK showed significant peak H2S level reductions, with a decrease in average H2S levels from 75ppm to less than 10ppm. The measure of success - odour complaints received by the Borough Council - showed sewage-related complaints dropping from an average of 60 to 6 for accountable events during the summer period.
Further trials were extended to treating pumping station pipelines in a 2km sewer. This demonstrated the ability of Dakarin to reliably maintain H2S levels of less than 5ppm and remove biofilm-harbouring odour-generating bacteria. Therefore, Dakarin serves as a natural solution for reduction of corrosion and fouling effects of H2S and FOG in pipelines, thus prolonging asset value.
Projects in southern Europe have successfully treated high odours, FOG, and problems with nocardia-related sludge bulking. Significant improvements in the microbiology of activated sludge plants have been observed, whilst maintaining H2S levels well below 5ppm.
The Eco-Bio process has also been tested successfully for package treatment plants by the EU CENTA (Experimental Wastewater Test Centre for Best Available Technologies) in Seville. CENTA is the Waste Water Technology Transfer Centre established by the EU to verify, compare and recommend technology practices. The data collected over the last three years of continuous operation show 80-90% BOD, COD and ammonia removal, using a system one third smaller than traditional packages and compliant with the pending release of prEN12566-3 standard. Implementations of packaged treatment plants are being put through their paces at a safari park in Portugal, holiday cabin communities in Scandinavia, and mining camps and production operations in Africa.
Other variations of the Dakarin formula have also been used in the waste management industry to increase the volumetric throughput of SBR leachate treatment plants by over 70% and to improve the ammonia and BOD effluent quality of consent failing plants. Thus is also provided an alternative method for sewage treatment plants to meet ammonia discharge consent.
As more applications demonstrate the capabilities of the Eco-Bio process, it presents the water industry with a means of reducing the capital investment required for plant upgrade, since the only investment required is for dosing equipment. Further, the application is well suited for use as an interim or emergency measure for odour and sewage treatment. The science of biocatalysis is about maximising existing asset use, which has to be the most cost-efficient way forward for the water industry.
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