Water & Wastewater Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/826791
36 | JUNE 2017 | WWT | www.wwtonline.co.uk Water. It o ered an update on the most recent research on FOG, bringing together water companies and their suppliers, restaurants, property managers and own- ers, catering equipment providers, food service kitchen designers, local authori- ties, environmental consultants, health o• cers and anyone else with an interest in FOG. More importantly, it helped to shape opinions and create a framework for future investigations. Cran• eld University has been involved in research on various aspects of the FOG problem for the last 10 years: from a more fundamental characterisation of FOG-rich wastewater and associated ƒ ow regimes, to physical and biological technologies to mitigate the FOG problem in kitchens and sewers. How to stem the tide? The most obvious and e ective way of mitigating FOG-related problems is to prevent their discharge in the • rst place. Although this is easier said than done for both businesses and individuals, by en- couraging good practice at source, backed up by information campaigns and regula- tor intervention, followed by pre-sewer separation or biological treatment on-line, we would be able to prevent many prob- lems occurring to begin with. Yet it is inevitable that FOG will reach the sewers, however well-intentioned the source, and so what options exist then? Fundamental to the success of both systems is an understanding of the characteristics of the material discarded. The composition of wastewater from food service establishments (FSEs) is very variable and linked to the size, type of cuisine and cleaning processes employed at each site. Key physical and chemical parameters of kitchen wastewater, such as particle size and zeta potential, are cen- tral to the most common FOG mitigation processes (gravity separation, air ƒ otation and electroƒ otation) but have been very rarely investigated. Until now. On-campus sampling and testing We did our own sampling campaign of on-site restaurants, which showed that FOG droplets have the right characteristics to be successfully separated using passive separators, and that wastewater ƒ ow in commercial kitchens is sporadic, depending on washing times and business operational factors. Figures 1 and 2 shows some of the data collected during the sampling campaign. It is, therefore, essential to monitor these parameters when trying to improve or assess the design of kitchen wastewater treatment systems. Initial evaluation of the data suggests that improvements can be achieved by simple design change, allowing longer retention times or preventing mechanical emulsion formation. Furthermore, despite the widespread use of biological FOG remediation, there is currently no method for assessing quantitatively their e• cacy. Cran• eld's work has also focused on the develop- ment of a robust test protocol for micro- bial additives commonly used in FSEs. The protocol includes a novel method for FOG quanti• cation in detergent-rich wastewaters. FOG quanti• cation is cur- rently done using hexane-based extrac- tion methods (liquid-liquid extraction or solid phase extraction), which have errors ranging between 30 and 40%. This range of error is unacceptable when trying to enforce FOG emission limits. The new method is simple and cheap and has both excellent recovery and precision down to below guideline concentration (typically 100 mg/l FOG) making it suitable for discharge monitoring in FSEs. A FOG-free future? FOG is here and likely to stay. But what our work with industry and government has shown is that there is a real desire from all the stakeholders to address the problem, as it goes well beyond the • nancial bottom line. Businesses have moral and reputational considerations to bear in mind; government should be supporting business, water providers and the public; and all should be conscious of their individual environmental legacies. And although prevention is always better than remedy, if business, government, academia and the wider society can con- tinue to work together, I am con• dent that we will be able to cut the cost of FOG to the country and the environment. Figure 1. Variation of chemical parameters across the diff erent samples Figure 2. Variation of particle size across the diff erent samples 25,000 20,000 15,000 10,000 5,000 0 3,000 2,500 2,000 1,500 1,000 500 0 COD and BOD (mgL-1) TSS and FOG (mgL-1) COD BOD TSS FOG 120 100 80 60 40 20 0 Sample no Chemical micro-emulsions Mechanical micro emulsions Macro-emulsions 0 50 100 150 200 250 300 350 Particle size d0.5(um)