Water & Wastewater Treatment Magazine
Issue link: https://read.utilityweek.co.uk/i/705933
In the know Getting to grips with... industrial effluent 32 | august 2016 | WWt | www.wwtonline.co.uk it may be important to fit screens. Additional chemical processes may be necessary to clear micropollutants, including heavy metals, bacteria and viruses. How is hard-to-treat effluent assessed and tested? Each case begins with a site visit in order for WPL engineers to understand the nature of the site and the nature of process taking place. Initially it is important to assess the quantities of effluent being produced. If the effluent strength is variable, this also has to be taken into account. Effluent samples are taken to our in-house laboratory and assessed for levels of COD and BOD and a range of micropollutants. The samples are then subjected to a range of different processes to assess their treatability with biological, physical and chemical processes. Once it has been established that the effluent can be successfully treated in the lab, it is important to carry out a pilot study onsite. Why is a pilot study important? During the pilot study, engineers will establish the parameters for treatment as well as calculating the whole-life running costs. Treatment options can be adjusted during the pilot to ensure the effluent is treated to optimal standards for a given site. At a large site, the pilot can be carried out by intercepting a sidestream of effluent, taking as little as five per cent of the total produced onsite. In other cases the pilot study will treat the entire effluent stream. A pilot study is carried out for one week on a chemical process and eight to twelve weeks for a biological process. Both capital and operational costs can be calculated, taking into account energy use, chemical costs and maintenance. Who benefits? Sewerage charges for industrial users are calculated by utilities using the Mogden formula. This means costs vary from month to month depending on the strength of the treated effluent released into the public sewers. In some cases sewerage charges for industrial and agricultural customers can increase tenfold if an unusually high level of contaminants is detected in effluent streams. Industrial users can even face fines if they exceed consents set by the water utility. For these reasons an increasing number of industrial clients are looking for stable, reliable onsite treatment which treats effluent to a consistently high standard. It is important to find the right combination of treatment for the effluent being treated, which is why WPL takes such a systematic approach to the issue. Hundreds of thousands of pounds are wasted every year on industrial treatment plants which are inadequate or unsuited to the job in hand. Investing in a custom-made plant, designed according to the nature of the effluent to be treated, is the answer to tackling hard-to-treat effluent. It is more efficient, better for the environment – and will deliver long-term cost savings. Hard treatment – four of the worst WPL has been called in to tackle some challenging effluents over its 25-year history. Here are a few of the worst. Disposal site for zoo animals An animal carcass disposal centre asked WPL to help it manage variable loadings from its rendering operation. The centre was responsible for disposing of the bodies of large animals such as whales, lions, elephants and dolphins on behalf of zoos and wildlife parks. The effluent produced by the site where the animal bodies were dismembered and rendered was of highly variable strength and load, depending on the kind of animal carcasses being processed. WPL installed a treatment system where the effluent was homogenised in a mixer tank then aerated and screened prior to treatment in a SAF tank. It was then allowed to settle before being discharged. The untreated effluent had a COD of between 8,000 and 10,000 mg/l. A er treatment COD levels were under 500mg/l. Blood processing plant A blood processing plant, which uses human blood to manufacture a range of blood-related products, was having difficulties managing high levels of biological solids in its effluent. WPL engineers assessed the existing treatment works and discovered that the settlement tanks were not working efficiently. The issue was addressed by adding fine screens to the end of the process to separate out the biological solids which were being missed by the treatment plant. By identifying the cause of the problem and improving the process, WPL saved the client from the expense of replacing the whole plant. Municipal waste A solid waste company processing black bin-bags was having difficulty treating the leachate seeping out from the crushed domestic refuse. The variability of the waste meant that identifying the appropriate treatment combination in this case was particularly challenging. WPL carried out extensive testing on dozens of samples in order to develop a customised chemical treatment process specifically designed for black bin-bag 'juice'. Fish processing A fish processing plant in Scotland needed help with its effluent which contained blood, scales and bones and was proving hard-to-treat. WPL designed a customised plant which fed the effluent through a filter before moving it to a DAF plant to separate out the solids. This was followed with treatment in a SAF plant to remove soluble pollutants. Contaminants were reduced by 95 per cent and the treated wastewater achieved environmental compliance for release into the sea.