Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | OCTOBER 2015 | 35 In the know Technically speaking: jar testing C urrent EU legislation has led to the implementation of new environmental quality standards in relation to specific trace contaminants in surface waters. This has created a focus on the reduction of trace substances resulting from point sources, including industry and municipal WwTW effluents. There are two main strands to this. The first is the chemical investigation programme (CIP), which started in 2009 by determining the concentration range of trace pollutants in WwTW effluents throughout the UK; the CIP has now progressed to a more Testing for traces With current legislation putting a focus on trace pollutants such as phosphorus, jar testing of wastewater can reveal the right balance of chemical dosing that may be required Andy Burgess LaBORaTORy ManagER aqua EnviRO focused approach, looking at specific site discharges and evaluating the environmental risk using a catchment- based approach. This has resulted in the implementation of tighter consents on a variety of parameters. The second factor at play is that new terms and consent limits for total phosphorus on municipal WwTW discharges are being implemented across the UK under the Water Framework Directive (WFD). WFD also uses a catchment-based approach, and employs the use of modelling to target specific works outlets, o‡en applying tighter consent limits to meet new environmental quality standards. Phosphorus (P) is an essential nutrient for the growth and metabolic reactions of all plants and animals, and its effect on watercourses is well understood. Within a watercourse, phosphorus concentration has a direct effect on ecological biodiversity. Increased phosporus concentration favours algal growth which in turn reduce macrophyte diversity, causing stagnant environments, resulting in the depletion of dissolved oxygen in water through eutrophication. The same level of understanding has not yet been achieved concerning CIP compounds such as steroid hormones and pharmaceuticals; however, this does not mean that such compounds may not have profound effects. dosing to eliminating trace pollutants Recent changes in consents have resulted in many new assets being installed to remove phosphorus, highlighting the need for wastewater treatment processes to be optimised to reduce specific trace substances in effluent discharge. The most basic form of treatment available for trace substances is chemical precipitation and settlement. This can take place at various stages of the wastewater treatment process and can be enhanced by optimising factors including contact time, mixing rate and chemical dosing. The advantages of chemical dosing include improved settlement rate, greater removal of colloidal BOD and potential for enhanced precipitation of trace substances within the settled fraction. When all of these factors are applied to primary stages of treatment, secondary and tertiary treatment capacity is increased. This creates potential for asset reuse in future schemes, reducing both CAPEX and OPEX. Dosing using metal salts is the most cost effective and widely used method of chemical precipitation. Metal salts aid coagulation by neutralizing negative charges on suspended and colloidal matter, to form compact flocs suitable for greater levels of removal by settlement. Metal salt dosing for phosphorus removal allows the precipitation of phosphorus through the formation of metal phosphate compounds, which are then combined within metal hydroxide flocs and finally removed via settlement. Adsorption and precipitation of CIP compounds with Jar testing in progress. The process tests the effects of a range of chemical doses

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