Water & Wastewater Treatment

WWT February 2019

Water & Wastewater Treatment Magazine

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The Knowledge www.wwtonline.co.uk | WWT | FEBRUARY 2018 | 21 Preparing for better phosphorus removal in AMP7 In order to meet the more stringent phosphorus removal requirements expected in 2020-25, wastewater utilities will need to find the right combination of techniques and technologies MARTIN JOLLY, BUSINESS DEVELOPMENT DIRECTOR, AQUA ENVIRO PAUL LAVENDER, BUSINESS DEVELOPMENT MANAGER, AQUA ENVIRO T he water industry is looking forward to around 1000 new final effluent phos- phorus consents which will come into force before 2025 as part of the Wa- ter Industry National Environ- ment Programme (WINEP). Currently, market available and economically viable phos- phorus removal options are generally limited to biological or chemical removal, with the latter being much more preva- lent due to the necessity for a year-round reliable carbon source to support biological phosphorus removal. Chemi- cal treatment uses a metal salt, most commonly iron, to precipitate ortho-phosphate. The precipitate forms as a solid and is removed in a solid's removal process, either a settlement tank or a tertiary solids capture process such as a disc or sand filter. In order to ensure that the new consents are met the industry has been carrying out its own research under the Chemical Investigation Programme 2 (CIP2). This has involved pilot trials to assess technologies capable of meeting the proposed low final effluent phosphorus consents in the most economic and reliable manner. The new technologies have mostly involved dosing metal salts (predominantly iron) with a variety of novel tertiary filtra- tion processes designed for highly efficient solids removal to meet the low concentrations required. However, there are some more novel alternatives such as algal treatment and sono-electrochemical technol- ogy. In order to upgrade a wastewater treatment plant to remove phosphorus, design- ers require information on the nature of the sewage to be treated. Final effluent consents are given as Total Phosphorus and measured as an annual average. Total phosphorus consists of orthophosphate, that can be removed by reac- tion with metal ions along with organic and inorganic phosphorus compounds which may be both soluble and particulate. In order to measure the total phosphorus, organic and condensed inorganic forms must be converted to reactive orthophosphate before analy- sis. Organic phosphates are converted to orthophosphate by heating with acid and persulphate. The orthophos- phate reacts with molybdate in an acid medium giving an intense molybdenum blue colour which is measured in a colorimeter. Chemical P removal Chemical addition can be employed for phosphorus removal before the primary tanks, into secondary biologi- cal treatment or in a dedicated tertiary treatment plant. To achieve consent limits of 1 mg/l or under, multi-point dosing will almost certainly be required. The molar ratio of metal ion to P required for effective phosphorus removal increases as the final effluent Jar testing to produce dose response curves

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