WATER & WASTE TREATMENT MAKING PHOSPHATE MEASUREMENT EASY


Julian Edwards of ABB Measurement & Analytics in the UK, explains how online analysers can measure and help control phosphate levels


There are several ways that phosphate can


find its way into water. The largest contributor is agriculture. Phosphates are a main ingredient in many agricultural fertilisers. When delivered as a liquid fertiliser or ploughed into fields, phosphates bind to soil particles. In locations near to streams or rivers, these particles can be washed into the water, raising phosphorous levels. Other sources include surface run-off from


lawns and public areas such as parks and golf courses, wastewater from industry and sewage. In the case of sewage, contributors can include common household detergents and human excreta which carry phosphate- based compounds. With even levels of 0.05mg/l of phosphates


As a way of providing a picture of current conditions, on-line phosphate monitoring enables a level of process control that is not possible with manual testing alone, enabling much greater control over phosphate levels and minimising the risk of compliance breaches


and organisms and reduce the effort needed to turn raw water into safe, fresh potable water supplies. For this reason, the quality of water discharged to the environment needs to be controlled to ensure this balance is kept. Achieving this requires various specific parameters to be continuously and accurately checked to keep them within acceptable limits. One such parameter is phosphorous. While


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highly beneficial for plant growth, phosphorous in its phosphate form can pose a serious threat to the health of aquatic systems if its levels are not controlled. High levels of soluble reactive phosphate (SRP), for example, are a key culprit behind the growth of algal blooms on lakes, reservoirs and rivers. Capable of rapid growth, algal blooms can quickly accumulate and destroy aquatic environments by consuming dissolved oxygen in the water. Known as eutrophication, this problem can


render whole bodies of water lifeless, killing fish and other aquatic life and generating unpleasant and toxic odours as the algae decays. As a further problem, algal blooms can also contain cyanobacteria, which can release potentially harmful toxins into the water that can cause complications during potable water treatment.


46 MAY 2021 | PROCESS & CONTROL


he nuances of water chemistry require a careful balance of substances to ensure optimum conditions for aquatic plant life


being sufficient to form an algal bloom, there is a need for levels to be tightly controlled before treated effluent water can be safely discharged to the environment. Measurements are also needed to be used as proof for regulatory consent requirements. In the UK, for example, where input levels are related to the size of the area being served and the characteristics of the water that is being discharged to, levels need to be maintained at the technically achievable limit (TAL) of 0.25 mg/l to satisfy phosphate discharge consent requirements, with operators obliged to show compliance. While manual sampling methods continue


to have their place in water treatment, advantages can be achieved by using online measurement equipment to continuously measure parameters. Given the 24 hour, seven days a week, 365


days a year nature of wastewater treatment, it is important to have systems in place that can provide an accurate indication of process performance and final water quality for any given moment. Capable of measuring


around the clock, online phosphate measurement analysers can be used to provide real or near-real-time data on phosphate levels. This data can be used both for compliance purposes and to help fine-tune treatment process performance, such as adjusting dosing of ferric chloride or aluminium sulphate during coagulation to reduce phosphate levels. The benefits of using online phosphate analysers is highlighted by an application at


Severn Trent Water. Faced with the need to accurately measure phosphate levels in wastewater effluent to meet consent limits set by the Environment Agency, Severn Trent Water opted to install 120 ABB Aztec 600 phosphate analysers at wastewater treatment plants in its operating area which have a phosphate consent limit in place. Operating alongside ABB iron and ammonia


analysers and turbidity monitors, the phosphate analysers, which operate on the colorimetric principle and can measure phosphate levels down to 0.0016mg/l, have reduced the company’s reliance on manual sampling. Using the resulting data, the company has been able to find ways to optimise its effluent treatment processes to ensure that phosphate levels can be reduced and maintained to meet consent targets. As an added benefit, the availability of real-


time data has also enabled Severn Trent Water to create a more proactive maintenance schedule matched to the actual needs of its treatment plants. As a means of continually monitoring water


quality throughout the water treatment process, online measurement instruments such as the Aztec 600 phosphate analyser offers cost saving benefits compared to manual sample collection and analysis. Foremost amongst these is the ability to


optimise plant operation and output consistency through: • Reduced likelihood of problems caused by


regulatory breaches or non-compliance • Optimising chemical dosing and reducing


costs • Reduced operator


intervention through the ability to carry out automatic monitoring • Decreased levels of


sludge, leading to a reduction in the cost and resources connected with sludge disposal The ability to measure


ABB’s Aztec 600 phosphate analysers


key parameters such as phosphates to help minimise the risk of environmental damage can help to ensure that available stocks of treatable water can be readily utilised, in order to meet the demands of a rising global population.


ABB www.abb.com/measurement


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