WET News

24 WET NEWS march 2015 continuous or semi-continuous high-frequency sampling maybe preferred but it comes with a heavy price ticket. The challenge: In-situ, high frequency nutrient monitoring Flow and level monitoring S pot samples can provide a good indication of the wa- ter quality and nutrient status of a river. However, this method incurs a significant error because intermittent nutrient pollution events that occur be- tween sampling periods go un- detected, leading to underesti- mation of pollution loads and a loss of process under- standing. Furthermore, labora- tory analysis incurs an extra cost, time delays and potential errors, as phosphorus species are not stable. The development in recent years of remote telemetry has significantly improved the efficiency of remote monitoring applications. However, the in- stallation and ongoing mainte- nance of in-situ nutrient moni- toring stations is time consuming and costly for several reasons including: THE CONCEPT • cycle-P is an in-situ total reactive phosphate analyser designed for operation by non-chemists • it combines microfluidics with state-of-the-art optics to provide high levels of precision and accuracy • cycle-P stores results in an onboard logger • combined with telemetry, cycle-P delivers almost real-time data at user-selectable intervals NEED TO KNOW 1 laboratory analysis incurs an extra cost, time delays and potential errors, as phosphorus species are not stable 2 Phosphate is considered to be one of the most important pollutants in surface waters 3 the river thames basin is facing growing pressures from rapid population growth, intensive agriculture, climate change and water resource challenges 4 the measurement of phosphate necessitates colorimetric analysis, which presents a significant challenge in remote locations THE VERDICT • "the cycle-P is working really well; the system operated independently for long periods and produced results that tracked our lab samples closely." dr mike Bowes, ceh thames monitoring programme uses ott hydrometry's latest analyser to monitor phosphate levels. A solution: Cycle-P keeps track remotely C entre for Ecology & Hy- drology (CEH) research- ers have conducted trials on the River Thames to evalu- ate a new remote phosphate monitoring technology (Cycle- P) as part of a high-frequency (hourly resolution) monitoring programme that is studying the cycle Po4 is battery powered and able to operate unattended in the field, running more than 1,000 tests before a field service is necessary to change the reagents • The time taken to visit remote sites • The time taken to identify suit- able monitoring sites • The installation of monitoring stations • Site security requirements (to avoid the…) • The cost of waste chemical dis- posal Traditional nutrient auto- analysers that employ colori- metric techniques usually require mains power to operate and this is o…en unavailable at remote sites, so alternative power generation is necessary, but weather dependent solar panels or wind chargers are inconsistent, so it may be neces- sary to install a local generator, powered by gas, petrol or diesel. Freezing ambient tempera- tures can cause both samples and reagents to freeze within the instrument, which adds further complication and expense to in- struments that employ wet chemistry. Similarly, extra pow- er may be required if an air- purge system is required to pre- vent the blocking of filters. This is particularly important because the concentration of the dissolved phosphorus fraction, SRP (soluble reactive phospho- rus), is of most interest because it is considered equivalent to bio-available P. SRP data can provide an indication of the im- portance of sewage effluent discharges within a system as SRP o…en correlates well with effluent markers and popu- lation density. In the UK, water quality P standards are also gen- erally set in terms of SRP con- centrations. Commercial sensors are available for temperature, pH, electrical conductivity, dissolved oxygen and chlorophyll, and also for some ionic species such as nitrate and ammonium. Ion selective electrodes can, in prin- ciple, be constructed for many other species but have, in prac- tice, been of limited use for envi- ronmental applications because of problems with fouling, limits of detection, probe dri… and lack of robustness. If high-frequency hydro- chemical monitoring is to be- come commonplace, new tech- nologies are needed to overcome the practical, scientific and financial restrictions that cur- rently exist. However, once these problems are resolved, the tem- poral and spatial resolution of monitoring will dramatically im- prove, and our understanding of how nutrient sources and their effects on river ecology will be greatly enhanced. river nutrient concentrations and how they are affected by algal abundance. The monitor- ing system ran continuously over last summer, measuring total reactive phosphate levels in the river, 24/7. These results have now been compared with manually collected samples that were analysed in a labora- tory with the traditional Mur- phy and Riley spectrophoto- metric method on unfiltered samples, and Dr Mike Bowes, senior nutrient hydrochemist at CEH, says: "The Cycle-P is working really well; the system operated independently for long periods and produced re- sults that tracked our lab sam- ples closely." Most water quality parame- ters are relatively simple to measure with low-power accu- rate sensors. However, the measurement of phosphate ne- cessitates colorimetric analysis and this presents a significant challenge in remote locations with difficult access or where mains power is not available. The Cycle PO4 (known as the Cycle-P) from OTT Hydrom- etry is gathering considerable interest because it is battery powered and able to operate unattended in the field, run- ning more than 1,000 tests be- fore a field service is necessary to change the reagents. The Cycle-P is an in-situ to- tal reactive phosphate analys- er designed for operation by non-chemists. Combining mi- crofluidics with state-of-the-art optics to provide high levels of precision and accuracy, the Cycle-P stores results in an on- board logger, but when com- bined with telemetry, delivers almost real-time data at user- selectable intervals (typically one to four hours). Phosphate is a key nutrient in the maintenance of aquatic animal and plant life. Howev- er, it is also considered to be one of the most important pol- lutants in surface waters. Ex- cessive quantities, through natural accumulation or de- rived from human activities such as wastewater treatment and agricultural run-off, can stimulate excessive growth of algae – algal blooms. This re- duces light for plants and can lead to oxygen depletion, bac- terial growth and eutrophica- tion. Also, some algal blooms produce toxins that are harm- ful to other organisms. The River Thames basin is facing growing pressures from rapid population growth, intensive agriculture, climate change and water resource challenges. Researchers are therefore in- vestigating the changes in wa- ter chemistry and ecology that are taking place as water qual- ity improvements are imple- mented under the EU Water Framework Directive. These monitoring activities provide vital scientific evidence that inform future catchment man- agement decisions. Dr Bowes has been running a Cycle-P in the Thames at Gor- ing in Oxfordshire as part of the CEH Thames Initiative Re- search Platform. He is head of the Water Quality Processes group, which has a long track record of using phosphorus auto-analysers, and is ideal to assess the merits of this new technology. Dr Bowes has tried a num- ber of phosphate monitoring technologies in the past but has found them to be either too unreliable or power-hun- gry. "Much of our work in- volves monitoring rivers in re- mote sites that do not have mains power, so I was natural- ly very interested to learn about the Cycle-P," he ex- plains. "Our research is de- signed to identify the causes of algal blooms and to under- stand the factors that trigger both blooms and algal die- back; the ability to monitor phosphate in remote locations is therefore critical to the suc- cess of our work, because man- ual or even automatic sam- pling for laboratory analysis, incurs significant delays and increases costs." OTT Hydrometry's Nigel Grimsley says: "The impact of phosphates from agricultural run-off and wastewater treat- ment is one of the major issues affecting surface water quality and reliable continuous moni- toring is essential if this issue is to be managed effectively. "The Cycle-P has already worked extremely well in a va- riety of international projects, but it was vital for its capabili- ties to be demonstrated in UK waters, and the CEH Thames Initiative provided an ideal platform to do so." n

• Cover