Engineers at Intellitect Water have developed a version of the company’s innovative multiparameter water quality monitoring sonde, the ‘Intellisonde FE’ that can continuously monitor final effluent without the need for chemicals or frequent maintenance and calibration.
A unit has been installed on the final effluent of Wessex Water’s Holdenhurst wastewater treatment plant in Bournemouth since January 2010 and initial results indicate that this new technology could bring the advantages of online monitoring to a much larger proportion of wastewater treatment plants.
The Intellisonde FE is a very small multiparameter monitor that is able to run unattended for weeks. Low capital and operational costs will mean that it will become possible to install continuous monitors at plants for which the costs were previously considered prohibitive.
The Bournemouth trial was conducted adjacent to traditional online monitoring instruments and Wessex Water’s Regional Waste Scientist Mike Robinson, says: "The trial is proceeding very well, with the Intellisonde FE producing measurements that closely mirror data from our other monitors and from manual tests. For example, we employ traditional online single parameter monitoring instruments at the outfall and we also utilise portable instruments to measure parameters such as clarity and ammonium."
The Intellisonde FE is located in a flow-through chamber which is fed by a submerged sampling pump located in a sump. A level gauge ensures that the sump does not pump dry. The trial unit has been fitted with a small strainer to prevent any possible accumulation of dirt in the measurement chamber. However, it has only been necessary to occasionally remove small stones and snails, although these did not have any effect on the measurements.
Inside the sonde head, tiny solid-state sensors continuously monitor conductivity, pH, temperature, turbidity and ammonium. The unit can log at intervals between one minute and one hour on all parameters simultaneously. Measurements are retained on an internal datalogger, however data is transmitted via GPRS to a dedicated server which feeds a web site to enable 24/7 access to (almost) live water quality information. The units are also able to provide an analogue output that could interface with a water company’s regional telemetry system, providing a closed-loop system for data protection.
The graph shows recorded data during February and March 2010, and Mike reports that no calibration or maintenance was necessary during this period. The data shows several weeks of unattended use, with reported ammonia levels agreeing well with a second instrument installed at the same point. Simultaneous monitoring of other parameters can indicate possible causes of variations in effluent quality, which may in turn lead to more efficient treatment management. For example, reduced conductivity may indicate a correlation between rainfall and ammonia. Without this data, it would be significantly more difficult to diagnose causes of variations in effluent quality, particularly at unmanned treatment works where data is restricted to discrete samples during the day. It should be noted that the ammonium peaks in this data are recorded during the night.
Intellitect Water’s Technical Director David Vincent, believes that recent changes in monitoring requirements will greatly enhance the demand for the new Intellisonde FE. He explains, "The Environment Agency (EA) is currently engaged upon a programme of passing the responsibility for collecting, analysing and reporting discharge quality to operators. At the same time, the level of monitoring required will depend on the level of pollution risk that each discharge represents. Consequently operators, such as the water industry and the process industries, will have to develop a monitoring strategy that meets the requirements of the EA."
The EA conducts infrequent audit checks on the plant effluent. However, the responsibility for maintaining effluent quality lies firmly with the water company and Mike Robinson believes that continuous monitoring offers substantial operational benefits. "One of the main advantages of 24/7 data is that it helps to identify spikes and enables process operators to determine the cause of the problem and thereby to adjust the treatment process," he says. "Continuous data also helps with the identification of treatment deficiency and data for multiple parameters provides a better understanding of the whole process. For example, conductivity and temperature can provide useful supplementary data."
Occasional sampling and analysis can be lower in cost than online monitoring. However, the main disadvantages are that a pollution incident could go undetected between sampling times and infrequent data does not support process optimisation. In contrast, David Vincent says, "The Intellisonde FE will provide continuous access to effluent quality data and thereby help to raise compliance levels even further."
The Intellisonde FE will also provide major financial advantages. It is priced for volume deployment, significantly below traditional effluent monitoring systems, which means that it will become cost-effective for a much larger proportion of works and will save the cost of sampler visits and analysis.
From a water company perspective, Mike Robinson says, "This trial is generating a lot of interest amongst the management team and if we can prove that the lifetime costs are as low as they appear and if the unit continues to perform reliably, the low capital and maintenance costs will mean that the Intellisonde FE could find application at a large number of treatment works."