Wessex Water Cuts Energy Costs

by Melanie Brown

Article first published in Water & Waste Treatment July 2002

Benchmarking (the comparison of similar plants operating at different sites) is becoming an increasingly important tool for optimising performance of process plant. It can identify areas where operating costs are unnecessarily high and where the use of power, water or raw materials can be reduced.

Wessex Water is undertaking a major evaluation of its power consumption at 28 of its wastewater treatment plants and five water treatment plants in conjunction with Meniscus Systems. The study includes 20 of Wessex' largest wastewater treatment plants and eight smaller plants, where power consumption is considered high. The project commenced in June 2001 at some of the smaller treatment plants and expanded in December 2001 to include the larger sites as well; monitoring is expected to continue until December 2002. The objective is to derive power costs for specific unit processes on all the sites to allow benchmarking to compare performance at different sites. Unit processes with excessively high energy consumption can be identified and this can trigger investigation and potential cost savings. The study is unique in measuring performance at monthly intervals over a 12-18 month period; previous attempts to compare performance at different plants have largely been one-off 'snapshot' assessments which have not taken account of monthly variations.

Wessex Water has established an extensive, systematic monitoring programme at all its water and wastewater treatment sites. The data collected is currently faxed to Meniscus Systems by operators at the different sites. Data can also be supplied to Meniscus via the web, a handheld computer, a Process Toolbox or a SCADA/telemetry system. If the frequency of monitoring increases, Wessex is likely to start entering data via the web site. Meniscus' web-based process management service provides analysis and interpretation to help to optimise plant performance and minimise costs. The Intelligent Plant Monitoring software uses a specialist monitoring and targeting database developed by Meniscus to enhance reporting and analysis. It provides detailed process and cost information and can generate an emailed response to highlight possible operating problems.

Monthly reports are sent to key Wessex personnel via the internet. By collecting data over many months, Meniscus has been able to establish operating trends for each Wessex site, which are displayed as three-dimensional plots for a number of processes. Meniscus receives a total of 1400 parameters on a monthly basis from all the wastewater treatment plant in five different areas of processing (Table).

Wessex is using the information to benchmark performance and to highlight sites with higher than average power consumption in the particular process areas. This allows further investigation and optimisation of power use. To date, process area monitoring has identified two sites with a 40% higher than average energy consumption for activated sludge treatment and this is currently being investigated. Some excessively high costs for ventilation and odour removal have also been highlighted at one plant. One of Wessex' two new membrane bioreactors has been shown to be operating at the lower end of its theoretical energy consumption, whereas the other is operating at the higher end; further investigation is underway to identify the cause of the high power consumption.

The project is also monitoring chemical consumption at the plants and is likely to include compliance monitoring at a later date. Wessex operators currently enter effluent compliance data into their mobile phones and text it to a central Vodaphone database. Meniscus is planning to incorporate this database into the plant monitoring system and display it on the web site. This could be used to generate email warnings if discharge consents were exceeded. The rapid response of the system allows warnings to be generated in as little as 1-2 minutes. While the first stage of the project is concerned with monitoring energy consumption, the second stage will apply statistical process control rules to the data to identify how energy consumption affects compliance. For example, the effect of reducing the power consumption for aeration on the compliance of the plant and the risk of breaching consent can be investigated.

Although the project is aimed at reducing power costs, it has also generated a lot of interest within Wessex on process design, since this is the first time that the company has been able to confirm the true power costs for each specific unit process. It has increased awareness of the costs of different processes and this is likely to affect plant design in the future.

Dave Andrews, Energy Manager at Wessex Water, explains that the external processing and management of data by Meniscus is an advantage because it saves operators and managers time and allows them to concentrate on analysing results and implementing solutions. The Meniscus system allows all the data from a series of remote sites to be stored in one central location so that it can be compared and managed by a central team. Wessex personnel find the three-dimensional, colour bar charts comparing energy consumption clear and easy to interpret.

Andrews considers the investment in the Meniscus process area management project has been well worth while. Additional monitoring was required to undertake the project, but it has already saved £50,000 at one activated sludge works, where the waste was being 'over-treated' by excessive aeration. He believes that it is realistic to expect to save up to 5% of the process budget by benchmarking energy costs. Wessex is also interested in benchmarking power consumption performance of its plants against plants operated by other water companies and believes that such a comparison could benefit the whole water industry.

Table: Process Areas in which Data is collected