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.
Drawn to the web
WW has established an extensive, systematic monitoring programme at all its
water and wastewater treatment plants. The data collected is currently faxed
to Meniscus Systems by operators at the different sites which takes about an
hour each month. 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, WW is likely to switch to entering data via the web site.
Meniscus’ web-based process management service provides analysis and interpretation
to help 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
Meniscus receives a total of 1,400 parameters a month from each wastewater
treatment plant and summarises these into a number of process and sub-process
areas. Monthly reports are sent to key WW personnel via the internet.
By collecting data over many months Meniscus has been able to establish operating
trends for each WW site, which are displayed as three-dimensional plots for
a number of processes. The graphs show how individual trends vary with the overall
trend of a group of processes. Dave Andrews, energy manager at WW, says “We
send Meniscus lots of data and they send us back information upon which we can
WW is using the information to benchmark performance and to highlight sites
with higher than average benchmark 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
benchmark energy consumption (kW/h/1,000 PE) 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 WW’s 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. WW 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 to 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 assessed.
Although the project is aimed at reducing power costs, it has also generated
interest within WW on process design, since this is the first time the company
has been able to confirm the 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.
Andrews believes 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 enables all the data from a series of remote sites to be stored in one
central location so it can be compared and managed by a central team.
Andrews considers the investment in the Meniscus process area management project
has been 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 it is realistic
to expect a saving of up to 5% of the process budget by benchmarking energy
costs. Wessex is also interested in benchmarking power consumption performance
of its plants against those operated by other water companies and believes that
such a comparison could benefit the whole water industry
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