Performance comparisons

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

operating problems.

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

act.”

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.

Time management

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