2 Dec 2008 What to look for in a domestic sewage treatment plant With clarity of information in short supply regarding the installation and performance of domestic sewage treatment products in the UK, the time is right to consider a number of key indicators common to the most specified plants in the country.
Modern, factory constructed package treatment plants (PTP) provide better than 90% pollutant removal performance. As septic tanks are relatively well understood it is the issues surrounding package treatment plants that we focus on here.
PTP improvements As well as process development, performance demands from customers and requests for simplicity of design from installers have driven the improvements now widely provided by PTP manufacturers including:
• High effluent constituent removal
• Uncomplicated installation
• Reliable, simple operation
• Ease of maintenance
• Low running costs
Today’s PTP specifier can choose from a multitude of designs incorporating a variety of processes including moving bed bioreactor, fixed film and suspended growth with both aerobic and anaerobic biology. It’s not just the processes that are becoming more sophisticated, the design of package plants is being altered to accommodate an ever changing market and new EU legislation.
Products are becoming shallower in design to accommodate high water tables and bedrock sites whilst simultaneously minimising excavation and backfill requirements. The introduction of BSEN 12566 Pt.3 also requires package plants to be fitted with an alarm system, something that was not previously common on small package plants. By including this, and other performance requirements related to CE accreditation, the monitoring of plants will be improved across the market. It is hoped that this will prevent the installation of poorly constructed and badly performing treatment plants across the EU.
Other positive aspects emanating from CE legislation relate to the accommodation of ‘real world’ test conditions for plant design. Once the plants have completed a start up period, designed to establish bacterial cultures, they are subjected to a variety of shock tests. These include no flow, 50% flow, overloading and power failure. Especially important for small plants, eg, single household, these simulations provide a much more realistic understanding of how plants accommodate fluctuations. It is likely that new designs will reflect these requirements with better surge control during peak flows and the ability to accommodate loading variations.
Material difference One of the most successful materials of construction for modern PTPs is high density polyethylene (HDPE), a thermoplastic which is easily shaped using the rotational moulding process. HDPE offers a number of advantages to the modern installer including high impact resistance and robustness during yard handling and installation.
In comparison to rotationally moulded HDPE, traditional glassfibre treatment plants can be prone to cracking if mishandled during storage and installation because of their inherent brittleness and old-fashioned concrete installations are no longer considered cost effective.
PTP maintenance In meeting the challenge to attain high quality effluent from domestic PTP, end-users must play their part and this involves undertaking a programme of commissioning and maintenance to ensure their plant operates at its full potential throughout its working life.
Professional installation, commissioning and servicing is now considered as important as the initial sizing and specification of a PTP. If these requirements are overlooked, for whatever reason, there is a high probability that the plant will eventually malfunction and this, more often than not, can be prevented.
Recognising their responsibilities as the sewage treatment market evolves, manufacturers are improving their commissioning and maintenance services to ensure that full support is available throughout the product’s life cycle. As with a car, regular servicing ensures a long lasting, efficient and reliable system that is capable of delivering continuous high quality performance.
This positive change in market ethos has been underpinned by bodies such as British Water, who have established a service training scheme for accreditation of engineers, and the updating of the Environment Agency’s ‘Pollution Prevention Guidelines Pt.4’.
Product and process knowledge There are a number of learning resources available these days and Aberdeen-based Balmoral Tanks has made a substantial investment in its online training library. Wastewater treatment help is now available in the form of a ‘bite-size’ web-based training course which has been developed by the company.
MD of Balmoral Tanks, Allan Joyce, said: “When our team is on the road speaking to customers they are frequently asked the same questions regarding product specification and installation.
“Not everyone needs to understand the science and mechanics of package treatment plants but we believe it is important that specifiers, installers and end-users have a basic grounding in product performance and the legislation that surrounds specification and installation.
“Our courses can be accessed at work or at home and are designed in easy to digest sections so users can cover as little or as much as they want in each session.
“We are optimistic that customers will see the value of these courses”, concluded Mr Joyce. “Staff members can develop their knowledge at a time that suits the business and gain training ‘points’ in the process.
“Simply call us on 01224 859000 to learn more or log on to www.balmoraltankstraining.com.”
Pic 1: PTP CE structural testing, Aachen, Germany
Pic 2: Balmoral HydroClear 6-pop PTP installation
Pic 3: Moving bed bioreactor (MBBR) process illustration
