Taking the more natural approach to sewage
David Barrett of natural wastewater treatment solutions provider ARM discusses the use of reed bed technology in sewage treatment in partnership with water companies across the UK
In 1985, ARM constructed its first horizontal reed bed system in the UK to trial their suitability to treat agricultural effluents. After years of research and development, the company now uses reed bed treatment systems for a range of effluents.
In addition to sewage and municipal wastewater, many industrial processes produce vast quantities of wastewater, which can be treated by reed beds. These industries range from brewing and distillation to food processing and manufacturing. Reed bed treatment systems can be designed to remove contaminants such as organic waste, hydrocarbons and heavy metals.
They offer a flexible treatment solution capable of treating a range of wastewaters. When creating a solution to meet the individual requirements of the particular industry, the reed bed is designed to operate in a variety of ways.
They may, for instance, employ vertical or horizontal flow. We also consider the best plant species for the task in hand. Plants that grow in water, such as reeds, rushes and sedges, and the media in which they are planted, have specific roles in contaminant removal.
ARM has been working with water companies across the country to develop the reed bed technology in association with tightening discharge consents and sustainability needs. These beds are designed to achieve a specific level of pollutant removal through biological, chemical and physical treatment of the wastewater. Here WWT looks at ARM's work with three UK water companies.
Jo Callan, innovation wastewater programme manager at Anglian Water, says: "We have been using conventional planted reed beds as tertiary treatment for a number of years. But floating reed beds are still in their infancy and new aspects are being discovered every day.
"They are not in widespread application, especially not for wastewater treatment. Narborough is the first floating reed bed to be used for municipal wastewater treatment in Anglian Water. The bed is planted on a lagoon which polishes tertiary effluent. We are aiming for enhanced polishing for removal of BOD, suspended solids and ammonia; and also to establish its capability to remove heavy metals and phosphorous."
"As a company, we are significantly impacted by the Habitats Directive. Chemical dosing is the widely accepted process solution for phosphorous removal. But at smaller sites there are significant impacts on the sustainability of this method such as biosolids tankering, chemical transportation and storage and the potential need for additional tertiary treatment processes.
"However, if we can consider our wastewater treatment discharges on a catchment level, we might be able to achieve our obligations under the Habitats Directive by balancing the phosphorous loadings from our large and small sites."
Paul Rossetti, who previously managed the project for Anglian Water, said: "After negotiation, ARM was chosen as the price was acceptable and they were committed to help in monitoring the plant growth aspect of the project. We have an agreement to share experimental data and ARM has attended the site since the reed bed was installed in March 2008, to inspect the plant growth and take samples of root and stem growth."
Paul Griffin, sludge process advisor with Severn Trent Water, says: "On 370 of our sites, we make use of reed beds for either tertiary, secondary or storm water treatment. These reeds beds are usually in place at the smaller sewage treatment works which serve population equivalents (PE) of fewer than 2,000 - although one bed serves 6,500 PE.
"We use the reed beds mainly as a polishing treatment at the tertiary stage - improving the quality of effluent produced after the biological and final settlement stages of the sewage treatment process. They are a low-tech, robust and reliable solution with an overall low lifetime cost and minimal maintenance or energy requirements."
Contracts manager, Dennis Jones of Severn Trent, says: "As the number of reed beds in operation has increased, the team at ARM have been instrumental in helping us to develop and deliver a routine maintenance regime. After four years working successfully with us, we recently awarded ARM a renewed maintenance framework agreement after they came out on top when assessed against our Order Winning Criteria. This agreement covers the provision and delivery of reed bed maintenance to a set cyclic programme and refurbishments when required. ARM will also continue to provide technical support and management information to support Severn Trent's reed bed assets."
· An innovative new gravel washer developed by ARM has proved to be a success with Severn Trent. The Aggregate Recycling Machine washes the gravel removed during the refurbishment process so saving on the expense - both financial and environmental - of new gravel.
Dwr Cymru Welsh Water's wastewater treatment works at Crynant, close to the Brecon Beacons, has undergone a complete design overhaul to meet tighter water discharge consents, which now include ammonia. As a result of the redesign, the works - which serves a 5,680 - now features a 2,400m2 vertical-flow reed bed which can treat up to 90l/s of wastewater.
The bed was designed and installed by ARM in conjunction with Imtech Process.
Ian Williams, area manager for Imtech, said: "We have seen the success stories a number of water companies have had throughout the UK with their use of constructed wetland technology. The reed bed option was chosen for its slightly lower capital and operational expenditure as well as being easier to construct."
Martin Kilroy, service delivery manager at Welsh Water, says: "ARM worked with us to create a custom solution which would do everything we needed. Keeping a watch on the environmental impact of our activities is very significant to us and, to that end, we are working with Imtech and ARM to reduce the carbon footprint of the wastewater treatment process."