Rapid supply of media helps brings works to ammonia consent
14 October 2004, News release from Marley Wastewater Treatment
Two projects at Anglian Water's Aylsham Sewage Treatment Works have brought the works up to new consent standard for ammonia and built in increased capacity for the future.
The whole scheme was re-evaluated earlier this year with the choice of plastic media in two separate projects. Cross-flow, structured biological media was used to provide high performance filtration in two separate waste streams through the plant.
Stream one comprised an oxidation (extended aeration) ditch with a final settlement tank, whilst the second stream comprised four primary settlement tanks, four trickling filter beds and four humus tanks, with both streams combining to pass through four sand filter units.
Anglian Water's Technology Group with main capital partners contractors Morgan=EST, and consultants Halcrow, designed the upgrading of the plant, including all civil engineering, pipeworks and pumps - under a very demanding time schedule. In turn, they chose Marley Wastewater Treatment as media supplier for the second phase, for three key reasons - the performance of the media, their ability to respond in the time available and the guarantee of the process performance of the media.
In February 2004, a new 9 metre diameter x 4.8 metre depth tank nitrifying trickling filter was installed on stream one, with a feed flow of 25 litres/sec, featuring some 40 cu metres of plastic media and designed to treat the effluent from the oxidation ditch, reducing the ammonia levels from (average) 31.4 to 5 mg/litre.
Two months later, two of the bio filters on stream two had the rock media removed and replaced with 1380 cu metres of the Marpak MXF150 cross flow media. This was to upgrade the ammonia removal on this stream and to reduce the load on the two remaining rock filters to improve their efficiency so that the whole plant could meet the ammonia consent of 5 mg/litre of ammonia.
All of the nitrifying filters have recirculation capabilities to maintain adequate flow during periods of low effluent flow levels.
"The plant is now working much more efficiently," says Anglian Water's Team Manager - Construction, Andrew Barnes. "It is much better balanced and requires much less intervention to maintain its performance within consent levels. It has been effectively upgraded by some 50%. During the installation of the media, which was carried out by Marley's own staff, we had to run the plant on one waste stream, but they kept downtime to a minimum and it was at full capacity very quickly."
Marley's Marpak cross-flow, structured biological media is manufactured in rigid PVC sheet, with corrugations at a 60° angle to the horizontal forming an open cross pattern matrix between adjacent sheets.
With 97% open area (compared with 25% for rock), the media is up to three times more efficient than rock. It does not block so has an 'infinite' process life, compared with rock filters that can block and pond in about 15 years.
The Aylsham Sewage Treatment Works now meets its consent levels across the board - 60 mg/l suspended solids, 40 mg, litre BOD and 5 mg/l ammonia.
For further information please email Marley Wastewater Treatment