An innovative three-stage biological sewage treatment process which has halved operational costs and made a 40% saving on capital expenditure is approaching final commissioning at Severn Trent Water’s Stoke Bardolph wastewater treatment works.
The Nottingham STW plant treats sewage from a 650,000 population as well as trade waste from a local livestock rendering plant.
In a UK first, STW and design– build subcontractor NMCNomenca worked with Dutch company Paques BV to introduce three suitable and complementary technologies to the site.
The combined use of Paques’ PHOSPAQTM, BIOPAQ® UASBplus and ANAMMOX® processes has enabled the water company to effectively remove phosphorus and to recover a phosphate fertiliser, as well as generating biogas and delivering efficient ammonia removal at the site. In addition to halving operational costs and delivering a 40% saving on capital expenditure, the plant’s physical footprint has been reduced by three-quarters.
The liquor dewatered from the sludge from the municipal sewage treatment is treated using two PHOSPAQTM reactors – the first in the UK - to remove the phosphorus, while the trade wastewater is run through a BIOPAQ® Upflow Anaerobic Sludge Blanket (UASB) reactor to produce biogas. Both streams are then combined and sent to an ANAMMOX® reactor to remove ammonia.
A key advantage of introducing the PHOSPAQTM reactor at Stoke Bardolph is alleviation of struvite-related damage to equipment further along the train. The high concentration of phosphorus in dewatering liquors ordinarily leads to excessive struvite (magnesium-ammonium-phosphate) deposits in pipes, pumps and other equipment, which can cause significant operational and maintenance problems.
Severn Trent Water expects to make an annual saving of some £70,000 per year by reducing maintenance costs incurred by struvite damage to plant equipment. Capturing the struvite as a resource will also yield approximately 736t/year of phosphorus for conversion into fertiliser, providing STW with an additional revenue stream.
The BIOPAQ® reactor for the trade waste converts organic compounds into mainly methane biogas anaerobically which is then used for the CHP engines onsite and produces approximately 3MWh/day, contributing 7% to the energy-neutral site’s total gas output.
NMCNomenca’s highly automated approach to mechanical and electrical control of treatment at Stoke Bardolph has been a step-change for Paques in the way its systems are operated. Paques’ process engineer Simon Kuitert said that all previous installations have been at more heavily manned sites, while in Nottingham the plant runs itself, flagging operational issues through an automated system.
Teresa Jeffcoat, NMCNomenca’s project manager commented:
“By working in close partnership with Paques and the client, Severn Trent Water, we have achieved a system that demands only 50% of the air of a standard activated-sludge plant. Power consumption and energy costs have been slashed.
“Savings are also made when the new processes are compared with conventional nitrification and denitrification processes. Operational costs are reduced by over 50%, as are CO2 emissions.“