Innovative process starts at sewage plant
10 Jun 2015
Nottingham’s Stoke Bardolph wastewater treatment works is close to completing a three-stage biological sewage treatment process, designed to cut costs and improve efficiency.
The Severn Trent Water (STW) plant treats sewage from a 650,000 population as well as trade waste from a local plant.
STW and its subcontractor NMCNomenca worked with Dutch company Paques to introduce three complementary technologies to the site.
It’s by far the most complex control system we’ve worked with
Paques process engineer Simon Kuitert
The combined use of Paques’ processes brings a range of benefits that include removal of phosphorus to recover a phosphate fertiliser, generation of biogas and efficient removal of ammonia at the site.
It has also halved operational costs, delivered a 40% saving on capital expenditure, and reduced the plant’s physical footprint by three-quarters, said STW.
The liquor dewatered from the sludge from the municipal sewage treatment is treated using two Phospaq 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.
Another benefit of introducing a Phospaq reactor at Stoke Bardolph is alleviation of struvite-related damage to equipment further along the train, said STW.
The high concentration of phosphorus in dewatering liquors ordinarily leads to excessive struvite (magnesium-ammoniumphosphate) deposits in pipes, pumps and other equipment, that can cause operational and maintenance problems.
STW expects to save about £70,000 per year by reducing maintenance costs incurred by these problems.
Capturing struvite as a resource will also yield an estimated 736t/ year of phosphorus for conversion into fertiliser, providing an additional revenue stream.
The Biopaq reactor for the trade waste converts organic compounds into mainly methane (CH4) biogas anaerobically, which is then used for the combined heat and power (CHP) engines on site, contributing 7% to this energy-neutral site’s total gas output.
Paques process engineer Simon Kuitert said that all previous installations had been at more heavily manned sites, while in Nottingham the plant runs itself through an automated system.
“It’s by far the most complex control system we’ve worked with,” said Kuitert.
“We’ve never automated Phospaq like this before. It [has] been a learning process.”
