Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/516873
JUNE 2015 WET NEWS 9 projEcT SpEcS • Replace a conventional activated sludge process at Severn Trent Water's Stoke Bardolph WwTW • Install three suitable and complemen- tary treatment technologies • Reduce the physical footprint of the treatment process • Recover phosphate fertiliser, generate biogas and deliver efficient ammonia and phosphate removal A n innovative three- stage biological sewage treatment process is cutting costs and improving efficiency at Nottingham's Stoke Bardolph wastewater treatment works. The Severn Trent Water plant serves a population equivalent of 650,000 and includes a stream of difficult-to- treat trade waste from a local rendering plant. A new phosphate consent along with the need to replace ageing assets at Stoke Bardolph provided Seven Trent with the opportunity to reduce the physical footprint of the process, target improved resource recovery and allow for the possibility of raised ammonia consents in the water industry's asset management period 2020-25 (AMP7). The £6.8M system at the Nottingham plant, which replaces a conventional activated sludge process (ASP), also presented particular challenges in terms of process and control for the project partners. An early feasibility study recognised the potential of carrying out efficient pre- treatment of the high-strength liquors. Severn Trent Asset Creation & Service Delivery and civil engineering, electrical and mechanical subcontractor NMCNomenca worked with Netherlands' company Paques to introduce three suitable and complementary technologies to the site in a first for the UK. Operational costs An all-Paques solution was decided upon to remove risk. Given the close interaction between the different treatment processes, it was felt that the points at which they interlink could not be controlled effectively if an array of contractors was used. The combined use of Paques' PHOSPAQ, BIOPAQ UASBplus and ANAMMOX processes has made it possible to recover phosphate fertiliser, generate biogas and deliver efficient ammonia and phosphate removal at the site. It has also halved operational costs, made possible a 40% saving on capital expenditure (capex) and reduced the plant's physical footprint by three-quarters. The sludge dewatering liquors from the municipal sewage stream are first treated in a PHOSPAQ phosphorus removal reactor. The trade waste stream is first treated in a BIOPAQ upflow anaerobic sludge blanket (UASB) reactor for biogas production and chemical oxygen demand (COD) removal. The two streams are then combined and treated in an ammonia-removing ANAMMOX reactor. The two PHOSPAQ reactors at Stoke Bardolph are the UK's first installation and only the third in Europe. The process takes place in an aerated reactor, which provides oxygen for the biological conversion of the COD. Aeration also provides optimal mixing conditions for struvite formation. Introducing a PHOSPAQ reactor as the first-stage of treatment for the 120m3/h sludge dewatering liquor at Stoke Bardolph effectively removes phosphorus, produces a phosphorus (P) fertiliser and Treatment recovery Paques a punch for Severn Trent • Can an innovative three-stage biological sewage treatment process cut costs and improve efficiency at Stoke Bardolph WwTW? Teresa Jeffcoat finds out. ONSITE SEWagE TREaTmENT NEED To KNoW 1 The scheme is expected to produce around 2t/day of high quality struvite, equivalent to 2,000t/day of mined rock 2 The CHPs produce approximately 3mWh/day, with the UaSB contributing 7% to this energy neutral site's total gas output 3 annual saving of around £70,000 a year are expected through reduced maintenance costs 4 18% of the EU's total phosphorus requirements could be met if all of the phosphorus in sewage sludge was recycled 5 The installation has removed the need for a further aSP plant and associated treatment tanks THE VErDIcT • "It's a win-win for Severn Trent Water. The 7% extra gas production from the UaSBplus reactor gives us a better yield on site, which has saved us having to bring in diesel oil" Dylan Thorley, Severn Trent Water View from above – the BIOPaQ UaSBplus reactors generate 7% of this energy total power output at the energy neutral site TEcHKNoW • The PHOSPaQ reactor combines phosphate and chemical oxygen demand (COD) removal • BIOPaQ UaSBplus reactor converts COD into biogas anaerobically, reducing effluent discharge costs and generating renewable biogas energy for use in power generation • The aNammOX reactor involves an anaerobic ammonium oxidation process that is a cost-effective, robust and sustainable way of removing ammonium from wastewater and waste gas • The PHOSPaQ reactors are equipped with separators that retain the struvite • The aNammOX reactor is self-sustaining under normal operation parameters