Peacehaven - at last
The new sewage works for Brighton & Hove has finally been commissioned. Natasha Wiseman took a look around
It has to be a good sign when the neighbours of a wastewater treatment plant serving a population of 300,000 do not know where it is. Having lost my way on a visit to Southern Water’s newly commissioned Peacehaven plant, I can testify that a random sample of residents in the tiny town on the East Sussex coast do not even know it exists.
This is especially noteworthy given the extraordinary planning process that the utility had to undergo in locating a suitable site and having it accepted. After the rejection of Southern Water’s initial planning application in 2001 for development of the existing Portobello site, a protracted search was carried out and a further 66 sites were eventually narrowed down to the one that was “least worst”.
The company’s success in hiding away from local residents lies partly on the roof. A 18,000m2 expanse of green turf, specially grown to match the hills of the surrounding South Downs, covers the building and is the largest of its kind in the UK.
The whole site, which sits in a dry valley, has been extensively landscaped to minimise impact in this environmentally sensitive and popular tourist location. Some 1Mm3 of material was excavated during construction, but none left the site.
“They didn’t want to see us, they didn’t want to smell us,” I was told.
The £300M scheme, which included a network of sewage tunnels from Brighton to Peacehaven and a new long sea outfall beyond, was carried out by 4Delivery, a consortium of Veolia Water, Costain and MWH. Technical design was provided by Mott MacDonald.
It was vital to meet the requirements of the European Urban Waste Water Treatment Directive as Brighton & Hove was the last conurbation to do so. Work finally started on the site in 2009. The new works treats the 95Ml/d of wastewater produced by the residents of the city of Brighton & Hove and surrounding areas.
The whole project involved nine construction sites along an 11km stretch of coast where a new network of tunnels has been developed. A 2.5km outfall also forms part of the scheme, replacing the 1.8km legacy pipe.
A penstock chamber situated under the main cliff walk at Brighton Marina transfers the wastewater from Brighton’s old Victorian sewer network to the new tunnel. The tunnel is 2.5m diameter along most of its length, with the sections from Brighton Marina to the Marine Drive PS and connecting the outfall measuring 1.8m.
Wastewater now travels along the coastal tunnel from Brighton Marina, mostly by gravity, at about 6km/h, taking two hours to reach Peacehaven. To maintain a reasonable depth for the tunnel, two pumping stations (PS) lie along its route.
Marine Drive PS, which is sited on an island between the two A259 carriageways at Roedean, has been designed as a landmark building, providing a gateway into Brighton from the East. The streamline domed zinc roof, which I am assured was not intended to look like a fish, conceals a 17.5m shaft with four pumps.
Portobello PS, which is set into the cliff at Telscombe, has been designed to blend into the landscape, and lifts wastewater 14m.
Seven access shafts were sunk along the length of the tunnel which gave access to the four laser-guided tunnel boring machines used to forge the route. The company says it worked closely with the local community to minimise the impact of the works at all sites.
Wastewater first came on site in September 2012. The commissioning process took place over several months. Each process was commissioned in turn, started with preliminary treatment, followed by primary and then secondary treatment.
The screened, degritted and degreased wastewater passes to chemically-enhanced primary settlement, which is carried out in Veolia Water Solutions’ (VWS) MultifloTM lamella settlers. The addition of ferric salts and polymer chemicals into the process causes materials such as colloids to coagulate and flocculate into larger, more easily settleable particles.
This means that a higher percentage of solids can be removed from the wastewater, so reducing the scale of secondary treatment required. A ten-cell VWS BiostyrTM biological aerated flooded filter (BAFF) system is in operation for secondary treatment. The partially-treated aerated sewage flows through submerged polystyrene media upon which the biomass growth attaches. This forms the stable concentrations needed to treat sewage at higher loading rates, between four and ten times that of conventional treatment systems, enabling more compact biological treatment.
The media is backwashed regularly to remove excess biomass and prevent clumping and the backwash water is returned to the head of the works.
To reduce vehicle movements to and from the site, a sludge-drying process has been adopted. Sludges are screened and stored in the co-settled sludge tanks and then thickened.
Raw cake imports from other sites are blended with a sludge stream from the co-settled tanks to 7% dry solids (DS) before screening and recombination with the thickened liquid sludge.
Thickened sludge is then fed along with clarified fats oils and grease (FOG) to three anaerobic digesters. After two weeks in the digestion process, which operates at 37oC, the sludges are passed through centrifuges and heated to 600oC.
Digested sludge is transferred to the drying building where it is dewatered in centrifuges to 23% DS in an Andritz rotating drum dryer. The remaining product is pelletised and bagged for use as agricultural soil conditioner.
Biogas from the AD process is captured and used to generate electricity for use on site through a combined heat and power (CHP) unit.
Given its proximity to a densely populated residential area, odour was a major consideration for the design. In fact the planning inspector said that the £8-10M system was the only reason planning permission was being given to build on the site.
Designed by Plasticon and maintained by ERG, the odour system is also the biggest user of power on the site. All processes are covered and any odours are captured and passed to the three-stage odour control plant for treatment before being released from the stack.
Believed to be one of the biggest odour systems of its kind in the UK, there are three separate ventilation lines: dryer air, odour hotspots and the buildings and BAFF plant. Air from the sludge dryer passes through a venturi scrubber to remove particulates, then an acid scrubber to remove ammonia.
Air from the hotspots passes through an acid scrubber. Both air streams are then combined with the general building air and pass to a caustic/hypochlorite scrubber. The final stage is heating and carbon scrubbing using copper oxide impregnated carbon.
Now completed, the new works will meet the latest UWWTD, one of the last areas of the UK to come in line. It will help improve the environment and provide cleaner seas to Sussex.
Should more stringent discharge standards be imposed, space has been set aside on the site for expansion of the plant, The BAFF system can be upgraded for nitrification and denitrification. A tertiary treatment stage could also be added if required..
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