Water and Effluent Treatment Magazine
Issue link: https://read.utilityweek.co.uk/i/283328
12 WET NEWS March 2014 TECHKNOW • The high rate primary sedimentation process includes a set of Lamella Clarifiers, pre-conditioned with polymer • The high rate biological treatment process consists of ten Biological Aerated Flooded Filters cells • The odour control includes multiple stages of scrubbing • The covered canopy is 70m long by 10m wide, and is formed with 12m high columns and 914 beams • The bespoke grass mix for the roof was grown at a specialist nursery in Cambridge • Shafts were constructed using pre-cast concrete segmental linings MOANS & GROANS • 12 years to obtain planning permission • A bad winter in 2009/10 with rain, snow and high winds, that slowed work • Massive public opposition to the site at Lower Hoddern Farm in Peacehaven • Narrow and limited access roads and congested urban area • Working in an area of outstanding natural beauty and keeping it that way • Corrosive marine environment • Hiding the site by putting an immense 'green' roof over the works 2,446m long and com- prises 686m of pipejacked tunnel that is 1.8m internal diameter and of 1,760m of SDR 26 PE pipe, 1.4m external diameter. The end of the outfall tapers to a diffuser section which is made up of 12 ports at 18m cen- tres, the risers for which vary from 350mm diameter to 450mm diameter. A 17m head of treated effluent will be available to drive the discharge from the dif- fuser section. The outfall diffuser, situated in 16m depth of water below Chart Datum, will discharge continuously, to stop inflow of seawater. Scour protection is provided around the diffuser ports to resist the increased cur- rents around the risers. The outfall pipe was laid in an open trench, dug by backhoe dredger, backfilled with the excavated material. The tun- nelled section and the pipe sec- tion were connected underwa- ter by a "spool piece", a short section of make-up pipe. The building housing the treatment works consists of a large, all-galvanized, steel THE VERDICT The many accolades and awards speak for the achievement and success of the Peacehaven Wastewater Treatment Works project. Awards include: • Major Civil Engineering Project of the Year at the British Construction Industry Awards (2013). • Thomas Brassey Award from the Southeast England branch of the Institution of Civil Engineers (2013). • Gaga Galvanizing in Engineering Award, organised by the Galvanizers Association (2013). • Silver Award at the Considerate Constructors Scheme's National Site Awards (2013). • Bali Award in the green roofs category (2012) • Roofing Award from the National Federation of Roofing Contractors (2012) interconnecting pipework between reception sha's and pumping station sha's, as well as the local network connections carried out using other tech- niques such as micro-tunnelling and traditional headings. "There are also two substan- tial 1,800mm diameter pipe- jacks at each end of the project totalling 1.6 kilometres in length," Goodridge says. Treatment works The wastewater treatment works at Peacehaven includes waste- water treatment, sludge recy- cling and odour treatment. The wastewater treatment includes inlet works comprising screens and screenings processing and fat, oil, grit and grease removal and processing. High rate pri- mary sedimentation process includes a set of Lamella Clarifi- ers, pre-conditioned with poly- mer to allow settlement of a floc- culated particle, and a circular scraped cone sludge collection zone. High rate biological treat- ment process consists of ten Biological Aerated Flooded Fil- ters cells, using buoyant media with up to five blowers, deliver- ing forced air to the cells through a common manifold. The sludge recycling includes indigenous sludge dewatering and processing: a series of thick- ening, straining and dewatering of sludge suitable for digestion, and imported sludge dewatering and processing. The plant will be capable of accepting and pro- cessing imported raw sludge and imported digested sludge from certain other Southern Water sites and imported cess from the local area. The odour treatment system, another crucial requirement of planning consent at Peace- haven, includes facilities to cap- ture and control all odours ema- nating from the WTW and SRC. The new long sea outfall is ONSITE PEACEHAVEN framed structure, constructed by Bourne Steel, covered by an award-winning parabolic roof that rises to 18m and dips to 14m above ground. The 18,000m2 of roof is covered with a specially grown turf made up of down- land grasses. The building is divided into two parts by a movement joint located along a steel covered canopy that connects the Sludge Recycling Centre to the larger Pre-Treatment Building part of the structure; an area which sits over the facility's 30m deep inlet sha'. The covered canopy spans part of the width of the structure and consequently it is 70m long by 10m wide and is formed with 12m high columns and 914 beams. The smaller Sludge Recycling Centre (SRC) structure contains two mezzanine floors and steel frames with precast concrete floor units. Large columns sup- port these levels as significant loads from equipment will be exerted. The larger Pre-Treatment Building section of the overall structure consists primarily of an open-plan space for treat- ment works; this was created through the erection of a series of roof trusses, which span up to 30m between two rows of inter- nal columns. The trusses vary in depth to create the curving roof, along with large box section purlins, which span between the trusses. Because of the roof 's unique shape, each pur- lin had to be individually set-out. Frosts provided the turf roof covering, one of the largest grass roofs in Europe. The bespoke grass mix was grown at a specialist nursery in Cam- bridge. The main product, over 3500m3 of substrate, was pro- duced locally and where possi- ble local suppliers were used for other materials. "In December 2010 we started installing the drainage, filter fleeces and sub- strate. Nearly a year later we began laying the specially grown turf with the last piece being laid on 24 October 2011," Frosts says. Commissioning Commissioning took place in three key stages. Stage 1 was to introduce flows from the old Victorian sewer at Brighton Marina into the new sewer tun- nel and transferring them, via the three pumping stations, to the treatment works at Peace- haven. At the treatment works, the flows received 'preliminary treatment', removing any in- organic matter, including grit, fat, oil and grease. Stage 2, once the pumping stations and pre- liminary treatment process were working correctly, involved the primary treatment process, Lamellas, where the sludge is removed from the wastewater through settlement. Stage 3, once the Lamellas were working correctly, was the Biological Aerated Flooded Fil- ters where the wastewater passes through a filter material that contains bacteria to remove any remaining organic material. Natural fluctuations in flows while bringing these processes into operation made commis- sioning difficult so the team restricted the amount of waste- water going into the new works over this period to ensure a steady flow. Phil Risbridger, contract manager at 4D, says: "This is a huge achievement and a credit to the team who have worked tirelessly to reach this goal. The breadth and complexity of the project has thrown up many challenges along the way, but we have risen to those chal- lenges and produced a fantastic asset for our client, Southern Water." n The site includes three pumping stations, with the deepest shaft on the project being the pumping station shaft at Marine Drive The facility features ten Biological Aerated Flooded Filters cells, using buoyant media with up to five blowers, delivering forced air to the cells through a common manifold The long-sea outfall is constructed of PE pipe, made in Norway and towed from there in three 550m long pieces. The pipe was connected by mechanical joints to create the continuous length Outfall "At Peacehaven alone, more than one million cubic metres of earth was moved, all of which was reused on site as part of the extensive landscaping" Richard Price, director of capital delivery, Southern Water