Articles & Case Studies

£300m high efficiency wastewater treatment scheme employs precision stainless pipework

Posted: Tuesday 10th June 2014

Southern Water has officially completed and opened a £300 million environmental improvement scheme that includes building a new wastewater treatment works for the catchment area of Brighton & Hove and surrounding districts. In order to meet ambitious environmental targets for the site, designers had to implement very space efficient processes, one of which was constructed and installed by expert provider of stainless steel process pipework, BCI Process.

Prior to the new scheme the Brighton and Hove catchment area had some of the oldest wastewater treatment infrastructure in the country, the Portobello site for instance had been in use since the 1870s. The works at Portobello have been upgraded and modernised several times in the intervening years before plans for the new, highly efficient treatment works were drawn up for the Peacehaven site where work started in mid-2009.

With the chosen location of a dry valley in the chalk downs just north of the coastal town of Peacehaven, both compactness and low profile were important selection criteria. Allowance also had to be made in the footprint for treatment expansion to meet possible future tightening of discharge consent conditions. In terms of the secondary treatment, it was important to select the most suitable compact treatment process that could fit in the constrained site and deliver the desired outputs.

Sites which have the luxury of space typically employ percolating filters with rotating spray bars, but these would have been impossible to implement in this situation. Designers required a high rate biological treatment process with a minimal footprint. The chosen system consists of 10 biological aerated flooded filter (BAFF) cells, using media which is held in suspension by air forced through the cells by five blowers delivering air through a common manifold.

All BAFF plants work on the principle of partially treated, aerated sewage flowing through a submerged medium upon which the biomass growth attaches to form the stable concentrations needed to treat sewage at loading rates of between four and ten times that of conventional treatment systems. BAFFs provide high rate, compact and robust sewage treatment plants that are capable of producing high quality sewage effluents.

Having passed through primary treatment, the wastewater is distributed equally between the 10 BAFF cells. The wastewater flows upwards together with air supplied by compressors though several metres of floating polystyrene beads. These beads are retained by a concrete slab perforated with nozzles that allow the water to pass but hold back the beads. Biological treatment is provided by the aerobic micro-organisms that grow on the beads in the presence of nutrients and oxygen, provided by the wastewater and air.

BCI Process won the contract to supply and install the aeration pipework in each of the 10 BAFF cells. All the pipework services were constructed from light gauge metric stainless steel to ensure the new installation would provide long lasting service. With the bulk of the fabrication completed at their premises, BCI was able to ensure the quality of the fabrications was consistent and assured. The second advantage of in-house fabrication was to allow a consistent flow of materials to their on-site engineers, allowing them to complete the installation on time and within budget.

Andrew Clouds of BCI Process remarked “Our reputation is for providing the very highest standards of workmanship, on time and on budget. Like any quality contractor we achieve this by rigorously training our staff, operating strict working procedures, risk assessments and method statements, and using the latest 3D CAD software to develop concept designs into working assemblies.”

BCI has been responsible for installing aeration distribution systems for many years at various locations around the country. During this time it has worked closely with engineers to develop the engineering design of the system to improve the construction process and provide a better solution for the customer.

BCI has become highly proficient in the manufacturing process, which is based on laser technology and precision metal forming, to provide a system with inherent adjustment capabilities which overcome and accommodate civil construction tolerances which are often encountered.

The aeration systems are manufactured from stainless steel tubing with a stainless support framework and Axilock couplings, which reduce or negate the necessity for positional welding and reduce the time to complete the installation. The stainless construction means that these plants have a long service life with minimal service requirements.

In some cases, the working area can be designated as a confined space, which imposes restrictions or prohibitions on working practices such as welding. In such cases, strict health and safety procedures must be followed which include working with gas monitors and escape systems, all of which are covered by BCI's personnel training scheme.

The new installation has been designed such that space has been set aside on the site for expansion of the plant should more stringent discharge standards be imposed in the future. The designers have ensured the BAFFs can be upgraded to include simultaneous nitrification/denitrification capability as well as leaving additional space for the introduction of a tertiary treatment stage, should additional treatments be required.

Southern Water’s £300 million Cleaner Seas for Sussex environmental scheme was officially opened on Monday, Oct 14 2013. The company’s largest ever project includes 11km of new sewer tunnel, two pumping stations, the wastewater treatment works and a 2.5km long sea outfall. The scheme ensures that the 95 million litres of wastewater produced each day by people in Peacehaven, Telscombe Cliffs, Saltdean, Rottingdean, Ovingdean and Brighton and Hove is treated to EU standards.

The new treatment works at Peacehaven is also covered by a green roof which is as big as three football pitches and one of the largest in the Europe. It is planted with downland grasses to help it blend into the surrounding landscape. 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. The treatment works covers just one third of the construction site, the rest having been returned to agricultural land and a new park for the community.

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