Fast-track phosphate treatment solution for North Hampshire

Faced with performance limitations in existing phosphate dosing equipment at Southern Water’s Fullerton Treatment Works, the company’s joint venture partnership with Morrison Utility services has carried out a fast-track system upgrade with the introduction of a bespoke Gee-built and fully containerised dosing unit.

Fullerton is a full treatment works with two-stage filtration and a sludge treatment centre, serving the 60,000 population of Andover and the north of Hampshire. The site has a phosphate standard of 2 mg/l as an annual average and an absolute consent for 2 mg/l as Fe on its effluent. Southern Water had picked up an iron failure - which was attributed to problems with old dosing equipment – and this drove the decision for its replacement with new equipment that comply with iron and phosphate standards.

“We had a fairly tight timescale to put the scheme in, which was why we wanted a bespoke unit in a container that could be brought in, coupled up and would be operational in a short space of time”, explains Southern Water’s Principal Process Engineer, Nigel Palmer. “This was one of the advantages to Southern Water, really, together with the ability to keep the old unit running and do a final changeover when we were ready – safeguarding our effluent compliance while we were doing so.

“We work with Morrison Utility Services as our main service provider, with them procuring equipment, installing it and then we take it over after commissioning. I had been working with Gee & Company on other K3 projects across the region, so we decided to go with Gee as the preferred supplier”, he adds.

Interestingly, Fullerton was the water company’s first site to introduce phosphate removal, about six years ago. “It was almost an experiment to help us decide what we needed,” continues Nigel Palmer. “We put ferric metering in initially to dose ferric chloride, although at times, we’ve moved to ferric sulphate. At that time, we just bought the system as a box of bits – a tank, some controls, pumps etc, which we’ve gradually improved to a point where we know what we need.

“Having also worked with Gee & Company on the K3 projects in order to refine the design standards that we use today, it was fairly natural to use this design to upgrade the plant here at Fullerton, so that we could get reliability. The beauty of what we put in is that it is a containerised factory unit, so it offered a quick solution. There was little time lost getting it commissioned”, he concludes.

The new Gee dosing container has two rooms, with the control panel situated in a dry room and an adjoining wet room used for the Signal chemical dosing pumps. These are housed in a dedicated kiosk and this whole unit is mounted above a bunded area that has the capacity to contain the tank contents plus 50 per cent.

The ferric dosing pumps themselves are twin Signal S200 mechanical diaphragm pumps, offering a duty and stand-by capability. A 4-20 milliamp signal from the incoming flow from the works is fed into a Chemitrol dosing unit, to give the variable dosing output required by the works.

Inside the container, phosphate and temperature protection are provided, together with coated walls and a coated floor to reduce condensation – and an anti-slip floor. For added safety, there is an eye bath in the container and a safety shower located by the external 35 cubic metres capacity tank, used for storage of either ferric sulphate or ferric chloride. For safety during chemical delivery, a further bunded drainage facility is provided.

“Operationally, the whole system has the ability to use a pre-settable diurnal phosphate profile if we need it to meet a phosphate load that’s coming in to the site,” explains Nigel Palmer. “However, we have tended to run on flow multiplied by a factor, as this seems to work reliably – the phosphate load seems to be proportional to the flow. However, we do cap the flow signal at about 2 dwf, so that, in storm conditions we don’t keep increasing the dose above this level. There’s the ability to set an upper limit at which we stop increasing the ferric”, he concludes.

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