Water & Wastewater Treatment

12 | MAY 2014 | WWT | www.wwtonline.co.uk Project focus S outhern Water is using ground- breaking new wastewater treatment equipment as part of its work to alleviate the impact of groundwater flooding of its sewers on customers. Southern Water is currently pilot- ing ten mobile biological treatment tanks at seven locations in Kent and Hampshire, and carrying out a water quality testing programme to confirm their effectiveness. The tanks have been developed in conjunction with Kent-based engineering firm Atac Solutions. Following the wettest winter on record, groundwater levels in the South East have been at record highs. As a result, the company's sewer network has been inundated by millions of litres of water it was never designed to deal with. As part of a multi-million pound effort to maintain services for its customers, Southern Water is using mobile biological treatment tanks – a first in the UK. The company has developed this experimental technology to treat the excess wastewater, highly diluted by groundwater, being pumped out of sewers to a much higher standard than could previously be achieved. It is then returned to the environment. Large areas of Southern Water's territory in Kent and Hampshire have experienced flooding due to rising groundwater levels and heavy rain- ● A first in the UK ● Improves river water quality ● Reduces need for tankering fall. Tankers have traditionally been used to deal with groundwater flood- ing and take away the wastewater to treatment plants. "There is a limit to how many tankers you can move in a day and usually you are limited to a single tanker per site," says Nigel Palmer, Technical Lead - Wastewater Treatment Process at Southern Water. "In some areas, to maintain ser- vices for customers we need to move larger volumes than is practical with tankers, so a static plant is a more attractive option," he says. "You can pump up to 1000 cubic metres a day with a static unit working day and night and that's a lot better than tankering. It eliminates an awful lot Nigel Palmer TechnicAl leAd - WAsTeWATer TreAT- MenT Process, SoUtheRn WAteR Southern Water purchased ten units, initially used to alleviate the impact of groundwater flooding on sewers • Drivers Mobile treatment Southern Water's new treatment equipment alleviates impact of groundwater flooding Paul KeNt AsseT sTrATegY MAnAger, SoUtheRn WAteR ● alleviate the impact of groundwater flooding on sewers, which in turn affects customers, and minimise the inconvenience which can be caused by tankering for customers ● return treated water to rivers to minimise environmental impact ● move larger volumes of groundwater-diluted wastewater than is practical with tankers www.wwtonline.co.uk | WWT | MAY 2014 | 13 of tanker movement that, although local residents recognise is neces- sary, can also create a lot of local inconvenience." "In the past we tended to put settlement tanks in where flow was pumped, with some form of straining to remove visible solids. However, that did not have a real effect in reducing ammonia levels or help improve BOD [biological oxygen demand] and oxygenation readings. We wanted to find a way to treat the flows to a higher standard on site, so we developed these new mobile treatment tanks from scratch." It is a three-fold treatment pro- cess, he says. "By using these mobile tanks we can remove some BOD and ammonia and end up giving 100 per cent saturated dissolved oxygen. "Basically it's the same technol- ogy as used at our wastetreatment plants, with a support media, such as furnace slag, clinker or plastic blocks that we use in wastewater treatment inside our submerged aerated filters, as a support mecha- nism to culture bacteria. With the mobile units we put a sewage feed onto the top of a plastic filter, water percolates down this, with the bacte- rial 'slime' digesting the BOD and ammonia." "The most difficult challenge was to try and get distribution right at the top of the unit. Working with Atac we designed a simple set of jets spraying water onto a series of plates that create a plume spray pattern. It's important to get an even distribution over the whole of the filter," Palmer says. It is a full treatment process. "The units tend to treat quite weak groundwater diluted sewage," Palmer says. The initial development plans had the units sized for 10 to 20 litres a second continuous flow, thus handling over 864 cubic metres a day. In terms of tankering, that is twenty five tanker loads. "We estimate that each tank can improve the quality of the water treated by as much as 40 per cent. Importantly, the tanks also allow more oxygen to be applied during the treatment process, helping to main- tain the natural balance of rivers and streams for local wildlife. We are tri- alling this innovative new approach, with a view to possibly using it on a wider scale in the future." The main driver for develop- ing the mobile treatment units was customer convenience, maintaining services by removing excess flows The most difficult challenge was to try to get distribution right at the top of the unit • Tank facts ● Each stainless steel tank is 3 metres high, 2.4 metres wide and 2.4 metres deep ● Each has six nozzles which distribute the water over a biological filter, with a maximum total throughput of 20 litres per second ● The filter is made of standard fixed film corrugated plastic and has a surface area equivalent to half a football pitch. Once 'seeded', it contains billions of waste-digesting bacteria ● It is protected from blocking by a layer of sponge to catch debris. This is changed on a regular basis ● Flow passing through the filter is collected on a benched false floor that discharges by gravity • Challenges 1 ● Design a system to operate independent of external power sources ● Treat wastewater at flow rate of 10 to 20 litres ps ● Reduce biological oxygen demand ● Reduce ammonia content ● Improve oxygen satu- ration ● Portability for use on roadsides or in fields • Perspectives Suppliers ● The project was in- spired by Southern Water, with initial design by Nigel Palmer and fabrica- tion by ATAC Solutions. ● There was nothing available on the mar- ket that met Southern Water's specific needs, especially the require- ment not to have an external power sup- ply. Palmer produced some initial designs and involved ATAC, already a framework supplier for Southern Water and with expertise in submerged aerated flooded filters. "They jumped at the chal- lenge and their location near us also meant we could see fabrication of the units at all stages," he says.

• Cover