August 2006

Orders from Thames & Anglian for Innovative Technology

ACWA Services has successfully installed and commissioned a 'NITREAT' plant for the removal of nitrates at the Sheafhouse WTW of Thames Water and as part of an agreement with Biwater Treatment Ltd, is currently building six of these plants at various treatment sites of Anglian Water.

The NITREAT System uses nitrate-selective resin to adsorb the nitrates in raw water. The process provides true counter-current ion exchange in which saturated resin is continually removed from the adsorption zone and regenerated, prior to being returned to the treatment system. The system eliminates lengthy periods of process down-time for regeneration, whilst maintaining consistent effluent characteristics.

Instead of packing a single large bed with resin (which can often lead to ineffective utilisation of the resin), the resin is distributed into a series of smaller vessels. The process ensures more complete utilisation of the resin and the beds are configured so that the total length of the series provides sufficient contact time for the adsorption of nitrates and subsequent regeneration of the resin.

Within the continuous system, vessels containing exhausted resin move out of the adsorption zone at one end, whilst vessels containing new regenerated resin enters the adsorption zone from the other side. Within the regeneration stage, the brine progressively increases in strength as it contacts with exhausted resin.

NITREAT systems are designed to be essentially operator-free processes, requiring little more than routine maintenance. Integral PLC controls respond instantaneously to fluctuations in nitrate levels and the overall system flow demands.

Process Operation

The NITREAT process uses a patented multi-port valve with twenty resin vessels arranged around it. All flows (feed water, treated water and the regeneration streams) feed to and from the multi-port valve. Fourteen of the vessels are active in the adsorption zone rate any one time, whilst the remaining six are at various stages of the regeneration cycle.

Process Zone Distribution

During the latter part of 2005, ACWA Services installed its first full scale NITREAT plant at the Sheafhouse WTW of Thames Water. The plant was set up to achieve a blended nitrate level of 42 mg/l as NO3, irrespective of the raw water nitrate levels. The treatment plant has been in supply for more than six months and has achieved all performance guarantees with regard to power consumption, waste production and chemical usage - all of which are considered to be extremely low when compared with more conventional methods of nitrate removal. Since commissioning, the plant has achieved target nitrate levels and responded efficiently to fluctuations in overall flow and nitrate concentrations.

Analysis of individual process zones provided a helpful insight into their performance. Analysis of the adsorption zone indicated that, as expected, the freshly regenerated vessel was producing nitrate levels near enough to zero, whereas the exhausted vessel was slightly higher.

The overall performance of the Sheafhouse plant was proven over a month of extensive sampling the treated and final blended flows and a six month period of continuous operation.