In 2002 IWVA started reusing secondary wastewater effluent for groundwater recharge of the existing dune water catchment ‘St-André’. This integration enabled sustainable groundwater management as the natural groundwater extraction was reduced. Consequently groundwater levels increased and on the long term, risk of seawater intrusion no longer is a point of concern. The public response towards this project is generally positive.
The Torreele plant, where the infiltration water is produced, is built besides the wastewater treatment plant of Wulpen, which is managed by Aquafin. The treatment at Torreele combines ultrafiltration (UF), using the submerged ZeeWeed system, and reverse osmosis (RO), using brackish water low energy membranes.
UF has proved to be a reliable technique for effluent treatment and a good pretreatment before RO. The UF system proved sustainable thanks to the use of air and the combination of filtrate backwashes with periodic extended backwashes adding hypochlorite. The maintenance cleaning of the membranes could be limited to once every month.
Despite the use of UF filtrate as source for the RO treatment an additional bio-fouling prevention scheme is in place. By dosing hypochlorite and ammonium-chloride to the UF filtrate, monochloramines are formed. This proved effective in controlling bio-fouling : after 4 and a half years of operation the same membranes are still in place. Scaling of the RO membranes is prevented by combining pH adjustment and dosing of scale inhibitor. Chemical cleanings of the RO membranes are performed on average 5 times every year. This is done alternating alkaline and acid cleanings or alkaline and biocide cleanings. Up to now the normalized fluxes still recover to around the initial values after cleaning.
Since the start-up of the Torreele plant, many optimizations have been performed, resulting in lower energy and chemical consumption. The RO filtrate produced in Torreele is pumped to the dunes of St-André. Just a small pH correction is performed. The groundwater recharge has proved to be effective : the groundwater level in the dunes increased enhancing not only the quality of this groundwater but also the natural values. The hardness of the drinking-water substantially decreased resulting in a higher comfort for the customer.