In Torreele, a wastewater treatment plant with ultrafiltration as pre-treatment and reverse osmosis was realised in 2002 for aquifer recharge.

Problem

Seawater infiltration makes drinking water production difficult in the coastal area of Belgium. To combat this problem, The Belgian Intermunicipal Water Company of the Veurne Region (IWVA) wanted to design a plant that could produce water suitable for aquifer recharge.

Surface water is typically used to recharge the aquifers, but since these water sources tend to experience reduced flows during the summer months, an alternate supply of continuous high quality water was required to protect the aquifers from seawater infiltration and to reduce demand on potable surface water.

Solution

After extensive piloting, IWVA selected a system which included ZENON’s ultrafiltration (UF) membranes in December 2000. This system's multi-barrier approach consisted of a ZeeWeed® system, followed by reverse osmosis (RO) and ultraviolet (UV) disinfection.

UF is the method of choice for RO pretreatment. When compared to conventional pretreatment, ZeeWeed® membranes remove suspended solids and colloidal material more reliably and with the use of fewer chemicals. The membrane is capable of handling solids spikes, and consistently produces an ideal RO feed typically yielding an SDI < 3. ZeeWeed® enables the RO system to operate with a higher sustainable flux, smaller system size, and lower cleaning frequency, thereby signifi cantly reducing operating and capital costs.

The new IWVA Station Torreele tertiary plant produces treated water equivalent to nearly 40 percent of the annual drinking water requirements for this area. The system also constantly meets the drinking water regulatory limits for parasites and salt.

Process Overview

The secondary effluent first passes through the headworks, consisting of a 1mm (0.04") mechanical screen. Once dosed with chlorine, the water is held in a reservoir, and then flows by gravity into the ZeeWeed® UF tanks. Filtration is achieved by drawing water to the inside of the membrane fiber using suction created by permeate pumps.

Permeate is then sent to an RO system, passes through a UV disinfection unit, and is pumped into the dune area. From there, the water seeps into the groundwater table over an open pond of approximately 2 hectares (20,000 m2).

The infiltration water is composed of 90 percent RO filtrate and 10 percent ZeeWeed® filtrate. This mixing is done to remineralize the RO filtration, so the salt content matches that of the natural dune water.

More information on http://www.iwva.be/docs/torreele_en.pdf.