In situ filtration of untreated water for injection

A new water recharge filtration system, which has been built and tested, is presented. The unit is gravity fed and can operate with heads as low as 3 m. The synthetic filter fabric can be easily changed to accommodate a wide range of sieve sizes. The fabric is mounted on the outside of a cylindrical, semi-open frame that is 1.5 m in height and 0.81 m in diameter. It fits inside a cylindrical tank 0.91 m in diameter. Raw canal water is fed to the outside of the cylindrical frame. The water passes through the filter and charges a storage tank, where it can be disinfected by chlorination. The storage tank allows uninterrupted flow to the well while the filter is being backwashed. It also minimizes the possibility of air entertainment into the well since air bubbles can float to the surface of the tank. The filter fabric is backwashed by directing filtered water from the storage tank through a series of rotating nozzles located in the center of the frame. The filter structures are of fiberglass and were constructed locally. Tests have demonstrated peak flows in excess of 4 m³/min, with the average flow depending on the quantity of algae present and the frequency of backwash.