Study On Rusing Backwash Wastewater From Filters By Ultrafiltration Technology

About 1%-5% of production was used to backwash filters in water plant, reusing this part of water can not only save the water resource, but also protect the environment. At present, backwash water was directly recycled to the upstream of water plant domestically if the backwash water was reused, the practice could disturb the main processes of water plant, and secure risks existed because the supernate of recovery tank still have many organic, microbial and heavy metal.Both of A and B water plants recycled backwash water, the backwash water of A water plant was from sand filters, when the backwash water of B water plant was from sand filters and active carbon filters, the quality of two water plants were different, therefore, the trials were carried out separately.The backwash water of A water plant was settled in recovery tank in a short time before recycled to the distribution well; the turbidity of the supernate which contains elevated levels of organic ranged greatly, especially, the supernate contains Cryptosporidium, consequently, the recycle processes could impact the plant performance and finished water.A pilot-scale trial of reusing backwash water in A water plant by pre-sedimentation-direct ultrafiltration was carried out, the results showed: total bacterial count in effluent of membrane were less than 3CFU/ml, permanganate number were about 1mg/l; after 57 days, the membrane that produced 2840m3 water was chemical cleaned, and the trial demonstrated that a recovery of more than 95%, as the cost counted to 0.216 yuan/m3.The backwash water of sand filters and active carbon filters in B water plant were both settled in recovery tank in a short time before recycled to the distribution well; the turbidity of the supernate which contains elevated levels of trihalomethanes formation potential, water leas and alga ranged greatly, especially, the supernate contains Cryptosporidium and Giardia; recycle processes lead to lower turbidity, but higher permanganate number and granule number.A pilot-scale trial of reusing backwash water in B water plant by presedimentation-direct ultrafiltration was carried out, the results showed: total bacterial count in effluent of membrane were less than 3CFU/ml, permanganate number were about 1mg/l; after 26 days, the membrane that producted 1135m3 water was chemical cleaned, and the trial demonstrated that a recovery of more than 95%.Backwash water of two water plants in S city were reused by pressedimentation-direct ultrafiltration, produced a permeate of good quality, the effluent could sent to cleaning water tank after disinfection, the practice not only ensured the security of reusing backwash water, but also reduced the impaction for main performance, furthermore, reduced the integration cost of performance.