Pilot Study Of Luanhe River Water Treatment By An Immersed Hollow-fiber Microfiltration Membrane System

Due to the shortage of water resource, the deterioration of water environment, the enhancement of drinking water quality standards and the limitations of traditional drinking water treatment processes, it has been a great subject that new water treatment technologies were explored to improve or replace traditional treatment processes in the area of drinking water treatment.Immersed microfiltration membrane with a nominal pore size of 0.1 μm was tested for treatment of Luanhe raw water with pilot-scale in the period of high temperature and high amount of algae. The effect of contaminants removal by immersed membrane system was investigated in the different pretreatment ways, and compared with conventional treatment processes. Three cleaning techniques to reduce membrane fouling were studied, and their operating parameters were optimized. The results and conclusions were as follows:1. It was proved that immersed microfiltration membrane system had high efficiency in the removal of turbidity and particles. The average permeate turbidity was 0.08 NTU. The particles in the permeate with a diameter greater than 2μm were less than 30 per mL, and with a diameter greater than 15μm removed almost completely. Pretreatment measures increased hadnt significantly enhanced the turbidity removal by the membrane system. The algaes were removed completely, the Fe in membrane-treated water was lower than 0.05 mg/L.2. Pretreatment processes increased could strengthen the membrane system to remove organic matter and make membrane-treated water quality more stable. By direct membrane filtration, the removals of COD_Mn was 12.5%-46.0%, the average removals of COD_Mn and UV₂₅₄ were 30.3 % and 1.5 % respectively. As pre-coagulation was applied prior to submerged membrane, the average removal of COD_Mn increased from 30.3% to 50.3% and UV₂₅₄ from 1.5% to 23.0%. A combination of pre-coagulation with pre-chlorination was applied in the third phase. The COD_Mn and UV₂₅₄ removal reached 52.7% and 26.4% respectively. In the period of high temperature and high amount of algae, some pretreatment measures must be taken to ensure that the concentration of organic matter in the permeate meets drinking water quality standards.3. A comparison was made on the effect of contaminant removal by conventional treatment processes and membrane processes. The results showed membrane processes had excellent performance in the removal of turbidity and little advantage in the removal of organic matter and NH3-N, but the dosage of coagulant was far lower than those required in the conventional processes. Disinfection must be introduced into the membrane process for water treatment.4. Periodic backwashing was necessary to membrane fouling prevention. The optimal backwashing time was 85s, and the best backwashing water flux was 15m-3/h in the specific test conditions. EFM was an effective technique against membrane fouling. In the specific test conditions, the optimal EFM cleaning time was 45min-60min, and the best cleaning agent was the solution of 0.41 wt% NaOH and 800ppm NaClO. Membrane performance could achieve a great recovery by chemical cleaning. It was preferable that physical cleaning was conducted three-time-continuous before the chemical cleaning and four times after the chemical cleaning. Membrane fouling was mostly caused by organic matters in the raw water in the period of high temperature and high amount of algae.