Optimization Of Conventional Treatment Technology Under Seasonal Variation Of Surface Source Water Quality

Aiming at the problems such as poor coagulation effect and large dosage fluctuation under seasonal water quality variation in a surface water plant in Xi’an,a pilot system was used to optimize the dosage combination and dosage.At the same time,in order to evaluate the filtration performance of ceramic sand and porcelain sand filter material,the conventional quartz sand filter material was taken as the reference,and the pilot test was conducted to investigate the turbidity removal performance,the increase of head loss and the backwash effect of the three filter materials,and the influence of filtration rate,turbidity of water after sedimentation and PAM concentration on turbidity removal performance was analyzed.The main conclusions are as follows:（1）The best combination of dosing during the high turbidity and the flood season was the addition of 35 mg/L of polyaluminum chloride and 10 mg/L of activated silica.At this time,good treatment results could be achieved at a lower reagent cost.The turbidity of the settled water was 1±0.15 NTU,and the removal rate of organic matter was 65±2.5%.The addition of PAM and KMn O₄ had no obvious effect on the removal of turbidity,but KMn O₄ promoted the removal of organic matter,which could be enhanced by KMn O₄ pre-oxidation.（2）The best dosing combination in winter’s low temperature and turbidity periods was adding 10 mg/L polyaluminium chloride and activating 4 mg/L silicate.Under this dosing condition,the turbidity of the settled water could be guaranteed to be below 1NTU and relatively economical,with a good removal effect on organic matter.Increasing or decreasing the water inflow load by 20%had little influence on the coagulation effect,and the turbidity of sinking water could still be stabilized within 2 NTU.（3）The biggest difference among the three filters was in gradation and particle size ratio.Ceramic sand had the best turbidity removal effect,followed by quartz sand and porcelain sand.Ceramic sand filter material could intercept impurities better because of its more uniform particle size distribution and higher proportion of fine sand.（4）Filtering speed about 8 m/h and turbidity of settling water below 3 NTU ensured that the filtering period of each filter material exceeded 45 h and the turbidity of filtered water was within 1 NTU;when PAM concentration was 0.25 mg/L,the three filters had the best removal effect on turbidity and organic matter,with removal rates of 75%and32%respectively,and the removal rates of ceramics filter material could reach 81.1%and49.07%respectively;the main organic compounds in raw water were humic acids,aromatic proteins,and fulvic acids by three-dimensional fluorescence analysis after sedimentation,the water mainly contained aromatic proteinⅡand fulvic acid organic matter,while after filtration,the water mainly contained fulvic acid and a small amount of aromatic protein organic matter.The optimization of the coagulation process provided a reference for the actual dosing of water plants under different seasonal conditions.The study of three kinds of filter materials from different angles provided a new idea for the application of ceramic sand and porcelain sand filter materials.