Study On Optimization Of Raw Water Treatment Process Under The Influence Of Seasonal Salt Tide In South China

The salt tide has a great impact on the water supply in coastal areas.Especially in winter and spring,the upstream rainfall is small,the river bed water level is low,and the seawater backflow is serious.Seawater backflow brings a lot of chloride and bromine ions,which increases the salt content of rivers and rivers.Drinking water with high salt content for a long time will increase the burden on the heart and kidney;Due to the backflow of the downstream pollution zone and the upward return of sediment,the organic matter and ammonia nitrogen rise,which seriously affects the water production of the water plant.Aiming at the periodic salt tide polluted raw water of B River in a city in the west coast of Guangdong,this paper carries out the optimization test of conventional process,ozone activated carbon process parameters,disinfection process and the treatment efficiency of conventional ozone activated carbon process on salt tide polluted raw water.The raw water of river B is the typical weak acid river water source in southern China.The water quality indicators in the conventional period are as follows:turbidity is 7.2～37.8 NTU,chroma is 2～15,pH is about 6.9,CODMn is 2.10～4.89 mg/L,and ammonia nitrogen is 0.05～0.05 64 mg/L。In case of salt tide pollution,the original water content of river B is divided into two water quality periods:①in case of slight salt tide pollution,the turbidity is 20.3～25.6 NTU,CODMn is 5.23～10.25 mg/L,ammonia nitrogen is 1.75～2.12 mg/L,chloride is 10.7～33.9 mg/L,and bromine ion is 32～69 mg/L μg/L;②Severe salt tide pollution period:turbidity is 25.6～42.2 NTU,CODMn is 10.25～25.3 mg/L,ammonia nitrogen is 2.12～5.13 mg/L,chloride is 100.7～243.0 mg/L,and bromine ion is 173～241 u g/L。In the period of conventional water quality,PAC is the best coagulant,and the best dosage is 17.5mg/l;Using anionic PAM as coagulant aid,the best dosage of PAM is 0.8mg/l,and the best dosage point is 2min after the beginning of coagulation.Coarse sand has good economy,with particle size of 0.9-1.35mm;When the filtration speed is 8～10m/h,the economy is the best.The filtration cycle is inversely proportional to the filtration speed,and the maximum cycle should not exceed 72 h.For ozone activated carbon process,the best ozone dosing method is two-point dosing,the ozone distribution ratio is 1:1,and the best ozone dosage is 1.5mg/l.Coconut shell carbon is the best carbon,the best residence time of activated carbon filter is 15min,and the longest filtration cycle of carbon filter is 7 days.Through the disinfection by-product test,the removal rates of dcaafp,tcaafp and haafp in the whole process are 20.6%,26.8%and 23.7%respectively,and the removal rates of chloroform precursor and trihalomethane precursor are 46.12%and 48.18%respectively.When sodium hypochlorite is selected as disinfectant,the disinfection time shall be≥30 min,and the dosage of sodium hypochlorite shall be between 1.5 mg/L and 4.0 mg/L;When chlorine dioxide is selected as disinfectant,the minimum disinfection time shall meet 60 min,and the dosage of chlorine dioxide shall be between 0.5 mg/L and 1.5 mg/L.During the salt tide pollution period,the removal of CODMn and ammonia nitrogen by the process changed.In the period of light pollution,the total removal rate of CODMn by the process is 88.27%,the effluent CODMn of sand filter is 4.42mg/l,and the effluent CODMn of carbon filter is 1.14mg/1;The total removal rate of ammonia nitrogen was 78.33%.The ammonia nitrogen in the effluent of sand filter is 1.47 mg/L and that of carbon filter is 0.43 mg/L,which meets the hygienic standard of drinking water.In the period of severe pollution,the removal rate of CODMn by the process is 83.70%,the effluent CODMn of sand filter is 14.71mg/l,and the effluent CODMn of carbon filter is 4.21mg/l;The removal rate of ammonia nitrogen in the process is 55.56%,the ammonia nitrogen in the effluent of sand filter is 3.77mg/l,and the ammonia nitrogen in the effluent of carbon filter is 2.12mg/l,which exceeds the hygienic standard of drinking water.The retention time of the carbon bed was extended from 8 min to 20 min,the removal rate of ammonia nitrogen by the biological activated carbon process increased from 31.14%to 84.28%,and the ammonia nitrogen in the effluent decreased from 2.03 mg/L to 0.44 mg/L.the effluent of the process reached the standard and further reduced the CODMn content in the effluent.During the salt tide,the dosage of ozone is controlled below 2.2 mg/L,and the effluent bromate meets the requirements of drinking water standards.The test results provide guidance for the process optimization,energy conservation and consumption reduction of the water plant,improve the water production efficiency of the water plant,improve the quality of factory water,and provide optimization parameters for the operation of the water plant and the design of new water plants.