Pilot Study On The Combined Ultrafiltration With Ozone Biological Activated Carbon In The Treatment Of Hyperalgal Raw Water

Most of the conventional water treatment processes in China are still staying in the routine treatment stages of coagulation,precipitation,filtration and disinfection,and the effluent quality cannot meet people’s demand for high-quality drinking water at the present stage.The newly developed membrane separation technology has been widely used in the renovation of old water plants and the construction of new water plants due to its good treatment effect and low operating cost.Flux attenuation caused by membrane fouling is a key problem in the application of membrane technology to water plants.In order to solve this problem,the combination of online coagulation and ultrafiltration is considered.The ozone-biological activated carbon process is the optimal depth treatment process to relieve the water treatment pressure in the high temperature and high algae stage of the water plant.Its disadvantage is that bacteria easily breed in the carbon column and threaten the water quality and biological safety,while the membrane technology can just make up for this problem.The online coagulation-ultrafiltration-ozone activated carbon combined process used in the pilot test is ideal for the effluent quality,and it ensures the safety of drinking water quality. Based on the demand of high quality drinking water,the raw water was taken from east taihu lake,which is prone to algal bloom,and the pilot study of ultrafiltration combined with ozone and activated carbon was carried out in combination with the existing conventional process in the water plant.Firstly,the water quality of raw water was analyzed and the operation parameters of the combined process were optimized.Secondly,the advantages and disadvantages of combined process and conventional process were compared.Finally,the long-term operation and maintenance of the combined process were investigated,which provided a new idea for the treatment of high algae raw water and a theoretical basis for the process transformation of the water plant with east taihu lake as the water source.The main results of this experiment are as follows: （1）The p H value of raw water in East Taihu Lake is relatively stable,and the turbidity,organic matter,ammonia nitrogen and algae content in the water body are greatly affected by seasonal changes.In summer,high temperature,high turbidity and high concentration of organic matter in water tend to be eutrophication,and serious algal bloom leads to rapid increase of algal 超滤-臭氧生物活性炭联用工艺处理高藻原水的中试研究 toxin and odor substances in water,which reaches the maximum throughout the year and threatens water quality safety.In the spring,the concentration drops slightly;In the case of low temperature,low turbidity and low organic matter concentration in autumn and winter,the coagulation sedimentation process is easily affected,resulting in poor effluent quality.Raw water organics in East Taihu Lake are composed of hydrophilic proteins,polysaccharides and highly hydrophobic humus,which are greatly affected by pollution caused by living and production water and aquatic metabolites. （2）The experiment confirmed that the on-line coagulation process could effectively alleviate the membrane pollution,and the system could run stably under the flux of 80 L/m~2·h.Based on the comprehensive effluent effect and water production cost,the operation parameters of the process were optimized as follows:the coagulant was selected with the dosage of 20 mg/L polyaluminum chloride(with Al³⁺),the dosage of ozone was 1.5 mg/L,the ozone contact time was 15 min,the thickness of carbon layer was 1.25 m,and the adsorption time of activated carbon was 12 min. （3）The online coagulation-ultrafiltration-ozone activated carbon process has an average removal rate of 99.89%,79.13%,75.88%,71.55%,and 94.08%for the total integral of turbidity,COD_Mn,UV₂₅₄,ammonia nitrogen,and CDOM,respectively.The combined process has an excellent removal effect on algae,and the average removal rate of algae density and chlorophyll a reached 99.65%and 98.18%,respectively.By comparing the conventional process-ozone-activated carbon combined process with the on-line coagulation-ultrafiltration ozone-activated carbon process,it is found that the combined process has a significant advantage in efficiency,so the membrane technology is considered to replace the conventional water treatment technology. （4）Humic acids are the main components that cause the reversible pollution of ultrafiltration membrane,which can be removed by periodic physical recoil.The online coagulation process also contributes to the removal of such substances.On-line chemical enhanced backwashing can remove the organic pollutants which cannot be removed by hydraulic backwashing in the raw water and which are deposited in the membrane pores and cause irreversible membrane pollution.The main components of the organic pollutants include aromatic protein substances and soluble microbial metabolites.Off-line chemical cleaning can effectively elute some stubborn organic pollutants that are difficult to be removed by online chemically enhanced backwashing.