Removal Of Filamentous Cyanobacteria And Odorants By Ozone Moderate Pre-Oxidation Coupled With Ozone/Hydrogen Advanced Treatment

In recent years,many countries and regions have found cyanobacteria bloom phenomenon in drinking water source caused by eutrophication,cyanobacteria bloom not only can cause a significant rise in water turbidity,chromaticity,and compounding matters,but produce algal toxins and odorous substances such as geosmin(GSM)and 2-methylisoborneol(2-MIB)during the metabolic process,which will seriously threaten the safety of drinking water.In drinking water plants,coagulation-sedimentation is the most critical process unit to remove algal cells from water.However,due to the high surface electronegativity and floatability of cyanobacteria cells,which will lead to the increase of the dosage of coagulant.In this study,the raw water of drinking water plant suffered from filamentous cyanobacteria bloom,compared with spherical cyanobacteria,its stronger floatability will seriously affect the sedimentation of flocs and make it more difficult to remove algae by coagulation-sedimentation.Hence,conventional coagulation-sedimentation is difficult to meet the water quality standard of water plants during the summer and autumn.In this study,ozone pre oxidation was used to enhance coagulation to remove algae cells in water.By controlling the degree of oxidation,the release of intracellular 2-MIB from the damaged cells should be avoided.Furthermore,ozone/hydrogen advanced treatment process was used to remove the residual odor substance in water.On the basis of optimization of the previous process,the continuous operation pilot test was carried out,and the applicability of the process was evaluated by real-time detection and analysis of different water indexes.Finally,the original and the optimized process are compared and analyzed from the three aspects of economic,social and environmental benefit.The main results are as follows:(1)After pre oxidation with low dose ozone(0.2 mg/L),the algal cells maintained basically intact.At the same time,the subsequent coagulation-sedimentation could be enhanced to remove the algal cells and avoid the release of intracellular organic matter and odorous substances(2-MIB)into the water owing to a large number of damaged algal cells.The ozone/hydrogen(2+2 mg/L)advanced treatment process can completely remove 2-MIB in the water,which is helpful to improve the effluent quality of the water and ensure the safety of drinking water.(2)The pilot test was run for 14 days.The stability and feasibility of the optimized process were verified by detecting and analyzing the algae density,turbidity,CODMn and 2-MIB at the beginning and end of operation under different treatment process units.(3)The cost per ton of water produced by the optimized process(0.222 yuan),which is slightly higher than that of the original process(0.138 yuan),but the original process failed to effectively remove the odor-causing compound 2-MIB.The optimized process can efficiently remove filamentous algae and remove 2-MIB from water by oxidative degradation,which also could improve the water quality of drinking water.Therefore,it has considerable social and environmental benefits.