Investigation On The Electrochemical Preparation Method And Coagulation Efficiency Of Two Kinds Of Coagulants With High Active Component Content

The water quality problem of surface drinking water sources is becoming more and more serious.In order to satisfy the upgrading criteria of drinking water,it is necessary to develop an efficient and economic water treatment technology.In this paper,the coagulation process technology of surface drinking water sources is taken as the research object.Two kinds of coagulants with high active component content were produced by electrolysis process.After optimizing the technological parameters of preparation and coagulation by the orthogonal test,the two coagulants are compared and evaluated via a series kind of characteristic methods.Based on previous studies,a pilot-scale process was established with the enhanced coagulation technology and the application prospects of these two kinds of coagulants with high active component content were analyzed by assessing their coagulation efficiency.The optimum preparation conditions of aluminum coagulant with high Al_b content and iron coagulant with high Fe_b content were obtained through orthogonal test.The content of active component was distinguished by Ferron complexation timed spectrophotometric method.The optimal preparation conditions are as follows.In the experiment of preparing aluminum coagulant,it used 1 mol/L NaCl solution as electrolyte.The Al_b was accounted for 73.98%of total Al with optimizing the current density of 50A/m²,electrolytic time of 30 min and initial pH of 4.By using 0.5 mol/L Na₂SO₄ as electrolyte,a kind of iron coagulant whose Fe_b was accounted for 52.11%of total Fe was produced with optimizing the current density of 50 A/m²,electrolytic time of 20 min and initial pH of 4.Compared with other preparation methods,coagulants containing more active component content can be prepared by electrochemical method.Compared with other aluminum coagulants prepared by different electrochemical methods,the new preparation method not only improves the efficiency of the coagulant,but also reduces the current density by 58.33%,the electrolysis time by 96.30%,and the electric quantity required by each square meter electrode plate by 98.46%,apparently reduce the cost and energy consume.After optimizing the coagulation condition,the optimal operational parameters of coagulation were determined as follows.When coagulant is the aluminum coagulant with high Al_b content,the best coagulant aid is PAM whose optimal dose is 0.06 mg/L and optimal time is 2 min after coagulant is added.When adding 3.90 mg/L aluminum coagulant with the stirring conditions of 100 r/min for 8 min,80 r/min for 8 min,20 r/min for 8 min,and then standing for 20 minutes,the highest removal rate of turbidity could reach to 96.27%,the highest removal rate of COD could reach to 81.19%and the concentration of residual aluminum could reach to 0.017 mg/L.When coagulant is the iron coagulant with high Fe_b content,the best coagulant aid is PAM whose optimal dose is 0.08 mg/L and optimal time is 2 min after coagulant is added.When adding 3.49 mg/L iron coagulant with the stirring conditions of 110 r/min for 8 min,80 r/min for 8 min,20r/min for 8 min,and then standing for 20 minutes,the highest removal rate of turbidity could reach to 92.00%and the highest removal rate of COD could reach to 74.02%.The results of pilot experiment show that these two kinds of coagulation processes can both run normally and stably in a short time.When coagulant is the aluminum coagulant with high Al_b content,the average removal rate for turbidity and COD has reached 94.25%and 60.49%respectively by selecting right operation parameters.When coagulant is the iron coagulant with high Fe_b content,the average removal rate for turbidity and COD has reached 87.43%and 58.12%respectively by selecting right operation parameters.The turbidity of effluent from these two kinds of pilot-scale processes could both meet the National Standard for Drinking Water Hygiene?GB5749-2006?.Safe effluent could be achieved with no nano-particles residue and low-concentration residual aluminum.The concentration of residual aluminum in the effluent could be maintained at 0.034 mg/L,the highest concentration is 0.038 mg/L which is far below the limits?0.2 mg/L?.These two kinds of coagulants with high active component content produced by electrolysis process are both adequate for the coagulation process technology of surface drinking water sources.They have their own advantages and adapt to different application environments.The coagulation process which use aluminum coagulant with high Al_b content as coagulant can achieve high efficiency and guarantee stable effluent water quality.The coagulation process which use iron coagulant with high Fe_b content as coagulant have more advantages in cost reduction and land occupation reduction.