Study On Operation Control For Liquid Crystal Display(LCD) Materials Production Wastewater Treatment

The wastewater quality of liquid crystal display(LCD) materials production is complex with high concentration pollutants and toxicity, which belongs to one of refractory organic wastewater.The treatment process of “first stage Fenton oxidation-A/O-second stage Fenton oxidation” was used for LCD materials production wastewater treatment with a treatment capacity of 400m3/d. The designed influent qualities were pH 6-9, COD 4200mg/L and NH3-N 100mg/L. The designed effluent qualities were pH 6-9, COD≤300mg/L and NH3-N≤40mg/L.Based on the experiment results, the optimal conditions of first stage Fenton oxidation were determined as follows: the reaction time was 120 min, pH was 3, the dose of 30% H2O2 was 15 ml/L, the mole ratio of H2O2 to Fe2 + was 10:3. Under the optimal conditions, the average removal rate of COD was 40.9% with effluent COD concentration of 2476 mg/L and ammonia nitrogen concentration of 80.5 mg/L when COD concentration was 4395.5~3946.4mg/L and ammonia nitrogen concentration was 70.9~90.6mg/L in the influent,.When dissolved oxygen concentration was controlled as 3~4 mg/L and the reflux ratio of nitration liquid was 1.5, the stable operation performance of A/O process was efficient. The operation results indicated that when COD concentration was 2422.4~2597 mg/L and ammonia nitrogen concentration was 79.4~94.6 mg/L in the influent, the COD and ammonia nitrogen removal rates were 84.2% and 61.4%, respectively. The average effluent COD concentration was 393.1 mg/L and average ammonia nitrogen concentration was 32.4 mg/L.The optimal conditions of second stage Fenton oxidation were determined as follows: the reaction time was 90 min, pH was 3, the dose of 30% H2O2 was 4 ml/L, the mole ratio of H2O2 to Fe2 + was 10:1. Under the optimal conditions, the average removal rate of COD was 41.9% with effluent COD concentration of 232.5 mg/L and ammonia nitrogen concentration of 32.1 mg/L, when COD concentration was 386.0~408.5 mg/L and ammonia nitrogen concentration was 30.6~34.8 mg/L in the influent. The performance of the treatment system was stable and efficient.When “first stage Fenton oxidation-A/O-second stage Fenton oxidation” was used to treat LCD materials production wastewater, the system effluent COD concentration was 232.5 mg/L and ammonia nitrogen concentration was 32.1 mg/L. The system COD removal rate was higher than 90% and ammonia nitrogen removal rate was higher than 65%. The effluent quality could meet the discharge limition. The COD reduction was 476.1 t/a and ammonia nitrogen reduction was 8.2 t/a, respectively, which would provide significant environmental benefits.The running cost of the wastewater treatment process was 4.9 yuan/m3. This was economically feasible.