Papers by Author: Li Hua Cheng

Abstract: Due to increasing water scarcity, reclamation and reuse of the secondary effluent of wastewater treatment plant are widely concerned in many countries. Before reuse, the residual contaminant in the secondary effluent should be further removed to guarantee safe reuse. Coagulation/sedimentation and subsequent chlorine dioxide(ClO₂) disinfection was adopted for tertiary treatment of secondary effluent. Selection of coagulant and optimization of tertiary treatment parameters were performed in this study. The results showed that coagulation could remove turbidity and total phosphours(TP) effectively. Polyaluminium chloride(PAC) was the most suitable coagulant. The optimal coagulation condition was as follows: PAC dosage of 10mg/L(measured as Al³⁺), reaction time of 20 min, settling time of 40 min, in this case, the average removal rate of turbidity, color, UV₂₅₄, TP and TOC could reach to 58.2%, 22.8%, 18.2%, 60.6% and 22.2%, respectively. ClO₂ could inactive bacteria and E. coli effectively. ClO₂ could further remove UV₂₅₄, color and TOC. In case of ClO₂ dosage of 5mg/L, the sterilization efficiency could reach 100%, and the removal rate of UV₂₅₄, color and TOC was higher than 25%, 70% and 25%, respectively. In the optimal condition, the removal efficiency of residual contaminant by the combination process was as follows: UV₂₅₄ of 45.9%, color of 76.5%, TOC of 66.7%, turbidity of 61.9% and TP of 96.3%.

Abstract: Sludge reduction by electrolysis and its subsequent influence on removal rate of COD, NH₃-N, PO₄^3- and on the sludge activity in the aeration tank were investigated. In this research, two parallel sequencing batch reactors were used with one set was operated in convention modality and the sludge of the other set was electrolyzed and then fed back to the reactor. The results showed that: sludge electrolyze could reduce the sludge production around 21% and had slight effect on substrate removal efficiency. After the sludge being electrolyzed, removal rate of COD and NH₃-N decreased by 1.1% and 6.9%, respectively. PO₄^3- removal rate increased by 6.1%. The number of protozoa, metazoan and protonema decreased and the structure of sludge floc became more compact. Moreover, the activity of microorganism and carbon source metabolism of sludge changed slightly, but the microbial community structure and metabolic function of microorganism had little change.

Abstract: Due to increasing water scarcity, appropriate technologies were need for advanced treatment of wastewater to enable reuse. Effect of iron-carbon internal electrolysis in tertiary treatment of wastewater was investigated in this study. Static experiment was adopted to evaluate influence of Fe/C ratio, pH, reaction time and aeration on pollutant removal by iron-carbon internal electrolysis. Then dynamic experiment was conducted to determine removal rate of CODcr, TP, chroma and NO₃^--N. The results showed that internal electrolysis could remove COD_cr, TP and chroma efficiently. The optimal ratio of Fe/C was 1:1. Initial pH could affect removal efficiency. In acid circumstance, the removal rate was higher. Degradation reaction by internal electrolysis was fast. when the reaction time was 10min, the removal rate could be ideal. In the process of internal electrolysis, aeration could increase pollutant removal rate. In aerated system, when the reaction time was only 15min, removal rate of COD_cr, TP and chroma could reach 49.2%, 89% and 75%. But in non-aerated system, only when the reaction time was 100min could removal rate of these indexes reach 46.5%, 81% and 85.1%. In dynamic experiment, removal rate of COD_cr, TP, chroma and NO₃- could reach above 40%, 90%, 75% and 20%, respectively.