Experimental Study On Domestic Sewage Treatment By An Internal-loop Air-lift Bioreactor

Internal-loop air-lift bioreactor is a new aerobic biotreatment reactor based on traditional bio-fluidized bed, which absorbed disorderly fluidization from chemical manipulation with the character of high sludge load, strong anti-shock loading capability and compact structure. This paper summarized the operational principle of the internal-loop air-lift bioreactor and its progress at home and abroad. Experiment applied internal-loop air-lift bioreactor treating domestic sewage, and the results revealed the optimal condition by the orthogonal method. We also analyzed the removal efficiencies of COD,NH4+-N,SS,TN and TP and studied the anti-shock loading capability and sludge characteristics of the internal-loop air-lift bioreactor.The results of experiment showed that:1. The orthogonal experimental results revealed the optimal conditions: the HRT was 10h,the QL was 0.55m3/h and the SRT was 5d.The result of experiment under those conditions shows that the average removal rate of COD, NH4+-N and SS were 90.17%,91.45% and 91.85% respectively which is qualified on the second class by Discharge standard of pollutants for municipal wastewater treatment plant(GB 18918-2002).2. The maximum and minimum influent concentration of COD were 229.71mg/L and 595.69mg/L with the average of 375.71mg/L. The COD removal rate was between 64.24% and 94.43% with the average of 81.24% and the COD effluent concentration was between 33.16mg/L and 96.17mg/L with the average of 63.24mg/L. Results showed that the internal-loop air-lift bioreactor has the average sludge load of 1.05kgCOD/(kgMLSS·d), which is higher than the traditional biotreatment reactor.3. The SS removal rate was between 87.72% and 93.35% with the average of 89.87%. It revealed by orthogonal experimental results that the sequence of the effect of the parameters to SS removal rate was SRT>QL>HRT, that is to say the SRT was the dominant parameter, QL was secondary and HRT affected least.4. The internal-loop air-lift bioreactor had higher capability of nitrogen and phosphorus removal than the traditional biotreatment bioreactor. The TN influent concentration was between 58.03mg/L and 73.54mg/L with the average removal rate of 55.61% which was higher than the traditional biotreatment bioreactor (20%-40%).The TP influent concentration was between 5.34mg/L and 19.19mg/L with the average removal rate of 57.72% which was also higher than the traditional biotreatment bioreactor (15%-20%).5. Anti-shock loading capability was studied by adding sucrose, and the result revealed that the COD effluent concentration was between 77.28mg/L and 128.65mg/L while the average COD influent concentration was 707.56mg/L, and the COD removal rate was between 84.85% and 89.66% with the average of 86.11%.The result also showed that the internal-loop air-lift bioreactor remained high COD removal rate in spite of the increase of the COD influent concentration.6. The average of SV and SVI were 15% and 93 respectively. The experimental result revealed that the SV curve and the SVI curve had the similar trend, and with the time going, this phenomenon was more obvious which indicated that the stability of activated sludge was enhanced.