Start-up of a membrane bioreactor bioaugmented with genetically engineered microorganism for enhanced treatment of atrazine containing wastewater

Efficient and stable atrazine removal could be realized after a start-up period in a membrane bioreactor (MBR) bioaugmented with genetically engineered microorganism (GEM) and the removal efficiency was above 90%. The start-up period was the key step of MBR bioaugmented with GEM and determined by operation conditions. The shortest start-up period was 2 days and the longest one was 12 days under different operation conditions. Initial influent atrazine loading, operation temperature and initial density of GEM affected the start-up period greatly. High initial influent atrazine loading, high operation temperature and large initial density of GEM were favorable to shorten the start-up period. The characteristics of the influent had little effect on the start-up period. Two kinds of influents — synthetic wastewater and real domestic wastewater, had the same start-up periods when other conditions were identical. The density of GEM varied remarkably in the start-up period: it decreased rapidly at the initial time and then tended to a constant. The logistic model was used to fit the density variation of GEM. The different values of model parameters accounted for the relationship between the atrazine removal performance and the density variation.

The start-up period was the key step for the bioaugmented MBR by using GEM to realize efficient and stable atrazine removal. Higher atrazine influent loading, higher operation temperature and higher initial GEM density were favorable to shorten the start-up period. The influent characteristics had little effect on the start-up period. The variation of GEM density was influenced by operation conditions and showed close relationship with atrazine removal in the start-up period. Acknowledgment The GEM used in this work was donated by Professor Cai Baoli, Nankai University, China. The authors thank him for his help in this study. This work was supported by the National Science Fund for Distinguished Young Scholars (No. 50725827).