The mechanism study of attached microalgae cultivation based on reverse osmosis concentrated water (WROC)

Abstract

Reverse osmosis membrane is widely applied in advanced wastewater treatment. Along with the production of clean water, 30%∼50% reverse osmosis concentrated water (WROC), containing massive nitrogen and phosphorus, is also produced. WROC would bring ecological risk if discharged into the natural water body. Hence, attached microalgae cultivation based on WROC was proposed to recovery the nutrients from water in this study. The results showed that the initial concentrations of nitrogen and phosphorus in WROC (TN≈50 mg/L, TP≈10 mg/L) were not too high to inhibit attached microalgae growth. Among the complex chemicals in WROC, non-oxidizing bacteriostatic agent had the worst impact on the growth of microalgae with an 8-day inhibition ratio of 25%. Compared with the microalgae cultured by nutrient medium, the lipid and protein contents in attached microalgae cultured by WROC were relatively high and stable during the whole cultivation period. Seen from the micro level, there was no obvious resistance to the transfer of TN and TP in the microalgae biofilm. However, the photosynthetic rate of microalgae in the biofilm decreases along with the depth. In conclusion, uneven light distribution in biofilm and the non-oxidizing bacteriostatic agent in WROC were the main resistance to the growth of attached cultured microalgae, which should be optimized or per-treated.