Comparison of different trophic cultivations in microalgal membrane bioreactor containing N-riched wastewater for simultaneous nutrient removal and biomass production

- Microalgae cultured under different cultivation types and nitrogen sources in MMBR.
- The highest mixotrophic biomass productivity was obtained in MMBR containing NH4+.
- High N and P removal rates were achieved by cultivating mixotrophic algae in MMBR.
- N removal amounts were assimilated to biomass (except autotrophic culture in NO3−).
- Photosynthetic activity of mixotrophic microalgae improved in nitrate source.

In this study, a submerged membrane was installed in a bioreactor to treat N-riched wastewater and obtain high biomass productivity. Chlorella vulgaris was cultivated under mixotrophic, heterotrophic, and photoautotrophic conditions in different kinds of nitrogen sources (nitrate and ammonium) to compare the microalgae growth and nutrient removal in a membrane bioreactor. Further, the respirometric and photosynthetic activities of microalgae were investigated to evaluate the viability of microalgae in different conditions. The highest biomass productivity was obtained under mixotrophic cultivation in ammonium source (0.230 ± 0.009 gr/L d). Moreover, with this type of cultivation and nitrogen source, specific oxygen uptake rate (SOUR) was higher than oxygen product rate (SOPR). However, SOPR improved in mixotrophic cultivation using nitrate source. In both nitrogen source types, the photosynthetic activity of mixotrophic microalgae was reduced at high cell density. Compared favorably with other cultivation types, mixotrophic microalgae could achieve high N and P removal rates (about 23.64-28.84 and 4.38-5.08 mg/L d, respectively). In all cultivation types (except photoautotrophic condition with nitrate source), N and P removal amounts were assimilated to biomass. Based on the obtained results, membrane bioreactor containing mixotrophic microalgae would be the most useful system for application in N-riched wastewater treatment systems.

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