Sulfonamide degradation and metabolite characterization in submerged membrane photobioreactors for livestock excreta treatment.

Residual veterinary antibiotics have been detected in livestock wastewater treatment plants. Despite the long retention time, antibiotic treatment efficiency has shown clear limitations. In this study, we evaluated submerged membrane photobioreactors (SMPBR) during sulfonamide antibiotic-containing livestock wastewater treatment under mixotrophic and photoautotrophic conditions. The results showed that microalgal sulfur degradation and consumption under mixotrophic conditions accelerated the biomass concentration increase to 2800 mg VSS/L compared to the 1800 mg VSS/L measured under photoautotrophic conditions. Although microalgal metabolites, such as soluble microbial products and extracellular polymeric substances, might cause membrane fouling in the SMPBR, we proved that microalgae could remove sulfonamide and release degradation-associated sulfur, along with nitrogen and phosphorus. Moreover, this study confirms the statistical correlation between metabolites and sulfonamides. In summary, the results of this study provide promising insights into antibiotic-containing livestock wastewater treatment.

Optimal Temperature and Light Intensity for Improved Mixotrophic Metabolism of Chlorella sorokiniana Treating Livestock Wastewater.

Mixotrophic microalgal growth gives a great premise for wastewater treatment based on photoautotrophic nutrient utilization and heterotrophic organic removal while producing renewable biomass. There remains a need for a control strategy to enrich them in a photobioreactor. This study performed a series of batch experiments using a mixotroph, Chlorella sorokiniana, to characterize optimal guidelines of mixotrophic growth based on a statistical design of the experiment. Using a central composite design, this study evaluated how temperature and light irradiance are associated with CO2 capture and organic carbon respiration through biomass production and ammonia removal kinetics. By conducting regressions on the experimental data, response surfaces were created to suggest proper ranges of temperature and light irradiance that mixotrophs can beneficially use as two types of energy sources. The results identified that efficient mixotrophic metabolism of Chlorella sorokiniana for organics and inorganics occurs at the temperature of 30-40°C and diurnal light condition of 150-200 µmol E·m2·s-1. The optimal specific growth rate and ammonia removal rate were recorded as 0.51/d and 0.56/h on average, respectively, and the confirmation test verified that the organic removal rate was 105 mg COD·l-1·d-1. These results support the development of a viable option for sustainable treatment and effluent quality management of problematic livestock wastewater.