Improving microalgal tolerance to high ammonia with simple organic carbon addition for more effective wastewater treatment

Due to ammonia toxicity in microalgal treatment systems, wastewaters with excessive ammonia require pretreatment, either dilution or chemical stripping, but this can be costly. Alternatively, the addition of organic carbon may help to alleviate toxicity. This study investigated effects of glucose addition on toxicity in three microalgal species. Glucose reduced toxicity at ammonia concentrations from 50 to 1000 mg L-1, in all species. Growth rate, cell count and biovolume significantly increased (p < 0.01) with glucose, at all ammonia concentrations. Carbon to nitrogen ratio (C:N) was important for maximising tolerance, varying with species, ammonia concentration and parameter measured. For Chlorella sorokiniana, the highest total biovolume yield (2.3 x 10(4) +/- 1.3 x 10(3) mu(-3) mL(-1)) was achieved at 25 mg L-1 and C:N = 5, for Coelastrum sp., (1.0 x 10(4) +/- 0.8 x 10(3) mu m(-3) mL(-1)) it was achieved at 750 mg L-1 and C:N = 9, and for Desmodesmus communis (6.9 x 10(7) +/- 5.2 x 10(6) mu m(-3) mL(-1)) it was achieved at 1000 mg L-1 and C:N = 5. When grown on food-waste centrate, effective quantum yield, light absorption, growth rate, biomass yield and nutrient removal were all inhibited at concentrations between 100 and 500 mg L-1. However, the addition of glucose at C:N = 1, or 5, alleviated ammonia toxicity, resulting in significantly higher (p < 0.01) biomass and nutrient removal. The simple addition of glucose was effective at reducing ammonia toxicity and improving micmalgal wastewater treatment in both defined medium and centrate at lab-scale. Further research is needed to assess effectiveness at scale for improved wastewater treatment.

Automated summary

This study investigated the effects of glucose addition on toxicity in three microalgal species. The results showed that glucose reduced ammonia toxicity and increased growth rate and biomass yield. The carbon to nitrogen ratio played an important role in maximizing tolerance, but varied with species, ammonia concentration, and parameter measured. The addition of glucose was effective at reducing ammonia toxicity and improving microalgal wastewater treatment.