Continuous cultivation of mixed-culture microalgae using anaerobic digestion effluent in photobioreactors with different strategies for adjusting nitrogen loading rate

This study examined continuous mixed-culture microalgae cultivation for nutrient removal from anaerobic digestion (AD) effluents in photobioreactors, while altering the NH4+-N loading rate (NLR) by adjusting either the hydraulic retention time (HRT) (reactor set RH) or the influent NH4+-N concentration (reactor set RS). Both RH and RS demonstrated efficient nutrient removal and microalgae cultivation at NLRs of 4-10 mg NH4+-N/L & BULL;d, reaching peak performance at 10 mg NH4+-N/L & BULL;d. Within this range, RH obtained greater biomass yield and productivity, while RS maintained higher microalgal concentrations. The cultivated biomasses obtained from RH and RS had good settleability and suitable fatty acid compositions as a biodiesel feedstock, although their organic composition varied considerably with NLR and HRT. Parachlorella overwhelmingly dominated the reactors' microalgal communities throughout the experiment, co-existing with various microalgae-associated bacteria. Changes in NLR significantly influenced the bacterial community structures, underscoring its critical role in determining reactor performance and microalgal-bacterial community behavior.

Automated summary

This study investigated continuous mixed-culture microalgae cultivation in photobioreactors for nutrient removal from anaerobic digestion effluents by altering NH4+-N loading rate. Results showed that both adjusting hydraulic retention time (RH) and influent NH4+-N concentration (RS) efficiently removed nutrients and cultivated microalgae at NLRs of 4-10 mg NH4+-N/L & BULL;d, with peak performance at 10 mg NH4+-N/L & BULL;d. RH achieved higher biomass yield and productivity, while RS maintained higher microalgal concentrations.