Inhibition of nitrification in municipal wastewater-treating photobioreactors: Effect on algal growth and nutrient uptake

•Microalgae were able to grow faster when nitrification was inhibited.•The inhibited reactors had Cryptomonas and Chlorella as the dominant genera.•Inhibition of nitrification did not affect the uptake rate for N and P.•Inhibition of nitrification affected N speciation in the reactors. The effect of inhibiting nitrification on algal growth and nutrient uptake was studied in photobioreactors treating municipal wastewater. As previous studies have indicated that algae prefer certain nitrogen species to others, and because nitrifying bacteria are inhibited by microalgae, it is important to shed more light on these interactions. In this study allylthiourea (ATU) was used to inhibit nitrification in wastewater-treating photobioreactors. The nitrification-inhibited reactors were compared to control reactors with no ATU added. Microalgae had higher growth in the inhibited reactors, resulting in a higher chlorophyll a concentration. The species mix also differed, with Chlorella and Scenedesmus being the dominant genera in the control reactors and Cryptomonas and Chlorella dominating in the inhibited reactors. The nitrogen speciation in the reactors after 8days incubation was also different in the two setups, with N existing mostly as NH4-N in the inhibited reactors and as NO3-N in the control reactors.