The joint effect of ammonium and pH on the growth of Chlorella vulgaris and ammonium removal in artificial liquid digestate.

Although ammonium containing digestate is an ideal alternative medium for microalgae cultivation, high ammonium or unfavorable pH may inhibit microalgal growth. In this study, the joint effect of ammonium and pH on the growth of C. vulgaris and nutrient removal in artificial digestate was investigated. Our results show that ammonium and pH both affected algal growth, but free ammonia (FA) was the main actual inhibitory factor. Algal specific growth rate presented a negative correlation with FA and their relationship was well fitted by a linear regression model. Microalgal growth was little affected below 36.8 mg L FA, while the obvious inhibition occurred at 184 mg L FA (EC), indicating a high tolerance to FA. Ammonium removal was well described by a first-order kinetics model. FA stress stimulated the production of extracellular organic matters (EOMs), which was good for microalgae adaptation but adverse to pollutant removal.