Role of phosphatase activity as an early warning indicator of inhibition in a single-phase anaerobic digester treating food waste

The objective of this study was to understand the role of phosphatase activity as an early warning indicator of inhibition that has been often observed in the anaerobic digestion(AD) of food waste.Tests were conducted in laboratory scale,single-phase CSTR reactors operated at loading rates ranged from 2.0 to 8.5kg VS/(m3?d).The activity of acid phosphatase(ACP) and alkaline phosphatase(ALP),volatile fatty acids(VFAs),volumetric gas production rate and pH were measured during the reactor operation.The average ACP and ALP activity at the start-up phase when the reactor loading rate ranged from 2.0 to 4.0kg VS/(m3?d) were measured as 14.1 and 9.8 μgNP/(h?mL),respectively;while 138.4 and 23.6μgNP/(h?mL) at the steady phase when the reactor loading rate was within 5.0 to 7.5kg VS/(m3?d).The ACP and ALP activity peaked at 318.1 and 51.5μgNP/(h?mL) when reactors were overloaded at 8.5kg VS/(m3?d),after which both activity significantly decreased.The sharp increase in phosphatase activity occurred two days prior to the loading rate increase and one day prior to the pH drop,which suggests it could be an early warning indicator of inhibition that often occurred in the anaerobic digestion of food waste.