Short-term effects of reduced graphene oxide on the anammox biomass activity at low temperatures.

Anaerobic ammonium oxidation (anammox) is an efficient process for nitrogen removal from wastewater, but its common use is limited by its relatively high optimal temperature (30 °C). One of the major bottlenecks of the implementation of mainstream PN/A process is the low activity of the anammox bacteria at low temperature. Due to this reason over the past years, numerous researchers have attempted to overcome this limitation. Recently it was shown that the reduced graphene oxide (RGO) can accelerate the anammox bacteria activity. However all these studies were performed at high temperatures (over 30 °C). Thus, in this study, supporting the anammox process at low temperatures (10-30 °C) by the RGO was investigated for the first time. The statistical analysis confirmed that RGO significantly affects the anammox activity. The stimulation effect of RGO on the anammox bacteria activity is of particular importance at low temperatures, when drastic decrease in process activity is observed at temperatures below 15 °C. The short-term experimental results demonstrated stimulation of the anammox activity at 13 °C, up to 28% by 15 mg RGO/L, but concentrations above 40 mg RGO/L caused the process inhibition, up to 30% with 50 mg RGO/L. However, the effect of RGO probably depends on the nanomaterial dose per biomass unit and the optimal range of this value was evaluated as 20 to 45 mg RGO/g VSS (volatile suspended solids).