Impact of microwave radiation on nitrogen removal and quantity of nitrifiers in biofilm

Abstract

The aim of this study was to determine the impact of microwave radiation on the efficiency of nitrification and on the percentage of ammonia-oxidizing bacteria in biofilm and to study the possibility of the occurrence of nonthermal effects caused by the interaction of microwaves and biofilm. Eight trickling filters with a biofilm were used in the experiment: four were exposed to microwave radiation, and four were heated with warm air as a control group. Microwave radiation at a frequency of 2·45  GHz was applied at an intensity of 18  W (0·01  W  cm−3 of the reactor packing), which increased the biofilm temperature by 6°C compared with the ambient temperature. The hydraulic loading averaged 0·30  m3  m−2  h−1, and the organic loading equalled 1·93  g chemical oxygen demand (COD)  m−2  d−1. Microwave radiation had an effect on the concentration of nitrogen compounds in the biofilm, and microwave heating triggered alterations within the biofilm that increased the efficiency of both nitrification and denitrification and the percentage of ammonia-oxidizing bacteria.