Application of biochar in a CIC reactor to relieve ammonia nitrogen stress and promote microbial community during food waste treatment

Ammonia nitrogen inhibition is a well-known issue in the anaerobic digestion of food waste. This study aims to investigate the influence of biochar on the performance and the microbial community structure of a controlling internal circulation (CIC) reactor for food waste treatment in presence of 1500 mg/L of ammonia nitrogen. When ammonia nitrogen concentration increased to 1500 mg/L in the influent, chemical oxygen demand (COD) removal efficiency was reduced to 76%, the fluorescence peaks of aromatic proteins disappeared, and the intensity of coenzyme F-420 was reduced in the three-dimensional excitation emission matrix (3D-EEM) spectra of soluble microbial products (SMP) and tightly-bound extracellular polymeric substances (TB-EPS). The band intensity at 1635 cm(-1), attributed to the C=O stretching vibrations, reduced, and the broad band values of 3400 cm(-1) implied a sharp peak of the amino group in the fourier transform infrared (FTIR) spectra of TB-EPS. In the CIC reactor, COD removal efficiency reached to about 90% with biochar. High-throughput sequencing revealed that the abundance of Clostridiales, Lactobacillales and Methanoculleus increased, while the abundance of Syntrophomonas decreased at high ammonia nitrogen concentrations. In presence of biochar, the abundance of Methanoregulaceae, Bacteroidales, Anaerolineales, and Syntrophobacterales increased. It was concluded that biochar addition could alleviate the inhibitory effect of high ammonia nitrogen concentration. (C) 2018 Elsevier Ltd. All rights reserved.