Effects of acid modification on the structure and adsorption NH4+-N properties of biochar

The adsorption by biochar can effectively alleviate the problem of ammonia inhibition in biogas engineering. Based on batch adsorption experiments, the effect of acid modifier on physicochemical and adsorption NH 4 + -N properties of biochar was explored, and anaerobic digestion (AD) with addition of modified biochar (MB) was designed and carried out. The results showed that after modification, the adsorption capacity of biochar was significantly improved, and the maximum adsorbance of MB was 1.57 times higher than that of original biochar. Acid modifier had demineralization and increased the number of acidic oxygen-containing functional groups. Chemical adsorption was the dominant adsorption mechanism, mainly including surface electrostatic adsorption and the interaction between ammonium ions and surface functional groups of biochar. With the addition of MB, gas production rate of the AD of chicken manure was increased and the effective gas production period was shortened to 18 days. This research has guidance significance for alleviation ammonia inhibition during the AD by adding MB. • Acid modification improved NH 4 + adsorption capacity of biochar. • Modified biochar (MB) shorten the effective gas production cycle to 18days. • MB can effectively relieve ammonia inhibition in anaerobic digestion. • The adsorption mechanism of acid MB was electrostatic attraction and complexation.