Hydrolysate from the enzymatic treatment of corn cob as a carbon source for heterotrophic denitrification process

Abstract

The application of hydrolysate obtained from the enzymatic treatment of agricultural waste as a denitrification carbon source is proposed. In this study, comparative experiments on six common agricultural wastes (corn cob, loofah, peanut shell, corn straw, rice straw, and wheat straw) revealed that corn cob released high COD and low relative content of N, and P pollutants and chromaticity, and was most suitable as a raw material for carbon source preparation. The conditions for the preparation of hydrolysate from corn cob were optimized by response surface methodology, and the optimal conditions were pH 5.44, temperature 49.56 °C, enzyme addition of 25 mg, and surfactant content of 0.1 %. The metal elements of the hydrolysate were analyzed and contained a large number of macronutrients (K, Ca, Na, and Mg) and trace elements (Fe, Mn, Co, Ni, Cu, Zn, and Se). The hydrolysate was applied to the denitrification reactor and the effluent TN removal rate reached more than 97 % and COD was below 61 mg/L when the carbon to nitrogen ratio was 5:1. Analysis of the microbial community revealed the presence of a large number of genera involved in the denitrification process and organic matter decomposition such as Thauera (19.08 %), Dechloromonas (7.59 %), and Paludibacter (2.11 %), thus indicating the feasibility of hydrolysate as a carbon source for denitrification. This research is expected to provide new insights into the development of new carbon sources in biological denitrification technologies.