Mass balances and distributions of C, N, and P in the anaerobic digestion of different substrates and relationships between products and substrates

Abstract

Knowledge of the distributions and mass balances of C, N, and P during anaerobic digestion (AD) processes serves several purposes; for instance, these values can be used to obtain reliable quantitative information on the fate of C, N, and P after AD, to understand carbon and nutrient balances, and to evaluate the contribution of AD processes to elemental cycles. In this paper, C, N, and P contents in the gas, liquid and solid phases were investigated for seven different substrates: corn straw, rice straw, wheat straw, swine manure from pigs fed feedstuff or foodstuff, cattle manure, and chicken manure. The conversion efficiency of C in a substrate into methane was found to be highest in swine manure from pigs fed foodstuff (15.8%), and greater liquid and solid stream nutrient levels were found in the swine manures and chicken manure than in the cattle manure and straws. The mass balances of C, N and P for each different substrate were distinct, but all balances were close to 100% in this study. Further study revealed that CH4 yields and substrate lignin fitted a linear negative relationship well, and the COD/TOC, NH4+-N and TP concentrations in the supernatant had positive linear relationships with the proteins, TAN/proteins and potassium of substrates, respectively.