Mathematical model of anaerobic propionate degradation by incorporating the r/K selection theory

Abstract

Although anaerobic digestion mathematical model (ADMM) has been widely applied for system optimization and mechanism understanding, the selection of key kinetic and stoichiometric parameter values for ADMM is still a challenge. An ADMM incorporating the r/K selection theory was proposed to examine the enrichment of r- and K-strategists in completely mixed reactors (CMRs) and sequencing batch reactors (SBRs). With the influent propionate concentration (PC) of 0.75 g COD/L, K-strategists predominated at the sludge retention time (SRT) higher than 13 d for propionate oxidizing bacteria (POB) and 9 d for acetoclastic methanogens (AM) in CMRs, while r-strategists dominated at the SRT less than 20 d for POB and 5 d for AM in SBRs. Under the SRT of 20 d, in CMRs, both K-strategists of POB and AM increased with increasing PCs, while r-strategists of POB only appeared when the PC exceeded 6 g COD/L and r-strategists of AM could not be enriched under all PC conditions; in SBRs, K-strategists of POB and AM showed the superiority when the PC was lower than 0.5 and 1.5 g COD/L, respectively. Only K-strategists of hydrogenotrophic methanogens (HM) were enriched in all simulated scenarios. Based on sensitivity analysis, SRT and the first order decay rate had a high influence on the enrichment of HM, AM, and POB. Overall, the selection of r-/K-strategists of POB and AM could be achieved by regulating SRT, operational mode, and PC.