Kinetics of carbon and nitrogen assimilation by heterotrophic microorganisms during wastewater treatment

The present study highlights microbial assimilation of carbon (glucose) and nitrogen (NH₃–N) from wastewater using heterotrophic bioconversion process. Experiments were conducted to study the role of heterotrophic microbes towards removal of carbon and nitrogen at varying initial concentrations of carbon (COD, 533 to 1600 mg/l) and nitrogen (NH₃–N, 73 to 249 mg/l) keeping the initial biomass of microorganisms constant. Removal of COD and ammonia from wastewater represented a first-order rate reaction, upon analysis of kinetics, indicating that the rate of reaction is dependent on the initial concentration of nutrients available. Rate equations were developed using the Monod model, and the maximum specific consumption rate (k₄) and half saturation constant (K_s) values for NH₃–N and COD were found to be 2.59 mg/l/h and 64.13 mg/l/h and 38.46 mg/l and 2162.69 mg/l, respectively. Assimilation of NH₃–N followed the Freundlich isotherm model. The mass transfer coefficient for COD and NH₃–N were found to be 0.13 h⁻¹ and 0.81 h⁻¹ respectively. The NH₃–N is converted to N₂O during nitrification, and observed values of N₂O coincided with the empirically predicted values indicating the activity of heterotrophic nitrifiers. The regeneration/doubling time of heterotrophic microbial biomass varied from 26 to 121 h. Statistical techniques, viz. analysis of variance, multi-linear regression analysis and principal component analysis, validated the results.