Carbon harvesting from organic liquid wastes for heterotrophic denitrification: Feasibility evaluation and cost and emergy optimization

Organic liquid hazardous wastes (LHWs) consist of plentiful, valuable carbon sources, during the recovery of which, simultaneous disposal of high-NO3- and organic LHWs is possible for the control of organic and nitrogen pollution. In this study, we propose an anaerobic hydrolytic acidogenic and denitrification integrated (AHDI) process and carefully evaluate the technical, economical, and sustainable properties toward this simultaneous disposal strategy using long-term pilot experiments. With consistently increasing initial nitrate (NO3-) concentrations ([NO3-](0)) from 355 to 30,000 mg/L and salinity from 0.5% to 7.8%, high removal efficiencies of 99.5% and 65.7% were observed for NO3- and chemical oxygen demand (CODCr), respectively, and the optimum C/N ratios were determined to be above 1.0 using volatile fatty acids (VFAs) upon the anaerobic hydrolytic acidification of organic LHWs as electron donors. A NO3- loading rate as high as 33.2 kg NO3-.m(3)/d was achieved at [NO3-](0) of 30,400 mg/L, and the concentrations of NO3- and nitrite (NO2-) in effluents were observed to be as low as 33.1 and 0.11 mg/L, respectively. Moreover, cost and emergy analysis indicated that the net annual cost and environmental loading ratio (ELR) were 42.3% and 47.6%, respectively, of those involved in the traditional separate disposal strategy. The proposed simultaneous disposal strategy is cost-effective and sustainable and exhibits improved emergy saving with lower environmental stress and less nonrenewable inputs required than the traditional process.