Techno-economic evaluation of biofertilizer production using wastewater biosolids: case study from municipal wastewater treatment plants in northwest region of Russia

The continuous and rapid growth of sewage sludge (biosolids) from wastewater treatment plants (WWTPs) poses both economic and environmental challenges. In many cities of Russia, the situation has exacerbated with time. In this study, three state-of-the-art biosolid management technologies, namely windrow composting (WC), tunnel composting (TC), and lime stabilization (LS), were evaluated for their economic feasibility to produce commercially biofertilizers from WWTP-derived biosolids. Based on an annual discharge of 22,000 m(3) of dewatered biosolids from the case WWTP, about 29,785, 22,453, and 35,056 m(3) biofertilizers could be produced through WC, TC, and LS, respectively. Analysis showed the selected WC, TC, and LS technological options to be feasible if the selling price of the produced biofertilizer would be maintained at 19 EUR/m(3) for WC and LS, and 77 EUR/m(3) for TC. The discounted payback period (DPP) of WC, LS, and TC would be 3.1, 18.1, and 25.3 years, respectively, with an IRR (internal rate of return) of 10%. The key characteristics of the treated WWTP-derived biosolids were found to be good enough to meet the existing environmental laws, standards, and regulations in Russia. From an investment perspective, this study is useful in developing WWTP-derived biosolids for biofertilizer production at enterprise level.