Exploring biorefinery alternatives for biowaste valorization: a techno-economic assessment of enzymatic hydrolysis coupled with anaerobic digestion or solid-state fermentation for high-value bioproducts

Abstract

Enzymatic hydrolysis of organic waste is gaining relevance as a complementary technology to conventional biological treatments. Moreover, biorefineries are emerging as a sustainable scenario to integrate waste valorization and high-value bioproducts production. However, their application on municipal solid waste is still limited. This study systematically evaluates the techno-economic feasibility of the conversion of the organic fraction of municipal solid waste (OFMSW) into high-value bioproducts through enzymatic hydrolysis. Two key variables are examined: (a) the source of the enzymes: commercial or on-site produced using OFMSW, and (b) the treatment of the solid hydrolyzate fraction: solid-state fermentation (SSF) for the production of biopesticides or anaerobic digestion for the production of energy. As a result, four different biorefinery scenarios are generated and compared in terms of profitability. Results showed that the most profitable scenario was to produce enzymes on-site and valorize the solid fraction via SSF, with an internal rate of return of 13%. This scenario led to higher profit margins (74%) and a reduced payback time (6 years), in contrast with commercial enzymes that led to an unprofitable biorefinery. Also, the simultaneous production of higher-value bioproducts and energy reduced the economic dependence of OFMSW treatment on policy instruments while remaining energetically self-sufficient. The profitability of the biorefinery scenarios evaluated was heavily dependent on the enzyme price and the efficiency of the anaerobic digestion process, highlighting the importance of cost-efficient enzyme production alternatives and high-quality OFMSW. This paper contributes to understanding the potential role of enzymes in future OFMSW biorefineries and offers economical insights on different configurations.

Keywords: Techno-economical assessment; anaerobic digestion; biopesticide; biorefinery; enzymatic hydrolysis; organic fraction of municipal solid waste; sensitivity analysis; solid-state fermentation; valorization.

Figure 1.

Process flowchart of the different biorefinery scenarios for the application of enzymatic hydrolysis in OFMSW treatment. (a) Scenario I, commercial enzymes and solid hydrolysate valorization through SSF. (b) Scenario II, commercial enzymes and solid hydrolysate valorization through anaerobic digestion. (c) Scenario III, in situ produced enzymes and solid hydrolysate valorization through SSF. (d) Scenario IV, in situ produced enzymes and solid hydrolyzate valorization through anaerobic digestion.

Figure 2.

Total energy consumption and production per ton of processed OFMSW in the different biorefinery processes for each scenario.

Figure 3.

Investment cost, operating cost, revenues and cumulative net present value (NPV) for the four OFMSW biorefinery scenarios. FOC, fixed operating cost. VOC, variable operating cost.

Figure 4.

Static tornado diagram for each scenario showing the sensitivity of net present value (NPV) to the variation (±25%) in each variable while other variables are held constant. The nominal value is displayed as a vertical line.

Figure 5.

(a) Cumulative cash flow diagram at different discount rates (0%, 6% and 12.8%) for scenario III. (b) Breakeven chart of scenario III.