Techno-economic anaerobic co-digestion feasibility study for two-phase olive oil mill pomace and pig slurry

Highlights

Influences over methane yields and process stability are analyzed for different TPOP/PS ratio feedstocks.

TPOP/PS 80:20 w/w improved considerably the methane yield and inhibition of TPOP mono-AD.

The NVP and IRR of AcoD plant were 782,493 € and 13.7%, respectively.

Electricity sale price was the largest determinant over the profitability of AcoD plant.

Under the current existing uncertainties, the TPOP mono-AD might be unprofitable.

Abstract

Anaerobic mono- (AmoD) and co-digestion (AcoD) of two-phase olive oil mill pomace (TPOP) and pig slurry (PS) at different ratios were studied in a semi-continuous stirred tank reactor (sCSTR) at mesophilic temperature (37 °C). The methane yields for AcoD experiments ranged from 150.9 to 274.3 L CH4 kg VS−1 d−1. The maximum chemical oxygen demand (COD) removal rate (59.60%) was achieved for TPOP/PS 80:20 w/w substrate composition at OLR 3.68 g VS Lreactor−1 d−1 and 24 days HRT. Despite the energy production from food waste is not a new process, the industrial implementation and application continue to be a challenge. Hence, the present paper also reports on the economic feasibility study of a full scale anaerobic co-digestion plant to treat 7000 t year−1 and 1750 t year−1 of TPOP and PS, respectively. The results of this study are compared against a conventional PS mono-digestion plant. Net present values (NPV) and payback time periods (PBT) were reported to be 782,493 € and 135,701 € and 6.7 and 9.2 years for AcoD and AmoD plants, respectively. Finally, the sensibility analysis concluded that AcoD configuration is less dependent on energy and compost sale prices variations.

Keywords

  • Biogas;
  • Energy;
  • Methane;
  • Total phenolic compounds inhibition;
  • Mesophilic temperature

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