Performance of a Full-Scale Biogas Plant Operation in Greece and Its Impact on the Circular Economy

Abstract

Biogas plants have been started to expand recently in Greece and their positive contribution to the economy is evident. A typical case study is presented which focuses on the long-term monitoring (lasting for one year) of a 500 kW mesophilic biogas plant consisting of an one-stage digester. The main feedstock used was cow manure, supplemented occasionally with chicken manure, corn silage, wheat/ray silage, glycerine, cheese whey, molasses and olive mill wastewater. The mixture of the feedstocks was adjusted based on their availability, cost and biochemical methane potential. The organic loading rate (OLR) varied at 3.42 ± 0.23 kg COD m−3 day−1 (or 2.74 ± 0.18 kg VS m−3 day−1) and resulted in a stable performance in terms of specific biogas production rate (1.27 ± 0.12 m3 m−3 day−1), biogas yield (0.46 ± 0.05 m3 kg−1 VS, 55 ± 1.3% in methane) and electricity production rate (12687 ± 1140 kWh day−1). There were no problems of foaming, nor was there a need for trace metal addition. The digestate was used by the neighboring farmers who observed an improvement in their crop yield. The profit estimates per feedstock indicate that chicken manure is superior to the other feedstocks, while molasses, silages and glycerin result in less profit due to the long distance of the biogas plant from their production source. Finally, the greenhouse gas emissions due to the digestate storage in the open air seem to be minor (0.81% of the methane consumed).

Application of Multi-Criteria Decision-Making Tools for Assessing Biogas Plants: A Case Study in Reykjavik, Iceland

“…Biogas yield was chosen because all the literature consulted agrees that it is a key parameter at any AD biogas plant [35][36][37][38].…”

Combined electrochemical treatment coupled to anaerobic digestion effluents

“…The anaerobic digester consisted of a continuously stirred tank reactor (CSTR) with 4200 m 3 working volume. The anaerobic digester had been in operation for more than a year in Northern Greece under mesophilic conditions (38-39 o C) treating solid (10 tn/d) and liquid wastes (129 tn/d) of dairy manure as described in Spyridonidis et al [9]. The applied hydraulic retention time was between 30 and 60 d.…”

Available Pathways for Operationalizing Circular Economy into the Olive Oil Supply Chain: Mapping Evidence from a Scoping Literature Review

“…A wide range of conversion technologies are available for energy valorization of the olive oil sector by-products, with different possible outputs. The existing literature explores the opportunities of producing: syngas, to obtain electrical and thermal energy, by feeding a heat and power biomass plant with olive pomace [55][56][57], olive stones [59,60,62], or olive tree pruning residues [54,61]; electric energy [68] through the combustion of pruning residues; methanol from olive pomace via gasification [69], or from OMW via anaerobic digestion [58,70]; biogas by means of anaerobic digestion of olive pomace [67,74] or OMWW [71]; biofuel-as a sustainable alternative of biofuels based on specialized grown crops [21]-obtained from pruning residues combustion [64], from solid part of olive pomace gasification [73], or from waste cooking oil through homogenously catalyzed esterification [19]; combustible products from olive pomace (torrefied biomass or charcoal obtained, respectively, through torrefaction or slow pyrolysis processes) as sustainable substitutes of fossil fuels, such as coal [46,65].…”