Purpose 3Local open markets, trading fruits and vegetables, are widespread in Mediterranean 4 countries, such as Tunisia and Jordan, producing large amounts of organic waste. 5Applying an anaerobic digestion process on this substrate makes it crucial to evaluate 6 the waste mixture composition and seasonal variability properly. In this study, after 7 defining an average composition of the fruit and vegetable waste (FVW) mixture 8 produced in Sfax (Tunisia) and Amman (Jordan) in three seasonal intervals (autumn-9 winter, spring, and summer), the biochemical methane potential (BMP) of an 10 artificially created FVW mixture was individually determined by three European 11 institutions located in Spain, Italy, and Greece. The average BMP from all three 12 seasons and laboratories was 286±52 NmL CH 4 g COD added -1 , close to the theoretical 13 maximum yield of 350 NmL CH 4 g COD added -1 , indicating a high biodegradability of 14 the waste. Τhe biochemical methane yields of the spring mixtures were not 15 statistically different across the three labs. The most significant differences among the 16 BMP results were obtained for the autumn/winter and the summer mixtures used in 17 Spain, likely due to the variety or ripeness of fruits and vegetables collected in the 18 local markets. In the other two labs in Italy and Greece, no statistical difference was 19 observed for the BMPs of the three season mixtures within the same lab. Therefore, 20 not a critical difference in the biodegradability of such FVW is expected along the 21 different seasons, indicating that the operation of a full-scale digester over a whole 22 year would constantly benefit from the supplementation of a high biochemical 23 methane potential feedstock.

BACKGROUND The growth of poultry farming has increased the amount of chicken manure (CM) being produced. In this study, CM was digested in a two‐stage anaerobic digestion (AD) system consisting of three leach bed reactors (LBRs) and a continuous stirred tank reactor (CSTR) coupled with sedimentation tanks (anaerobic contact process). The accumulated biomass and supernatant from the sedimentation tank were returned to the CSTR and the LBRs, respectively, resulting in an almost closed (water) circuit process. In addition, zeolite was used as bulking agent and adsorbent for ammonia in the LBRs. RESULTS This study revealed that the methane yield remained on average at 0.17 NL g−1 of Volatile Solids (VS), corresponding to the 43% of the CM biochemical methane potential as determined in separate batch tests (0.40 NL g−1 VS). Electrical conductivity gradually increased from 22 to 26 mS cm−1; however, the ammonia nitrogen concentration was stable at 2.28 g L−1, which was attributed to zeolite used as LBRs' bulking agent. A preliminary design of a full‐scale LBR‐CSTR facility was conducted for a poultry farm growing one million broilers per year. Its CO2 footprint was evaluated based on literature indices. CONCLUSION The proposed facility has a capacity of 130 kW Combined Heat and Power (CHP) and a payback period of 8.6 years. In terms of GHG emissions, implementing the LBR‐CSTR system for biogas production could potentially reduce the CO2 footprint of the farm from 1.38 to 0.49 kg CO2 eq/head. © 2022 Society of Chemical Industry (SCI).

BACKGROUND: Biogas can be upgraded to biomethane, which can be used as vehicle fuel and natural gas substitute. Bioelectrochemical biogas upgrade is an innovative alternative to energy-consuming physicochemical processes and bio-upgrade methods which require H 2 supply. Bioelectrochemical biogas upgrade is conducted by methanogenic microorganisms that convert CO 2 into CH 4 , in the biocathode of a bioelectrochemical system (BES), using electric current as energy source. The aim of the present work was to study the efficiency of an H-type BES in the conversion of CO 2 into CH 4 , by applying different potentials at the electromethanogenic biocathode.RESULTS: The H-type BES was operated in a three-electrode configuration (working: graphite rod; counter: Pt/Ti; reference: Ag/AgCl) with a potentiostat, which set the biocathode's potential initially at −0.7 V versus a standard hydrogen electrode (SHE) and monitored the current demand. Based on cyclic voltammetry runs, a highly electroactive methanogenic biocathode was developed in a short time. The methane production rate (MPR) at a cathode potential of −0.7 V versus SHE was 31.1 mmol m −2 d −1 , with an electron capture efficiency of 77.6%. The efficiency of the BES was reduced by applying a potential of −0.5 V versus SHE at the biocathode, resulting in negligible CH 4 production. The BES achieved its maximum performance at a potential of −0.9 V versus SHE with a MPR of 53.8 mmol m −2 d −1 and an electron capture efficiency of 86%. The CO 2 consumption rate achieved was 0.8 mmol d −1 .CONCLUSIONS: The H-type BES achieved an effective biolectrochemically driven methane production, while the biocathode electroactive behavior was evaluated during the whole operation of the system.

Fruit and vegetable wastes produced massively in open markets are a suitable feedstock for biogas production and digestate of high fertilizing value. A first step of designing anaerobic digestion systems for treating these wastes efficiently is to study the impact of the seasonal variation on the biochemical methane potential. Moreover, during mechanical pretreatment applied to reduce the size of the waste mixtures, several fractions derive which affect the rate of the methane production as well as the ultimate methane yield. Fractionation of the chopped wastes through sieving resulted in fractions of different parts of wastes and size, affecting the initial rate and the ultimate methane yield. It was found that the smaller fraction yielded methane at an initial higher rate but at lower ultimate value than the larger fraction. These results were consistent in all waste mixtures chosen to represent the typical composition of the organic fraction of wastes generated in open market in autumn/winter, spring and summer. In all cases examined the BMP of these wastes varied between 360 and 527 ΝmL CH4 g VS-1 with an average value of 436±51 ΝmL CH4 g VS-1.