• Energy Research

The co-production of biohydrogen and methane from the organic fraction of municipal solid waste was investigated using a two-stage AD system, composed of a pilot scale dark fermenter (DF) and a continuous methanogenic biofilm reactor. From the DF process, a biohydrogen yield of 41.7 (+/- 2.3) ml H-2/gVS(added) was achieved. The liquid DF effluent (DFE) was rich in short chain volatile fatty acids, i.e., mainly acetic and butyric acid. The DFE was valorized by producing methane in the methanogenic biofilm reactor. Two methanogenic biofilm reactors were used to assess the biotic and abiotic role of the DFE on the performance of the reactors. Regardless of the different DFE feeding (i.e., biotic and abiotic), similar and stable operational performance of the two methanogenic biofilm reactors were observed with a respective methane yield and COD removal efficiency of 280-300 ml CH4/gCOD(removed) and 80-90%. Both methanogenic biofilm reactors showed significant resistance toward organic shock loads and recovered fast after reactor disturbance. The total estimated energy recovered in the form of hydrogen and methane gas was, respectively, 28 and 72%, of the initial COD.

Among agricultural residues, lignocellulosic materials (LMs) are highly attractive substrates for anaerobic digestion (AD), given their high availability, low cost and no direct competition with food and feed production. Hemp (Cannabis sativa L.) is a multipurpose crop, and its cultivation has boosted again in the last years. Nevertheless, due to contrasting legislation, in some European Countries the harvesting and manufacturing of plant components (e.g. leaves and inflorescences) has stopped, resulting in a massive amount of lignocellulosic biomass to be diversely disposed. This research explores the valorization of hemp biomass (whole stalk, bast fiber, decorticated hurds, and a mixture of leaves and inflorescences) by AD, as a first major step for the establishment of a wider, future biorefinery platform. Both physical (grinding) and chemical (acid and alkali) pretreatments have been investigated to break down the lignocellulosic matrix of different hemp biomass components. Their biomethane yield has been then evaluated through batch biochemical methane potential (BMP) tests performed in 100 mL serum bottles under controlled mesophilic (37°C) conditions for 45 days. The highest cumulative biomethane production (422 mL CH4/g VS) was obtained with the raw bast fiber, while the BMP of the raw whole stalk and decorticated hurds reached 271 and 240 mL CH4/g VS, respectively. The alkali pretreatment with NaOH increased the BMP of the hurds by 15% obtaining a final biomethane yield of 277 mL CH4/g VS. The mixture of leaves and inflorescences resulted in the lowest BMP values, with the NaOH-pretreated material reaching approximately 150 mL CH4/g VS.

This paper reviews pretreatment techniques to enhance the anaerobic digestion of organic solid waste, including mechanical, thermal, chemical and biological methods. The effects of various pretreatment methods are discussed independently and in combination. Pretreatment methods are compared in terms of their efficiency, energy balance, environmental sustainability as well as capital, operational and maintenance costs. Based on the comparison, thermal pretreatment at low (<110 C) temperatures and twostage anaerobic digestion methods result in a more cost-effective process performance as compared to other pretreatment methods.

This study investigated the effect of the salinity level, buffering agent and carbon source on the hydrogen (H2) and lactic acid synthesis under capnophilic (CO2-assisted) lactic fermentation (CLF) by Thermotoga neapolitana cf capnolactica (DSM 33003). Several series of batch fermentation experiments were performed either in 0.12 L serum bottles for selection of the best performing conditions or in a 3 L fermenter for the best possible combination of conditions. The serum bottle study revealed that change in the salinity level of the culture medium from 0 to 35 g L−1 NaCl increased lactic acid synthesis by 7.5 times without affecting the H2 yield. Use of different buffers (MOPS, TRIS or HEPES) did not affect the average H2 yield of 3.0 ± 0.24 mol H2 mol−1 of glucose and lactic acid synthesis of 13.7 ± 1.03mM when the cultures were sparged by CO2. Among the carbon sources investigated, glucose was found to be the best performing carbon source for the CLF fermentation with 35 g L−1 of NaCl and 0.01M of phosphate buffer. Hence, an up-scale experiment using a 3 L fermenter and the combination of the best performing conditions showed a 2.2 times more lactic acid synthesis compared to the 0.12 L serum bottle experiments. The study reveals the robustness and flexibility of the CLF-based technology using T. neapolitana cf capnolactica fermentation under various operating environmental conditions.

This study investigated the feasibility of coupling simultaneous partial nitrification and denitrification (SPND) to biological phosphorus removal in continuous-flow intermittently-aerated moving bed biofilm reactors (MBBRs) fed with different carbon sources, i.e. ethanol and acetate. Bacterial cultivation at pH 8.2 (±0.2), 26-28 °C and SRT of 4 day and microaerobic/aerobic MBBR operation allowed to achieve average dissolved organic carbon (DOC), total inorganic nitrogen (TIN) and P-PO43- removal efficiencies (REs) of 100%, 81-88% and 83-86% at HRT of 1 day, dissolved oxygen (DO) range of 0.2-3 mg L-1 and feed C/N and C/P ratios of 3.6 and 11, respectively. Acetate supplementation favored a diversified microbial community, while overgrowth of heterotrophs was observed when increasing feed C/N ratio in ethanol-fed MBBR. Illumina sequencing displayed the presence of putative phosphorus accumulating organisms (PAOs) such as Hydrogenophaga and Pseudomonas in MBBR biofilm and suspended biomass, whereas no typical NOB was identified during the study.