Seaweeds represent a promising and sustainable feedstock for biofuel production which raises increasing research interests. Their high availability, easy fermentable composition, and good degradation potential make them a suitable candidate for alternating fossil fuels as an advantageous energy resource. This comprehensive review aims to summarize and discuss data from the literature on the biochemical composition of seaweeds and its potential for biomethane and biohydrogen production, as well as to investigate the effect of the common pretreatment methods. Satisfactory yields comparable to terrestrial biomass could be obtained through anaerobic digestion; concerning dark fermentation, the challenge remains to better define the operating conditions allowing a stable production of biohydrogen. Finally, we propose a potential energy production scheme with the seaweed found by the Caribbean Islands of Guadeloupe and Martinique, as well as current techno-economic challenges and future prospects. An annual energy potential of 66 GWh could be attained via a two-stage biohythane production process, this tends to be promising in terms of energetic valorization and coastal management.

The impact of hygienization as mild thermal pretreatment on the methane production of various organic wastes was investigated, including digestate issued from hydrolysis tank, thickened sludge from a municipal wastewater treatment plant (MWWTP sludge) and from a mixed domestic-industrial wastewater treatment plant (D-I WWTP sludge), sludge from a meat-processing plant (MP sludge), sieving rejection from a pork slaughterhouse, pork liver, cattle slurry, cattle scraping slurry and date seeds. They were thermally pretreated at 70 °C for one hour and subsequently put into AD digesters incubated at 37 °C for individual methane potential test. The modified Gompertz model was employed to evaluate the kinetic parameters of methane production curves (R² = 0.944–0.999). The results were compared with the untreated samples. Significant enhancement of methane potentials induced by thermal treatment (p < 0.05) was observed when it comes to the pork liver (+8.6%), the slaughterhouse sieving rejection (+11.1%), the thickened MWWTP sludge (+12.5%) and the digestate issued from hydrolysis tank (+18.0%). The maximum methane production rates of the 4 substrates mentioned above were increased by thermal pretreatment as well (from 13.5% to 64%, p < 0.05). The lag time of the methane production was shortened for the digestate from hydrolysis tank and the MWWTP sludge (by 48.6% and 62.2% respectively, p < 0.05). No significant enhancement was obtained for the cattle slurry, the cattle scraping slurry and the D-I WWTP sludge. Additionally, the maximum methane production rate and the methane potential were reduced by thermal pretreatment for the MP sludge and the date seeds respectively (p < 0.05). In this paper, possible mechanisms were discussed to explain the different methane production behaviors of substrates after the mild thermal pretreatment.

Poultry waste are rich in organic matter, allowing its use as substrates for biogas production by anaerobic digestion (AD). The major difficulty in the anaerobic digestion of this protein-rich waste is the ammonia inhibition. Different results of biochemical methane potential (BMP) were obtained after the mesophilic anaerobic digestion of different avian waste in batch mode. It was shown that using two different inoculum (Liger and Saint-Brieuc) sources and different substrate to inoculum (S/I) ratios does not have a significant effect on the biochemical methane potential of organic laying hen droppings (OLHD); an average of 0.272 Nm³ CH₄ · kg^-1 VS was obtained with both inocula. Otherwise, it affects the hydrolysis constant K_H, it decreases when substrate to inoculum ratio increases. Furthermore, Liger is the most suitable inoculum for our substrate because it shows a stability during the process even with different organic load. Comparing the biochemical methane potential of multiple avian waste such as organic laying hen droppings and different slaughterhouse waste highlights the importance of slaughterhouse waste in the anaerobic digestion process because of the high methane yield observed specially with the viscera (0.779 Nm³ CH₄ · kg^-1 VS, SD = 0.027 Nm³ CH₄ · kg^-1 VS). Moreover, methane production was affected by increasing the ammonia concentrations; when [N-NH₃] > 9.8 g N-NH₃ · L^-1 the biochemical methane potential decreases and the lag phase increases (λ > 30 days); a total inhibition of the process was observed when ammonia concentration is above 21.8 g · L^-1. GRAPHICAL ABSTRACT

Poultry waste is rich in organic matter, which allows its treatment by the process of anaerobic digestion (AD) to reinforce economic and environmental green strategies. The aim of this study is to assess the technical feasibility of poultry waste AD in semi-continuous mode and to intensify methane production by co-digestion with physico-chemical sludge, i.e., the product of the primary treatment of wastewater after the slaughtering process. First, the AD of poultry droppings is conducted in a continuous stirred anaerobic digester (CSAD) at 37 °C. A volume of 0.791 and 0.623 Nm³·Nm⁻³ reactor·days⁻¹ of biogas and methane, respectively, were produced during the entire process stabilization period. Biochemical characterization of the substrate and the final digestate show high reduction rates of the biochemical fractions, which corroborates with methane yield. In addition, the co-digestion of poultry droppings with two different ratios of physico-chemical sludge (20% and 40% added sludge considering the amount of volatile solids) shows an increase in methane production versus droppings alone, with a higher increase of 54% with a sludge ratio of 40%. Altogether, these promising results were obtained in stable processes, highlighting the pertinence of our study.

Animal by-products (ABP) can be valorized via anaerobic digestion (AD) for biogas energy generation. The digestate issued from AD process is usually used to fertilize farming land for agricultural activities, which may cause potential sanitary risk to the environment. The European Union (EU) requires that certain ABP be thermally pasteurized in order to minimize this sanitary risk. This process is called hygienization, which can be replaced by alternative nonthermal technologies like pulsed electric field (PEF). In the present study, Enterococcus faecalis ATCC 19433 and Escherichia coli ATCC 25922 were used as indicator bacteria. Their resistance to thermal pasteurization and PEF treatment were characterized. Results show that Ent. faecalis and E. coli are reduced by 5 log10 in less than 1 min during thermal pasteurization at 70 °C. The critical electric field strength was estimated at 18 kV∙cm⁻¹ for Ent. faecalis and 1 kV∙cm⁻¹ for E. coli. “G+” bacteria Ent. faecalis are generally more resistant than “G−” bacteria E. coli. AD process also plays an important role in pathogens inactivation, whose performance depends on the microorganisms considered, digestion temperature, residence time, and type of feedstock. Thermophilic digestion is usually more efficient in pathogens removal than mesophilic digestion.