No abstract

Adequate waste management is essential not only to ensure healthy living conditions but also to mitigate climate change. Accordingly, the research on developing strategies to boost the circularity of waste management systems is ongoing. In this context, two waste streams are concurrently managed to recover energy and materials in the present study. Specifically, real leachate collected from a full-scale mature landfill site was preliminarily treated through active filtration to remove inhibitory substances partially and then tested, at the laboratory scale, as a nutrient solution for semi-continuous anaerobic digestion of a carbonaceous substrate represented by market waste. The results demonstrate that, at an organic loading rate of 1.0 gVS∙L-1∙d-1, the process was impossible without using the nutrient solution, while the nitrogen present in the pretreated leachate could balance the carbon content of the market waste and provide the system with the necessary buffering capacity, ensuring process stability. The average methane yield (approximately 0.29 NL∙gVS-1) was satisfactory and consistent with the literature. Despite the increases in both the organic loading rate (up to 1.5 gVS∙L-1∙d-1) and volume of added pretreated leachate (up to 100% of the dilution medium), the process remained stable with a slightly lower methane yield of 0.21 NL∙gVS-1, thanks to nitrogen supplementation. The potential use of produced methane as a renewable energy source and residual digestate as fertilizer would close the loop of managing these waste streams.

Orange peel waste (OPW) has a remarkable biorefinery potential. In this paper, a biorefinery strategy is proposed at a laboratory scale in order to overcome the issue of the OPW seasonality. OPW was preliminary subjected to a long-term ensiling (up to 12 weeks) with the twofold purpose of preserving the OPW potential for methane production through anaerobic digestion (AD) and stimulating the production of value-added compounds by means of biological (leachate of a previous ensiling process) and chemical (MnCl2) supplements and/or their combination. On the liquid fraction of the ensiled OPW, lactic acid (LA), acetic acid (AA), and ethanol concentrations were detected. Instead, solid fractions were used as substrates for AD both in batch and semi-continuous modes. Specifically, the combined stimulation led to LA and AA yields of 54.5 and 16.6 g kgTS –1, respectively, after 8 weeks, whereas the largest yield of ethanol (i.e., 70.4 g kgTS –1) was achieved after 8 weeks of ensiling without any stimulation. Chemical and combined stimulation allowed us to preserve in the solid fraction, separated by centrifugation after long-term (8–12 weeks) ensiling, about 50% of the methane potential of the fresh OPW. Moreover, semi-continuous AD resulted in semi-stable processes for all the solid fractions (methane yields ranging from 0.23 to 0.28 NL gVSloaded –1) even though nutrients supplementation was necessary.

Anaerobic digestion (AD) is a suitable management option for the energy valorization of many wastes, including the organic fraction of municipal solid waste (OFMSW). However, in some cases, long storage after the separate collection of this waste is required for management reasons, especially when the amount of waste to be treated temporarily exceeds the capacity of available AD plants. This study evaluates the biochemical methane potential (BMP) of the OFMSW after preliminary storage of 2, 6, and 10 days, in order to assess whether they are still suitable for AD or not. Moreover, the accuracy of three kinetic models (first order, Gompertz, and logistic models) in estimating the methane yield of stored OFMSW is tested. The resulting methane yield was between about 500 and 650 NmL·gVS−1 and slightly increased with the increase of the storage time after collection. Overall, this study has demonstrated that storage of OFMSW, when the collected amount of solid waste exceeds the treatment capacity of AD plants, a storage time up to 10 days does not impact the methane yield of the process.

Several anchovies species are captured all over the world; they are consumed fresh but also preserved by the industry, either by brine-fermentation or canning in oil. The industrial process generates large amounts of residue (about 50% of the original fish biomass) that is generally used to produce fish flour. In this paper, the advancement of a recently proposed process for the full valorisation of anchovies aimed at the extraction of fish oil (to be used as an omega-3 source) and at the production of biomethane through anaerobic digestion is presented. Particularly, in the experiments presented, a co-digestion of anchovy sludge—used as a nitrogen supplement—and market waste (5% and 95% on a Total Solids basis) was performed. Since the proposed extraction process uses, as a green-solvent, d-limonene, the well-known problems of toxicity for the anaerobic biomass must be overcome during the digestion process. As discussed below, the granular activated carbon (GAC) is used to reclaim and improve anaerobic digestion processes in a reactor displaying clear signs of inhibition. In fact, GAC demonstrates multiple benefits for anaerobic digestion, such as adsorption of toxic substances, biomass selection, and triggering of direct interspecies electron transfer (DIET).