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The organic residues from agro-food sector can be transformed into valuable economic resources rather than representing an unmanageable waste, whose disposal in landfills contributes to increase both soil pollution and the greenhouse effect. With this in mind, the aim of the investigation is to design eco-friendly compatible innovative biological processes for producing lactic acid (LA) from fermentable sugars using as substrate tomato pomace. In the first part of the investigation, we show the physico-chemical characterization of tomato pomace produced in the 2017 season with or without thermal pre-treatment. pH, total and volatile solids content, sugars and cellulose are measured. The microorganism consortia suitable for lactic acid production are selected from buffalo dung, and compared with commercial strains of lactic acid producing bacteria. Both bacteria consortia are used as inoculum for the anaerobic fermentation of tomato pomace as sole substrate for producing fermentable sugars and convert them in LA. Sugars are measured by a spectrophotometric- coupled enzyme assay and LA by HPLC with electrical conductivity detector. The molecular analysis of the isolated bacteria is performed by using the denaturing gradient gel electrophoresis (DGGE). Anaerobic fermentation of tomato pomace is also performed using different initial pH values of the substrate. The final goal is to design biological processes aimed at achieving the highest LA recovery yields.

Industry has the severe problem to accumulate, treat and dispose food processing wastes and by-products. The main objective of many recent studies is to test innovative processes and technologies for recycling and upgrading these wastes for recovering high-value-added marketable materials in compliance with the European Sustainable Waste Management Guidelines and the principles of the "circular economy”. In particular, new, innovative and profitable management strategies for sludgy waste from tomato processing industries could be fostered in Campania. Alternative and valuable process chains are possible in which different players working together to “eco-friendly” recycle, reuse and promote tomato industry residual biomasses could obtain high value-added products with a sustainable approach. One of the possible added value product that can be obtained by tomato industrial processing waste is lactic acid, whose production could have a remarkable economic and ecological impact. In this study we provide an estimate of the available tomato industry processing waste and related potential for lactic acid production in Campania, carrying out a survey on the more suitable production technologies. Maximum radius distance of industries from a possible/hypothetical centralized transformation plant according to the biomass availability and transportation facilities is calculated. Feasibility studies of eco-friendly processes able to convert tomato processing waste in lactic acid are considered, evaluating the actual amount, reuse or disposal in waste dumps or soil of the tomato pomace. The benefits of the correct management of tomato processing waste is considered, evaluating the possible economic revenue resulting from the proposed system.

In this paper we study the anaerobic digestion of water buffalo manure collected during a period of three years with the goal of investigating the effect of the substrate C/N ratio on the bio-methane production. The investigated samples show a C/N ratio between 9 and 50, this interval being much wider than that typically considered optimal in the literature for the waste digestion processes. The experimental tests are performed in batch mode, at 37 °C and with a starting pH equal either to 6 or 7, uncontrolled during the digestion process. We observe that, regardless of the C/N ratio of tested samples, the Gompertz productivity, expressed in terms of bio-methane volume fraction, is always larger than 54 %. A slightly larger productivity is recorded for substrates digested starting from an initial pH set to 7. We may then conclude that the C/N ratio of water buffalo manure does not really affect the bio-methane yield.

Animal manure can be profitably used to produce energy in anaerobic fermenters increasing energy independence and reducing disposal costs and pollution. Animal manure is a low cost substrate rich in carbohydrates, especially suitable for biofuels production, such as hydrogen and methane. We preliminary studied the effect of mechanical manure pre-treatments on the fermentation process focusing on the biogas yield and composition. In particular, we investigated both the H2 and CH4 oriented fermentation. Our batch reactors consist in 280 ml serum glass bottles hermetically sealed with pierceable rubber cups. The products of fermentation were measured with a micro gas chromatograph, equipped with two capillary columns. To individuate the most suitable conditions for H2 production, a manure thermal pre-treatment, used to isolate the H2-producing bacteria, was investigated. Preliminary results show that the mechanical pre-treatments do not systematically alter the fermentation process. Concerning the thermal pre-treatment, we found that the CH4 production is inhibited when the manure is heated at the 90 °C for several hours. Moreover, we identified the most favorable conditions to optimize the production of H2: i) thermal pre-treatment on the substrate; ii) initial pH ~ 5.0; iii) process temperature of 55 °C. The favorable conditions to optimize the production of CH4 are: i) initial pH ~ 7.0;ii) process temperature of 37 °C.

Animal manure is a low cost substrate suitable for biofuels production, such as hydrogen and methane, via anaerobic fermentation (Kyazze et al., 2007). Previous studies attributed the higher biogas yield from certain types of manure to the presence of a native microflora (Yeole and Ranande, 1992) and/or a higher or better carbon-nitrogen (C/N) ratio (Fulford, 1988). Probably the main difference between the different types of dung is related to the specific food the animal eat, which changes the overall C content and C/N ratio. We measured the C/N ratio and the native microflora of dung collected during one year. We related it to the biogas yield during anaerobic fermentation both for lactating and non-lactating buffaloes manure. The results showed that the buffalo manure was in both cases plenty of carbohydrates with a C percentage content based on the dry sample weight of 36.2 ± 2.0 % and 31.4 ± 1.5 %, respectively. The C/N ratio was 18.6 ± 1.5 % and 20.6 ± 2.9 %, respectively, and it changed during the different seasons because of the fluctuating N content. Indeed we found an acceptable correlation (R = 0.75) between the average environmental temperature and the C/N ratio of lactating buffalo manure. Neither the C or N content nor the C/N ratio appeared to be strongly correlated to the biogas production. The manure was fermented in batch reactors at 37 °C and pH = 6.0 after different pretreatments of the collected manure. The analysis of the microbial community was carried out using denaturing gradient gel electrophoresis (DGGE) to generate fingerprints of 16S rRNA genes (Carillo et al., 2012). The sequences analysis revealed that the Eubacterial community during fermentation in batch reactors was much more taxon rich and diversified than the Archeal community. The study of Archeal community instead showed the presence of only three main methanogen strains very active in methane production and largely predominant.

In this work hydrogen and methane production from buffalo manure has been scrutinized, by means of the anaerobic dark fermentation process and different process conditions. Animal manure characteristics are largely variable during different periods of the year because of the unavoidable changes in animal food supply and digestion apparatus of buffalo. A very significant variability was observed for water buffaloes manure, collected from the same supplier. This implies also a large variability in biogas production by anaerobic fermentation of such substrates. To overcome this variability, we mixed fresh with digested manure. This procedure is consolidated as regard methane production. We also investigated a similar strategy to optimize and stabilize H2 yield. We were able to find optimal process conditions for hydrogen and methane production with this type of substrate. The experiments have been run in batch mode. The products of fermentation, H2, CO2 and CH4, have been measured with a micro-gas chromatograph. Moreover the potential production of H2 has been maximized by thermally pre-treating the substrate and using a process temperature of the fermenter equal to 55 °C and an initial pH value of 5.5, while very high levels of potential production of CH4 have been obtained at 37 °C and with an initial pH of 7.0. The effect of different strategies has also been analyzed to highlight the different microbial community present in the substrate using the denaturing gradient gel electrophoresis (DGGE). This investigation has been carried out with the aim at isolating and selecting of natural bacterial species to use as inoculum to improve and stabilize the fermentation process of buffalo manure. More results concerning the microbial communities present in the substrate and responsible for biogas production are presented in a companion paper. Here we only list the main types of bacteria identified in the manure.