Bioenergy Production through Mono and Co-Digestion of Tomato Residues

Abstract

The agro-industry of tomato generates three types of residues: ripe rotten tomato (unfit for consumption) (RT), green (unripe) tomato (GT), and tomato branches including leaves and stems (TB). These materials are commonly wasted or used as feed for livestock. Energy production through anaerobic digestion is an alternative way to manage and simultaneously valorise these materials. Initially, the operating conditions of mono anaerobic digestion were investigated using RT. Thus, a design of experiments based on a two-level fractional factorial design with resolution V was performed to determine the factors that affect biochemical methane potential (BMP). The substrate to inoculum ratio (SIR), total volatile solids concentration (VSt), working volume (WV), presence of nutrients (Nu), and the pre-incubation of the inoculum (Inc) were investigated. The results showed that SIR is the most important factor. The maximum BMP for RT was 297 NmLCH4/gVS with SIR = 0.5; tVS = 20 g/L; WV = 20%; no pre-incubation and the presence of nutrients. Using these optimum operating conditions, co-digestion was investigated through a mixture design approach. The substrates RT and GT presented similar BMP values, whereas TB led to a significantly lower BMP. Indeed, when high concentrations of TB were used, a significant decrease in methane production was observed. Nonetheless, the highest BMP was achieved with a mixture of 63% RT + 20% GT + 17% TB, with a production of 324 NmLCH4/gVS, corresponding to a synergetic co-digestion performance index of about 1.20. In general, although the substrate RT generates the highest BMP, the mixture with GT did not impair the methane yield. Overall, the co-digestion of tomato residues must be conducted with SIR close to 0.5 and the content of tomato branches in the reaction mixture should be kept low (up to 20%).

Tomato Residue Management from a Biorefinery Perspective and towards a Circular Economy

“… a References [ 5 , 12 , 13 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]; b [ 5 , 12 , 13 ]; c [ 26 , 33 , 34 , 35 , 36 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]; d [ 51 , 52 , 53 , 54 , 55 , 56 ]; e [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ]. …”

“…From these multiple combinations tested, a methane yield of about 300 mL/g VS can be achieved [ 28 , 131 , 146 ]. Almeida et al [ 5 ] performed a DoE to determine the best substrate combination for digesting rotten tomatoes, green tomatoes, and tomato plants. Only combinations with a high amount of tomato plants impaired the BMP results.…”

“…Only combinations with a high amount of tomato plants impaired the BMP results. Nonetheless, a maximum of 324 NmL CH4 /g VS was achieved with a mixture of 63% of rotten tomato, 20% of green tomato, and 17% of tomato plant [ 5 ]. Thus, a tomato industry can treat and valorize simultaneously the multiple residues generated.…”

“…The recovery of value-added compounds (proteins, pectin, antioxidants, carotenoids, phenolic compounds, etc. ), energy, and nutrients from multiple agro-residues have been widely studied [ 3 , 4 , 5 , 6 ]. The use of processes such as extraction, fermentation, anaerobic digestion, pyrolysis, gasification, and composting are the main processes assessed to valorize agro-industrial residues [ 1 , 7 , 8 , 9 , 10 , 11 ].…”

Energy valorisation of the residual biomass from greenhouses in the framework of a circular economy

“…It is essential to select residues of high methane potential, which can be assessed through the Biochemical Methane Potential (BMP) test. In the literature, the BMP of the whole tomato plant at the end of the cultivating season was reported equal to 140 ± 40 mL g -1 VS [4], while the BMP of fresh leaves and stems taken from tomato and cucumber plants grown in a greenhouse were equal to 301 ± 5 mL g -1 VS and 280 ± 5 mL g -1 VS, respectively. [5].…”