Anaerobic digestion of organic fraction combinations from food waste, for an optimal dynamic release of biogas, using H2 as an indicator.

The objective of this study is to assess the effects of mixing the three elemental organic waste fractions (fruit and vegetable, meat, and fish) during anaerobic digestion. Batch experiments were carried out with fraction mixtures of different proportions. The results were compared, concerning the single digestion of each fraction, the gas generation, and the process performance, using H2 as an indicator. It was determined that the optimal mixture was the one with the fractions in equal proportion. This mixture achieved a balanced composition, a faster process by 58 %, and a 12 % increase in methane production. It was also determined that, as a rule, mixtures increase the hydrolysis speed and that the meat fraction mixtures manage to make this substrate suitable for anaerobic treatment by increasing the rate of hydrolysis by 148 % and buffering the acidification inhibition that suffers in its single digestion.

Enhancing Energy Recovery in Form of Biogas, from Vegetable and Fruit Wholesale Markets By-Products and Wastes, with Pretreatments.

Residues and by-products from vegetables and fruit wholesale markets are suitable for recovery in the form of energy through anaerobic digestion, allowing waste recovery and introducing them into the circular economy. This suitability is due to their composition, structural characteristics, and to the biogas generation process, which is stable and without inhibition. However, it has been observed that the proportion of methane and the level of degradation of the substrate is low. It is decided to study whether the effect of pretreatments on the substrate is beneficial. Freezing, ultrafreezing and lyophilization pretreatments are studied. A characterization of the substrates has been performed, the route of action of pretreatment determined, and the digestion process studied to calculate the generation of biogas, methane, hydrogen and the proportions among these. Also, a complete analysis of the process has been performed by processing the data with mathematical and statistical methods to obtain disintegration constants and levels of degradation. It has been observed that the three pretreatments have positive effects, when increasing the solubility of the substrate, increasing porosity, and improving the accessibility of microorganisms to the substrate. Generation of gases are greatly increased, reaching a methane enrichment of 59.751%. Freezing seems to be the best pretreatment, as it increases the biodegradation level, the speed of the process and the disintegration constant by 306%.

Anaerobic digestion in wastewater reactors of separated organic fractions from wholesale markets waste. Compositional and batch characterization. Energy and environmental feasibility.

The food industry is one of the major industrial sectors in Europe and Spain, and therefore one of the major waste emitters, especially organic ones that can be classified into three different fractions (fruit and vegetables, meat and fish). One way to treat this waste environmentally responsible, energy-sustainable and economically cost-effective is anaerobic digestion. The generated biogas can be used as fuel and renewable energy source (providing a solution to the energy problem from an environmental point of view). As there must be a sewage treatment plant with anaerobic digesters in the wholesale markets, and if waste is treated on it, these facilities can be converted into power generators. It has been studied that, when treated along with sludge from a UASB reactor, the residue of fruit and vegetables produces about 900 ml per 100 g of residue with a stable and robust process; the meat residue generates 1300 ml of biogas per 100 g with a process that is slightly affected by the accumulation of acidic elements, internally reversed by the buffer effect of ammonia released; and the fish residue generates 700 ml of biogas, but with very low novels of methane since the process is inhibited early by excessive accumulation of ammonia. The proposed solution is positive, and the methods used to determine it are novel and robust, such as the use of hydrogen as an indicator of process stability. A deep characterization of the development of the process is provided, and feasibility for its application at the industrial level is studied. It is thus proven that wholesale markets can be converted into power generating plants up to 600 kW, assuming a reduction of up to 70 tons of CO2 equivalent (50%) if the generated biogas is used, replacing a conventional source such as natural gas.