The constant increase in the amount of food waste accumulating in landfills and discharged into the water reservoirs causes environment pollution and threatens human health. Solid and liquid food wastes include fruit, vegetable, and meat residues, alcohol bard, and sewage from various food enterprises. These products contain high concentrations of biodegradable organic compounds and represent an inexpensive and renewable substrate for the hydrogen fermentation. The goal of the work was to study the efficiency of hydrogen obtaining and decomposition of solid and liquid food waste via fermentation by granular microbial preparation (GMP). The application of GMP improved the efficiency of the dark fermentation of food waste. Hydrogen yields reached 102 L/kg of solid waste and 2.3 L/L of liquid waste. The fermentation resulted in the 91-fold reduction in the weight of the solid waste, while the concentration of organics in the liquid waste decreased 3-fold. Our results demonstrated the potential of granular microbial preparations in the production of hydrogen via dark fermentation. Further development of this technology may help to clean up the environment and reduce the reliance on fossil fuels by generating green hydrogen via recycling of household and industrial organic wastes.
The aquatic plant Pistia stratiotes L. is environmentally hazardous and requires effective methods for its utilization. The harmfulness of these plants is determined by their excessive growth in water bodies and degradation of local aquatic ecosystems. Mechanical removal of these plants is widespread but requires fairly resource-intensive technology. However, these aquatic plants are polymer-containing substrates and have a great potential for conversion into bioenergy. The aim of the work was to determine the main patterns of Pistia stratiotes L. degradation via granular microbial preparation (GMP) to obtain biomethane gas while simultaneously detoxifying toxic copper compounds. The composition of the gas phase was determined via gas chromatography. The pH and redox potential parameters were determined potentiometrically, and Cu(II) concentration photocolorimetrically. Applying the preparation, high efficiency of biomethane fermentation of aquatic plants and Cu(II) detoxification were achieved. Biomethane yield reached 68.0 ± 11.1 L/kg VS of Pistia stratiotes L. biomass. The plants’ weight was decreased by 9 times. The Cu(II) was completely removed after 3 and 10 days of fermentation from initial concentrations of 100 ppm and 200 ppm, respectively. The result confirms the possibility of using the GMP to obtain biomethane from environmentally hazardous substrates and detoxify copper-contaminated fluids.
Solid food waste is a significant threat to the environment. Thermodynamic calculations allow determining theoretically possible metabolic pathways for degradation of organic compounds by microorganisms, and to select the optimal one to increase efficiency of food waste recycling. The purpose of our work was application of thermodynamic calculations to find out suitable fermentation parameters for regulation of microbial metabolism Environmental Research, Engineering and Management 2018/74/4 32 to ensure a high rate of waste decomposition and formation of valuable products. The following methods were used: colorimetric and potentiometric for pH and oxidation-reduction potential (ORP) measurement, volumetric and chromatographic for the study of volume and composition of synthesised gas, and mathematical for fermentation parameters calculation. Fermentation of multicomponent kitchen food waste under theoretically calculated optimal parameters pH = 7.0 and Eh in the range form-250 to-350 mV provided extremely high metabolic activity of a hydrogen-producing microbial community, which resulted in a decrease in duration of batch fermentation to three days and an increase in hydrogen yield from 16 to 80-115 L/kg of dry waste. The coefficient of waste destruction (Kd), i.e., the ratio of initial and final weight of waste, reached 91. Obtained after fermentation, an unfermented lignocellulosic substrate was shown to be applied as plant probiotics and to supply mineral nitrogen for plant nutrition in an arid condition. Thus, high efficiency of application of a thermodynamic prognosis method of microbial interaction with organic compounds was shown to become the base for biotechnology of destruction of environmentally hazardous solid food waste with simultaneous obtainment of valuable products: environmentally friendly energy carrier-molecular hydrogen, as well as a lignocellulosic substrate to increase crop yields.
Despite the promising application of microorganisms for purification of metal-containing wastewater such biotechnologies have not been widely used since their empirical basis. Therefore, the aim of our work was to apply thermodynamic prognosis to determine the optimal pathway of microbial removal of toxic metals (CrO42-, Cu2+) and its experimental justification. There was theoretically substantiated on the base of thermodynamic prognosis and experimentally confirmed integration of microbial reduction of metals, and their precipitation by microorganisms. Developed approach is the methodological basis for fast and effective purification of metal-containing wastewater.
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