Waste management in the agro-industrial sector is an important issue as it offers ways to prevent the toxic discharges of harmful pollutants into the environment, and at the same time to obtain a series of value-added products. Liquid organic wastes from the agro-industrial sector are usually in the state of continuing digestion and are capable of rendering toxic effects on plants and living organisms. Conventional technologies require a lot of treatment time and large volumes of reservoirs. The aim of this research was to intensify anaerobic fermentation using the additives of bioactive substances introduced directly into the digested biomass. The results obtained testify that substances of natural origin used as additives demonstrate pronounced effects on the alcoholic fermentation of vinasse under mesophilic conditions. The comparative assessment of different additives' action in the studied processes has demonstrated that dihydrofumaric acid caused the emission of 266 cm3 CO2 during 76 hours, aescinum – 251 cm3 during 55 hours, tomatin – 233 cm3 during 78 hours of fermentation.
TopIntroduction
Waste management from the agro-industrial sector, aimed at the prevention of environmental pollution with toxic components and at the same time, obtaining value-added products, is an important issue requiring a thorough and complex approach. The waste treatment technology should be selected proceeding from the initial wastes’ nature, composition, and amounts, which, in their turn, are functions on the main production cycle, raw materials specifics, process technology, and conditions.
This is especially relevant for the agricultural regions having the wine, spirit, beer, and juice-producing industries, where the liquid wastes are generated in the state of continued digestion, which implies the strict prevention of their discharges/dumping directly into the landfills, natural water bodies or other environmental compartments as they can destroy the chemical composition of the soil, violate the natural balance of microorganisms, plants, and other living organisms, including the negative effects on human health (Duca, 2017; Duca et al, 2021, Vaseashta et al, 2022).
Existing methods of solid organic waste management involve their application in agriculture, burning (although the rather costly process associated with air emissions), anaerobic digestion, composting, etc. The most common methods for liquid waste treatment from the agro-industrial sector are sedimentation, decanting in stabilization ponds, anaerobic fermentation, etc.
For ethanol production from carbohydrate-containing raw materials, the digestion process is applied commercially (Busic et al., 2018). Alcohol is obtained by fermentation of the sugars present in different raw materials, which are metabolized by microorganisms belonging to the genera Saccharomyces, Zymomonas, Kluyveromyces, and Zygosaccharomyces (Moreno-Arribas and Polo, 2005). Structural carbohydrates in biomass components are broken down into sugars with the help of various enzymes. Then, the sugars released are transformed by microorganisms into alcohols, hydrocarbons, or some organic acids during the fermentation process under atmospheric pressure and a temperature of 25-70oC. Intermediate sugars can be also utilized to obtain certain useful chemicals (Binder and Rainer, 2010).
Currently, the operation of numerous processing industries in agriculture, including those dealing with grain processing into alcohol, remains unsafe for the environment and living organisms (Christofoletti et al., 2013; Grossi-Botelho et al., 2012). Meanwhile, closed ecologically safe production cycles will make it possible to resolve fundamental issues such as the rational use of natural raw resources, environmental protection, and improving the quality of the final product (Hidalgo et al., 2019). The alcohol industry affects first the water resources, then air and soil.
Specific consumption of fresh water makes 195-325 m3/t alcohol (10-17 L water/ 1 L alcohol produced), depending on the raw material type and processing technology, namely, recycled water supply (Wu et al., 2009; Liu et al., 2019). Such high amounts of water used trigger the high volumes of liquid wastes thus formed (Mikucka and Zielińska 2010; Gerbens-Leenes and Hoekstra, 2012; Vaseashta et al, 2021). The admixtures contained in the waste waters contain mineral and organic substances of vegetable origin. Such waste is poorly filtrated, quickly rotting, and releasing unpleasant odors.