Conventional and nonconventional biodegradation technologies for agro-industrial liquid waste management

Abstract

Nowadays, the world is in a period of waste accumulation in large quantities, which strongly influences the health of ecosystems and ultimately the human community. Many companies worldwide produce thousands of effluents whose alternative uses are still unclear. Therefore, every agro-industrial sector has greater responsibility toward safe utilization of agro-materials, either through waste recycling or the correct treatment of waste to reduce their toxicity and the environmental burden. Many biodegradation technologies have been developed in order to address this problem such as vermicomposting, unicellular protein production, energy generation (e.g., biogas, biofuels, and hydrogen) and waste utilization as co-substrate in fermentation processes. Thus, new studies and green nonconventional methods have been settled aiming at waste recycling like biohythane production, dark fermentation, and bioremediation. Other alternatives are based on physicochemical processes such as fertigation, livestock feed production, combustion, gasification, membrane operations, and electrochemical processes. Many treatments consist of a combination of both technologies: biological and physicochemical processes. Agro-industrial liquid wastes (ALW) contain a considerable amount of organic matter, which can be decomposed by biodegradation reactions. Biodegradation is the process by which organic compounds are fragmented into smaller substances. Organic material can be degraded aerobically, with oxygen, or anaerobically, without oxygen. These reactions occur in order to obtain energy for microbial growth, and it is commonly associated with the production of value-added products such as enzymes, pigments, biopolymers, biofuels, food flavoring compounds and bioactive compounds, among others. However, ALW are characterized by high values of biochemical and chemical oxygen demands (BOD, COD), suspended solids, high electrical conductivity, phenols, aromatic compounds, low pH values, and the prohibition of disposal on soil or rivers. Many conventional technologies increase the emissions of CO2, CH4, N2O, and other volatile greenhouse gases emissions. In addition, the increase of compounds like NO3-, NH4+, K+, Ca2+, Mg2+, Na+, and other metals in soil might contaminate groundwater when leached out. Wrong treatment also promotes eutrophication and undesirable changes in ecosystems and their proper functioning.