The effect of hybrid corona-spark discharges plasma on emissions of anaerobically digested wastewater

The integration of anaerobic digestion technology into the production chains of livestock enterprises is associated with the challenge of managing organic wastewater (effluent). Existing disposal methods can generate by-product emissions and require substantial material and equipment costs. Plasma treatment of effluent represents a promising alternative technology for reducing such emissions, although several issues remain unresolved. (Research purpose) The study aimed to investigate the effect of discharge plasma on effluent. (Materials and methods) A laboratory setup generating hybrid plasma produced by above-water corona discharges and underwater spark discharges was used. Mesophilic effluent obtained from a pig-breeding enterprise was used as the substrate. (Results and discussion) The use of hybrid plasma resulted in a decrease in the potential of hydrogen from 9 to 6 and an increase in electrical conductivity from 1 to 2 millisiemens per centimeter, while the oxidation–reduction potential rose from 300 to 600 millivolts. These changes correlated with a reduction in gas emissions. A direct correlation was observed between the decrease in the potential of hydrogen and the increase in nitrate concentration from 0 to 600 milligrams per liter, which is associated with nitrate stability and low reactivity. The inverse relationship between acidity changes and nitrogen dioxide content is explained by its participation in reactions with oxygen to produce peroxynitrite. The increase in oxidation-reduction potential shifts the ammonia-ammonium chemical equilibrium toward a non-volatile form, thereby reducing ammonia emissions into the ambient air. When used separately, spark discharges had only a limited effect on the effluent; however, as part of the hybrid plasma system, their contribution was more pronounced, both in changing the electrochemical properties by 3–20 percent, and in increasing the concentration of reactive oxygen and nitrogen species by 7–9 percent compared with corona discharges. (Conclusions) Improved environmental safety, the absence of harmful chemical by-products, reduced gas emissions, foam prevention, and scalability are the main advantages of treatment with hybrid discharge plasma compared with existing wastewater disposal methods.

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