Changes in the Composition of Digestate Liquid Fraction after Ozone and Ultrasonic Post-Treatment

Abstract

There is a growing concern about environmental pollution with digestate, which is produced in significant amounts in the anaerobic digestion process. The inappropriate application of digestate in agriculture may lead to ammonia emission to the atmosphere, nutrients infiltration to groundwater and surface waters eutrophication. There is a great interest in the development of efficient downstream technologies that will help better handle digestate. This study assessed the effect of three different disintegration methods (ozonation, ultrasonication, combination of ozonation and ultrasound) on solids content, nutrient concentration and biodegradability of the liquid fraction of sugar beet pulp digestate. The influence of initial pH (7, 8, 9), ozone dose (0.05–0.45 g O3/g TS), specific ultrasound energy (10,381–51,903 kJ/kg TS) and vibration amplitude (50, 100%) on the performance of digestate liquid fraction treatment was investigated. The highest removal efficiencies of organic substances, total and ammonia nitrogen averaging at 13.81, 20.04 and 28.70%, respectively, in separate ozonation and ultrasonication processes, was obtained at ozone dose of 0.25 g O3/g TS, specific energy of 41, 522 kJ/kg TS and amplitude of 100%. The application of combined processes, first ultrasonication and then ozonation, resulted in an increase in the above-mentioned removal efficiencies to 58.16, 36.60 and 48.71%, respectively.

Organic Fertilizers and Bio-Waste for Sustainable Soil Management to Support Crops and Control Greenhouse Gas Emissions in Mediterranean Agroecosystems: A Review

“…Digestate is ordinarily separated into two fractions according to the dry matter content: a liquid fraction (dry matter of 2-8%) and a solid fraction (dry matter of 22-30%) [20,21]. The liquid fraction has an alkaline pH, total organic C of 0.5-3.2 g L −1 , total N of 0.5-3.0 g L −1 (18-70% represented by ammonium-N), P of 0.2-2.0 g L −1 , and K of 0.5-6.0 g L −1 [22][23][24][25]. The solid fraction is characterized by an alkaline pH, total organic C concentration of about 400 g kg −1 , total N content ranging from 15 to 150 g kg −1 mostly represented by the ammonium-N form (up to 67%), P concentration variable of 0.2-70 g kg −1 , and a relatively high K content (from 1 to 100 g kg −1 ) [26][27][28].…”