Research of the effect of iron compounds on the sludge digestion process

Abstract

One of the most commonly used sludge treatment methods is anaerobic sludge digestion. In some treatment plants, due to increased sludge volumes, the loading of digesters becomes a limiting factor, preventing the achievement of the required sludge degradation level. As a result, during the dewatering of digested sludge, the quality of sludge water deteriorates, and the amount of pollutants entering the wastewater treatment process increases. Due to the increased pollution, higher wastewater treatment plant capacity is required, leading to greater energy consumption. To accelerate the sludge digestion process and improve sludge water quality, this study utilized additives based on iron compounds. The results showed that the highest efficiency of biodegradable dry matter (BDM) degradation was achieved using SBG Plus and SBG additives – their concentrations decreased by 38% and 37%, which is 9.1 and 8.1 percentage points more than in the sludge without additives variant (29%). The Fe(OH)3 additive also improved degradation – BDM decreased by 36.3%, which is 7.4 percentage points more than in the sludge without additives variant. The use of additives increased biogas production: SBG – 11.8%, SBG Plus – 5.1% more than in the sludge without additives variant. Meanwhile, the Fe(OH)3 additive generated more biogas between days 7–11, but the final amount was 5.1% lower than in the sludge without additives variant. The highest methane production was achieved using the SBG additive (27 L, +12.1%), while the highest methane concentration (70.3%) was reached with the Fe(OH)3 additive. In conclusion, the most effective additive for optimizing the anaerobic digestion process was the SBG additive, as it ensured the highest biogas production and methane release.