Abstract
The advanced oxidation processes (AOPs) play an important role in the degradation of hardly decomposable organic pollutants. AOPs methods rely on the production of highly reactive hydroxyl OH• radicals. The aim of the conducted research was to intensify biogas production in the methane fermentation process of excess sludge subjected to the process of deep oxidation with Fenton's reagent. In the process of oxidation of sewage sludge with the Fenton reagent, doses of iron ions in the range 0.02–0.14 g Fe2+/g TS (total solids) were used Hydrogen peroxide was measured in the proportions 1: 1–1:10 in relation to the mass of iron ions. The basic substrate of the study was excess sludge. In the case of excess sludge oxidation with the use of Fenton's reagent, the most favorable process conditions were considered to be the dose of iron ions 0.08 g Fe2+/g d.m. and a Fe2+: H2O2 ratio of 1:5. As a result of subjecting the excess sludge to disintegration with the Fenton reagent in the above-mentioned dose, with respect to the fermentation process of unprocessed sludge, about two-fold increase in the digestion degree of excess sludge and about 35% increase of the biogas yield was obtained.
Highlights
Irreversible destruction of protein structure, i.e. denaturation, can be caused by physical or chemical factors, such as ionizing radiation, ultrasound, high content of metal ions, or the presence of peroxides
Depending on the volume of excess hydrogen peroxide introduced into the sludge, using the tested doses of iron ions, a different course of oxidation processes of organic substances contained in excess sludge was observed
In the case of examined doses of iron ions for the dose of Fe2+ ions equal to 0.02 g Fe/g total solids (TS), the smallest increase in soluble chemical oxygen demand (SCOD) value was obtained for the remaining doses, while conducting oxidation with doses of iron ions from 0.08; 0.10 and 0.12 g Fe2+/g TS there has been an intense increase in the value of SCOD, already with the introduction of the smallest volume of hydrogen peroxide used, with the ratio of Fe2+: H2O2 of 1: 1. Analyzing the effectiveness of the Fenton reagent on the disintegration process, there was a significant increase in the degree of disintegration in the range of iron ions doses of 0.02–0.08 g Fe/g TS
Summary
Irreversible destruction of protein structure, i.e. denaturation, can be caused by physical or chemical factors, such as ionizing radiation, ultrasound, high content of metal ions, or the presence of peroxides. Andrews et al [5], as a result of subjecting preliminary sludge and waste activated sludge to oxidation with the Fenton reagent, they noticed an improvement in their susceptibility to dehydration as well as a significant reduction in the number of pathogenic microorganisms present in them. They observed a decrease in the content of copper, zinc, cadmium and nickel in the prepared sludge. The aim of the conducted research was to intensify biogas production in the methane fermentation process of excess sludge subjected to the process of deep oxidation with Fenton's reagent
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