The hydrolysis of sludge organic matter is the rate-limiting step of anaerobic sludge digestion. Because pretreatments can effectively convert the solid organic matter into dissolved organic matter, it can improve the degradation rate and methane conversion rate of organic matter. In this study, the effects of heat and heat-alkaline treatments (two common pretreatments) on the composition, relative molecular weight distribution, and structure of dissolved organic matter in sludge were studied. The results showed that the heat and heat-alkaline treatments released a large amount of organic matter, which resulted in the SCOD increasing 21.9 times (heat treatment) and 47.8 times (heat-alkaline treatment). These pretreatments changed the molecular weight distribution of dissolved organic matter and decreased the molecular weight of the organic matter to the greatest degree. The results of three-dimensional fluorescence spectroscopy showed that both of the pretreatments can hydrolyze protein, the main component of sludge soluble organic matter, with the heat-alkaline treatment being more significant. In dissolved organic matter, the byproducts of the microorganisms and humic acids are not easily hydrolyzed further by the two pretreatments. In addition, the two pretreatments led to the appearance of new organic structures and the change and even disappearance of the original organic matter.
Keywords: dissolved organic matter; molecular weight distribution; organic structures; pretreatment; sludge disintegration.