Agents to be ed for improving sludge dewatering performance

A large amount of surplus sewage will be produced in the process of sewage biochemical treatment, and the moisture content of these sludge usually exceeds 99%. High sludge moisture content is often accompanied by large sludge volume, which leads to high transportation cost, difficult transportation and occupation of a large number of treatment sites. Therefore, the development of high-efficiency sludge dewatering technology has become one of the important topics for environmental protection workers in China. Generally speaking, the water in sludge includes free water (about 70%), interstitial water (about 20%), adsorbed water (about 7%) and bound water (about 3%).

The chemical composition of sludge is the key factor to determine its dehydration. Among them, extracellular polymeric substances (EPS) account for 60% ~ 80% of the total sludge, and the distribution and composition of EPS have the most significant effect on the dewatering of sludge J. I. Houghton's research shows that the content of EPS in sludge determines the dewaterability of sludge. When the dewaterability of each sludge reaches the best, it has its corresponding extracellular polymer content. At the same time, EPS content determines the charge of sludge, the content of dry solids after filtration and the stability of flocs The research shows that the proportion of protein and polysaccharide in EPS affects the dewatering of sludge. Compared with polysaccharides, some studies believe that protein has a more significant effect on sludge dewatering, and the content of high bound protein is not conducive to sludge dewatering. At the same time, murtgy et al. (1999) also showed that sludge dewatering deteriorates with the increase of protein content in EPS.

Traditional chemical conditioning agents such as PAC, FeCl3 and PAM mainly improve sludge dewatering by promoting sludge particle flocculation through electric neutralization and bridging. Other methods, such as oxidation, acid-base and heat treatment, destroy sludge floc structure and promote EPS dissolution, so as to convert bound water into free water and reduce the moisture content of dewatered sludge The technologies that have been studied mainly include photo Fenton / Fenton oxidation technology, acid-base treatment, heat treatment and so on Iron hydroxide is a kind of coagulant that can oxidize and reduce iron ions at the same time. As a green water treatment agent, potassium ferrate (K2FeO4) is widely used in drinking water, domestic sewage and industrial water treatment projects Research on K2FeO4 in sludge conditioning has been reported. At present, K2FeO4 conditioning can strengthen sludge dewatering under the condition of pH value of 3, while when pH value is 4 ~ 8, the sludge dewatering after treatment worsens. At the same time, the total amount of loose EPS (lb|eps) and the content of protein and polysaccharide increased with the increase of K2FeO4 dosage, and the change of tightly bound EPS was opposite to that of lb|eps.