Abstract
Sludge conditioning is important for improved dewatering, with the sludge characteristics impacting the effect of conditioning. A composite conditioner, Fe2+-activated sodium persulfate (Fe2+/SPS) combined with phosphogypsum (PG), was used to examine its impact on sludges with different organic contents (34.6-43.8%) or different solid contents (2.8-5.9%). Response surface optimization analysis shows that when the best conditioning is achieved, the reduction of the specific resistance to filtration (SRF) is not sensitive to organic matter content, but the dewatering performance of the sludge is greatly affected by the solid content. The oxidation role of Fe2+/SPS and the skeleton builder role of PG together affect the conditioning, oxidation playing a major role in conditioning, especially for greater organic matter content. The organic content (maximum ηSOL value was 0.32) also affects the effectiveness of the skeleton builder more than the solid content (Maximum ηSOL value was 0.25). Changes in PG significantly impacts the optimal molar ratio and dosage of Fe2+/SPS. Sludge with greater solid content requires greater Fe2+/SPS dosage to provide stronger oxidation to destroy flocs, and the maximum Fe2+:SPS molar ratio was 1.14 with solid content of 5.9 wt%. The composite conditioning decreases the content of extracellular polymeric substances and proteins/polysaccharides. This study provides new insight into the relationship between the oxidation role of Fe2+/SPS and the skeleton builder role of PG for sludge conditioning strategies according to the optimal conditions.
Highlights
With the growth of urban populations and the continuous improvement of municipal service facilities and sewage treatment technology, the amount of sewage sludge produced by urban sewage treatment plants is increasing
The results showed that optimization of oxidation reagent based on volatile solid content is more plausible than that of based on dry solid content for different sewage sludge with different organic matter contents
A quadric surface model was established for the specific resistance to filterability (SRF) value, water content (WC), and organic matter content of the filter cakes of the different sludges
Summary
With the growth of urban populations and the continuous improvement of municipal service facilities and sewage treatment technology, the amount of sewage sludge produced by urban sewage treatment plants is increasing. Sewage treatment plants often use conditioning before mechanical dewatering for improved sludge dewatering performance (Cao et al 2021, Wu et al 2020). Advanced oxidation technology has become a subject of research interest in the area of chemical conditioning due to the advantages of low secondary pollution and fast reaction times (Bian et al 2021, Chen et al 2021, Chen et al 2020, Kim et al 2016, Ni et al 2019, Wei et al 2020, Zhang et al 2020b). Our previous research used Fe2+ activated sodium persulfate (SPS) combined with phosphogypsum (PG) for sludge conditioning and found both oxidation and skeleton building effects (Shi et al 2015). Fe2+/SPS oxidation promoted the rapid generation of column-shaped dihydrated phases of CaSO4·2H2O from the hemihydrate phases of CaSO4·0.5H2O
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