Adaptability of organic matter and solid content to Fe²⁺/persulfate and skeleton builder conditioner for waste...

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 η_SOL value was 0.32) also affects the effectiveness of the skeleton builder more than the solid content (Maximum η_SOL 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.