Harnessing microbial power: Enhancing phosphorus recovery through initial carbon and phosphorus ratio modulation in sewage sludge compost

Phosphorus is an essential nutrient for organisms, but excessive amounts can cause environmental pollution. Phosphorus-rich sludge can solve the problem of the loss of phosphorus resources after resource treatment. This study aimed to explore the mechanism between phosphorus functional genes and phosphorus availability by regulating the initial carbon and phosphorus ratio in sludge compost, with the goal of improving sludge phosphorus recovery efficiency. The results showed that a higher initial carbon and phosphorus ratio can promote the conversion of phosphorus from sludge to Olsen phosphorus and increase the contents of Water soluble phosphorus and Citric acid phosphorus in compost products. With the increase of the initial carbon and phosphorus ratio, phoD gene and pqqC gene abundance (P < 0.05) were significantly up-regulated, thus increasing the secretion of phosphodiesterase and organic acid, improving the phosphorus availability in compost products. The potential host of phosphorus solubilizing genes was gradually transitioned from Proteobacteria to Firmicutes. The ppk gene and phosphorus accumulating bacteria abundance were significantly higher (CP20, CP25) at the later stage of composting (P < 0.05), indicating that the phosphorus accumulating potential of the bacterial community was more prominent in the low initial carbon and phosphorus ratio compost. This study elucidated the potential mechanism of action between functional genes and phosphorus availability, and demonstrated the feasibility of improving sludge phosphorus recovery efficiency by regulating the initial carbon and phosphorus ratio.