Influence of paraments on the transformation behaviors and directional adjustment strategies of phosphorus forms during different thermochemical treatments of sludge

•Influence mechanism of technique type and paraments on P forms were clarified.•Controlling factors on the conversion of P forms were identified.•Correlation mechanism between P and accessory elements is well explained.•The conversion pathways of P forms during thermal treatments were proposed.•Strategies for form regulation and technical optimization were provided.