Volume and mass reduction of sludge formed by polymerized-organic-Al-Zn-Fe (POAZF) coagulant in treating sewage

Abstract

A coagulant of polymerized-organic-Al-Zn-Fe (POAZF) was prepared. The volume and mass reduction sludge of POAZF, poly-Al-Zn-Fe (PAZF), and polyaluminum chloride (PAC) were investigated with fluorescence microscope, Field Emission Scanning Electron Microscopy and Jar test. The results indicated that the volume reduction of wet sludge of POAZF ranged from 33.3 to 38.5%, 19.5 to 46.2%, and 26.7 to 61.5% (compared with PAZF),and from 42.9 to 52.4%, 21.5 to 51.4%, and 63.3 to 74.1% (compared with PAC) at dosages of 62, 186, and 372 mg L−1, respectively. Dry sludge reduction of POAZF was from 18.4 to 38% (compared with PAZF) and from 23.2 to 40.6% (compared with PAC) at the same coagulation performance with dosage of 62–122 mg L−1, respectively. POAZF having different amount of similar hydrolysis species from PAZF and having different hydrolysis species and species composition from PAC may be the microscopic reason that the dry sludge of POAZF posed the following surface characteristics. The surface morphology of the dry sludge of POAZF consists of some sort of ball-like or coral-like loose floc structures and bulk crystal-like structures, which is the reason that POAZF has lower dosage than PAZF and PAC when achieving the same coagulation effect and is also the reason that POAZF has large mass reduction of dry sludge.