Preparation, characterization and coagulation behaviour of polyferric magnesium silicate (PFMSi) coagulant.

A composite coagulant polyferric magnesium silicate (PFMSi) was synthesized by co-polymerization. The structure and morphology of PFMSi were characterized by X-ray diffraction, Fourier transform infrared spectra and scanning electron microscope microphotographs; meanwhile, the coagulation efficiency was evaluated under different ratios of Fe/Si, Mg/Si, basicity ([OH]/[M] ratio), and dosage. The results suggested that the PFMSi coagulant shows an amorphous phase structure, and new chemical compounds had been formed; simultaneously, the different preparation conditions had major effects on coagulation performance. Additionally, the raw water collected from Pearl River was used as a treated water sample to verify the coagulation efficiency of PFMSi. Overall, it is suggested that PFMSi is an efficient coagulant in the removal of turbidity, UV254 and total organic carbon, and it shows a markedly better coagulation performance than polymeric aluminium and non-modified coagulant. The study of coagulation kinetics and zeta potential showed that adsorption-bridging was the main mechanism for the introduction of silicon.

Impact of diatomite on the slightly polluted algae-containing raw water treatment process using ozone oxidation coupled with polyaluminum chloride coagulation.

The impact of adding diatomite on the treatment performance of slightly polluted algae-containing raw water using ozone pre-oxidation and polyaluminum chloride (PAC) coagulation was investigated. Results demonstrated that the addition of diatomite is advantageous due to reduction of the PAC dose (58.33%) and improvement of the removal efficiency of algae, turbidity, and dissolved organic matter (DOM) in raw water. When the ozone concentration was 1.0 mg L⁻¹ and the PAC dosage was 2.5 mg L⁻¹, the removal rates of algae, turbidity, UV254, and TOC were improved by 6.39%, 7.06%, 6.76%, and 4.03%, respectively, with the addition of 0.4 g L⁻¹ diatomite. It has been found that the DOM presented in the Pearl River raw water mainly consisted of small molecules (<1 kDa) and large ones (> 50 kDa). After adding diatomite (0.4 g L⁻¹), the additional removal of 5.77% TOC and 14.82% UV254 for small molecules (<1 kDa) of DOM, and 8.62% TOC and 7.33% UV254 for large ones (>50 kDa) could be achieved, respectively, at an ozone concentration of 1.0 mg L⁻¹ and a PAC dose of 2.5 mg L⁻¹. The growth of anabaena flos-aquae (A.F.) was observed by an atomic force microscope (AFM) before and after adding diatomite. AFM images demonstrate that diatomite may have a certain adsorption on A.F.