Optimized Coagulation For Humic Acid Control With Polymer Aluminum

High Al13/Al30contend polyaluminum chlorides and inorganic composite polyaluminum with sulfate were developed, and the the coagulation behavior of them were investigased for humic acid (one typical disinfection by-products (DBPs) precursor) removal. The mechanisms of coagulation were investigated simultaneously.Firstly, hazards and control technologies of DBPs, application of coagulation and optimized coagulation, and development, application and characterization of polymeric aluminum coagulants were reviewed in this article. Then, the commercial humic acids (HA) were analyzed by modern analytical methods, and the properties of simulated raw water with the commercial HA were studied.Polyaluminum chlorides with a high Al13content (PAC-Al13) and with a high Al30content (PAC-Al30) were prepared in laboratory for HA removal. The basicity (B=[OH-]/[A13+]) of PAC-Al13and PAC-Al30was controlled to be1.2.1.8, and2.4respectively. Poly-Aluminum Chloride Sulfate (PACS) and High-Poly-Aluminum Chloride Sulfate (HPACS) coagulants were prepared by adding SO42-in preparation process of polyaluminum chlorides. The sulfate addition ratio (S=[SO42-]/[A13+]) was0.00,0.02,0.06and0.10respectively.Compared with AICl3, coagulation behaviors of PAC-Al13、PAC-Al30、PACS and HPACS were investigated by jar tests, and the influence of initial pH, coagulation dosage, coexisting cations and inorganic particles, the charge neutralization performance and the floc formation capacity were considered. The results showed that the best HA removal efficiency of PAC-Al13、PAC-Al30、PACS and HPACS were97.6%、98.5%、99.4%and97.3%, respectively. Initial pH and coagulants dosage showed different effects on the coagulation of PAC-Al13and PAC-Al30with different B values, and PACS and HPACS with different S values. Generally, PAC-Al13and PAC-Al30with the B value of2.4showed more excellent coagulation effect than the other PAC coagulants, and S=0.06was the best choice for PACS and HPACS preparation. PAC-Al30(B=2.4) not only performed a more effective HA removal at low coagulant dosage but also exhibited less re-stabilization at a high dosage, compared with PAC-Al13(B=2.4) and AlCl3. Although PACS (S=0.06) achieved the highest HA removal efficiency of99.4%. higher coagulant dosage of PACS (S=0.06) was needed to get the best HA removal than that of HPACS (S=0.06). HPACS (S=0.06) performed a more effective HA removal at the low coagulant dosage and in a basic medium, compared with PACS (S=0.06). The appropriate type and dosage of coagulants should be optimized based on the source water quality in practice. When the coagulant dosage was low, the exsiting of Ca2+and kaolin promoted HA removal through double-layer compression and bridging adsorption, but these effects became insignificant when the coagulant dosage was sufficient. Besides HA removal, the residual Al concentration and pH of the treated water were also investigated. The results indicated that residual Al concentration and pH met the requirement of drinking water quality for polymeric aluminum coagulants application under most conditions, while AICI3might be not suitable for source water treatment from this consideration.Crystal morphology, scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Al-Ferron timed complexation colorimetric and some other physical and chemical properties like laser scattering particle size, dencity and hygroscopic etc. of prepared coagulants were studied, and the coagulation mechanisms of HA removal were discussed combining with the coagulate characteristics. The branching morphology and prismatic crystals of polymeric aluminum, which usually were observed by SEM or AMF, were found with the simple crystallization. The Alc detected by Al-Ferron timed complexation colorimetric might be more effective for HA coagulation than the Alb-The laser scattering particle size, dencity and hygroscopic of coagulants also reflected and affected the coagulation performance to some extent.This study provides a foundation for development and application of new polymeric aluminum coagulants, showing an important theoretical and practical significance for development of high-effective coagulants. The optimal coagulation conditions and the analysis of influence factors would provide a cost-effective apporch for HA removal by optimized coagulation.