初始 pH 值对连续投加铝盐混凝去除小分子有机物的影响机制

To improve the removal efficiency of small molecular organics in the secondary effluent from the wastewater treatment plants, continuous dosing coagulation (CDC) was proposed. Salicylic acid (SA) was chosen as model small molecular organics to evaluate effects of initial pH value on the removal performance in the CDC process and the complexation characteristics of SA and aluminum. The CDC process with initial pH 6had the best removal efficiency that was 13.8% higher than that of conventional coagulation (CC). But the CDC process with initial pH 5 and 7 had limited promotion effect. According to the EEM results, the complexation characteristics of SA and aluminum varied with pH value. According to the XPS and ESI-MS results, 1:1 complexes Al(OH)(C₇H₄O₃)(H₂O)₂ formed in the early stage of CDC process with initial pH 5. The complexation reaction was strong so the stable complexes were difficult to remove. In the early stage of CDC process with initial pH 6, the medium polymer Al (such as in situ Al₁₃) formed and complexed with SA, which could polymerize with added aluminum and form coral reef-like flocs with rough surface and loose structure. As a result, the removal of SA was enhanced. The small molecular organics were removed by the adsorption of floc surface at initial pH 7 due to the formation of amorphous aluminum hydroxide.