Influence of allochthonous organic matters on algae removal: Organic removal and floc characteristics

Abstract

Algae are ubiquitous in surface water and affect the quality of surface water resources significantly by producing toxins as well as taste and odor compounds which adversely affect aquatic ecosystems and human health. This study was conducted to evaluate the effectiveness of three aluminum coagulants on algae removal by coagulation. Laboratory tests demonstrated that the maximum algae removal rates was 98.3% and 96.7% respectively by using PACl and Al13 as coagulants, while the maximum algae removal rate was 88.3% by using Al2(SO4)3 as coagulant at 0.1 mmol/L. According to the results, it also can be noticed that PACl and Al13 had a wide working pH range. In addition, the influence of allochthonous organic matters on algae removal during coagulation was also discussed. The removal rate was increased with a low bovine serum albumin (BSA) concentration owing to improving the adsorption-bridging. A poor coagulation performance was observed with the increasing of BSA dosage since the excess BSA molecules may prevent molecules from approaching and seize the active sites, causing coagulation inhibited. The addition of humic acid (HA) and sodium alginate (NaAlg) had adverse effects on the removal of turbidity and algae, attributed to the preferentially reaction between negative functional groups in HA/NaAlg and coagulant. Thick flocs were formed with the increasing of allochthonous organic matters as the calculation results of fractal dimension (Df). According to high pressure size exclusion chromatography (HPSEC) and three-dimensional fluorescence excitation-emission matrix spectrometry (3D-EEMs), allochthonous organic matter with high molecular weight (MW) can be completely removed, while the organics with low MW regardless of its origin were difficult to remove.