Galil N I, Wolf D
Faculty of Civil Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel.
Water Sci Technol. 2001;43(8):107-13.
The dissolved air flotation (DAF) method has an important role in the removal of hydrocarbons, as well as in the protection of the biological treatment, which usually follows the DAF. The aims of this study were to evaluate the removal efficiencies of suspended solids, general organic matter, hydrocarbons and phenols by DAF, as influenced by the flocculant type, aluminum sulfate (alum) or a cationic polyelectrolyte. Laboratory batch experiments included chemical flocculation followed by DAF, controlling the flocculant dose and the air to solids ratio. The characterization of the influent and effluent was based on general analysis of organic matter (COD), suspended solids, hydrocarbons and phenols. The influent to all experiments was supplied daily from the outlet of a full scale oil-water gravitational separation unit at a petrochemical complex in Haifa, Israel. The influent contained hydrocarbons in the range of 20 to 77 mg/L. Usually less than 10% were found in "free" form, 70 to 80% were emulsified and 10 to 20% were dissolved. The DAF process enabled us to reduce the general hydrocarbon content by 50 to 90%. The effluent was characterized by stable and uniform levels of suspended solids, and oil, almost without depending on the influent concentrations. The results indicate that the chemical flocculation followed by DAF removed efficiently the emulsified phase, which could be aggregated and separated to the surface. However, it was found that the process could also remove substantial amounts of dissolved organic matter. This mechanism could be explained by the hydrophobic characteristics of some of the substances, which could bind to the solid surfaces. It was found that aggregates created by the flocculation with the cationic polyelectrolite (C-577) could remove up to 40% from the dissolved hydrocarbon. Alum flocs also indicated removal of soluble materials, mainly phenols. The results obtained in this study indicated the possibility to improve the protection of the biological treatment process by preliminary removal of hydrophobic compounds, usually considered as either inhibitory or toxic. This removal can be based on sorption onto aggregates created by chemical flocculation, which can be efficiently removed by dissolved air flotation.
溶解空气浮选（DAF）法在去除碳氢化合物以及保护通常在DAF之后进行的生物处理方面具有重要作用。本研究的目的是评估DAF对悬浮固体、一般有机物、碳氢化合物和酚类的去除效率，这些效率受絮凝剂类型（硫酸铝或阳离子聚电解质）的影响。实验室批次实验包括化学絮凝后接DAF，控制絮凝剂剂量和空气与固体的比例。进水和出水的特性基于对有机物（化学需氧量）、悬浮固体、碳氢化合物和酚类的常规分析。所有实验的进水每天从以色列海法一家石化厂的全尺寸油水重力分离装置的出口供应。进水含有的碳氢化合物浓度在20至77毫克/升之间。通常发现“游离”形式的碳氢化合物不到10%，70至80%是乳化的，10至20%是溶解的。DAF工艺使我们能够将总碳氢化合物含量降低50%至90%。出水的特点是悬浮固体和油的水平稳定且均匀，几乎不依赖进水浓度。结果表明，化学絮凝后接DAF能有效去除乳化相，乳化相可聚集并分离到表面。然而，发现该工艺也能去除大量溶解有机物。这种机制可以用某些物质的疏水特性来解释，这些物质可以与固体表面结合。发现用阳离子聚电解质（C - 577）絮凝产生的聚集体能去除高达40%的溶解碳氢化合物。明矾絮凝物也表明能去除可溶性物质，主要是酚类。本研究获得的结果表明，通过预先去除通常被认为具有抑制性或毒性的疏水化合物，有可能改善对生物处理过程的保护。这种去除可以基于吸附到化学絮凝产生的聚集体上，而这些聚集体可以通过溶解空气浮选有效去除。
