一体式絮体-超滤工艺去除腐殖酸效能与机制

近年来,一体式吸附剂-超滤膜组合工艺以其效率高、膜污染程度低且占地面积小等优势逐渐在水处理中广泛应用.然而,目前所用吸附剂多为颗粒型,如粉末活性炭、碳纳米管、纳米铁等.不仅长期运行极易引起膜表面损伤,且多数吸附剂成本较高.为有效克服上述问题,以水处理中广泛应用的铝盐混凝剂水解絮体为吸附剂,以天然水体中普遍存在的腐殖酸为目标污染物,考察了松散且密度低的絮体直接注入膜池后腐殖酸的去除效率及膜污染行为.结果表明,曝气方式、絮体注入频率及注入量均能不同程度地影响该组合工艺效能.与间歇曝气和一次性注入相比,采用连续曝气且分批次注入时,絮体在膜表面形成松散"保护膜",充分发挥了絮体作用,腐殖酸去除效率较高,膜污染程度显著降低.单独HA污染超滤膜时,5d内跨膜压差急剧增至74.8 k Pa,而连续曝气且每次2 d注入5.4 mmol·L-1絮体运行8 d后跨膜压差仅增至6.3 k Pa.此时HA去除率为73.3%(8 d),远高于无絮体注入时(5 d,32.1%).此外,分批次注入絮体时仅有少量腐殖酸吸附于膜孔,松散滤饼层为主要污染方式,且单次注入量越大,运行结束经水洗后膜表面平均孔径也越大.本研究表明一体式松散絮体-超滤膜组合工艺在水处理中具有潜在应用前景.

Removal Efficiency and Mechanism of Removal by Humic Acid of the Integrated Floc-ultrafiltration Process

In recent years, the integrated ultrafiltration (UF) membrane process has been widely used due to its high removal efficiency, slight membrane fouling, and small land use. However, a number of problems gradually occurred regarding the integrated UF process caused by the granular adsorbents used, such as powdered activated carbon, carbon nano-tube, nanoscale zerovalent iron, etc. Severe membrane surface damage was easily caused by these granular adsorbents after a long running time, and the cost of most adsorbents was very high. In this study, to effectively overcome these problems, cheap and loose aluminum hydrolyzed flocs were directly injected into the membrane tank in the presence of humic acid (HA), with the aim of investigating the removal efficiency of HA and the corresponding membrane behavior. The results showed that the removal efficiency of HA could be influenced by aeration mode, floc injection frequency, and floc dosage. Compared with intermittent aeration and one-time injection, a loose "protection membrane" layer was formed with continuous aeration and batch injections. Therefore, HA molecules were largely removed, leading to the dramatic alleviation of membrane fouling. The transmembrane pressure significantly increased to 74.8 kPa in the absence of flocs after running for 5 days, but that only increased by 6.3 kPa with continuous aeration and an injection frequency of once every 2 d (each addition consisted of 5.4 mmol·L^-1 flocs) after running for 8 days. The removal efficiency of HA was 73.3% (8 d), which was much higher than in the absence of flocs (5 d, 32.1%). Additionally, only a few HA molecules were adsorbed onto the membrane pores with the batch injections, and a loose cake layer was the main fouling mechanism. With higher dosages of flocs injected each time, the average membrane pore diameter was larger after washing. Based on this excellent performance, this floc-integrated UF membrane technology indeed shows large application potential in water treatment.