污水处理场MBR膜通量下降原因及缓解措施

中国石化海南炼油化工有限公司的污水处理场采用了MBR工艺处理其炼油污水,设计处理能力为450m3/h.进入2008年以后,MBR膜在运行中出现膜通量下降较快的问题,造成实际生产能力不到设计值的1/2.通过分析,造成膜通量下降的原因为:系统中污泥龄较长,污泥颗粒细小,沉降性能差,容易形成生物黏泥；进水油含量超标以及吹扫风带油,造成油类污染；反洗频次较高,而且反洗水质得不到保证;系统膜组件的抖动风设计不合理,风量供应不均,风孔有堵塞现象；现场操作不当,导致膜丝间积存大量活性污泥,缠裹膜丝.采取了有针对性的措施:缩短污泥龄,降低活性污泥对膜的粘附性;调整清洗方案及药剂,采用1％氢氧化钠和0.3％次氯酸钠对膜件进行离线化学清洗；提高膜区风量,改进膜件底部的布气设施;优化工艺操作,控制进水油含量和吹扫风带油；加强溶气浮选的运行控制以及现场操作.措施实施后,MBR系统处理量由2006～2009年的180～220m3/h提高到2012年的140～160m3/h,跨膜压差控制在35～55kPa,膜通量的下降幅度远远低于前措施实施前,出水水质保持稳定.

Causes of MBR Membrane Flux Decline at Sewage Treatment Plants and Mitigation Measures

Sinopec Hainan Refining and Chemical Co.,Ltd.′s sewage treatment plant uses MBR technology to treat refinery sewage,with a designed capacity of 450m3/h.In 2008,the MBR membrane′s flux dropped dramatically,resulting in the actual production capacity to drop to less than 1/2 of the designed value.After analysis,researchers found out the reasons for the decline in membrane flux:a.The long age and small grain of the sludge in the system had led to a deterioration of sludge settling properties and easily produced biofouling;b.the excessively high content of oil in the inflow water and the carrying of oil in the purging air had resulted in an oil contamination;c.the frequency of backwashing had been too high and the quality of water for backwashing was not stable;d.the vibrating air design of the membrane component was irrational,resulting in uneven supply of air and blockage of vents;e.improper operation had led to deposition of a large amount of active sludge between membrane silks,in turn wrapping up the membrane silks.Countermeasures taken included:Shortening sludge age and reducing the adhesiveness of active sludge to the membranes;adjusting cleaning plans and cleaning agents by adopting 1% sodium hydroxide and 0.3% sodium hypochlorite to conduct an offline chemical cleaning of the membrane component;raising air flow for the membrane area and optimizing the air distribution devices at the bottom of the membrane component;optimizing operating conditions to control the oil content of inflow water and the carrying of oil by purging air;and strengthening the control of dissolved air floatation operation and field operations.As a result of these measures,the treatment capacity of the MBR system rose to 140-160m3/h in 2012 from 180-220m3/h in 2006-2009,the trans-membrane pressure difference was controlled between 35 and 55kPa,the decline in membrane flux slowed dramatically compared to before the above measures were taken,and the quality of outflow water became stable.