Research On Treatment Of Micro-polluted Source Water By Attapulgite-MBR Combined Process

With the rapid development of socio-economic and the growing urban population,lots of organic matters and ammonia as well as other pollutants was discharged withindustrial wastewater and domestic sewage into rivers, lakes or other water sources，which results in serious water pollution, especially for the dissolved organicmatter(DOM) and ammonia pollution problem. Nowadays, the requirments ofindicators in the Standards for Drinking Water Quality (GB5749-2006) was muchmore strict, therefore the conventional water treatment process can not satisfy thisrequirement. This paper proposes Attapulgite-MBR combined process for treatingmicro-polluted water containing ammonia. As a carrier attapulgite in the membranebioreactor can enhance the removal of ammonia nitrogen and organic matter and alsoretard the membrane fouling.It was found that Attapulgite-MBR system has a better performance in treatingmicro-polluted source water and sludge mixture performance as well as the membranefouling rate. Moreover, the removal of organic matters and inorganic nitrogen inAttapulgite-MBR system was improved obviously. With a stable feed, the removal ofpermanganate index in MBR and attapulgite-MBR combined process was64.3%to84.6%and75.3%to90.2%, respectively; average removal rate of TOC is83.2%and90.5%,while the average removal of UV254was76.6%and83.0%in the initial stageof the experiment, the average removal of ammonia in the two reactors was86.95%and93.45%, and the highest removal of total nitrogen reached to35.0%and59.2%,separately. With a water quality loading shock, the removal efficiency of organic andinorganic nitrogen in attapulgite-MBR system was less affected than the MBR system,reflecting the greatly enhanced stability of attapulgite-MBR system.The performance of sludge mixture in MBR and attapulgite-MBR reactor was alsoinvestigated in this paper. The sludge activity and nitrification activity inattapulgite-MBR system were increased by11.9%and23.2%, respectively. Theproportion of large particle size sludge decreased and distribution of sludge particlesize is more uniform, reducing the Zeta potential by11%to34%, which improved theremoval efficiency of organic matter with the molecular weight of3K-10K,10K- 100K, and>100K Dalton. Moreover, the structure and composition of organic materexisting in sludge mixture was also changed, types and quantity of organic matterscomposing the layer was also reduced significantly.It was also showed that the removalof humic acid and macromolecular proteins, which were difficult to biodegradable, hasalso been improved slightly.The membrane fouling in two reactors was also studied.It can be found that dosingAttapulgite to MBR system can make the membrane fouling much faster at the earlystage than the normal MBR,however,for a long-running process, membrane pollutionlevels of Attapulgite-MBR can be mitigated. Through comparing images of newmembrane,the fouled membrane and the cleaned membrane taken by scanningelectron microscopy,it can be found that under the same operating conditions,attapulgite enable the contamination layer on membrane surface to bethinner.Furthermore, the recovery ratio of membrane flux is much higher after backwashing, indicating the antifouling characteristic of membrane has been improved tosome extent.