Removal Of Micro-polluted Organics In Source Water By Membrane Bioreator Combined With Powdered Activated Carbon

The conventional treatment techniques for micro-polluted water resourceencounter many problems, such as complicated configuration, large footprintrequirement, and unstable removal effectiveness for refractory organics, all ofwhich are the reasons for the difficulties of meeting the new drinking water qualitystandards. Membrane bioreactor (MBR), a combination of membrane separation andbio-degradation process, has been deemed as a highly efficient water treatmenttechnology. In the present works, additional particle activated carbon (PAC) dosageinto MBR was developed for enhanced typical contaminants removal frommicro-polluted water resources. Series of batch tests were conducted to reveal thecontaminants removal pathway and to evaluate the role of PAC, both of which areimportant to understand the MBR application in drinking wate treatment and toguide their real practical experience.Firstly, a single MBR was used for micro-polluted water treatment and itseffectiveness for comtaminants removal was evaluated. The results showed that thesuspended sludge and formed cake layers on the UF membrane surface took themajor responsible for the ammonia-N, NOM and refractory organics remova.Notwithstanding, the organic compounds with volatile property were mainlyremoved through aeration stripping process. After the optimization of the MBRoperational conditions, the treatment performance was improved to some extent,reflected by that the removal efficiency UV254and TOC was greater than53%and43%respectively, and those of trichloroethylene (TCE), nitrobenzene (NB),trichlorophenol (TCP) were up to63%.Afterwards, the PAC dosage in to MBR formed a PAC-MBR system for furtherpollutants removal and treatment stability. The PAC dosage in a batch modedisplayed significantly stable removal efficiencies than the all-in-one mode.Through a long-term experimental study, the PAC-MBR (10mg PAC per1liter rawwater) demonstrated consistently higher removal efficiencies compared with thesingle MBR system: during the steady-state phase, the average removal efficiencyof UV254, TOC, ammonia-N, NB and TCP increased by27%,18%,41%,22%and21%, respectively. Moreover, PAC-MBR showed a higher resistance against theinfluent loading shock, and the produced water could meet the relevant waterquality standards stably.PAC addition in MBR could also mitigate the membrane fouling, and themembrane cleaning cycle in PAC-MBR is prolonged more than1.6times comparedwith that in MBR. By observation of three-dimensional fluorescence spectroscopy, PAC preferentially adsorbed fulvic and humic acid that were difficult to be removedin single MBR. Particle size distribution in reactor mixture showed the floc sizeincreased after PAC dodage, which may result to less pore block in the UFmembrane. These results could be confirmed by SEM observation, where thefouling layer of MBR membrane was more dense and showed clear membrane pores,while the PAC-MBR membrane surface fouling layer was more loose withdistinguish membrane pores.Accordingly, the removal pathway of typical contaminants in PAC-MBR wasestimated. It was found that aeration stripping was the major way for TCE removal,however, the TCP and NB removal mainly attributed to PAC adsorption, other thanaeration stripping. Upon the analysis of the reaction kinetics, the TCP and NBadsorption reaction conformed to the psudo-second-order and psudo-first-orderkinetics, respectively. By Langmuir model regression, the maximum adsorptioncapacity of TCP and NB was around31.81mg/g and31.99mg/g, respectively. Theactivated sludge in PAC-MBR could adsorb these three contaminants in a certainlevel, although the adsorption capabilities were very limited. Notwithstanding, themaximum specific substrate utilization rate, qmax, which were determined using asteady fed-batch reactor process (FBR), was higher than those in MBR, indicatingthat the biodegradability and shock load capacity of PAC-MBR sludge were high.Finally, the mass balance was calculated to estimate the typical contaminants inthe PAC-MBR. The TCE was removed by the stripping effect completely, while theNB removal by biodegradation, PAC adsorption was58%and29%, respectively. Incontrast, more than75%TCP was removed by biodegradation and16%by aerationstripping.