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Effect of the Chemical Coagulant and Oxidizer on the Membrane Fouling During the Treatment of Wastewater Using a Membrane Bioreactor

Zarei Baygi, Ali | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47093 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Moslemi, Mohammad Reza
  7. Abstract:
  8. Membrane bioreactor (MBR) is a combination of conventional activated sludge (CAS) and membrane filtration which owing to its advantages such as high quality effluent and low excess sludge production, has gained increasing application in wastewater treatment. The major drawback of a MBR is the membrane fouling that reduces the permeate flux, which in turn increases the overall operational costs due to high energy requirements. In existing study, the combination of sludge oxidation and coagulation/flocculation addition was investigated for mitigation of membrane fouling in a membrane bioreactor. Oxidation can facilitate sludge flocculation and hence improve the properties of mixed liquor. The optimum dosages of the coagulants (Al2(SO4)3, FeCl3) and flocculant (Cationic polyelectrolyte K530CF), alone and along with the oxidation agent (KMnO4), in order to improve the soluble microbial products (SMPs) removal was found through batch experiments. Consequently, potassium permanganate in conjunction with cationic polyelectrolyte was selected as the prominent method to be further examined in the membrane bioreactor. Continuous flow experiments were divided into three stages. The first stage (stage I) was carried out in the absence of chemical addition, the second stage (stage II) was conducted in the presence of cationic polyelectrolyte, and in the third stage (stage III) KMnO4 and cationic polyelectrolyte were employed simultaneously. The results revealed that the concentration of COD in the effluent of the third stage, was 57.1% and 51.1% lower than the first and second stage, respectively. Furthermore, NH3-N and PO43- removal was enhanced by combining KMnO4 and K530CF. MLSS and MLVSS/MLSS ratio remained approximately constant through out each stage, suggesting that polyelectrolyte and KMnO4 had no negative influence on the microbial growth. When KMnO4 was used along with polyelectrolyte, the zeta potential was neutralized to a greater extent which resulted in an improvement in the flocculation process which subsequently increased the size of the flocs about 21% (versus 14% increase in stage II). It was also observed that the SMP of the mixed liquor reduced through entrapment into flocs and adsorption by manganese dioxide particles. Increase of the particle size and reduction of the SMP compounds together caused fouling rate to be decrease from 2.2×1013 1/(m.h) and 1.4×1013 1/(m.h) in stage I and II to 0.4×1013 1/(m.h) in stage III. When compared to the experiments in the absence of chemical additives and in the presence of polyelectrolyte, KMnO4 in conjunction with polyelectrolyte increased the membrane operating time by about 4 and 2.7 times, respectively. These findings confirmed that KMnO4 with polyelectrolyte significantly reduced membrane fouling
  9. Keywords:
  10. Flocculation ; Membrane Bioreactor ; Fouling ; Oxidation ; Mixed Liquor

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