Civil Engineering

 

Date of this Version

Summer 8-2011

Comments

A THESIS Presented to the Faculty of The graduate college at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Sciences, Major: Civil Engineering, Under the Supervision of Professor Tian C. Zhang. Lincoln, Nebraska: August, 2011

Copyright 2011 Meng Hu

Abstract

Water scarcity is a pressing global issue. Greywater (GW) reclamation is a viable option to reduce freshwater demand. The objectives of this work were to: a) evaluate the feasibility of the combination of shredded tire biofilter (STB) technology and membrane bioreactor (MBR) technology in GW reclamation; b) study the effects of various parameters on STB performance; and c) understand the fouling mechanisms to lower the energy consumption in MBRs. Bench-scale STBs and MBRs (flat-sheet membranes) were constructed to address the first two objectives, while an independent membrane (hollow-fiber membranes) fouling experiment was designed for the third objective.

It was found that STBs packed with tire shreds not only could pre-treat GW before MBRs, but also present an alternative to the issue of tire disposal. The investigation on the biofilm in STBs showed that shredded tires could support the growth of microorganisms, which may extend their use in bio-retention basins, constructed wetlands, etc. The effluent from STBs was further treated in MBRs, the effluent of which reached the wastewater reuse guidelines suggested by the U.S. Environmental Protection Agency (EPA). The combination was thus proved to be capable of producing reusable water for non-potable purposes.

With the aid of confocal laser scanning microscopy (CLSM) and the image analysis software (ImageJ and Imaris®), the fundamental membrane fouling mechanisms were studied in terms of internal and external fouling. In an independent MBR experiment, sampling of membranes were such designed to represent the 3-stage fouling map, that changes in foulants contribution were monitored throughout an entire filtration process. Protein and polysaccharides were found to be the major foulants. Internal fouling was responsible for the two trans-membrane pressure (TMP) jumps at the first and third stages, while external fouling dominated the extended second stage. A mathematical model was proposed to link the porosities and TMP from the basic filtration theory point of view. The model verifies the experimental findings.

Advisor: Tian C. Zhang

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