Date of Award

5-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Engineering and Earth Science

Committee Chair/Advisor

David Ladner

Committee Member

Sudeep Popat

Committee Member

Fei Peng

Committee Member

Larry Murdoch

Abstract

Membranes are an advanced and mature water and wastewater treatment technology. Membrane fouling is a key difficulty for all membrane filtration processes, leading to significant attention in the literature over the years. A common problem in laboratory-scale membrane research is that the testing methods in the laboratory are often quite different than industrial applications due to the limitations of manual experimental setups. An automated membrane filtration apparatus was built in the lab to solve this problem by allowing long-term filtration, frequent backwash and CIP, and high-accuracy operation. The filtration system achieves different cleaning strategies for both theoretical research and practical water and wastewater scale-up experiments. The embedded control algorithms achieve operational accuracy in terms of maintaining flux and/or trans-membrane pressure (TMP) at their desired set points. A flux-step function enables operators to measure critical flux automatically. The filtration system handles a variety of microfiltration and ultrafiltration membranes in crossflow or dead-end mode with backwash integration, CIP capability, and aeration scouring. Synthetic rendering wastewater and raw rendering wastewater were applied to test the apparatus in the lab and in the field, respectively. The control algorithms successfully dampened oscillations using custom calibration curves. Three backwash-CIP strategies were tested with both wastewater types. The first was time-triggered backwash and cycle number-triggered CIP, which resulted in stable and reliable operation but required close operator control and thus was not fully automated. The second strategy was time-triggered backwash with TMP-triggered CIP, which responded quickly to water quality fluctuations and achieved full automation, but the TMP target had to be carefully set to enhance the efficiency of CIP. The third strategy was target-TMP backwash with duration triggered CIP, which can achieve the most advanced and flexible filtration system, though setting up this level of automation complexity in the field was challenging. Both backwash and CIP frequencies responded to real-time performance automatically. Ultimately, the automated lab-scale filtration apparatus operated similarly to full-scale systems, which should help fill the gap between laboratory research and scale-up of industrial applications.

By using the automated filtration apparatus, supersaturated CO2-enhanced backwash (SCEB) was tested as an alternative to clean-water backwash to enhance the effectiveness of foulant removal for ceramic microfiltration membranes. Membrane backwash and chemical-enhanced backwash are standard methods to clean fouled membranes. Air bubbles are also commonly used to tangentially scour the feed side surface of micro- and ultrafiltration membranes to add scouring and loosen cake layers; this is called air-assisted backwash. Unlike air-assisted backwash, SCEB forces dissolved CO2 and CO2 bubbles through membrane pores. In this study, transmembrane pressure (TMP) and flux profile during SCEB were directly analyzed to reveal the exact nucleation location. The results from constant-flux filtration show that SCEB recovered more filtration TMP compared to DI water backwash, which saved 6.5%, 2.7%, and 6.9% of the energy during lake water, activated sludge, and rendering wastewater filtration, respectively. Visualization of the membrane permeate was done for the first time, confirming that CO2 bubbles did not form before entering the membrane matrix. The pressure and flux profiles of SCEB itself were directly monitored. The pressure profile from constant-flux backwash was analyzed to further understand the cleaning mechanism. The results from constant-flux SCEB showed more negative pressure than DI water backwash, which means that CO2 bubbles went through the membrane pores and created more resistance during SCEB. The visualization confirms that CO2 bubbles nucleated inside the membrane pores rather than on the filtrate side to clear the foulant blocked deep inside the membrane matrix. The behavior of CO2 bubbles can be divided into three stages during SCEB: i) permeate flush out, ii) bubble concentration growth, and iii) bubble concentration equilibrium. The last stage had the highest concentration of CO2 bubbles, which work as pore-scrubbing entities and play an important role in better cleaning effectiveness because of the higher nucleation rate, extra shear stress, and greater lifting force.

Membrane cleaning for membrane bioreactors is also challenging, especially for the anaerobic membrane bioreactors (AnMBRs). A pilot scale AnMBR system was used to treat synthetic municipal wastewater combined with pretreated crop harvest waste for direct hydroponic reuse. The AnMBR system was built on top of the automated filtration apparatus to improve some shortcomings, allowing an even higher data acquisition rate, more flexible parameter inputs, and more accurate flow rate results. Membrane performance was evaluated at different hydraulic retention times (HRT) and cross-flow velocities (CFV), suggesting that both parameters influenced membrane performance. When HRT was higher than 1 day, CFV dominated the membrane performance, and membrane resistance showed a decreasing trend. When HRT was lower than 1 day, even though the CFV was increased correspondingly, membrane resistance presented an increasing trend. Membrane performance was also evaluated with crop harvest waste addition. Crop harvest waste was pre-treated with two methods: physical grinding and biological fermentation. Two harvest waste additions both increased membrane resistance; fermented harvest waste increased the membrane resistance more than the other type. Bioreactor performance under the two pretreatment methods was similar; fermented harvest waste produced more methane due to its high ratio of volatile fatty acid concentration. Desired nutrients, such as ammonia, total phosphorus, and sulfate, were leached from both harvest waste types, which could be a way to reduce fertilizer use in future direct hydroponic reuse applications.

Author ORCID Identifier

0009-0000-8640-5700

Download

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.