Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Civil Engineering

Advisor

Lee, Cindy M

Committee Member

Aziz , Nadim M

Committee Member

Klotz , Leidy E

Abstract

Around the world, water scarcity is driving people to practice water reuse. One form of water reuse is the recycling of greywater, which is household wastewater excluding toilet waste. With adequate treatment, greywater may be recycled onsite for applications that do not require potable water, such as irrigation or toilet flushing. Membrane filtration (including microfiltration (MF)) is one option for greywater treatment. The small footprint, modular nature, and predictable performance of MF make it an attractive option. However, direct MF of greywater can lead to rapid membrane fouling. This thesis investigated two possible pretreatments for reducing membrane fouling and improving effluent water quality: granular activated carbon (GAC) and silica sand. To test these pretreatments, synthetic greywater (representing effluent from bathroom sinks and showers) was prepared using a recipe from NSF/ANSI Standard 350 and then treated using a pressure-driven MF membrane in a dead-end configuration. Samples were taken before pretreatment, after pretreatment, and after microfiltration and analyzed for four parameters: turbidity, total organic carbon (TOC), chemical oxygen demand (COD), and surfactants. Membrane flux was also monitored.
The results indicate that for the given experimental conditions, GAC and sand pretreatments improved effluent water quality but did not significantly reduce membrane fouling. GAC was more effective than sand at removing surfactants, while sand was more effective than GAC at removing turbidity. GAC and sand were comparable in their ability to remove TOC and COD once the flows through the columns had stabilized (i.e., within one minute). After microfiltration (MF), samples that had been pretreated with GAC exhibited the lowest level of contamination in all categories. Nevertheless, according to guidelines published by the US Environmental Protection Agency the final treated effluent was unsuitable for direct reuse because it exceeded the recommended threshold for TOC. (Currently there is no recommended threshold for water reuse regarding surfactants.) These results imply that physical treatment alone may be insufficient to remove contaminants from greywater, especially dissolved contaminants such as surfactants, which are prevalent in greywater. Future research could investigate the effect of different operating conditions (e.g., longer pretreatment contact time, upflow configuration through GAC, different membrane types), different pretreatment setup (e.g., dual layer pretreatment media with both GAC and sand), and incorporation of a biological component (i.e., allowing biofilm to develop on filter media or using a membrane bioreactor instead of strict membrane filtration).

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