Award Date

May 2017

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Daniel Gerrity

Second Committee Member

Sajjad Ahmad

Third Committee Member

Jacimaria Batista

Fourth Committee Member

Boo S. Tseng

Number of Pages

147

Abstract

In areas where water shortages have compromised water supplies, potable reuse is a promising solution. However, additional research is needed to identify and/or optimize cost-effective treatment technologies to demonstrate compliance with potable reuse regulations. Treatment trains employing reverse osmosis (RO) and advanced oxidation, a combination known as ‘full advanced treatment’ (FAT), are required by the California Division of Drinking Water (CDDW) for surface water augmentation and direct injection of recycled water into local aquifers. A maximum concentration of 0.5 mg/L of wastewater-derived total organic carbon (TOC) is also required by CDDW in all groundwater recharge applications. This appears to be very conservative when compared to typical TOC concentrations in conventional drinking waters. Although FAT can reliably achieve the TOC benchmark, the capital and operations and maintenance (O&M) costs may be unattractive and even prohibitive in some applications. Previous studies have shown that ozone-biofiltration systems are less costly and energy intensive but often achieve TOC removals of only 15-30%. This hinders compliance with the CDDW TOC requirement unless significant blending ratios are achieved. However, this issue may be overcome by optimizing operational conditions (e.g., ozone dose and empty bed contact time) or by developing an alternative regulatory framework for bulk organic matter. As with conventional drinking water, the formation of disinfection byproducts (DBPs) is also a concern for potable reuse applications. When free chlorine is applied as a final disinfectant (e.g., in direct potable reuse applications), trihalomethanes (THMs) and haloacetic acids (HAAs), among other regulated and unregulated disinfection byproducts, are formed. The U.S. Environmental Protection Agency regulates four THMs (i.e., total THMs or TTHMs) and five haloacetic acids (i.e., the HAA5s) in drinking water at 80 and 60 μg/L, respectively.

The purpose of this research was to investigate the impacts of ozone dose and empty bed contact time (EBCT) on DBP formation in potable reuse applications, as well as to evaluate the possibility of using DBP formation potential as an alternative regulatory framework for TOC removal. A pilot-scale ozone-biofiltration system was operated with ozone/TOC ratios ranging from 0.1-2.5 and EBCTs ranging from 1-20 minutes. The biofiltration columns contained anthracite or biological activated carbon (BAC). Bench-scale chlorination was performed using the uniform formation conditions (UFC) approach, and quenched samples were analyzed for TTHMs and HAA5s. The data demonstrated that ozone-biofiltration achieved TOC removals ranging from ~15-30%, depending on operational conditions, but biofiltration without ozone consistently achieved <10% TOC removal. UFC testing demonstrated that ozone alone was efficient in transforming bulk organic matter and reducing DBP formation by ~10-30%. Ozone-biofiltration was able to reduce TTHM formation by ~20-35% and HAA5 formation by ~40-55%. Maximum TOC concentrations of 3.3 mg/L and 6.0 mg/L were identified as treatment targets for compliance with the U.S. EPA’s TTHM and HAA5 regulations. Finally, microbial community characterization through sequencing of 16s rDNA indicated that Bradyrhizobium was the dominant genus in media samples collected from three biofilters. Minimal differences were observed between columns containing BAC receiving non-ozonated vs. ozonated effluent, indicating that preozonation did not interfere on microbial community. According to PAC analysis, there was significant difference from anthracite and BAC samples, suggesting that origin of media used in this current study might have contributed to difference in microbial community.

Keywords

Biofiltration; Chlorination; Disinfection byproducts; Microbial community; Ozone; Total Organic Carbon

Disciplines

Environmental Engineering

Language

English


Share

COinS