Date of Award

Fall 2018

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

James P. Malley

Second Advisor

Weiwei Mo

Third Advisor

Phil Ramsey

Abstract

Public water systems (PWSs) must provide 4-log virus inactivation to comply with EPA’s Surface Water Rule (LT2ESWTR) or Ground Water Rule (GWR), while also complying with the Disinfection Byproduct Rule (Stage 2 DBPR). A UV dose of 186 mJ/cm2 meets this inactivation requirement, but increases energy use, capital and operation costs, and causes technical challenges for validating UV performance. The result: many water systems resort to solely using chemical disinfectants, increasing their risk of disinfection byproduct (DBP) formation. This required UV dose is based off previous studies on the wavelength response adenovirus at 254nm, where traditional low pressure (LP) lamps emit UV light. Surrogate microbes like MS2 are used in place of adenovirus in UV reactor validation because they are non-pathogenic and have a similar wavelength response at 254nm. However, recent research shows that adenovirus is more sensitive to low wavelengths (LWs) in the 200nm – 240nm range than MS2. This suggests that adenovirus inactivation can be accomplished more efficiently than its surrogate suggested if polychromatic, medium pressure (MP) lamps are used because they emit UV light in this LW region. Yet MP UV systems do not monitor doses delivered at LWs, so they cannot take credit for the contribution of these doses in adenovirus inactivation. New sensors are being developed by UV manufacturers that look to monitor doses delivered at LWs. These sensors, however, must be proven reliable before they can be used in PWS applications.

A water treatment facility in Bethlehem, NH was chosen to host a pilot study, and was outfitted with a Trojan UVSwift 4L12 reactor equipped with innovative LW sensors. The system PLC monitored flow, UVT, sensor responses, and lamp power level. This data was used to analyze system trends and determine the ability of LW sensors to record LWs reliably. LW sensor performance was examined with 5 analyses that measured the precision and accuracy of the sensors. The results of these analyses suggest that the LW sensors have a high level of precision. The sensors were observed to be accurate under low lamp power conditions, however, one analysis suggested there may be secondary sensor response peaks. While further research is recommended to confirm their accuracy, LW sensors are certainly close to being acceptable for PWS use. With this in mind, a life cycle assessment (LCA) was conducted to compare the current disinfection strategy at Bethlehem (chlorination) with a strategy using MP UV that accounts for doses delivered at LWs. The LCA included data from DBP formation studies, chlorine demand studies, and models on reactor energy use after taking credit for LW doses. The LCA quantified the tradeoffs of switching to a MP UV disinfection strategy; comparing the increase in energy use and operation costs with the benefits of higher public health protection through a reduction in DBP concentrations, which would put the system back into compliance with the DBPR. While the data used was specific to Bethlehem, the methodology of the LCA can serve as guidance for stakeholders of other PWS that would benefit from a lifecycle perspective examination of the tradeoffs in disinfection strategies.

Download

Share

COinS