Graduation Year

2022

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Engineering

Major Professor

Jeffrey Cunningham, Ph.D.

Committee Member

Sarina Ergas, Ph.D.

Committee Member

Ivy Drexler, Ph.D.

Keywords

Bromoform, Chlorine Contact Chamber, Chloroform, Disinfection Byproducts, Wastewater Treatment

Abstract

South Cross Bayou Advanced Water Reclamation Facility (SCB) in Pinellas County, Florida, recently had a spike in effluent concentrations of bromodichloromethane (BDCM) and dibromochloromethane (DBCM) above the regulated limits, due to relying fully on chlorination instead of a combination of chlorination and ultraviolet light. The objective of this study was to determine the operating parameters most strongly affecting the formation of THMs. This was completed by analysis of long-term data sets obtained from SCB by multiple linear regression to create models describing THM formation. In addition, sampling of the chlorine contact chamber (CCC) was done to determine the effects of increasing methanol dosage.

It was found that THM formation is strongly influenced by previous conditions in the CCC for up to 24hrs, not just by instantaneous present operating conditions. Chloroform and BDCM showed opposing formation patterns to DBCM and bromoform, with increases in chloroform and BDCM concentrations correlated with decreases in DBCM and bromoform concentrations. The most influential operating parameters were determined to be the chlorine contact chambers (CCC) influent total organic carbon (TOC) concentration, bromide (Br-) concentration, and temperature, with residence time and chlorine dose having a moderate influence over formation of the THMs.

THMs at SCB exhibited signs of having sequential formation. Sequential formation of THMs starts with chloroform being formed first then chloroform progresses to BDCM and then BDCM progresses to DBCM and finally DBCM progresses to bromoform. An indicator of this pattern is the temperature having a negative correlation with on chloroforms formation instead of positive; it is hypothesized this is due to the reaction rates for the formation of the other THMs from chloroform outcompete chloroform formation. In addition, the chloroform concentration stays consistent throughout the CCC, while the other THMs are steadily increasing. This indicates that something is stopping the increase in chloroform concentration, most likely this is a result of chloroform decaying or forming other THMs. Methanol concentration was shown to have a high impact on the speciation of the THMs in a short-term sampling experiment of the CCC, with higher dosing of methanol resulting in higher bromoform concentrations. However, due to the lack of other operating parameters for the short-term test and previous research to support this finding makes this finding questionable.

The results from this study can be used to manipulate the possible production of THMs by altering TOC concentration or temperature. Methanol doses can be lowered to shift the speciation from higher concentrations of chloroform to higher concentrations of bromoform based on findings from the long-term data analysis. Shifting the speciation from chloroform dominated to bromoform dominated would be ideal due to DBCM having a higher effluent standard than BDCM. However, methanol doses can only be manipulated so far since too low of a dose will result in less nitrogen removal and dosing too high of a dose can result in too many THMs being formed. However, during experimentation, the increase in methanol did not show an increase in the total amount of THMs formed. Shade balls are already installed at SCB to help lower the temperature of the water in the CCC, which will theoretically have the effect of lowering the concentration of THMs by reducing reaction rates.

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