AWWARF
Project # 2775
Ozone-enhanced Biofiltration
for Geosmin and MIB Removal
click here to return to Westerhoff's T&O webpage
Send an email to Prof. Paul Westerhoff (PI) at p.westerhoff@asu.edu
Project
Abstract
Earthy-musty odors are the most prevalent taste and
odor (T&O) customer complaint and are typically associated with the presence
of MIB or Geosmin. National surveys
conducted by research team members found the median duration of taste and odor
episodes was two weeks and there were two episodes per year; 3% of utilities had
a continuous problem and 10% of utilities had greater than 150 days per year of
T&O problems. While powdered
activated carbon (PAC) is widely used to treat such episodes, the use of ozone
and biofiltration provide a high degree of treatment in addition to other water
quality benefits (e.g., disinfection credit, improved TOC removal, decreased DBP
formation, decreased chlorine demand, and improved biostability of finished
water). Biofilters commonly use
sand, anthracite/sand, or granular activated carbon (GAC)/sand designs.
Once bioacclimated the GAC is termed biological activated carbon (BAC).
Experience in design and operation of ozone-biofiltration plants has been
well documented, and the process is at a mature stage of understanding.
This project builds upon years of project team members experience to
optimize the ozone-biofiltration process for MIB and Geosmin removal.
Our approach will allow utilities to (1) better anticipate removal of MIB/Geosmin
across ozonation, (2) apply existing strategies that optimize ozone-biofiltration
processes for multiple water quality benefits (particle removal, TOC and BOM
removal, reduced DBP formation), and finally (3) optimize biofiltration design
as to better anticipate potential MIB and Geosmin removal across the filters.
Critical gaps in the understanding of ozonation to remove MIB and Geosmin
will be filled. Empirical and
mechanistic models for MIB and Geosmin oxidation will be calibrated, based upon
existing models. Side-by-side
comparisons will be demonstrated for different filter media types (sand,
anthracite sand, BAC/sand) and the ability of the biofilters to improve water
quality (particulate removal, TOC removal, biostability, and DBP formation).
The researchers will build upon their previous studies for MIB and
Geosmin removal by PAC and GAC (isotherms and RSSCTs) on different sources
(lignite, bituminous, wood) and different natural waters.
A well planned series of biofiltration pilot-plant testing programs will
then evaluate MIB and Geosmin removal during biofiltration, and facilitate
improved understanding of the mechanisms of MIB and Geosmin removal (biofilm
sorption, filter media sorption, biodegradation).
Existing biofiltration models, already calibrated and applied to
full-scale biofiltration plants, will be expanded and calibrated to MIB and
Geosmin removal. Besides physical filter parameters (contact time, loading rate,
media size, etc) these relatively complex models require only two measurable
parameters (1) biomass in the biofilter, and (2) biologically degradable organic
carbon (BDOC) loaded onto the filter. Existing
work by the investigators have demonstrated that a relatively predictable
vertical distribution of biomass in biofilters exist, and the total biomass in
the biofilter can be well estimated based upon collection of a sample from the
top of the biofilter. This work
will be verified during pilot testing, and the concept will be applied to
full-scale ozone-biofiltration plants to validate a design optimization model.
Investigator experience, literature reviews, plus bench-, pilot-, and
full-scale work involving several participating utilities geographically
distributed around the US will be used to develop design and operating criteria
that optimize ozone-enhanced biofiltration systems for MIB and Geosmin removal.
Existing plants currently rely primarily on the ozonation process when
elevated MIB and Geosmin levels enter the plant, but this research will
hopefully establish tools that estimate the potential MIB and Geosmin removal
during biofiltration. This is
important as utilities balance improving the T&O of finished water against
increased energy costs for generating ozone and formation of ozonation
disinfection by-products (e.g., bromate) that can be produced at higher ozone
dosages.
The goal of this project will be to optimize the
performance of biofiltration, following ozone use, for Geosmin, MIB,
particulate, and BOM removal while considering other factors such as AOC or DBP
formation and headloss development. Field
operational data suggests that ozone can oxide 10% to >90% of the MIB &
Geosmin, and typical biofiltration can remove ~50% of the influent MIB &
Geosmin. However, very few
published dose-response relationships have been developed for ozone oxidation of
MIB and Geosmin. Furthermore, the
mechanisms of these removal processes (oxidation and biodegradation), and how to
optimize the overall treatment process, have not been well documented.
Ozone to TOC doses in the range of 0.5 to 1.5 mgO3/mgTOC have
been reported to remove 50% to >90% of the influent MIB, with higher ozone
doses increasing MIB oxidation (Glaze et al., 1990; Ferguson et al., 1990;
Nerenberg et al., 2000). However
most full-scale WTPs that apply ozone for T&O control generally operate at
quite low ozone doses (< 0.3 mgO3/mgTOC), while optimal
biofiltration for TOC removal may occur around 1 mgO3/mgTOC.
A disparity exists in knowledge for optimizing ozone-enhanced
biofiltration systems for MIB/Geosmin removal.
After quantifying removals and mechanisms for oxidation of MIB and
Geosmin during ozonation, the project will then optimize biofiltration for BOM
and particulate removal prior to optimizing biofiltration for MIB and Geosmin
removal. Process models, based upon
existing model formulations, will be developed to facilitate optimization of
ozone-enhanced biofiltration design and operating criteria.
The project work will be divided into the following five tasks, which are
detailed in subsequent sections (analytical methods are in QA/QC section):
 |
Task 1 – Literature Review |
|
Task 2 – Ozone Oxidation of Geosmin & MIB |
|
Task 3 – Pilot testing Geosmin & MIB Removal and Filter
Performance after Ozonation |
|
Task 4 – Full-Scale Treatment & Process Evaluation |
|
Task 5 – Design & Operation Criteria and Costs |
Recent Results
The project will start January 1, 2002. The first activities will include a literature review and laboratory ozonation experiments with water from several participating utilities. The purpose of the ozonation work is to determine rates of MIB and Geosmin oxidation by molecular ozone and HO radicals, and to attempt to model the degradation in natural waters.
======================================
Personnel:
Principal
Investigator:
Name:
Paul Westerhoff, Ph.D., PE
Organization:
Arizona State University – Department of Civil and Environmental
Engineering
Address: Box 5306 Tempe, AZ 85287-5306
Phone/Fax/e-mail:
480-965-2885 480-965-0557
p.westerhoff@asu.edu
Co-Principal
Investigator:
Name:
Scott Summers, Ph.D.
Organization: University of Colorado – Department of Civil, Environmental, and Architectural Engineering
Address: Box 428 Boulder, CO
Phone/Fax/e-mail:
303-492-6644 303-492-7317
r.summers@colorado.edu
Co-Principal
Investigator:
Name:
Zaid Chowdhury, Ph.D., PE
Organization: Malcolm Pirnie Inc.
Address: 432 N 44th Street Phoenix AZ 85008-7603
Phone/Fax/e-mail:
602-231-5544 602-231-0131 zchowdhury@pirnie.com
Participating
Utilities and Other Organizations:
City of Chandler, AZ Contra Costa Water District, CA City of Ann Arbor, MI;
Town of Gilbert, AZ Milwaukee Water Works, WI City of Philadelphia, PA
Indianapolis Water Works, IN City of Fort Worth, TX Central Lake County Joint Action Water Agency, IL