removed. Coagulation mainly removed
high-molecular weight NOM, hydrophobic
DOC, and THM precursor DOC. Membrane
filtration was the best option for removing
hydrophilic DOC. With powdered activated
carbon (PAC) addition, ultrafiltration (UF)
removed transphilic DOC predominantly
and THM precursor DOC selectively.
Ozonation removed or transformed
hydrophobic NOM into transphilic and
hydrophilic NOM, which was preferentially
removed by biofiltration over hydrophobic
NOM. Biofiltration selectively removed
HAA precursors but not THM precursors.
Finally, anion exchange removed primarily
hydrophobic and transphilic NOM.
In-depth studies of NOM removal processes
are described below, along with other THM
and HAA control options the Foundation’s
research has looked into, including removal
of THMs and HAAs themselves and
strategic treatment operations.
Enhanced Coagulation and Enhanced
Softening for Precursor Removal
Stage 1 Disinfectants/Disinfection By-Products Rule (DBPR) requires water
systems that use surface water or
groundwater under the direct influence of
surface water and use conventional filtration
treatment to remove set percentages of
TOC that may react with disinfectants to
form DBPs with enhanced coagulation or
enhanced softening. Based on the DBP data
collected under the ICR from 296 public
water systems (500 treatment plants) during
the period from July 1997 to December
1998, the Foundation report Information
Collection Rule Data Analysis concluded
that the ICR data supported the Stage 1
DBPR’s 3 × 3 matrix of source water, TOC,
and alkalinity. On average, ICR plants’ TOC
removal was consistent with the removal
specified in the matrix.
For Removal of DBP Precursors by
Enhanced Coagulation and Lime
Softening (1999, order #90783/project #814),
researchers conducted testing of enhanced
coagulation on 19 raw water supplies at
bench-scale and at pilot- or full-scale at
six sites. The results demonstrated that,
on both equivalent basis and weight basis,
ferric coagulants at high dosage were more
effective in removing TOC than aluminum
coagulants. However, at a dosage lower than
20 mg/L, aluminum coagulants sometimes
removed slightly more TOC than ferric
coagulants. With a given coagulant, removal
of TOC can be optimized by increasing the
coagulant dose and lowering the pH.
Aiming at THM control, the authors of the
report, Humic Substance Removal and
Minimizing Trihalomethanes by Ferric
Chloride Coagulation (1989, order #90665/
project #531), performed coagulation jar tests
on DOM isolated from the Suwannee River
and Lake Allatoona using ferric chloride. The
supernatant in the jar tests was subsequently
filtered and chlorinated for THMFP testing.
The results showed that the removal efficiency
of non-purgeable organic carbon ranged
from 15 to 85% depending on composition
and characteristics of the organic matter. The
removal was, in general, effective within the
pH range of 4–6 and coagulant dosage range
of 10–100 mg/L ferric chloride. This study also
concluded that THMFP for a particular water
depended on specific conditions of dosage
and pH. Therefore, achieving minimum
THMFP may require pH adjustment and
laboratory- or pilot-scale testing to determine
the optimal conditions.
A case study presented in the report, Case
Studies of Modified Treatment Practices
for Disinfection By-Product Control (2003,
order #90946F/project #369), demonstrated
that for the water tested, reducing coagulation
pH effectively improved removal of DOC,
