Population-growth-driven increased water demands and prolonged drought
conditions along with source water contamination by upstream wastewater
treatment plants (WWTPs) is prompting many water purveyors to rethink current
and future water management practices. Water purveyors are now, more than
ever, faced with the challenges of a dwindling water supply, and a greater
fraction of treated wastewater is now finding its way to drinking water supplies.
Many wastewater facilities are now practicing or exploring various technologies
(e.g., advanced biological treatment, membranes, soil aquifer treatment) as part
of reclamation, recharge, recycling, and reuse (i.e., direct use) programs.
Attention has focused on pharmaceuticals and endocrine disruptors, but WWTPs
are also sources of disinfection byproducts (DBPs), if chlorine disinfection is
practiced, and DBP precursors. Operational conditions, treated wastewater quality, fate-and-transport
phenomenon in the receiving body, and the relative flow of the WWTP discharge
to that of the receiving stream will determine the overall impact of wastewater-derived
DBPs on drinking water supplies. Moreover, very little is known about
how best to invest public money between WWTPs and DWTPs in order to
maximize societal benefits while minimizing the health risks posed by
wastewater-derived DBPs.
To understand these important issues, a comprehensive study was undertaken.
More than 20 WWTPs and DWTPs from various geographical locations in the
U.S. participated in a study sponsored by the Awwa Research Foundation
(AwwaRF) and U.S. Environmental Protection Agency (USEPA). A cost benefit
analyses (CBA) was performed as part of this study. This paper discusses, step by
step, the approach to CBA in predicting finished
water DBPs level at DWTPs whose source water is impacted by treated
wastewater. The approach included a detailed characterization of the wastewater effluent by treatment type, followed by fate-and-transport (and
dilution) in the receiving body prior to its treatment at the DWTP, and ultimately
assessing the amount of DBPs to form at the DWTP and in the distribution
system.
To predict DBP precursor levels in receiving bodies after wastewater treatment,
several fate-and-transport models were developed and used. These models
predicted the impact of biodegradation on DBP precursor levels in a river. The
predicted influent water quality to the DWTP was then used with the USEPA's
Water Treatment Plant (WTP) model to predict finished water concentrations for
regulated DBPs (i.e., trihalomethanes [THMs] and haloacetic acids [HAAs]) in the
plant effluent and in the distribution system. Cost curves were also developed for
both DWTPs and WWTPs in ascribing the costs associated with different
treatment types. The cost of improved treatment at the WWTP versus at the
DWTP or a combination of the two in order to ensure compliance at the DWTP
with the drinking water maximum contaminant levels (MCLs) with various
upstream WWTP scenarios was evaluated. A CBA was performed that included
the control of both halogenated DBPs (i.e., THMs, HAAs) as well a nonhalogenated
DBP (i.e., N-nitrosodimethylamine [NDMA]). The CBA model was developed to address the following issues:
level of wastewater treatment and its impact on the effluent water quality
(i.e., effluent organic matter [EfOM]) of the WWTP;
conveyance of DBP precursors from the WWTP to the DWTP (i.e.,
discharge into a receiving body and its dilution factor) and the impact of
fate and transport (e.g., biodegradation) on the DBP precursors; type of treatment used at the DWTP (e.g., conventional or advanced
treatment) and its effectiveness in removing DBP precursor (i.e., total
organic carbon [TOC], ultraviolet absorbance [UVA], dissolved organic
nitrogen [DON]) prior to disinfection at the DWTP; and, disinfection practices at the DWTP (i.e., chlorine and/or alternative
disinfectants) and its impact on the type and quantity of DBPs formed at
the DWTP and in th
| Edition : | Vol. - No. |
| File Size : | 1
file
, 290 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 9 |
| Published : | 06/01/2006 |
