<p><a>This dissertation focused on better understanding the
fundamental processes that control organic and inorganic contaminant
interaction with plastic plumbing pipes. Plastic pipes are increasingly being
installed for drinking water plumbing, but their role in affecting drinking
water quality has received little study. It is well-known that plastic pipes
can sorb and release organic contaminants and be difficult to decontaminate.
Several problems were identified in the literature and through discussions with
industry: (1) Past guidance issued to communities affected by petroleum
contaminated water does not seem to specifically consider plastic plumbing pipe
remediation, (2) investigators have also identified heavy metals can accumulate
on pipe inner walls, (3) Others have proposed certain heavy metals can catalyze
plastic water pipe degradation, (4) No nondestructive cleaning methods were found
for removing metal scales from plastic pipes.</a> These topics were a basis for
studies conducted because lack of information inhibits greater protection of
public health, safety, and welfare.</p>
This dissertation involved the application of
knowledge and techniques from the environmental engineering and science,
polymer engineering, and material science disciplines. Chapter 1 focused on the
response of copper and plastic pipes (i.e., chlorinated polyvinylchloride (cPVC),
high-density polyethylene (HDPE), crosslinked polyethylene (PEX)) exposed to
petroleum contaminated drinking water. Bench-scale results revealed that pipe
rinsing followed by a single 3 day water stagnation period removed target
monoaromatic hydrocarbons (MAH) from copper pipes, but much longer (<u>></u>15
days) time was required for decontaminating cPVC, HDPC, and PEX pipes. Benzene,
trimethylbenzene and polynuclear aromatic hydrocarbons, some of which are not
typically considered in drinking water contamination investigations, were found
desorbed into clean drinking water from pipes. Future plumbing decontamination
guidance should consider the conditions necessary for plastic pipe remediation.
Chapter 2 describes the influence of drinking water conditions on heavy metal
contaminant – low density polyethylene (LDPE) pellet surface interactions.
Mixed metal drinking water solutions were applied and contained Cu, Fe, Mn, Pb
and Zn at 30 µg/L. LDPE was selected as the model polymer because of its prior
use for piping in Europe, use in bench-scale studies by others, and similarity
to products used for the manufacture of more complex materials in the USA
(HDPE, PEX). As expected, metal loadings were about 5 times greater for aged
LDPE pellets suspended in solution compared to new LDPE pellets. This difference
was attributed to the aged plastic surfaces having oxygen containing functional
groups, increased surface area, and enhanced hydrophilicity. Metal loading was
lower at pH >9.5 and in the presence of dissolved organic contaminants. The
presence of free chlorine and corrosion inhibitor also decreased metal
adsorption onto LDPE pellets. These factors likely enabled metal precipitation
thereby not allowing metal species to adsorb to LDPE pellets suspended in
water. XPS results showed deposited metals (i.e., Cu, Pb, Zn) primarily
consisted of hydroxides and oxides. To further understand heavy metal – plastic
pipe interactions, Chapter 3 involved the use of metal and plastic pipe rigs
and exhumed PEX plumbing pipes. Exhumed cold and hot water PEX pipes contained
a noticeable amount of heavy metals (i.e., most abundant metals were 2049 mg/m<sup>2</sup>
Fe, 400 mg/m<sup>2</sup> Ca, 438 mg/m<sup>2</sup> Zn and 150 mg/m<sup>2</sup> P). Metal
release and deposition onto PEX pipe was examined using bench-scale pipe rigs
that contained new PEX pipe, brass valves, and copper pipe. Two water matrices
(pH 4 and 7.5) and two temperatures (23<sup>o</sup>C and 55<sup>o</sup>C) were
explored. The pH 4 water often accelerated metal leaching from brass valves,
and a greater amount of heavy metals deposited on PEX pipes at high water pH
and temperature (pH 4 and 55<sup>o</sup>C) conditions. Oxygen containing
functional groups were detected on PEX pipes connected to a brass valve or a
brass valve combined copper pipe, but were not found on PEX pipe only
(controls) samples, indicating that certain configurations may facilitate
plastic pipe degradation. The last chapter describes the ability of a new
lignin derived ligand to remove metal deposits from exhumed PEX plumbing pipes.
When the ligand concentration was ≥ 5mM, more than 95% of sorbed metals (i.e.,
Cu, Fe, Mn, Pb and Zn) were removed. The ligand favored certain metals over
others (Cu > Zn > Fe > Mn > Pb) and heavy metal removal mechanisms
were proposed. This dissertation provides insights into the role of plastic
pipes on drinking water quality. As plastic pipes continue to be installed, it
is in the interest of public health, welfare, and safety to understand their
role in positively and negatively affecting drinking water safety.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/7409177 |
| Date | 17 January 2019 |
| Creators | Xiangning Huang (5929781) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Towards_A_Better_Understanding_of_Contaminant_Fate_in_Plastic_Plumbing_Systems_and_Their_Remediation/7409177 |
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