Using Thermoplastics in Water Treatment Applications



The water crisis in Flint, Michigan has brought about renewed public attention to the quality of water in the United States and the verdict is damning: only nine states report safe levels of lead in the water supply. As the American public and lawmakers continue to scrutinize water quality, municipal water companies across the country will feel pressure to upgrade their systems to meet new regulations and improve their storage facilities.

The storage and distribution of public drinking water is complicated. Water quality is governed by the U.S. Safe Drinking Water Act (SDWA), but hampered by a host of complications arising from storage designs. Selecting the right structural design and internal coating material is crucial to minimize physical, chemical, and biological issues that can harm human health.

Thermoplastics like polyethylene have been used for decades as a waterproofing barrier. Today, products made of these materials offer a unique method to safely line water storage facilities.

Water quality: A brief history of regulations

In 1948, the U.S. Federal Water Pollution Control Act passed in an effort to address water pollution after growing public awareness pushed the issue forward. In 1972, the law was significantly amended and became SDWA. Today, SDWA is enforced by the Environmental Protection Agency (EPA), which regulates and controls the presence of 91 containments from exceeding the Maximum Contaminant Level (MCL). The MCL of each containment are enforceable standards and are the highest level that a containment is allowed in drinking water (2).

Factors leading poor quality water in storage

Water quality problems in storage facilities can be classified as microbiological, chemical or physical (Table 1). Excessive water age in many facilities is the most important factor related to water quality deterioration. When water is stored for long periods of time, the water age increases and is conducive to microbial growth and chemical changes.

Table 1. Summary of Water Quality Problems Associated with Finished Water Storage Facilities (from reference 1)

Chemical Issues Biological Issues Physical Issues
Disinfectant Decay Microbial Regrowth Corrosion
Chemical Contaminants Nitrification Temperature/Stratification
DBP Formation Pathogen Contamination Sediment
Taste and Odors Taste and Odors

Water age is caused when water is not cycled through the facility or isn’t given enough time to circulate within the reservoir. Additionally, while storage facility are normally enclosed structures, numerous access points can become entry points for debris and contaminants. These pathways may include roof top access hatches and appurtenances, sidewall joints, vents, and overflow piping (1).

Water storage inspection and repair process

Up to a third of all water tank inspections will reveal a serious sanitary defect. During such an occurrence, the first step is to drain the tank to pinpoint the problem with a thorough inspection of the tank’s interior. Some tanks, for example, will show widespread coating failure on the tank sidewalls as well as accumulated sediment if there were gaps or openings in some of the entry points.

Traditional coatings used in finished water storage facilities were primarily selected for their corrosion resistance and ease of application. Common coatings included coal tars, greases, waxes, and lead paints. These products offered exceptional corrosion performance, but many contributed significant toxic chemicals to the drinking water. And some coatings even acted as a food source for bacteria, resulting in reduced chlorine residuals (1).

Applying a new coating or liner is a laborious task, requiring a sandblasting phase and cleaning phase followed by a cleaning and disinfection round. The final step is to choose a new coating.

Overcoming modern water storage coating and lining limitations with AGRU Hydroclick®

As municipal water companies seek to upgrade their water storage facilities, they will look for options that meet a number of requirements. These include a smooth surface that is easy to clean, a sealed surface, offers concrete protection against carbonation and hydrolytic corrosion, protects the stored water from ground water infiltration, and demonstrate a long service life time without maintenance. Mineral and epoxy coatings are two common options that meet some of these requirements, but with some drawbacks.

AGRU America’s Hydroclick is a rehabilitative concrete tank liner that features fast and secure installation, minimal downtime and low maintenance. The system is a cost-saving solution for the prompt availability of clean water. Developed in cooperation with ETERTUB AG, a Swiss company with 30-years of expertise in potable water applications ranging from the capturing natural springs to water storage, Hydroclick is made with high-quality polyethylene.

This thermoplastic-based lining is well-suited for water treatment applications because it meets the requirements for purity, mechanical strength, and long-life expectancy. The Hydroclick design provides a fast and secure installation for both new construction and renovations/rehabilitation. Other benefits include: frost-proof and corrosion resistance, with the capacity to resist chlorination of up to 5 mg/L in long-term applications, clean installation (pretreatment of existing structure is not necessary), and prefabrication of components to reduce field installation efforts.

Citations

  • “Finished Water Storage Facilities.” EPA. 2002. Accessed 14 August 2017. https://www.epa.gov/sites/production/files/2015-09/documents/2007_05_18_disinfection_tcr_whitepaper_tcr_storage.pdf.
  • “National Primary Drinking Water Regulations.” EPA. Accessed 14 August 2017. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#one