CARTWRIGHT CONSULTING CO., LLC

WHAT IS IT WITH OUR DRINKING WATER?

Drinking water quality issues are commanding increasing attention lately on social media sites, in news articles and on TV.

• Why is this?
• Is water becoming less safe to drink?
• Are there more health-related contaminants in it?

PFAS CONTAMINATION IN DRINKING WATER SUPPLIES

Introduction

PFAS is the acronym for “per- and polyfluoroalkyl substances.” They are a class of human-made (anthropogenic) chemicals containing at least one carbon-fluorine chemical bond. These chemicals have been manufactured since the 50s and there are estimated to be over 15,000 different PFAS now in the environment.

They are everywhere: in water, air, soil, food and in the bodies of virtually all living beings, including we humans. Because the carbon-fluorine bond is extremely difficult to break, most PFAS are considered indestructible and termed “forever chemicals.”

Those PFAS most closely studied, PFOA and PFOS, are known to bioaccumulate in humans and other animals. Extremely low concentrations (nanograms/liter) are suspected to cause health issues. The vast majority of PFAS have not been evaluated for toxicity, but significant investigations are underway.

This combination of chemical inertness, ubiquitous presence in the environment and suspected toxicity at low concentrations, have earned PFAS the title of the most consequential water contaminant in our lifetime.
Although PFAS have been in use for many years, concerns about environmental impacts are relatively new and only recently have these water contaminants attracted the attention of the public.

Many comprehensive investigations are underway, but we currently know very little about PFAS behavior in the environment, specific health effects, removal options and destruction technologies.

POINT OF USE REVERSE OSMOSIS SYSTEMS – FUNDAMENTALS, FACTS and FICTION

Background

Reverse osmosis is a popular, widely employed water treatment process. Technically called crossflow, pressure-driven membrane separation, it utilizes pressure to force water through a semipermeable polymeric membrane to remove contaminants from the water. To understand reverse osmosis (RO), it helps to first understand osmosis, a fundamental biological process. Osmosis is the movement of water through a membrane from a region of low solute (dissolved solids) concentration to a region of high solute concentration. The goal is to achieve the same concentration of solute on both sides of the membrane, and osmosis is the primary mechanism by which water is transported in and out of cells in plants and animals. If pressure is applied to the high solute concentration side of the membrane, osmosis is reversed, and water will pass back through the membrane and become purified. It is important to emphasize that basically only the solvent (water) will pass through the membrane so this process, reverse osmosis, will generate purified water. The key to the success of reverse osmosis was the development of a semipermeable membrane, and the first commercially successful one was invented in the late 1950s. It was made from cellulose acetate polymer; however, a vastly superior membrane, made from complex polyamide chemistry and known as Thin Film Composite came into the industry in the early 80s. Meanwhile, the spiral-wound membrane element was invented in 1964, and this element configuration now dominates the reverse osmosis market.

It is important to understand that RO involves the movement of water through the membrane and that contaminants are left behind in the concentrate stream which is typically discarded. The treated water is known as permeate and the discarded water known as either concentrate or reject.

The driving force to effect separation of the contaminants from water is pressure. This process is illustrated below.