SciTech

Water Purification and PWSA

With a simple turn of a handle, you have access to clean water. And, as residents of Pittsburgh have discovered in the past week, the cleanliness of water dramatically affects one’s quality of life.

Access to clean water is vital for the survival of individuals and communities. In July 2010, the United Nations General Assembly acknowledged the human right to water and sanitation through Resolution 64/292. In Nov. 2002, the United Nations Committee on Economic, Social, and Cultural Rights adopted General Comment No. 15, in which Article I.1 states: “The human right to water is indispensable for leading a life in human dignity. It is a prerequisite for the realization of other human rights.”

By some accounts, efforts to obtain clean drinking water date back even prior to the discovery of fire. Ancient people relied on taste to tell if water was clean, which is actually not a viable method. In one of the earliest documentations dating back to the 15th century, archaeologists found Sanskrit writings in ancient Egyptian tombs depicting water treatment. In the Sus’ruta Samhita, from 2000 BCE, there are a number of different water treatment methods described, including boiling and heating water, filtering through gravel and sand, and dipping hot iron into it.

In terms of water distribution, the earliest account of piping dates back to 3000 BCE, with Mesopotamia’s baked clay pipes, China’s bamboo pipes and Egypt’s copper sheets that were hammered into cylinders, all of which were used to transport water. In 400 BCE, Rome’s aqueduct system carried water throughout the entire city.

Pittsburgh as a city was established a little more recently than Rome, in 1816. Before the public water supply began in 1802 with the digging of four 47-foot wells, residents relied on river water. As the population grew, it became necessary to expand the water distribution, and the city built several pumping stations that pumped water directly from the rivers with no purification. By the end of the 19th century, however, the river water had become too contaminated and scientists had found evidence that drinking impure water could negatively affect health through waterborne diseases such as cholera and typhoid fever.

Thus, by 1905, construction began on plants that implemented slow sand filtration (SSF). SSF is a technique in which contaminated freshwater (river water, in Pittsburgh’s case) flows into a reservoir and through a layer of sand, where it is both physically filtered and biologically treated to remove pathogens and sediments.

The key difference between SSF and rapid sand filtration (RSF), apart from the speed at which the water is filtered, is the fact that SSF is primarily biological while RSP is primarily physical. In SSF, a microbial community known as the “schmutzdecke” is established on the top layer of sand, causing the top layer to be biologically active. These predatory bacteria, which generally come from the source water, feed on microbes from the water that pass through the SSF, which is particularly effective in removing bacteria, viruses and heavy metals, but is not effective in removing chemicals.

In 1911, the city began using chlorine as an additional disinfectant. Chlorination of water is the most commonly used method of killing microorganisms in freshwater.
According to the Center for Disease Control and Prevention, chlorine levels of up to four milligrams per liter are considered safe in drinking water.
At this level, chlorine is effective against pathogenic bacteria, but not strong enough to kill all viruses, cysts and worms. However, combined with filtration, it is effective at disinfecting water supplies.

By the second half of the 20th century, the SSF system had aged and an upgrade to the water purification system occurred in two stages. First, a clarifier pretreatment station was constructed in 1962 to chemically treat freshwater and remove iron, manganese, tastes, odors, and colors from the water before it reached filtration. Second, the SSF stations were replaced with RSF stations in 1969.

In 1984, the Pittsburgh Water and Sewage Authority (PWSA) was officially formed, taking charge of maintenance and construction of all water distribution systems in Pittsburgh. According to their website, PWSA’s vision is “to provide water and wastewater services that meet or exceed all regulations and customer expectations at the lowest possible cost.”
Last week, on Jan. 31, the Pittsburgh Water and Sewage Authority issued a precautionary flush and boil water advisory for residents of Pittsburgh. When testing near a Highland Park water filtration plant, some tests showed that the treated drinking water had levels of chlorine that were below regulation of the Pennsylvania Department of Environment (DEP); there was a risk that the treated drinking water still contained microorganisms.

Later that day, the PWSA issued another statement saying they took the Highland Park plant out of service and added chlorine to the water to maintain DEP regulations.
On Feb. 2, the PWSA lifted the precautionary flush and boil water advisory, confirming that there was no longer a risk to the drinking water supply. Although the entire affair only took place over the course of a few days, it brings a sharp reminder that access to clean water is as much a privilege as it is a right.