3.3 Water Treatment

An Introduction to Water Treatment

Water treatment is two main forms. Water pumped from surface water and groundwater is treated before it is piped out to the public. Typically, such water is brought up to drinking-water standards, since public water systems serve many uses. Water that has been used but not used up – wastewater from residential, municipal, and industrial uses – is treated to remove pollutants before it can be returned to  receiving surface waters or groundwater.

Watch the video at https://www.youtube.com/watch?v=KsVfshmK0Ak to learn about standard methods of drinking water treatment and wastewater treatment.

Limitations of Water Treatment

Water treatment can eliminate many forms of contamination. However, some contaminants are not removed by standard treatment methods. Some of these difficult contaminants have only been developed or detected recently. Others have been known for a long time but are difficult to address.

Nitrate ions, one of the common forms of fertilizer are not removed from standard water treatment because the only effective methods are quite expensive. Nitrates are not usually a problem, but in agricultural areas, they can rise to high levels and then they pose a risk to pregnant women and infants. “Blue baby syndrome” is the result of high nitrate levels that impede oxygen delivery through the blood of very young children.

Heavy metals are well-known category of pollutants that cannot be degraded by bacteria during water treatment because they are elements and cannot be broken down. In addition, they undergo complicated chemistry with organic molecules that defeats most of the standard treatment approaches. The different heavy metals behave differently in terms of solubility and chemical reactivity, making it difficult to develop a single solution for their removal.

Microplastics – tiny fragments of plastic (< 5 mm in length and often much smaller) that result from physical fragmentation of larger pieces – can be too small to be removed during most treatment methods. The smallest fragments don’t settle well and none can be biodegraded by bacteria. The smallest microplastics are small enough to move from drinking water through the walls of the gut and into the blood stream and then into organs, including the brain. Microplastics can clog the digestive processes of aquatic organisms, particularly planktonic animals, and can then bioaccumulate and biomagnify in aquatic food chains. Because they do not biodegrade but simply get smaller and smaller, they are classified as “forever chemicals.” Research on impacts to humans is ongoing, but so far has suggested that cancer, heart problems and reproductive problems may be involved, as well as neurological damage and inflammatory diseases.

Many pharmaceutical compounds are not removed during water treatment for the simple reason that the treatment processes are not designed to remove them. Some also resist being broken down. As a result, birth-control drugs and caffeine eliminated in urine produce daily spikes in municipal waterways, and fish behaviors including migration and reproduction are altered by measurables levels of antidepressants, hormones, opiates, and other drugs. Resistance to antibiotics increases due to continual environmental exposure. The impacts of these inadvertent drug exposures on humans include antibiotic-resistant diseases, endocrine disruption (disruption to hormone pathways including reproductive hormones), and possibly immune-response and neurological effects.

Water treatment, itself, can introduce harmful compounds into drinking water. Chemical disinfection to address pathogens often uses halogens, particularly chlorinated compounds that produce chlorinated byproducts that are toxic and are not removed by other aspects of water treatment. Disinfection byproducts from chlorination can cause mutations and cancers. Ozone disinfection produces fewer and different harmful byproducts, but ozonation is more expensive than traditional chlorination methods and is less often used, particularly in smaller treatment plants.