Wastewater & the Environment

The World Health Organization has estimated that 1.1 billion people do not have access to safe drinking water. Fecal contamination of drinking water is a persistent, worldwide problem that is further exacerbated as humans continue to increase demands on the water supply and populations expand. When released into the environment untreated, our waste can be detrimental to human and ecosystem health.

Why is releasing wastewater into lakes and rivers a bad thing? Won't all those nutrients just help the organisms that live there? The problem here is eutrophication. Nutrients released do cause the plants in the water (particularly algae) to grow rapidly. But when these plants die and decay, the process of decomposition consumes oxygen in the water, which can kill fish and other organisms.

In addition to decreasing species diversity, algal blooms make natural bodies of water less pleasant for human use. Eutrophication is a major problem in many of our lakes, streams and estuaries. In freshwater ecosystems, phosphorous is often responsible for eutrophication, while in salt water, nitrogen is more often the culprit.

Biodegradable Organics

Humans produce solid waste that is rich in organic carbon. These organic solids (poop) are biodegraded by the respiration of aerobic bacteria that convert organic carbon into carbon dioxide. Aerobic respiration (taking place where oxygen is abundant) is represented by the following chemical equation:

Nitrogen

Organisms use nitrogen to make DNA, protein and many other important molecules. In wastewater, nitrogen can appear in organic or inorganic forms. Nitrogen removal involves several chemical changes before it can be released as a harmless gas (79% of the atmosphere is nitrogen gas).  Excess nitrogen in salt water ecosystems causes eutrophication.

Phosphorus

Living organisms use phosphorus to make ATP, which is the main source of energy for cells. Phosphorus enters wastewater not just through human waste but also as soaps and detergents. In freshwater ecosystems, excess phosphorus is often responsible for eutrophication.

Pathogens

Pathogens are disease-causing organisms which include bacteria, protozoa and viruses passed through human waste into water. If not treated, they can create serious public health risks. Fecal contamination of drinking water is responsible for an estimated 2.2 million diarrheal disease deaths worldwide, most victims being children.

Toxic Materials

Municipal wastewater may contain toxic substances used in the home such as motor oil, paint, household cleaners, pesticides, and toxic substances released by industries such as heavy metals and synthetic organic compounds. In sufficient doses, these component may present serious hazards to human and aquatic organism health. 

Primary Treatment

Primary treatment begins after you flush the toilet, when your waste flows through the pipes of your house to either an underground septic system or to sewer pipes in your city, and finally to a sewage treatment plant. The first task is to separate solids from liquids. Liquids and dissolved nutrients, being mostly water, can be treated much more quickly than solids. Solids must be kept in the system longer in order to be broken down.

Solids can be separated in a couple of different ways. Screening is used to separate larger solids, while smaller particles settle out in a still tank. Septic systems use a similar settling process to separate liquids and solids.

Secondary Treatment

In secondary treatment, wastewater is vigorously bubbled with air to promote the breakdown of organic material by aerobic bacteria. Aerobic bacteria use waste as food. Like us, they use sugars, carbohydrates and lipids to get energy through the process of respiration.

Tertiary Treatment

Tertiary treatment is the process by which nutrients like nitrogen and phosphorus are removed from wastewater. In most conventional sewage treatment and septic systems, very little tertiary treatment is performed because it is expensive. Traditional wastewater treatment plants often add ferric (iron) oxide which reacts with phosphorus to form a solid that can then be easily removed. The ferric oxide used is a recycled byproduct of steel manufacture. Wastewater is then released into a natural body of water. Septic systems release wastewater into the ground, where the soil absorbs many of the nutrients.

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