Wastewater 101

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, human 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 a process known as cultural 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, phosphorus is often responsible for eutrophication, while in salt water, nitrogen is more often the culprit.

Wastewater Constituents

  • 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 generic chemical equation: CH2O (organic matter) + O2 --> CO2 + H2O + energy
  • Nitrogen. Organisms use nitrogen to make DNA, protein and many other important molecules. In wastewater, nitrogen exists in organic or inorganic forms. Nitrogen removal involves several chemical changes before it can be released as a harmless dinitrogen gas (79% of the atmosphere we breathe is N2). Excess nitrogen causes eutrophication, especially in saltwater systems.
  • Phosphorus. Living organisms use phosphorus in a variety of ways, for example it is at the center of ATP, which is the main direct currency by which energy is used in cells. Phosphorus enters wastewater not just through human waste but also as soaps and detergents. Excess phosphorus is often responsible for eutrophication, especially in fresh water systems.
  • 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 are 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. Part of the challenge in wastewater treatment is that industrial wastewater, than contains toxins, is typically mixed with residential wastewater which is largely toxin free. Although composted nutrient residues from the wastewater treatment process are nutrient rich fertilizers that can provide a valuable soil amendment for commercial agriculture, because of the potential for mixing toxins, the USDA does not allow certified organic farms to apply fertilizers developed from wastewater treatment systems.

Primary clarifiers at a conventional treatment facility, where solids are allowed to settle out of the mix.

The Living Machine shares many of the same processes as conventional wastewater treatment plants, but it enhances tertiary treatment by mimicking the purification methods of wetland ecosystems.

The Steps of Sewage Treatment

  1. 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.
  2. 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.
  3. 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 III) 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.