Wastewater is Derived From Manufacturing and Mining Processes

The water used in homes, businesses and industries must be cleaned before it is released back to the environment. This is known as preliminary treatment or sewage treatment, and it is vital to protect public health and sustain natural water sources.

Wastewater contains a wide variety of material, including excrement, soaps, detergents, food scraps, oils, plastics, metals, salts, sand, grit and other debris from residential, commercial and industrial activities. Wastewater can also contain chemicals that are harmful to the environment and human health. Most people are familiar with the concept of clean drinking water, but few know that much of our water is dirty and needs to be cleaned before it can be reused.

Almost all communities produce some amount of wastewater. Some of this wastewater is derived from manufacturing and mining processes, while other industrial activities can contribute to the production of toxic or hazardous wastewater as well. Common sources of hazardous wastewater include batteries, chemical manufacturing, electric power plants, iron and steel manufacturing, oil and gas exploration, smelting, pulp and paper production, textile mills and wood preserving.

There are a number of ways that wastewater is treated before it can be returned to the water cycle. Typically, the first step in wastewater treatment involves removing coarse material. This can be accomplished through screening, comminution (the process of reducing a material to smaller particles or fragments) and sedimentation.

After coarse material is removed from the wastewater, it is usually chemically treated. Chemicals such as coagulants and flocculants are added to the water to destabilize the fine solid particles in the wastewater, so they will bind together to form larger groups and settle out of the water. Other chemicals such as phosphorus removers, nitrate reducers, de-chlorinators and deodorizers are used to treat the wastewater to make it safe for reuse.

Following mechanical and chemical treatment, the wastewater is often treated with microorganisms to break down organic compounds in the water. Bacteria and protozoa consume biodegradable soluble contaminants, such as sugars, fats and organic short-chain carbon molecules from human waste, laundry detergents and kitchen waste, and release carbon dioxide, hydrogen and other byproducts.

Once the dissolved substances in the wastewater have been broken down, the next step is to neutralize the pH of the water. A pH of 7 is considered safe for re-entering the environment.

In some cases, the reclaimed wastewater is used for irrigation of parks, gardens and farms, or for replenishing surface water and groundwater sources through water reclamation and aquifer recharge. In other instances, the wastewater is treated to meet drinking water standards and is used to fulfill certain purposes in residences and businesses, such as toilet flushing.

In most communities, sewage is either pumped out of the city into a lake, river or stream where it can be naturally self-purified by dilution and natural flows, or is applied to land for a number of uses including groundwater recharge and evapotranspiration. In many densely populated areas, however, this is not an option and the sewage must be treated before it can be discharged into natural bodies of water.