Water and wastewater treatment - Ozone and AOPs increasingly used to remove contaminants and improve effluent quality.

Water and wastewater treatment are two critical processes for public health and environmental protection. While they both involve purifying water, they serve different purposes and use distinct methods.

Water Treatment focuses on purifying raw water from sources like rivers, lakes, and groundwater to make it safe for human consumption or other specific uses, such as for industrial processes or irrigation. The goal is to remove contaminants and undesirable components to meet drinking water standards.

Wastewater Treatment, on the other hand, is the process of cleaning used water, or wastewater, that has been contaminated by domestic, industrial, or agricultural activities. Its purpose is to remove harmful pollutants and contaminants before the water is returned to the environment, preventing pollution and allowing for potential reuse.

The Process of Wastewater Treatment
Wastewater treatment is typically a multi-stage process that combines physical, biological, and chemical methods.

Preliminary Treatment: This initial stage focuses on removing large, easily removable solids from the wastewater. This involves passing the water through screens to catch items like rags, sticks, and plastics. A grit chamber then allows heavier, inorganic materials like sand and gravel to settle out to protect downstream equipment from damage.

Primary Treatment: In this stage, the wastewater flows into large sedimentation tanks, often called clarifiers. Gravity causes the heavier organic solids to settle to the bottom, forming a layer of sludge, while lighter materials like oil and grease float to the top as scum. Both the sludge and scum are then removed for further processing. This step can remove a significant portion of suspended solids.

Secondary Treatment: This is a biological process designed to remove the dissolved organic matter that remains after primary treatment. The wastewater is moved into aeration tanks where air is pumped in to encourage the growth of beneficial microorganisms. These microorganisms consume the organic pollutants, converting them into a harmless solid mass. This "activated sludge" is then separated from the clean water in a secondary settling tank.

Tertiary Treatment (Advanced Treatment): This optional but increasingly common stage further purifies the water to meet stringent quality standards for discharge into sensitive environments or for reuse. It can involve various advanced processes to remove specific contaminants:

Filtration: Using sand, activated carbon, or membranes to remove any remaining suspended solids.

Disinfection: Killing any remaining disease-causing microorganisms using methods like chlorine, ultraviolet (UV) light, or ozone.

Nutrient Removal: Advanced methods can be used to remove nutrients like nitrogen and phosphorus, which can cause harmful algal blooms in rivers and lakes.

After all these stages, the treated wastewater, now called effluent, is safe to be released back into a river, lake, or ocean. The sludge that was removed at each stage is also treated, often through anaerobic digestion, to produce a reusable product like biosolids for agriculture or biogas for energy.

Water Treatment Technologies
The processes for purifying raw water into drinking water share some similarities with wastewater treatment but are tailored for different needs. Common technologies include:

Coagulation and Flocculation: Chemicals are added to the water to cause small suspended particles to clump together into larger, heavier clumps called "flocs."

Sedimentation: The heavy flocs settle at the bottom of a tank and are removed.

Filtration: The water is passed through a variety of filters, such as layers of sand, gravel, and charcoal, to remove any remaining particles.

Disinfection: Disinfectants, most commonly chlorine, are added to kill any bacteria, viruses, or other pathogens that may still be in the water. Other methods like UV light and ozone are also used.