What Is Water Pollution Control & How Does It Work

What is Water Pollution Control?

Before there was a water pollution control facility in Simsbury every drop of water, and everything that was mixed with it, that drained from a sink, a toilet, or a factory into the public sewer system simply flowed into the Farmington River. Think about it…every drop.

As our population grew and our waste stream increased, fish became inedible, and often were killed, the river smelled terrible, and disease germs made the water unsafe for recreation.

Thanks to modern technology, now the waste water we release into the Farmington River is cleaner than the natural flow that arrives in Simsbury. Most of us don’t think about what is required to achieve this, but we ought to.

Water is one of our most precious resources and the quality of our water can no longer be taken for granted. Therefore, how we dispose of waste into the environment takes on extraordinary importance. The convenience of discharging material into bodies of water really means we are using our streams and rivers as natural sewers. This has become accepted practice, and modern water pollution control plants such as ours make it environmentally acceptable.

How Water Pollution Control Occurs at Our Facility

There are four components of our waste water stream that must be reduced by our pollution control plant. Solid material suspended in the water would make the river cloudy, block sunlight, contain biodegradable materials, and eventually settle to the bottom as muck. The biodegradable materials would extract oxygen from the river and reduce what is available for fish and other forms of life. Nitrogen and phosphorous are nutrients in the wastewater that stimulate growth of plants and algae. When the plants die they extract oxygen from the water as they decay. So much nutrient flows into western Long Island Sound that there is insufficient oxygen for lobsters and other marine life near the sea bottom. Finally, there are bacteria in waste water, some capable of causing disease.   

Our plant removes 97% of the solids that come in the waste water, 98% of the biodegradable materials and 87% of nitrogen nutrients, and then disinfects the water before releasing it into the river. In the future, we will upgrade the plant again to reduce phosphorous nutrients. Some day we may need to address the currently small but growing concern of pharmaceutical residues in our sewage system.

In brief, this is what our facility does to the material it receives from the sanitary sewer system in Simsbury, Granby, and parts of Avon to prepare it for release into the Farmington River. Following is a step by step description of how the pollutants in the wastewater are treated.


Material that is abrasive, primarily sand, that could accelerate wear of equipment is removed. Rags, paper, plastic and other items that could clog the equipment are collected on screens. All this material is washed and sent to a landfill.


Next the waste water flows into a large tank where the flow rate is reduced to allow heavier solids suspended in the water to sink to the bottom and lighter solids to float to the top. The solids, called sludge, are removed from the bottom of the tank.


In the first tank, naturally occurring bacteria use oxygen to digest the biodegradable material in the waste water. Large quantities of oxygen are provided by pumping air into the tank and conditions are controlled to keep the bacteria growing and multiplying rapidly, grouping together in clumps. Also, the waste water contains nitrogen in the form of ammonia. Bacteria that can convert ammonia to nitrate are provided with sufficient oxygen convert the ammonia into nitrate.

In another tank, a different type of bacteria is deprived of oxygen, which causes them to convert the nitrate to nitrogen gas. The nitrogen gas is released into the atmosphere, which is already 78% nitrogen, so this is benign.

When the waste water is pumped into the next tank, the flow rate is reduced to allow the clumps of bacteria to settle to the bottom and be returned to the first tank to digest newly arrived biodegradable material and ammonia.


The next step in waste water treatment is to lower the concentration of bacteria to levels that will not result in infection. The requirement for waste water discharge is the same as for swimming pools and beaches. Simsbury uses ultraviolet (UV) light for disinfection, which disrupts the ability of bacteria to reproduce. The waste water is now clean and safe enough to release into the Farmington River.


The products of wastewater treatment are clean water and sludge. The sludge results from the settling processes in the tanks. In Simsbury, the sludge is stored in covered tanks and aerated to limit odor production. Then water is squeezed out of it to form sludge cake, which is hauled to the Metropolitan District Commission treatment facility in Hartford and burned in their incinerator.