Wastewater treatment plants do just as they say. They treat the water that goes down our drains before releasing it back into the environment. Wastewater treatment plants have evolved considerably over time. Their first, and most important purpose is to clear the water we use in our homes of solid materials. This process of screening and settlement is known as primary treatment. Although this removes the largest debris items, the wastewater is still full of organic material, which doesn’t smell great and, if dumped directly into our water bodies, can contaminate them and consume available oxygen as it decomposes. This is why virtually all treatment plants in the U.S. use a process of aeration to encourage the growth of beneficial microorganism which break down the biological material in the waste, in a process called secondary treatment. In many cases the water is then discharged, often after sterilization with Ultra Violet light which kills potentially disease causing bacteria and viruses. This was the case here in Rhode Island until about 2005. However as city populations grow, more and more nutrients are going into the wastewater treatment facilities and being discharged into our waterways. These excess nutrients act like fertilizer to the plants and algae living in the water. Unfortunately, too much fertilizer in the Bay is a bad thing. Phytoplankton (tiny microscopic plants) begin to bloom uncontrollably, blocking out sunlight needed by other plants lower in the water column. Once the algae reaches maximum capacity it begins to die off in mass numbers. The dead cells sink to the bottom where bacteria decompose the cells, using up oxygen in the process. As the bacteria pull oxygen out of the water, the fish, shellfish and other organism in the area begin to suffocate. Those that cannot swim away eventually die, providing more food for the oxygen-consuming bacteria.
However, recent advancements in technology and awareness have brought about new technologies which can treat wastewater to remove these nutrients is done in the third phase, known as tertiary treatment. Click here to download an article about wastewater treatment in Rhode Island, and learn “what happens after you flush.”
|Countless fish and shellfish |
died in Greenwich Bay in 2003
when dissolved oxygen reached
critically low levels for an
extended period of time.
Following the Greenwich Bay fish kill in 2003, Rhode Island passed a law requiring a 50 percent reduction in nitrogen discharges coming out of wastewater treatment plants in the Upper Bay. To date, nine wastewater treatment facilities in the Narragansett Bay Watershed have completed their upgrades, with three more following closely behind. However, the largest treatment facility in Rhode Island, Fields Point, is still under construction.
As these upgrades come on line, we can expect to see conditions clear up in Narragansett Bay. But it won’t happen over night. The Bay, and the creatures living in it will have to adjust to the cleaner waters. Scientists throughout the region are studying various parameters that will likely be affected and improved over time so we can have a baseline understanding of the current conditions and assess the improvements over time.
Come back soon to read about the Nutrient Budget being developed for Narragansett Bay!