Wastewater: The Little Patuxent Water Reclamation Plant

One of the most successful areas of the Chesapeake's restoration comes from the upgrades made to wastewater treatment and reclamation plants. Thanks to improved technology, we are releasing less bacteria and nutrients into the Bay and have been able to reach the 2025 Chesapeake Bay TMDL goal a decade early. Since 2010, nitrogen levels entering the water have been cut from 52 million pounds to 38 million pounds annually. And from 1985-2015, almost a billion pounds of nutrients have been prevented from entering the Bay thanks to these updates. Overall, nitrogen has been reduced by nearly 57% and phosphorus by 75%.

The first wastewater treatment plants were very different from what we see today. At first, the plants were only responsible for removing the settleable or easily removable items from the water. The systems would use screens to capture grit and physical material. And gravity would settle any sludge to the bottom of tanks for removal. There was no further treatment beyond just removing the easy stuff! The water would then be dumped in streams and rivers and flow straight to the bay. Difficult to imagine that sort of system in place today.

By the 1950s, a secondary treatment was introduced. These were biological treatment systems. They were living systems that relied on cultures to break down waste that could not be removed by the initial process. The waste would be broken down further and would then settle to the bottom of the tank, allowing for easy removal. This process achieved 85 to 90% reduction in pollutants.

In the 1980s, when more attention was drawn to nutrients entering the Bay, water treatment plants were upgraded to remove nitrogen and phosphorus. This is another biological process that didn’t use any sort of chemicals to clean the water, just naturally occurring organisms.In the Biological Nutrient Removal system (BNR), organisms break down nitrogen and phosphorus and remove pollutants from the water by up to 90%.

Today, plants have been upgraded to an Enhanced Nutrient Removal system (ENR) that further breaks down nutrients using denitrifying microorganisms. These bacteria break apart the nitrate to gain oxygen, which they need to survive. The nitrate is reduced to nitrous oxide and then to nitrogen gas. Once it is in its gaseous form, it’s released into the atmosphere where it is naturally occurring. Before the water is released into nearby streams, it passes through a UV light which doesn’t kill bacteria, but keeps it from multiplying.

I recently visited the Little Patuxent Water Reclamation Plant (LPWRP) in Howard County, Maryland which underwent a $92 million upgrade (with funding through the state) to the ENR system. With this upgrade, the plant can now remove 37,000 pounds of suspended solids, 4,730 pounds of nitrogen, and 965 pounds of phosphorus every day. According to my tour guide and plant manager, Rob, they average about 20 million gallons of water a day entering the plant. They consider this a water “reclamation” plant because they are doing more than just treating the water before releasing it to the Little Patuxent River, they reuse and supply the water to nearby agencies for industrial use (NSA uses some to cool their massive computer center).

At the LPWRP, wastewater goes through a series of treatments before being released into the Patuxent 3 miles away. It pretty much follows the evolution of plants through the years. It starts with removing the large debris, then the water is moved to the clarifying tanks which use gravity to remove particles. Next, the water goes to chambers which uses microbes to break down waste and nutrients, then it’s off to the ENR system which uses the denitrifying microorganisms to break down nutrients even further.

The LPWRP also has an upgraded phosphorus capturing system which forms the nutrient into small beads which can be applied to farmland. The good thing about these beads is that they release the nutrient slowly over time instead of quickly being washed away. Rob said that if other plants in the area upgrade to this phosphorus capturing system, he’d like to band together and sell the beads for agricultural use in the midwest, where he says the soil lacks phosphorus. But as it stands, the LPWRP doesn’t make enough on their own and they’re the only other plant in the area that has this system. The only other plant Rob knew that had this system, the AirPrex, was near Denver.

More recently, the LPWRP received another upgrade which helps dry the solid waste, killing the bacteria, and using those solids as agricultural fertilizer. The process was approved by the Maryland Department of the Environment and can be used on any non-human consumed vegetation, like corn used for livestock or ethanol production.

With plants similar to the LPWRP, it makes sense that the pollution from wastewater continues to decline in the Chesapeake area. Maryland is upgrading all of their publicly-owned plants, and Pennsylvania and Virginia have spent billions upgrading theirs as well. Still, there are challenges facing water treatment and reclamation plants. Any sort of chemical imbalance or interference can upset the ENR system, which can be extremely difficult to reestablish in colder months. These systems also require additional energy use, which increases the plant’s carbon footprint.

Before I left, I asked Rob what advice he has for people to help make sure the plant is able to function optimally. He told me that wet-wipes, even the “flushable” kind, are a pain to deal with and difficult to process. He also said never to flush old medication, as the plant can’t process or treat those chemicals, so they just end up directly into the Bay. Other than that, just use common sense and don’t flush things like bricks, plywood, and toys (all things that have ended up at the plant).