Learn more about the Water Pollution Control Plant’s Solids Master Plan.
The Arlington County Water Pollution Control Plant – winner of the Virginia Water Environment Association 2018 Safety Award
Arlington: Leading in Limited Nitrogen Discharge
The County has been doing essential things to help protect and preserve the environment. And much of the work has occurred since Arlington instituted Master Plan 2001. This comprehensive plan was our attempt to protect existing high-quality waters and reduce external bypasses (partially treated water that is discharged into County waters), with an overarching goal of supporting the Chesapeake Bay Preservation Ordinance, a statewide program to help restore the bay to health, first adopted by the County in 1992.
Why Limiting Nitrogen and Phosphorous Is Important
Excess nutrients like nitrogen and phosphorous allow algae blooms to occur. When the algae dies, it causes oxygen depletion from streams, rivers and the bay, resulting in dead zones, reduced life, and a reduction in the economic and recreational value of the bay and surrounding areas.
Staff monitors the plant process control system, which provides real-time information, notifications and historical data for all of the plant processes.
Helping Save the Bay
With the Master Plan 2001, the County Board authorized up to $568 million to help protect, restore and safeguard state waters. In 2003, we pursued limit-of-technology standards concerning nutrient removal set by the Virginia Department of Environmental Quality (DEQ). And Arlington County has been more than up to the challenge for years now.
For 2012, the County registered an average of .79 milligrams per liter of nitrogen discharge into area waters. How impressive is this number? Well, current parameters set forth by DEQ call for a limit of 3 milligrams per liter of nitrogen discharge. In fact, in December 2012, Arlington achieved an incredible .25 milligrams nitrogen discharge rating. How low is that? No other state wastewater treatment plant has recorded anything close to that finding. Yes, you might’ve guessed that Arlington is ranked first in the state for milligram-per-liter nitrogen discharge. And the Master Plan 2001? It was completed under budget and approximately one and a half years ahead of schedule.
Your tax dollars are at work helping to save the mighty Chesapeake Bay. Residents should be proud of this fact.
The Water Pollution Control Plant uses five wastewater treatment and solids handling systems. Learn more.
1. Preliminary Treatment
Wastewater reaches the plant via four interceptors. Bar screens and grit cyclones remove large objects and coarse solids from the water, including rags, plastics, coffee grounds, eggshells, grit, rocks, etc. These materials, along with grease and scum, are hauled directly to a municipal solid waste incinerator.
2. Primary Treatment
Next, the wastewater flows into primary settling tanks at approximately 1-foot-per-second, a slow speed that allows heavier solids to settle to the bottom of the tank while grease and scum collect on the surface. Solids that settle on the bottom, called primary sludge, are pumped into a gravity thickener for a dewatering process. Grease and scum are blended with grit and screenings from preliminary treatment.
To properly manage daily flow fluctuations and wet weather flow surges, the plant temporarily stores wastewater in equalization tanks, where it’s kept until it can be reintroduced into the wastewater treatment system.
3. Secondary Treatment
This is a two-step process. Chemicals (ferric chloride) are added to partially remove phosphorous. Wastewater is then combined with return activated sludge — the “bugs” —and travels through up to six parallel, 2.5 million gallon, four-pass aeration tanks, configured for biological nutrient removal.
The next step consists of processing the wastewater through circular secondary clarifiers, where the “bugs,” which are slightly heavier than water, settle as activated sludge. Much of the activated sludge is returned to the aeration tanks while the excess is sent to a dissolved air flotation thickener, and then dewatered.
4. Tertiary Treatment/Chemical Addition
From the secondary clarifiers, wastewater goes through a process designed to remove nitrogen and the remaining phosphorus. Methanol is added to the water, which then passes through a sand filter where “bugs” grow. The ” bugs” then convert the remaining nitrogen oxides to nitrogen gas.
A 5 percent sodium hypochlorite solution disinfects the water, then another chemical, sodium bisulfite, neutralizes the residual chlorine. Finally, air is diffused into the water to add oxygen so that fish and other life forms can survive in it. This makes the water safe for release through the plant’s outfall into Four Mile Run.
5. Treatment of Solids
Throughout the treatment process, solids that are removed from wastewater must be disposed of in a safe and environmentally friendly manner. The plant ships screenings and scum from the primary treatment process to a solid waste incinerator. The final treatment for sludge includes collecting, thickening and dewatering before disposal. Dewatered sludge then processes through lime stabilization, to reduce pathogens and odors.
The facility produces about 100 wet tons of biosolids each day. Arlington’s biosolids are land-applied on permitted sites throughout rural Virginia. This is one of the largest recycling programs in the County and minimizes the generation of greenhouse gases. The plant’s extensive chemical wet scrubber odor control system removes the bulk of odors that the various primary, dewatering, lime stabilization and truck-loading processes generate.
Overview
When people use, wash, or dispose of products that contain PFAS, these chemicals can go down drains and enter Arlington County’s wastewater system. Remember, everything you put down the drain ends up at the wastewater treatment plant!
Low Levels to Date
Arlington County proactively tests for common types of PFAS in the wastewater and solids entering and leaving our Water Pollution Control Plant. Results so far show low PFAS levels relative to proposed regulatory thresholds and industry benchmarks.
These low levels are consistent with the characteristics of our sewer system. The County serves very little industrial activity and no heavy industry, meaning our primary PFAS sources are from consumer products used in homes, businesses, and institutions such as offices, schools, and healthcare facilities.
Regulations
PFAS are not currently regulated in wastewater at the federal level by the U.S. Environmental Protection Agency. However, the Virginia General Assembly passed two bills in 2026 directing the Department of Environmental Quality (VDEQ) to address PFAS at the state level. These laws require the development of PFAS monitoring programs for wastewater systems (HB 1443 for utilities and HB 938 for industries connected to public wastewater systems) and establish permit requirements related to PFAS in biosolid-based fertilizers used on farmland (HB 1443).
Treatment
Like all other conventional wastewater treatment facilities, Arlington County’s Water Pollution Control Plant does not destroy PFAS. Depending on their chemical properties, PFAS may pass through the plant in treated water (effluent), biosolids, or be split between the two.
Technologies to remove PFAS from effluent and biosolids are an active area of research. Most methods are not recommended for systems like ours with low PFAS concentrations.
Effluent Treatment
Theoretically, the same advanced treatment technologies used to remove PFAS from drinking water – typically granular activated carbon filtration or ion exchange – can also be applied to treated wastewater effluent. However, PFAS removal is significantly more complex and expensive with wastewater, which is full of organic matter, suspended solids, oils and grease, and many other competing substances. These materials rapidly exhaust carbon filter media or ion exchange resins, reducing their effectiveness for PFAS removal. As a result, wastewater must be pretreated to near-drinking water quality before the PFAS removal technologies can work effectively.
This costly and energy-intensive approach typically makes sense for highly industrialized PFAS sources or when a community wants to invest in wastewater reuse as a long-term drinking water supply.
Biosolids Treatment
Unlike liquid wastewater, treatment methods to destroy or remove PFAS in nutrient-rich biosolids are still under study. Several thermal treatment technologies – such as pyrolysis, gasification, and supercritical water oxidation – have been shown to reduce PFAS concentrations in biosolids. However, a major knowledge gap remains regarding their fate. It is not clear whether the PFAS are destroyed, transformed into other fluorinated compounds, or displaced into air emissions, liquid recycle streams, or other treatment byproducts.
Although a limited number of thermal treatment facilities operate worldwide, these approaches are not yet considered technologically and economically ready for widespread, utility-scale use. In wastewater systems with relatively low PFAS concentrations like that of Arlington County, concerns related to performance, cost, energy consumption, and the potential transfer of PFAS to other waste streams highlight the need for continued research.
Proactive PFAS Management
While state and federal regulatory guidance continues to develop, Arlington County is proactively taking these steps:
- Monitoring for PFAS in the Water Pollution Control Plant’s influent, effluent, and biosolids.
- Supporting research to improve understanding and treatment of PFAS.
- Educating customers about PFAS and encouraging use of PFAS-free products.
Reducing PFAS at their sources, before they enter the wastewater system, is one of the most effective ways people can protect themselves, public health, and local water resources.
PFAS in Drinking Water
Find more information on PFAS and how Arlington County is managing potential risks in the About PFAS webpage.
Additional Resources