Factsheets

Patterns of Use

Wastewater treatment protects human and ecological health from waterborne diseases. Since the early 1970s, effluent water quality has been improved at Publicly Owned Treatment Works (POTWs) and other point source discharges through major public and private investments prescribed by the Clean Water Act (CWA). Despite the improvement in effluent quality, point source discharges continue to contribute to the degradation of surface water quality. In addition, much existing wastewater infrastructure, including collection systems, treatment plants, and equipment is in need of repair or replacement. 

Contamination and Impacts

• Pollutants contaminate receiving waters via many pathways, including point sources, non-point sources (e.g., air deposition, agriculture), combined sewer overflows (CSO), sanitary sewer overflows (SSO), stormwater runoff, and hydrologic modifications (e.g., channelization and dredging).
• CSOs are untreated discharges into surface waters from older combined collection systems designed to carry both stormwater and sewage. SSOs are untreated sewage discharges from separate collection systems.¹
• Nationally, CSO discharges have decreased over time.² For example, 8.8B gal of untreated wastewater were discharged into Michigan waterways in 2021 from CSOs, down from 25B gal in 2011.¹
• Inflow and infiltration (I/I) are unintended water entries into sewer systems from surface water sources like rivers and springs and from groundwater through cracks in pipes.²
• In the U.S., 58% of river and stream miles, 40% of lake acres, 17% of estuarine square miles, and 23% of Great Lakes shoreline miles assessed by the U.S. EPA have excess nutrients.⁴ These can come from agriculture, urban runoff, and wastewater treatment and cause water quality problems, such as algal blooms and fish kills.⁴
• Around 16% of households are not served by public sewers and depend on septic systems to treat wastewater.⁵ These systems discharge more than 4B gal of wastewater per day below the ground’s surface.⁶  Failing septic systems may contaminate surface and groundwater.⁷ 

Municipal Wastewater Tranport³

Image

Treatment of Municipal Wastewater

• A common form of wastewater treatment is activated sludge, an aerobic process that exposes microbes to oxygen within the treatment cascade to break down organic waste.⁸
• Almost 15,000 POTWs treat and discharge over 34B gal/d of wastewater into U.S. waterways.^9,10 1.3M mi of piping flow toward POTWs provide wastewater collection, treatment, and disposal service to more than 238M people.⁹
• Use of reclaimed water for consumption is becoming more common, particularly in regions prone to drought or with growing water demand (such as the U.S. southwest).¹¹
• POTWs generate over 13.8M ton (dry weight) of sludge (biosolids) annually.¹⁰ Sludge treatment accounts for one-third of electricity use by POTWs.¹²
• In the U.S., chlorination is the most common means of disinfection. Chlorination may be followed by dechlorination to avoid impacting ecological health of the receiving stream and the production of carcinogenic by-products.¹³ Ultraviolet (UV) disinfection is an alternative to chlorination that does not add chemicals to the water; this method can have higher maintenance, energy and capital costs.¹⁴
• Classes of unregulated compounds known as “contaminants of emerging concern” (CECs) are found in products such as pharmaceuticals and personal care products.¹⁶ Per- and polyfluoroalkyl substances (PFAS) and polybrominated diphenyl ethers (PBDEs) have become CECs due to their wide distribution and persistence in the environment.¹⁷ Some of these chemicals are endocrine disruptors and affect growth and reproduction.¹⁸ Many of these chemicals are not removed by POTWs.¹⁹ Researchers are currently studying technologies for removing PFAS from drinking and wastewater.²⁰

Wastewater Treatment Process¹⁵

Image

Biosolids End-of-Life

• Biosolids is nutrient-rich treated sludge that results from POTW treatment of municipal wastewater.²¹
• U.S. management practices result in 54% of biosolids being applied to agricultural sites, with minor amounts applied to forests, reclamation sites (e.g., Superfund & brownfield lands)  and urban areas.²²

Life Cycle Impacts

Wastewater treatment systems reduce environmental impacts in the receiving water, but create other life cycle impacts, mainly through energy use. GHG emissions are associated with both energy and chemicals used in wastewater treatment and the degradation of organic materials in the POTW. 

Electricity Consumption and Emissions

• About 2% of U.S. electricity use goes towards pumping and treating water and wastewater.¹²
• In 2022, energy-related emissions resulting from POTW operations, excluding organic sludge degradation, were 11.3 Tg CO₂e, 6.48 Gg SO₂, and 6.904 Gg NOx.^12,24
• In 2022, an estimated 20.8 and 21.9M Mt CO₂e of CH₄ and N₂O, respectively, resulted from wastewater treatment processes, about 0.7% of U.S. GHG emissions.²⁵

Social and Economic Impacts

• In the U.S., an average single family household pays around $500 annually for wastewater collection and treatment.²⁶
• Although the lifetime of a sewer system (50 years) is longer than that of treatment equipment (15 to 20 years), renovation needs of a sewer system can be more costly. An EPA analysis estimated that, without renovating 600,000 miles of existing sewer systems, deteriorated pipes would make up 44% of the total network by 2020.²⁷
• U.S. costs for building new and updating existing wastewater treatment plants, pipe repair and new pipes, and combined sewer overflow corrections totalled around $250B in 2012.⁹
• The federal government’s share of capital investment in wastewater from 1977 to 2017 fell from 63% to 9%.²⁶

Solutions and Sustainable Actions

Administrative Strategy

• Investment in wastewater treatment systems is shifting from new construction to maintenance of original capacity and function (asset management). Life cycle costing should be embedded in capital budgeting, and programs for CSO, SSO, and stormwater asset management need to be permanent.²⁸
• To  meet ambient water quality standards, total maximum daily loads (TMDLs) including both point and non-point source pollutant loadings can be developed.²⁹
• Federal and state governments have developed strategies to effectively remove emerging pollutants, such as PFAS, from point sources. By requiring POTWs & industries to sample for emerging pollutants, sources can be identified and corrected.³ 

Reduce Loading

• Projects to reduce or divert wastewater flow include disconnecting household rainwater drainage from sanitary sewers, installing green roofs, and replacing impervious surfaces with porous pavement, swales, or French drains. 

• Toilets, showers, and faucets represent 64% of all indoor water use. Install high-efficiency toilets, composting toilets, low-flow shower heads, faucet aerators, and rain barrels.³⁰ Efficient appliances have contributed to a 22% decline in household water use since 1999.³¹

Technology Improvements and System Design

• Aeration, which facilitates microbial degradation of organic matter, can account for 25% to 60% of the energy use in wastewater treatment plants. Flexible designs allow the system to meet oxygen demands as they fluctuate with time of day and season.³² Pumping systems use 10-15% of the energy at wastewater treatment plants, and can be made more efficient when pumps, flow control, and motors are mismatched to treatment plant needs.¹²
• A number of treatment plants are using methane generated from anaerobic digestion of biosolids as an energy resource.¹² 
• Water reuse can significantly decrease system energy use and reduce nutrient loads to receiving waters.³³
• Large-scale urine diversion could decrease nutrient loading in wastewater treatment plants and lead to reductions of up to 47% in GHG emissions and 41% in energy use.^34,35

Great Lakes Water Authority (Detroit POTW)³⁶

Image