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Views: 222 Author: Carie Publish Time: 2025-05-28 Origin: Site
Content Menu
● Overview of Sewage Treatment Processes
>> 1. Pharmaceuticals and Personal Care Products (PPCPs)
>> 2. Polyfluoroalkyl Substances (PFAS)
>> 5. Persistent Organic Pollutants (POPs)
● Are These Pollutants Difficult to Remove?
>> Activated Carbon Adsorption
>> Advanced Oxidation Processes (AOPs)
>> Biological Treatments with Specialized Microbes
● FAQ
>> 1. What are pharmaceuticals and personal care products (PPCPs) in wastewater?
>> 2. Why are PFAS so hard to remove in sewage treatment?
>> 3. Can heavy metals be completely removed by wastewater treatment?
>> 4. What health risks do trihalomethanes (THMs) pose?
>> 5. Are there any treatment technologies that can remove these persistent pollutants?
Water pollution is a critical environmental issue worldwide. Sewage treatment plants are designed to remove a variety of contaminants from wastewater before it is discharged back into the environment or reused. However, not all pollutants can be effectively removed by standard sewage treatment processes. This article explores the key water pollutants that persist despite treatment, the reasons behind their resilience, and the implications for ecosystems and human health.
Sewage treatment typically involves several stages:
- Preliminary treatment: Removal of large solids and debris.
- Primary treatment: Sedimentation to remove suspended solids.
- Secondary treatment: Biological processes to degrade organic matter and nutrients.
- Tertiary treatment: Advanced filtration and chemical processes to reduce nutrients and pathogens.
Despite these comprehensive steps, certain pollutants evade complete removal due to their chemical nature or persistence.
Pharmaceuticals and personal care products include prescription drugs, over-the-counter medications, shampoos, lotions, and antibacterial soaps. These substances enter wastewater primarily through human excretion and disposal.
- Why they persist: Many PPCPs have complex chemical structures that are not fully broken down by conventional biological treatment processes. For example, antibiotics, hormones, and antidepressants are designed to be biologically active and stable, which makes them resistant to microbial degradation.
- Environmental impact: Trace amounts of antibiotics and synthetic hormones can disrupt aquatic ecosystems by affecting reproduction and development in wildlife. There is also a growing concern about antibiotic resistance due to continuous low-level exposure.
PFAS are a group of synthetic chemicals used in products like firefighting foams, non-stick cookware, and waterproof fabrics.
- Why they persist: PFAS are highly stable organofluorine compounds that resist degradation by conventional treatment methods. Studies show that wastewater treatment plants remove less than 25% of PFAS contamination. Their carbon-fluorine bonds are among the strongest in organic chemistry, making them extremely persistent.
- Health risks: PFAS are linked to cancer, liver and kidney damage, and developmental problems in children. Regulatory efforts are ongoing, but current treatment technologies are insufficient to eliminate these contaminants effectively.
Heavy metals such as arsenic, mercury, cadmium, and lead enter wastewater from industrial discharges and urban runoff.
- Why they persist: Although treatment processes can reduce heavy metal concentrations, complete removal is challenging, especially at low concentrations. Metals do not degrade but can be transformed between different chemical forms.
- Environmental impact: Heavy metals can accumulate in sediments and aquatic organisms, posing long-term risks to ecosystems and human health. For instance, mercury can bioaccumulate in fish, leading to toxic effects in wildlife and humans consuming contaminated fish.
THMs are byproducts formed when chlorine used for disinfection reacts with organic matter in water.
- Why they persist: THMs are chemically stable and difficult to remove once formed during the chlorination step of treatment. They are volatile and can evaporate into the air or remain dissolved in water.
- Health risks: Exposure to THMs is associated with increased cancer risk and reproductive health issues. Regulatory agencies limit their concentration in drinking water, but their presence in treated wastewater remains a concern.
POPs include pesticides, industrial chemicals, and other organic compounds that resist environmental degradation.
- Why they persist: Their chemical stability and low biodegradability make them difficult to eliminate in standard treatment plants. POPs often have hydrophobic properties, causing them to bind to sediments and organic matter.
- Environmental impact: POPs bioaccumulate in the food chain, causing toxic effects to wildlife and humans. Examples include DDT and polychlorinated biphenyls (PCBs), which have been banned but persist in the environment due to their longevity.
Several factors contribute to the difficulty in removing these pollutants:
- Chemical Stability: Many pollutants like PFAS and POPs have strong chemical bonds that resist biological and chemical breakdown. Their molecular structures are designed or evolved to be resistant to degradation.
- Dissolved State: Unlike solids, dissolved pollutants do not settle out and are not easily filtered. They remain suspended in the water phase, making physical removal challenging.
- Low Concentrations: Trace amounts are difficult to detect and remove completely. Even small concentrations can have significant ecological or health impacts.
- Treatment Design Limitations: Most plants are designed to remove organic matter, solids, nutrients, and pathogens, not emerging contaminants. The infrastructure and processes may not be optimized for micropollutants.
To address these challenges, some advanced methods are being explored or implemented:
Activated carbon can adsorb many organic micropollutants, including PPCPs and some POPs. It is often used in tertiary treatment stages.
AOPs use reactive species such as hydroxyl radicals generated by ozone, UV light, or hydrogen peroxide to break down complex chemicals into simpler, less harmful substances.
Techniques like nanofiltration and reverse osmosis physically remove dissolved pollutants by forcing water through semi-permeable membranes. These methods can remove heavy metals, PFAS, and many organic contaminants.
Research is ongoing to identify and cultivate microbes capable of degrading specific pollutants like pharmaceuticals. These biological treatments could complement existing processes.
The persistence of these pollutants in treated wastewater leads to:
- Contamination of surface and groundwater sources: Pollutants discharged into rivers and lakes can infiltrate drinking water supplies.
- Bioaccumulation in aquatic organisms: This affects biodiversity and can lead to toxic effects in fish, birds, and mammals.
- Potential human exposure: Through drinking water, recreational activities, and consumption of contaminated fish or crops irrigated with treated wastewater.
- Increased antibiotic resistance: Pharmaceutical residues create selective pressure on bacteria, promoting resistant strains that threaten public health.
While sewage treatment plants play a vital role in protecting water quality, several water pollutants such as pharmaceuticals, PFAS, heavy metals, trihalomethanes, and persistent organic pollutants remain challenging to remove completely. Addressing these contaminants requires advancements in treatment technologies, stricter regulations, and increased public awareness to prevent their release into wastewater streams. Continued research and investment are essential to safeguard environmental and human health from these elusive pollutants.
PPCPs include medications, shampoos, lotions, and other personal hygiene products that enter wastewater mainly through human excretion and disposal. They are difficult to remove due to their chemical diversity and persistence in treatment processes.
PFAS chemicals have strong carbon-fluorine bonds making them highly stable and resistant to degradation by conventional treatment methods. Most plants remove less than 25% of PFAS contamination.
Heavy metals can be reduced but not always completely removed, especially at low concentrations. Their persistence poses risks of accumulation in the environment.
THMs formed during chlorination are linked to increased cancer risk and reproductive health problems if consumed in excess.
Advanced methods like activated carbon adsorption, advanced oxidation, membrane filtration, and specialized biological treatments can improve removal but are costly and not universally implemented.
