How do STP Plants Handle Emerging Contaminants?
Municipal sewage treatment facilities are designed and operated to remove conventional contaminants like organic matter, solids, nutrients, and pathogens from wastewater before discharging into receiving waters. However, over the past few decades, numerous previously unmonitored synthetic chemicals have been detected in wastewater influent, effluent, and biosolids. These "emerging contaminants" pose challenges for conventional sewage treatment, given their diversity of sources and potential impacts.
We are going to discuss how sewage treatment plants handle emerging contaminants. So, let’s get going...
What are Emerging Contaminants?
Emerging contaminants encompass a broad range of compounds found in waste streams that conventional treatment methods were not necessarily designed to remove, including:
• Pharmaceuticals - prescription drugs, over-the-counter medications
• Personal Care Products - soaps, disinfectants, sunscreen agents
• Endocrine Disruptors - hormones, plasticisers, flame retardants
• Microplastics - fibers and microbeads from clothes, products
• Nanoparticles - engineered particles from electronics, cosmetics
• PFAS compounds - highly fluorinated industrial compounds
• Illicit Drugs and Metabolites - cocaine, methamphetamine, etc.
Many of these compounds are not effectively removed during primary and secondary biological treatment. Some are persistent, bypassing treatment entirely, while others transform into new byproducts.
Sources and Pathways into Wastewater
Emerging contaminants originate from diverse residential, commercial and industrial sources:
• Excretion of drugs and hormones via human waste
• Disposal of pharmaceuticals into drains, toilets
• Washing of products down drains containing compounds
• Discharge from hospitals, healthcare facilities
• Runoff from agriculture containing residual veterinary pharmaceuticals
• Industrial effluents containing processing chemicals, coolants, lubricants
• Leaching from landfillsites into groundwater
Once entering sewers, contaminants may volatilise, adsorb onto solids, transform through biotransformation, photolysis or undergo further reactions.
Treatment Challenges & Approaches
Most sewage treatment plants employ multi-stage processes originally designed to remove conventional contaminants. Their ability to reduce loadings of emerging contaminants varies:
Conventional Treatment Limitations
• Activated sludge systems exhibit poor removal of many hydrophilic, non-volatile compounds
• Certain pharmaceuticals, antibiotics are primarily discharged in effluent
• Other compounds like flame retardants, microplastics primarily partition into biosolids
Treatment Process Modifications
• Increasing solids retention times (SRTs) in activated sludge enhances biodegradation
• Membrane bioreactors combining activated sludge with ultrafiltration improve removal
• Employing anaerobic digesters helps degrade certain recalcitrant organics in biosolids
Advanced Treatment Solutions
• Reverse osmosis (RO) and nanofiltration effectively reject most compounds
• Advanced oxidation processes like ozone/UV degrade many trace organics
• Activated carbon adsorption with GAC/PAC captures a wide range of contaminants
• Ion exchange resins can remove ionisable compounds like perfluorinated acids
Few plants currently employ advanced treatment given costs, though discharge limits could drive adoption.
Biosolids Management Impacts
With many compounds tending to concentrate in sewage sludges during treatment processes, biosolids management policies are impacted:
Land Application Limitations
• Strict limits enacted in many states/countries on PFAS, microplastics in biosolids
• Application rates controlled to limit loadings of pharmaceuticals, EDCs to soil
Thermal Destruction
• Extreme heat in incineration helps degrade organics
• But incomplete combustion can produce dioxins, furans as byproducts
Enhancing treatment processes and product quality standards for land-applied biosolids continues to be an area of scrutiny.
Environmental & Health Concerns
While the field is still emerging, research indicates several potential concerns over emerging contaminants in wastewater:
• Endocrine disruption in aquatic species and wildlife from hormones, phenolics
• Antimicrobial resistance promotion from antibiotic residues discharged
• PFAS bioaccumulation potential in organisms posing exposure risks
• Ecotoxicity impacts to plants and organisms, though variable
• Limited human health risk assessment data requires more monitoring
Even at low, part-per-trillion concentrations, continual discharge and environmental persistence raises concerns.
Industry Best Practices
With the diversity of potential emerging contaminants, treatment facilities employ the following practices:
Source Control
• Establishing proper medication disposal programs
• Pretreatment standards and monitoring for industrial dischargers
• Public education to avoid flushing/washing products down drains
Optimising Treatment
• Extending SRTs to promote biodegradation of soluble contaminants
• Testing to verify contaminant removal for existing treatment trains
• Considering future-proofing designs for advanced treatment additions
Residuals Management
• Screening biosolids for contaminants before land applications
• Installing treatment upgrades like thermal hydrolysis, drying, air curtain destruction
Toxicity and Environmental Monitoring
• Evaluating effluent and biosolids using bioassays cell tests for toxicity
• Monitoring environmental media like groundwater, surface waters, soils
• Participation in academic industry research studies
With treatment performance data still limited, proactive monitoring, studying process modifications, and planning for upgrades remain prudent strategies.
Conclusion
Municipal sewage treatment operations face an evolving challenge with the increase of emerging contaminants entering waste streams from diverse sources. From pharmaceuticals and personal care products to microplastics and PFAS, these compounds are not effectively removed by conventional treatment. Discharge and biosolids regulations are still developing but are expected to become stricter, driven by environmental monitoring, aquatic toxicity studies, and public health concerns. While optimised conventional treatment offers partial solutions like longer SRTs and membrane bioreactors, more advanced processes like ozonation, activated carbon, and reverse osmosis will likely be needed.
To explore customised commercial RO plants, Industrial RO plants, ETP or STP solutions for your needs in your areas and nearby regions, contact Netsol Water at:
Phone: +91-965-060-8473, Email: enquiry@netsolwater.com
