How Do ETPs and STPs Address Emerging Contaminants in Wastewater?
Modern wastewater treatment plants face a complex challenge - removing both conventional pollutants as well as thousands of unregulated “emerging” contaminants that find their way into sewage and industrial effluent. These compounds originate from pharmaceuticals, personal care products, pesticides, industrial chemicals, and other sources. Even at low concentrations, their cumulative effects raise ecological and health concerns. As these novel pollutants continue to emerge, effluent treatment plants (ETPs) and sewage treatment plants (STPs) must adapt to address them before wastewater is discharged back into the environment.
The Increasing Problem of Emerging Contaminants
Arising toxins envelop a wide scope of manufactured or normally happening synthetics that are not at present managed or usually checked in wastewater treatment. This incorporates drugs (solution and non-prescription medications), chemicals, sunscreens, aromas, cleansers, fire retardants, pesticides, plasticizers, and various modern synthetics and side-effects.
Trace amounts of these compounds enter wastewater through human waste, bathing, laundry, medical facilities, urban runoff, and industrial processes. Many are not effectively removed by conventional primary and secondary wastewater treatment methods originally designed to eliminate organic matter, solids, and nutrients like nitrogen and phosphorus. Ongoing discharge of these bioactive substances into surface waters raises concerns about chronic toxicity and ecological harm, even at very low concentrations.
Checking concentrates by the U.S. Ecological Assurance Organization (EPA) and different offices have identified many arising foreign substances in treated wastewater profluent, including antidepressants, anti-toxins, manufactured chemicals, sanitizers, plasticizers, and pesticides. Their presence also raises potential human health risks when contaminants re-enter drinking water supplies or accumulate in recreational waters and fish tissue. Developing solutions to address this new class of pollutants is a priority for ETPs and STPs.
Primary Treatment Methods
Preliminary treatment steps at ETPs and STPs include screens, sedimentation tanks, and clarifiers which help remove some solids, trace metals, and particulate-bound contaminants through physical separation and settling processes. However, many emerging contaminants remain dissolved in the effluent.
Adding chemically enhanced primary treatment using iron salts or aluminum salts boosts particulate removal through coagulation and flocculation. But removal rates for most emerging contaminants are still rather low at this stage, although useful for some pesticides, phthalate plasticizers, parabens, and fragrances associated with solids.
Secondary Biological Treatment
The secondary stage utilizes microbial digestion and biological processes to eliminate organics and nutrients. Methods like activated sludge processing and trickling filters reduce certain emerging contaminants that can be partially broken down and metabolized by bacteria and other microbes.
However, biological treatment is less effective for recalcitrant compounds including some pharmaceuticals, muscle relaxants, pesticides, flame retardants, and artificial sweeteners that resist biodegradation. Overall removal capacity for most trace emerging contaminants by conventional primary and secondary methods is limited, necessitating tertiary treatment upgrades at many ETPs and STPs.
Advanced Tertiary Treatment Technologies
To deal with emerging contaminants in wastewater, modern facilities are increasingly implementing advanced tertiary treatment trains with technologies such as:
- Ozonation: Ozone oxidation effectively breaks down pharmaceuticals, pesticides, surfactants, dyes, and many other compounds. However, optimal ozone dosing is needed to avoid unintended byproducts.
- Granular Activated Carbon (GAC) Filters: GAC absorption effectively removes hormone drugs, pharmaceuticals, pesticides, and semivolatile compounds through adsorption. Periodic GAC replacement is required.
- Powdered Activated Carbon: Enhances removal of trace organics when added directly to treatment processes.
- Reverse Osmosis: Makes use of semipermeable membranes to filter out dissolved pharmaceuticals, hormones, metals, and salts.
- Advanced Oxidation Processes: Hydroxyl radicals help mineralize recalcitrant organics. Options include UV, ozone/hydrogen peroxide, and photocatalytic oxidation.
- Constructed Wetlands: Natural substrate, vegetation, and microbial communities provideadditional polishing to break down contaminants.
- Microfiltration/Ultrafiltration: Small pore membranes filter out bacteria and particulates down to 25-100 nanometers.
- Nanofiltration/Reverse Osmosis: Removing contaminants above 150-300 daltons including pharmaceuticals and pesticides.
These can be combined into hybrid systems to leverage advantages of multiple methods. Upgrading ETPs and STPs with one or more advanced tertiary technologies significantly boosts emerging contaminant removal prior to final disinfection and discharge. However, energy, infrastructure costs, and waste disposal requirements need consideration.
Future Solutions and Prospects
Promising future techniques for removing trace emerging pollutants include alternative adsorbent materials, biosorption, enzymatic degradation, electrochemical oxidation, and magnetic nanoparticle separation. Bioaugmentation with specialized treatment bacteria, algae, or fungi offers another approach.
Online sensors and AI-powered predictive analytics to dynamically model and optimize treatment performance are other innovations. As new compounds are identified through expanded monitoring and detection, treatment options can be adapted. Designing smarter “one-stop” modular systems that integrate targeted removal of specific contaminants groups is another goal.
The challenges are complex, but so are the emerging solutions. With expanded regulations, monitoring, research, and advanced treatment upgrades, ETPs and STPs can cost-effectively combat the issue of trace emerging contaminants. This will further improve effluent quality and environmental protection as wastewater treatment continues evolving in the 21st century.