Water Filtration and Greywater Treatment: From Basic Principles to Advanced Solutions for PFAS/PFOS and Emerging Contaminants
- Earth & Clay
- 1 day ago
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Water filtration is essential for safe drinking water, industrial processes, and sustainable greywater reuse. Greywater, which comes from sinks, showers, and laundry, contains suspended solids, microorganisms, organic matter, and chemical contaminants. Proper filtration ensures water can be safely reused for irrigation, toilet flushing, or industrial applications, while protecting human health and the environment.
This article provides an overview of general water filtration methods, the challenges of PFAS/PFOS removal, and the role of specialty minerals like diatomaceous earth (DE) and attapulgite clay in enhancing both potable water and greywater treatment systems.
Basic Principles of Water Filtration
Water filtration involves physically, chemically, or biologically removing contaminants. Key methods include:
Mechanical Filtration: Removes suspended solids and particles through sand, ceramic, or DE filters.
Adsorption Filtration: Uses media like activated carbon, zeolites, or resins to bind organic chemicals, metals, and odours.
Membrane Filtration: High-pressure membranes (nanofiltration, reverse osmosis) remove dissolved ions, PFAS/PFOS, and fine particulates.
Coagulation and Flocculation: Mineral or chemical additives, like attapulgite clay, aggregate fine particles for easier removal.
Filtration systems often combine multiple methods in multi-stage setups to remove both physical and chemical contaminants effectively.
Greywater and Emerging Contaminants: PFAS and PFOS
Greywater can contain emerging contaminants including per- and polyfluoroalkyl substances (PFAS), such as PFOA and PFOS. These chemicals are highly resistant to degradation and persist in water systems, posing human health and environmental risks.
“Because of the chemical properties of PFAS, traditional water treatment technologies are not able to remove them. Certain technologies have been found to remove PFAS from drinking water, especially perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). Those technologies include activated carbon adsorption, ion exchange resins, and high‑pressure membranes. High‑pressure membrane systems (e.g., reverse osmosis) have been extremely effective at removing PFAS, typically more than 90 percent effective at removing a wide range of PFAS, including shorter‑chain PFAS.” — U.S. EPA, Reducing PFAS in Drinking Water
Implication: Conventional greywater filters, such as sand or ceramic systems, are insufficient for PFAS/PFOS removal. Advanced adsorption or membrane systems are necessary for safe reuse.
Advanced Filtration Technologies for Water and Greywater
1. Adsorption-Based Filtration
Utilizes activated carbon, ion exchange resins, zeolites, or engineered materials.
Removes PFAS, organic chemicals, and some metals.
“Adsorption technology utilizes adsorbents to attract PFAS, concentrating them on the surface of the adsorbents and thus reducing their concentration in water. Materials such as activated carbon, ion exchange resins, zeolites, and graphene have demonstrated excellent capabilities for removing PFAS from wastewater.” — MDPI, Water Journal
2. Membrane Filtration
Nanofiltration (NF) and reverse osmosis (RO) membranes remove dissolved ions, PFAS, and micro-particles.
Bench-scale studies show variable removal efficiencies depending on compound and system design.
“In bench‑scale membrane filtration experiments with NF membranes, average rejection varied between 71 and 80% for PFOA and between 42 and 80% for PFOS in spiked water samples.” — Springer, Environmental Science & Pollution Research
3. Emerging and Hybrid Technologies
Novel adsorbents, nanoparticles, metal-organic frameworks, and plasma-based methods are being researched for rapid PFAS removal and degradation.
“Recent research has focused on novel materials and hybrid systems, including engineered adsorbents (e.g., magnetic nanoparticles, metal-organic frameworks) and plasma-based technologies, that show promise for rapid and efficient PFAS removal and degradation, though real-world implementation at scale remains under investigation.” — ACS Publications, Advanced PFAS Remediation
Specialty Minerals in Water and Greywater Filtration
Certain minerals enhance filtration by improving particle removal, turbidity reduction, and chemical adsorption.
1️⃣ Diatomaceous Earth (DE)
How it works:
Composed of fossilized silica shells (diatoms) with high porosity.
Acts as a mechanical filter, trapping fine particles, bacteria, and suspended solids.
Adsorbs some organic compounds due to high surface area.
Common applications:
Application | Type of Filtration | Notes |
Swimming pools | Gravity or pressure DE filters | Captures particles ~1–3 microns |
Food & beverage | Beer, wine, juices | Filter aid; clarifies liquids without affecting taste |
Industrial water | Oil, chemicals, wastewater | Removes fine suspended solids |
Key advantages:
Fine filtration (1–5 microns)
Chemically inert and safe for potable water
Forms a porous cake that can be backwashed
Limitations:
Messy; requires pressure/vacuum systems
Dust inhalation hazard
Rarely used in home filter cartridges
2️⃣ Attapulgite Clay
How it works:
Fibrous magnesium-aluminum silicate clay
Functions as adsorbent and coagulant aid
Binds oils, suspended solids, and heavy metals
Common applications:
Application | Function |
Industrial wastewater | Adsorption of oils, greases, and metals |
Drinking water / municipal | Coagulant aid/flocculant |
Pool / aquaculture | Sediment/algae control |
Key advantages:
High adsorption capacity
Improves turbidity removal with other media
Limitations:
Does not filter to micron scale
Usually supplemental to other filtration systems
3️⃣ Comparison Table
Feature | DE | Attapulgite |
Filtration type | Mechanical / particle removal | Adsorption / flocculation |
Particle size captured | 1–5 microns | >5 microns; binds pollutants |
Primary use | Pools, beverages, industrial water | Industrial wastewater, oil/chemical absorption |
Regeneration | Yes (backwashable) | Limited; usually disposed |
Safety | Safe if wetted; dusty DE inhalation hazard | Generally safe; dust caution |
4️⃣ Bottom Line
DE excels at fine particulate removal in industrial and large-scale water treatment.
Attapulgite clay is ideal for chemical adsorption and sediment control.
For home-scale filtration, ceramic, activated carbon, or resin media dominate; DE and attapulgite are supplementary.
Integrating Filtration for Greywater Systems
PFAS/PFOS removal requires advanced adsorption or membrane systems.
DE and attapulgite enhance turbidity, particle, and chemical removal, improving downstream efficiency.
Multi-stage filtration combining ceramic, activated carbon, membranes, and specialty minerals ensures safe greywater reuse.
Summary: Relying solely on sand or ceramic filters is insufficient for PFAS/PFOS removal. Integrating specialty minerals and advanced technologies is essential for safe greywater treatment.
Conclusion
Water filtration, including greywater treatment, is vital for safe reuse and environmental sustainability. While PFAS/PFOS present emerging challenges, combining mechanical, adsorption, and membrane technologies, supplemented by specialty minerals like DE and attapulgite clay, provides comprehensive water treatment solutions.
Properly designed multi-stage systems ensure safe, reliable water for households, industry, and irrigation, supporting public health and sustainable water management.
References
U.S. EPA. Reducing PFAS in Drinking Water: Treatment Technologies. https://www.epa.gov/sciencematters/reducing-pfas-drinking-water-treatment-technologies
MDPI, Water Journal. Adsorption techniques for PFAS removal. https://www.mdpi.com/2073-4441/17/9/1319
Springer, Environmental Science & Pollution Research. Bench-scale NF membrane experiments for PFAS removal. https://link.springer.com/article/10.1007/s41742-025-00996-0
ACS Publications, Advanced PFAS Remediation Technologies. https://pubs.acs.org/doi/10.1021/acs.est.1c03974
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