Zeolite for Rainwater Purification Systems

Q: What does zeolite reduce in rainwater and stormwater?

Through cation exchange with a CEC of 1.6–2.0 meq/g, natural clinoptilolite selectively captures ammonium (NH₄⁺) in rainwater and stormwater, and also adsorbs some heavy-metal cations (Pb, Zn, etc.). In granular column studies, NH₄⁺ removal by natural zeolite is reported at 72–86% depending on conditions, reaching the 90% range at low velocity with sufficient bed depth. However, because the framework is negatively charged, anions such as nitrate-nitrogen (NO₃⁻) and phosphate are barely captured in the unmodified state; to capture them, an SMZ whose surface has been modified with a cationic surfactant such as HDTMA is a prerequisite. Sweeney et al. (2022) reported that zeolite-amended bioretention media improved nitrogen removal from stormwater, and rooftop rainwater filtration (Widiastuti et al., 2018) confirmed improvements in turbidity and ammonium. Because it does not replace disinfection, it is appropriate to consider it as a pretreatment and filtration-support material.

Q: Which particle size (mesh) should I use for bioretention versus a rainwater storage tank?

For bioretention and infiltration planters that must maintain permeability, blend roughly 10–30% by volume of Coarse Granule (8×14 mesh) to Medium Granule (14×40 mesh); for small-scale fine filtration downstream of a rainwater storage tank, Fine Granule (30×50 mesh) is suitable. Please refer to the application-based product selection guide.

Q: Rainfall is intermittent, so do I need to replace the media frequently?

During the dry periods between rainfall events, nitrifying microorganisms on the media surface convert the captured ammonium to nitrate, which is reported to partially regenerate the zeolite's exchange sites. However, the actual breakthrough point and the backwash/replacement cycle vary with the on-site NH₄⁺ and SS concentrations of the stormwater, so they must be confirmed by pilot testing.

Q: Can rainwater be reused as drinking or household water?

Zeolite is a pretreatment and filtration-support material that reduces nitrogen, turbidity, and the like; it does not replace disinfection or sterilization processes. If reused for human-contact purposes, you must separately verify the water-quality standards and certification requirements for that use, and design it together with a disinfection process.

Q: Can I receive test samples and certification documents?

Yes. KMIZEOLITE supports the provision of samples in 1kg–22kg units and holds certifications including OMRI Listed (KMI-10365), FDA GRAS (21 CFR 182.2729), TSCA compliance, and EN-71-3 PASS. Please check the sample request page and the certification documents page.

What Is the Problem in Rainwater Purification and Stormwater Reuse

Contrary to the common assumption that it will be "clean," rainwater collected from rooftops or stormwater running off roads and parking lots concentrates nitrogen, ammonium, suspended solids (SS), heavy metals (Pb, Zn, Cu), and organic matter in the first flush. In rooftop collection, the main load comes from atmospheric deposition and contaminants leached from roofing materials; in road stormwater, it comes from tire wear, brake dust, and vehicle oil leakage.

When such rainwater is treated by rainwater storage tanks, rainwater utilization facilities, or urban non-point-source bioretention systems, vegetated swales, and infiltration planters, simple sand and gravel filtration captures almost no dissolved nitrogen or ammonium. Because rainfall events are intermittent, flow fluctuations (rapid changes in SV) are large, and the load is concentrated at the start of rainfall, an ion-exchange medium that can hold dissolved nutrients even during short contact times is required.

Why Zeolite Is Considered as a Rainwater Medium

Based on its negatively charged microporous framework (pore diameter 4.0–7.0 Å) and high cation exchange capacity (CEC 1.6–2.0 meq/g), natural clinoptilolite selectively exchanges and retains the ammonium (NH₄⁺) in rainwater. Clinoptilolite's selectivity for NH₄⁺ tends to be higher than for Na⁺, Ca²⁺, and Mg²⁺, so it preferentially captures ammonium even in stormwater where hardness components coexist. Unlike ordinary sand filter media, which rely solely on physical straining, zeolite holds dissolved ammonium and some heavy-metal cations (Pb²⁺, Zn²⁺, Cu²⁺) at exchange sites within the framework, thereby improving non-point-source pollution-reduction efficiency. The batch ammonium equilibrium adsorption capacity of natural clinoptilolite is reported to be roughly in the 5–22 mg-N/g range; in granular column operation it is safer to design for an effective capacity lower than this, depending on the flow conditions and EBCT.

Important — distinguishing cations vs. anions: Because the framework is negatively charged, natural (unmodified) clinoptilolite acts directly only on the cation NH₄⁺, and barely adsorbs anions such as nitrate-nitrogen (NO₃⁻-N) and phosphate (total phosphorus, including PO₄³⁻), which are another key part of the stormwater load, due to electrostatic repulsion. To also capture NO₃⁻-N and TP in stormwater treatment, an SMZ (surfactant-modified zeolite) whose surface has been modified with a cationic surfactant such as hexadecyltrimethylammonium (HDTMA) is a prerequisite, and anion removal must not be explained using cation-exchange logic. A study of HDTMA-modified bioretention media (2022, Frontiers in Environmental Science, DOI: 10.3389/fenvs.2022.918259) quantitatively demonstrated an adsorption–hydraulic trade-off: modification improved NO₃⁻-N removal by up to about 38 percentage points, while increasing the amount of modification (e.g., surface HDTMA loading from 0.05 to 0.09 meq/g) also changed the media's water retention capacity (WRC) and runoff-reduction performance.

Rainwater applications in particular allow the nitrifying microorganisms on the media surface time to convert the captured ammonium to nitrate during the dry periods between rainfall events, so the zeolite acts as a "temporary ammonium reservoir" and is reported to buffer the shock load of rainfall peaks. Sweeney et al. (2022, Agricultural & Environmental Letters) reported that bioretention media amended with zeolite significantly improved nitrogen removal (especially ammonium-nitrogen) from stormwater compared with conventional media (DOI: 10.1002/ael2.20060). However, observations of phosphorus (P) leaching when only unmodified natural zeolite is used have also been reported, so for road runoff with a high phosphorus load, a modified type or the combined use of a phosphorus-adsorbing supplementary material should be considered.

KMIZEOLITE's natural clinoptilolite has a purity of 97% and is mined and processed at a mine in Amargosa Valley, Nevada, USA. With a specific surface area of 40.0 m²/g, a stable pH range of 3.0–10.0, and a hardness of 4.0–5.0 Mohs, it operates stably without particle breakdown even in rainwater that ranges from weakly acidic to neutral and under repeated flow conditions.

Rainwater-Application Evidence Confirmed by Research

Rooftop rainwater harvesting filtration: Widiastuti et al. (2018, MATEC Web of Conferences) reported that water-quality indicators such as turbidity and ammonium improved in rooftop rainwater harvesting filtration using zeolite (DOI: 10.1051/matecconf/201820403016).
Quantification of ammonium removal in granular clinoptilolite columns: Sprynskyy et al. (2008, Journal of Environmental Engineering and Landscape Management) reported, in flow experiments with Transcarpathian natural clinoptilolite granular media, 72–86% NH₄⁺ removal for 0.63 mm particles, and removal of about 96% at a 95 mm bed depth and a filtration velocity of 3 m/h for an initial influent of 10 mg/L. However, they also showed that as flow progressed, the interval meeting hygiene standards gradually shortened, requiring breakthrough management (DOI: 10.3846/1648-6897.2008.16.38-44).
Modified-zeolite bioretention (adsorption–hydraulic trade-off): A study of bioretention with zeolite surface-modified by HDTMA (2022, Frontiers in Environmental Science) quantitatively showed that NO₃⁻-N and TP removal improved while water retention and runoff reduction decreased as the amount of modification increased. In other words, where hydraulic performance is the top priority, the modification level should be set conservatively (DOI: 10.3389/fenvs.2022.918259).
Urban stormwater treatment (natural vs. modified): A study on the treatment of urban road runoff using natural and magnetite-modified zeolite (2024, Water Conservation Science and Engineering) also confirmed the cation removal of natural zeolite and the potential to expand the application range through modification (DOI: 10.1007/s41101-024-00326-z).

KMIZEOLITE Key Properties

Property	Value
Clinoptilolite purity	97%
Cation exchange capacity (CEC)	1.6–2.0 meq/g
Specific surface area	40.0 m²/g
Pore diameter	4.0–7.0 Å
Stable pH range	3.0–10.0
Hardness	4.0–5.0 Mohs
Thermal stability	700°C
Specific gravity	1.89
Bulk density	45–54 lbs/ft³
Certifications	OMRI KMI-10365, FDA GRAS, TSCA, EN-71-3

Rainwater Purification System Application Examples

Below are representative application scenarios in which zeolite is considered in the rainwater and stormwater treatment field, along with recommended operating values. Actual figures must be calibrated by pilot testing according to on-site rainfall characteristics and load.

Bioretention and infiltration-planter media blending: A method that reinforces ammonium retention by blending zeolite at roughly 10–30% by volume into sand- and planting-soil-based media. A granular form (8×14 to 14×40 mesh) is used to secure the hydraulic conductivity (Ks). If NO₃⁻-N and phosphorus must also be captured, natural zeolite alone is insufficient, so an HDTMA-modified type or the combined use of an external carbon source or phosphorus-adsorbing material should be considered.
Filling the filter layer of rainwater utilization facilities: Filling zeolite as a packed bed into the filter column/filter downstream of a rainwater storage tank to stabilize the quality of reuse water. It is typically considered within a filtration velocity (LV) of 5–15 m/h, a space velocity (SV) of 5–20 1/h, and an empty bed contact time (EBCT) ranging from a few minutes to over ten minutes. In column studies, lowering the filtration velocity to around 3 m/h and securing sufficient bed depth raised the NH₄⁺ removal rate into the 90% range, whereas a fast velocity or shallow bed depth reduced efficiency.
Rooftop rainwater harvesting pretreatment: A method that places Fine to Medium Granule behind a primary strainer to reduce the turbidity and ammonium of first-flush stormwater. Rooftop water has a lower SS and heavy-metal load than road runoff, so the cation exchange of natural zeolite is relatively effective.
Road stormwater treatment facilities (filtration-type non-point-source reduction): Filling Coarse Granule to buffer the shock load of road runoff and to distribute the load at the start of rainfall. Because road runoff carries NO₃⁻-N, phosphorus, and heavy metals together, natural zeolite alone has limitations, so modified types and multi-stage configurations are also evaluated.
Test/pilot application: A method that uses 1kg–22kg small samples to verify in advance the breakthrough point and backwash cycle at the actual NH₄⁺ and SS concentrations of on-site rainwater.

Recommended Particle Size and Product Specifications

In rainwater and stormwater treatment, the balance between permeability and adsorption surface area is key. For locations that must secure hydraulic conductivity, such as bioretention and infiltration-type facilities, Coarse Granule (8×14 mesh) or Medium Granule (14×40 mesh) is suitable, while Fine Granule (30×50 mesh) is suitable for small-scale fine filtration downstream of a rainwater storage tank. Refer to the table below to select the product family that matches your facility type.

Product Family	Mesh	Particle Size	Typical Use
Powder	100 mesh or finer	<150μm	Pozzolan, feed, powder adsorption
Fine Granule	30×50 mesh	0.3–0.6mm	Water treatment, filtration, soil
Medium Granule	14×40 mesh	0.4–1.4mm	Filter layers, bedding, litter
Coarse Granule	8×14 mesh	1.4–2.4mm	Swimming pools, de-icing, large filtration
Extra Coarse	4×8 mesh	2.4–4.8mm	Packed beds, air scrubbers

→ View products by mesh size · Application-based product selection guide

Pilot Test and On-Site Review Points

When applying zeolite to rainwater and stormwater treatment, the following items must be confirmed together, taking into account the intermittency of rainfall and the concentration of the first-flush load.

First-flush load analysis: Analyze the ammonia-nitrogen, total nitrogen, SS, turbidity, heavy metals (Pb, Zn), and pH of first-flush stormwater. Rooftop water and road runoff have very different contamination profiles.
Hydraulic design: Calculate the peak flow according to the design rainfall intensity, the filtration velocity (LV) and space velocity (SV), the hydraulic conductivity, and the retention time. For bioretention, maintaining permeability may take priority over nitrogen removal.
Breakthrough and regeneration management: Predict the breakthrough point of the ammonium exchange sites, and determine whether on-site regeneration occurs via nitrification during inter-rainfall dry periods as well as the backwash/replacement cycle.
Maintenance: Review pretreatment (strainer/grit chamber) design to guard against surface clogging by fallen leaves and fine soil, and the replacement ratio relative to sand media.
Regulatory verification: Establish the installation-reporting criteria for non-point-source reduction facilities, the water-quality standards for reuse water from rainwater utilization facilities, and a treated-water monitoring plan.
Field-specific considerations: If reused rainwater is used for human-contact purposes such as drinking or washing, be sure to separately verify the water-quality and certification standards for that use, and design on the premise that zeolite is a pretreatment and filtration-support material that does not replace the disinfection process.

→ Check the TDS (Technical Data Sheet) · Check the MSDS (Safety Data Sheet)

Rainwater Purification FAQ

What does zeolite reduce in rainwater and stormwater?

Through cation exchange with a CEC of 1.6–2.0 meq/g, natural clinoptilolite selectively captures ammonium (NH₄⁺) in rainwater and stormwater, and also adsorbs some heavy-metal cations (Pb, Zn, etc.). In granular column studies, NH₄⁺ removal by natural zeolite is reported at 72–86% depending on conditions, reaching the 90% range at low velocity with sufficient bed depth. However, because the framework is negatively charged, anions such as nitrate-nitrogen (NO₃⁻) and phosphate are barely captured in the unmodified state; to capture them, an SMZ whose surface has been modified with a cationic surfactant such as HDTMA is a prerequisite. Sweeney et al. (2022) reported that zeolite-amended bioretention media improved nitrogen removal from stormwater, and rooftop rainwater filtration (Widiastuti et al., 2018) also confirmed improvements in turbidity and ammonium. Because it does not replace disinfection, it is appropriate to consider it as a pretreatment and filtration-support material.

Which particle size (mesh) should I use for bioretention versus a rainwater storage tank?

For bioretention and infiltration planters that must maintain permeability, blend roughly 10–30% by volume of Coarse Granule (8×14 mesh) to Medium Granule (14×40 mesh); for small-scale fine filtration downstream of a rainwater storage tank, Fine Granule (30×50 mesh) is suitable. Please refer to the application-based product selection guide.

Rainfall is intermittent, so do I need to replace the media frequently?

During the dry periods between rainfall events, nitrifying microorganisms on the media surface convert the captured ammonium to nitrate, which is reported to partially regenerate the zeolite's exchange sites. However, the actual breakthrough point and the backwash/replacement cycle vary with the on-site NH₄⁺ and SS concentrations of the stormwater, so they must be confirmed by pilot testing.

Can rainwater be reused as drinking or household water?

Zeolite is a pretreatment and filtration-support material that reduces nitrogen, turbidity, and the like; it does not replace disinfection or sterilization processes. If reused for human-contact purposes, you must separately verify the water-quality standards and certification requirements for that use, and design it together with a disinfection process.

Can I receive test samples and certification documents?

Yes. KMIZEOLITE supports the provision of samples in 1kg–22kg units and holds certifications including OMRI Listed (KMI-10365), FDA GRAS (21 CFR 182.2729), TSCA compliance, and EN-71-3 PASS. Please check the sample request page and the certification documents page.

Inquiries and Sample Requests

If you are considering applying zeolite to the field of zeolite for rainwater purification systems, please contact us through the channels below.

Notice

Whether the application is suitable may vary depending on site conditions, regulations, and test results. Before actual application, a test review tailored to the site conditions must always be carried out first. Zeolite is best understood not as an all-purpose solution for this field, but as a material that supports existing processes.