Activated carbon filters, ion-exchange resins, and constructed wetlands each target a different slice of agricultural runoff. Picking the right one depends on what’s in the water — and how clean it has to be.
Fertilized fields don’t just grow crops — they leak dissolved contaminants. Nutrient ions like nitrate‑N, ammonium, and phosphate, plus trace organics such as pesticides and herbicides, routinely show up in drainage and tile flows. Indonesian health standards cap nitrate in drinking water at 50 mg/L NO₃ (Permenkes 90/2002), yet fertilized field drainage routinely exceeds this limit (researchgate.net).
There isn’t a one-size-fits-all fix. Three proven approaches — activated carbon filtration, ion exchange, and constructed wetlands — come with distinct strengths for specific contaminants (pmc.ncbi.nlm.nih.gov; researchgate.net).
Activated carbon adsorption (AC)
Activated carbon (AC) adsorption binds dissolved organics onto high‑surface‑area carbon media. It is the “most efficient and … widely used” method for pesticides and similar micropollutants (pmc.ncbi.nlm.nih.gov). In a field trial, a biochar (a carbon medium) filter treating runoff from 437 ha of farmland reduced pesticide concentrations by >99% initially and remained ≥50% effective even after 34 weeks of continuous use (pmc.ncbi.nlm.nih.gov).
Smaller granular activated carbon (GAC) units have also cut organophosphates and pyrethroids by 98–99% in irrigation runoff (pmc.ncbi.nlm.nih.gov). Even trace pesticide levels of ~0.4 μg/L were reduced below 0.1 μg/L in pilot GAC filters (pmc.ncbi.nlm.nih.gov). These systems polish hydrophobic/adsorbable pollutants (herbicides, hormones, and similar compounds) down to sub‑ppm levels. Typical configurations use granular carbon beds following sediment pretreatment, and they are widely applied in drinking‑water plants and increasingly in agricultural runoff applications.
Trade‑offs matter: AC excels on diverse organics but has limited impact on strongly soluble ions such as nitrates; it also requires media replacement or regeneration. For engineered deployments, growers commonly specify dedicated carbon media such as activated‑carbon units to achieve pesticide polishing performance consistent with the >98–99% removals reported in field trials (pmc.ncbi.nlm.nih.gov).
Ion‑exchange resins (IX) for ionic pollutants
Ion exchange (IX) swaps targeted ions in water with ions bound to a solid resin. Strong‑base anion resins (quaternary amines) remove nitrate (NO₃⁻) and perchlorate, while cation resins capture metal cations and ammonium (NH₄⁺). Benchwork has shown nitrate uptake up to ~445 mg NO₃‑N per gram of resin at high influent loads (1000 mg/L) (researchgate.net).
In continuous operation, a 6 L anion‑resin column (600 L/d) treating wetland effluent averaged ~70% NO₃‑N reduction over 29 days (researchgate.net). Properly managed IX can lower nitrates to near‑zero until breakthrough, after which resins are typically regenerated with a sodium‑chloride (NaCl) brine. The approach is compact and established (akin to water softeners), but it requires prefiltration, chemical regenerants, and brine disposal.
Where nitrate standards are stringent — for example, targets of <50 mg/L — IX is often recommended in high‑nitrate regions or as polishing after biological treatment in wetlands (researchgate.net). System designers typically pair packaged IX systems such as Ion‑Exchange skids with appropriately selected media like ion‑exchange resins to target NO₃⁻ and NH₄⁺ selectively.
Constructed wetlands for nutrients and organics
Constructed wetlands are shallow, vegetated basins where plants and microbes remove pollutants. Nitrogen is reduced through plant uptake and microbial nitrification/denitrification (conversion of ammonia to nitrate and then to nitrogen gas by bacteria), while phosphorus is partly taken up by biomass and partly adsorbed to sediments. In a rice‑paddy wetland planted with water spinach, field data showed ~54% NH₄‑N removal, ~43% NO₃‑N removal, and ~36% total phosphorus removal over a crop season (mdpi.com; mdpi.com).
Unaided wetlands typically remove on the order of 30–60% of incoming nitrogen and 20–40% of phosphorus. Engineered substrates can lift those numbers: zeolite‑amended wetlands have reported ~80–92% total N removal and ~70% P removal, while brick/fly‑ash media achieved 89% NH₄‑N and 81% total P removal (mdpi.com; mdpi.com). Wetlands also pare down dissolved organics, reducing BOD/COD (biochemical/chemical oxygen demand, general measures of organic load) by ~70–95%, and remove some metals and pathogens.
They are low‑energy and confer ecosystem benefits, but they need land and adequate detention; in practice, space can be 5–20% of the drained area to achieve major nutrient removal. Performance is sustained in warm/tropical climates, where year‑round plant growth (as in Indonesia) supports ongoing nutrient uptake (mdpi.com).
Selection criteria and decision framework
- Pollutant type: Use ion exchange for ionic pollutants (nitrate, ammonium, arsenic) and activated carbon for organic micropollutants (pesticides, herbicides) (pmc.ncbi.nlm.nih.gov; researchgate.net). Highly soluble neonicotinoid insecticides have passed through simple ditch systems untreated, indicating the need for AC filtration (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov). Use wetlands for broad nutrient removal (N and P) when multiple species co‑occur.
- Regulatory targets: Match treatment to required quality. If drinking‑water limits apply (e.g., NO₃‑N≤50 mg/L, citing the 50 mg/L NO₃ cap in Permenkes 90/2002; researchgate.net), single wetlands often leave NO₃ above safe levels (e.g., 54% removal could still leave ~25–75 mg/L from a 50–150 mg/L influent; mdpi.com). A polishing stage is needed — for instance, following a wetland or VTS with anion‑exchange, where pilot units removed an additional ~70% of NO₃ (researchgate.net). AC polishing is similarly used when pesticide MCLs are strict; AC units can cut targets from sub‑μg/L to near‑zero (>98% in field trials; pmc.ncbi.nlm.nih.gov).
- Flow and scale: At low‑to‑moderate flow rates with high contaminant loads (e.g., concentrated tile drainage), engineered systems (AC, IX columns) are practical. For large diffuse flows, wetlands are more economical. As a benchmark, a pilot eliminating 70% of NO₃ from 2.3 m³/day via a 6 L resin suggests very high flows would necessitate very large resin volumes (mdpi.com).
- Space and climate: Limited land favors compact systems (AC or IX). With ample land and warm climates, wetlands — including floating or vegetated variants — offer passive operation. Wetlands need minimal O&M; AC/IX require routine media checks. In Indonesia’s year‑round growing season, wetland plants continually remove nutrients.
- Costs and maintenance: Wetlands have low O&M costs (mainly vegetation management) but high upfront land and excavation demands. AC/IX systems entail higher recurring costs (media replacement, regenerant chemicals). Cost‑effectiveness studies show nutrient removal via wetlands can range widely, often tens to hundreds of USD per kg N removed depending on design (mdpi.com). A business decision should compare life‑cycle costs, such as AC media costs ($/kg) versus wetland land costs ($/m²).
- Hybrid approaches: Multi‑stage trains often win. A vegetated ditch wetland followed by an AC filter treats both nutrients and organics. Laboratory and field work show biochar filtration after vegetated treatment can reduce remaining pesticides and toxicity to non‑detects (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov). Decision matrices are straightforward: if nitrate >50 mg/L, use IX; if pesticide residues >1 μg/L, use AC; if nitrogen and phosphorus are high and land is available, use wetlands first.
Recommendation and expected outcomes
Match treatment to contaminants. If nitrates dominate, consider IX or biological denitrification in wetlands for bulk removal, while planning for brine disposal from IX. If organics dominate, specify AC filters capable of >95% removal — consistent with field evidence of ≥98–99% reductions in pesticide‑laden runoff (pmc.ncbi.nlm.nih.gov). If loads are mixed, combine stages — for example, a wetland that pares down 40–80% of nitrogen (typical 30–60%, and up to ~80–92% with engineered media) followed by AC to capture trace organics — to maximize overall performance (mdpi.com; mdpi.com). Pilot testing under local conditions is advised.
References
Zieliński, B., Miądlicki, P., Przepiórski, J. Development of activated carbon for removal of pesticides from water: case study. Sci. Rep. 12, 20869 (2022). DOI:10.1038/s41598-022-25247-6 (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov).
Phillips, B.M., McCalla‑Fuller, L., Siegler, K., Deng, X., Tjeerdema, R.S. Treating Agricultural Runoff with a Mobile Carbon Filtration Unit. Arch. Environ. Contam. Toxicol. 82, 455–466 (2022). DOI:10.1007/s00244-022-00925-8 (pmc.ncbi.nlm.nih.gov; pmc.ncbi.nlm.nih.gov).
Yaragal, R., Mutnuri, S. Nitrates removal using ion exchange resin: batch, column and pilot‑scale studies. Int. J. Environ. Sci. Technol. 20, 1365–1379 (2023). DOI:10.1007/s13762-021-03836-8 (researchgate.net; researchgate.net).
Hsu, C.-Y., Yan, G.-E. Constructed Wetlands as a Landscape Management Practice for Nutrient Removal from Agricultural Runoff – A Case Study in Taiwan. Water 13, 2973 (2020). DOI:10.3390/w13212973 (mdpi.com; mdpi.com).
Chang, Y., Zhao, B., et al. The Use of Constructed Wetland for Mitigating Nitrogen and Phosphorus from Agricultural Runoff: A Review. Water 13, 476 (2021). DOI:10.3390/w13040476 (mdpi.com; mdpi.com).
Singh, B., Sekhon, G.S. Fertilizer‑N use efficiency and nitrate pollution of groundwater in developing countries. J. Contam. Hydrol. 20(3), 167–184 (1995). (Citing Indonesia Permenkes 90/2002 limit of 50 mg/L) (researchgate.net).
