Only 11% of treated effluent is reused globally, yet Israel reuses about 85% and Spain 70% of municipal wastewater for agriculture. Agricultural lagoons still push out pathogen‑heavy water, forcing farms to pick between chlorination, UV, and ozonation to meet food‑safety rules and irrigation targets.
Industry: Agriculture | Process: Wastewater_Lagoons_&_Treatment
Water‑stressed growers are eyeing every drop. Worldwide, just 11% of treated effluent gets reused (mdpi.com), even as leaders like Israel reclaim roughly 85% and Spain 70% of municipal wastewater for agriculture (mdpi.com). On working farms, anaerobic lagoons tame organics but leave behind microbes: U.S. swine‑farm lagoon liquid carried 10³–10⁴ MPN/100mL Salmonella (MPN, most probable number, is a standard microbial count), with only 1–2 log₁₀ reductions in single‑stage lagoons and ~2–3 log₁₀ in two‑stage designs (porkcheckoff.org).
Those levels overshoot public‑health goals. WHO’s “unrestricted” irrigation guideline is ≤10³ fecal coliforms/100mL (and a child‑exposure limit of 10³ when children or flood irrigation are involved; helminth eggs are constrained to 1 egg/L) (pmc.ncbi.nlm.nih.gov). Disinfection beyond lagooning is non‑negotiable.
Rules differ by market. In Indonesia, standards focus on discharge (BOD/COD/TSS under PP 82/2001) rather than reuse quality, but projects like Bali’s Nusa Dua already irrigate golf courses and hotel landscapes with reclaimed effluent (mdpi.com). A local review flags advanced disinfection, including ozonation, to “adjust to regulatory demands” (ojs.unida.ac.id). In the EU, Regulation 2020/741 codifies reclaimed‑water Classes A–D by E. coli limits and irrigation method: Class A (fruits eaten raw or raw root crops) requires E. coli ≤10/100mL and tertiary treatment (filtration + disinfection), while Class D (non‑food or industrial crops) allows up to 10⁴/100mL with secondary treatment + disinfection (eur-lex.europa.eu).
Lagoon effluent pathogen baselines
Pathogens persist even after storage. The swine‑lagoon dataset shows post‑lagoon liquid with 10³–10⁴ MPN/100mL Salmonella and “similarly high fecal coliforms,” with single‑stage lagoons cutting ~1–2 log₁₀ and two‑stage lagoons ~2–3 log₁₀ (porkcheckoff.org). That far exceeds WHO’s ≤10³ fecal coliforms/100mL target and helminth eggs ≤1 egg/L for unrestricted irrigation (pmc.ncbi.nlm.nih.gov).
EU benchmarks steer technology choice: Class A irrigation demands E. coli ≤10/100mL with filtration plus disinfection; Class D allows up to 10⁴/100mL with secondary treatment plus disinfection (eur-lex.europa.eu).
Chlorination: mechanism, efficacy, limits
Mechanism: Chlorine gas or hypochlorite forms hypochlorous acid (HOCl), a strong oxidant that penetrates microbial cells. Efficacy depends on dose and water chemistry; above pH 7, most chlorine is hypochlorite ion (OCl⁻), which is less biocidal than HOCl (eco-web.com).
Performance: In secondary effluent, ~32 mg/L free chlorine for 15 minutes eliminated total/fecal coliforms, Pseudomonas, and Staph (researchgate.net). In raw swine‑lagoon samples, even ~30 mg/L achieved only ~2.2–3.4 log₁₀ reduction, with resistant microbes (including spore‑formers like Bacillus) curbing returns at higher doses (scholarsmine.mst.edu).
Protozoa: Chlorine performs poorly on hardy cysts and eggs. Cryptosporidium oocysts resist conventional chlorination, while recent UV systems are described as “highly effective” against them, even more so than chlorine (uvsolutionsmag.com).
Byproducts: Chlorination reacts with organics to form disinfection byproducts (DBPs) such as trihalomethanes and haloacetic acids; DBPs raise concerns for soil/crop health and often force additional treatment to strip free chlorine and byproducts (watertechonline.com; uv-l.com). Any chlorine above regulated limits creates DBP hazards and necessitates post‑treatment (watertechonline.com).
Costs and operations: Chlorination is low‑cost and simple—chemical prices are modest and capital needs are basic—but O&M is driven by recurring chemicals and labor (eco-web.com). A comparative economic study ranked chlorination as the lowest life‑cycle cost among the three methods (researchgate.net). Many agricultural operations favor it for low upfront cost and a residual disinfectant effect (novagric.com). For dosing, farms commonly rely on dedicated chemical feed equipment such as a dosing pump.
Design anchors: EPA CT (concentration × time) tables indicate ~2–3 log inactivation of E. coli at ≈2–3 mg·min/L chlorine; in practice, 10–20 mg/L for 1–2 minutes may yield >3 logs in suitable waters. “Shock” chlorination of ponds at 50+ mg/L appears in some farm operations, though it is intensive. Residual chlorine often must be quenched before field application, which can be addressed with a dechlorination agent or activated carbon media polishing.
UV irradiation: physical, chemical‑free kill
Mechanism: UV‑C light (often at 254 nm) damages microbial DNA/RNA so organisms cannot replicate. It is a physical process without adding chemicals.
Efficacy: UV inactivates bacteria, viruses, and many protozoa. Recent systems are credited with 3–4 log₁₀ Cryptosporidium kill, “even more so than chlorine” (uvsolutionsmag.com). In a secondary‑effluent study, ~164 mJ/cm² achieved ~3 log total coliform removal and complete inactivation of fecal coliforms and Pseudomonas (researchgate.net). Typical design doses of 30–60 mJ/cm² are often used by EPA/WHO to ensure reliability.
Water quality sensitivity: Organics and suspended solids absorb/scatter UV; turbid lagoon effluent needs pre‑filtration to prevent “shadowing” (eco-web.com; eco-web.com). Guidance notes sand filtration to below roughly 30 µm before UV (novagric.com); farms implement this with media beds such as a sand filter. UV has no residual, so recontamination is possible after treatment.
Operations and byproducts: UV produces essentially no harmful DBPs at normal doses (waterworld.com). Modern reactors start instantly; low‑pressure or medium‑pressure lamps commonly last beyond 10,000 hours, with reports “to well over 12,000 hours” (waterworld.com). Lamps need replacement roughly every 12–24 months (uv-l.com), and sleeves should be kept clean. Some reclaimed‑water schemes cite UV’s co‑benefits on micropollutants like pharmaceuticals and pesticides (uvsolutionsmag.com). In practice, farms deploy packaged UV systems such as an inline ultraviolet reactor.
Ozonation: high‑power oxidation and disinfection
Mechanism: Ozone (O₃) is a strong oxidant generated on site (corona discharge or UV). It disrupts cell walls and viral capsids and oxidizes color, odor, and organics. It leaves no durable chemical residual and decays to oxygen.
Efficacy: In secondary effluent, adding ~15 mg/L ozone for 15 minutes achieved complete removal of coliforms and vegetative bacteria (researchgate.net). In raw swine wastewater, ~100 mg/L ozone yielded ~3.3–3.9 log₁₀ reductions—stronger than comparable chlorine doses (scholarsmine.mst.edu). A field rule of thumb puts “1 mg/L for 1 minute” as adequate for basic bacterial control, though required CT hinges on water demand and target pathogens (watertechonline.com).
Byproducts and cautions: In bromide‑bearing waters, ozonation may form carcinogenic bromate; industry guidance warns ozone “should never be used” under such conditions (watertechonline.com). Other organics (e.g., formaldehyde) can form depending on wastewater makeup (ojs.unida.ac.id). Ozonated water tends to be more acidic and can be corrosive. Ozone cannot be stored; it must be generated on demand from clean air or oxygen, with safety interlocks to prevent worker exposure.
Costs: Ozone demands the highest capital and energy. Generators commonly consume on the order of 10–20 kWh per kg O₃ produced, and O&M extends beyond the skid itself (researchgate.net). Comparative analyses consistently rank ozone as the most expensive of the three (researchgate.net). In Indonesia, reviews still conclude ozonation can meet stringent standards and adapt to regulatory demands (ojs.unida.ac.id).
Effectiveness and cost comparisons
Potency in raw waters trends ozone ≥ UV > chlorine. In secondary effluent, ~15 mg/L O₃ for 15 minutes and ~32 mg/L Cl₂ for 15 minutes both fully eliminated fecal coliforms and key bacteria (researchgate.net), while UV at ~164 mJ/cm² delivered ~3‑log total coliform removal (researchgate.net). In raw lagoon water, ~30 mg/L Cl₂ reached ~2.2–3.4 log₁₀ reduction (scholarsmine.mst.edu), while ~100 mg/L O₃ achieved ~3.3–3.9 log₁₀ (scholarsmine.mst.edu).
Dose efficiency: Comparative data show ozone’s required CT for virus inactivation is far lower than many alternatives; one summary indicates ozone can be ~8.5× more efficient than chlorine dioxide for viruses (eco-web.com). Cryptosporidium needs extremely high CT with chlorine, whereas modern UV achieves >4‑log inactivation (uvsolutionsmag.com).
DBPs and residues: Chlorination’s DBPs (e.g., THMs, HAAs) impose regulatory and agronomic costs (watertechonline.com). Ozone carries bromate risk in bromide‑rich waters (watertechonline.com). UV produces essentially no harmful DBPs (waterworld.com).
Costs: Economics typically rank capital+O&M as sodium hypochlorite (NaOCl) < UV < ozone (researchgate.net). Chlorine’s costs are recurring chemicals/labor (eco-web.com), UV’s are energy and lamps (with Novagric pointing to low operational costs due to modest power draw and minimal consumables; novagric.com), and ozone’s are dominated by generators, oxygen prep, contactors, and energy (researchgate.net).
Selection guide by reuse application
High‑exposure crops: For raw‑eaten fruits/vegetables or raw root crops, aim at EU Class A or WHO “unrestricted” quality (E. coli ≤10–100/100mL; helminth eggs ≤1 egg/L; child‑exposure limit of 10³ for flood irrigation/children) (eur-lex.europa.eu; pmc.ncbi.nlm.nih.gov). Achieving this generally requires tertiary treatment (filtration + disinfection). UV with prior filtration or ozone is often preferred because of strong virus/protozoa inactivation without chemical residues. Hitting Class A solely with chlorine is difficult; after lagoon treatment, even ~30 mg/L Cl₂ has left counts above 10³ MPN/100mL in studies (scholarsmine.mst.edu; eur-lex.europa.eu).
Lower‑risk irrigation: For non‑food crops, drip on tree crops (EU Class B/C), or fodder under WHO “restricted” conditions, standards relax toward 10³–10⁵ CFU/100mL (pmc.ncbi.nlm.nih.gov; eur-lex.europa.eu). Moderate chlorination (e.g., ~10–20 mg/L for a few minutes) can suffice, especially post‑lagoon. Residual chlorine can offer short‑term in‑field suppression. Combining filtration and Cl₂ helps control DBPs and dose; operators sometimes add fine screening before dosing using an automatic screen filter.
Regulatory credits: EU guidance assigns log₁₀ reduction credits by process/chain; engineers design safety margins over the standard (eur-lex.europa.eu; eur-lex.europa.eu). As a rule, if raw effluent is ~10⁶–10⁷ FC/100mL, design for >4‑log reduction to meet 100 FC/100mL.
Pretreatment and water quality management
UV/ozone demand clear water. Guidance points to sand/DAF filtration to <10 NTU for reliable UV performance, and sand beds down to ~30 µm to avoid shadowing (novagric.com). Farms frequently deploy dissolved‑air flotation for solids control via a DAF unit and then polish with granular media.
Chlorine is less sensitive to turbidity but reacts with ammonia (forming slower‑acting chloramines) and organics (raising DBPs) (eco-web.com). Where polishing is needed to contain DBPs and residual chlorine before irrigation, growers add an activated carbon filter. Upstream, primary solids control is often handled as mechanical separation; farms use screens in front of treatment, aligned with packaged wastewater physical separation strategies.
Scale, power, and safety considerations
Small sites (<100 m³/day): simplicity and minimal power favor chlorine systems; dosing is straightforward and equipment inexpensive (eco-web.com). Where chemical handling is a concern, compact UV skids are feasible and chemical‑free, with low operating energy cited by vendors (novagric.com).
Large farms/centralized reuse: UV reactors amortize well at flow; ozone is chosen when ultimate pathogen kill or co‑benefits (odor/COD oxidation) justify higher capital and energy (10–20 kWh/kg O₃) (researchgate.net). Indonesian industry commentary notes that ozone can meet stringent standards and future regulatory demands (ojs.unida.ac.id).
Power and residuals: Chlorine needs little power but involves hazardous handling. UV requires stable electricity and lamp maintenance (12–24‑month replacements; >10,000–12,000 hour lifetimes) (uv-l.com; waterworld.com). Ozone requires high‑voltage power, clean oxygen feed, and leak‑prevention systems.
Hybrid trains and field practice
Strict reuse (e.g., vegetables): a common chain is secondary lagoon → sand filtration → UV, sometimes with a small chlorine residual afterward. For moderate reuse (e.g., fodder), farms often run lagoon → chlorine contact only. Inline UV skids such as a UV reactor slot into tertiary treatment, while chlorine contactors are fed by a dosing pump.
For UV, farms target pre‑UV turbidity using media beds and compact flotation; packaged lines often include a DAF clarifier. For chlorine, residual control prior to field application is handled with a dechlorination agent. Some operators front‑end debris removal with an automatic screen to protect downstream equipment.
Bottom line and next steps
Chlorine is cheapest and simplest, effective for routine bacterial control and small‑scale uses, but struggles with protozoa and creates DBPs (watertechonline.com; uv-l.com). UV is highly effective—especially on chlorine‑resistant pathogens—chemical‑free, and favored for stringent Class A targets, but needs clear water and power (uvsolutionsmag.com; waterworld.com). Ozone is the most powerful disinfectant and also trims organics, but high capital/energy and bromate risk limit it to larger, well‑resourced facilities (researchgate.net; watertechonline.com; ojs.unida.ac.id).
System selection should map to crop risk, measured effluent quality, and rules—designing for necessary log₁₀ reductions with multi‑barrier chains and validated credits where applicable (eur-lex.europa.eu). In Indonesia, discharge standards (PP 82/2001) still dominate, but real‑world reuse—from Bali’s Nusa Dua to hotel landscapes—shows the path forward (mdpi.com). The technology palette is ready; the constraint is choosing the right one for the target field.
Key sources and data points in this report are drawn from peer‑reviewed and technical references: swine lagoons and disinfection performance (scholarsmine.mst.edu; scholarsmine.mst.edu), WHO reuse guidelines (pmc.ncbi.nlm.nih.gov), EU Regulation 2020/741 (eur-lex.europa.eu) and guidance (eur-lex.europa.eu), comparative disinfection studies and economics (researchgate.net; eco-web.com; eco-web.com), UV performance and DBPs (waterworld.com; uvsolutionsmag.com; uv-l.com), chlorine DBPs and ozone cautions (watertechonline.com), reuse context in Indonesia and Bali (mdpi.com; mdpi.com; ojs.unida.ac.id), and practical vendor insights (novagric.com; novagric.com).
