Farm Lagoons Meet the Lab: The real costs of hitting Indonesia’s strict discharge limits

The bar is high and the clock is ticking. Indonesia’s Ministerial Regulation No.11/2009 (updated by Permen LHK No.5/2014) sets livestock effluent at BOD<30 mg/L, COD<80 mg/L, TSS<60 mg/L, pH 6–9 for cattle, with pigs even tighter at BOD<6 mg/L and TSS<12 mg/L (text-id.123dok.com). Biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS) are core compliance metrics; pH is acidity/alkalinity.

Most agricultural lagoons discharge organics and solids in the hundreds of mg/L, so a polishing step is not optional. The short list: an intermittent sand filter (ISF), a constructed wetland (CW), or a compact biological package plant — a sequencing batch reactor (SBR) or membrane bioreactor (MBR). Table 1 summarizes typical pollutant removal and costs, and the ranges tell a clear story.

Indonesia’s limits and the lagoon gap

Regulated endpoints are unforgiving: cattle farm effluent BOD<30 mg/L, COD<80 mg/L, TSS<60 mg/L, pH 6–9; pig farms face BOD<6 mg/L and TSS<12 mg/L (text-id.123dok.com). Lagoons alone rarely meet these numbers — lagoon effluent often has hundreds of mg/L of organics and solids — driving demand for post‑treatment.

Candidate post-treatments include an intermittent sand filter, a constructed wetland, or a compact biological plant (SBR or MBR). Table 1 summarizes typical pollutant removal and costs.

Intermittent sand filter (ISF) performance and cost

An ISF polishes lagoon effluent by intermittent dosing through sand or gravel. Reported BOD and TSS removals are typically ~70–90% (pmc.ncbi.nlm.nih.gov) and ~70–80% (www.climate-policy-watcher.org), yielding much clearer effluent.

Nutrient removal is minimal: nitrogen is hardly reduced (≤20%) and phosphorus removal is poor (pmc.ncbi.nlm.nih.gov). In practice, BOD in the effluent can drop to ~10–30 mg/L, but NH₄–N often remains high. A U.S. EPA example shows a ~350 gpd (≈1.3 m³/d) system at ~$10.8k in 1999 (~$8k per m³/d design flow) (nepis.epa.gov), with pumping costs at ~$0.03–$0.06/day (nepis.epa.gov) and very small labor.

Advantages include low CapEx and energy (≈0.01 kWh/m³ for pumps only, where kWh/m³ is energy per cubic meter treated: nepis.epa.gov), compact footprint (~5–20 m² per 10 m³/d), and simplicity. Drawbacks: insufficient for strict N/P standards; additional N‑removal or P‑precipitation would be needed for compliance. ISFs rely on granular media; many operators specify sand media similar to sand/silica filtration media for consistent dosing and cleaning.

Constructed wetland nutrient polishing

A subsurface‑flow wetland (planted gravel bed) uses biological pathways to remove organics and nutrients. Typical removals are ~75–85% COD/BOD and ~70–85% total N and P at hydraulic retention of ~5–10 days (pmc.ncbi.nlm.nih.gov). For example, De la Mora‑Orozco et al. reported ~76–80% COD and ~70–85% TKN/NH₃/TP removal in pig slurry wetlands (pmc.ncbi.nlm.nih.gov).

Effluent (5‑day HRT) often meets BOD/TSS ~20–50 mg/L while cutting N/P by ~70%. CapEx typically runs ≳$30–250 per m² (www.mdpi.com), with a real project in the Philippines (~multi‑family scale) reported at ~$180k installed, 8–10‑year lifetime and ~<$4k/yr O&M (www.mdpi.com).

Energy is ~0–0.01 kWh/m³ (pumps, hardly any) (www.mdpi.com), maintenance is minimal (periodic vegetation harvest, sludge skimming), and O&M is very low (~2–5% CapEx: www.mdpi.com). Pros include very good nutrient removal, passive operation, and co‑benefits (wildlife, carbon). Cons include land needs — large footprints, often ~10–100 m² per 10 m³/d at ~20 cm/d loading (www.mdpi.com) — plus slower start‑up in cold climates. Vymazal (2010) reports subsurface wetland total CapEx spanning $29/m² up to €257/m² (www.mdpi.com).

SBR package plant: compact and consistent

A sequencing batch reactor (SBR) is an activated‑sludge process with time‑sequenced fill–react–settle cycles. Well‑designed SBRs remove ~90–95% of organics and achieve strong nitrification–denitrification; Alagha et al. (2020) report ~91% COD (≈BOD) removal, 83% total N removal, and 90% P removal (pmc.ncbi.nlm.nih.gov).

In practice, final BOD and TSS are often <20 mg/L, though nitrates can run high if denitrification is incomplete, so a short post‑anoxic step or longer solids retention may be needed for total N targets. Equipment costs run to ~$94k for ~0.04 MGD (~45 m³/day), ≈$2,000/m³·d — scales down as size increases — per industry data (web.deu.edu.tr). Power demand is ~0.5–1.0 kWh/m³, and sludge production is ~0.3–0.5 kg TSS/kg BOD removed.

O&M is higher than passive systems (continuous aeration, skilled labor), but the footprint is moderate (~2–5 m² per 10 m³/d) and effluent quality is consistent. For operators standardizing on packaged units, see category examples such as a sequence batch reactor (SBR).

MBR: high performance, high cost

A membrane bioreactor (MBR) couples suspended growth with immersed ultrafiltration membranes to produce reuse‑grade effluent. TSS removal is essentially 100%, BOD/COD removals are typically ≥95%, and with nitrification tank & disinfection they can produce reuse‑grade water. Although few readily‑citable studies cover livestock vs. municipal directly, MBRs routinely achieve effluent BOD <10–15 mg/L and NH₃–N often <1–2 mg/L; for reference, an SBR study saw ~91% COD and 83% N removal, and an MBR would do at least as well or better since solids never overflow to effluent (pmc.ncbi.nlm.nih.gov).

Costs are the highest: small commercial units (~50–500 m³/d) can run ~$500–$1,000+ per m³·d capacity (pubmed.ncbi.nlm.nih.gov), and energy is typically ~1.5–2.5 kWh/m³ (aeration plus membrane scouring). O&M is intensive (chemicals and downtime for cleaning/replacement every few years). Pros: minimal land (very small footprint, ~<2 m² per 10 m³/d), discharge often <2 mg/L turbidity, capable of meeting any standard. Cons: ~2–3× the capital cost of an equivalent SBR and 2–3× the energy use, plus technical demands; less proven in rural/ag settings in Indonesia. For context on equipment classes, see membrane bioreactors and supporting ultrafiltration modules.

Performance and cost benchmarks (Table 1)

Typical removal and cost ranges across options are:

• BOD₅ removal: Lagoon only ~30–50%; Sand filter ~70–90% (pmc.ncbi.nlm.nih.gov); Wetland ~70–85% (pmc.ncbi.nlm.nih.gov); SBR ~90–95% (pmc.ncbi.nlm.nih.gov); MBR ~95–99% (very high).
• TSS removal: Lagoon only ~30–50%; Sand filter ~70–80% (www.climate-policy-watcher.org); Wetland ~80–90% (often high); SBR ~90–98%; MBR ~99% (nearly complete).
• Total N (TN) removal: Lagoon only ~10–30% (lotic algae); Sand filter ~10–20% (poor) (pmc.ncbi.nlm.nih.gov); Wetland ~70–85% (pmc.ncbi.nlm.nih.gov); SBR ~80–90% (pmc.ncbi.nlm.nih.gov); MBR ~85–95%.
• Total P (TP) removal: Lagoon only ~10–30%; Sand filter ~30–50% (no treatment) (pmc.ncbi.nlm.nih.gov); Wetland ~70–85% (pmc.ncbi.nlm.nih.gov); SBR ~85–90% (pmc.ncbi.nlm.nih.gov); MBR ~85–95%.
• Footprint: Lagoon large; Sand filter small (~5–20 m² per 10 m³/d); Wetland large (~10–100 m² per 10 m³/d); SBR moderate (~2–5 m² per 10 m³/d); MBR very small (~<2 m² per 10 m³/d).
• Energy (kWh/m³): Lagoon Tg. (~0); Sand filter ~0.01 (pumps only) (nepis.epa.gov); Wetland ~0–0.01 (pumps, hardly any) (www.mdpi.com); SBR ~0.5–1.0; MBR ~1.5–2.5 (aeration + membranes).
• CapEx per capacity: Lagoon low (existing); Sand filter low–moderate (e.g. ~$8–10k per 1.3 m³/d) (nepis.epa.gov); Wetland moderate (≳$30–250 per m²: www.mdpi.com); SBR moderate ($94k for 0.04 MGD: web.deu.edu.tr); MBR high (~2–3× SBR: pubmed.ncbi.nlm.nih.gov).
• O&M (annual): Lagoon sludge haul; Sand filter very low (screening/filtration: nepis.epa.gov); Wetland very low (~2–5% CapEx: www.mdpi.com); SBR high (power, aeration, skilled labor); MBR very high (power, membrane cleaning).

Cost–benefit summary and tradeoffs

Sand filters have the lowest capital and energy cost (nepis.epa.gov; nepis.epa.gov) but only polish solids/organics; they cannot meet strict N/P standards (pmc.ncbi.nlm.nih.gov).

Constructed wetlands have moderate upfront cost (soil‑lining, gravel, plants) but essentially free operation (www.mdpi.com); they excel at nutrient removal (pmc.ncbi.nlm.nih.gov) but need ample land. SBRs require higher CapEx and continuous O&M, but deliver reliably high treatment (meeting ~30 mg/L BOD and often <1 mg/L NH₃ after polishing) (pmc.ncbi.nlm.nih.gov).

MBRs produce the best effluent (often <10 mg/L BOD, essentially no solids) but at ~2–3× the capital cost of an equivalent SBR and 2–3× the energy use. Where clarifiers or primary settling are part of the train, the category analog is a clarifier for suspended solids removal ahead of polishing.

Example outcomes for a 200 m³/day lagoon

• Sand filter: ~$150–200k (plus settling tanks) and cut BOD from ~200→30 mg/L but leave e.g. 20–30 mg/L NH₃.
• Constructed wetland: ~0.3 ha at ~$200k–$300k, reduce TN/TP by ~80%, yielding effluent ~20 mg/L BOD, ~10 mg/L TN.
• SBR package: ~$250–$400k and reliably meet BOD<10–20 mg/L, TN<5–10 mg/L (with step‑feed or post‑anoxic zone).
• MBR system: ~$500k+, with effluent BOD<5 mg/L and TN<2 mg/L.

In practice, decision‑makers weigh tradeoffs. If capital and land are constrained but reuse‑quality water is required, an MBR is ideal despite its cost. If budget is limited and stringent nutrient removal is needed, a wetland offers strong “bang‑for‑buck” (high nutrient reduction per dollar) (pmc.ncbi.nlm.nih.gov; www.mdpi.com). A mid‑range SBR gives strong performance with moderate investment. Conversely, a simple sand filter is only justified when BOD/TSS polishing is needed — and even then usually with a septic/primary step, such as a clarifier, because it cannot alone meet Class I‑A criteria in Indonesia.

Sources and standards

Government and peer‑reviewed data were used for all figures. Regulatory limits are from Indonesian Ministerial Reg. No.11/2009 (text-id.123dok.com). Sand‑filter performance is documented in Laaksonen et al. (2017) (pmc.ncbi.nlm.nih.gov) and classical summaries (www.climate-policy-watcher.org). Wetland removal efficiencies are from pilot studies (pmc.ncbi.nlm.nih.gov) and reviews (www.mdpi.com), plus a Philippines case study (www.mdpi.com). SBR yields are from Alagha et al. (2020) (pmc.ncbi.nlm.nih.gov). Cost data reference EPA ISF fact sheets (nepis.epa.gov; nepis.epa.gov), Vymazal (2010) wetland costs (www.mdpi.com), the SBR equipment example (web.deu.edu.tr), and MBR cost/energy correlations (pubmed.ncbi.nlm.nih.gov).

Where project scopes require equipment context rather than design prescriptions, category pages such as a sequence batch reactor, a membrane bioreactor, and a primary clarifier can anchor procurement, while granular media selection mirrors sand filtration media used in ISFs.