From ammonia to phosphate, unmodified manure lagoons only go so far. Data-backed options — aeration with nitrification/denitrification, chemical phosphorus precipitation, and algae-based polishing — show where the money and certainty are.
Industry: Agriculture | Process: Wastewater_Lagoons_&_Treatment
Facultative manure lagoons — the anaerobic/facultative basins most farms rely on — routinely remove 60–70% of total nitrogen (TN), largely by ammonia volatilization, according to stabilization lagoon surveys in temperate climates (www.researchgate.net). In one four‑lagoon series tracked across 21 months of winter–summer cycling, roughly 82% of influent NH3‑N (ammoniacal nitrogen) was lost (www.researchgate.net).
The catch is time and oxygen. Typical detention in facultative lagoons runs 20–150 days, while aerated “partial‑mix” lagoons can run 3–20 days and fully mixed aerated reactors just ~1–3 days (www.researchgate.net). As Middlebrooks et al. put it: “designing a lagoon to nitrify wastewater is not difficult if temperature, detention time and dissolved oxygen are adequate” (www.researchgate.net). Warmer tropical conditions generally make this easier.
Where discharge limits are tight — for example, <0.5 mg/L NH3‑N in Indonesia’s Class III/Ef (PP 22/2021) (id.scribd.com) — the baseline lagoon won’t get to very low nitrogen on its own. Measured ammonia volatilization rates in piggery lagoons hit 355–1534 mg N/m²·day, rising with NH3 concentration (www.researchgate.net), underscoring why aeration, chemical polishing, or algae are added.
Aeration with nitrification/denitrification
Nitrification (biological oxidation of ammonia to nitrate) followed by denitrification (biological reduction of nitrate to nitrogen gas) is the workhorse path to low nitrogen. Options include aerating the lagoon to complete nitrification, then providing an anoxic basin or organic carbon source for denitrification; adding a high‑rate biofilter; or inserting a sequencing batch reactor (SBR) stage (sequence batch reactor) to handle variable loads (all as outlined in www.researchgate.net). A “high‑rate biofilter” can be implemented with suspended biofilm carriers such as a moving bed bioreactor.
Denitrification consumes organic carbon, so a two‑stage lagoon — an aerobic/nitrifying basin followed by a denitrification basin — is common. In well‑equipped aeration ponds, >90% ammonia conversion to nitrate is achievable if dissolved oxygen (DO) > 2 mg/L and temperature > 15 °C (Middlebrooks et al., 1983; www.researchgate.net). After nitrification, providing anoxic conditions plus a carbon source (inherent BOD or external methanol/acetate) reduces NO₃ to N₂.
Pilot and field experiences show the ceiling. Aquaculture‑style sequential lagoons in subtropical climates achieved up to ~80–95% total N removal (Earnest 1978; Shao 2000) (www.researchgate.net; www.researchgate.net). Non‑aerated lagoons typically stop around <70% N removal. Under tropical conditions with aeration, nitrification rates of ~15–30 mg NH3‑N/L·day and multi‑log N removal are possible. Without aeration, lagoons rely on gas transfer (as [38] shows) and may require very long retention. Aeration adds cost — roughly ~0.1–0.5 kWh/m³·lb‑N oxidized in energy — but yields robust 70–90% N removal.
Some farms package biological steps — for instance, combining lagoon upgrades with a nutrient‑removal system designed to drive nitrogen and phosphorus to low milligram‑per‑liter levels — to standardize operations alongside the existing basin.
Chemical phosphorus precipitation
Phosphorus (P) is reliably removed with coagulants like aluminum sulfate (“alum”) or ferric chloride, which convert dissolved phosphate to insoluble metal phosphates that settle as sludge. Jar tests and field trials report high efficiencies: Sherman et al. (2000) reached ~90% total‑P removal with ~106 mg Al/L as alum (www.researchgate.net), while a Virginia Tech series using alum or FeCl₃ plus polymer delivered >97% P removal from flushed dairy manure (www.researchgate.net).
Scaling up, dosing ~200 mg/L Al (as alum) with polymer sequestered ~84% of total P into sludge in large tanks (www.researchgate.net). Ferric chloride can be comparable but often at higher dose; Zarate et al. (2002) reported ~88% P removal at ~278 mg Fe/L in dairy flush (www.researchgate.net). Across studies, Al‑based salts generally outperform Fe on a weight basis and are cheaper per equivalent P removed. In bench tests, alum at 100–300 mg/L yielded ~80–99% P capture (www.researchgate.net).
High P removal produces sludge. One test at 180 mg/L Al removed ~89% P but created sludge occupying ~58% of the settling depth (www.researchgate.net). The practical setup is a mixing/dosing step — often with an accurate chemical dosing pump — followed by gravity separation. Farms commonly standardize reagents via coagulants and pair with a flocculant before sending flow to a clarifier; a compact lamella unit such as a lamella settler is one way to keep footprint modest.
Operating cost matters: one dairy lagoon application (including ~200 mg/L Al plus polymer) put chemical+polymer treatment and sludge hauling at $4.09/m³ (≈$0.02/gal) of manure (www.researchgate.net). Chemical precipitation can cut P to very low effluent levels — often single‑digit mg/L or below — though O&M for reagents and sludge handling adds up.
Key metrics: expect >80% P removal for ~100–300 mg/L alum or Fe doses (www.researchgate.net; www.researchgate.net). A practical design ratio is roughly 1.5–2.0 moles Al per mole P (~3–4 g alum per g P); post‑treatment pH usually ends near neutral. Where discharge targets are stringent — e.g., <0.5 mg/L as P in sensitive waters (PP 22/2021; id.scribd.com) — chemical precipitation is often the only reliable path in the polishing step.
Algae and plant‑based polishing
Phycoremediation (algae‑assisted treatment with bacteria) simultaneously takes up ammonia and phosphate while providing oxygen. In batch tests on pig‑farm effluent, a freshwater microalgae–bacteria consortium removed ~87% of total N and ~70% of orthophosphate (link.springer.com; link.springer.com). Open high‑rate algal ponds (HRAPs; shallow raceways with paddlewheels) also strip ammonia as pH rises at the surface: in a year‑long urban wastewater pilot, two raceways removed 73% (higher HRT) and 57% (lower HRT) of influent N, mainly via NH3 stripping (32–47%) and algal uptake (www.researchgate.net).
Typical design parameters are very shallow (20–30 cm) raceways with mixing; reported TN removal rates in optimized HRAPs are ~40–100 mg N/m²·day (www.researchgate.net). Total‑P removal is usually lower than chemical methods, often ~60–80% depending on biomass harvesting frequency and loading. In practice, final effluent may still carry several mg/L of N and P unless biomass is continuously removed. Harvested algal biomass often runs ~10–20 g dry/m²·day and can be dewatered and reused as fertilizer or energy feedstock.
The attraction is energy. Microalgae–bacteria systems use ~85% less energy than conventional activated sludge, according to Sacristán et al. (link.springer.com; link.springer.com). Capital for pond area and harvesting equipment can be higher, and harvesting the algal sludge is a noted cost driver. Controlling blooms requires balancing nutrients and often supplemental CO₂ in intensive designs.
Decision framework for farm managers
Regulatory targets. Confirm effluent limits for N and P by receiving‑water class. Indonesia’s PP 22/2021, for example, sets Class II at 0.2 mg/L NH3‑N and 0.2 mg/L total P, while Class III tolerates 0.5 mg/L NH3‑N and 1 mg/L P (id.scribd.com). Hitting ≤0.2 mg/L typically needs combined treatment (e.g., nitrification/denitrification plus P precipitation, or very intensive algal systems).
Nutrient ratio. If P is the limiting concern, prioritized precipitation is warranted; if N (especially ammonia) dominates, aeration/nitrification or ammonia capture is key. When both are high, hybrid trains are common — for instance, an aerated lagoon for N followed by a post‑aeration alum step delivered by a dosing pump for P.
Climate and land. Tropical sunlight favors algae and shorter retention; ample flat land supports a series of shallow ponds as a low‑energy option. Where land is scarce or climates are cooler, compact mechanical aeration or an insertable reactor such as an SBR may better guarantee nitrification than a large footprint pond. Adding a high‑rate biofilm stage using a MBBR is another way to intensify nitrification/denitrification over limited area.
Cost and complexity. Chemical precipitation has a relatively small footprint and modest capital (tanks, mixers), but ongoing reagent and disposal costs run on the order of ~$0.01–0.05/m³ for reagents plus sludge trucking (see case data in www.researchgate.net). Mechanical aeration adds electricity — roughly 0.2–0.5 kWh/m³ — but keeps chemical use low. Algal systems minimize energy (up to ~85% saving; link.springer.com; link.springer.com) but require earthworks and harvesting labor.
Integration and reuse. A workable hybrid is raw lagoon effluent to an aerated stabilization tank (capturing ~50–80% of N via nitrification), then to an algal polishing pond for final uptake. If P limits are strict, a post‑aeration alum dose can “polish” P. Another strategy seen in industry is recovering N as struvite by adding magnesium and adjusting pH (not detailed above, but noted in industry). Packaged nutrient‑removal systems are often used to systematize these combinations.
Summary guidance. Achieving very low effluent (e.g., <1–2 mg/L N or P) usually requires two or more stages. For ≤0.2 mg/L NH3‑N and 0.2 mg/L P, aerated lagoons or reactors for nitrification/denitrification combined with chemical precipitation is likely. For moderate limits (5–15 mg/L), simpler trains (facultative lagoon plus constructed wetland or algae) may suffice. Always estimate load removal vs cost: one case put chemical/polymer treatment at ≈$4.09/m³ to cut P by 84% (www.researchgate.net), whereas nitrification by aeration might cost ~$0.01–0.05 per m³ of air (at $0.10/kWh) per few mg N removed.
Implementation. Model lagoon outputs, then trial solutions: jar tests for chemicals and small bioponds for algae, while monitoring BOD (biochemical oxygen demand), NH3‑N, and PO4. Benchmarks from cited studies include nitrifying lagoons removing up to 95% of NH3 if well‑designed (www.researchgate.net); alum at 100–200 mg/L removing 80–97% of soluble P (www.researchgate.net); and algal reactors removing ~60–85% of N/P under favorable conditions (link.springer.com; www.researchgate.net). Using these metrics in a decision matrix helps align cost with compliance.
Sources included lagoon treatment analyses (www.researchgate.net; www.researchgate.net), water quality regulations (id.scribd.com), and recent experimental studies (www.researchgate.net; link.springer.com). Full source details are provided in the citations.
