Turning Manure Into Marketable Fertilizer: The Rise of On‑Farm Ammonia Capture

A quiet shift is underway on livestock operations: instead of losing nitrogen to the air and waterways, farms are installing compact systems that capture ammonia from manure and convert it into saleable fertilizer. The approach—sometimes called ammonia stripping and recovery or manure-to-fertilizer—is moving from pilot projects to commercial deployments as producers seek to cut emissions, improve neighbor relations, and hedge against volatile fertilizer prices.

Why Ammonia Recovery Is Gaining Attention

• Economic pressure: Synthetic nitrogen prices have seesawed in recent years with energy costs and geopolitics. Recovering nitrogen on-site can offset purchases or create a new revenue stream.
• Environmental compliance: Ammonia from manure contributes to odor, fine particulate pollution (PM2.5 via ammonium salts), and nitrogen deposition. Capturing it at the source reduces air emissions and downstream water impacts.
• Digesters need it: Anaerobic digesters improve manure management and generate renewable gas, but high ammonium levels in digestate can complicate land application. Recovery units downstream of digesters “polish” nutrients while adding value.
• Practical co-benefits: Captured nitrogen becomes a standardized product that’s easier to store, transport, and apply precisely compared to bulk slurry.

How the Technology Works

Several process routes exist, but most commercial systems follow two core steps: first, get ammonia into a controlled gas stream; second, capture and convert it into a stable salt solution or solid.

1) Covered storage and gas collection

Manure in lagoons or tanks emits ammonia continuously, especially when warm or agitated. By adding impermeable covers and light vacuum or sweep air, farms direct ammonia (and other gases) to a treatment skid. This step alone can reduce odor and fugitive emissions dramatically.

2) Stripping and absorption (the workhorse pathway)

Ammonia is more volatile at higher pH and temperature. Systems exploit this by:

• Raising pH with alkaline chemicals or by removing carbon dioxide from digestate, shifting the ammonium/ammonia balance toward gaseous NH₃.
• Increasing temperature modestly with waste heat or heat pumps to boost mass transfer.
• Passing liquid through a packed tower while air or biogas flows counter-current. Ammonia leaves the liquid and enters the gas stream.

The ammonia-laden gas then goes through an acid scrubber, where it reacts to form a stable salt—most commonly ammonium sulfate using sulfuric acid, or less often ammonium nitrate with nitric acid. The result is a fertilizer solution typically containing 6–9% nitrogen by weight, compatible with standard fertigation equipment. The stoichiometry is favorable: producing ammonium sulfate requires about 3.5 kg of sulfuric acid per kilogram of nitrogen captured, plus some allowance for inefficiencies.

Membrane contactors (gas transfer without towers)

Hydrophobic hollow-fiber membranes can separate the manure side from an acid absorbent stream. Ammonia diffuses across the membrane and is fixed as a salt with minimal airflow and compact equipment. These systems can be efficient at lower temperatures, are modular, and reduce corrosion and aerosol formation, though membrane fouling control and pretreatment are critical.

Ion exchange and electrochemical capture

Emerging systems use selective resins to capture ammonium from liquid and regenerate it with acid, or they employ electrodialysis with bipolar membranes to move ammonium ions and generate acid/base on-site. Electrochemical approaches cut chemical trucking but require clean power and careful control to avoid byproducts.

Pairing With Anaerobic Digesters

Digesters convert volatile solids to biogas, concentrating ammonium in the liquid phase. That makes digestate an excellent feed for ammonia recovery. Integration points include:

• Heat integration: Use hot-water loops from combined heat and power (CHP) engines or gas upgrading to warm stripping columns.
• CO₂ utilization: Digesters produce CO₂; some systems capture ammonia as ammonium bicarbonate by contacting NH₃ with CO₂, producing a fertilizer with different agronomic properties and lower acid use.
• Load smoothing: Balancing digester flows with buffer tanks and equalization avoids surges that can upset pH and capture efficiency.

Performance Benchmarks and Costs

Results vary by manure type, climate, and design. Typical ranges reported by vendors and independent evaluations:

• Ammonia capture efficiency: 60–90% of inlet ammonia under steady operation; higher with optimized pH and temperature control.
• Energy use: Approximately 0.5–2.5 kWh per kilogram of nitrogen captured for air/membrane systems without heavy heating; thermal stripping that targets higher temperatures can reach 3–6 kWh/kg N.
• Chemical consumption: 3.5–4.0 kg sulfuric acid per kg N for ammonium sulfate; alkali demand depends on incoming pH and buffering capacity.
• Capital cost: For a mid-sized dairy or swine site, installed costs often land between $0.8–3.0 million for covers plus a recovery skid, depending on scale, level of automation, and integration with existing infrastructure.
• Operating cost drivers: Acid and alkali, electricity for blowers/pumps, membrane replacement or media, labor for solids management and routine cleaning.

To put scale in perspective, a 1,000‑cow dairy can excrete on the order of 100,000–150,000 kg of nitrogen annually. If 30–50% is practically recoverable, that equates to 30,000–75,000 kg N captured per year—roughly 140–360 metric tons of ammonium sulfate solution on a nitrogen-equivalent basis. At typical market values, the fertilizer alone does not always cover all costs, but avoided odor issues, emission reductions, nutrient management flexibility, and policy incentives can tip projects into the black.

Environmental and Community Impacts

• Air quality: Capturing ammonia at the source can substantially reduce localized odor and cut precursor emissions for PM2.5 formation.
• Water protection: Removing nitrogen from liquid streams before land application lowers the risk of nitrate leaching and runoff.
• Greenhouse gases: Indirect nitrous oxide emissions tied to ammonia deposition can be reduced. When paired with digesters, farms also mitigate methane from manure storage. Quantification methods vary by jurisdiction.
• Nutrient circularity: Converting waste nitrogen into a standardized input supports regional nutrient balance, particularly in watersheds where land application capacity is constrained.

Operational Lessons From Early Adopters

• Solids are the enemy of uptime: Fine pretreatment—screens, dissolved air flotation, or centrifuges—prevents fouling of towers and membranes.
• pH control is pivotal: Automated dosing and good sensors stabilize volatilization without overspending on chemicals.
• Materials matter: Acid and ammonium salts are corrosive. Proper alloys, plastics, and coatings extend equipment life.
• Don’t waste waste heat: Even moderate heating (to the 30–50°C range) can lift capture efficiency if low-grade heat is available.
• Plan for fertilizer logistics: Storage tanks, loadout, and basic quality assurance (e.g., nitrogen concentration checks) smooth sales and on-farm use.

Policy and Market Signals

Regulations and incentives differ widely by region, but a few trends are consistent:

• Nutrient management plans increasingly value technologies that reduce land application loadings and document nitrogen flows.
• Air quality rules in some jurisdictions encourage covered storage and emission controls; recovery systems help meet those expectations.
• Water quality trading and watershed programs in select basins offer payments for verified nitrogen reductions.
• Carbon markets are exploring protocols that quantify avoided emissions from manure management; stacking these with renewable gas revenues can improve project economics.

What to Watch in 2025

• Electrochemical systems at farm scale: Projects that generate acid and base in situ could cut trucked chemicals and simplify operations.
• Hybrid designs: Pairing membrane contactors for baseline capture with polishing scrubbers during peak loads to maintain efficiency.
• Product diversification: Beyond ammonium sulfate, interest is growing in ammonium bicarbonate or blended liquids tailored for local crops and soils.
• Digital controls: Smarter automation that ties pH/temperature control to real-time emissions and energy pricing.
• Procurement by retailers: Food companies and cooperatives piloting offtake agreements for recovered-nutrient fertilizers as part of supply-chain sustainability goals.

Bottom Line

On-farm ammonia capture is evolving from a niche environmental add-on to a strategic tool for nutrient management and revenue diversification. While success depends on careful design, pretreatment, and chemical and energy optimization, early deployments show that farms can turn a persistent liability—ammonia emissions—into a standardized fertilizer product with tangible economic and environmental benefits.