How Thermal Ammonia Stripping Works: The Science Behind OTAR®

Thermal ammonia stripping converts dissolved ammonium ions into free ammonia gas using heat, then captures that gas as a controllable stream — for destruction or recovery. The chemistry is simple; the engineering is where two decades of operational refinement create real performance differences between a well-designed system and a poorly optimised one.

The chemistry is elegant: shift the pH-temperature equilibrium, release ammonia as a gas, then capture it as a product. The engineering, however, is where OTAR®’s 20+ years of experience creates a competitive advantage. Because of that experience, the difference between a compliance cost and a new revenue stream usually comes down to design, not chemistry.

The Chemistry in Plain English: How Does Ammonia Stripping Work?

Ammonia exists in water in two forms:

ionised ammonium ion (NH₄⁺) and free ammonia gas (NH₃).

governed by the equilibrium NH4+ + OH- ⇌ NH3 + H2O.

At low temperature and low pH, almost all ammonia stays ionised in solution, essentially trapped as a dissolved salt. As temperature rises — or pH increases above roughly 9 — the equilibrium shifts strongly toward free ammonia, which can then be driven out of solution into the gas phase, in the same way that gas comes out of solution more readily from a warm drink than a cold one. OTAR® uses thermal energy as the primary driving force behind this shift, rather than relying on chemical pH adjustment alone.

Why Temperature Is the More Efficient Lever

Raising temperature and raising pH both push the same equilibrium in the same direction, but they come with very different operating costs. pH adjustment requires continuous chemical dosing — lime or caustic soda to raise pH, then acid to bring it back down before discharge — an ongoing consumable cost that scales with flow. Heat, particularly waste heat already generated on-site by an engine, boiler or flare, is frequently available at low or no marginal cost.

This is why OTAR®’s thermally-driven variants are typically the lower-operating-cost configuration wherever a waste heat source exists.

Energy Source: Waste Heat Recovery or Heat Recycling

What sets OTAR® apart from conventional ambient-temperature air stripping is its thermal drive. Many industrial and agricultural sites already produce surplus heat, from biogas engines at piggery or dairy digesters, to landfill gas at municipal sites, to process cooling at food and beverage plants. OTAR® captures this energy to heat the incoming liquid. As a result, the ammonia equilibrium shifts and stripping efficiency increases dramatically.

Where waste heat isn’t available, Variant 4’s heat recycling system instead uses electricity and steam compression, achieving the same thermal conditions with a coefficient of performance exceeding 15.

The Absorption Stage: Turning Ammonia Gas Into a Fertilizer Product

The ammonia-rich gas leaving the stripping column doesn’t have to go to waste — it is routed to an absorption stage matched to the chosen variant: clean water for ammonium hydroxide (Variant 2), sulphuric acid for ammonium sulphate (Variant 3), or a thermal oxidiser for destruction (Variant 1). This modular absorption stage, sitting downstream of an otherwise identical stripping process, is what makes OTAR® a platform rather than a fixed-function device — the same core engineering serves compliance-only sites and product-recovery sites alike.

Why Thermal Drive Matters for Product Quality

Because the process depends on physical equilibrium rather than a living microbial population, its performance does not degrade in the presence of inhibitory compounds, does not require an acclimation period after a shock load, and does not fail unpredictably the way a biological nitrifying culture can under stress. For operators managing high-strength, variable-composition streams — landfill leachate, digestate, industrial process water — this predictability is often as valuable as the removal efficiency itself.

Where Ammonia Stripping Systems Can be Applied Across Indonesian Industry

Total ammoniacal nitrogen (TAN) shows up in a wide range of nitrogen-rich waste streams. Because of that, ammonia stripping now serves several very different sectors across Indonesia. Here’s where it fits — and where to read the full picture for each one.

Palm Oil & Agro-Industry

Palm oil mills generate palm oil mill effluent (POME), a high-ammonia stream that concentrates further once mills add anaerobic digesters to capture methane. Permen LH No. 5/2014’s palm oil annex governs discharge here. Thermal ammonia recovery lets mills turn that load into ammonium sulphate — a fertiliser already distributed nationally as Pupuk ZA. Read our full guide: POME’s Next Problem.

Intensive Livestock & Poultry Operations

Poultry, pig and dairy operations generate large volumes of liquid manure and digestate. For these operators, thermal ammonia recovery turns a compliance cost into a locally marketable crop fertiliser. It also eases pressure on nutrient management and cuts reliance on bought-in fertiliser.

Industrial Food & Beverage Processing

Tofu and tempeh producers, fisheries processors, dairy plants and RPH (Rumah Potong Hewan) meat processors all generate protein-rich effluent with elevated Total Kjeldahl Nitrogen. Ammonia stripping reduces that load before discharge, helping smaller processors stay within municipal and provincial baku mutu limits that are tightening over time. Read our full guide: Ammonia Recovery for Tofu, Tempeh and Fisheries Wastewater.

Landfill & Waste Management (TPA)

Municipal and private landfill operators use ammonia stripping to manage heavy TAN loads in leachate, meeting Permen LHK No. 59/2016’s leachate standard with a low-maintenance, long-term solution that doesn’t depend on hauling leachate off-site. Read our full guide: Ammonia Recovery for Landfill Leachate.

Anaerobic digestion & biogas developers

Co-digestion plants, food-waste processors and agricultural biogas facilities use ammonia stripping to prevent ammonia inhibition and toxicity inside the digester. That protects methane yield, while creating a second revenue stream from recovered fertiliser.

Municipal & Industrial Wastewater Treatment Plants

Plant operators and engineers apply ammonia stripping to high-strength side-streams such as dewatering centrate and reject water. Doing so cuts the aeration, chemical and energy load these flows place on secondary biological treatment.

OTAR (Organics Thermal Ammonia Recovery)