OTAR® (On-site Thermal Ammonia Recovery) is a flexible, modular platform. It features five configurable variants for different site conditions. Each variant answers two practical questions. First, where does the stripping heat come from? Second, what happens to the ammonia after it leaves the liquid phase? Therefore, the best configuration depends on the site’s heat source, wastewater profile, discharge requirement, and recovery objective.
Indonesia’s Regulatory Backbone
Indonesia uses a layered framework for industrial wastewater discharge. Peraturan Menteri Lingkungan Hidup No. 5 Tahun 2014 sets baku mutu air limbah for defined sectors, including palm oil. Meanwhile, sector-specific rules cover other industries. For example, Peraturan Menteri LHK No. 16 Tahun 2019 covers textile wastewater, while Peraturan Menteri LHK No. 59 Tahun 2016 covers landfill leachate. In addition, Peraturan Menteri LHK No. 68 Tahun 2016 covers domestic-type effluent that may enter industrial estate treatment systems.
Ammonia therefore deserves close attention during compliance planning. In many cases, the applicable limit appears as Total Nitrogen or NH3-N. Palm oil mills face a 50 mg/L Total Nitrogen ceiling in the stated framework. Textile operations face an NH3-N ceiling of 8.0 mg/L. Furthermore, compliance performance feeds into PROPER, Indonesia’s public environmental-performance ranking, which is now governed by Peraturan Menteri Lingkungan Hidup/Badan Pengendalian Lingkungan Hidup No. 7 Tahun 2025.
Nickel HPAL presents a different situation. High Pressure Acid Leach liquor does not appear as a named sector in the cited Permen LH No. 5/2014 annexes. Consequently, high-ammonia HPAL streams at sites in Nickel Industries are typically addressed through a site-specific Persetujuan Teknis under PP 22/2021. The required ammonia performance can therefore become part of the limit established and defended in the site’s Pertek and Amdal documentation.
Variant 1
Waste Heat with Thermal Destruction
Variant 1 uses available waste heat to strip ammonia from the wastewater. A thermal destruction unit then oxidises the ammonia to nitrogen gas and water vapour. As a result, the configuration does not require absorption chemistry or product handling.
This route suits sites where compliance is the main objective. It also suits facilities that do not want chemical handling or product offtake logistics. Hong Kong leachate sites provide a precedent, where waste heat from landfill gas and biogas engines supports ammonia treatment. Likewise, Indonesian TPA operators can consider this route when landfill gas provides usable heat. Palm oil mills can also use it when Total Nitrogen compliance matters more than fertiliser revenue.
Variant 2
Waste Heat to Recover Ammonium Hydroxide
Variant 2 absorbs stripped ammonia into water without using acid. The process produces ammonium hydroxide, typically at about 20–25% NH3. Therefore, the route can recover nitrogen as a useful product rather than destroy it.
This configuration works best when a nearby buyer can use the recovered product. For example, a petrochemical or fertiliser plant may recycle ammonium hydroxide into its nitrogen feedstock. That approach can offset purchased ammonia. Similarly, an HPAL site may benefit when a chemical-industry offtake partner operates within the same industrial estate. The route also generates no salt waste and is eligible for OMRI organic-agriculture certification.
Variant 3
Waste Heat to Recover Ammonium Sulphate
Variant 3 reacts stripped ammonia with sulphuric acid. The reaction produces ammonium sulphate, which Indonesia distributes at national scale as Pupuk ZA through Pupuk Indonesia’s subsidised programme. Therefore, this configuration connects ammonia treatment with an established fertiliser market.
However, the route needs a reliable sulphuric acid supply chain. It also does not qualify for OMRI certification. Nevertheless, an established agricultural market can make the product pathway attractive. Palm oil mills can consider this option when nearby estate or smallholder demand can support product use. Other industrial sites can also consider it when local fertiliser demand and acid availability align.
Variant 4
Heat Recycling
Variant 4 addresses sites without reliable waste heat. An electricity-driven heat-recycling system compresses and recycles steam to provide stripping heat. The stated coefficient of performance exceeds 15. In practical terms, the system can deliver more than 15 units of usable stripping heat for each unit of electrical energy consumed.
The heat-recycling stage can pair with the product pathways used in Variants 2 and 3. Consequently, a site can select heat recovery separately from its ammonia product route. This option is particularly relevant to remote or standalone HPAL sites where existing waste heat already serves the smelting process. It can also suit petrochemical and fertiliser plants without a spare combustion source, provided grid or captive power is available.
Variant 5
pH-Driven Conversion
Variant 5 uses chemistry rather than high-temperature heat to shift ammonia into the free-gas form. The process raises wastewater pH to around 11 with lime or caustic soda. As a result, the wastewater can release more ammonia for subsequent stripping and recovery.
Textile dyeing and finishing effluent can be a natural fit. Such wastewater is frequently alkaline because of earlier process steps. Therefore, the extra dosing needed to reach stripping pH may remain modest. This matters when the applicable NH3-N limit under Permen LHK No. 16/2019 is 8.0 mg/L. Variant 5 can also serve smaller landfill sites that lack a gas engine for waste heat. Furthermore, the configuration can work with the recovery routes described above.
Which Ammonia Recovery System Variant Fits Your Facility?
Use this quick-reference guide to identify the OTAR configuration most likely to fit your site’s energy availability, ammonia load and product market:
Kelapa sawit, POME and biogas
Variant 1 provides a compliance baseline against the stated 50 mg/L Total Nitrogen limit. However, operators can upgrade the route to Variant 2 or 3 by pairing existing biogas-engine or boiler waste heat with an absorption stage.
Nickel smelters and HPAL sites
Example are the sites in Morowali or Weda Bay, Variant 2 or 3 can suit sites with an offtake partner inside the industrial estate. Meanwhile, Variant 4 can provide stripping heat when existing waste heat already serves the smelting process.
Petrochemical, fertiliser and industrial chemical plants
Variant 2 or 3 can recover ammonia as recyclable feedstock or a saleable co-product. Therefore, the site can potentially turn a discharge liability into a resource.
Landfill leachate
Variant 1 can suit sites where a landfill-gas engine already supplies waste heat. Alternatively, Variant 5 can suit sites without that heat source.
Textile and dyeing industries
Variant 5 can take advantage of already-alkaline effluent. Alternatively, Variant 2 can suit a site with a nearby ammonium hydroxide buyer. In either case, the treatment objective remains the applicable 8.0 mg/L NH3-N limit stated for the sector.
Why the Configuration Matters
The five OTAR® variants should not be treated as five unrelated products. Instead, they form one platform with different heat and ammonia-handling arrangements. Therefore, the first question should not be, “Which technology should I buy?” The better question is, “What does my site already have, what does its applicable baku mutu require, and what outcome does the site need?”
A feasibility assessment can answer those questions systematically. It should consider flow rate, ammonia concentration, available waste heat, applicable discharge standard, and access to a product market. From there, the assessment can identify the most suitable OTAR® configuration. It can also identify a practical upgrade path if site conditions change later.