Most international content on ammonia recovery treats ammonium hydroxide as the premium product, because that is what UK and European organic agriculture markets reward through OMRI certification. Indonesia’s largest nitrogen fertiliser market works differently. OTAR® configuration makes the most commercial sense here.
ZA: An Established, Government-Recognised Fertiliser
Ammonium sulphate is widely known in Indonesia as Pupuk ZA, or Zwavelzure Ammoniak. It is distributed nationally through Pupuk Indonesia’s subsidised fertilizer program, alongside urea and NPK products. In addition, sugarcane and other crops can benefit from its combined nitrogen and sulphur supply.
Indonesia’s domestic fertilizer production covers only part of national nitrogen fertilizer demand, while government subsidies help keep fertilizer prices affordable for farmers. Therefore, Pupuk ZA is not a niche product. It is an established fertilizer with an existing market and distribution network in Indonesia.
How OTAR® Variant 3 Produces It
OTAR® Variant 3 first removes ammonia from wastewater using waste heat. The recovered ammonia then reacts with sulphuric acid in an acid-scrubbing absorption stage. This process produces ammonium sulphate as a liquid fertilizer or crystalline solid. The overall reaction is: 2NH3 + H2SO4 → (NH4)2SO4.
However, Variant 3 requires a reliable sulphuric acid supply. Sites would typically source the acid from industrial chemical suppliers rather than produce it on-site. In addition, the finished product must meet the applicable agricultural quality requirements. This route does not qualify for OMRI organic certification because sulphuric acid is not permitted under the relevant organic agriculture standards.
Why That Trade-Off Matters Less Here Than in Europe
OMRI certification can open a premium organic agriculture market. However, that market is more established in the UK and Europe than in Indonesia. Meanwhile, Indonesia already has a mainstream fertilizer market for ammonium sulphate. Pupuk Indonesia also provides an established distribution network for the product.
Therefore, Variant 3 can offer a direct route to market for sites near agricultural buyers. This can be especially relevant in established sugarcane-growing areas across Java and Sumatra. By comparison, Variant 2 may offer stronger value where an industrial buyer or an export-oriented organic supply chain is available.
Comparing the Two Recovery Routes
- Ammonium hydroxide (Variant 2)
Ammonium hydroxide, produced through Variant 2, does not require an acid input. It also avoids salt formation and can be further concentrated into anhydrous ammonia. Therefore, this route can suit sites with industrial buyers or export-oriented organic supply chains.
- Ammonium sulphate (Variant 3)
Ammonium sulphate, produced through Variant 3, requires a reliable acid supply. However, it creates a stable liquid or solid product for an established fertilizer market in Indonesia. Therefore, this route can suit sites close to agricultural offtake with practical access to sulphuric acid.
Choosing Between the Two
The better route depends on the conditions at each site.
- First, the project should assess local sulphuric acid availability and delivered cost.
- Next, it should assess potential industrial buyers for ammonium hydroxide.
The study should also consider agricultural demand, buyer distance, product requirements, and future hydrogen-carrier opportunities.
Organics evaluates these factors during feasibility studies. Therefore, the selection does not rely only on which OTAR® configuration is common in another market. Instead, the project team can select the route that best matches the local feedstock, utilities, market access, and commercial objectives.
Frequently Asked Questions
Q: What is Pupuk ZA and how is it different from urea?
Pupuk ZA is Indonesia’s common name for ammonium sulphate fertilizer, distinct from urea in that it supplies both nitrogen and sulphur. It is distributed as one of several products under Pupuk Indonesia’s subsidized fertilizer program.
Q: Does recovered ammonium sulphate meet Indonesia's SNI fertilizer standard?
To be sold as Pupuk ZA, ammonium sulphate must meet SNI 02-1760-2005, Indonesia’s mandatory quality standard requiring a minimum of 20.8% nitrogen and 23.8% sulphur content, with maximum limits on free acid and moisture. OTAR® Variant 3’s acid-scrubbing process is designed to meet this specification, and product testing against SNI parameters should be part of commissioning for any site planning to sell into the agricultural market.
Q: Can recovered ammonium sulphate be sold into Indonesia's subsidized fertilizer program directly?
Entering the government subsidy distribution chain directly involves separate regulatory and commercial arrangements. The more common and immediately practical route is selling recovered, SNI-compliant ammonium sulphate to agricultural buyers or distributors in the open market, which does not require entering the subsidy program itself.
Q: Is ammonium sulphate more valuable than ammonium hydroxide in Indonesia?
Value depends entirely on local market access, not a fixed hierarchy. Ammonium sulphate benefits from an established, SNI-regulated, high-volume mainstream fertilizer market in Indonesia specifically, while ammonium hydroxide suits sites with an industrial buyer or export-oriented supply chain.