What is the environmental impact of FAS?

Direct Answer

Direct Answer There is an impact, but it is manageable and generally lighter than a conventional sodium dithionite process.

Decomposition products

formamidinesulfinic acid (FAS) decomposes in water, under alkaline conditions or on heating, and the end products are sulphate and urea. Sulphur leaves in the effluent as sulphate, nitrogen leaves as urea and counts towards total and ammoniacal nitrogen. The end products contain no heavy metals and form no chlorinated organics.

What has to be controlled

The effluent parameters that matter are COD and total nitrogen. This is the structural weakness of FAS relative to dithionite: it contains nitrogen and dithionite does not. Where total nitrogen discharge is tightly regulated, the load has to be calculated before switching, and this step cannot be skipped.

The advantage from the dose

On equal reducing equivalents FAS is dosed at about 0.62 times the dithionite weight, and allowing for the difference in effective utilisation the practical dose is lower still. Less material enters the process per unit of production, so the effluent load falls with it.

Aquatic toxicity

Under international criteria it falls in the band described as harmful to aquatic life rather than highly toxic. Algae are the most sensitive endpoint, followed by daphnia and fish. At typical concentrations the inhibition of biological treatment is limited.

Practical guidance

• Concentrated spent liquor containing sulphite and urea should not be discharged directly; aerate to oxidise the sulphite first, then rely on biological denitrification
• Before switching, calculate the load using your actual effluent volume and existing treatment train
• Where local total nitrogen limits are strict, include the cost of denitrification in the switch assessment

Bottom line

The environmental burden is generally lighter than with dithionite, but nitrogen content is a structural weakness, and the total nitrogen load has to be calculated before the switch is made.

Ecotoxicological data (from our safety data sheet)

Algae are the most sensitive of the three endpoints and are therefore the priority indicator when assessing discharge. The safety data sheet does not give a PBT or vPvB conclusion, so it should not be stated externally that the substance has been confirmed as non-PBT.

Sources

1. The effect of bleaching reagents on bleachabilities of DIP and environmental loads，KTAPPI 47(1), 2015，DOI 10.7584/ktappi.2015.47.1.066
2. 我司产品 SDS 与 TDS（危害分类、运输分类、热分解温度、溶解度等物性数据）
3. 我司产品安全数据表《Material Safety Data Sheet — THIOUREA DIOXIDE》（MSDS，签发日期 2023-03-03）
4. 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）