Why did early branched alkylbenzene sulfonate detergents create persistent foam in wastewater?

Early branched alkylbenzene sulfonate detergents created persistent foam in wastewater because of their chemical structure. These detergents utilized tetrapropylene, which features a branched carbon chain.1

Unlike straight-chain molecules, this branched structure is resistant to biological degradation by bacteria. Because the molecules could not be easily broken down, the foam they produced remained stable and persisted as it traveled through drains, sewage systems, and into natural waterways. This persistence caused significant environmental and operational challenges, including the obstruction of river navigation and the inhibition of organic material decomposition in water treatment systems.1

To address these issues, researchers in the 1960s developed detergents with straight carbon chains, which are more readily decomposed by microorganisms.1