Why are we still adhering to API, when it comes down to oil-water separator? API design is an age-old technology, and in my opinion, its output or efficiency of the separator designed with API is not in line with present stringent environment norms. "The API method also makes the assumption of an inlet droplet size of 150 micrometers, which is inaccurate for environmental oil water separators because a spectrum of droplet sizes will be present, most of which are smaller than 150 μm" Also in its own document, it sumps up in section 2.3 - Performance. The API 421 document (section 2.3) sums this up: “Based on the 1985 API refinery survey of 32 conventional separators, such separators should not be expected to achieve effluent oil levels lower than 100 parts per million.” The snapshot is attached from API 421 docs. I think it is high time, design engineers and EPC consultants should stop copy-pasting of old specifications for OWS in any project and if they still want to, then they should add one line, as other efficient technology which can provide required ppm level in discharge water are welcome and can also make their offer or quote for the same project.