No one is really concerned about the biological crap on your bottom, if that is all there was. The big issue is that bottom paints are biocides, designed to kill living things, really really tough living things, like barnacles. So they are loaded with heavy metals, copper, tin, in the past lead, etc. If you look at NJ discharge limits, it is a whole list of metals. Metals are toxic, you can get brain swelling from getting bottom paint on your skin while scraping it off the bottom.
Sewer plants are biological plants. Metals interfere with that biology, and the metals get concentrated in the sludge, meaning it can't be land applied, it has to go to landfills for all of eternity.
Removing metals is very tough. My first job with this company was a metals job, took us 3 years to get it running right! So the this wash water issue is legit, and it will only be a short time before all states institute the same laws. I just wish we had a cost effective solution. Lots of business if we did!
Gary H. Lucas