AndyIES, I found this site that has a paper on the subject.
Good Luck,
Vergenie.
srmwww.gov.bc.ca/clrg/britannia/downloads/reports/tech_reports/ WTP_cemi_final_pilot_plant_report.pdf
zavier98, I agree with jproj and freebo, the best way is to look through a microscope. The filamentous bacteria (usually ones called sphaerotilus nathans) look just like filaments. But another tip: I had filamentous bacteria problems in my treatment plant and I also had a denitrification...