Microscopic exam is a good way to survey biomass health in suspended growth systems. Conventional and extended aeration activated sludge systems are designed to operate at decline to endogenous phase on the growth curve. Protozoa indicative of good operating conditions include free-swimming ciliates, crawling ciliates, and stalk ciliates/suctorians. All of these protozoa are single cell organisms associated with floc formation and sufficient dissolved oxygen. As we move further into endogenous phase - lower F/M and longer MCRT - we start to see multicellular organisms in the MLSS. The most common being rotifers - these organisms are very common in large lagoon systems, fixed film, and activated sludge with low loadings. As we increase populations of rotifers and start seeing worms, tardigrades, and gastrotrichs, the polymers holding the floc together start to "digest" inside the aeration basin. In effect, the aeration basin becomes an aerobic digester. The multicellular indicators need higher dissolved oxygen and lower F/M conditions than the single cell protozoa - and thrive in extreme low F/M conditions. So what can be the problem when multicellular organisms predominate over protozoa?
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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