India Ink test - an easy way to monitor floc extracellular polymers

The easiest way to gauge EPS in activated sludge floc is to use the India Ink test with your existing microscope. In addition to being easy, India Ink requires no specific equipment or skills - just a bottle of $10 India Ink that will last for years. Unlike most inks, India Ink contains finely ground carbon particles that are suspended in water. You can find India Ink in many craft stores or online - Amazon India Ink with dropper. 

To use India Ink with your microscope follow these steps:

1. Pipette a small droplet of MLSS onto a glass slide 
2. Add an even smaller droplet of India Ink to the slide - just enough to color the water droplet dark gray/black.
3. Place coverslip on the slide
4. Observe using a standard microscope - you can use either regular light objective or phase contrast.
   
5. The India Ink should move through the water and stain the slide. The clear zones with light shining through are floc with high levels of EPS that India Ink does not penetrate.
6. Note the size and number of clear zones in the droplet.
7. That is all that is required. I recommend doing India Ink tests at least 2x weekly and note any changes in EPS.

With respect to EPS, remember that some is needed to function as the glue that keeps floc together. Probelems arise when excess EPS creates a gelatin like matrix that entraps water and creates viscous bulking/non-filamentous bulking conditions.