Look at both the water and MLSS color. In systems with dye and highly colored influent, color observations are less accurate, but changes should still be monitored. A healthy MLSS is brown in color. The brown color results from bacteria cells, biological polymers, and particulate materials. Lighter brown usually indicates an immature biomass - where biopolymers are not at optimal levels. Dark colors - trending towards gray/black indicate older sludge, septicity, and if accompanied by odors, a problem with aeration/mixing. Colors are subjective and depend upon ambient light, so try to monitor changes and record observations. In summmary:
- Light colors - indicate a younger sludge or less accumulation of particulates/biopolymers
- Brown - usually a healthy sludge with a mixed microbial aggregate/biofilm
- Dark brown - older sludge with more inert/particulates
- Gray - very old sludge, start to lose biopolymer cohesion
- Black - septicity, low D.O., also can be dyes
Foam originates from influent surfactants, biological polymers, and even microbial produce surfactants. For observation purposes: record depth, color, and foam stability. As foam is directly related to biological activity (again high surfactants in the influent can confound this observation) - it gives you great information on microbial activity. Here is how I interpret foam observations:
- Deep, white foam that is stable - usually from influent surfactants
- White foam that is not stable under water spray - biological foam from normal bacteria action. Very white foam often indicates younger sludge and log growth
- Light brown foam - as the MLSS matures some of the brown color gets to the foam. This is normal.
- Thick brown, stable greasy foam - this is often growth of Nocardia forms. These organisms thrive on long chain fatty acids and long sludge ages. Once you have foam, they are in excessive abundance and need to be wasted.
- Gray, pumice like foam - this can be an indicator of "old" slduge or anaerobic conditions in the system.
Remember, noting color and foam are just observational tests. They should be done in conjunction with normal physical and laboratory tests. An observant operator can see if something has changed by looking at color or foam in a few seconds - unlike lab tests that can take several hours or days. So, start recording observations and it will help you maintain good biological waste treatment.