Biofilm is a living complex of organic and inorganic components that becomes established on surfaces that are in regular contact with water. Such surfaces include pressurized irrigation lines, non-pressurized recirculation system return lines, holding tanks, mixing tanks, containment vessels and so on. Largely comprised of highly adaptive bacteria, biofilm layers attach themselves to hard surfaces and then grow, becoming thicker and quite established over time.

In horticultural operations such as greenhouses and nurseries, common fertilizer injection serves as an accelerant to biofilm growth. Most growers are quite familiar with the presence of biofilm in their fertilizer lines. The layer of slimy growth is seen whenever a line is cut into for repair. However, biofilm growth is not restricted to fertilizer lines, but is also common in clear water lines, although usually by a slightly less dramatic presence.

An interesting relationship exists between the bacterial complexes making up biofilm and algae. The relationship is a synergistic one; what one needs the other provides. In fact, they work so well together that biofilm is able to provide algae with sufficient energy to substitute for algae’s need for sunlight. Any grower who has scratched his or her head after cutting into an underground pipe and found it lined with green, algae-laden biofilm in the absence of sunlight has personally experienced this phenomenon. Consider this a highly evolved organic system, one that has survived the test of time.

It’s no wonder most wastewater treatment technologies cannot break biofilm down. The photo at left shows sections of PVC pipe cut longitudinally to show the inner surface; top – new line, middle – clear water line showing tan colored biofilm contamination, bottom – fertilizer line showing algae and biofilm complex.