Factors regulating microbial biofilm development in a system with slowly flowing seawater.

Microbial biofilm development was followed under growth conditions similar to those of a projected salinity power plant. Microscope glass cover slips were piled in biofilm reactors to imitate the membrane stacks in such a plant. A staining technique closely correlating absorbance values with biofilm dry weight was used for the study. Generally, the biofilms consisted of solitary and filamentous bacteria which were evenly distributed with considerable amounts of various protozoa and entrapped debris of organic origin. Protozoa predation was shown to decrease the amount of biofilm produced. The biofilm development lag phase was longer at lower temperatures. The subsequent growth phase was approximately arithmetic until stationary phase appeared. Adaptation of a hyperbolic saturation function gave curves that agreed well with the logarithm of the amount of biofilm as a function of time. Increased flow velocity, temperature, and nutrient concentration increased the biofilm production rate. An exponential relationship was shown between biofilm production rate and flow velocity within the range of 0 to 15 cm s. Intervals in which the biofilms were exposed to fresh water decreased the biofilm production rate more than four times. If the cover slips were inoculated with untreated seawater for 24 h, subsequent UV treatment had an insignificant effect on the biofilm formation.