Natural processes to control microbial fouling are optimized and are, by definition, environmentally compatible. These natural strategies are comprised of systems to recognize the problem, remedy it, and then regulate the remedy. Successful industrial programs are often inadvertent imitations of natural microbial control strategies. Several examples of natural microbial control programs are given and compared to recent industrial innovations. A new stabilized liquid bromine product is discussed and compared to natural microbial fouling control agents; new performance data for stabilized liquid bromine are given. The opportunity for innovation in microbial fouling control is to observe how it is done in nature and imitate.
Cooling water treatment is mostly about managing surface-fouling processes. There are three such processes to manage (microbial, scaling, corrosion) and they occur simultaneously. Of these three, the microbial fouling process is the most complex, hardest to measure, requires use of the most potentially hazardous products, and is the least understood. Effective control of microbial biofilms is the key to water treatment. Modern scale and corrosion inhibition chemicals simply do not work unless microbial fouling is properly controlled.
Advancement in the science and technology of microbial fouling control is necessary in order to develop fundamental breakthrough water treatment technology. The best strategies have already been established in nature and should be imitated. Environmental compatibility is optimized with programs that copy natural processes. Industrial programs can be explained within the context of those ancient natural strategies that have stood the test of competition and natural selection.
NATURAL DISINFECTION
Many people do not realize that the industrial use of hypohalous acids (water reacted with chlorine, bromine, or iodine) is an inadvertent imitation of natural microbial fouling control. Hypohalous acids are generated in nature on the surfaces of certain aquatic plants, fungi, and in the human immune system, for example, as follows.
Red and brown algae in the ocean (seaweed) and also in freshwater environments make hypobromous acid (HOBr) by selectively oxidizing bromide with peroxy compounds and enzymes called bromoperoxidases. This fact was fust reported in 1926; since then, a fascinating scientific literature on the subject has developed. In one such study published in 1991, the brown seaweed, Ascophyllum nodosum was shown to produce substantial quantities of hypobromous acid directly upon its surface. This aquatic plant may annually produce as much as 1,800 kg (3,960 lbs) of HOBr in the top few centimeters of the 30 km (18 mile) North Atlantic stretch of seawater studied (1). Many other macroalgae similarly produce hypobromous acid including the brown seaweeds (Laminaria saccharin, L. digitata, Fucus vesiculosis, Pelvetia canaliculata) and the red seaweeds (Antithamnionella sarniensis, Antithamnion plumula, Chondrus crispuys, Placamium hamatum). Hypobromous acid so produced from the naturally occurring bromide in the ocean is rapidly consumed upon demand and is nontoxic to the plant. This natural process helps explain why seaweeds are not covered by microbial biomass and macrofoulants that, for example, rapidly foul the surfaces of ships and piers. Although chloride is far more abundant than bromide in the sea, hypobromous acid is preferentially made by seaweed. Superior antimicrobial activity in alkaline pH (seawater is always above pH 8), in the presence of nitrogenous organic matter, and due to lower volatility has been documented for bromine antimicrobial (2). These technical attributes
