In recent years, numerous polymers and biocides have been developed to enhance or augment cooling water treatment programs. The polymers were designed to treat either corrosion or fouling problems in cooling water systems and heat exchanger equipment. However, few of these polymers can function as both a corrosion inhibitor and a scale inhibitor. In addition, many of these polymers and biocides still had some environment drawbacks that rendered them harmful to aquatic life when discharge to receiving waters. In this paper we look at a multiple-year field application of biodegradable polymers and biocides.
Manufacturers continue to introduce new chemicals and treatment programs onto the market, and old products have been discontinued. Many manufacturers claim that the new chemical and treatments are more environmentally friendly and safer for the plant workers and the users. The U.S. Army Corps of Engineers (USACE) has not evaluated these new chemicals in over ten (10) years; therefore Army installations may be uninformed as to new treatment technologies.
The U.S. Army Engineer Research and Development Center Construction Engineering Research Laboratory has undertaken a research effort to look at these new chemical treatments. The objective of this work is to develop "green" water treatment chemicals that control biological growth, corrosion, and scale while reducing or eliminating the generation of toxic substances during the manufacture, use, and disposal processes. 1 A strong secondary goal is to develop treatment programs that are safer for operators and handlers of chemical treatments. To this end, acid for alkalinity control is not desired and automation that minimizes user handling of products is sought.
In 2001 SurTech Corporation was contracted to develop a user friendly, environmentally safer treatment program and to conduct a two-year's trial on a cooling system at the US Army Rock Island Arsenal in Rock Island, Illinois. The green chemistry employed had been developed over the past few years in response to a need by a large midwestem university for a low pollution treatment progranl The chemicals utilized were a low molecular weight thermally polymerized aspartate (TPA) for scale and corrosion inhibition and the biocide tetrakis (hydroxymethyl) phosphoniumsulfate (THPS). Both of these chemicals had won the US Presidential Green Chemistry Challenge Award. 2,3
The TPA polymer is a polypeptide, derived via thermal polymerization of aspartic acid, one of the 20 or so common amino acids found in proteins. Aspartic acid is one of the few amino acids that will thermally homopolymerize. Heating aspartic acid, either alone or with a catalyst, leads to a linear thermal polycondensation polymer known as polysuccinimide (PSI). The polymerization is economically accomplished without the use of organic solvents. Hydrolysis of polysuccinimide with aqueous base, such as sodium hydroxide, leads to a random copolymer of ~ and aspartate units, with the 13 aspartate comprising about 70%-75% of the repeating units. 4 The polymer is also completely racemic (a 1"1 D/L mixture), in contrast to natural proteins, which generally contain only L amino acids. The chemical structure of Thermal Polyaspartate is shown in Figure 1.
