COMPLEX-FORMING COMPOUNDS IN ALKALINE CLE ANERS

Using a laboratory-scale CIP test rig under process conditions (temper ature fluid dynamics, time) based on values found in practical cleanin g of dairy plant heat exchangers comparative cleaning experiments were carried out. For testing circular stainless steel elements of 50 mm i n diameter were used which had been soiled with deposits consisting ma inly of denatured whey proteins in a specific heating procedure using fresh raw milk. Deposit removal was monitored by use of a video camera . Single digitized frames showing different stages of soil removal wer e transmitted to a computer and analyzed with the aid of an image proc essing software (surface clean/still soiled). As a basic substrate an aqueous solution of sodium hydroxide in tap water (17 degrees dH) was used to which 12 complexing agents had been added in a comparable conc entration. According to the test results EDTA is still the most effici ent product, although due to its poor biodegradability in conventional sewage treatment plants, it should be substituted by other substrates . Na-3-SDA proved to be nearly as efficient as EDTA, but due to its hi gh production costs it is, at present, not competitive on the market. NTA, which is recommended by the Ministry for Environment and Reactor Safety, Bonn, and the Federal Health Office, Berlin, was found as a we ll suited biodegradable substitute for ETDA. The biodegradable structu res Na-3-MGDA (Trilon ES 9964), Na-3-EGDA and Na-4-ASDA were as effect ive as NTA, whilst IDA and Na-2-IDA as well as Na-2-MIDA, Na-2-HEIDA, and NA3-ISDA produced no effect. With respect to us comparability to N TA, and the justifiable production costs, Na-3-MGDA (Trilon ES 9964) i s the product of choice for a field test for cleaning a plate heat exc hanger in a dairy plant.