Wednesday, 1 June 2011

Green Bottles - The Problem of Algal Contamination

Bottles which are heavily contaminated always must be discarded and never enter the bottle washer. However, those showing slight algal growth can be treated and reused. The requirements are to use an  oxidizing chemical, good mechanical action and hot water. If good mechanical action is not possible, then the chemical should be used at a higher concentration. Chemicals that have been used include the following:

peracetic acid
hydrogen peroxide
hypochlorite solution
nitric acid

Nitric acid is effective but dangerous to handle. Hypochlorite is also effective, but has to be rinsed thoroughly to avoid chlorine taint on the polycarbonate bottle. Hydrogen peroxide has been used, but is not as effective as peracetic acid. Peracetic acid is commonly used and normally available as 5% or 15% concentrates. These should be diluted down to 1% for use in de-greening bottles. Water temperatures of 60-70°C should be used. Mechanical action is very important and the use of brushes is needed. From a safety point of view it is better to use a special rig for cleaning the bottles rather than a manual process. This may be home-made, or, much better, be of the type shown in the photograph which is specially designed for pre-washing bottles using hot water and rotating brushes.


Brush Configuration in Pre-Washer