Green bottles have always been something of a vexed question. Once the filled bottle leaves your plant, you have little control over what happens to it, particularly when it is empty and left for collection.
Bottles left in sunlight and a warm environment are susceptible to algal growth. When green bottles are returned for filling what do you do? On the one hand you can throw them away, but if the algal growth is not too bad perhaps they can be cleaned and returned to the wash/fill cycle.
Green bottles should never be put through the normal washing process, otherwise the bottlewasher quickly becomes contaminated with algae. A separate process is required using good mechanical action, preferably with brushes, and a strong bleaching detergent. Good rinsing is essential.
Simple rigs can be set up to carry out this task and the best detergent to use is a low foam chlorinated alkali at a temperature of about 55 deg C. The temperature must not exceed 60 deg C otherwise the chlorinated product will degrade and cause corrosion, even of stainless steel.