Practically it has been found that it is possible to successfully treat some batches as small as 1,500 to 2,000 litres. Below this, problems of dilution arise because of mixing in the system. In any case, the real problem is the inefficiency of trying to treat such small batches. It takes as long to travel to the site; set up; clean the equipment and lines before and after then pack up for small and large jobs. Therefore a minimum fee applies and this can make the treatment of small batches unattractive.