We operate a private sewage treatment plant serving an office business park. Throughput is about 8,000 litres per day. We have had a lot of trouble meeting Environment Agency criteria for BOD, Suspended Solids and Ammonia, in the final effluent. As a pre-treatment stage, we have added an activated sludge plant, with continuous aeration. We have also slowed down the flow through the treatment plant. Our BOD and SS are now well within EA criteria, but ammonia is stubbornly high at about 30 mg/litre (our limit is 10 mg/litre) We are adding Organica 33, in the intermediate and final stages of the plant, with some success. I would be interested to hear whether other subscribers have had similar problems, and whether they have found an inexpensive solution. CW