tant has a hard time getting to them. There can be plenty of chlorine in the water, but if there are numerous particles in the water, there may still be healthy bacteria waiting for an opportunity to take up residence in your body. Another problem is that a large amount of chlorine is used up in attacking the particles themselves, SO there may not be enough left to finish off the bacteria. For these reasons, is it not practical to disinfect home sewage effluent without prior filtration. Another important factor is contact time between the disinfectant LOW-IMPACT SYSTEMS and the bacteria. Chlorine does not necessarily kill the bacteria immediately as it is introduced into the sewage. It must diffuse throughout the liquid, and may take a while to pass through the slime that many bacteria secrete around themselves. Swimming pool water is recirculated, so that the disinfectant has a long time to do its thing. But the bacteria in the sewage effluent are on a one-way trip to the soil, and the time between leaving the septic tank and reaching the soil may be too short to give the disinfectant sufficient opportunity to complete its job. Because of this contact time problem, the dosing chamber (a nor- mal part of the land application system) doubles as a contact cham- ber, holding the treated effluent until the disinfectant finishes its work. If there is no dosing chamber, a contact chamber should be added. The third problem is that of disinfectant concentration. With the dry feed unit, the concentration is regulated by the strength of the disinfectant tablets (normally 70% free chlorine) and the number of tablets exposed to the sewage flow at any one time. The rate of dissolution of the tablets is supposed to be directly proportional to the rate of liquid flow through the tube, but this is not always the case. The Operation and Maintenance part of this section discusses how to achieve a proper concentration in the effluent. Design The dry feed unit should be placed between the septic tank outlet and the dosing chamber or