The frequency of emptying a sewage treatment plant is typically recommended by the manufacturer. For domestic systems serving a single dwelling, it is often advised to have the system emptied once a year. It is good practice to leave some activated sludge in the tank during emptying to maintain the performance of the bacteria. The size of the system and the number of people using it should also be considered. Systems are usually oversized, providing a buffer and potential for longer intervals between emptying if there is low loading. Additional factors to consider are whether homeowners are using feeders or reducers to improve performance and reduce sludge accumulation. Feeders introduce bacteria-enhancing substances, while reducers help maintain an optimal sludge level of around 40 to 60%. The use of such products can extend the time between emptying. Commercial systems may require more frequent emptying, typically two to four times a year, depending on the application and waste volume. So with emptying of a treatment plant, again the frequency is kind of indicated by the manufacturer initially. So certainly on a domestic level, so for a single dwelling, most manufacturers would size the systems in accordance with getting the system emptied once per year. And generally most people should be doing that anyway just to ensure that you’ve got a good [inaudible 00:00:37] process in the tank. When you empty a wastewater treatment plants, it’s generally quite good practice to leave some of the activated sludge in the base of the tank so you don’t fully empty it. So we can get a continued working performance from the bacteria in the tank and you always got very good quality left. In addition to that, you generally want to consider I suppose, the number of people feeding it, which is… And of course the size. So wastewater treatment systems are generally sized in terms of maximum potential number of people you can have in the property, which is most of the time oversized based on the number of people feeding it. So you may get a little bit of a buffer in terms of, how much longer you would have. So if they say a year, you may be able to get a little bit more than that if you’ve got low loading. You then also need to consider if the homeowner is feeding the system so you can introduce a feed for the bacteria to improve the performance or a kick starter to get it working more quickly. And there are also other products in the market which reduce the amount of sludge in the tank, which again, if you’re using a reducer, that means you’re going to have to get it emptied less often. Reducers are generally quite good because they retain like a static level of sludge in the tank, which is generally around about 40 to 60%. And to really get optimal treatment performance in terms of from the bacteria, that’s kind of where you want it to be. That’s when you get very good quality of effluent. So something else to consider if you are going to be using feeders, reducers to improve performance, that will of course have an influence in terms of the frequency of how often you get emptied. But generally on a domestic level, try to stick with a year. On commercial level, it will be more frequent. Again, the manufacturer will give you a guideline based on the sludge storage volume for the tank, but it could be that it’s anything from two to four times a year. Again, very dependent on the application, the sources of waste coming into the tank and how much waste is entering it versus the sludge storage chamber.
