Fats, oil and greases – collectively known as FOGs – interfere with the efficiency of your onsite wastewater treatment system. This is why they need to be separated and treated separately. Here are specific problems that FOGs may create in your system:
These are animal fats that come from food remains; specific examples include washing utensils, disposing of food scraps in the garbage disposal unit or down the sink. Fats aren't toxic, but they are still problematic for your system. For example, they are liquid at high temperatures, but they will solidify and separate from the other FOG components when they cool down.
When this happens, the solidified fats will stay in the system tank and may block (even if partially) the outlets. The fats may also clog other parts of the system such as the pumps and pipes downstream. They also reduce the amount of air within the tank and slow down the aerobic processes. This interferes with waste treatment/breakdown.
The oils in FOGS are mostly vegetable oils, which is used in food preparation. Temperature affects oils differently (as compared to how it affects fats). Oils stay in their liquid states even at room temperatures. This means that they can pass through the system and aren't toxic too.
However, just because oils are liquids doesn't mean that they are easy to separate from the rest of the waste. This is unfortunate because they do need to be separated – they are harder to break down than other organic wastes and hence slow down the treatment process too.
Only free oils rise to the surface of the wastewater and can be separated. However, emulsified oils, for example, those that have been acted upon by extremely high temperatures, may be harder to separate.
Unlike the other FOG components, grease is not organic – it is a petroleum product. It comes from soaps and beauty products such as lotions. This means that the main source of grease is the bathroom where most of the washing activities take place. Grease is both toxic and resistant to the biological processes that break down sewage effluent. The toxicity of grease means that it can harm the microbes involved in the anaerobic processes that are involved in the treatment of wastes.
It is for these reasons that you need to trap FOGs before the effluents run into the treatment tanks. It's also important to repair this part of the system, in case of a breakdown, early enough to prevent further problems downstream. Pretreatment components for trapping FOGs include grease traps and septic systems.