What term describes non-soluble materials produced from the breakdown of waste in septic systems?

The term that describes non-soluble materials produced from the breakdown of waste in septic systems is "sludge." In the context of a septic system, sludge refers to the layer of solid material that settles at the bottom of the septic tank. This solid waste is primarily made up of organic matter, bacteria, and other debris that has decomposed and is too heavy to remain suspended in wastewater.

Understanding sludge is important because it plays a critical role in the operation of a septic system. It must be monitored and periodically pumped out to prevent it from overflowing into the drain field, which could cause system failure and environmental contamination.

Other terms mentioned relate to different phenomena occurring within septic systems or treatments of wastewater. For instance, scum refers to the layer of floating material (such as oils and fats) on the surface of the septic tank, while filtrate pertains to the liquid that passes through a filter, and residue generally refers to the remaining material after a process (which can include both soluble and insoluble substances). These distinctions highlight the unique properties and behaviors of waste materials within septic systems.