All of the solids present whether suspended or dissolved. Volatile solids are those solids in water or other liquids that are lost on ignition of dry solids at 550°C. It is a water quality measure obtained from the loss on ignition of total suspended solids. It has great importance in water and wastewater treatment.
It normally represents the amount of organic solids in water. The greater the concentration of organic or volatile solids, the stronger the wastewater. It is helpful in assessing the amount biologically inert organic matter, such as lignin in case of wood pulping waste liquids.
A volatile solid is a substance that can easily transform from its solid phase to vapor phase without going through a liquid phase. In domestic wastewater, solids are about 50 percent organic, which in turn contaminates the ground and fresh water. These solids are generally from plants, dead animal matter and synthetic organic compounds. They can be ignited or burned. Because the organic fraction can be driven off at high temperatures, they are called volatile solids.
A test for volatile solids is normally applied to sludge. It is indispensable in the design and operation of sludge digest, vacuum filter and incineration plants. The determination of volatile and fixed components in residue is useful in the control of wastewater plant operation because it offers an approximate amount of organic matter present in the solid fraction of wastewater.