28/04/2016 · Hi, The difference is calculated by knowing the dry solid content of the sludge. For sludge produced in wastewater treatment plants, we talk about moisture content in terms of percentages or g/L. This is the amount of dry solids per 1L of sludge. When you have 1 ton of sludge at 20% dryness, this equates to t of dry matter (1 x 20%).