. . Sewage sludge refers to the residual and semi-solid material that is produced as a by-product during wastewater treatment of industrial or municipal wastewater.. The global market value of sewage sludge is estimated to be US $ xx million in 2020 and is expected to reach US $ xx million by the end of 2026, with a compound annual growth rate of xx% over the period 2021-2026.. . . .