Sludge drying system has been installed at FEIS. The conventional drying system, which involves steam, requires emission treatment and is subject to higher costs and more stringent environmental requirements. The hot air circulation inside the low-temperature heat pump drying system may eliminate exhaust, and the exhaust emitted at the outlet where sludge bag is connected, which is minor, is collected and discharged. The design is more energy efficient and reduces the moisture content in sludge down to less than 30%. The sludge drying system will further reduce the moisture content to approximately 20%. The total volume of sludge has been reduced by 50% in 2020.