A cost analysis of sewage sludge composting for small and mid-scale municipal wastewater treatment plants

Abstract

Abstract The costs of building and operating windrow, aerated static pile (ASP), and horizontal agitated solids bed (HASB) sewage sludge composting facilities for small and mid-scale municipal wastewater treatment plants are analyzed. The capital costs and total annual costs of the composting facilities analyzed range from US$164 200 to US$349 000 and from US$100 000 to US$295 700, respectively. On a per-input-dry-Mg basis, composting costs range from US$55.31 to US$173.66/dry Mg handled depending on the type of system and the moisture content of sewage sludge. Moisture content of sewage sludge is the key factor of capital costs and operating costs for different composting facilities. The lower the moisture content of sewage sludge, the less the capital and operating costs for different composting facilities. A windrow composting facility is cheaper to build and operate than ASP and HASB composting facilities. The dominant components of capital costs for windrow are land acquisition and surfacing, and that for ASP and HASB is equipment. Bulking agents and labor are the key factors of operating costs for sludge composting facilities. The availability of land and the costs of bulking agent will significantly limit the spreading of windrow system in small and mid-scale municipal wastewater treatment plants; however, it is suitable for spreading ASP and HASB sewage sludge composting systems for small and mid-scale municipal wastewater treatment plants in China.