Assessment of Sewage Sludge Generation, Characteristics, and Potential Treatment Methods in Rapidly Expanding Population Regions

Abstract

This study assesses sewage sludge generation, characterizes its physicochemical properties, and evaluates viable treatment strategies tailored to local conditions. Grab samples were collected from two operating wastewater treatment plants (Shariya and Avro City). Sludge and wastewater were analyzed for total solids, total dissolved and suspended solids, biochemical oxygen demand, chemical oxygen demand (COD), and selected heavy metals. 35 years of climatic data were reviewed, and a socioeconomic survey was conducted. Results indicated substantial current and projected sludge volumes, about 19,895 tons of dry matter for the study area and about 51,268 tons for the governorate per year. The estimated sludge generation rate was 32.9 kg/capita/year. The sludge shows high organic content and extremely elevated COD (for example, Shariya ≈115,800 mg/L). These characteristics indicate significant potential for energy recovery via anaerobic digestion. Chemical analyses revealed localized heavy metal enrichment (notably aluminum and lead in Shariya) that constrains direct land application without pretreatment. Socioeconomically, whereas 90% of respondents reported connections to a water supply, 40% reported insufficiency. Comparison of treatment scenarios indicates that the most viable near-term options for resource recovery and pathogen reduction are low-cost sludge treatment wetlands and mesophilic anaerobic digestion. This study constitutes the first research conducted on sewage sludge management in Duhok City. The results serve as an important database that can be used by policymakers and engineers to develop a sludge management system not only for Duhok but also for other growing Iraqi cities and similar regions.