Source identification of heavy metals in sewage sludge and the effect of influent characteristics: a case study from China

To advance the reclamation of sewage sludge and evaluate the potential risk during sludge application, wastewater and sludge were sampled from seven secondary wastewater treatment plants seasonally in 2016 and 2017. The influent characteristics and the accumulation of eight toxic heavy metals in sludge were analyzed. According to the results, copper, chromium, nickle and zinc were the main heavy metals constraining reclamation of sewage sludge in Shanghai and they were mainly from domestic wastewater. Influent concentration, treatment process and coexisting elements had significant effects on accumulation of heavy metals in sludge. Lead concentration in sludge from AAC plants was generally higher than that from AAO plants, but for other metals the differences were insignificant or depended on the initial concentrations. Nutrients, suspended solids and coexisting heavy metals had significant effects on heavy metal accumulation in sludge when the initial concentration was controlled.