Sludge and scum blends from water and sewage treatment plants for energy recovering toward a circular economy perspective

Abstract

Here, we investigate how to improve the energetic potential of different sludge and scum from water and sewage treatment plants through co-combustion of their blends. We collected samples in Curitiba, Brazil, from: (a) anaerobic sewage treatment sludge; (b) aerobic sewage treatment sludge; (c) sewage treatment scum; (d) drinking water treatment sludge. We characterized the samples in terms of their energetic potential—by thermal analysis—and chemical composition—by scanning electron microscopy and X-ray diffractometry. The aerobic treatment sewage sludge and sewage treatment sludge had the highest useful heating value (9.47 MJ kg−1), whereas pure drinking water treatment sludge had the lowest one (4.62 MJ kg−1), which was increased upon blending with anaerobic sewage treatment sludge (7.29 MJ kg−1). Sewage treatment scum and aerobic treatment sewage sludge were mainly composed by quartz and gypsum, and both the blends and pure samples had the same crystalline structure. In conclusion, mixing aerobic/anaerobic sludges and sewage treatment sludge/drinking water treatment sludge improved their energetic potential compared to the pure samples. Thus, blending is a promising alternative to manage water and sewage by-products in a circular economy perspective.