Speciation distributions and risk assessments of trace elements in sludge and coal co-combustion ash

The co-combustion of sludge and coal has advantages such as utilizing the energy in sludge and reducing the treatment difficulty of sludge ash. Due to a wide source of sewage, the distributions of trace elements in co-combustion ash may differ from coal ash. Under laboratory conditions, the study examined the speciation distribution by the BCR method and evaluated the environmental risks and health risks of six typical trace elements in the co-combustion ash of sludge and coal. There is a significant difference in trace elements between sludge ash and coal ash, the highest content of heavy metals in coal ash and sludge ash is chromium (141.4 mg/kg) and zinc (1455.4 mg/kg), respectively. Coal ash has a lower heavy metal content and effective fraction than sludge ash, and coal ash is more stable. Risk assessment code analysis shows that most elements in co-combustion ash are at the low risk level, and when the blending ratio reaches 50%, chromium is at the medium risk level. According to Nemerow pollution index, cadmium can cause pollution to the environment when pH < 7.5. The risk of heavy metals in co-combustion ash on human health is at the acceptable level.