Effect of slag-based solidification material on the solidification and stabilization of sewage sludge

Abstract

Solidification/stabilization is considered to be a well-established disposal technique for reducing sludge handling and disposal obstacles. In this work, a slag-based solidification material (SBSM) was developed, using slag and dihydrate gypsum as the solidifier and sulphoaluminate cement clinker as the additive, to improve the performance of sludge solidification and thus making sludge disposal and recycling possible. The behaviour of pastes fabricated with various mass ratios of slag/sulphoaluminate cement clinker/dihydrate gypsum has been analysed in terms of mechanical strength, hydration products, microstructure, and toxicity characteristics. The results show that the strength of solidified sludge increased significantly with the addition of SBSM and the sulphoaluminate cement clinker content in SBSM. The use of sulphoaluminate cement clinker significantly improved the solidification/stabilization performance, causing a higher strength level. X-ray diffraction and scanning electron microscopy investigations revealed that a large amount of ettringite was present in the solidified sludge, leading to a crystallizing network in the solidified products and therefore the enhancement of the strength. Environmental assessment of the final products in compliance leaching tests demonstrated that the concentration of heavy metals were below the detection limits (GB5085.3-2007) set in China.