Technology transition strategies for textile-dyeing sludge management in China from the environmental and economic perspectives

Textile-dyeing sludge reutilization is considered as an effective management scheme in the transition to low-carbon and sustainable development from the conventional incineration or landfilling. However, few studies have focused on its assessment from environmental and economic perspectives. In this study, a bin-to-grave life cycle thinking is applied to compare the environmental and economic performances of four promising and newly industrialized sludge reutilization technologies (i.e., pyrolysis-gasification-incineration, co-combustion in coal-fired power plants, sludge-to-brick, and sludge-to-biochar) with the traditional landfill option. Results indicate that technology transition to sludge-to-biochar option outperforms other transition strategies. The sludge-to-biochar option could gain environmental benefits in 7 categories i.e., primary energy demand (-6.1 x 10(3) MJ/t sludge), abiotic depletion potential (-4.9 x 10(-4) kg antimony eq./t sludge), eutrophication (-0.15 kg PO43- eq./t sludge), ozone depletion(-1.67 x 10(-5) kg CFC-11 eq./t sludge), photochemical ozone formation (-2.25 kg NMVOC eq./t sludge), ionizing radiation-human health effects (-3.1 kg U235 eq./t sludge), and ecological toxicity (14.4 CTUe/t sludge). Direct emissions of GHG in sludge reutilization technologies contribute to >70 % of the global warming potential category. Adopting the preferred sludge-to-biochar option at the provincial scale could mitigate approximately 0.81 million t of CO2 eq./year, which is equivalent to the amount of CO2 annually absorbed by 44.1 million trees in China. Feedstock (i.e., chemicals) contributes to about 77.9 %-97.9 % of toxicity-related environmental loads (i.e., human toxicity-cancer effects and ecological toxicity) for sludge-to-biochar, whereas in other utilization technologies, the key factor is heavy metal emission. The sludge reutilization technologies could break even within 3 years except pyrolysis-gasification-incineration (7 years). Meanwhile, contribution, sensitivity, and scenario analyses indicate that reducing primary energy consumption and improving the product quality and yield could effectively alleviate environmental burdens. A reasonable sludge disposal fee could help with the circular regeneration of textile-dyeing sludge. Despite that sludge-to-biochar stands as the foremost advantageous option for the technology transition in managing textile-dyeing sludge, certain aspects (for example, product quality and feedstock consumption) still necessitate further enhancements before its large-scale application in China.