Comprehensive assessment of the ultrasound lysis–cryptic growth technology for in situ sludge reduction: Mass balance and environmental and economic analyses

The ultrasonic lysis–cryptic growth technology can achieve in situ sludge reduction that relies on ultrasound to accelerate sludge lysis to provide organics for microorganism growth and utilization. However, it may be accompanied by high costs and unclear environmental and economic impacts. Therefore, this study evaluates the effect of the ultrasonic lysis–cryptic growth technology from the environmental and economic perspectives. For this purpose, a mass balance evaluation, life cycle assessment, comprehensive environmental assessment and economic assessment are conducted and three typical ultrasonic lysis frequencies (i.e. R1: 1/3d, R2: 1/d and R3: 2/d) are selected for verification. The mass balance evaluation results indicate that the ultrasonic lysis–cryptic growth technology increases CO2 release by 11% compared to conventional technology. The environmental and economic impacts of the ultrasound lysis frequency of 2/d are reduced by 26% and 49%, respectively. The comprehensive assessment shows that the optimal parameter is the ultrasound lysis frequency at 1/d because it can reduce carbon emission and reduce the total cost of 45.62%. In conclusion, the ultrasonic lysis–cryptic growth technology is better than the conventional technology with respect to the environmental and economic aspects. Therefore, the comprehensive assessment of ultrasound treatment sludge technology can lay the foundation for practical application.