An emergy evaluation of the sewage sludge treatment system with earthworm compositing technology in Chengdu, China

- The environmental sustainability of a sewage sludge treatment system was investigated.
- This resource recovery of waste can promote resource conservation greatly.
- Emissions' impact slightly reduces the comprehensive performance.
- Great dependence on nonrenewable resources leads to its un-sustainability in the long term.

With the continuous social and economic development, the output of municipal sewage sludge is increasingly rising. Sludge treatment and disposal technologies need economical investment and resource consumption, and their comprehensive performance should be investigated from pros and cons, to provide systematic information for policy-makers. Based on the characteristics of sludge treatment and/or disposal systems, this study proposed an improved emergy approach which considered emissions' impact, and then it presented a set of indicator system to explore the comprehensive performance of sewage treatment/disposal practice. Application of the proposed method and indictors to one sewage sludge treatment system with earthworm compositing technology located in Chengdu, China results show that (1) the dewatered sludge is the main contributor to this system, followed by mushroom dregs; (2) direct emissions from diesel use should be emphasized; (3) this system can promote resource conservation effectively through lower emergy investment; (4) emissions' impact slightly reduces the comprehensive performance; (5) this system is not sustainable in the long term due to great dependence on nonrenewable resources. Finally, this work puts forward some improvement suggestions for the sewage sludge treatment practice.