Economic and environmental assessment of small and decentralized wastewater treatment systems

摘要

The aim of the present work was the assessment of economic and environmental aspects of decentralisedenergy-saving wastewater treatment systems. The formulated investment and operation cost functionswere adjusted by a power law function. The different wastewater systems serving population settlementsbetween 50 p.e. and 250 p.e., presented associated investment costs varying from 400 €/p.e. to 200 €/p.e.and annual operation costs in the range of 70 €/p.e. to 20 €/p.e., respectively. A Life Cycle Analysisapproach was used to compare the environmental impact alternative wastewater systems. The assessmentwas focused on two energy-saving systems (constructed wetland and slow rate infiltration) and aconventional one (activated sludge process). The low environmental impact of the energy-savingwastewater treatment systems was demonstrated, being the most relevant the global warming indicator.Options for reduction of life cycle impacts were assessed including materials used in construction andoperation lifetime of the systems. A 10 % extension of operation lifetime of constructed wetland and slowrate infiltration systems lead to a 5 % and 7 % decrease in the abiotic depletion indicator, respectively,and to a 1 % decrease in CO2 emissions in both systems. Replacing steel with HDPE in the activatedsludge tank resulted in a 1 % reduction in CO2 emission and 1 % in the abiotic depletion indicator. In thecase of the Imhoff tank a 1 % reduction in CO2 emissions and 5 % in abiotic depletion indicator wereobserved when concrete was replaced by HDPE. Therefore, considering the huge potential of energysaving wastewater treatment systems, the overall environmental impact of such design alternatives shouldnot be discarded.