Case Study on Life Cycle Carbon Dioxide Discharge in Small-Scale Wastewater Treatment Plant

Abstract
As a method of comprehensively evaluating human activities from the viewpoint of the global environment, LCA has been introduced. However, noting LCCO2 in which CO2 is assessed, we investigated CO2 discharge affecting global warming during the construction and operation of small-scale wastewater treatment plants, as well as changes in CO2 discharge according to the size of the plant in the range of the evaluated scale. The findings are as follows:
(1) The CO2 discharge during construction was the highest in the smallest scale plants that require construction of an inflow pump tank, but decreased as the scale of the plant increased. The maximum CO2 discharge by a johkasou system at a BOD concentration of 20 mg/L of effluent was 30% higher than that by a johkasou system at a BOD concentration of 60 mg/L of effluent.
(2) When advanced treatment was added to the johkasou system at a BOD concentration of 20mg/L of effluent, the CO2 discharge during construction increased threefold.
(3) In the johkasou system at a BOD concentration of 20 mg/L of effluent, the maximum CO2 discharge during operation was 26 times that during construction.
(4) In the johkasou system at a BOD concentration of 20mg/L of effluent with an inflow 65m3/d,the CO2 discharge by the RC system was 1.6 times that of the FRP system.
(5) The CO2 discharge during operation accounted for 94-97% of all CO2 discharge during both construction and operation.

Key words: LCCO2, small-scale wastewater treatment plant, CO2 discharge, johkasou system