Identifying improvements in water management of bus-washing stations in Brazil

Bus-washing stations play a great role in an urban metropolis daily life. On working days, 15,064 vehicles circulating in Sao Paulo are washed at the end of each day, and transport companies consume approximately 2,200,000 m3 of water per year in this activity. This study compares three bus-washing systems operating in São Paulo. Two of these companies use the conventional washing system, using water of artesian wells and disposing the effluent in the public network or in water bodies. The third company uses a rainwater catchment system together with a treatment plant for water reuse. The environmental accounting in emergy concerns to the efficiencies of bus-washing processes, the calculation of emergy indicators, and the potential for the improvement of the three systems. The results of the environmental accounting suggest that the wastewater reuse and the rainwater collection improve the environmental performance of bus-washing activity. The comparison of the environmental cost of the wastewater treatments showed that the best environmental option is the installation of a wastewater treatment plant within the companies for internal water reuse. Opportunities of rainwater catchment and shampoo reduction were also evaluated, showing that there are considerable environmental gains for the companies and for the region of São Paulo. A first opportunity of improvement was applied to companies B and C by installing a rainwater catchment system, decreasing the indice of environmental load from 900 to 170. For companies A and B, there is an opportunity to reduce the use of shampoo during operation in 20% in weight, which leads to an increase of the global productivity of 12%. Global productivity of companies B and C may increase 20% by the installation of a wastewater treatment plant, but to achieve a performance comparable to that of Company A, reuse of the treated water must be implemented.