Environmental assessment of urban wastewater reuse: treatment alternatives and applications.

The main function of a Wastewater Treatment Plant is to minimize the environmental impact of discharging untreated water into natural water systems. Also a Wastewater Treatment Plant may get a resource from wastewater carrying out a tertiary treatment on the treated wastewater which can be reused in non-potable applications. Water reuse strategies are intended to address the problem of water scarcity without aggravating other environmental problems, thus reflecting the need of their environmental assessment. In this paper we used Life Cycle Assessment to evaluate different disinfection treatments (chlorination plus ultraviolet treatment, ozonation and ozonation plus hydrogen peroxide) and to assess the environmental advantages and drawbacks of urban wastewater reuse in non-potable applications. To do so, we compared the environmental impacts of producing 1m(3) of water for non-potable uses from reclaimed water, potable water and desalinated water sources. The calculation has used current operating data from a Wastewater Treatment Plant located in the Mediterranean area, although the results can be applied to any other plant with similar technology. The ozonation and ozonation plus hydrogen peroxide disinfection treatment technologies have similar environmental profiles. However most of the indicators are about 50% higher than the ultraviolet disinfection except for the acidification (100% higher) and photochemical oxidation (less than 5%). Non-potable uses (both agricultural and urban uses) of reclaimed water have environmental and economical advantages. Reuse of treated wastewater is particularly beneficial when it can replace desalinated water. Consequently, reclaimed water should be promoted for non-potable uses, when there is scarcity of freshwater.

LCA as a decision support tool for the environmental improvement of the operation of a municipal wastewater treatment plant.

Life cycle assessment (LCA) methodology is used to evaluate the environmental profile of a product or process from its origin to its final destination. In this paper we used LCA to evaluate the current situation of a wastewater treatment plant and identify improvement alternatives. Currently, the highest environmental impacts are caused by the stages of the plant with the highest energy consumption, the use of biogas from anaerobic digestion (95% burned in torch) and the final destination of the sludge (98.6% for agricultural use and 1.4% for compost). We propose four alternatives for biogas applications and five alternatives for sludge applications and compare them to the current situation. The alternatives were incorporated in a decision support system to identify and prioritize the most positive environmental option. Using biogas to produce electricity or a combination of electricity and heat provided the best environmental options since the energy produced would be enough to supply all the stages of the plant, thus reducing their environmental impact. The best environmental option for the final destination of the sludge is to combine the current situation (fertilizer replacement) with use of the sludge in a cement plant (as a replacement for fuel and raw material).