Environmental performance of a municipal wastewater treatment plant

Goal, Scope and BackgroundNowadays, every strategy must be developed taking into account the global impact on the environment; if this aspect is forgotten, a change of environmental loads or their effect will be caused and no reduction will be attained. For instance, a wastewater treatment plant (WWIP), which is considereda priori as an ecological treatment system, gives rise to an environmental impact due to its energy consumption, use of chemical compounds, emissions to the atmosphere and sludge production, the post-treatment of which will also have diverse environmental effects. The goal of this study is to evaluate the potential environmental impact corresponding to a municipal WW1P and to identify the hot spots associated with the process.MethodsIn this study, the Centre of Environmental Science (CML) of Leiden University methodology has been considered to quantify the potential environmental impact associated with the system under study. A comprehensive analysis of the WWTP was evaluated for the physico-chemical characterisation of the wastewaters as well as the inventory of all the inputs (energy, chemical compounds, ...) and outputs (emissions to air, water, soil and solid waste generation) associated with the global process. Regarding Life Cycle Inventory Assessment, SimaPro 5.0 was used and in particular CML factors (updated in 2002) were chosen for characterisation and normalisation stages.Results and DiscussionA comprehensive inventory of empirical data from water, sludge and gas flows during 2000 and 2001 was obtained. Two impact categories arise due to their significance: eutrophication and terrestrial ecotoxicity. Consequently, the aspects to be minimised in order to reduce the environmental impact of the system are the pollutant load at the watercourse discharge (mainly NH3, PO4[3- and COD, even when all of them are below legal limits) and the emissions to soil (mainly Cr, Hg and Zn, even when they are present in low concentrations) when the sludge is used for agricultural application.ConclusionsAs far as the environmental impact is concerned, differentiation between humid and dry season is not required as results are practically equal for both situations. Water discharge and sludge application to land have turned out to be the main contributors in the environmental performance of a WWTP. Regarding the former, the removal of nitrogen by means of a nitrification-denitrification system coupled to conventional biological aerobic treatment impl