LCA of municipal wastewater treatment plants from small population centres

Nowadays, all the processes must be analyzed from a global environmental point of view, even those that are considered treatment systems of emissions such as wastewater treatment plants (WWTP). In these plants different processes take place: energy is consumed, chemical reagents are used, sludge and emissions to the atmosphere are generated. One of the main challenges for the European water policy is the water treatment in small population centres. In fact, the European Directive 91/271 (well-known as "The European Water Act") forces that by 1st January 2006, all the generated emissions from populations between 10,000 and 15,000 hab. must be treated with a secondary treatment, except in the coastal zones, where only primary treatment can be applied. This fact justifies the environmental study of the different applied technologies in centres with a reduced number of inhabitants. At the present time, 17 WWTPs of Galicia (northwest of Spain) are being studied. They are classified into three groups (Group 1: 50,000-10,000 inhab. eq; Group 2: 10,000-2,000 inhab. eq.; Group 3: less than 2,000 inhab. eq.). This classification is similar to the one included in the Directive 91/271. In this paper, the results concerning the second group are presented. The wastewater treatment process was considered as a global system, which can be divided in five subsystems (Figure 1): subsystem 1 (pre-treatment and primary treatment), subsystem 2 (secondary treatment), subsystem 3 (sludge line), subsystem 4 (auxiliary activities) and subsystem 5 (sludge leaving the WWTP). For the analysis of the potential environmental impacts of these WWTPs, the methodology of the Centre of Environmental Science (CLM) of the University of Leiden was used. An exhaustive inventory of each WWTP was evaluated considering the inputs (chemical reagents, energy...) and the outputs (emissions to water, air, soil and generation of solid waste).