Evaluation of the environmental implications to include structural changes in a wastewater treatment plant Nu ´ria Vidal, 1 Manel Poch, 1 Euge `nia Martı ´ 2 and Ignasi Rodrı ´guez-Roda 1 * 1 Laboratori d’Enginyeria Quı´mica i Ambiental, Universitat de Girona, Campus Montilivi s/n, 17071 Girona, Spain 2 Centre d’Estudis Avanc ¸ats de Blanes, CSIC, Camı´de Santa Ba `rbara s/n, 17300 Blanes, Spain Abstract: The environmental implications of including structural changes in a wastewater treatment plant to decrease effluent concentrations of nitrogen were evaluated in this study. Environmental effects from these structural changes were assessed by using the Life Cycle Assessment theoretical framework. The wastewater treatment plant selected as a reference scenario had an activated sludge configuration. The Ludzack–Ettinger and Oxidation Ditch configurations were selected as modifi- cations of the reference scenario. Results from this study show that the inclusion of nitrogen removal mechanisms in the configuration of the plant reduces the effect of the plant on the eutrophication, but simultaneously increases the effect on the consumption of abiotic resources, global warming, acidification and human toxicity. These general trends, however, vary depending on the configuration selected to remove nitrogen. Taking all the impacts together, the Oxidation Ditch configuration would cause less environmental impact than the Ludzack–Ettinger configuration, given the characteristics of the selected scenarios. # 2002 Society of Chemical Industry Keywords: environmental; biotechnology; wastewater; nitrogen; life cycle assessment; eutrophication Notation BOD 5 Biochemical Oxygen Demand (g m 3 ) C ij Potential contribution of a given emission j to the environmental impact i (kg equivalent) COD Chemical Oxygen Demand (g m 3 ) DO Dissolved Oxygen concentration (g m 3 ) E j Emission or resource consumption (g t 1 wastewater) F/M Sludge loading (kg BOD 5 kg 1 MLVSS) MLVSS Mixed Liquor Volatile Suspended Solids (gm 3 ) SRT Sludge Retention Time (d) SS Suspended Solids (g m 3 ) TKN Total Kjeldhal Nitrogen (g m 3 ) W ij Weighting factor of a given emission j to the environmental impact i 1 INTRODUCTION Environmental preservation has recently become a key issue in society. Human activities are major contribut- ing factors to environmental degradation. Conse- quently, environmental legislation is increasingly restrictive in terms of emissions from human activities. For instance, the European Water Act (91/271/EC) establishes restrictive thresholds on the concentrations of wastewater emissions. To cope with these laws, over the last decades there has been an exponential increase in the implementation of end-of-pipe technologies. Whilst these technologies have greatly contributed to ameliorating environmental quality, they all have environmental side-effects, such as emissions to the atmosphere, use of natural resources (either renewable or not), energy consumption, and generation of by- products. 1 Additionally, some of the existing end-of- pipe technologies need to be restructured to fulfil the requirements of the new legislation. The objective of this study was to evaluate the environmental implications derived from including changes in one of these end-of-pipe technologies to comply with the actual legislation. In particular, we studied a wastewater treatment plant (WWTP) which had to be modified to include biological nitrogen removal. Environmental effects from these structural changes were assessed by using the Life Cycle Assessment theoretical framework. Life Cycle Assessment (LCA) is a tool that helps to identify the overall environmental effects associated with the whole life of a product or process. 2 This assessment is done by a systematic four-step procedure (Received 9 August 2001; revised version received 5 April 2002; accepted 11 April 2002) * Correspondence to: Ignasi Rodrı ´guez-Roda, Laboratori d’Enginyeria Quı ´mica i Ambiental, Universitat de Girona, Campus Montilivi s/n, 17071 Girona, Spain Contract/grant sponsor: Catalonian Water Agency Contract/grant sponsor: Spanish MCyT; contract/grant number: DP1-0665-C02-01 # 2002 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2002/$30.00 1206 Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 77:1206–1211 (online: 2002) DOI: 10.1002/jctb.674