Cost-Effectiveness Analysis of Sewer Mining versus Centralized Wastewater Treatment: Case Study of Arga River Basin (Spain)

ABSTRACT:In the context of the EU Water Framework Directive, a Cost-Effectiveness Analysis (CEA) was performed to compare centralized and decentralized wastewater treatment strategies aimed to improve the ecological status of a Spanish river. The implementation of several hybrid membrane bioreactors within the urban framework for sewer mining (SM) was compared with the more common wastewater treatment plant enlargement option. The assessment ranked 6 alternatives based on 12 potential scenarios, aimed at narrowing the uncertainty of the CEA. The cost analysis illustrated that SM is the most expensive option regarding both investment and operation and maintenance costs. However, the effectiveness of the alternatives evaluated depends significantly on the scenarios considered, being SM the most effective in most cases. Finally, the cost-effectiveness ratio showed SM as the best cost-effective alternative. CEA provides an ecological-economic indicator useful to prioritize wastewater treatment alternatives to achieve a given objective

Feasibility of hydraulic separation in a novel anaerobic-anoxic upflow reactor for biological nutrient removal

ABSTRACT : This contribution deals with a novel anaerobic-anoxic reactor for biological nutrient removal (BNR) from wastewater, termed AnoxAn. In the AnoxAn reactor, the anaerobic and anoxic zones for phosphate removal and denitrification are integrated in a single continuous upflow sludge blanket reactor, aiming at high compactness and efficiency. Its application is envisaged in those cases where retrofitting of existing wastewater treatment plants for BNR, or the construction of new ones, is limited by the available surface area. The environmental conditions are vertically divided up inside the reactor with the anaerobic zone at the bottom and the anoxic zone above. The capability of the AnoxAn configuration to establish two hydraulically separated zones inside the single reactor was assessed by means of hydraulic characterization experiments and model simulations. Residence time distribution (RTD) experiments in clean water were performed in a bench-scale (48.4 L) AnoxAn prototype. The required hydraulic separation between the anaerobic and anoxic zones, as well as adequate mixing in the individual zones, was obtained through selected mixing devices. The observed behaviour was described by a hydraulic model consisting of continuous stirred tank reactors and plug-flow reactors. The impact of the denitrification process in the anoxic zone on the hydraulic separation was subsequently evaluated through model simulations. The desired hydraulic behaviour proved feasible, involving little mixing between the anaerobic and anoxic zones (mixing flowrate 40.2% of influent flowrate) and negligible nitrate concentration in the anaerobic zone (less than 0.1 mgN L-1) when denitrification was considered

Hybrid biological reactors for wastewater treatment : evaluation of innovative applications

RESUMEN: Esta tesis doctoral evalúa diferentes aplicaciones de procesos biológicos híbridos, que integran biomasa en suspensión y biopelícula en el mismo reactor, para el tratamiento de aguas residuales. Se presenta la experiencia alcanzada en una planta piloto configurada según el esquema UCT para eliminación de nutrientes, instalando reactores híbridos de lecho fijo en la etapa anóxica y la aerobia y tratando agua residual urbana. Los resultados demuestran el incremento de la capacidad del sistema en cuanto a eliminación de nitrógeno gracias a la existencia de biopelícula en los reactores híbridos, así como la capacidad de la biomasa en suspensión para eliminar fósforo. Además, se desarrolló un modelo utilizando AQUASIM para simular el comportamiento del sistema y, en concreto, de la biopelícula y la biomasa en suspensión presentes en el reactor anóxico híbrido. El modelo permitió establecer condiciones de operación que se consideran recomendables para lograr altos rendimientos de depuración en los reactores anóxicos híbridos. Por último, se propone y evalúa la aplicación de sistemas híbridos en reactores aerobios con membranas para sewer mining frente a otras más convencionales para lograr mejorar la calidad de las aguas superficiales mediante un análisis coste-eficacia aplicado a un caso de estudio.ABSTRACT: This PhD thesis evaluates different applications of hybrid biological processes, which integrate suspended biomass and biofilm in the same reactor, for wastewater treatment. The experience gained in a pilot plant treating urban wastewater configured according to UCT scheme for nutrient removal, having hybrid fixed bed reactors in the anoxic and aerobic stages, is presented. The results demonstrate that the presence of biofilms in the hybrid reactors increases the system capacity in terms of nitrogen removal, and also show the ability of the suspended biomass to remove phosphorus in these systems. An AQUASIM based model was developed to simulate the behavior of the system and, specifically, the behavior of the biofilm and suspended biomass present in the hybrid anoxic reactor. This model allowed to establish the operating conditions that are considered desirable to achieve high removal performance in hybrid anoxic reactors. Finally, the application of hybrid systems in aerobic reactors with membranes is assessed for sewer mining, in order to improve the quality of surface waters and evaluated compared to more conventional approaches through a cost-effectiveness analysis applied to a case study

Feasibility of hydraulic separation in a novel anaerobic-anoxic upflow reactor for biological nutrient removal

This contribution deals with a novel anaerobic-anoxic reactor for biological nutrient removal (BNR) from wastewater, termed AnoxAn. In the AnoxAn reactor, the anaerobic and anoxic zones for phosphate removal and denitrification are integrated in a single continuous upflow sludge blanket reactor, aiming at high compactness and efficiency. Its application is envisaged in those cases where retrofitting of existing wastewater treatment plants for BNR, or the construction of new ones, is limited by the available surface area. The environmental conditions are vertically divided up inside the reactor with the anaerobic zone at the bottom and the anoxic zone above. The capability of the AnoxAn configuration to establish two hydraulically separated zones inside the single reactor was assessed by means of hydraulic characterization experiments and model simulations. Residence time distribution (RTD) experiments in clean water were performed in a bench-scale (48.4 L) AnoxAn prototype. The required hydraulic separation between the anaerobic and anoxic zones, as well as adequate mixing in the individual zones, were obtained through selected mixing devices. The observed behaviour was described by a hydraulic model consisting of continuous stirred tank reactors and plug-flow reactors. The impact of the denitrification process in the anoxic zone on the hydraulic separation was subsequently evaluated through model simulations. The desired hydraulic behaviour proved feasible, involving little mixing between the anaerobic and anoxic zones (mixing flowrate 40.2 % of influent flowrate) and negligible nitrate concentration in the anaerobic zone (less than 0.1 mgN L-1) when denitrification was considered