Artigos de Revista

Wastewater treatment plants (WWTPs) are facing challenges concerning the service’s effectiveness and reliability, as well as the efficiency and sustainability of resource utilization, where energy represents one of the higher costs in activated sludge (AS) treatment. This paper presents the latest developments in the new energy performance indices (PXs) we have been developing for benchmarking, i.e., assessing and improving the performance of this widely used treatment. PXs compare the energy consumption with the energy requirements for the carbon and nitrogen removals needed for the plant’s compliance with the discharge consents (the closer they are, the better the performance). PXs are computed by applying to the state variables a performance function that is defined by the reference values for excellent, acceptable, and unsatisfactory performance. This paper shows the rationale for selecting the state variables for the AS energy performance and the comprehensive derivation of the equations to determine the reference values for energy consumption, which incorporate the effect of key parameters (flows, concentrations, and operating conditions). Reference values for the operating conditions affecting the energy performance are also proposed. A sensitivity analysis identified the key parameters for improving the aeration performance: ?, F, and SOTE for air diffusers, and ? and N0 for mechanical aerators. Fourteen Portuguese urban WWTPs (very diverse in size and inflows) were analyzed, and aeration (0.08–1.03 kWh/m3) represented 25–80% of total energy consumption (0.23–1.30 kWh/m3). The reference values for excellent performance were 0.23–0.39 kWh/m3 (P25–P75) for AS systems with air diffusers and 0.33–0.80 kWh/m3 for those with mechanical aerators. A comprehensive application in one WWTP (16–18 d solids retention time) showed the system’s ability at identifying which operating conditions to adjust (to F/M ratio lower than 0.09 d?1 and decreasing aeration during the low season) to improve the energy performance/savings while maintaining the treatment’s effectiveness and reliability.

This paper aims at proposing and demonstrating the application of a novel distress-based condition assessment approach to evaluate the physical condition of inspectable urban water assets based on the classification of anomalies in terms of severity, intensity and extension using three new deterioration indices. These indices are, firstly, calculated at the asset component level and, then, aggregated at the asset level and at the infrastructure level by weighing the component indices with the respective replacement cost or criticality. A condition grading classification associated with the deterioration indices is proposed. The novel distress-based condition assessment approach is applied to 22 drinking water storage tanks and 17 wastewater pumping stations located in Portugal, that have been specifically inspected for this purpose. Results of deterioration indices are compared with those obtained by the value-based condition assessment approach. Results demonstrate that the proposed approach allows a more reliable assessment of the assets’ condition and a more robust establishment of priority rehabilitation or maintenance interventions

Circular/spherical rigid particle models that were initially applied to rock fracture studies were not able to match the ratio of the compressive strength to tensile strength that occurs in rock. In addition, the predicted macroscopic friction angle was much lower than the known hard rock experimental values. Several enhancements have been proposed to address these issues, namely the use of a clumped particle logic or the adoption of polygonal/polyhedral grain structures, either rigid or flexible. In this work, a flexible 2D DEM based particle model (PM) that allows deformable particles to interact in a simplified way is presented. The proposed flexible PM model keeps the contact interaction simplicity and the reduced computational costs characteristic of circular rigid particle models. The PM model is tested using biaxial tests and Brazilian tests. A discussion re- garding the influence of the grain deformability on the macroscopic elastic and strength response is presented. It is shown that, when compared with a rigid model, the proposed flexible PM model predicts more reasonable indirect tensile strength to direct tensile strength ratio and requires a smaller value of contact fracture energy to give a good agreement with known experimental data. It is also shown that the proposed flexible PM model can predict a behaviour similar to that ob- tained using a flexible PM model through inner particle discretization that is more computationally demanding.

This paper presents a novel energy balance scheme tailored for assessing energy efficiency in wastewater systems. It provides a consistent method to calculate the energy components associated with wastewater transport processes, allowing the quantification of the main water-energy inefficiencies. Three assessment levels are described (macro, meso and micro-level), depending on available information and scope. This balance allows a holistic approach of wastewater systems energy efficiency, including the system layout, losses in pipes/manholes, energy associated with undue inflows, exceedance volumes and energy recovery. The energy balance is applied to realcase studies. The energy associated with undue inflows represents from 20% to 44% of the external energy, with low average efficiencies of wastewater pumping systems (34%) and inflow intrinsic energy representing 64% of the total energy. This energy balance supports the performance diagnosis and the development of energy efficiency improvement measures.

This paper aims at compiling the most relevant information concerning the use of cement-based mortars and concretes in the rehabilitation, retrofitting, and strengthening of hydraulic structures, namely concrete dams. The most important properties of cementbased mortars and concretes as repair materials are addressed, with a special focus on its compatibility with the concrete substrate. After a brief allusion to generic preparatory works, some of the most common practices are described. The main topics are mortar and concrete toppings, i.e., patches and overlays and thickening of the dam section. Among overlays, shotcrete and underwater works are addressed in detail. Littlerock, Oberems, and Storfinnforsen dam interventions are briefly described as successful rehabilitations involving the shotcrete method, whereas the Albbruck-Dogern dam intervention is given as an example of effective underwater repair works. As for dam section modifications, Kölnbrein, Olef, and Sasanagare dams are presented as conventional mass concrete placements within rehabilitation operations, while Les Toules, Gibraltar, Santa Cruz, and Littlerock dams are references for roller compacted concrete strengthening.

A simple and consolidated reliability-based method widely used to unveil the real reliability and stability of wastewater treatment plants (WWTPs) is herein proposed to trigger decision making on operational improvements and asset management for maintaining or improving treatment effectiveness, reliability, and efficiency.

Em Portugal há cerca de seis dezenas de grandes barragens de betão com observação continuada, sendo que cerca de um terço estão afetadas por reações expansivas de origem interna do betão. Uma delas, a barragem do Alto Ceira, foi mesmo substituída em 2013, já que não era viável a sua reabilitação. Há três que apresentam valores médios das extensões acumuladas no tempo superiores a 1000×10–6 (Pracana, Santa Luzia e Fagilde). A barragem de Pracana sofreu importantes obras de reabilitação na década de 1980. Atualmente apenas a barragem de Fagilde apresenta taxas de expansão anuais superiores a 100×10–6. Nas outras barragens afetadas os processos de deterioração são ainda de pequena a moderada magnitude, mas em algumas delas as taxas de expansão têm aumentado nos últimos anos. Apresenta-se uma síntese das principais atividades de observação (monitorização, inspeção e ensaios) das obras e dos resultados de alguns estudos realizados, no âmbito do acompanhamento do comportamento deste conjunto de barragens.

Urban water drainage systems' primary function is to transport sanitary or stormwater. The intrusion of saline waters has recognized detrimental effects. Especially in coastal areas, saline inflows can compromise performance by increasing the risk of untreated discharges, weakening the structural condition of concrete or metallic components, reducing the effectiveness of wastewater treatment processes and limiting the potential reuse for irrigation. Performance deterioration can be prevented by an early assessment of exposure to saline water, followed by timely actions to control its causes and consequences. The paper describes a procedure for diagnosing undue saline inflows. The procedure is based on the determination of saline inflow's magnitude, acceptance levels, and contribution to the system's performance. Contextual factors and performance indicators, and their reference values, are selected for the assessment. Options to address the problem are proposed, depending on the results. These options can relate to organizational, operational, and structural actions. Application to a case study allowed to validate the method and discuss the results. Here, saline volumes entering the system are quite relevant (almost 30%), posing problems regarding corrosion, treatment plant operation and significant concrete exposure to intermittent saline waters.

A aplicação de argamassas de desempenho térmico melhorado em sistemas multicamada de isolamento térmico pelo exterior tem sido cada vez mais frequente, quer em construção nova, quer na reabilitação térmica de fachadas de edifícios. Com o presente estudo, pretende-se avaliar a resistência à biocolonização e o desempenho à água de três argamassas térmicas aplicadas em sistemas multicamada. Os resultados demonstram a importância de um bom desempenho de todos os componentes do sistema para um aumento da eficiência e durabilidade do conjunto.