This paper presents the theoretical basis and the main results obtained during the development and full-scale experimental validation of the new supervisory control strategy designed for the Galindo-Bilbao wastewater treatment plant (WWTP). The different phases of the project have been carried out over the last 8 years, combining model simulations, pilot-plant experimentation and full-scale validation. The final control strategy combines three complementary control loops to optimise the nitrogen removal in pre-denitrifying activated sludge plants. The first controller was designed to maintain the average concentration of the ammonia in the effluent via the automatic selection of the most appropriate DO set point in the aerobic reactors. The second control loop optimises the use of the denitrification potential and finally, the third control loop maintains the selected amount of biomass in the biological reactors by automatic manipulation of the wastage rate. Mobile-averaged windows have been implemented to incorporate commonly used averaged values in the control objectives. The performance of the controllers has been successfully assessed through the full-scale experimental validation in one of the lines of the WWTP.

The theoretical basis, practical implementation, and experimental validation of an on–off control strategy for dissolved oxygen (DO) in aerobic reactors of pilot‐scale activated‐sludge plants with simultaneous estimation of oxygen uptake rate are presented. The effect of dead time and a long response time for robust DO probes has been carefully analyzed and corrected through modeling of the dynamic response of the sensor. Study results indicate that the amplitude of the control band depends on the dead time of the probe. Simultaneous estimation of the volumetric mass‐transfer coefficient for DO (KLa) permits a continuous check of the aeration equipment. Experimental validation has been achieved in a continuous pilot‐scale plant.

The potential and limits of different configurations of the BioDenitro-alternating process to suit the various design cases that can arise depending on the wastewater characteristics, space necessary and effluent nitrogen requirements were analysed through simulations of the activated sludge model No. 2. The first analysis involved the combination in one cycle of the main phase in the alternating reactors with an aerated phase having the two reactors in aerobic conditions and/or a hydraulic phase using the flow only in the anoxic reactor. This option has been found to have a very high potential for cases with strict requirements concerning effluent total nitrogen, but limited when the requirements are low effluent NH4-N, relatively high effluent total nitrogen and minimum solids and hydraulic retention times. When the latter conditions have to be fulfilled the incorporation of a post-aeration reactor to the alternating reactor was found to be very effective. In addition the configuration is very flexible because multiple combinations of post-aeration reactor volumes and in the duration of the different phases in the alternating reactors can be selected to achieve effluent nitrogen requirements. This flexibility is limited to the use of moderate values in the post-aeration reactor volumes and in the duration of the aerated phase. An experimental trial of the latter configuration was carried out and demonstrated its operational simplicity by achieving the desired nitrogen requirements in the effluent simply by changing the duration of the aerated phase for a given post-aeration reactor volume. From the experimental results an enhanced simultaneous nitrification-denitrification at the start of aeration in the alternating reactors was found and the ASM2 model was shown to have a satisfactory predictive capacity.

This paper presents the real-time control strategies developed to regulate both the ammonia and nitrate concentration in the effluent of the new Vitoria WWTP (Spain). Nitrate control aims at the optimal use of the denitrification potential at any moment. For this purpose, the proposed control algorithm continuously adapts the internal recycle flow in order to maintain a desired nitrate set-point in the anoxic zone. Ammonia control aims at maintaining the required average concentration of ammonia in the effluent by manipulating the Dissolved Oxygen (DO) set-point. The control strategies have been based on a hierarchical structure where a high-level or supervisory control selects the set-point of the low-level or conventional controllers. The design of the controllers was carried out using the Quantitative Feedback Theory QFT for the design of robust control systems. Moving average values of some variables have been introduced in order to eliminate the perturbations associated with the daily 24-hour profiles. The controllers have been verified using long-time dynamic simulations based on a mathematical model previously calibrated in pilot plant. Influent load and temperature used in the simulations correspond to the real values measured in the full-scale WWTP during 12 months. The results obtained in the simulations show the good performance and stability of the control strategies independently from external disturbances. A short-time experimental verification of the controllers in pilot plant with real wastewater is also presented.

The Camp de Tarragona Water Reuse Project is an emblematic example of how regional water scarcity can be overcome by considering reclaimed secondary effluent, which would otherwise be disposed of in the Mediterranean Sea, as an essential component of integrated water resources management. An advanced water reclamation plant (AWRP) was completed in 2011 to reclaim municipal secondary effluent from Tarragona and Vilaseca-Salou wastewater treatment plants. The reclaimed effluent is used for cooling and process water at the nearby Tarragona petrochemical park. The AWRP's current (2014) capacity is 19,000 m3/d (Phase I), and further expansions are planned to produce 29,000 m3/d (Phase II) and 55,000 m3/d (Phase III) in coming years. This locally available additional water supply will replace surface water supplies currently transferred from the Ebro River for use at the petrochemical park; as a result, an equivalent volume of surface water will be available for urban water supply in the coastal areas of Tarragona province. By developing this new and locally available water supply source, industrial growth in a water scarce region has been supported, while promoting local industry's sustainability. This industrial water reuse project provided 0.20 hm3 of water from September to December 2012, its first operational year, and 1.37 hm3 in 2013. The paper presents and discusses the planning, design, construction and operation phases of this water reclamation and reuse project, including start-up and commissioning, facilities preservation protocols from construction completion to servicing start-up, and the operational, management and economic arrangements adopted to provide a reliable source of reclaimed water for cooling water systems and demineralized water for boiler feed at the Tarragona petrochemical park and a nearby cogeneration power plant.