The Spanish National Water Quality Plan (PNCA) features a number of actions that seek to achieve full compliance with Directive 91/271/EEC on urban wastewater treatment, as well as achieving the target of good ecological status set out in the Water Framework Directive. The Casaquemada WWTP, located in the municipal district of San Fernando de Henares (Madrid) and managed by Canal de Isabel II, the publicly-owned company responsible for the integrated urban water cycle in the Autonomous Community of Madrid, required upgrading to achieve compliance with the provisions of these Directives, particularly as regards nutrient removal. The contract for the drafting of the design and the execution of the works was awarded to the UTE EDAR CASAQUEMADA consortium, made up of Acciona Construcción S.A. and Acciona Agua, S.A.U.
Location and site
The WWTP site is flanked on the western side by the M-206 motorway and the northern boundary is marked by la Huerta and the irrigation ditches belonging to the “Real Sitio de San Fernando hydraulic system”, which are included in the Directory of buildings, elements, spaces and areas of singular value associated with the Review of the General Urban Development Plan (PGOU 2002). The eastern boundary is marked by an industrial building located very close to the Jarama River on Protected Land that cannot be developed due to the fact that it is within the grounds of the Southeast Regional Park. And the southern boundary of the plant is adjacent to the San Fernando de Henares Cemetery and a green belt classified as a General Green Zone System. Due to the characteristics of the land adjoining the EDAR site, the upgrading work could not involve enlargement of this site.
Meeting the more stringent effluent discharge parameters set out in current legislation with respect to nitrogen and phosphorus would have required an extension to the existing bioreactor, which implemented a conventional activated sludge process for nitrogen and phosphorus removal. However, this was not possible due to the limitations on site enlargement outlined above.
It was decided to implement a process that would maximise the organic matter and nitrogen removal capacity of the existing reactor by carrying out the necessary modifications, thus ensuring treatment of the current inflow to the plant in accordance with the requirements of the National Water Quality Plan and other applicable legislation.
WORK CARRIED OUT
The work carried out within the framework of the project included:
• Upgrading of biological treatment to achieve compliance with the Spanish National Water Quality Plan
• Complementary actions
Upgrading of biological treatment to achieve compliance with the Spanish National Water Quality Plan
The actions executed for the purpose of modifying biological treatment in order to achieve the nutrient removal capacity needed to meet the requirements of the National Water Quality Plan were as follows:
• Complete emptying of the bioreactors requiring renovation, cleaning and conditioning of the reactors, and complete isolation of the units to enable the necessary work to be carried out in conditions compliant with occupational health and safety regulations.
• Disassembly of existing diffuser grids.
• Disassembly of existing mixers in the original facultative zones
• Adaptation of internal spaces and walls within the bioreactors to optimise the layout of chambers for the new process.
• Installation of new submersible mixers in facultative (anoxic and anaerobic zones) and anoxic zones of each bioreactor.
• Replacement of aeration blower of the out-of-service bioreactor with a new unit with a flow rate of 6,000 m3/h.
• Adaptation and extension of the aeration network (conduits, pipes, etc.) from the air production units to the bioreactors.
• Installation of new air distribution grids featuring perforated stainless steel pipes in the aerated zones of the remodelled bioreactors.
• Remodelling of recirculated sludge inlet channels to each of the bioreactors to enable the sludge to enter at two different points.
• Installation of two mixed liquor recirculation pumps (internal and complementary) to meet the requirements of the process implemented, with separate submersible pumps and pipes in each bioreactor.
• Supply and installation of plastic media carriers for the Integrated Fixed-Film Activated Sludge (IFAS) process, as well as perforated pipes to connect the different compartments of the reactors.
• Installation of instrumentation and PLCs needed for the IFAS biological process, and the corresponding cables and wiring.
• Programming, control and automation, and sequential commissioning and maintenance of the new installations as they were completed, in such a way as to maintain the required treatment capacity during the execution of the works.
Published in: FuturENVIRO #67 February 2020