Construction and operation of the MIDES plant

This chapter presents the construction, operation, and validation of all the MIDES systems, including water pre-treatment, wastewater pre-treatment, the microbial desalination cell (MDC), low-pressure reverse osmosis (RO), and post-treatment (remineralization and disinfection). MIDES technology has been validated with different water sources: brackish water from Demo Site 1, (Racons Brackish Water Desalination Plant (BWDP), located in Denia, Spain) and seawater from Demo Site 2 (Fonsalía Seawater Desalination Plant (SWDP), located in Guía de Isora, Spain). In this chapter, the preparation of both demo sites for the reception and installation of the pilot plants is also presented.

New frontiers and outlook

The main goal of this chapter is to outline the areas for further development and research of microbial desalination cells (MDCs) for production of low energy drinking water. This chapter highlights the challenges ahead in the context of membrane and electrode development, scaling-up, construction, environmental challenges, capital and operational costs, social acceptancy and further identification of niche areas for MDCs.

Introduction to desalination and microbial desalination cells

This chapter presents desalination as one of the technologies to alleviate water scarcity and its contribution to the sustainable development goals. An overview of the world and regional desalination capacity is presented and areas where desalination has potential for development are identified. The overall concept of the microbial desalination cells is presented and the areas where key innovations were developed is presented. A discussion on the energy costs and production costs in seawater reverse osmosis is briefly discussed.

Microbial desalination cell design & bioengineering assays: Main concepts

The main goal of this chapter is to present the main concepts and principles for the microbial desalination process. Also, a rational explanation of the electrochemical behaviour of the microbial desalination cell (MDC) setup under different experimental conditions is presented. The final section of the chapter shows the design and construction of an MDC pre-pilot unit, as well as the main results of desalination and water treatment capacity for the scaled-up device.

Simulation and control systems in MIDES

This chapter presents the work concerning the modelling and simulation of the overall MDC process, as well as its performance analysis and optimization. It also focuses on the support that the work brings for operational decisions on desalination plants, specifically applied to a microbial-powered approach for water treatment and desalination, starting from the stages of process modelling, process simulation, optimization and lab-validation, through the stages of plant monitoring and automated control. The work is based on the application of the environment IPSEpro from SimTech for the stage of process modelling and simulation; and on the system Databridge from Oncontrol for automated control, which employs techniques of machine learning.

Key elements and materials in microbial desalination cells

This chapter presents the most relevant advances achieved during the MIDES project in relation to material development of key elements for microbial desalination cells. The first section is devoted to electrodes. Providing a general overview of the requirements of carbon-based materials to serve either as anodes or cathodes for microbial desalination cells. Advances achieved during MIDES in the development of materials for anode and cathode application are listed. The second section is focussed on ion-exchange membranes for microbial desalination cells. General considerations for the use of these membranes are reported as well as key parameters. Finally, advances in ion-exchange membrane development, in terms of antifouling and their performance in desalination trials, achieved during the MIDES project, are reported.

Environmental assessment for desalination projects including microbial desalination cells

For MIDES it was necessary to analyse the aspects that should be considered for the environmental assessment of desalination projects that integrate the microbial desalination cells as pre-treatment for reverse osmosis. The approach used to that end was to combine three methods: revision of existing guidance for environmental and social assessment of desalination projects to compile a list of components and impacts; life cycle analysis based on a pre-pilot MDC to determine impacts associated with its construction and operation; and risk assessment to determine risks of the potential release of nanoparticles. The results showed that, at project level, existing guidance needs to pay more attention to the effects that the local and regional environment could have on a desalination project and to the regional cumulative effects to which a project could contribute. At the level of the MDC, the main impacts were the contribution to climate change and toxicity resulting from the 20:1 ratio of catholyte to feed water; however, preliminary data for the operation of a pilot MDC showed a reduction to a 5:1 ratio, with largely reduced impacts. At the structural level, the risk assessment showed that the release of nanoparticles from the cathodes and membranes is negligible.

Design of the MIDES plant

This chapter presents the full design of two microbial desalination cells (MDCs) at pilot-plant scale from the MIDES project. The final MDC pilot unit design was based on the knowledge gained through up scaling of the MDC from lab- to prepilot scale. The MDC pilot plant consists of one stack of 15 MDC pilot units with 0.4 m2 electrode area. This chapter also presents the piping and instrumentation diagram (P&ID) and layout of the MDC pilot plant. The MIDES pilot plants are comprised of an MDC pilot plant housed in a 40-ft container with the rest of the peripheral elements. Finally, this chapter presents the improvement made from the first to the second MDC stack in terms of stability and the chemical compatibility of the end plates.