The biological filter for an innovative Sustainable Product System to recycle domestic wastewater

The reuse and saving of water in the domestic cycle is pivotal to achieve the sustainability of cities. An important step in the recycling of wastewaters (WWs) is the use of multispecific microbial consortia able to degrade and mineralize the organic matter present in the WWs; they can be used either attached or suspended, acting as biofilters. In this framework, the reduction and upcycling of WWs represents the main goal of the innovative Sustainable Product System (SPS) made of a dishwasher integrated with an indoor planting device, under development in a multidisciplinary co-design team. This SPS includes, among other components, a biological filter, engineered with different microbial strains, some of them collected among the dishwasher wastewater colonizers. In this study we selected and co-cultivated filamentous, biofilm forming, cyanobacteria (Trichormus spp.), isolated from dystrophic environments, together with some of the common heterotrophic bacteria present in the dishwashing WWs as Acinetobacter, Exiguobacterium and Pseudomonas spp.. Different combinations were tested in a set of culture systems and conditions (light, temperature, flow velocity and WW dilutions) to evaluate the efficiency in cleaning WWs, stripping of gross particulate, degrading of organic load, with ultimate nutrient mineralization used to support the growth of edible plants included in the integrated device. Simultaneous metagenomic analysis and community-based culture collection of the dishwasher wastewater allow (i) to directly explore the entire pool of microbial genomes and (ii) to identify and cultivate the bacterial populations ensuring the most efficient mineralization of dishwasher WWs. This strategy will lead to the assemblage of a self-sustaining, highly effective and customized microbial consortium/filter. This filter will be beneficial to both the environment and the economic circular domains, by reducing water use and wastewater discharge but simultaneously permitting the up-cycling of domestic WWs in on site food production.