A dirty job: dishwasher wastewater reuse and upcycle through an ad hoc engineered microbial consortium

In the framework of regenerative circular economy and Sustainable Development Goals #6, water demand and wastewater production are a crucial environmental issue. To cope with this, a system called Zero Mile has been conceived to reuse/upcycle the dishwasher wastewater in both fertilisation of a vertical garden (for home plant production at zero mile) and the subsequent dishwasher rinsing cycle. The core of the Zero Mile system is a biofilter constituted by an ad hoc engineered microbial consortium, based on the mutualistic relationship between autotrophic and heterotrophic microbial partners, that makes the biodegradative process sustainable over time. Two semi-batch tests were performed to evaluate the capability and the efficiency of the microbial consortium to operate in conditions mimicking the Zero Mile system: consortia were challenged in two dishwasher wastewater volumes (50 and 500 mL), with a replenishing rate of 4 days for ¼ of the dishwasher wastewater volume. The results of these tests showed that the consortium thrives well in dishwasher wastewater over time and can survive with the volume and rates of replenishments. Next Generation Sequencing showed that the microbial consortium maintains a stable taxonomic composition, and chemical analyses demonstrated a very high bioremediation efficiency (total nitrogen and phosphorus removal). Aiming to contribute to the circular economy approach, the consortium ‘treated’ dishwasher wastewater was useful for plant fertilisation, as demonstrated by pigment content and quality indices (total phenols and flavonoids, soluble solids) measured in the lettuce plants grown in the Zero Mile demonstrator and watered with consortium reclaimed dishwasher wastewater.