UASB reactors are mostly applied in industrial facilities. Advantages are being cost-saving, low footprint requirements, high removal efficiency at ambient temperatures, and hydraulic retention times of a few hours. This process is favoured in warm regions. In HYDROUSA, the UASB technology will operate even at relatively low temperatures, taking advantage of the much lower flows of sewage in winter, which allow to increase the hydraulic retention time (HRT). HYDROUSA establishes the optimal operating conditions under which COD removal and biogas production are maximised. The excess sludge from the UASB reactor will be composted. According to legal constraints the UASB effluent will either be treated in constructed wetlands (CWs), filtered and disinfected for reuse in agriculture, or will directly be used for fertigation after disinfection. The produced biogas will be upgraded to methane to be valorised as a fuel.

CWs applied for wastewater treatment are mainly thought as end-of-pipe solutions for removing contaminants; their application in a circular economy approach has to be optimised. Plants in current CWs are used to catalyse the biological processes, and are mostly planted in monocultures. HYDROUSA´s CWs will be richer in diversity, resulting in more resilient ecosystems. Three systems will be established in parallel: (1) a full-scale CW, (2) a pilot scale electroactive wetland system and (3) an aerated CW. (2) and (3) are defined as “enhanced CWs” and will be used to reach treatment needs in summer when wastewater generation increases. (1) Will is a combined UASB-CW scheme, already demonstrated at full-scale and will be optimised for water reuse joined to nutrients recovery.

This innovation is based on the design of the bio-cultivator, a self-irrigated home planting system in a closed vessel system with a composting process underneath. Organic residues are introduced in a vermicomposting unit to produce liquid fertilizer. The “compost-cultivator” of HYDROUSA takes this design to an upscale and a modification of the compost process. Sewage sludge from the UASB will be injected on top of a layer of biomass, like in trickle-bed filters. This biomass filter will let the liquid parts pass, whereas the solid parts will be retained for composting in batch mode. Permeate can either be used directly for fertigation or is sent to the CWs. The whole system will be aerated. Above of the composting system plants will be placed for odour treatment and vapour catchment.

In HYDROUSA the advantages of ancient water management (water channels built of stone) are combined with modern ICT. Integrated sensors generate data on water quality and quantity. Data will be validated and automated systems will control water flows diversion to ensure (a) water quality and (b) appropriate moisture throughout the cultivated area. This solution will be capable to be deployed in traditional construction techniques used in the Mediterranean areas.

HYDROUSA’s ICT infrastructure will follow the trend for low-cost water management and will be based on low cost components (sensors, controllers, actuators). All components will have low energy consumption, and their communication will be achieved using a Low Power Wide Area Network (LoRaWAN), allowing the components to work efficiently using mini solar panels. For increased interoperability and extendibility, HYDROUSA’s ICT infrastructure will be based on open source technologies as: Arduino based boards for communication and controlling implementation; Apache Hadoop open-source library for Big Data infrastructure for developing the data repository; and Grafana open source monitoring platform for developing HYDROUSA’s monitoring and controlling platform.

Besides EIP-AGRI, the PRIMA initiative recognized agroforestry as a means of soil and water conservation to restore soil health and avoid water depletion, while sustainably increasing food production.29 HYDROUSA will implement a biodiverse agroforestry system, depending on the output of the local community (T4.1), where fruit trees will be used as wind protectors and shade providers, shrubs as superfood providers, and several local varieties of vegetable crops and aromatic plants as added value products. High value plants will be combined with beneficial organisms attracting other species to create resilience with diversity.

The Mangrove Still, which is the basic technology for the tropical greenhouse, is able to generate distilled water from saline water via a process of evaporation and condensation run by sunlight. Similar technologies, known as “solar stills”, have been developed by many research groups worldwide, though very few are available on the market as single units producing around 3-4 l/day/m² in optimal conditions. Due to this limited water production compared to the devices’ high price, the use has been limited to single users or very small poor communities in coastal areas. Desalinated water via traditional thermal and membranes technologies is also rarely used for agricultural purpose, due to its high cost. The difficulties in assembling modular units into larger systems (generating higher amounts of water) and the use of rather expensive materials are limiting factors. The Mangrove Still approach aims at overcoming these limitations by:

• Increased efficiency compared to the production costs using cheaper materials and improved design
• Capacity to be produced locally with available materials
• Capacity to be assembled into systems in order to increase fresh water production
• Facilitate the recovery of edible salt for additional income generation
• Use the high humidity in the greenhouse for cropping tropical plants

The novel aquifer storage and recovery system will store excess rainwater during the winter to reuse in summer. Rainwater will be collected in storage tanks and will be recharging an existing well/aquifer after appropriate treatment. These subsurface water solutions have been tested in field scale pilots31 and provide innovative, practical concepts for advanced freshwater management. They build on sophisticated ICT controlled water management based on enhanced groundwater monitoring/modelling and can be applied at a range of scales, from the agricultural field to the scale of small watersheds, to water well fields of large cities.

Humidity catchment in HYDROUSA derives from fog harvesting plants32 and desert bugs. These principles are mimicked by creating a low-tech, net-like structure. Further transport of the water will be driven by PV energy. Another innovation is based on a chemical phenomenon of water absorbing materials, which absorb moisture out of humid air mainly during night, and use the heat during day to convert absorbed water into liquid. Incorporated PV panels supply the electricity for fans and sensors.

The project will develop the dedicated data acquisition platform and unique key performance indicators (KPI) of the individual nodes of HYDROUSA nexus. The field data will be fused to provide: (1) metrics of performance in productivity of plant processes; (2) energy consumption; (3) GHG emissions for WW; (4) product quality. What distinguishes the proposed solution is the unique product tracking and traceability (T&T) system (real-time), that enables the majority to be identified throughout the supply chain36 and removed in relative speed (responsiveness and agility). The products virtual passports will be updated at any single stage of the life cycle. Blockchain approach has gained momentum in recent years; the T&T of HYDROUSA will explore the potential adoption of some of the protocols of blockchains data constructs and management for the virtual tags of products in the HYDROUSA nexus.

Identifying and interrelating the key performance factors of water preservation in HYDROUSA. The models will include the energy signature of the processes, associated production and distribution of products throughout their life cycles. By finding the levels of sensitivity between such factors and water loop efficiency and effectiveness, we will develop an inferential model. A sensitivity analysis of the parameters that affect the performance of the products in the market with respect to quality, acceptability and consumer satisfaction will be developed. It will be the basis for comparison of products with existing non-circular systems. The overall methods of production and the value-added activities in the circular economy will be integrated to measure the overall impact of the food nexus.

New innovative business models38 for circular economy include different technologies and services, (relationships with) customers, production processes and different revenue models, eventually including other types of values than financial profit. In HYDROUSA, different business cases for each technology will be identified to build innovative business models which map costs, resulting in economic, social, human and natural benefits. Cost models for sustainable circular economy projects calculate the true-cost; several initiatives have provided methodological references to consider natural capital and human wellbeing. HYDROUSA business analysis will consider the provision of services, regulation and maintenance services as well as cultural and social services.

There is general lack of knowledge about human health risks associated with the consumption of vegetables irrigated by reclaimed water. HYDROUSA will contribute to expand relevant knowledge. Contaminants will be selected as a function of: i) environmental relevance based on available risk indexes; ii) suitability as markers of pollution source. This platform will be applied to the entire water cycle in the demonstration sites. Environmental risk assessment of treated water and produced crops safety will be evaluated. Campaigns for bacterial antibiotics resistance in the soil will be undertaken to determine if wastewater fertigation influences this factor.