The development of an urban green infrastructure which is based on hydroponic system and mimics the treatment of wastewater by constructed wetlands for the production of value crops

The human population has become an urban species. In the past society was sustained in the countryside by Ecological Services. The city’s use of these resources, per area, is exponential compared to that of traditional country living. Intrinsically, the carrying capacity of local and global Ecological Services has become exacerbated. As society has emigrated from the countryside to the cities so can the Ecological Services be integrated in the built environment, in the form of Green Infrastructure? This research aims to develop a hydroponic system that bio-mimics the treatment of waste water by wetlands, as a part of buildings, utilising Value Crops. The research started with the principles of constructed wetlands to engineer green infrastructure systems for urban farming. It was hypothesised that access to oxygen was the key limiting factor for the system and it was proposed that a hydroponic system would mimic wetlands ability to provide oxygen to the rhizosphere. Initial experiments were carried out in batch systems to confirm the tolerance of macrophyte and anoxic sensitive plants to hypoxic condition. The first experiments showed that the basil and tomato plants perished when hypoxic conditions were reached and rice, a macrophyte, was able to survive the conditions. In the field, six different forms of hydroponics were investigated to understand how they influenced the concentration of oxygen around the root system. It was found across the systems that dissolved oxygen increased (29% - 52%) but those systems that created a moist, nutrient filled environment had the greatest growth (136%). To understand if a risk of pathogen escaping a hydroponic system an investigation in an environmental chamber was undertaken. It was found that no E. coli escaped the system, into the surrounding atmosphere; however, the results were inconclusive as to whether the system directly decreased the bacteria count. Based on the experiments the Key Design Element was developed and several novel design concepts of a vertical treatment system were proposed. These designs were prototyped and found that plants grew successfully. It was concluded that the system due to its utilisation, production of Value Crops at source and minimal use of additional energy could be considered as a sustainable solution for urban water re-use