A review of nature-based solutions for resource recovery in cities

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future

Biochar for agricultural water management

Agricultural runoff and wastewater can contain considerable nutrient loads released to the environment without precaution and lack of treatment. Capturing and reusing these nutrients in agriculture can have significant economic and environmental potential. In this work, various types of biochar produced from sidestreams were assessed for nutrient uptake. Biochar has been shown to increase both soil water holding capacity and available water capacity, but it also has the potential to recover nutrients from runoff. However, the biochar’s efficiency depends on its properties, soil texture, the raw material(s) and processing conditions. Char activation increases the char’s specific surface and active sites and will likely improve the nutrient adsorptive efficiency. This work assessed commercially available biochars’ capacity to adsorb nutrients from a solution and their potential to act as a substrate for retaining nutrients from runoff water. The biochar materials were pyrolysis products of various organic materials, wood and agricultural sidestreams. In addition zeolite – a recognised adsorption material was included for the sake of comparison The results indicate that most biochar has some capacity to retain NH4-N. The capacity to retain NO3-N again varied between not considerable to ca 0.34 mg/g NO3-N (Mg(OH)2 cherry biochar). Thermal activation of biochar increases the number of adsorption sites and thus also improves the adsorption efficiency.Commercial biochars did not show any significant affinity towards phosphate, but only after being coated with Mg(OH)2. Instead, the natural phosphorous content of biochar seems to leach into a solution easily. However, phosphorous leaching did not have any noticeable fertilising effect, neither that of NO3-N nor NH4 -N. In conclusion, Mg(OH)2-coated biochar performed better than all other materials to retain NO3-N (0.34 mg/g or 74% retention rate) and PO4 (0.25 mg/g or 98% retention rate). Zeolite retained better NH4-N (78%) compared to all other materials, followed by coated cherry biochar (48% retention rate) and coated biochar (34% retention rate).Biochar is a circular product which has been successfully applied as a soil amendment, thereby improving the structure and water-retaining capacity of various soils. Based on the results obtained here, tested substrates’ role in contributing to the nutrient balance varies between nutrients and materials applied. <br/

A review of nature-based solutions for resource recovery in cities

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future