Search

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro-or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges., QC 20220602

Many industrial wastes and wastewaters, e.g. dairy, beverage, slaughterhouse wastewater, and food processing waste streams contain appreciable quantities of protein. Anaerobic treatment is appropriate for wastewaters and wastes rich in organics to achieve pollution control and resource recovery, e.g. energy rich methane or important chemical platforms such as volatile fatty acids (VFA) or added-valuable amino acids. However, the understanding of the hydrolysis, especially of proteins, is still limited, resulting in non-optimized anaerobic systems dealing with these protein rich wastewaters. Therefore, this thesis aimed to investigate anaerobic conversion of proteins, focussing on the hydrolysis process to accomplish sufficient protein degradation for VFA and methane production. Batch and completely-stirred tank reactor (CSTR) experiments were carried out to study the effect of different environmental and microbial factors on hydrolysis and further degradation of gelatine, a model protein, at mesophilic conditions. Results show that in contrast to earlier suggestions in literature, carbohydrates did not directly affect the protein hydrolysis rates either under methanogenic or non-methanogenic conditions at neutral pH. However, the high VFA concentrations strongly inhibited the protein hydrolysis rate in the batch experiments. Methanogenesis did not stimulate the rate of hydrolysis and acidification of protein at pH 7. Yet, protein hydrolysis was inhibited at pH 5. The hydrolysis rate constant for protein at pH 5 (0.05 L g-1 VSS day-1) was much lower than at pH 7 (0.62 L g-1 VSS day-1). Even long-term exposure (480 days) of the microbial population to pH 5 did not result in an enhanced hydrolysis of dissolved protein. Hydrolysis always is the rate-limiting step of protein degradation at pH 5 between a solid retention time (SRT) of 12 and 30 days. At pH 7, protein degradation was limited by hydrolysis at SRTs >8 days or acidogenesis at SRTs ≤ 8 days. The pH also determ

Domestic wastewater contains resources, such as nutrients, water, organic matter which can be reused in agriculture. Nitrogen (N) and phosphorus (P) are two essential macronutrients for crop production. The reuse of recovered products containing these nutrients can contribute to lowered use of fossil energy and saves P reserves. This reuse enhances economic circularity of cities, urban areas or small islands. A number of sanitation planning approaches have been developed aiming to solve the aforementioned problems. However, some challenges on planning have not been addressed in a holistic way when considering the full train of sanitation technologies and is not better integrated with agricultural systems. The assessments are also not considering the four domains of sustainability: environmental, technological, social-economic, and economic, and also trends of future development. Hence, a new planning approach needs to be developed to promote resource recovery and reuse under different future developments.

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.

Developments in urban agriculture and new sanitation systems bring about new narratives to the status quo of both food production and human excreta management, and reintroduce the opportunity to partially close nutrient cycles at the urban scale. Urban agriculture is the production of food in and around (peri-urban) a city. New sanitation systems collect, transport and treat streams containing human excreta and aim to recover valuable resources from those streams. The recognition of the mutual benefit for nutrient exchange between urban agriculture and new sanitation has increased. In this regard, urban agriculture has a demand for nutrients and new sanitation a supply of nutrients, which if matched, can facilitate nutrient recycling and thereby minimize nutrient losses. Nevertheless, numerous challenges remain to match nutrient flows between urban agriculture and new sanitation. Not only do the quantities and qualities of nutrient demand and supply need to be matched – taking into account parameters for plant requirements, as well as human hygiene and environmental safety (e.g. pathogens, heavy metals) – but also spatial and temporal dynamics of demand and supply (e.g. when and where fertilizers are needed and when and where nutrients are excreted) need to be optimized for coupling of nutrient flows. This thesis contributes to uncovering the potential of integrating urban agriculture and new sanitation so as to establish nutrient recirculation between the two. Specific objectives include (i) an analysis of nutrient demand and supply, (ii) an evaluation of spatial and temporal aspects of supply and demand matching, and (iii) a reflection on trade-offs for improved nutrient recycling within the urban environment. This thesis primarily focuses on the three macronutrients, nitrogen (N), phosphorus (P) and potassium (K), as well as organic matter (OM), although, other macro- and micronutrients are tangentially discussed.Chapter 2 presents a first exploration of closing, Het doel van dit onderzoek is bij te dragen aan het begrijpen van het potentieel om de recirculatie van nutriënten tussen nieuwe sanitatie en stadslandbouw tot stand te brengen. Specifieke doelstellingen zijn (i) een analyse van de vraag naar en het aanbod van nutriënten, (ii) een evaluatie van ruimtelijke en temporele aspecten van de koppeling tussen vraag en aanbod, en (iii) een reflectie op de mogelijke afwegingen van het hergebruik van nutriënten in de stedelijke omgeving. Dit proefschrift richt zich voornamelijk op de drie macronutriënten stikstof (N), fosfor (P) en kalium (K), evenals organische stof (OM); andere macro- en micronutriënten worden in beperkte mate besproken. De centrale vraag van dit proefschrift is: ‘wat is het potentieel om nutriënten die aanwezig zijn in menselijke ontlasting als meststof her te gebruiken in de stadslandbouw’.

Household digesters are anaerobic reactors applied mostly in rural areas of developing countries with tropical climate. The Chinese dome digester is the most popular household digester type in Asia and Africa, and has become the basis for contemporary developments in the household digester sector around the world. Household digesters are operated at ambient temperatures and have no internal mixing device, making them simple to operate. In the absence of internal mixing mechanism, the Chinese dome digester is mixed via pressure variation during gas production, gas use and feeding. Since mixing is limited in household digesters, they are operated at low organic loading rates and long hydraulic retention time when compared with forced mixed reactors. This review analyses and presents the various types of domestic biogas plants and operating parameters, with emphasis on mixing. Experimental results of household reactors, forced mixed reactors with different mixing modes and intensities were also reviewed and compared.