Treatment of Source-Separated Blackwater: A Decentralized Strategy for Nutrient Recovery towards a Circular Economy

Envisioning the innovative approaches to achieve circular economy in the water and wastewater sector

Given the challenges of urbanization and rapid resource depletion, policymakers have been compelled to abandon the old sequential paradigm of "take-make-use-dispose" to a circular approach that prioritizes preservation of natural resources. The circular economy represents a sustainable management concept that focuses on reducing, recovering, reusing, and recycling waste. While significant strides have been made in implementing circular economy principles in various industries such as automotive, electronics, and construction, particular attention has been given to the water and wastewater domains due to imbalances in water resources. Here we review the global progress of circular economy adoptability in the water and wastewater domains, considering technical, environmental, economic, and social perspectives. It assesses the current state of circular economy integration in the wastewater domain worldwide and presents approaches to promote and accelerate its adoption. The study critically examines the principles of waste management, known as the 6Rs (reclaim, restore, recycle, reduce, recover, reuse), in order to formulate effective strategies for integrating circular economy practices in the water and wastewater domains. Additionally, the study provides an overview of existing research conducted on different aspects of circular economy. Finally, the study analyzes the challenges and opportunities associated with implementing circular economy principles in the water sector.

Environmental synergies in decentralized wastewater treatment at a hotel resort

Climate change and water scarcity are clearly related environmental problems, making them global environmental issues. Accordingly, the water cycle management deserves a revision in its approach, integrating the concept of circular economy within an efficient and sustainable management of water resources and the design of wastewater facilities. In this sense, newly engineered decentralized facilities have emerged as a viable option for the treatment of segregated wastewater flows. The design has not only integrated the wastewater treatment function, but also resource recovery, such as water reclamation for agricultural and irrigation activities, fertigation, fertilization and energy sustainability. Based on these premises, the concept of decentralized wastewater management deserves the same degree of attention and development that has so far been reserved for conventional centralized management systems. Therefore, this paper proposes a progressive substitution of the business-as-usual scenario or centralized system by applying a small-scale wastewater management scheme performing a more efficient resource and water recovery in a medium-sized 4-5-star resort hotel. The spotlight was a membrane technology for the anaerobic digestion of the blackwater instead of the greywater treatment. A favorable environmental profile was found for the decentralized scenario under two circumstances: a large system boundary including the beneficial environmental impacts of the products and, based on the results obtained from a sensitivity analysis, an energy demand for the operation of the AnMBR lower than 2 kWh·m^-3. The global warming potential results (around 9%) were even for such high demand and much larger benefits were obtained for other impact categories (94% for SOD and 98% for LU). Nevertheless, the operation (gate-to-gate approach) of these on-site recovery facilities is far from being optimized and further research should follow to decrease the 39.8% difference in the global warming potential between decentralized and centralized systems.

Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems

In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5-35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s^-1, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.

Review of Circular Economy in urban water sector: Challenges and opportunities in India

Increasing urbanization and rapid depletion of resources have forced authorities to shift from traditional linear system of take-make-use-dispose to circular system of resource conservation. Circular Economy (CE) is a sustainable development approach that works on the waste management strategy of reduce, reuse, recycle, and recover. Considerable work has been performed on CE in various sectors such as in electronic sector, construction sector, automotive sector, etc. However, CE in the water sector is gaining rapid attention, because of imbalance in water resources and the prevailing linear approach. The aim of this study is to review the world-wide growth of CE concept in the water sector from an economic, environmental, social, and technical perspective. 98 publications were selected by systematic literature review and categorized in economic, environmental, social, and technical criteria including a combination of multiple criteria. In this study, the world-wide status of CE implementation in the water sector is assessed and strategies to encourage and enhance CE implementation are proposed. The six BS8001:2017 principles and 6Rs (reduce, reuse, recycle, reclaim, recover, restore) of waste management are critically analyzed for deriving recommendations and successful implementation of CE in water sector. Finally, challenges and opportunities to implement CE in the water sector in India are discussed.

Nutrient Recovery from Anaerobically Treated Blackwater and Improving Its Effluent Quality through Microalgae Biomass Production

The blackwater stream of domestic wastewater contains energy and the majority of nutrients that can contribute to a circular economy. Hygienically safe and odor-free nutrient solution produced from anaerobically treated source-separated blackwater through an integrated post-treatment unit can be used as a source of liquid fertilizer. However, the high water content in the liquid fertilizer represents a storage or transportation challenge when utilized on agricultural areas, which are often situated far from the urban areas. Integration of microalgae into treated source-separated blackwater (BW) has been shown to effectively assimilate and recover phosphorus (P) and nitrogen (N) in the form of green biomass to be used as slow release biofertilizer and hence close the nutrient loop. With this objective, a lab-scale flat panel photobioreactor was used to cultivate Chlorella sorokiniana strain NIVA CHL 176 in a chemostat mode of operation. The growth of C. sorokiniana on treated source-separated blackwater as a substrate was monitored by measuring dry biomass concentration at a dilution rate of 1.38 d−1, temperature of 37 °C and pH of 7. The results indicate that the N and P recovery rates of C. sorokiniana were 99 mg N L−1d−1 and 8 mg P L−1d−1 for 10% treated BW and reached 213 mg N L−1d−1 and 35 mg P L−1d−1, respectively when using 20% treated BW as a substrate. The corresponding biomass yield on light, N and P on the 20% treated BW substrate were 0.37 g (mol photon)−1, 9.1 g g−1 and 54.1 g g−1, respectively, and up to 99% of N and P were removed from the blackwater.

Evaluating Circular Economy under a Multi-Parametric Approach: A Technological Review

A circular economy (CE) is conceptualized under different rounds of materials and energy cycling flows and is a matter of a three-level deployment: inter-enterprise circulation, regional circulation, and social circulation. Regarding them, the aim of this research was to get an update on the current technological advances and the perspectives of its implementation. Thus, a multi-parametric approach has been conducted to analyze the functionality of technologies in wastewater treatment, organic waste management, agrarian development, and food waste in the context of CE. Beside the narrative of the technological view, a critical approach assimilates the environmental, marketing, economic, governmental, and procedural viewpoints and leads to key indicators which are subject to positive and negative externalities. Due to this co-existence, we denoted the complexity of CE principle implementation and the need for specific envisage in each case, while proposing strategies are formulated in the light of social-environmental impact. Finally, further research gaps were proposed for deeper consideration.

Distributed treatment systems

This section presents a review of the scientific literature published in 2018 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics.