Decentralised schemes for integrated management of wastewater and domestic organic waste: the case of a small community

"Food waste-wastewater-energy/resource" nexus: Integrating food waste management with wastewater treatment towards urban sustainability

Sustainable food waste management is a global issue with high priority for improving food security and conserving natural resources and ecosystems. Diverting food waste from the solid waste stream to the wastewater stream is a promising way for food waste source separation, collection, treatment, and disposal. Given the advances in wastewater treatment, this integrated system has great potential for the concurrent recovery of water, resource, and energy. To this end, many efforts from lab-scale to full-scale studies have been devoted to evaluating the feasibility and associated impacts on both solid waste and wastewater systems. This paper summarizes the current status of food waste diversion from the aspects of principle and application. The impacts of food waste diversion on solid waste treatment, sewer system, wastewater treatment, and environmental benefits have been comprehensively reviewed and analysed. In the context of the critical review, this paper further identified the challenges of food waste diversion in unified definitions of the field, sewer network assessment, emerging wastewater treatment technologies, scale-up studies, and policy drivers. Perspectives on the contribution of food waste diversion to a food waste management hierarchy were discussed for initiating the nexus of "food waste-wastewater-energy/resource". We conclude that food waste diversion could facilitate sustainable urban development, but the area-specific factors (e.g., household practices, water resource, sewerage system condition, and treatment techniques) require adequate evaluations to determine the implementation. The outcomes of this study could contribute to the practice and policy-making of food waste management towards urban sustainability.

Benchmarking environmental and economic indicators of sludge management alternatives aimed at enhanced energy efficiency and nutrient recovery

Wastewater treatment plants (WWTPs) have been developed as multifunctional systems that aim to eliminate pollutants present in wastewater, manage the sludge produced and improve energy efficiency. Specifically, sludge management accounts for the largest share in operational costs. Considering the relevant role of sludge treatment within the overall management scheme, this study aims to evaluate different alternatives and strategies for sludge management and treatment from the perspective of life cycle analysis, with special emphasis on those options that reduce environmental impacts and economic costs. Two pre-treatments (chemical or thermal) and two post-treatments (composting unit followed by land application or incineration) were evaluated to improve the eco-balance of the anaerobic digestion (AD) process in terms of operational (biogas production and digested sludge), environmental and economic indicators. According to the results obtained, both sludge pre-treatment alternatives proved to be an adequate alternative to improve biogas production without negatively affecting environmental and economic impacts. Finally, if the final disposal of the digestate is analysed, its application to the soil as a biofertiliser is recommended, since it presents a better environmental profile than incineration.

Life Cycle Assessment of Municipal Wastewater Treatment Processes Regarding Energy Production from the Sludge Line

The efficient and timely removal of organic matter and nutrients from water used in normal municipal functions is considered to be the main task of wastewater treatment plants (WWTPs). Therefore, these facilities are considered to be essential units that are required to avoid pollution of the water environment and decrease the possibility of triggering eutrophication. Even though these benefits are undeniable, they remain at odds with the high energy demand of wastewater treatment and sludge processes. As a consequence, WWTPs have various environmental impacts, which can be estimated and categorized using Life Cycle Assessment (LCA) analysis. In this study, a municipal WWTP based in Poznań, Poland, was examined using the method defined in ISO 14040. ReCiPe Endpoint and Midpoint (v1.11), in a hierarchical approach, were used to evaluate the environmental impacts regarding 18 different categories. All calculations were conducted using a detailed database from 2019, which describes each chosen facility. It was found that the energy component, related to the wastewater treatment process demand and electricity production, is the main determinant of the sum of the environmental impact indicators in light of the modelled energy mix. Therefore, it determines the entire process as an environmentally friendly activity.

Unravelling the environmental and economic impacts of innovative technologies for the enhancement of biogas production and sludge management in wastewater systems

The retrofitting of wastewater treatment plants (WWTPs) should be addressed under sustainability criteria. It is well known that there are two elements that most penalize wastewater treatment: (i) energy requirements and (ii) sludge management. New technologies should reduce both of these drawbacks to address technical efficiency, carbon neutrality and reduced economic costs. In this context, the main objective of this work was to evaluate two real plants of different size in which major modifications were considered: enhanced recovery of organic matter (OM) in the primary treatment and partial-anammox nitrification process in the secondary treatment. Plant-wide modelling provided an estimate of the input and output flows of each process unit as well as the diagnosis of the main performance indicators, which served as a basis for the calculation of environmental and economic indicators using the LCA methodology. The combination of high-rate activated sludge (HRAS) + partial nitrification Anammox can decrease the environmental impacts by about 70% in the climate change (CC) category and 50% in the eutrophication potential (EP) category. Moreover, costs can be reduced by 35-45% depending on the size of the plant. In addition, the enhanced rotating belt filter (ERBF) can also improve the environmental profile, but to a lesser extent than the previous scenario, only up to 10% for CC and 15% for EP. These positive results are only possible considering the production of energy through biogas valorization according to the waste-to-energy scheme.

Up-Flow Anaerobic Sludge Blanket (UASB) Technology for Energy Recovery: A Review on State-of-the-Art and Recent Technological Advances

Up-flow anaerobic sludge blanket (UASB) reactor belongs to high-rate systems, able to perform anaerobic reaction at reduced hydraulic retention time, if compared to traditional digesters. In this review, the most recent advances in UASB reactor applications are critically summarized and discussed, with outline on the most critical aspects for further possible future developments. Beside traditional anaerobic treatment of soluble and biodegradable substrates, research is actually focusing on the treatment of refractory and slowly degradable matrices, thanks to an improved understanding of microbial community composition and reactor hydrodynamics, together with utilization of powerful modeling tools. Innovative approaches include the use of UASB reactor for nitrogen removal, as well as for hydrogen and volatile fatty acid production. Co-digestion of complementary substrates available in the same territory is being extensively studied to increase biogas yield and provide smooth continuous operations in a circular economy perspective. Particular importance is being given to decentralized treatment, able to provide electricity and heat to local users with possible integration with other renewable energies. Proper pre-treatment application increases biogas yield, while a successive post-treatment is needed to meet required effluent standards, also from a toxicological perspective. An increased full-scale application of UASB technology is desirable to achieve circular economy and sustainability scopes, with efficient biogas exploitation, fulfilling renewable energy targets and green-house gases emission reduction, in particular in tropical countries, where limited reactor heating is required.

Smart Approaches to Food Waste Final Disposal

Food waste, among the organic wastes, is one of the most promising substrates to be used as a renewable resource. Wide availability of food waste and the high greenhouse gas impacts derived from its inappropriate disposal, boost research through food waste valorization. Several innovative technologies are applied nowadays, mainly focused on bioenergy and bioresource recovery, within a circular economy approach. Nevertheless, food waste treatment should be evaluated in terms of sustainability and considering the availability of an optimized separate collection and a suitable treatment facility. Anaerobic codigestion of waste-activated sludge with food waste is a way to fully utilize available anaerobic digestion plants, increasing biogas production, energy, and nutrient recovery and reducing greenhouse gas (GHG) emissions. Codigestion implementation in Europe is explored and discussed in this paper, taking into account different food waste collection approaches in relation to anaerobic digestion treatment and confirming the sustainability of the anaerobic process based on case studies. Household food waste disposal implementation is also analyzed, and the results show that such a waste management system is able to reduce GHG emissions due to transport reduction and increase wastewater treatment performance.

High-rate activated sludge processes for municipal wastewater treatment: the effect of food waste addition and hydraulic limits of the system

Conventional activated sludge (CAS) process is one of the most commonly applied processes for municipal wastewater treatment. However, it requires a high energy input and does not promote energy recovery. Currently, high-rate activated sludge (HRAS) process is gaining importance as a good option to reduce the energy demand of wastewater treatment and to capture organic matter for valorizing through anaerobic digestion (AD). Besides, food waste addition to wastewater can help to increase the organic matter content of wastewater and thus, energy recovery in AD. The objective of this study is to evaluate the applicability of co-treatment of municipal wastewater and food waste in a pilot-scale HRAS system as well as to test the minimal hydraulic retention times (HRTs) such as 60 and 30 min. Food waste addition to the wastewater resulted in a 10% increase in chemical oxygen demand (COD) concentration of influent. In the following stages of the study, the pilot-scale system was operated with wastewater solely under the HRTs of 60 and 30 min. With the decrease of HRT, particulate COD removal increased; however, soluble COD removal decreased. The results demonstrated that if the settling process is optimized, more particulate matter can be diverted to sludge stream.