Study on the process wastewater reuse and valorisation during hydrothermal co-carbonization of food and yard waste.

The commercial success of hydrothermal carbonization (HTC) is contingent on seeking solutions for the downstream wastewater (process water) generated during the process which is still regarded largely as a nuisance. In the present study, the reusability and valorization strategy of process wastewater generated during co-HTC of organic fraction of municipal solid waste (food and yard waste) at 220 °C for 1 h was established. The process wastewater was anaerobically digested in the first part to determine its methane-generating capacity; and in the second part, it was recirculated up to five times to understand the evolution of physicochemical and fuel characteristics of hydrochar. The process water was characterized by the presence of high total organic carbon (up to 40 g/L) and chemical oxygen demand (up to 96 g/L). The decreasing trend of heavy metals with increasing recirculation suggested possible adsorption/immobilization mechanism taking place to the hydrochar surface. The process water generated from co-HTC condition has anaerobic biodegradability of 72% while experimental and theoretical methane yield observed were 224 mL/g COD and 308 mL/g COD, respectively. The presence of high organic and ionic species in recirculated process water promoted the overall carbonization process which was evident from the increased energy yield (86 to 92%), carbon content (68 to 71%) and calorific value (20 to 27 MJ/kg). The recirculation also enhanced overall combustion characteristics of hydrochar as analyzed by thermogravimetric analysis. The recirculation strategy enhanced fuel properties of hydrochar while making sure upstream and downstream water related burden is reduced (as illustrated by life cycle analysis) to create a cleaner production system for renewable solid biofuels production.

Circular economy approach in solid waste management system to achieve UN-SDGs: Solutions for post-COVID recovery.

The COVID-19 pandemic and the ensuing socioeconomic crisis has impeded progress towards the UN Sustainable Development Goals (UN-SDGs). This paper investigates the impact of COVID 19 on the progress of the SDGs and provides insight into how green recovery stimulus, driven by circular economy (CE)-based solid waste management (SWM) could assist in attaining the intended targets of UN-SDG. It was understood in this review that the guiding principles of the UN-SDGs such as, public health, environmental concerns, resource value and economic development are similar to those that have driven the growth of waste management activities; thus, in order to achieve the goals of UN-SDG, a circular economy approach in solid waste management system should be prioritized in the post-COVID economic agenda. However, policy, technology and public involvement issues may hinder the shift to the CE model; therefore, niche growth might come from developing distinctive waste management-driven green jobs, formalizing informal waste pickers and by focusing in education and training of informal worker. The review also emphasized in creating green jobs by investing in recycling infrastructure which would enable us to address the climate change related concerns which is one of the key target of UN- SDG. The CE-based product designs and business models would emphasize multifunctional goods, extending the lifespan of products and their parts, and intelligent manufacturing to help the public and private sectors maximise product utility (thus reducing waste generation) while providing long-term economic and environmental benefits. The study also recommended strong policies that prioritized investments in decentralization of solid waste systems, localization of supply chains, recycling and green recovery, information sharing, and international collaboration in order to achieve the UN-SDGs.