• Energy Research

Abstract Solid state anaerobic digestion of food waste (FW) with yard waste (YW) appears to be an efficient technique for bioenergy production. However, the reluctant nature of YW and nutrient imbalance due to high C/N ratio are the two major obstacles for maximum methane production. In this study to improve the methane production potential, YW was thermally pretreated to reduce its recalcitrance nature and then the pretreated YW was co-digested with FW to balance nutrient for anaerobic co-digestion. Moreover, optimization of F/M (Food/Microorganism) ratios (1.0, 1.5, 2.0 and 2.5) for solid state anaerobic co-digestion was also considered. The highest methane production of 431 mL/gVSadded was observed for co-digestion of FW with microwave pretreated YW at the F/M ratio of 1.5. Energy balance of the pretreatment technique was conducted and the highest net energy gain 3.98 kJ/gVS (= output energy of 14.04 kJ/gVS - input energy of 10.05 kJ/g VS) obtained at the F/M ratio of 1.0.

Abstract Solid state anaerobic digestion of food waste (FW) with yard waste (YW) appears to be an efficient technique for bioenergy production. However, the reluctant nature of YW and nutrient imbalance due to high C/N ratio are the two major obstacles for maximum methane production. In this study to improve the methane production potential, YW was thermally pretreated to reduce its recalcitrance nature and then the pretreated YW was co-digested with FW to balance nutrient for anaerobic co-digestion. Moreover, optimization of F/M (Food/Microorganism) ratios (1.0, 1.5, 2.0 and 2.5) for solid state anaerobic co-digestion was also considered. The highest methane production of 431 mL/gVSadded was observed for co-digestion of FW with microwave pretreated YW at the F/M ratio of 1.5. Energy balance of the pretreatment technique was conducted and the highest net energy gain 3.98 kJ/gVS (= output energy of 14.04 kJ/gVS - input energy of 10.05 kJ/g VS) obtained at the F/M ratio of 1.0.

The crisis brought upon by the COVID-19 pandemic has altered global waste generation dynamics and therefore has necessitated special attention. The unexpected fluctuations in waste composition and quantity also require a dynamic response from policymakers. This study highlights the challenges faced by the solid waste management sector during the pandemic and the underlying opportunities to fill existing loopholes in the system. The study presents specific cases for biomedical waste, plastic waste, and food waste management - all of which have been a major cause of concern during this crisis. Further, without active citizen participation and cooperation, commingled virus-laden biomedical waste with the regular solid waste stream pose significant negative health and safety issues to sanitation workers. Single-use plastic usage is set to bounce back due to growing concerns of hygiene, particularly from products used for personal protection and healthcare purposes. It is expected that household food waste generation may reduce due to increased conscious buying of more non-perishable items during lockdown and due to concerns of food shortage. However, there is a chance of increase in food waste from the broken supply chains such as food items getting stuck on road due to restriction in vehicle movements, lack of workers in the warehouse for handling the food products, etc. The study also stresses the need for building localized resilient supply chains to counter such situations during future pandemics. While offering innovative solutions to existing waste management challenges, the study also suggests some key recommendations to the policymakers to help handle probable future pandemics if any holistically.

The crisis brought upon by the COVID-19 pandemic has altered global waste generation dynamics and therefore has necessitated special attention. The unexpected fluctuations in waste composition and quantity also require a dynamic response from policymakers. This study highlights the challenges faced by the solid waste management sector during the pandemic and the underlying opportunities to fill existing loopholes in the system. The study presents specific cases for biomedical waste, plastic waste, and food waste management - all of which have been a major cause of concern during this crisis. Further, without active citizen participation and cooperation, commingled virus-laden biomedical waste with the regular solid waste stream pose significant negative health and safety issues to sanitation workers. Single-use plastic usage is set to bounce back due to growing concerns of hygiene, particularly from products used for personal protection and healthcare purposes. It is expected that household food waste generation may reduce due to increased conscious buying of more non-perishable items during lockdown and due to concerns of food shortage. However, there is a chance of increase in food waste from the broken supply chains such as food items getting stuck on road due to restriction in vehicle movements, lack of workers in the warehouse for handling the food products, etc. The study also stresses the need for building localized resilient supply chains to counter such situations during future pandemics. While offering innovative solutions to existing waste management challenges, the study also suggests some key recommendations to the policymakers to help handle probable future pandemics if any holistically.

Abstract The energy demand of the world is expected to reach 739 quadrillions BTU in 2040, which therefore demand for exploring more alternative source of renewable energy. Waste biomass though vast in reserve for generating renewable energy has its own downside. High moisture, fibrous nature, high bulk volume, hydrophilic nature and low calorific value are some of the inferior quality of waste biomass which creates bottleneck for easy renewable energy generation. Pre-treatment of biomass to overcome these challenges has created a new research interest. Among the treatment options available, the hydrothermal carbonization (HTC) method, which can process wet waste has become the most preferred choice among researchers recently. The HTC eliminates energy-intensive pre-drying process needed for other treatment methods such as pyrolysis, dry torrefaction and incineration. Through this article, we attempt to provide a detailed review of how renewable biomass can be effectively used to produce renewable energy by improving their inherent inferior characteristics. The review also highlights bottlenecks that constrain the deployment of renewable energy using HTC methods. The scope of further research direction is well identified in this review. The paper also present recent advancements which are filling the knowledge gap of HTC technology that were there earlier. Critical analysis of microwave assisted HTC and conventional heated HTC is also presented in this review. The analysis in this paper reveals that biomass is a valuable resource, and should be explored to take advantage of its renewable energy generation potential. The HTC method of biomass upgradation improves transport, storage and fuel characteristics by improving grindability, pellets durability, hydrophobicity, energy density, combustion behaviour and calorific value, and also helps in improving the environmental performance of solid fuel produced. Despite the fact that the technology is in the early stage of development and there still exist knowledge gap and shortcomings, the vast literature reviewed suggests that it has a potential of being future technology. Therefore, it needs further investigation which should fill existing shortcoming of the technology.

Abstract The energy demand of the world is expected to reach 739 quadrillions BTU in 2040, which therefore demand for exploring more alternative source of renewable energy. Waste biomass though vast in reserve for generating renewable energy has its own downside. High moisture, fibrous nature, high bulk volume, hydrophilic nature and low calorific value are some of the inferior quality of waste biomass which creates bottleneck for easy renewable energy generation. Pre-treatment of biomass to overcome these challenges has created a new research interest. Among the treatment options available, the hydrothermal carbonization (HTC) method, which can process wet waste has become the most preferred choice among researchers recently. The HTC eliminates energy-intensive pre-drying process needed for other treatment methods such as pyrolysis, dry torrefaction and incineration. Through this article, we attempt to provide a detailed review of how renewable biomass can be effectively used to produce renewable energy by improving their inherent inferior characteristics. The review also highlights bottlenecks that constrain the deployment of renewable energy using HTC methods. The scope of further research direction is well identified in this review. The paper also present recent advancements which are filling the knowledge gap of HTC technology that were there earlier. Critical analysis of microwave assisted HTC and conventional heated HTC is also presented in this review. The analysis in this paper reveals that biomass is a valuable resource, and should be explored to take advantage of its renewable energy generation potential. The HTC method of biomass upgradation improves transport, storage and fuel characteristics by improving grindability, pellets durability, hydrophobicity, energy density, combustion behaviour and calorific value, and also helps in improving the environmental performance of solid fuel produced. Despite the fact that the technology is in the early stage of development and there still exist knowledge gap and shortcomings, the vast literature reviewed suggests that it has a potential of being future technology. Therefore, it needs further investigation which should fill existing shortcoming of the technology.

Yard waste is either dumped or is being openly burned to get rid of it, instead of using it as a valuable renewable energy source. In this study, hydrothermal carbonization of yard waste was conducted to valorize it as a solid bio fuel, using a batch reactor. The effect of process parameter on yield, energy and physicochemical properties of the valorized solid bio fuel (hydrochar) was examined in this study by varying reaction temperature (160-200 °C for 2 h) and reaction time (2-24 h at 200 °C). The calorific value of hydrochar was within a range of 17.72-24.59 MJ/kg as compared to 15.37 MJ/kg for untreated yard waste. Hydrochar mass yield decreased from 78.6% at operating temperature - time of 160 °C -2 h to 45.6% at 200 °C -24 h. The plot of atomic ratios (H/C and O/C) demonstrates improvement in the coalification process which was mainly governed by decarboxylation and dehydration reactions. The grindability of the prepared hydrochar was comparable to that of coal. Hydrochar produced at lower reaction condition (160-200 °C at 2 h) have better flowability as compared to that produced at higher reaction condition (4-24 h at 200 °C). The reaction time longer than 12 h has a minimal effect on the yield, energy and physicochemical properties of hydrochar. Increasing reaction time and temperature improved the ignition and burnt temperature of hydrochar. All reaction condition has an energy ratio (energy output to energy input) of more than one making HTC process a net energy producer.

Yard waste is either dumped or is being openly burned to get rid of it, instead of using it as a valuable renewable energy source. In this study, hydrothermal carbonization of yard waste was conducted to valorize it as a solid bio fuel, using a batch reactor. The effect of process parameter on yield, energy and physicochemical properties of the valorized solid bio fuel (hydrochar) was examined in this study by varying reaction temperature (160-200 °C for 2 h) and reaction time (2-24 h at 200 °C). The calorific value of hydrochar was within a range of 17.72-24.59 MJ/kg as compared to 15.37 MJ/kg for untreated yard waste. Hydrochar mass yield decreased from 78.6% at operating temperature - time of 160 °C -2 h to 45.6% at 200 °C -24 h. The plot of atomic ratios (H/C and O/C) demonstrates improvement in the coalification process which was mainly governed by decarboxylation and dehydration reactions. The grindability of the prepared hydrochar was comparable to that of coal. Hydrochar produced at lower reaction condition (160-200 °C at 2 h) have better flowability as compared to that produced at higher reaction condition (4-24 h at 200 °C). The reaction time longer than 12 h has a minimal effect on the yield, energy and physicochemical properties of hydrochar. Increasing reaction time and temperature improved the ignition and burnt temperature of hydrochar. All reaction condition has an energy ratio (energy output to energy input) of more than one making HTC process a net energy producer.

Food waste constitutes a remarkable portion of municipal solid waste. About one-third of the global food waste produced is lost with the food supply chain. Food waste in many countries is still dumped of in landfill or incinerated simultaneously with other municipal wastes. Food waste requires proper management and recycling techniques in order to minimise its environmental burden and risk to human life. Despite considerable research on food waste conversion still, there is a shortage of comprehensive reviews of the published literature. In this review, we provide a mini global perspective of food waste with special emphasis on New Zealand and their conversion into the useful material through hydrothermal carbonisation (HTC). Other thermal technologies such as incineration and pyrolysis are also briefly discussed. The review discusses why HTC is more suitable thermal technology than others, which are currently available. Recognising the importance of techno-economic feasibility of HTC, we present a cost analysis on the production of value-added products via HTC with examples taken from the literature to gather information in the feasibility assessment process. Finally, key challenges and future directions for a better productive way of handling food waste are being suggested.