Anaerobic digestion fundamentals, challenges, and technological advances

Anaerobic digestion (AD) is a natural biochemical process that converts organic materials into combustible biogas. AD has been long practiced for agricultural and urban waste management; however, this process is getting more attention as an alternative energy source nowadays. Additionally, various biogas-derived value-added chemicals and transportation fuels are turning AD into a profitable biorefinery business model. Despite its numerous potentials, AD technologies still face challenges in conversion efficiency, process stability, product quality, and economic feasibility. Researchers have been devising various mechanisms to tackle these challenges. However, a widespread adoption of commercial-scale AD is yet to be visible. The development of AD technology requires a concerted effort of scientists from different backgrounds to ensure rapid expansion.

Process Design for Biohydrogen Production from Waste Materials and Its Application

Biohydrogen is regarded as an attractive future clean energy carrier due to its high energy content and environmentally friendly conversion. Biohydrogen reactor is widely used in studies concerning the anaerobic co-digestion of food waste, sewage sludge, wastewater and other organic solids. Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material (biomass or waste feedstock) in the absence of oxygen to produce biogas, which may generate electricity and heat, or can be processed into renewable natural gas and transportation fuels. This review article explains the scientific processes of anaerobic digestion process such as hydrolysis, acidogenesis, acetogenesis and hydrogenesis as well as methods to produce biohydrogen gas such as fermentation and biophotolysis for the waste management technology and sources of renewable energy and concludes with solutions that may allow anaerobic digestion to become more widely adopted throughout the developing countries to control the waste management system.

Investigation the combined effects of exhaust gas recirculation (EGR) and alcohol-diesel blends in improvement of NOX-PM Trade-off in compression ignition (CI) diesel engine

The increasing demand to decrease the greenhouse gas emissions leads to find clean fuel and renewable fuel such as ethanol and methanol that good replacement of oil-derived transportation fuels. The combined effects of alcohols blends (ethanol-diesel and methanol-diesel) and with and without EGR on NOX-PM Trade-off in diesel engine were investigated under variable engine loads and speeds. The EGR is considered efficient technology to reduce the NOX emissions in compression ignition (CI) diesel engines. The current study highlighted on the trade-off between nitrogen oxides (NOX) and particulate matter (PM). The oxygenating content in the ethanol blend (E10) and methanol blend (M10) decrease the PM concentrations in the exhaust pipe compared to the diesel fuel for different engine operating conditions with keep NOX emissions in the moderate level. It was found that the NOX/PM concentrations significantly decreased from the combustion of E10 and M10 under variable engine loads and speeds.

Analysis of the optimum pH and salinity conditions for the cultivation and biomass production of Chlorella vulgaris from cassava waste

Biofuel serves as an alternative energy to the common fossil fuels currently in use globally and are drawing increasing attention worldwide as substitutes for petroleum-derived transportation fuels to help address challenges associated with petroleum derived fuels. Third generation biofuels, also termed advanced biofuels, are produced from fast growing microalgae and are potential replacements for conventional fuels. The growth and biomass production of these microalgae is dependent on the conditions they are cultivated such as pH and Salinity. Cassava waste mixtures were cultivated on Chlorella vulgaris stock culture at different concentration ratio at ambient temperature, natural light and dark conditions at 670nm absorbance for 14 days. Optimum growth was obtained at 160:40 for cassava peel water to cassava waste water CP:CW. pH variations 6.0, 6.5, 7.0, 7.5, 8.0, 8.5 and 9.0 were checked to determine the optimum pH for the growth and biomass production of Chlorella vulgaris on the optimum cassava waste mixture concentration. It revealed that at pH 6.5, optimal growth and biomass production was achieved, minimal growth was observed at pH 8.0 while minimal biomass was produced at pH 9.0. Salinity variations of 5, 10, 15, 20, 25, 30, 35 and 40 mg/l were used to determine the growth response and biomass production of Chlorella vulgaris. It revealed that salinity variation at 10ppm will be necessary for highest growth on the cassava waste as well as in biomass production. The use of optimal pH and salinity can significantly increase biomass production thus enhancing biofuel production.

An assessment of the underlying relationship between land transportation and climate change: Case study Mauritius

Introduction: Land transportation encompasses the movement of people and goods and is therefore a major contributor of global greenhouses gases. The main share of such emissions is mostly from the release of carbon dioxide into the air as a result of burning transportation fuels obtained from petroleum, a major driver of climate change. While today the defining issue is a changing climate, the number of vehicles on roads keep on rising around the world. Materials and methods: This study assessed the relationship between land transportation and climate change using a system dynamics model based on a 3-layered taxonomy using Mauritius Island as case study. Over 100 papers were analyzed and the variables that link land transportation and climate change in the Mauritian context were selected and a taxonomy divided into sub-units was built. Results: This innovative taxonomy was divided into 3 sections related to the land transportation sector including a vehicle layer, transport system layer and society layer. Using these variables, three stock and flow diagrams were constructed on Vensim, namely climate change impacts, transport related carbon dioxide and socio-economic models. Conclusion: While there is a complex relationship between land transportation and climate change globally, Mauritius must find ways to become more climate friendly in the land transportation sector.

A Colorado-specific life cycle assessment model to support evaluation of low-carbon transportation fuels and policy

The transportation sector accounts for over 20 percent of greenhouse gas (GHG) emissions in Colorado which without intervention will grow to over 30 million metric tons (MMT) of GHG emissions per year. This study seeks to develop a specific characterization of the Colorado fuel and transportation system using a customized life cycle assessment (LCA) model. The model (CO-GT) was developed as an analytical tool to define Colorado’s 2020 baseline life cycle GHG emissions for the transportation sector, and to examine Colorado-specific pathways for GHG reductions through fuel types and volumes changes that might be associated with a state clean fuel standard (CFS). By developing a life cycle assessment of transportation fuels that is specific to the state of Colorado’s geography, fleet makeup, policies, energy sector and more, these tools can evaluate various proposals for the transition towards a more sustainable state transportation system. The results of this study include a quantification of the Colorado-specific roles of clean fuels, electricity, extant policies, and fleet transition in projections of the state’s 2030 transportation sector GHG emissions. Relative to a 2020 baseline, electrification of the vehicle fleet is found to reduce state-wide lifecycle GHG emissions by 7.7 MMT CO2e by 2030, and a model CFS policy able to achieve similar reductions in the carbon intensity of clean fuels as was achieved by California in the first 10 years of its CFS policies is found to only reduce state-wide lifecycle GHG emissions by 0.2 MMT CO2e by 2030. These results illustrate the insensitivity of Colorado’s transportation fleet GHG emissions reductions to the presence of CFS policies, as proposed to date.

Pyrolysis: A Convenient Route for Production of Eco-Friendly Fuels and Precursors for Chemical and Allied Industries

Thermochemical decomposition of post harvest agro-wastes (biomass) to solid carbonaceous material called as bio-char, condensable vapors (bio-oils and bio-tars) and non-condensable vapors (bio-gas or syn-gas) is referred as pyrolysis. The yield of these products from biomass pyrolysis depends on temperature and other conditions (such as vapor retention time and heating rate) of thermal decomposition in air or oxygen excluded reactor. Bio-char is often used as adsorbent in treatment of water contaminated with dye effluent from textile industry and/or emerging contaminants from other industries. It is also used in production of supercapacitor for energy storage, fertilizer composite and soil amendment for slow release of nutrients for plants and stabilizing pH, enhances water holding and ion exchange capacity of soil. Bio-oils are used for transportation fuels, soaps and other cosmetics production. Bio-tars are also used for transportation fuels but with high heating values and also as organic solvents in chemical, biological and biochemical laboratories. Non-condensable vapors are mostly used as bio-fuels. Products of biomass pyrolysis are potential alternative eco-friendly precursors for chemical and allied industries.

Recent Research Activities in Solid and Liquid Bioenergy from Lignocellulosic Biomass

The increase in energy demand, the lack of petroleum resources, and concern over global climate change have placed great emphasis on the development of new alternative energy technologies that can be used to replace fossil transportation fuels (Himmel et al. 2007; Labbe et al. 2008; Lee et al. 2009a,b,c; Teramoto et al. 2008, 2009). In this context, many countries have initiated extensive research and development programs for bioenergy. Bioenergy can be classified into three kinds of solid, liquid, and gas bioenergy. For the effective production and utilization of these three types of bioenergy, different technologies are required (Figure 1). Lignocellulosic biomass, such as wood and agricultural residues, are widely distributed and easily accessible at relatively low costs. Of these, wood has the benefit of having a higher energy content per volume, lower ash content, and nitrogen content. In this review, recent research trends and advances in bioenergy from lignocellulosic biomass will be summarized from the author’s point of view.

Performance evaluation of a Compression Ignition Engine using Sand Apple (Parinari polyandra B.) ethyl ester (biodiesel)

The quest for non-edible oil for the production of alternative fuel (bio-fuel) using homogeneous catalysts continues to supplement and replace in totality the traditional transportation fuels that are not environmentally friendly. The use of biodiesel in Compression Ignition Engines (CIE) to evaluate the engine performance is a norm and blends of biodiesel and Automotive Gas Oil (AGO) are also used in the engine performance processes to ascertain its usage in the CIE. Therefore, this study evaluated the performance of a compression-ignition engine (CIE) fuelled with biodiesel produced from sand apple oil using eggshell as a heterogeneous catalyst. Transesterification of Sand Apple Oil (SAO) with ethanol to produce ethyl ester and glycerol was optimized. Sand Apple Ethyl Esters (SAEE) was blended with Automotive Gas Oil (AGO) at 5 – 25% mix to evaluate the performance of a 3.68 kW diesel engine at five loading conditions (0, 25. 50, 75, 100%). Performance tests were carried out to determine torque, speed, exhaust gas temperature and fuel consumption rate. Data obtained were analyzed using ANOVA at P < 0.05 significant level. Results of parameters tested ranged from 6.50 – 6.60 Nm, 2795 – 2950 rpm, 385 – 400 °C and 2.93 – 5.00 × 10−6 kg/s, respectively for all the blends. The study established that the performance of the diesel engine using 5 – 25% SAEE-AGO blends was similar to using AGO alone and SAEE is therefore suitable for use in the CIE.