Slow-pyrolysis of biomass for the production of biochar, a stable carbon-rich solid by-product, has gained considerable interest due to its proven role and application in the multidisciplinary areas of science and engineering. An alternative to slow-pyrolysis is a relatively new process called hydrothermal carbonization (HTC) of biomass, where the biomass is treated with hot compressed water instead of drying, has shown promising results. The HTC process offers several advantages over conventional dry-thermal pre-treatments like slow-pyrolysis in terms of improvements in the process performances and economic efficiency, especially its ability to process wet feedstock without pre-drying requirement. Char produced from both the processes exhibits significantly different physiochemical properties that affect their potential applications, which includes but is not limited to carbon sequestration, soil amelioration, bioenergy production, and wastewater pollution remediation. This paper provides an updated review on the fundamentals and reaction mechanisms of the slow-pyrolysis and HTC processes, identifies research gaps, and summarizes the physicochemical characteristics of chars for different applications in the industry. The literature reviewed in this study suggests that hydrochar (HTC char) is a valuable resource and is superior to biochar in certain ways. For example, it contains a reduced alkali and alkaline earth and heavy metal content, and an increased higher heating value compared to the biochar produced at the same operating process temperature. However, its effective utilization would require further experimental research and investigations in terms of feeding of biomass against pressure; effects and relationships among feedstocks compositions, hydrochar characteristics and process conditions; advancement in the production technique(s) for improvement in the physicochemical behavior of hydrochar; and development of a diverse range of processing options to produce hydrochar with characteristics required for various industry applications.

A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications

Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

Biomass gasification is a widely used thermochemical process for obtaining products with more value and potential applications than the raw material itself. Cutting-edge, innovative and economical gasification techniques with high efficiencies are a prerequisite for the development of this technology. This paper delivers an assessment on the fundamentals such as feedstock types, the impact of different operating parameters, tar formation and cracking, and modelling approaches for biomass gasification. Furthermore, the authors comparatively discuss various conventional mechanisms for gasification as well as recent advances in biomass gasification. Unique gasifiers along with multi-generation strategies are discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. A strategy to improve the feasibility and sustainability of biomass gasification is via technological advancement and the minimization of socio-environmental effects. This paper sheds light on diverse areas of biomass gasification as a potentially sustainable and environmentally friendly technology.

/pdf/an-overview-of-advances-in-biomass-gasification-3qwzqn5oyi.pdf

An overview of advances in biomass gasification

A review was conducted on the use of thermochemical biomass gasification for producing biofuels, biopower and chemicals. The upstream processes for gasification are similar to other biomass processing methods. However, challenges remain in the gasification and downstream processing for viable commercial applications. The challenges with gasification are to understand the effects of operating conditions on gasification reactions for reliably predicting and optimizing the product compositions, and for obtaining maximal efficiencies. Product gases can be converted to biofuels and chemicals such as Fischer-Tropsch fuels, green gasoline, hydrogen, dimethyl ether, ethanol, methanol, and higher alcohols. Processes and challenges for these conversions are also summarized.

https://www.mdpi.com/1996-1073/2/3/556/pdf

Thermochemical biomass gasification—a review of the current status of the technology

Sustainable–Smart–Resilient–Low Carbon–Eco–Knowledge Cities; Making sense of a multitude of concepts promoting sustainable urbanization

Studies on the effect of size, structure, environment, temperature, heating rate, composition of biomass and ash are reviewed. Based on the observations reported so far, auto-gasification of biomass by the bio-oxygen and the catalytic ash would be feasible. The auto-gasification may be explained in terms of heterogeneous catalytic reaction. Better understanding of auto-gasification is possible by further studies carrying out on the effect of heating rate on auto-gasification.

A review on gasification of biomass

Of all the renewable energy sources (RESs)―except direct solar heat and light―wind energy is believed to have the least adverse environmental impacts. It is also one of the RES which has become economically affordable much before several other RESs have. As a result, next to biomass (and excluding large hydro), wind energy is the RES being most extensively tapped by the world at present. Despite carrying the drawback of intermittency, wind energy has found favor due to its perceived twin virtues of relatively lesser production cost and environment-friendliness. But with increasing use of turbines for harnessing wind energy, the adverse environmental impacts of this RES are increasingly coming to light. The present paper summarizes the current understanding of these impacts and assesses the challenges they are posing. One among the major hurdles has been the NYMBI (not in my backyard) syndrome due to which there is increasing emphasis on installing windfarms several kilometers offshore. But such moves have serious implications for marine life which is already under great stress due to impacts of overfishing, marine pollution, global warming, ozone hole and ocean acidification. Evidence is also emerging that the adverse impacts of wind power plants on wildlife, especially birds and bats, are likely to be much greater than is reflected in the hitherto reported figures of individuals killed per turbine. Likewise recent findings on the impact of noise and flicker generated by the wind turbines indicate that these can have traumatic impacts on individuals who have certain predispositions. But the greatest of emerging concerns is the likely impact of large wind farms on the weather, and possibly the climate. The prospects of wind energy are discussed in the backdrop of these and other rising environmental concerns.

http://www.sesync.org/sites/default/files/resources/Tabassum-Abbasi%20et%20al.%202014.pdf

Wind energy: Increasing deployment, rising environmental concerns

As the global population continues to rise, and attempts to increase arable land area come in sharp conflict with the necessity to retain forests on one hand and pressures of urbanization on the other, the wave of global food shortage that has hit the world recently is likely to hit us again and again. The increasing pressure on land is making meat production from macro-livestock less sustainable than ever before. To add to the diminishing pastures and broadening demand-supply gap of food grains are the shortages arising due to the diversion of some of the food crops for biofuel production. There is also an increasing use of fodder for generating biomass energy. The result is that even as the demand for animal protein keeps on rising with the swelling global population, there is every possibility that attempts to meet this demand would face serious crises in the coming years. The adverse impacts of global warming are conspiring to make the situation even worse than it otherwise would have been. The present review brings home the fact that one of the possible ways to get around this problem is to extend the practice of entomophagy – use of insects as human food. As of now entomophagy is practiced in some regions and some cultures, but, by-and-large, the bulk of global population stay away from it. It is even looked down in several cultures and forbidden in some others. The review brings out the irrationality of omitting edible insects from human diet given the generally higher quality of nutrition they contain as compared to food based on macro-livestock. This aspect, coupled with much lesser consumption of energy and natural resources associated with insect-based protein production, makes entomophagy an option which deserves urgent global attention. The authors highlight the relatively stronger sustainability of animal protein production by way of insect farming because, pound to pound, the production of insect protein takes much less land and energy than the more widely consumed forms of animal protein. It is estimated that over a thousand insect species are already a part of human diet and the nutrition offered by several of the species matches or surpasses that which is contained in traditional non-vegetarian foods. The paper also deals with the relevance of entomophagy as a potentially more ecologically compatible and sustainable source of animal protein than the red and the white meat on which most of the world presently depends. In the emerging global pattern based on an expanding share of renewable energy sources, entomophagy fits in as a renewable source of food energy for the future.

/pdf/energy-efficient-food-production-to-reduce-global-warming-2ktyfx6qfo.pdf

Energy-efficient food production to reduce global warming and ecodegradation: The use of edible insects

Carbon dioxide sequestration using microalgae is the most promising method for combating global warming. Growth of microalgae is influenced by the availability of carbon dioxide, number of photons, initial concentration of microalgae and nutrients. The transfer of carbon dioxide from flue gas and absorption of photons from sunlight are influenced by the surface area/volume ratio of photobioreactor. The growth rate of microalgae follows lag, log, deceleration and stationary phases. The rate of growth increases with concentration of microalgae till an optimum concentration of algae is reached and then decreases for any fixed operating conditions and selected microalgae. At an optimum concentration the rate is the highest always. Operating a photobioreactor at this optimum concentration with highest surface area to volume ratio would require the smallest size of photobioreactor for a given production rate. Based on the review on the performance of various existing photobioreactors and the growth mechanism of microalgae it is observed that the design and operation of an efficient photo bioreactor system should consider (1) providing highest spread area to volume ratio (2) maintaining optimum concentration matching the highest rate (3) harvesting the excess microalgae formed over the optimum concentration to maintain the optimum concentration and (4) adding nutrients to the growth medium to maintain nutrient concentration at a constant level.

M. Premalatha

Papers

A review on gasification of biomass

Wind energy: Increasing deployment, rising environmental concerns

Energy-efficient food production to reduce global warming and ecodegradation: The use of edible insects

Parameters influencing the design of photobioreactor for the growth of microalgae

Methane capture from livestock manure.