It is my privilege to feature Professor Gerardo Diaz from the Department of Mechanical Engineering at the University of California, Merced, for this BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More Expert Profile.
As a profound and distinguished figure in thermal science, Professor Diaz’s work represents the critical intersection of advanced engineering and applied environmental solutions. His leadership as the Director of the Sustainable Plasma GasificationGasification is a high-temperature, thermochemical process that converts carbon-based materials into a gaseous fuel called syngas and solid by-products. It takes place in an oxygen-deficient environment at temperatures typically above 750°C. Unlike combustion, which fully burns material to produce heat and carbon dioxide (CO2), gasification More Lab and his authorship of the definitive book, Voltage-Enhanced Processing of Biomass and Biochar, have established him as a foremost authority on next-generation biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More conversion technologies.
Professor Diaz’s expertise spans the full spectrum of the field, from optimizing the performance of accessible, low-cost TLUD reactors to pioneering the use of non-thermal plasma for biochar activation. His research provides critical insights into some of the most pressing challenges in the circular bioeconomy, including the development of mobile biochar units for on-farm methane reduction and the creation of novel biochar-based insulation materials. His work is not confined to the laboratory; he has also served as a Research Member for the Biochar Research Advisory Group for the California Governor’s Office of Planning and Research.
I am pleased to present his insights on this vital and evolving technology for the readers of Biochar Today.
Shanthi Prabha: Your research spans from thermal systems to sustainable energy. What initially drew you to the field of biochar, and how do you see it as an interdisciplinary nexus between engineering and environmental science?
Dr. Gerardo Diaz: I started working on biomass gasification systems with the intent of generating power and/or industrial heat. In my interactions with commercial partners, it became obvious that if they did not sell their biochar, their companies might not be economically feasible. That is how I became involved in biochar. Identifying industrial applications for this material is the fastest way to increase production volume and utilization. Once those volumes are reached, the cost of the material might be low enough to meet the cost demands of soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity. More and agriculture applications. It is essential to apply engineering principles in a manner that is consistent with environmental science.
SP: Your work on a Top-Lit Updraft (TLUD) reactor for biochar production is a key contribution to low-cost technology. Can you elaborate on the specific physicochemical properties you were able to control, such as elemental composition and BET surface area, by adjusting operational parameters like airflow and insulation?
GD: Large-scale pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More systems, even those with rotating-cylinder configurations, still produce biochar with a degree of variability in its properties. Conversion of feedstocks with a large variation in sizes and aspect ratios can yield a wide range of biochar properties. Shredding or milling to a small particle size is usually not cost-effective, so materials that naturally have a small variation in their size and characteristics (such as fruit pits, and almond, walnut, or pistachio shells) help reduce the variability of the resulting biochar’s properties.
Consistency in the results of ultimate and proximate analysis can be achieved by controlling the operating conditions of a TLUD reactor. By adjusting parameters such as air flow rate and heat losses, the velocity of the pyrolysis front can be controlled and thus, the material is more consistent. Surface area and porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More distribution are two important properties that benefit from controlled processing of the biomass.
SP: The concept of a mobile biochar production unit is a significant innovation. From an engineering and logistics perspective, what are the primary challenges and opportunities in making such a system economically and technically viable for on-site biomass utilization, particularly on dairy farms?
GD: Mobile units are extremely useful when the feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More source is located in regions of difficult access. They are also useful when the quantity of biomass produced is not enough to justify a centralized biomass processing plant.
Some of the main challenges are related to the energy source. If the unit requires electricity to generate the heat, it means that in addition to the unit, a generator is needed too. If the unit requires propane or other fuel, then again, this resource needs to be available, or it needs to be carried with the mobile unit. This adds a level of complication depending on how isolated or difficult to access is the source of biomass.
Units that use air to generate partial oxidation heat have an advantage (also because they are cheaper to run) but then they are more affected by ambient conditions (hot, cold days, air humidity) and they are likely to produce more variability in the material depending on the season when the material is processed. However, when the intent is to reduce biomass volume, mainly due to wildfire potential, air-curtain units or TLUDS are great ways to accomplish that goal at a low cost.
SP: Your study on methane and nitrous oxide emissions during biochar co-composting is highly relevant to climate mitigation. What are the key mechanisms by which biochar addition influences aggregate formation and subsequently reduces these potent greenhouse gas emissions?
GD: It is important to note that too little biochar in the mixture or too much biochar leads to high methane emissions. There is a small range of optimal mixtures (around 6% by weight). My colleague Prof. Rebecca Ryals has done extensive work on these mixtures. Proper aeration helps to reduce the formation of methane, so it is a combination of the addition of biochar and the proper mixing of the material over time. Too much biochar (around 20%) leads to aggregation which forms manure spheres where the center does not get aerated and then methane production increases due to anaerobic reactions.
SP: Your research on almond shell biochar focuses on its impact on soil. Could you discuss the relationship between the biochar’s application rate and particle size and its observed effects on soil physical and hydraulic characteristics, such as moisture retention and bulk density
GD: I am not a soil scientist so I can refer you to Prof. Rebecca Ryals, Prof. Asmeret Berhe, or Prof. Ghezzehei for the characterization of the effects of biochar in soil. My group concentrates in the conversion of biomass and in the industrial uses of biochar.
SP: You have a background in thermal and fluid systems. How have you applied principles from fluid mechanics and heat transfer to optimize the pyrolysis process for creating biochar with targeted characteristics for different applications?
GD: Yes, we recently submitted a manuscript that includes a comparison of both, a first principles computational model and a machine learning model to predict pyrolysis behavior of mixtures of feedstocks. In the past, we have also developed models for other processing configurations such as plasma gasification of biomass.
SP: Your book, Voltage-Enhanced Processing of Biomass and Biochar, suggests an advanced approach. Can you explain the fundamental principles behind voltage-enhanced pyrolysis and how this technology could revolutionize biochar production in terms of efficiency, yield, and final product properties?
GD: Several advantages can be obtained with the use of either thermal or non-thermal plasmas. The conditions reached with any of these techniques cannot be reached with conventional conversion systems because of the large number of highly reactive species that are formed. For instance, with thermal plasmas, both the electrons and ions are at temperatures of 3000 oC or higher and there is a high degree of ionization. Feedstocks with high level of moisture were exposed to the plasma torch and very high levels of hydrogen were obtained in the product gas. The highly energetic condition was also beneficial in reducing tars. It is important to note that larger systems have better energy efficiencies compared to smaller systems due to heat losses.
For non-thermal plasmas, we have obtained that the discharge can be used to break down tars and increase the amount of hydrogen and carbon monoxide fraction in the product gas. In addition, in plasma activation of biochar, the non-thermal plasma discharge helps to lower the activation energy and thus higher surface areas can be obtained operating at moderate neutral-gas temperatures as opposed to the high operating temperatures needed for conventional physical activation. There is no waste-streams produced as in chemical activation.
SP: Looking at your publications, you’ve investigated biochar from various feedstocks, including rice hulls, wood chips, and almond shells. What are the most critical factors that determine the selection of a feedstock for a specific application, and how does the feedstock influence the resulting biochar’s carbon stability?
GD: For conventional processing, moisture levels affect the process significantly. If the material is dried (less than 10% of moisture) then aspect ratio becomes important too. Wood sticks and shredded material with large aspect ratios tend to “bridge” and not allow flow of the gases through the pyrolyzer or gasifier. On the other hand, if there are too many voids, then this is also problematic. One of the strategies that we are using now is to blend materials such as orchard tree sticks and branches with other smaller material that can provide a relatively uniform void distribution inside the reactors.
Mechanical properties are also important. If a material produces biochar than can be crushed easily, it might not be very useful as a filter material, especially in large tanks. Even after activating it, the large surface area is not useful if the material becomes a powder due to the weight of the material inside a large tank (like in wastewater treatment plants). Therefore, mechanical properties are also important depending on the application.
SP: Beyond soil and waste management, your work touches on biomass utilization and sustainable energy. Where do you see the most promising, yet under-explored, applications of biochar in the broader field of renewable energy conversion?
GD: We have achieved remarkable performance improvements by mixing biochar with natural fiber in insulation panels. The improvement is not significant in insulation, but the fire retardancy capabilities increase significantly. Additionally, after activation, filtering applications and charge storage, such as those found in capacitors and supercapacitors, are potential industrial applications where the use of biochar is underexplored.
SP: Your research on the synergistic effects of co-composting suggests a move away from biochar as a standalone product. What is your perspective on integrating biochar with other organic amendments, and what are the primary research questions that still need to be answered to optimize these complex interactions?
GD: I am not a soil scientist, but my work in collaboration with them has shown that less fertilizer is needed when using composting material made from dairy manure mixed with biochar. The nitrogen in the manure was beneficial in reducing the need for external applications of conventional commercial fertilizers. However, farmers who have applied pure biochar for growing avocadoes, papayas, and even flowers, have shown large yield increases with the application of just biochar. More research is needed in this area.
SP: As a professor and mentor, you have guided many students into this field. What is your message to young and budding biochar researchers who are just starting out, and what foundational knowledge should they prioritize?
GD: The main message is that we can do better in re-utilizing materials that have traditionally been considered as waste. Most of the time, biomass ends up being burned in open piles, which generates a substantial amount of pollution and has a negative impact in public health. Biomass can be utilized not only in gasifiers and pyrolyzers, but also in fermentation or other processing routes to obtain value-added products. Some companies are making biodegradable plastics from biomass. The important aspect is to find new ways to convert this material, rather than simply discarding it. That is why the concept of the circular bioeconomy is helping to change the way that society deals with materials such as biomass.
New ways of processing biomass can be found with a wide variety of foundational knowledge. Some types of biomass and processes are more aligned with biology, others with thermal analysis others with chemistry, and others with materials or with optimization. There is no single area of knowledge needed; each area can contribute, and team collaboration with different expertise is beneficial.
SP: The adoption of biochar technologies on a larger scale requires not only scientific breakthroughs but also supportive policy and economic frameworks. What do you believe is the next critical step for the biochar industry to transition from a research-driven field to a widely implemented commercial solution?
GD: Standards are important. Not all biochars are made the same. Therefore, consistency in the material for specific applications will help establish a robust market.
SP: Considering the global push for carbon sequestration, how do you see the role of biochar evolving over the next decade, and what advice would you give to young researchers interested in making a significant impact in this field?
GD: There are many large changes currently happening at the same time. For instance, mobile electrification, clean hydrogen production, renewed interest in nuclear reactors, fusion, etc. Together with carbon sequestration, these technologies are a means for humanity to continue existing in a way that does not harm our planet. My advice would be to continue working in areas that do not harm this planet or any other planet we might colonize in the future.
SP: For our readers, the research works of Dr Gerardo Diaz can be tracked at:
Leave a Reply