Grantee Research Project Results

Final Report: Community-Scale Gasification and Biochar Retort Hubs for Rural Areas: A “Closed Loop” System for Sustainable Agriculture and Bioenergy

EPA Grant Number: SU835706
Title: Community-Scale Gasification and Biochar Retort Hubs for Rural Areas: A “Closed Loop” System for Sustainable Agriculture and Bioenergy
Investigators: Halden, Rolf U. , Driver, Erin M , Tallman, Dakota , DePinte, Daniel , Kavazanjian, Edward , Epshtein, Olga , Hart, Steven , Kim, Yeon-Su
Institution: Arizona State University , Northern Arizona University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities

Objective:

Gasification of biowaste and its conversion to biochar (a charcoal-like material made in oxygen limited conditions) is a cost-effective and sustainable solution to the management of resources mislabeled as ‘waste.’ Towards this end, we are investigating the beneficial effect of the biochar produced by these facilities on crop yields and its environmental impact. Globally, negative environmental impacts are increasing, and few value-adding processes are widely available for recovering valuable resources from this overabundant stock of organic wastes, more than 8 billion tons of which are collected around the world each year. Repurposing agricultural biowaste eases pressure on non-renewable resources and provides a sanitary method for waste disposal and management. Developing a method by which a low-cost byproduct of gasification (biochar) could be used to fix volatile constituents in agrochemicals and biosolids will reduce downstream environmental impacts. Biochar can also augment marginal soils, resulting in the creation of new agricultural land resources and reducing deforestation-related losses of carbon sequestration and wildlife habitat.  

The primary objectives of Phase I were to develop a better understanding of the feedbacks between biochar, plant growth, and transport dynamics, and to lay the groundwork for Phase II by developing a methodology for multidisciplinary experiments we will carry out in parallel to test the design of a novel applications of biochar to agricultural soil augmentation. A key objective of all Phase I tasks was the screening of the most promising parameters or scenarios to test during Phase II. The outcomes of the project will promote the use of an inherently benign structural amendment in place of toxic agrochemicals and biosolids (solids byproduct of municipal wastewater treatment that is treated sufficiently to comply with regulations for disposal on land), and the sequestration/remediation of harmful substances present in these materials.  

Summary/Accomplishments (Outputs/Outcomes):

Overall, the pH of all soil-biochar mixtures is within the optimum 5.5 to 7.5 pH range for most agricultural crops. Initial results from grain size distribution experiments demonstrate that even at 8% biochar by volume, particle size distributions of the overall soil mixture are not significantly affected. The addition of biochar does, however, impact initial soil moisture content and soil bulk density, by making the soil less dense and increasing soil water content. The addition of biochar has a positive effect on the drought tolerance of beets by increasing the days plants remained virtually unaffected by drought (simulated as complete withholding of water until plants reached permanent wilting point and died) by an average of 2.5 days (for soils amended with 4% biochar) and 1.7 days (for soils amended with 8% biochar). However, for lettuce, a 4% addition of biochar had a negative effect on the average days to the first sign of wilting, which arrived 0.1 days sooner than soil with no biochar amendment. At 8%, the effect on lettuce was very slight – the plants showed their first signs of wilting only 0.3 days later than soils without biochar. The difference in effect biochar had on beets and lettuce plants can be attributed to the differences in plant physiology, such as rooting depth and water storage capacity. With respect to crop yield, the average yield of beet crops increased with the addition of biochar. Lettuce crop yield peaked at 4% biochar amendment but showed no significant improvement with an 8% amendment. These results are consistent with the observed effect of biochar on the drought tolerance characteristics of these crops. Average moisture retention increased with the addition of biochar (at both 4% and 8% amendment by volume), but the impact of additional biochar added to the 8% mixture had a lesser effect, suggesting potential thresholds for the impact biochar can play on soil water holding capacity, particularly if offset by greater plant productivity and corresponding water demand.   

  

Conclusions:

Based on our initial results we can already see that biochar can increase crop yield and improve drought tolerance by increasing the soil water retention capacity of soils, thus prolonging the period before onset of permanent wilting point (plant mortality). Relatively small additions of biochar (4% and 8% by volume) can have a 0.1-0.2 pH unit increase on native soil pH. This can be particularly useful for soils falling just outside the desirable 5.5-7.5 pH range, or for improving a specific portion of farmland for crops requiring more alkaline soils, such as asparagus, summer squash, pumpkins, and muskmelon. Based on preliminary data for soil bulk density, initial soil moisture, and water retention, biochar amended soils can be expected to decrease runoff during rainfall or irrigation. Decreased runoff corresponds to less nutrient and sediment loading to receiving waters. Preliminary data for organic content suggest biochar will positively affect agrochemical immobilization and degradation via better retention in the soil column due to increased soil cohesion and natural attenuation facilitated by microbial processes.  

The observed impact on plant growth is particularly promising when we consider that the soil used in the experiments had inherently favorable structural characteristics, an agriculturally-desirable pH, and was sourced from an organic farm where legacy contamination is unlikely. Biochar could have an even more pronounced impact on crop yield in marginal soils – such as those with legacy agrochemical contamination, poor drainage characteristics, or high acidity, in which the addition of biochar would bring soil pH into the desirable 5.5-7.5 range at which most crop growth is highest and drainage characteristics improve considerably. These soils, and the regions in which they occur, would stand to benefit substantially from additional amendment by biochar and inexpensive nutrient-rich biosolids – provided we adequately understand and can anticipate the fate and transport of constituents of concern out of biosolids, and can immobilize or attenuate the migration using biochar. In Phase I, we have established the procedure for evaluating the impact of biochar on plant growth, and are now poised to do groundbreaking work by finding a new, more sustainable, and less threatening use of the 13 billion pounds of biosolids produced in the United States annually, and the hundreds of billions of pounds more produced around the world.  

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

bioremediation of agricultural chemicals, bio-based feed stocks, environmentally benign substitute, toxic use reduction, agricultural byproducts, waste to energy