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The Shell Center for Sustainability's mission is to foster an interdisciplinary program of research, outreach, and education to address actions that can be taken to ensure the sustainable development of communities' living standards, interpreted broadly, to encompass all factors affecting the overall quality of life.

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Dynamic Modeling of the Nitrogen Cycle of Biochar-amended Soils, and Economic Assessment of Biochar Benefits

A holistic cost/benefit analysis that includes avoided costs and benefits, and the dynamics of full nitrogen cycle with varying properties and climate characteristics


Caroline Masiello, Department of Earth Sciences, Rice University

Kyriacos Zygourakis, Department of Chemical and Biomolecular Engineering, Rice University

Kenneth Medlock, James A. Baker, III, and Susan G. Baker Fellow in Energy and Resource Economics; Senior Director, Center for Energy Studies, Rice University

Christian Davies, Shell Oil Company

Ghasideh Pourhashem, Postdoctoral research fellow, Baker Institute Center for Energy Studies, Rice University

  Masiello pic w   Zygourakis Kyriacos sm pic Medlock Ken sm pic     Davies Christian pic 2015
Caroline Masiello Kyriacos Zygourakis Kenneth Medlock Christian Davies
  Pourhashem sm pic  
Ghasideh Pourhashem

Project Background


Dr. Ghasideh Pourhashem’s economic model is the first attempt at a holistic cost/benefit analysis of biochar production and application, including both expenses associated with biochar production and avoided costs.  This model is a significant extension of an earlier, smaller-scale technoeconomic model conducted by Dr. Christian Davies at Shell, which compared only biochar facility construction costs to the benefit from expected improvement in crop production. The new model proposed by Dr. Pourhashem will include many types of avoided costs (like more effective water retention, nutrient pollution reduction, air pollution reduction, fertilizer cost reduction, improved crop performance) and additional benefits (like utilization of the energy of pyrolysis products, heat integration and co-production of electricity).  Her postdoctoral research is formally co-advised by Dr. Davies from Shell along with Dr. Ken Medlock (Economics) and Dr. Carrie Masiello (Earth science). She currently informally co-advised by Dr. Kyriacos Zygourakis.

Pourhashem’s model will accomplish the following goals:

1.     provide the first holistic cost/benefit estimate for a range of biochar soil application scenarios;

2.     determine which benefits trigger the most significant economic benefits; and

3.     make possible uncertainty tests.

The uncertainty tests are perhaps the most powerful outcome of Dr. Pourhashem’s model because they will enable us to determine what physicochemical processes must be better understood before we can obtain more accurate economic estimates of biochar soil amendment.  The dynamic nitrogen cycling model (DNC) will provide the undergirding science to understand the N cycle benefits of biochar.

The second component of the project will proceed in parallel with the first component and will focus on modeling the dynamics of the full nitrogen cycle within biochar-amended soils with varying properties (soil type, permeability) and for different climate characteristics (rainfall, temperature).

To properly account for all these factors, the model will consider nitrogen transport and reaction through beds with two porous adsorbent phases:soil and biochar.  More specifically, it will consider:

  (a)   adsorption and desorption of ammonium and nitrate on biochar and soil;

(b)  nitrification and denitrification reactions that convert ammonium and nitrate to nitrous oxide (N2O), NOx (that is NO and NO2) and nitrogen;

(c)   uptake of the ammonium and nitrate by plants; and

(d)  microbial immobilization of N. 


designer biochars fig 1

Figure 1: This simplified schematic of the model reactions indicates that N in both its ammonium and nitrate forms can be taken by the plants and fixed by soil microbes. The process of Figure 1 take place at every point in the bed as the ammonium and nitrate are transported through the soil by rainwater or water provided by irrigation.

Such mechanistic models are extremely time and cost-effective tools. Without them, the only way to determine the relationship between biochar amendment and specific benefit is to perform physical experiments under every possible soil grain size, rainfall rate, and fertilizer application scenario. Models like the one used here, however, allow us to determine the range of potential effects quickly, without having to set up hundreds of time-consuming experiments.




·      Sun, H., Brewer, C. E., Masiello, C. A., & Zygourakis, K. (2015). Nutrient Transport in Soils Amended with Biochar: A Transient Model with Two Stationary Phases and Intraparticle Diffusion. Industrial & Engineering Chemistry Research, 54, 4123–4135.



·      H. Sun, C. A. Masiello and K. Zygourakis, “Dynamic Modeling of the Nitrogen Cycle in Biochar Amended Soils: A New Approach for Rapid Screening of Designer Biochars,” Invited Talk, Plenary Session of the Computing & Systems Technology Division, 2015 Annual Meeting of the American Institute of Chemical Engineers, Salt Lake City, UT, November, 2015.


·      Gooding, P. Markenscoff and K. Zygourakis, “Characterizing the Pore Structure of Biochars Using Multiscale Models and Reactivity Data,” 2015 Annual Meeting of the American Institute of Chemical Engineers, Salt Lake City, UT, November, 2015.


·      K. Zygourakis, “Dynamic Modeling of the Nitrogen Cycle in Biochar Amended Soils,” Invited Seminar, Oklahoma State University, Stillwater, OK, January 2016.

·      Pourhashem G., Masiello C. A., Medlock K.B., Davies C.A., “Environmental and economic benefits of biochar application for resource management”, 8th International Conference of the International Society for Industrial Ecology, ISIE 2015, Surrey, England, July 2015


·      Pourhashem G., Masiello C. A., Medlock K.B., Davies C.A., “Environmental and economic benefits of biochar application for agricultural soil amendment”, Water and Energy Workshop: Understanding impacts and Trade-offs to Facilitate Transitions, May 2015, Rice University, Houston, TX, USA (poster presentation)




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