About

Dr. Robert Anex is a Professor in the Department of Biological Systems Engineering at the University of Wisconsin–Madison. His research focuses on developing and assessing systems for producing energy, fuels, and products from biorenewable resources. He studies the economic and environmental feasibility of biorenewable chemicals, nutrient recovery and cycling in biofuel systems, and the impacts of biomass production on the hydrologic cycle. Dr. Anex's work combines laboratory process development with large-scale model-based assessments of agricultural-industrial systems, utilizing tools such as Life Cycle Assessment (LCA) and Techno-economic Analysis (TEA) to evaluate the sustainability and efficiency of biobased products. His research aims to understand the interdependencies among agricultural and industrial systems to ensure food, water, and energy security for a growing population.

Research topics

• Environmental science
• Engineering
• Chemistry
• Medicine
• Biology
• Environmental engineering
• Pulp and paper industry
• Environmental chemistry
• Waste management
• Economics
• Geography
• Agricultural economics
• Environmental health

Selected publications

• High-Throughput Screening of Geopolymerization Kinetics for Rapid Mixture Design Optimization

  Industrial & Engineering Chemistry Research · 2026-03-10

  article

  Geopolymer binders derived from industrial mineral wastes (IMWs) offer a sustainable alternative to Portland cement concrete. However, the variability in IMW feedstock composition necessitates careful optimization of activator formulations and processing conditions, a challenge that remains time- and resource-intensive. To address this, we developed a high-throughput (HT) FTIR-based screening methodology to rapidly evaluate the geopolymerization kinetics of carbonated ground granulated blast furnace slag (GGBS). Carbonated GGBS IMW was alkali-activated using sodium hydroxide and sodium silicate solutions under systematically varied liquid-to-solid (L/S) ratios (33–60 wt %), activator (Na2Si3O7/NaOH) volume ratios, and reaction temperatures (ambient, 40 °C, and 70 °C). The geopolymerization process, leading to the formation of sodium or calcium aluminosilicate hydrate (N–A–S–H/C–A–S–H) gel, was monitored by ATR-FTIR spectroscopy, which tracked characteristic vibrational bands associated with (Si–Al)–OH linkages, enabling the extraction of reaction rate parameters. The results demonstrated that increasing temperature accelerates geopolymerization kinetics, with alkali-activation rates following the trend 70 °C > 40 °C > ambient for most formulations, particularly at moderate silicate contents and L/S ≥ 50 wt %, while excessive silicate led to diffusion-limited behavior at elevated temperatures. Regression analysis using polynomial surface fitting revealed nonlinear interactions between silicate ratio and liquid fraction, with predictive fits reaching R2 = 0.94 under ambient conditions. Importantly, high-throughput FTIR-derived alkali-activation rates strongly correlated with compressive strength values (1–28 days), with optimized formulations achieving up to 67.6 MPa at 28 days. Overall, this study demonstrates a quantitative high-throughput framework for a rapid evaluation of geopolymerization kinetics and relating those to the long-term compressive strength of carbonated slag-based geopolymer systems.

  PublisherDOI

• Impacts of agrisolar co-location on the food–energy–water nexus and economic security

  Nature Sustainability · 2025-04-21 · 17 citations

  articleOpen accessSenior author

  Understanding how solar PV installations affect the landscape and its critical resources is crucial to achieve sustainable net-zero energy production. To enhance this understanding, we investigate the consequences of converting agricultural fields to solar photovoltaic installations, which we refer to as ‘agrisolar’ co-location. We present a food, energy, water and economic impact analysis of agricultural output offset by agrisolar co-location for 925 arrays (2.53 GWp covering 3,930 ha) spanning the California Central Valley. We find that agrisolar co-location displaces food production but increases economic security and water sustainability for farmers. Given the unprecedented pace of solar PV expansion globally, these results highlight the need for a deeper understanding of the multifaceted outcomes of agricultural and solar PV co-location decisions. This analysis looks at the impacts and outcomes from installing solar arrays on agricultural land, finding that these ‘agrisolar’ projects can displace food production but simultaneously provide economic security and offset water use.

  PublisherOA PDFDOI

• Carbon Removal Accounting for a Sustainable Future: Distributing CO2 Flows in Multiservice Systems

  Sustainability · 2024-12-12 · 2 citations

  articleOpen accessSenior authorCorresponding

  Carbon dioxide removal (CDR) systems are an integral part of sustainable pathways limiting global warming to less than 2.0 °C. When the sole purpose of CDR is capturing and storing atmospheric CO2, carbon registries offer detailed procedures to calculate the carbon removal credits. However, the registries do not address how to distribute CO2 flows when CDR provides additional services. Standardized, transparent rules for distributing CO2 flows among CDR services are required for the formation of efficient private and public carbon markets. The lack of such rules could result in double counting if those reductions are allocated to more than one service, decreasing the trustworthiness of carbon removal credits or deterring the delivery of an additional low-carbon service, thus limiting the economic viability and deployment of CDR. We examine allocation rules in carbon registries and carbon accounting guidelines, including their life cycle assessment (LCA) principles. We evaluate physical (mass-based) and non-physical (economic) allocation methods using a generic CDR system and find both to be unworkable. We then develop a mass balance (MB) approach which can reliably allocate captured and stored carbon (CSC) between carbon removal credits and other services based on the value CO2 removal in those markets. This practical approach to allocation can be used in a transparent way to provide flexibility that would allow CDR services to capture the value of the multiple services they provide and, through this, promote the deployment of these sustainable alternatives.

  PublisherOA PDFDOI

• Renewable natural gas: A case study of Minnesota

  Biomass and Bioenergy · 2024-03-19 · 5 citations

  articleSenior authorCorresponding
  PublisherDOI

• Putting the genie back in the bottle: Decarbonizing petroleum with direct air capture and enhanced oil recovery

  International journal of greenhouse gas control · 2024-11-14 · 4 citations

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Issue Information, Cover, and Table of Contents

  Journal of Industrial Ecology · 2023-12-01

  paratextOpen access
  PublisherOA PDFDOI

• From Fields to Photovoltaics: Effects of Agrisolar Co-Location on Food, Energy, Water, and Economic Security

  Research Square · 2023-11-02

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Direct Air Capture and Sequestration of CO₂ by Accelerated Indirect Aqueous Mineral Carbonation under Ambient Conditions

  ACS Sustainable Chemistry & Engineering · 2022 · 44 citations

  • Chemistry
  • Environmental science
  • Waste management

  Mineralization of gaseous carbon dioxide into solid carbonates using alkaline industrial residues such as coal fly ash has a dual advantage of reducing the carbon dioxide footprint of coal power plants and improving ash utilization. However, the slow mineral carbonation rate under atmospheric conditions is a major challenge, especially when using natural minerals or industrial residues for direct air capture (DAC) of CO2. In this study, using coal fly ash samples and concentrated alkali carbonate aqueous solutions as a recyclable solvent, we show the feasibility of coupling mineral carbonation with DAC under atmospheric conditions. Findings show that carbonation efficiency is best under alkaline conditions, achieving as high as ∼80% conversion to calcium carbonates within 1 h in a 1.9 M sodium carbonate solution. Based on the experimental results, a process coupling DAC and mineral carbonation that operates entirely under ambient conditions is proposed. The techno-economic and life cycle assessments for the proposed process project a levelized cost of $116–133/t-CO2-sequestered (US $2019) and process carbon emissions (GWP) in the range of 0.03–0.25 t-CO2e/t-CO2-sequestered. Considering the low cost, simplicity, and gigaton-scale sequestration potential, we believe that DAC based on alkaline industrial residue carbonation can be considered a “low-hanging fruit” in the pursuit of negative emissions to combat climate change.

  PublisherOA PDFDOI

• Economic and environmental performance of non-cellulosic fermentable carbohydrates production for biofuels and chemicals

  Journal of Cleaner Production · 2022-04-01 · 8 citations

  articleSenior author
  PublisherDOI

• Declining greenhouse gas emissions in the US diet (2003–2018): Drivers and demographic trends

  Journal of Cleaner Production · 2022 · 33 citations

  Senior authorCorresponding
  • Agricultural economics
  • Environmental science
  • Geography

  The food system is a major driver of climate change, and many have noted that a shift in consumption patterns is necessary to achieve greenhouse gas (GHG) emission reduction targets that can limit global mean temperature rise ≤2 °C. Beef is the largest GHG emitting commodity in the United States, and in recent years national consumption has been declining. Little is understood about how this change in consumption and other dietary trends have influenced the overall GHGs associated with the US diet. The objective of this study is to estimate the GHGs of changing dietary patterns from individual self-selected diets in the United States from 2003 to 2018 and evaluate trends and potential disparities among demographic subgroups. Life cycle emissions factors (representing food production impacts) for food commodities from dataFIELD were used to estimate GHGs associated with food items described by US adults (>20 years, n = 39,750) in the National Health and Nutrition Examination Survey (NHANES). From 2003 to 2018, the mean GHG emissions associated with the US diet fell by more than 35%, from 4.02 kg CO2e per day per capita, to 2.45 kg CO2e per day per capita, despite average caloric intake remaining relatively stable over the same period. Average beef consumption declined 40% per capita over the study period, which contributed to more than 50% of the observed GHG savings in the diet over the study period. All demographic variables included in this analysis (age, gender, race/ethnicity, and ratio of family income to the federal poverty level) exhibited a reduction in GHG emissions associated with their diets. However, GHGs and overall rate of change differed across demographic subgroups. Black women had the lowest GHG emissions associated with their diet, 1.92 kg CO2e per capita per day. Men aged 20–34 had the largest rate of reduction in GHGs associated with diet changes, with an average annual decline of 210g CO2e per day per capita over the study period. Despite GHGs associated with the US diet falling over the last 15 years, the US diet is still exceeding established GHG limits to meet global targets, such as the Paris Agreement. Additional research is needed to better understand motivations and drivers that have reduced emissions in the diet over this period, particularly in demographic subgroups that showed both low impact and a rapid decline in emissions.

  PublisherDOI

Recent grants

• Biofuels and the Hydrologic Cycle

  NSF · $164k · 2010–2012

• BE MUSES: Biocomplexity in the Bioeconomy: The Natural and Industrial Ecology of Biobased Products

  NSF · $1.8M · 2004–2011

Frequent coauthors

• Jay R. Lund

  University of California, Davis

  12 shared

• D. Raj Raman

  Western Michigan University

  10 shared

• Daryl Herzmann

  Iowa State University

  6 shared

• Matt Liebman

  Iowa State University

  6 shared

• Sami Khanal

  The Ohio State University

  6 shared

• D. W. Hyndman

  5 shared

• Brian Gelder

  Iowa State University

  5 shared

• A. D. Kendall

  5 shared

Education

• Ph.D., Civil & Environmental Engineering

  University of California Davis

  1995

• M.S., Mechanical Engineering

  University of California Davis

  1983

• B.S., Mechanical Engineering

  University of California Davis

  1981

Awards & honors

• Federal Biomass Research & Development Technical Advisory Co…
• USDA National Institutes of Food and Agriculture, 2016 Partn…
• U.S. Environmental Protection Agency (EPA) Board of Scientif…
• National Biodiesel Board Sustainability Task Force Advisory…
• OECD Fellow, Biological Resource Management for Sustainable…