About

Christopher Muller is a Professor of Sociology at Harvard University, having joined the Harvard faculty in 2023 after teaching at the University of California, Berkeley. His research centers on the political economy of incarceration in the United States from the Reconstruction era to the present. Muller focuses particularly on how agricultural labor markets, migration, and struggles over land and labor have influenced incarceration rates and contributed to racial and class inequalities within the prison system. He has also explored the causes and effects of environmental inequality and disparities in mortality from infectious diseases. His current work investigates long-term patterns in Black and White incarceration rates since slavery, examining why the Black incarceration rate was lower in the South than in the North for much of the 20th century, why it was lowest in the South's cotton belt, and why it began to rise in the early 1970s. This research aims to clarify the connections between incarceration, slavery, peonage, and broader shifts in the U.S. agricultural economy.

Research topics

• Political Science
• Sociology
• Demographic economics
• Criminology
• Economics
• Law
• Geography
• Waste management
• Engineering
• Process engineering
• Labour economics
• Pulp and paper industry
• Chemistry
• Environmental science
• Gender studies

Selected publications

• Methane production and microbial adaptation in high-load vacuum-enhanced anaerobic digestion: Addressing ammonia and propionate toxicity

  Chemical Engineering Journal · 2025-03-01 · 7 citations

  articleOpen access

  • IntensiCarb technology processed 6 times the OLR of conventional AD. • Methane yield decreased linearly with increasing propionate concentrations over 2.20 g/L. • Side-stream vacuum increased ammonia toxicity resilience by a factor of 3. • Population of propionate degraders in IC was different from conventional AD. • Methanosaeta dominated conventional AD, while Methanosarcinaceae dominated IC reactors. Ex-situ vacuum-enhanced anaerobic digestion (IntensiCarb-AD) of primary and thickened waste activated sludge (PS/TWAS) was tested at an organic loading rate (OLR) of 11.0–11.3 kg COD/m 3 -d. IC-AD reactors with similar solids retention times (SRT = 20 d) and OLR, were operated at hydraulic retention times (HRT) of 5 days (IF defined as SRT/HRT of 4) and 3.33 days (IF6). IF4 had a higher steady-state methane yield of 0.214 ± 0.009 L-CH 4 /gCOD fed compared to 0.148 ± 0.029 L-CH 4 /gCOD fed in IF6. COD removals of 53.5 %±2.25 % were obtained with IF4 but fluctuated with IF6 (37.0 %±7.25 %). Both IF4 and IF6 processed 6 times the OLR of a conventional AD with comparable volatile solids reduction efficiency. The relative instability in IF6 was linked to a greater reduction in microbial activity due to longer vacuum application and higher propionate concentrations (>2.20 g/L), which affected the performance of hydrogenotrophic methanogens. Methanosarcinaceae and Methanobacteriaceae populations were 10.8 % and 35.2 % more abundant in IF4 than in IF6, respectively, corroborating the significantly higher methane yields observed in IF4 compared with IF6. Ammonia recovery efficiencies of 52.0 % and 49.1 % were observed in IF4 and IF6 respectively. Batch ammonia toxicity tests indicated a higher inhibitory constant (K i ) for IC-AD (5.60–5.70 gN/L) compared to conventional AD (1.90 gN/L). Acetate degradation was effective even with ammonia and propionate concentrations as high as 2,000 mg/L and 4,000 mg/L, respectively.

  PublisherDOI

• Are Your Digesters Up to the Task? Aligning Resource Recovery Planning with Reality

  Proceedings of the Water Environment Federation · 2025-05-04

  articleSenior author
  PublisherDOI

• Enhanced energy recovery from lignin-rich cattle manure: impact of coupling mesophilic anaerobic digestion with hyperthermophilic hydrolysis

  Chemical Engineering Journal · 2025-09-03 · 2 citations

  articleOpen access

  The recalcitrance of lignin in cattle manure significantly limits energy recovery during anaerobic digestion. Mesophilic anaerobic digestion of cattle manure (CM) was investigated in continuously stirred tank reactors (CSTRs). In phase 1, the control mother reactor (MR) was operated at an SRT of 30 d, while in phase 2 the MR was followed by a hyper-thermophilic hydrolysis reactor (HTH) at 75 °C and SRT of 2 d (HTH2), with recirculation back to the MR which operated at an SRT of 22.4 d. The average steady-state biodegradability based on methane yields, in the MR, after recirculation, was 46 % ± 3 % compared to 42 % ± 5 %, without recirculation, primarily due to enhanced lignin removal of 20 % (12 % without recirculation). HTH1 (1d SRT) was tested at 75 °C to investigate the impact of SRT on solubilization of digested cattle manure (DCM). Biomethanation potential tests (BMP) conducted at 37 °C on DCM, HTH1and HTH2 achieved biodegradabilities of 17 %, 19 %, and 26 %, respectively. Specific methanogenic activity tests (SMA) at mesophilic conditions for DCM and HTH2 showed comparable maximum specific methane production rate (MSMPR) of 14.6 and 14.1 mL CH 4 /g VSS.d for DCM and HTH2. However, at 55 °C, the MSMPR for HTH2 was roughly 3 times higher than at 37 °C but comparable for DCM at both temperatures. Firmicutes and Bacteroidota were the main phyla in MR effluent, HTH2 and all SMA tests at different temperatures (37 °C and 55 °C). Methanosarcina was the most abundant methanogen at mesophilic and thermophilic temperatures. The predominant mechanism for the enhancement of methane production by the HTH recirculation was not solubilization but the enhanced biodegradation kinetics of particulate organics, including lignin, cellulose, and hemicellulose. • Coupling HTH with AD enhanced lignin-rich CM biodegradability from 42% to 46% • Recycling HTH digestate improved the digestibility of DCM by 28.8% at the same SRT. • The degree of solubilization of DCM after HTH ranged from 69-91 mg SCOD/PCOD. • HTH digestate recycling improved lignin, cellulose, and hemicellulose removal. • Firmicutes and Bacteroidota were enriched in the MR and HTH highlighting increased hydrolysis and fermentation. • Methanosarcina was enriched at 37 and 55 °C, while Methanothermobacter was only enriched at 55 °C.

  PublisherDOI

• Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency of Aerated Anaerobically Digested Solids: A Pilot Study

  Proceedings of the Water Environment Federation · 2025-05-04

  article
  PublisherDOI

• High-Rate Vacuum-Enhanced anaerobic Digestion: Performance, ammonia recovery and process kinetics

  Chemical Engineering Science · 2025-08-22 · 2 citations

  articleOpen access

  • Operation at 4x OLR of a conventional AD with comparable COD and VSS destruction. • Ex-situ vacuum enriched Methanosarcinaceae population and weakened Methanosaeta. • Recovery of 44%-47% of ammonia mitigated potential ammonia inhibition. • Vacuum-resistant syntrophs were detected. • Smithella was weakened under ex-situ vacuum and high OLR. This study investigated the applicability of side-stream vacuum for intensification of anaerobic digestion (AD) at organic loading rates (OLRs) of 3.8–4.5 kgVS/m 3 /d (6.1–7.3 kgCOD/m 3 /d), and ammonia recovery at four times the OLR of a conventional AD. Initial operation showed a performance decline due to Methanosaeta dominance and its inability to resist vacuum, resulting in low methane yield (0.06 L/gCOD feed , 15 % COD destruction) and high SCOD accumulation (12 g/L). Methanosarcinaceae enrichment under vacuum restored stability, achieving 49 %–53 % VSS destruction. Ammonia inhibition was mitigated by 44 %–47 % TKN recovery through ex-situ vacuum stripping, maintaining ammonia concentrations below 1 gN/L, compared to a potential inhibitory level of > 4 gN/L without ex-situ vacuum. The dominance of Methanosarcinaceae and successful ammonia recovery corresponded with stable operation at four times the OLR of conventional digesters. Biokinetic studies revealed a 155 %–232 % improvement in biomass-specific acetoclastic methanogenic activity through ex-situ vacuum. Fluorescence excitation-emission matrix-parallel factor analysis showed accumulation of the slowly biodegradable fluorescing organic. High fermentative bacterial counts were maintained, with increased populations of DMER64 , Mesotoga , Synergistaceae , Clostridium_sensu_stricto_1 , Pelotomaculum, and Syntrophomonas , suggesting resistance to vacuum stress, while Smithella decreased.

  PublisherDOI

• Building A New Digester or Intensifying the Existing Anaerobic Digesters? A Deep Dive into Advanced AD Intensification Technologies in North America

  Proceedings of the Water Environment Federation · 2025-09-16

  article
  PublisherDOI

• Micro-aeration for hydrogen sulfide reduction in full-scale anaerobic digesters with limited headspace: Performance and sulfide reduction kinetics

  Process Safety and Environmental Protection · 2025-02-13 · 7 citations

  articleOpen access

  A full-scale trial of micro-aeration was conducted at a municipal wastewater plant using two anaerobic digesters with limited headspace, one as a control and one as a test. A reduction of approximately 13 %–16 % in hydrogen sulfide biogas concentrations was observed in the test digester. Microbial community analyses were also conducted at steady-state conditions to determine differences between the microbial ecology of the test and the control digesters. Although sulfide removal typically occurs in the headspace of a micro-aerated digester, the data generated by this pilot study developed a new approach to quantify the contribution of liquid phase sulfide oxidizing microbes (SOM).

  PublisherDOI

• Falling racial inequality and rising educational inequality in US prison admissions for drug, violent, and property crimes

  CrimRxiv · 2025-02-05 · 1 citations

  preprintOpen access1st authorCorresponding

  Using administrative and survey data, we show that there has been a sea change in the contours of American imprisonment. At the end of the twentieth century, inequality in the prison admission rates of Black and White Americans was comparable to inequality in the prison admission rates of people with and without a college education. However, educational inequality is now much greater than racial inequality in prison admissions for all major crime types. Violent offenses have replaced drug offenses as the primary driver of Black prison admissions and Black–White inequality in the prison admission rate. The prison admission rate of Black Americans has fallen, but the prison admission rate of White Americans with no college education has dramatically increased for all offense categories. These findings, which are robust to adjustments for changing selection into college attendance, contribute to a growing body of evidence documenting narrowing racial inequality and widening educational inequality in Americans’ life chances.

  PublisherOA PDFDOI

• Bench Scale Comparison of Vacuum Evaporation Enhanced Anaerobic Digestion (IntensiCarbTM) with Thermal Hydrolysis

  Proceedings of the Water Environment Federation · 2025-09-16

  article1st authorCorresponding
  PublisherDOI

• Falling racial inequality and rising educational inequality in US prison admissions for drug, violent, and property crimes

  Proceedings of the National Academy of Sciences · 2025-01-21 · 3 citations

  articleOpen access1st authorCorresponding

  Using administrative and survey data, we show that there has been a sea change in the contours of American imprisonment. At the end of the twentieth century, inequality in the prison admission rates of Black and White Americans was comparable to inequality in the prison admission rates of people with and without a college education. However, educational inequality is now much greater than racial inequality in prison admissions for all major crime types. Violent offenses have replaced drug offenses as the primary driver of Black prison admissions and Black-White inequality in the prison admission rate. The prison admission rate of Black Americans has fallen, but the prison admission rate of White Americans with no college education has dramatically increased for all offense categories. These findings, which are robust to adjustments for changing selection into college attendance, contribute to a growing body of evidence documenting narrowing racial inequality and widening educational inequality in Americans' life chances.

  PublisherOA PDFDOI

Frequent coauthors

• James Feigenbaum

  National Bureau of Economic Research

  12 shared

• John T. Novak

  12 shared

• Christopher Wildeman

  Rockwool Foundation

  8 shared

• Ahmed Al‐Omari

  7 shared

• Katherine Y. Bell

  6 shared

• Elizabeth Wrigley‐Field

  6 shared

• Mohammad Abu‐Orf

  6 shared

• Domenico Santoro

  5 shared

Education

• Ph.D., Sociology

  Harvard University

  2005

• B.A., Sociology

  University of California, Berkeley

  1999