Award Date

December 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Eakalak Khan

Second Committee Member

Erica Marti

Third Committee Member

Jacimaria Batista

Fourth Committee Member

Jaeyun Moon

Fifth Committee Member

Stephen Lepp

Number of Pages

286

Abstract

In recent years, the application of biochar as a soil amendment has gained attention as a potential solution for nutrient management and environmental remediation. Biochar, a carbon-rich material produced through the pyrolysis of biomass under oxygen-limited conditions, exhibits unique physicochemical properties making it an effective sorbent for nutrients and contaminants. Its high surface area, porosity, and stability provide an ideal matrix for nutrient retention and release, as well as the immobilization of pollutants. One area of particular interest is the application of biochar for nutrient recovery from source-separated human urine. Source separation of urine has gained momentum as a sustainable sanitation practice, as it allows for the separate collection and treatment of urine, which is rich in essential plant nutrients such as nitrogen, phosphorus, and potassium. However, the widespread use of antibiotics in livestock production and human healthcare has led to the presence of antibiotic residues in animal manure and wastewater, posing a threat to ecosystems and contributing to the development of antibiotic resistance. This dissertation research unveils the potential of biochar in addressing the challenges associated with nutrient management and the risks associated with antibiotic release to the environment.

This research includes antibiotics from five different classes: macrolide (azithromycin (AZ)), fluoroquinolones (ciprofloxacin (CPX)), sulfonamides (sulfamethoxazole (SMX)), tetracycline (tetracycline (TC)), and aminopyrimidine (trimethoprim (TMP)). These antibiotics are widely used for medical and veterinary purposes and are frequently found in human urine, wastewater effluent, surface water, and drinking water. There are three major research tasks where batch adsorption experiments were conducted using virgin and/or modified biochar prepared from oak wood (OW), paper mill sludge (PMS), and/or sewage sludge (SS) to elucidate the effects of adsorption time, pH, and adsorbent dose. Various adsorption isotherm models (Langmuir, Freundlich, Temkin, and Redlich-Peterson) and kinetic models (pseudo-first order, pseudo-second order, Elovich, and intra-particle diffusion) were employed to describe the experimental results. Brunauer–Emmett–Teller analysis, X-ray diffraction (XRD) spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) techniques were used to characterize the physical and chemical properties of the biochar.

The first task aimed to investigate the simultaneous adsorption of nutrients and antibiotics on biochar under different environmental conditions using virgin OW and PMS biochar. Hydrogen bonding and π-π interactions were identified as potential adsorption mechanisms. The findings suggest that biochar can simultaneously adsorb nutrients (43.30–266.67 mg/g) and antibiotics (246.70–389.00 μg/g). Lower solution pH (< 5) was better for antibiotic adsorption, while higher solution pH (> 5) favored nutrient recovery. Also, desorption of the antibiotics was observed, which might raise concerns due to possible environmental release of antibiotics. To improve antibiotic adsorption selectivity, there is a need to go beyond pristine biochar, such as biochar with surface modification.

In the second task, non-traditional modifiers, dimethyl sulfoxide and deep eutectic solvent (DES), were selected to modify the SS biochar to selectively remove antibiotics from human urine. The modifications of biochar introduced hydrophilic functional groups (-OH/-COOH) on the surface, enhancing selective adsorption of antibiotics. The maximum adsorption capacities of AZ, TMP, TC, SMX, and CPX were 196.08, 370.37, 833.33, 81.30, and 263.16 μg/g, respectively. The regeneration efficiencies of the modified biochar for antibiotics were higher than those for nutrients after five cycles. However, the accumulation of solvents and the possible formation of unidentified byproducts on the biochar surface caused a decline in regeneration efficiency between cycles.

Chlorine, a widely used cleaning agent for toilet cleaners, is commonly detected in source-separated human urine. In the last task, the interference of chlorine during the adsorption of nutrients and antibiotics by SS biochar was studied. There was a significant difference between the adsorption capacities of nutrients and antibiotics with chlorine and without chlorine. The DES-modified SS biochar adsorbed 714 µg/g and 170 µg/g for TMP and 2,500 µg/g and 833 µg/g for CPX for the adsorption processes with and without chlorine, respectively. Based on the adsorption kinetics and isotherm results in combination with EDS, FTIR, and XRD analyses, it was concluded that the presence of chlorine in urine impacts with the adsorption processes by the formation of amines and disinfection by-products. The lower oxidizing ability of chlorine and deprotonation of antibiotics at higher pH explained the lower difference in removal capacity between the adsorption with chlorine and without chlorine.

The sustainable management of nutrients in agricultural systems is crucial for ensuring food security and environmental sustainability. The concept of using biochar to recover nutrients from urine while mitigating the risks associated with antibiotic residues holds great promise. By adsorbing and immobilizing nutrients, while preventing the release of antibiotics, biochar can provide a sustainable pathway for nutrient recycling without compromising environmental and human health. This dissertation research highlights the application of biochar for antibiotic-free nutrient recovery from source-separated human urine as a potential solution for sustainable agriculture, resource conservation, and environmental protection.

Keywords

Adsorption; Chlorine; COSMO-RS; Dimethylsulfoxide; Engineered biochar; Regeneration

Disciplines

Civil Engineering | Environmental Engineering

File Format

pdf

File Size

23630 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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