Novel Amorphous Carbons for the Adsorption of Phosphate: Part I. Elucidation of Chemical Structure of N-Metal-Doped Chars.

Due to phosphate's necessity in agriculture and its danger to the environment, the development of adsorbents for its removal has been the subject of intensive research activity. Although the introduction of nitrogen functionality to chars and modification of biochar with metals have proven to change the character of the char structure, making it more active toward nutrients, there is no study regarding the doping of biochar with metals and nitrogen simultaneously for the adsorption of phosphates. This paper is the first of two in which we report the production, characterization, and evaluation of N-metal-doped biochars from cellulose for phosphate removal from liquid effluents. In this part, we describe the production and characterization of N-Ca-, N-Fe-, and N-Mg-doped biochars. The elemental composition and surface area of each of the materials produced is reported. Elemental and surface characterization of the chars are reported with the largest N content appearing at a temperature of 800 °C (12.5 wt %) and a maximum surface area for biochar produced at 900 °C (1314 m2/g). All of the adsorbents were visualized by scanning electron microscope (SEM), confirming that although there are some crystals on the surface of the biochar produced, most of the N, Mg, and Ca are part of the polyaromatic ring structure. Transmission electron microscope (TEM) images clearly show the formation of nanoclusters with the metals in the case of N-Fe and N-Ca biochars. The N-Mg biochars show a uniform distribution of the Mg through the carbon surface. X-ray photoelectron spectroscopy (XPS) studies of the biochars produced with metals and varying nitrogen levels clearly show Mg and Ca peaks shifting their position in the presence of N, suggesting the formation of stable structures between metals and N in the carbon polyaromatic ring system. To elucidate the nature of these structures, we conducted DFT-based calculations on different configurations of the nitrogenated structures. The calculated binding energy shifts were found to closely match the XPS experimental binding energy, confirming the likelihood of these structures in biochar. Finally, based on our experimental and modeling results, we hypothesize that an important fraction of the Mg and Ca is introduced to these biochars at the edges. Another fraction of Mg and Ca is in the form of phthalocyanine-like internal structures. More experimental studies are needed to confirm the formation of these very interesting structures and their potential use as adsorbents or catalysts.

Weak-base pretreatment to increase biomethane production from wheat straw.

Weak-base pretreatment of wheat straw was investigated for its ability to improve biomethane production. Anaerobic digestion (AD) was performed on wheat straw pretreated with 3%, 5%, or 7% Na2CO3 as a weak base. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) spectra demonstrated disruption of lignocellulosic structures by pretreatment. In the 5% Na2CO3 treatment group, cellulose and hemicellulose were retained effectively, with efficient removal of lignin. The removal rates of cellulose, hemicellulose, and lignin were 27.9%, 20.4%, and 31.0%, respectively, after 5% Na2CO3 pretreatment. The methane content (53.3-77.3%) was improved in the 5% Na2CO3 treatment group, with maximum methane production (307.9 L/kg VS) that was 41.6% higher than that of the untreated sample. Cellulose and hemicelluloses were degraded 59.3% and 56.3% after AD. It took 20 days to reach 80% of the maximum cumulative methane production for the 5% Na2CO3 pretreatment group, which was 4 days faster than the untreated group. These results indicate that 5% Na2CO3 pretreatment improve the lignocellulose structure of wheat straw, allowing better biodegradability of wheat straw in AD for increased biogas production, enhanced methane content, and decreased digestion time.

Nitrogen doped char from anaerobically digested fiber for phosphate removal in aqueous solutions.

This study explores the use of an engineered char produced from the pyrolysis of anaerobically digested fiber (ADF) to adsorb phosphate from aqueous solutions. Two series of engineered chars were produced. The first series was a CO2 activated (CA) char produced via slow pyrolysis between 350 and 750 °C. The second series was a nitrogen doped (ND) char activated in the presence of ammonia at comparable temperatures. Proximate analysis, elemental composition, gas physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray powder diffraction (XRD) techniques were used to characterize properties of resulting products. The surface area of the carbon product increased after nitrogen doping through ammonization (166.6-463.1 m2/g) compared to CO2 activated chars (156.5-413.1 m2/g). Phosphate adsorption isotherms for both CO2 activated and nitrogen doped chars can be described by the Langmuir- Freundlich and Redlich Peterson adsorption models. Nitrogen doped carbon phosphate sorption capacity in aqueous solutions was twice compared to CO2 activated carbons. As carbonization/activation temperature increased the sorption capacity increased from 3.4 to 33.3 mg g-1 for CA char and 6.3-63.1 mg g-1 for nitrogen doped char.

Characterization of solid and vapor products from thermochemical conversion of municipal solid waste woody fractions.

The ever-increasing consumption of material goods with economic growth is resulting in an increasing generation of municipal solid waste (MSW) and the rapid filling of landfills. Fractions of municipal solid waste containing wood-based products have the potential to be used for the development of value added products. In this paper we produced and characterized biochar and pyrolysis vapors from municipal solid waste (MSW) woody fractions to demonstrate their suitability towards soil amendments. Carbonization work focused on compost overs, molded wood pallets, treated wood, sawmill cut ends, wood derived fuels, furniture, painted wood, plywood, oriented strand board and particle boards from Washington State recycling facilities. The goal of this research is to use these biochars as soil amendments; however, there are concerns with both the potential presence of condensed organic pollutants and trace metals. The presence of trace metals and polycyclic aromatic hydrocarbons (PAH) in all the biochars produced were examined. GC-MS analyses of liquid extracts did not reveal the presence of soluble PAH compounds. High concentrations of mercury (Hg) and arsenic (As) were found in the biochar made from painted wood and treated wood, respectively. Among the methods tested for the removal of trace metals, acid washing was found to be the most effective. The volatiles released from the analyzed MSW fractions were also analyzed in Py-GC-MS studies. Among these volatile compounds, many contained Cl, N, or S, which could be potential sources of pollution if the pyrolysis vapors are combusted.