Adrian T. Hanson

Anaerobic digestion of municipal solid waste and agricultural waste and the effect of co-digestion with dairy cow manure

Anaerobic digestion of dairy cow manure (CM), the organic fraction of municipal solid waste (OFMSW), and cotton gin waste (CGW) was investigated with a two-phase pilot-scale anaerobic digestion (AD) system. The OFMSW and CM were digested as single wastes and as combined wastes. The single waste digestion of CM resulted in 62m3 methane/ton of CM on dry weight basis. The single waste digestion of OFMSW produced 37m3 methane/ton of dry waste. Co-digestion of OFMSW and CM resulted in 172m3 methane/ton of dry waste. Co-digestion of CGW and CM produced 87m3 methane/ton of dry waste. Comparing the single waste digestions with co-digestion of combined wastes, it was shown that co-digestion resulted in higher methane gas yields. In addition, co-digestion of OFMSW and CM promotes synergistic effects resulting in higher mass conversion and lower weight and volume of digested residual.

Energy recovery from grass using two-phase anaerobic digestion

Municipal solid wastes are major sources of air, water and soil contamination. There is a need for alternative waste management techniques to better utilize the waste and minimize its adverse environmental impact. A two-phase pilot-scale bio-fermentation system was used to evaluate the feasibility of producing methane from grass waste, a major constituent of solid wastes. The bi-phasic system consists of a solid phase and a methane phase. Leachate is re-circulated through the solid phase until a desired level of volatile fatty acid (VFA) is accumulated in the leachate. The leachate is then transferred to the methane reactor where the VFA is converted to methane. The results showed that 67% of the volatile solids in the waste can be converted into soluble chemical oxygen demand in a period of six months. The system produced an average of 0.15 m3 of methane per kg of grass. The average methane concentration in the produced gas was 71%. A mathematical model was developed to estimate the methane and carbon dioxide concentrations in the gas phase as a function of reactor properties.

Remediation of lead contaminated soil by EDTA. I. Batch and column studies

Extraction using ethylenediaminetetraacetic acid (EDTA), and other chelates has been demonstrated to be an effective method of removal of Pb from many contaminated soils. However, column leaching of Pb from alkaline soils with EDTA has been problematic due to extremely low soil permeability. The first purpose of this study was to develop batch extraction procedures and methods of analysis of batch extraction data to provide Pb solubility information which can be used to model the column extraction of Pb from soils. The second purpose was to determine the effect of the addition of KOH and CaCl2 to K2H2EDTA extract solution on both hydraulic conductivity and Pb removal. A Pb-contaminated soil sample was collected from an abandoned battery recycling facility. Both batch shaker extractions and column leaching experiments were completed using 5 different EDTA extract solutions. When only CaCl2 was added to EDTA no change in the amount of Pb removed by batch extraction was observed. As expected, lead solubility was observed to decrease as pH was increased by the addition of KOH. However, Pb solubility was only slightly decreased by the addition of both CaCl2 and KOH. The amount of time required to leach 6.0 L of extraction solution through the soil columns varied from 2 to 33 days. The addition of CaCl2 and/or KOH resulted in increased soil hydraulic conductivity relative to the EDTA-only solution. The hydraulic conductivity was related to residual calcium carbonate content, suggesting that dissolution of CaCO3 and subsequent production of CO2 gas in the soil pores was partially responsible for the observed reductions in soil permeability. However, Pb removal was diminished with the addition of CaCl2 and KOH because of the decreased Pb solubility and also kinetic limitations associated with the shorter residence time of the extract solution in the column.

Rapid oxidation of sulfide mine tailings by reaction with potassium ferrate

The chemistry of sulfide mine tailings treated with potassium ferrate (K2FeO4) in aqueous slurry has been investigated. The reaction system is believed to parallel a geochemical oxidation in which ferrate ion replaces oxygen. This chemical system utilized in a pipeline (as a plug flow reactor) may have application eliminating the potential for tailings to leach acid while recovering the metal from the tailings. Elemental analyses were performed using an ICP spectrometer for the aqueous phase extract of the treated tailings; and an SEM-EDX for the tailing solids. Solids were analyzed before and after treatments were applied. ICP shows that as the mass ratio of ferrate ion to tailings increases, the concentration of metals in the extract solution increases; while EDX indicates a corresponding decrease in sulfur content of the tailing solids. The extraction of metal and reduction in sulfide content is significant. The kinetic timeframe is on the order of minutes.

Remediation of Lead Contaminated Soil by Column Extraction with EDTA: II. Modeling

Lead contamination of soils is a common problem throughout the world. Laboratory batch test and bench scale experiments have shown that EDTA can be used to remove lead from contaminated soils. However, due to the high cost and laborious task associated with actual environmental remediation of a lead contaminated soil, there is a need to be able to predict the outcome of a remediation process in advance in order to optimize the process and minimize the cost. This paper describes the development and validation of a computer model which can be used to simulate the removal of lead from a contaminated soil column using EDTA as the chelating agent. The model is able to simulate the lead removal from soil based on equilibrium as well as kinetic dissolution of Pb. The comparison of the simulated results with actual lead concentrations both in effluent and soil shows that the model can predict the lead removal process with reasonable accuracy.

Converting gin and dairy wastes to methane

Alternatives to gin trash and manure disposal would benefit both the cotton ginning and dairy industries. Anaerobic digestion produces both methane gas and a class A soil amendment. Gin and dairy wastes were combined in the solid phase portion of a two-phase anaerobic system to determine the combinations of temperature, rewetting interval, and mixture ratio that maximize potential methane gas production and minimize process completion time. No significant volatile fatty acid formation occurred after leachate pH approached 7.0, indicating process completion. This took approximately three weeks when temperatures were above 32°C (90°F), mixture ratios were below 5:1 (gin to dairy waste, dry mass basis), and the solid phase was wetted twice daily. Ten percent of the mass was converted to soluble chemical oxygen demand (COD), which has potential for conversion to methane in the second phase.

PRODUCING ENERGY AND SOIL AMENDMENT FROM DAIRY MANURE AND COTTON GIN WASTE

Millions of tonnes of feedlot manure and cotton gin waste are generated in the U.S. each year. Dairy and feedlot operations in New Mexico produce 1.2 million tonnes of manure annually. Traditionally, manure has been used as a soil amendment in agriculture. However, land application of manure is limited in New Mexico due to problems with salinity, potential groundwater contamination, and limited availability of agricultural land. Waste treatment alternatives are sought. A two-phase anaerobic digestion system was used to evaluate the feasibility of producing methane and soil amendment from mixed agricultural wastes. Cotton gin waste and dairy manure were combined and used as feedstock. Under mesophilic conditions, 48% of the combined waste was converted into biogas. The gas yield was 87 m3 of methane per tonne of mixed waste. Methane concentration in the biogas averaged 72%. Gas production with mixed waste increased 35% compared to digesting dairy waste alone. Nutrient analyses of the residuals showed that they could be used as soil amendments. Residual solid material from the two-phase anaerobic digester had a considerably higher nitrogen and lower sodium content than aerobically composted manure. Anaerobic digestion lasted from one to three months and required 0.15 m3 of water per 1 m3 of waste. Aerobic composting of similar waste in New Mexico takes eight to nine months and consumes 1.2 m3 of water per 1 m3 of waste.

Ozonation of Continuous-Flow Activated Sludge for Reduction of Waste Solids

The ultimate disposal of wastewater sludge has been, and continues to be, one of the most expensive problems faced by wastewater utilities in the United States. The objective of this research was to apply cell lysis and cryptic growth principles to activated sludge to study the applicability of ozonation to reduce the mass of secondary sludge. The study produced data and details for application of ozone to reduce secondary sludge production. The application of ozone reduced the mass of waste sludge by 30 to 50% depending on the ozonation rate and period.

Predicting Arsenate Adsorption on Iron-Coated Sand Based on a Surface Complexation Model

AbstractEquations were developed to predict arsenate sorption on iron oxide coated sand, on the basis of the constant capacitance surface complexation model, assuming formation of bidentate surface complexes between arsenate and iron oxyhydroxide surface sites. The developed equations can predict arsenate adsorption when initial arsenate concentration, adsorbent concentration, and solution pH are known. The average discrepancy between experimental data and modeling results was less than 5%. The maximum arsenate sorption capacity is the only parameter required that needs to be estimated from experimental data. The developed equations were validated by modeling arsenate adsorption on iron oxide sand over the pH range 5–8, under various initial arsenate concentrations and iron oxide coated sand solid concentrations. The developed predictive equation can also be used for calculating arsenate adsorption performance on iron impregnated activated carbon. Finally, the developed equation can be used to calculate s...

Retention and Transport of Nitrate and Ammonium in Loamy Sand Amended with Clinoptilolite Zeolite

AbstractAgricultural soils of southern New Mexico, especially sand and sandy loams receiving numerous nitrogen (N) fertilizations, are prone to leaching large amounts of N to shallow groundwater. Adsorption and leaching experiments were conducted to investigate the use of clinoptilolite zeolite (CZ) as an amendment to sandy soils to increase N retention and reduce nitrate (NO3−) leaching. Urea-ammonium-nitrate (UAN 32) fertilizer was applied to four soil treatments to simulate crop irrigation. The treatments were composed of 100% CZ, 100% loamy sand (LS), a mixture of 80∶20% (LS:CZ), and a mixture 60∶40% (LS:CZ) by mass, respectively. Results from the experiments showed an inverse relationship between nitrate-nitrogen (NO3−-N) adsorption and the amount of CZ added to soil caused by anion exclusion and a direct relationship between ammonium-nitrogen (NH4+-N) adsorption and the amount of CZ mixed with LS due to NH4+-N entrapment by the CZ molecules. It is therefore recommended to use other types of fertiliz...