Nutrient Recovery from Biomass and Agricultural Wastes by Hydrothermal Carbonization Process
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Authors
Vahed Qaramaleki, Saeed
Issue Date
2022
Type
Dissertation
Language
Keywords
Crystallization , Hydrothermal carbonization , Resource recovery , Thermochemical biomass conversion , Waste treatment , Wet pyrolysis
Alternative Title
Abstract
Over the past few decades, livestock farming has undergone a significant transformation. Production has shifted from smaller family-owned farms to larger farms called confined animal feeding operations or CAFOs. While this kind of animal farming has many benefits in terms of efficiency, it has also caused many environmental issues. The most pressing issue associated with CAFOs stems from the sheer amount of manure they produce. For instance, some farms can overtake some US cities in waste generation. The numbers varied between 2800 to 1.6 million metric tons. Even though manure is valuable in farming, it becomes highly problematic when generated in such a tremendous amount. Because most of these CAFOs don’t have their pasture land to apply the manure as fertilizer, instead, they buy animal feed from outside. In addition, the capacity of the cropland to absorb that amount of waste is limited. Thus, problems related to runoff and leaching nutrients into the groundwater causing eutrophication, are common. Also, atmospheric emissions and foul odor from the manure handling and storage add to the extent of the manure issue. In this dissertation, we tried to address these problems by developing a new manure management strategy that treats the farm's waste in a hydrothermal process. This process produces a solid product called hydrochar and a liquid stream containing nutrients such as nitrogen, phosphorous, and some soluble organic. The stream then undergoes crystallization to separate the recovered nutrients as solid fertilizer. The brine out of the crystallization step is partly recycled and mostly put into a membrane distillation process to generate sanitary water to be used back on the farm. This research mainly focuses on hydrothermal carbonization, crystallization or separation of nutrients, and characterization of hydrothermal products. Hydrothermal carbonization (HTC), also known as "aqueous carbonization at elevated temperature and pressure," is a thermochemical process for treating wet organic compounds. It has a better carbon efficiency than other biomass conversion methods such as anaerobic digestion, Ficher-Tropch synthesis, fermentation, etc. Moreover, it allows pressing biomass without drying, which is a colossal advantage. In reality, HTC uses subcritical water or hot compressed water as the reaction media. The research as part of this dissertation can be classified into several subprojects. In the first project, the main goal was extracting nutrients from biomass. In this project, a series of experiments were conducted to evaluate the effects of reaction time (5, 30, and 120 min), temperature (170, 200, and 230 °C), and the addition of acids (citric acid and HCl) at several concentrations (0.1, 0.3, and 0.5 M) on the solubilization of phosphate and organic nitrogen to the aqueous phase. Statistical analysis of the experimental results revealed a significant effect of reaction temperature, acid addition, and concentration on phosphate extraction. Within the range of conditions studied low HTC temperature and adding either citric acid or HCl resulted in enhanced phosphate recovery in the aqueous phase. The maximum P solubilization (98% of the total P) in the aqueous phase occurred at 170 °C with the addition of citric acid. On the other hand, the results indicate only a minor effect of the experimental conditions concerning N solubilization. The nitrogen mass balance showed that roughly 60% of the overall N was extracted into the aqueous phase. The second project aimed at nutrient separation from the HTC process water with crystallization. The dissolution of nutrients (phosphorus and nitrogen) from cow manure by the HTC process into the aqueous phase was demonstrated. Three organic acids (formic acid, oxalic acid, and citric acid) and sulfuric acid were evaluated as additives in HTC. The results indicated that more than 90% of the phosphorous content of cow manure could be leached to the process water as PO4 at 170°C with all acids. Ammonia was extracted with relatively high efficiency in sulfuric and oxalic acids. Nutrients were recovered through reactive crystallization (precipitation) from process water by adjusting the molar concentration of the ionic species with pH = 9.5. Subsequently, nutrient-rich solids containing almost all (>95%) of the dissolved phosphorus in the sulfuric and formic acid-assisted runs were recovered and characterized for their elemental composition. Morphology and qualitative chemical analysis of the precipitates were determined. In the third project, hydrothermal carbonization (HTC) of cow and pig manure under sulfuric and acetic acid as catalysts was done. The main goal was to characterize the different products of the HTC process. HTC experiments were carried out at 170°C for 10 min, and the concentration of acids was 0.3M. Based on our observation, acid catalysts increased the carbonization, thus energy densification for both types of manure, with sulfuric acid having the most significant impact. Both sulfuric and acetic acids increased the leaching of the inorganic minerals such as Ca, K, Mg, and Fe, albeit to varying degrees. Phosphorus leaching was increased with acid catalysts as well. The results confirmed above 90% conversion of total phosphorous to phosphate in hydrothermal conditions. The phosphorus contents of pig manure and its HTC liquid product were an order of magnitude above those of cow manure. Acetic acid barely affected nitrogen extraction and even caused a reduction in pig manure. On the other hand, sulfuric acid increased nitrogen’s hydrothermal leaching for both types of manure and enhanced the relative ammonia fraction. Further analysis of the aqueous products signified the formation of acetic acid, furfural, and 3-aminopyrazine 1-oxide compounds for the sulfuric acid-catalyzed hydrothermal treatment of both types of manure. Analysis of the residual gas confirmed a trace amount of H2S, NO2, and SO2 formation. The addition of sulfuric acid increased NO2 significantly. Finally, detailed mass balances of the carbon and macronutrients (NPK) are presented. Finally, the project running for the longest time was dedicated to the construction, commissioning, and test work of a continuous flow HTC reactor. A comparison of the batch and continuous reactor performance was made as a part of this project. In addition, the hydrochar obtained by HTC of glucose from the batch and continuous flow reactor were analyzed for their similarities and differences. The modification of the continuous reactor to improve the mixing and heat transfer was discussed and explained.
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Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 United States