7 research outputs found
A Mixture of Green Waste Compost and Biomass Combustion Ash for Recycled Nutrient Delivery to Soil
The use of major nutrient-containing solid residuals, such as recycled solid waste materials, has a strong potential in closing the broken nutrient cycles. In this work, biofuel ash (BA) combined with green waste compost (GWC) was used as a nutrient source to improve soil properties and enhance wheat and triticale yields. The main goal was to obtain the nutrient and heavy metal release dynamics and ascertain whether GWC together with BA can potentially be used for concurrent bioremediation to mitigate any negative solid waste effects on the environment. Both BA and GWC were applied in the first year of study. No fertilization was performed in the second year of the study. The results obtained in this work showed the highest spring wheat yield when the GWC (20 t ha−1) and BA (4.5 t ha−1) mixture was used. After the first harvest, the increase in the mobile forms of all measured nutrients was detected in the soil with complex composted materials (GWC + BA). The content of heavy metals (Cd, Zn, and Cr) in the soil increased significantly with BA and all GWC + BA mixtures. In both experiment years, the application of BA together with GWC resulted in fewer heavy metals transferred to the crops than with BA alone
Transformation of Liquid Digestate from the Solid-Separated Biogas Digestion Reactor Effluent into a Solid NH\u3csub\u3e4\u3c/sub\u3eHCO\u3csub\u3e3\u3c/sub\u3eFertilizer: Sustainable Process Engineering and Life Cycle Assessment
The growing interest in biogas production to obtain renewable electricity has led to the increasing availability of liquid digestate byproducts containing major nutrients, such as nitrogen, and the need for sustainable engineering developments toward its utilization. Currently, digestate return to the fields has been most popular but suffers from many problems, such as potent greenhouse gas emissions, including N2O, during storage, transport, and application. This work describes a newly designed process for the production of solid nitrogen fertilizers from liquid biogas production waste that circumvents many of the problems associated with handling and applying liquid digestate. In particular, solid ammonium bicarbonate (NH4HCO3) is engineered using solid separated biogas digestion reactor effluent to yield sustainable nitrogenous fertilizers. NH4HCO3 is considered a marketable fertilizer with a N content of 18% that represents an added value to the biogas producing facilities. The process design was performed to obtain an optimized recovery with virtually no nitrogen losses. The process developed relies on digestate distillation at 3.3 bar with the condenser operating at 49 °C and using cooling water. Solid crystals are obtained in a crystallizer at 12 °C and recovered via drying. For comparison, an open-loop air stripping process was developed to obtain ammonium sulfate ((NH4)2SO4) solid fertilizer. The resulting economics of both processes show that the capital cost associated with the NH4HCO3 process is much lower together with the consumption of the utilities. A life cycle assessment approach was used to evaluate the environmental impacts of the new NH4HCO3 process using distillation and the (NH4)2SO4 process using air stripping technology, compared to the base case with liquid digestate applied directly onto the fields. The two primary impact categories of concern in this technical area are global warming potential (GWP) and eutrophication potential (EP). In particular, NH4HCO3 and (NH4)2SO4 processes have ∼25% lower GWP impact because of the reduced land application which is negated because of the utility use. EP was reduced by ∼50 and 20%. Notable was the negative and sizeable effect of both scenarios on ecotoxicity which stemmed from the need to use defoaming agents to address any potential transport problems across the vapor/liquid boundary
Solar Steam Generation Integration into the Ammonium Bicarbonate Recovery from Liquid Biomass Digestate: Process Modeling and Life Cycle Assessment
Current management strategies for utilizing increasing amounts of liquid digestate, the main byproduct of anaerobic agricultural and municipal solid waste digestion, pose significant environmental risks if utilized directly for agricultural purposes as a nutrient-containing soil improver. Instead, efficient removal and precipitation of nitrogen present in the digestate have been recently proposed in the form of ammonium bicarbonate, NH4HCO3, and a new process was designed to produce solid NH4HCO3 fertilizer material from the liquid digestate using distillation. Environmental impacts of this new process can be advantageous over the direct disposal of digestate to the soil. To further understand and improve the underlying economic and environmental implications of this technology, several new scenarios are proposed and evaluated in this work, which examines the influence of key process variables, including (a) process improvement to obtain a portion of the heat necessary for the distillation process using solar concentrators and (b) fate of the post-processed liquid digestate stream, including disposal into the wastewater treatment plant, release into the water body, or direct land application. An optimized solid NH4HCO3 synthesis scenario was designed using a distillation column with 95% nitrogen recovery. Solar steam generation was incorporated to reduce fossil fuel-generated steam consumption in the distillation column reboiler. This resulted in the distillation column operating at 1.5 bar and a low reflux ratio. This allowed column bottoms to operate at 118 °C for 5 h per day utilizing only solar steam. A detailed economic analysis of the overall process was performed and showed that 0.10/lb in the most realistic base case scenario. The life cycle assessment (LCA) modeling results obtained suggest that the integration of solar heating can provide important benefits in regard to the overall environmental impacts, but for many environmental impact metrics, including greenhouse gas (GHG) emissions and eutrophication potential, the choices of where to dispose of the post-processed digestate stream and the resulting assumptions about N and C mobilization at that stage can exert a larger influence on the overall environmental impact. Further experimental work is needed to provide certainty to the factors that are used to estimate nitrogen and carbon fate within LCA modeling frameworks
Comprehensive process and environmental impact analysis of integrated DBD plasma steam methane reforming
Utilization of electricity generated from renewable sources to obtain hydrogen, H2, is of critical importance to decrease the overall carbon footprint. In this work, integration of a dielectric discharge barrier (DBD) plasma reactor to convert low calorific value gas, such as landfill gas or coal mine gas into hydrogen, into the existing steam methane reforming (SMR) technology was evaluated using process design considerations. In particular, a DBD-enhanced catalytic SMR reactor was modeled to operate at near atmospheric pressure and 500 °C sequentially with the conventional reformer to obtain ~ 65 kmol/hr H2 for distributed production. This allowed decreasing the size of the conventional reformer albeit at the increased overall electricity consumption. Calculated process economics showed that only at an electricity cost of less than $0.004/kWh does the hybrid DBD plasma process derived H2 price become competitive with that of the conventional SMR. A Life Cycle Assessment framework was used to compare environmental impacts from the conventional SMR, hybrid DBD SMR and hybrid DBD SMR utilizing only onshore wind-derived electricity. Larger environmental impacts in the plasma reformer were obtained due to the use of electricity for the plasma reforming operation, which was modeled as coming from the typical U.S. grid mix. Utilizing only 100% wind-derived electricity provided certain environmental benefits, except for the ecotoxicity impact where the wind power scenario modeled here only reduced ecotoxicity impacts associated with electricity by 30%
Recovering, Stabilizing, and Reusing Nitrogen and Carbon from Nutrient-Containing Liquid Waste as Ammonium Carbonate Fertilizer
Ammonium carbonates are a group of fertilizer materials that include ammonium bicarbonate, ammonium carbonate hydrate, and ammonium carbamate. They can be synthesized from diverse nutrient-bearing liquid waste streams but are unstable in a moist environment. While extensively utilized several decades ago, their use gradually decreased in favor of large-scale, facility-synthesized urea fertilizers. The emergence of sustainable agriculture, however, necessitates the recovery and reuse of nutrients using conventional feedstocks, such as natural gas and air-derived nitrogen, and nutrient-containing biogenic waste streams. To this extent, anaerobic digestion liquid presents a convenient source of solid nitrogen and carbon to produce solid fertilizers, since no significant chemical transformations are needed as nitrogen is already present as an ammonium ion. This review describes detailed examples of such feedstocks and the methods required to concentrate and crystallize solid ammonium carbonates. The technologies currently proposed or utilized to stabilize ammonium carbonate materials in the environment are described in detail. Finally, the agricultural efficiency of these materials as nitrogen and carbon source is also described
Scale-Up of Agrochemical Urea-Gypsum Cocrystal Synthesis Using Thermally Controlled Mechanochemistry
Atom- and energy-efficient synthesis of a crystalline calcium urea sulfate ([Ca(urea)4]SO4) cocrystal was explored using thermally controlled mechanochemical methods with calcium sulfate compounds containing various amounts of crystalline water (CaSO·xHO, x = 0, 0.5, 2). Small-scale (200 mg) experiments in a shaker mill were first performed, and the progress was monitored by in situ Raman spectroscopy and in situ synchrotron powder X-ray diffraction. Time-resolved spectroscopy data revealed that the presence of water in the reagents’ crystalline structure was essential to the reaction and largely determined the observed reactivity of different calcium sulfate forms. Reactions at elevated temperatures were shown to proceed significantly faster on all synthetic scales, while changes in rheology caused by adding external water hindered the reaction progress. The average yield of a 21 mm horizontal twin-screw extruder experiment was ∼5.5 g/min of extrusion (∼330 g/h). Energy consumption during the milling reactions required to achieve complete conversion ranged from 7.6 W h/g at 70 °C for a mixer mill to 3.0 W h/g at a 50 g scale and 4.0 W h/g at a 100 g scale for a planetary mill or 4.0 W h/g at both 70 °C and RT for a twin-screw extruder, showing a significant improvement in energy efficiency at large-scale production. The obtained crystalline cocrystal exhibited a significantly lower solubility in aqueous solutions, nearly 20 times lower per molar basis compared to that of urea. Furthermore, reactive nitrogen emissions in air at 90% relative humidity, measured as NH3, showed slow and nearly linear nitrogen loss for the cocrystal over 90 days, while the same level of emissions was achieved with urea after 1–2 weeks, showing the potential of this cocrystal material as a large-scale nitrogen-efficient fertilizer