<p>Air conditioning, space heating, and refrigeration account for approximately 40% of the electricity usage in the U.S. residential and commercial building sector. To improve energy utilization and reduce energy consumption in space conditioning applications, advanced heat pumping technologies are needed. The chemical looping heat pump (CLHP) is a promising thermodynamic cycle that has shown the potential to achieve a cooling coefficient of performance (COP_c) increase of over 20% relative to conventional vapor compression (VC) systems.</p> <p><br></p> <p>The overarching goal of this study is to evaluate the chemical looping heat pump concept for residential applications, including thermodynamic potential, as well as technical and economic feasibility before developing and deploying a pilot scale system. The evaluation process includes advanced thermodynamic modeling for better assessments of working fluids and systems, techno-economic analysis for initial cost assessment of the scaled-up system, and small-scale experiments for proof-of-concept.</p> <p><br></p> <p>A working fluid screening process was developed to identify suitable working substance pairs for CLHP systems. The key metrics for evaluating the working fluids are associated with the possibility of phase change after a chemical reaction, reversible cell potential and power consumption, and cooling capacity of the system. Such metrics were applied to several fluids to assess their suitability. It was found that isopropanol/acetone working substances showed the highest cooling capability for a given power consumption. Even though this approach was applied to particular organic fluids (e.g., alcohols and ketones), this analysis can be generalized to other single-component fluids, multi-component fluids, and several chemical designs.</p> <p><br></p> <p>A modeling framework to estimate operating cost, capital cost, and levelized cost of energy was developed to enable a direct early-stage comparison of a CLHP with conventional VC systems. The models were helpful in understanding the influence of key factors such as efficiency, unit utilization (annual cooling and heating delivered, kWh_t/yr), and price of electricity ($/kWh_e) with the goal of determining target markets for initial CLHP products. The LCOE of CLHP could be less than that of VC in the case of high utilization (≥  20,000 kWh_t) with high performance improvements (COP_CLHP/COP_VC = 1.3) even though the capital cost of the CLHP is nearly 1.5-2 times higher than VC.</p> <p><br></p> <p>The key process of a CLHP cycle, which is electrochemically driven phase transformation, was experimentally demonstrated based on the advanced test rig and electrochemical cell. A polymer electrolyte membrane flow cell with a self-fabricated membrane electrode assembly and flow channels was employed to drive the reaction. The breakdown voltage analysis indicates that ohmic and mass transfer overpotentials account for more than 90% irreversibilities of the reactions. In addition, the results showed the possibility of phase transition of 20-30% at current density of ~0.003 A/cm² and the cell voltage of 0.025 V. The extent of a chemical reaction can be further improved by increasing the current and reducing the flow rate.</p> <p><br></p> <p>A semi-empirical cycle model was leveraged to predict realistic system performance. The model includes an electrochemical cell model with other component models in a CLHP cycle. The Second law efficiency was 50% of the Carnot limit with a cooling capacity of 2.24 mW (cooling density of 1.6 W/m²) at sink temperature of 40 °C  and source temperature of 23 °C. The cause for the precipitous drop in COP_c with increasing current density was overpotential, which requires further research on the optimization of membrane and catalytic materials as well as a geometry of flow channels to minimize the losses. Higher efficiency can theoretically be achieved at an elevated fluid temperature as long as an electrochemical cell can achieve a greater degree of conversion.</p> <p><br></p> <p>There are several challenges that should be reconciled in a future operational device and cycle at scale. Additional research on both material- and system-level performance is indispensable to meet practical size requirements. Nevertheless, this study is intriguing in terms of the possibility of developing a high efficiency device with the ability to use more environmentally friendly working fluids. Broadly, this CLHP research can contribute to accelerating the development of the newly emerging field, which is thermal systems coupled with electrochemical processes, that can maximize system efficiency using low-GWP fluids.</p>

Fish farming is an important process of food production that seeks to meet the population growth, however is a source of pollution generating large volumes of contaminated water, causing environmental pollution. In order to minimize this impact, this study aimed to evaluate the efficiency of two advanced oxidative techniques to treat real effluent from fish farming, the Fenton reaction and electrochemistry. Treatments were carry out on a pilot scale (60L) and laboratory scale (250 mL). The efficiency of the reactions was assessed by the reduction of turbidity and COD of the effluent, as well as the toxicity of the effluent after treatment in germination lettuce (Lactura sativa) and mortality and sensory performance of the Nile tilapia (Oreochromis niloticus). For the Fenton reaction, it assessed the influence of the concentration of Fenton reagent (Fe2+ and H2O2), and the electrochemical process evaluated the applied current density and the supporting electrolyte (Na2SO4, H2SO4 and NaCl). According to the results of the physicochemical analyzes, both technologies were also effective in the treatment of this effluent, with reductions of 99% and 95% of the turbidity and COD respectively, for the Fenton reaction followed by flocculation; and 95% to 89% in turbidity and COD respectively, for the electrochemical process. In the electrochemical process the efficiency was associated with direct and indirect oxidation of pollutants and flotation of the particulate material through electrogenerated gas. In toxicological test of Fenton reagent with lettuce seeds, the Fe2+ concentrations showed no toxicity, since the H2O2 concentrations indicated high toxicity. Tests with Nile tilapia corroborate the results of lettuce seeds. After the treatment with Fenton's reaction effluent treated with 10 mmol of H2O2 L-1 and 0.5 mmol Fe2+ had the same germination and root growth rates of the raw wastewater, as in the tests with Nile tilapia effluent showed considerable toxicity, possibly due to residual peroxide. In the electrochemical process the best results were obtained when employed the H2SO4 as supporting electrolyte and the lowest current density (10 mA cm-2). The toxicology tests with lettuce and Nile tilapia indicated that the treated effluent has low toxicity with germination rate and lettuce radicle growth equal to control, and Nile tilapia the mortality rate was zero, even after 96 hours of fish contact with the treated effluent. The techniques applied in this study showed high efficiency in the treatment of real effluent from fish farming, making it adequate for disposal or reutilization. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A piscicultura é um importante processo de produção de alimentos que busca atender o crescimento populacional, porém pode ser uma fonte poluidora, gerando grandes volumes de água contaminada, causando poluição ambiental. Visando minimizar esse impacto, esse trabalho teve como objetivo avaliar a eficiência de dois processos oxidativas avançadas no tratamento de efluente real gerado pela piscicultura, a reação de Fenton e a eletroquímica. Os tratamentos foram realizados em escalas, piloto (60 L) e de bancada (250 mL). A eficiência das reações foi avaliada pela redução da turbidez e DQO (Demanda Química de Oxigênio) do efluente, bem como a toxicidade do efluente após o tratamento frente à germinação da alface (Lactura sativa) e mortandade e comportamento sensorial da tilápia do Nilo (Oreochromis niloticus). Para a reação de Fenton, avaliou-se a influência da concentração dos seus reagentes (Fe2+ e H2O2), e para o processo eletroquímico avaliou-se a densidade de corrente aplicada e o eletrólito suporte (Na2SO4, H2SO4 e NaCl). De acordo com os resultados das análises físico-químicas, os dois processos apresentaram alta eficiência no tratamento deste efluente, com reduções de 99% (turbidez) e 95% (DQO), para a reação de Fenton seguida de floculação, e para o processo eletroquímico as reduções foram de 95% (turbidez) e 89% (DQO). No processo eletroquímico a eficiência foi associada à oxidação direta e indireta dos poluentes e flotação do material particulado através dos gases eletrogerados. Nos ensaios toxicológicos dos reagentes de Fenton com sementes da alface, as concentrações de Fe+2 não apresentaram toxicidade, já as concentrações de H2O2 indicaram elevado grau toxicológico. Os ensaios com tilápia do Nilo corroboraram com os resultados das sementes da alface. Após o tratamento com reação de Fenton o efluente tratado com 10 mmol L-1 de H2O2 e 0,5 mmol de Fe2+ apresentou os mesmos índices de germinação e crescimento da radícula do efluente bruto, já nos testes com tilápia do Nilo o efluente apresentou considerável toxicidade, possivelmente devido a peróxido residual. No processo eletroquímico os melhores resultados foram obtidos quando empregado H2SO4 como eletrólito suporte e a menor densidade de corrente (10 mA cm-2). Os testes toxicológicos com alface e tilápia do Nilo indicaram que o efluente tratado apresenta baixa toxicidade com índice de germinação e de crescimento da radícula da alface igual a do controle, e com tilápia do Nilo o índice de mortandade foi nulo, mesmo após 96h de contato dos peixes com o efluente tratado. As técnicas aplicadas neste estudo apresentaram alta eficácia no tratamento do efluente real da piscicultura, tornando-o adequado para descarte ou mesmo reutilizado em sistema de ciclo fechado.

Metals occur naturally and are commonly found as contaminants in areas where industrial and municipal effluents are discharged. Aquatic sediments/environments are often polluted by heavy metals due to the temporal variations in anthropogenic input of contaminants via atmospheric deposition, catchment runoff, effluent inflow and dumping from industrial transportation, mining, agricultural and waste disposal sources [EPA, 1989]. The transfer of contaminants associated with settling inorganic particulates and/or biotic detritus from the water column to the sediments, no disturbance of sediments by physical mixing, slumping or bioturbation after deposition, no post-depositional degradation or mobility of the contaminants and the establishment of a reliable time axis. Therefore, metal contamination in aquatic environment is one of the problems. Rivers, coastal waters, sediments, soils, etc. were mostly contaminated by industrial and mining activities. Recently, the metal discharged from the industries have been controlled in the most developed countries. Even so, till the heavy metals dispersed in river sediments still need to be dealt with. Mainly, characterization, transformation, transport and fate of metal contaminants in the sediment to the aquatic environment need to be studied, because the sediment has great capacity to accumulate the contaminants. Exploitation and utilization of mines discharges heavy metals into the environment and contaminates neighboring aquatic ecosystem...

Metals occur naturally and are commonly found as contaminants in areas where industrial and municipal effluents are discharged. Aquatic sediments/environments are often polluted by heavy metals due to the temporal variations in anthropogenic input of contaminants via atmospheric deposition, catchment runoff, effluent inflow and dumping from industrial transportation, mining, agricultural and waste disposal sources [EPA, 1989]. The transfer of contaminants associated with settling inorganic particulates and/or biotic detritus from the water column to the sediments, no disturbance of sediments by physical mixing, slumping or bioturbation after deposition, no post-depositional degradation or mobility of the contaminants and the establishment of a reliable time axis. Therefore, metal contamination in aquatic environment is one of the problems. Rivers, coastal waters, sediments, soils, etc. were mostly contaminated by industrial and mining activities. Recently, the metal discharged from the industries have been controlled in the most developed countries. Even so, till the heavy metals dispersed in river sediments still need to be dealt with. Mainly, characterization, transformation, transport and fate of metal contaminants in the sediment to the aquatic environment need to be studied, because the sediment has great capacity to accumulate the contaminants. Exploitation and utilization of mines discharges heavy metals into the environment and contaminates neighboring aquatic ecosystem...