Citric Acid and EDTA as chelating agents in phytoremediation of heavy metal in polluted soil: a review

The application of metal chelating agents in phytoremediation has been shown to increase plant efficiency for heavy metal uptake in phytoextraction significantly. EDTA is a famous chelating agent used in phytoextraction. However, future use of EDTA is likely to be limited to ex-situ conditions where leachate control can be achieved, so there are limitations to its use that need to be studied. So that many phytoremediation studies have been carried out on organic chelating agents that are not expected to be harmful to the environment, one of which is Citric Acid. The purpose of this review is to compare commonly chelating agents, namely: EDTA as synthetic and Citric Acid as a natural matter for phytoremediation in polluted soils. This review also discusses the ability of Citric Acid and EDTA on phytoremediation, their effect on soil physiology and soil microbiology, advantages and disadvantages of each on the prospects of phytoremediation. EDTA can increase phytoextraction better than Citric Acid but can increase the risk of groundwater pollution because EDTA is difficult to degrade by the environment. In contrast, Citric Acid has been shown to increase phytoextraction, phytostabilization and harmless to the environment.

Comparative exergy and energy assessment of a biogas plant with biological purification process: A multigeneration system

The improved systems of biogas production usually increase the energy consumption of biogas plants. Therefore, it is very important to determine an appropriate improvement system to increase plant efficiency. For this purpose, a biogas plant with a biological self-purification system was energetically and exergetically analyzed, and its performance was compared with that of a base plant. To keep the temperature of digesters up to 310.2 K, a solar water heater was used. It was able to maintain a high level of efficiency for both plants. The energy analysis of the plants indicated that the overall energetic efficiency of both plants was very close. The exergy analysis of the plants showed that the overall exergetic efficiency of the self-purification biogas plant (76.24%) was higher than that of the base plant (66.78%). This is due to the fact that the total exergy destruction rate of the self-purification plant was lower than that of the base plant and the exergy rate of biogas output of the self-purification plant was higher than that of the base plant. The exergy analyses of both plant components showed that although the highest exergy destruction rates were attributed to the principle digester and separation unit, they showed the highest exergetic improvement potential rates. These results confirm that the digesters in biogas plants have a great potential to be improved exergetically, and the self-purification system is a suitable improvement system to increase the plant efficiency exergetically.

Optimized Performance and Cost Potential for Indirect Supercritical CO2 Coal Fired Power Plants

Indirect-fired supercritical CO2 (sCO2) power cycles are being explored as an attractive alternative to steam Rankine cycles for a variety of heat sources including fossil, concentrated solar power (CSP), nuclear, waste heat etc. Therefore, understanding their performance and cost potential is important for commercialization of the technology. This study presents the techno-economic global optimization results of coal-fired utility scale power plants based on indirect sCO2 power cycles with and without carbon capture and storage (CCS). Four power cycle configurations are considered for optimization – recompression cycle (RC) with and without turbine reheat and partial cooling cycle (PCC) with and without turbine reheat. Several design variables are identified for each power cycle configuration and these design variables are optimized to minimize the levelized cost of electricity (LCOE) for each plant. The optimization design variables included parameters such as turbine inlet temperatures and pressure, sCO2 cooler outlet temperatures, recuperator approach temperatures and pressure drops etc. The optimization is conducted using automated derivative free optimization algorithms available under NETL’s Framework for Optimization and Quantification of Uncertainty and Sensitivity (FOQUS) platform. For sCO2 power plants both with and without CCS, recompression cycle with reheat (RC with reheat) has the highest plant efficiency and lowest LCOE among the considered power cycle configurations. For plants with CCS, the RC with reheat configuration offered 8 percentage points higher plant efficiency (HHV basis) and 14.6% lower LCOE compared to a state-of-the-art (SOA) PC-fired supercritical steam Rankine plant with CCS. For plants without CCS, the RC with reheat configuration offered 4.7 percentage points higher plant efficiency and 7% lower LCOE compared to a SOA PC-fired supercritical steam Rankine plant without CCS.

Underground pumped storage hydropower (UPSH) and its interaction with the saturated subsurface medium: effects of the water exchanges on the environment and the plant efficiency

<p>Underground pumped storage hydropower (UPSH) is an alternative energy storage system (ESS) for flat regions, where conventional pumped storage hydropower plants cannot be constructed due to topographical limitations. UPSH plants consist in two reservoirs, the upper one is located at the surface or possibly underground (but at shallow depth) while the lower one is underground. Although the underground reservoir can be drilled, the use of abandoned mines (deep or open pit mines) as underground reservoir is a more efficient alternative that is also beneficial for local communities after the cessation of mining activities. Given that mines are rarely waterproofed, water exchanges between UPSH plants and the underground medium are expected. Water exchanges may have negative consequences for the environment, but also for the feasibility of UPSH plants. The impacts on the environment and the plant efficiency may have hydraulic (changes of the natural piezometric head distribution, effects in the hydraulic head difference between the two reservoirs, etc.) or hydrochemical nature (dissolution and/or precipitation of minerals in the aquifer and in the reservoirs, corrosion of facilities, modification of pH, etc.). At this stage, it is required a sound understanding of all the impacts produced by the water exchanges and evaluate under which circumstances they are mitigated. This assessment will allow ascertaining criteria for the selection of the best places to construct future UPSH plants.</p>

Techno-Economic Analyses of the CaO/CaCO3 Post-Combustion CO2 Capture From NGCC Power Plants

Calcium looping is a post-combustion technology that enables CO2 capture from the flue gases of industrial processes. While considerable studies have been performed at various levels from fundamental reaction kinetics to the overall plant efficiency, research work on techno-economic analyses of the calcium looping processes is quite limited, particularly for the Natural Gas Combined Cycle (NGCC). Earlier work has shown that theoretically, a high thermal efficiency can be obtained when integrating calcium looping in the NGCC using advanced process configurations and a synthetic CaO sorbent. This paper presents an investigation of calcium looping capture for the NGCC through a techno-economic study. One simple and one advanced calcium looping processes for CO2 capture from NGCC are evaluated. Detailed sizing of non-conventional equipment such as the carbonator/calciner and the solid-solid heat exchanger are performed for cost analyses. The study shows that the CO2 avoided cost is 86–95 €/tCO2, avoided, which is considerably more expensive than the reference amine (MEA) capture system (49 €/tCO2, avoided). The calcium looping processes considered have thus been found not to be competitive with the reference MEA process for CO2 capture from NGCC with the inputs assumed in this work. Significant improvements would be required, for example, in terms of equipment capital cost, plant efficiency and sorbent annual cost in order to be make the calcium looping technology more attractive for capturing CO2 from NGCC plants.