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AbstractThe integration of power plants and desalination systems has attracted increasing attention over the past few years as an effective solution to tackle sustainable development and climate change issues. In this light, this paper introduces a novel modelling and optimization approach for a combined-cycle power plant (CCPP) integrated with reverse osmosis (RO) and multi-effect distillation (MED) desalination systems. The integrated CCPP and RO–MED desalination system is thermodynamically modelled utilizing MATLAB and EES software environments, and the results are validated via Thermoflex software simulations. Comprehensive energy, exergic, exergoeconomic, and exergoenvironmental (4E) analyses are performed to assess the performance of the integrated system. Furthermore, a new multi-objective water cycle algorithm (MOWCA) is implemented to optimize the main performance parameters of the integrated system. Finally, a real-world case study is performed based on Iran's Shahid Salimi Neka power plant. The results reveal that the system exergy efficiency is increased from 8.4 to 51.1% through the proposed MOWCA approach, and the energy and freshwater costs are reduced by 8.4% and 29.4%, respectively. The latter results correspond to an environmental impact reduction of 14.2% and 33.5%. Hence, the objective functions are improved from all exergic, exergoeconomic, and exergoenvironmental perspectives, proving the approach to be a valuable tool towards implementing more sustainable combined power plants and desalination systems.

Wastewater containing ammonia nitrogen compounds is considered as a harmful material to environment due to eutrophication and toxicity effects; hence, finding practical methods for treating this type of wastewater seems necessary. In this study, performance of two sequencing batch reactors have been assessed for simultaneous nitrification and denitrification in treating synthesized wastewater containing ammonium nitrogen, using leachate obtained from cow dung as the biomass. The leachate obtained from cow dung as the source of bio‐sludge added to the reactors. Experiments were designed according to central composition design and response surface methodology with four operating variables including pH (6, 7.5, 9), cycle time (CT) (4, 12, 20 h), ratio (5, 10, 15) and carbon source (Sodium acetate: , Glucose: ). According to statistical analysis, experimental responses were in acceptable agreement with model predictions. CT was the most important operating variable in chemical oxygen demand (COD) and removal. The maximum percentage of ammonium nitrogen removal was attained at pH 7.5 and CT 21.5 h. The optimum conditions were composed of pH 7.67, CT 19.15 h, 10.95 and sodium acetate as carbon source, while COD, and total nitrogen removals were 94.96%, 94.93% and 93.60%, respectively. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1638–1646, 2018

Ammonia production through more efficient technologies can be achieved using exergy analysis. Ammonia production is one of the most important but also one of most energy consuming processes in the chemical industry. Based on a panel of solutions previously developed, this study helps to identify potential areas of improvement using an exergy analysis that covers all aspects of conventional ammonia synthesis and separation. The total internal and external exergy losses are calculated as 3,152 and 6,364 kJ/kg, respectively. The process is then divided into five main functional blocks based on their exergy losses. The reforming block contains the largest exergy loss (3,098 kJ/kg) and thus the largest potential for improvement including preheating cold feed through an economizer, developing technology towards isobaric mixing, and pressure drop reduction in the secondary reformer as the main contributors to the irreversibility (1,302 kJ/kg) in this block. The second largest exergy loss resides in the ammonia synthesis block (3,075 kJ/kg) where solutions such as reduced temperature rise across the compressor, proper compressor isolation, reducing undesired components such as argon in the reactor feed, and using lower temperatures for reactor outlet streams, are proposed to decrease the exergy losses. Throttling process in the syngas separator is the key contributing mechanism for the irreversibility (1,635 kJ/kg exergy losses) in the gas upgrading block. The exergy losses in the residual ammonia removal block (833 kJ/kg exergy losses) are mainly due to the stripper and the absorber column where a modified column design might be helpful. The highest exergy loss in the preheating block belongs to the compressors (518 kJ/kg exergy losses) where a lower inlet temperature and better system isolation could help to reduce losses.

Abstract This study presents and evaluates the feasibility of a novel hybridization of modified Kalina cycle, reverse osmosis desalination, and low-temperature water electrolysis utilizing geothermal energy to yield power, distilled water, and hydrogen, respectively. The scientific impact of the current work has been improved considering the features of Sabalan flash-binary geothermal wells in Iran as a real model through a case study. In addition to designing a novel setup, the smart use of multi-heat recovery technique, modifying the base cycle, and utilizing a part of generated distilled water to produce hydrogen by the electrolyzer are the other structural originalities, distinguishing the current work from the previous studies. The suggested system is scrutinized via a parametric study and optimized based on a genetic algorithm. The parametric study demonstrated that the highest sensitivity of varying the performance criteria of the whole system is attributed to the change in flash tank pressure. Moreover, the multi-objective optimization led to achieving the exergy efficiency and trigeneration gain output ratio as 51.3% and 1.7 for the system, respectively. Furthermore, the system was able to produce 4795 kW of power, 5.3 kg/h of hydrogen, and 19.9 kg/s of distilled water.

Use of a pilot-scale fixed-film bioreactor was investigated for remediation of bromate contamination within groundwater. Bromate reduction with stoichiometric production of bromide was observed, providing supporting evidence for complete reduction of bromate with no production of stable intermediates. Reduction of 87-90% bromate from an influent concentration of 1.1 mg L(-1) was observed with retention times of 40-80 h. Lower retention times led to decreases in bromate reduction capability, with 11.5% removal at a 10 h retention time. Nitrate reduction of 76-99% from a 30.7 mg L(-1) as NO(3)(-) influent was observed at retention times of 10-80 h, although an increase in nitrite production to 2.7 mg L(-1) occurred with a 10 h retention time. Backwashing was not required, with the large plastic packing media able to accommodate biomass accumulation without decreases in operational efficiency. This study has provided proof of concept and demonstrated the potential of biological bromate reduction by fixed-film processes for remediation of a bromate contaminated groundwater source.

The phosphate (P) fertilizer industry generates a highly hazardous and acidic wastewater. The present study reports the evaluation of an integrated precipitation and Enhanced Biological Phosphorus Removal (EBPR) process for the treatment of fertilizer plant wastewater and effluent detoxification, assessed by microtoxicity and seed germination tests. Effluent samples were collected from a local P fertilizer industry and were characterized by their high fluoride and P content. First, the samples were pre‐treated by precipitation of P and fluoride ions using hydrated lime. The resulting low‐fluoride and phosphorus effluent was then treated with the EBPR process to monitor the simultaneous removal of carbon, nitrogen, and phosphorus. Phosphorus removal included a two‐stage anaerobic/aerobic system operating under continuous flow. Pre‐treated wastewater was added to the activated sludge and operated for 160 days in the reactor. The operating strategy included increasing the organic loading rate from 0.3 to 1.2 g chemical oxygen demand (COD)/L day. The stable and high removal rates of COD, NH4+‐N, and PO43−‐P were then recorded. The mean concentrations of the influent were approximately 3600 mg COD/L, 60 mg N/L and 14 mg P/L, which corresponded to removal efficiencies of approximately 98%, 86%, and 92%, respectively. The microtoxicity of the treated wastewater was then monitored by LUMIStox and its phytotoxicity was investigated on cress, tomato, wheat, maize, ryegrass, and alfalfa seed germination. LUMIStox tests showed that treatment allowed a significant toxicity removal. Moreover, the untreated wastewater inhibited the species germination even when diluted 10 times, whereas a positive effect of treated wastewater was noticed. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 463–471, 2014

Mercury (Hg) represents a growing environmental and health major concern. It originates from natural sources and mainly from anthropogenic processes and it is widely distributed in the natural media. According to the last Global Mercury Assessment (2013), annual global emissions from both sources were estimated to be from 5,000 to 8,000 metric tons per year. Among the different mercury species released to the environment, methylmercury (MeHg) is considered as the most toxic form due to its ability to bioaccumulate, being then threatening even at very low concentrations.Its presence depends onHg(II) bioavailability and global amount.This explains the urgent need to ensure a continuous Hg(II) monitoring. Many efforts have been made in order to develop reliable systems able to deliver quick data and to comply with low detection limits, in accordance with the threshold value delivered by the World Health Organization (1µg L-1/ 5 nM). Spectroscopic techniques such as CV-AFS and CV-AAS are routinely used for Hg(II) determination. Although these methods can afford good sensitivity and low concentrations determination, they require sample preparation step, complex procedures and expensive material, which limits their use for on-site measurements. In this context, electrochemical sensors present excellent candidates for in situ Hg(II) trace analysis, taking in account their numerous advantages compared to spectroscopic techniques: easier handling, simple procedure, low energy consuming, low cost material and portability. In this work, we will propose a new electrochemical approach aiming to conceive and optimize an electrochemical Hg(II) sensor. The method consists in the functionalization of a glassy carbon electrode (GC) with gold nanoparticles (AuNPs) and Diazonium Salts. The main idea is to combine the interesting properties of both AuNPs and Diazonium salts. AuNPs were chosen for their electrocatalytic effect, large surface area, mass transport enhancement and for the strong affinity to mercury which will improve the sensor sensitivity. On the other hand, diazonium salts are used to improve the sensor stability by anchoring the AuNPs to the GC surface. First, nanometricorganic layer were grafted of the polished GC surface, by electrochemical reduction of 1.5 mM4-thiophenol diazonium (SH) using Constant Potential Electrolysis (CPE) in 0.1 M HCl solution at -0.55 V for 300 seconds. Electrochemical characterization performed by Cyclic Voltammetry (CV) and redox probes (ferricyanide and hexaamineruthenium(III)) revealed a total suppression of the signal, confirming the formation of a continuous blocking layer. This was confirmed by Atomic Force Microscopy (AFM)used to estimate the layer thickness, which was found to be 4 nm. Second, AuNPs were electrodeposited, for the first time, onto the diazonium multilayer by CPE in NaNO3 solution containing 0.25 mM HAuCl4for 300 seconds. Once more, redox probes were used to characterize the resulting interface and a total signal restauration and enhancement was observed after AuNPs electrodeposition, which highlights the effective AuNPs onto the organic layers. Field emission gun scanning microscopy (FEG-SEM) was used to provided further evidence and to quantify particle size and density of the AuNPs deposits. Both size and density are dependent on the CPE duration. Small homogeneous AuNPs with 27±3 nm average diameter and 158 NPs/µm2density were observed when the CPE was carried out during 300 seconds, while larger particles with 63±6 nm average diameter and lower density (63 NPs/µm2) were obtained when a longer CPE duration (600 seconds) is used. Finally, AuNPs were activated by cyclic voltammetry in H2SO4 prior to Hg(II) detection in order to homogenize the surface and to rearrange the crystallographic plans of the AuNPs. Herein, the well-known gold oxides reduction peak was observed and used to calculate the electroactive surface area (ESA) of the functionlized electrode. The electrochemical response of the final generated GC/SH/AuNPs interface towards Hg(II) was recorded by Square Wave Anodic Stripping Voltammetry (SWASV) in 0.01 M HCl solution containing different amounts of Hg(II). The SWASV procedure consists on the Hg(II) preconcentration at the electrode surface followed by the preconcentrated Hg(0) reoxidation in Hg(II). Under optimized conditions, and for a preconcentration time of 300 seconds, a well-defined peak, corresponding to Hg(0) reoxidation, was observed around 0.5 V/ECS. The sensor showed a linearity range from 1 up to 10 nM and allowed to reach picomolar level. The stability in HCl, phosphate buffer and air was also studied over several weeks: Once a week, the activation procedure was performed and followed by Hg(II) determination in order to evaluate the analytical performances of the sensor over time. Finally, Hg(II) detection assays were conducted in natural water samples collected from different sampling points. Figure 1

<p>High temperature aquifer thermal energy storage (HT-ATES) can play a key role for a sustainable interplay between different energy sources and in the overall reduction of CO<sub>2</sub>emission. In this study, we numerically investigate the thermo-hydraulic processes of an HT-ATES in the Greater Geneva Basin (Switzerland). The main objective is to investigate how to handle the yearly excess of heat produced by a nearby waste-to-energy plant. We consider potential aquifers located in different stratigraphic units and design the model from available geological and geophysical data. Aquifer properties, flow conditions and well strategies are successively tested to evaluate their influence on the HT-ATES economic performance and environmental impact. This was achieved using a new open-access, user-friendly and efficient code that we also introduce here as a possible tool for geothermal applications.</p><p> </p><p>The results highlight the importance of thorough numerical simulations based on more realistic exploitation when designing HT-ATES systems. We show that relations between thermal performance and the shape of the injected thermal volume are generally hard to derive when complex well schedules are imposed because the injected/produced volumes may not be equal. Despite more complex storage strategies to comply with legal regulations, the shallower group of investigated aquifers in this study remains economically more suitable for storage up to 90ºC. In average four well doublets will be required to store the yearly excess of energy. The deeper group of investigated aquifers, however, become interesting for storage at higher temperatures.</p>