Deep Removal Research Articles

A low-cost crosslinked polystyrene derived from environmental wastes for adsorption of phenolic compounds from aqueous solution

Waste polystyrene (WPS) and CCl4 are typical environmental wastes. They belong to white pollution resource and ozone depleting substance, respectively. A porous crosslinked polystyrene (CPS), which was successfully synthesized by WPS and CCl4, can effectively adsorb various phenolic compounds from aqueous solution. The adsorption performance of CPS originated from its Lewis basicity, hydrophobicity, and coexistent micro- and mesopores. The Lewis basicity and the hydrophobicity facilitated deep removal for 2,4-dimethylphenol, salicylic acid, and tannic acid (TA). The coexistent micro- and mesopores enabled the simultaneous removal for 4-chlorophenol and TA. For the adsorption mechanism, the interaction between CPS and the phenolic compounds was confirmed as H-bonding and π-π stacking. For the better understanding of adsorption behaviour of CPS to various phenolic compounds, functional relationships between the Freundlich parameters KF and n were studied for several sorbents. The relationships indicated that the Lewis basicity of CPS might be deactivated by its mesopores and needed to be activated by the phenolic acids.

Phosphate removal from wastewater using reinforced feed material at the tertiary treatment stage

In recent years, eutrophication processes have posed a serious threat to water bodies. As a result of excess inputs of nutrients (nitrogen and phosphorus) from drainage basins, natural water quality deteriorates, which is usually accompanied by changes in the water bodies ecosystem structure. The increased concentration of nutrients leads to the rapid development of blue-green algae, reduced dissolved oxygen, fish-kill, coastal zones overgrowth, treated water processing complication. The article provides relevant information in the field of phosphate-removing wastewater treatment. The article presents advanced chemical and physical-chemical methods of phosphate-removing wastewater treatment. The article presents the results of the research on phosphate-removing wastewater treatment methods using iron-bearing feed material. The evidence of physical-chemical nature of deep phosphate-removing purification of water is presented. Deep phosphate removal is mainly due to physical-chemical processes of phosphate coagulation with ferrous ions, the source of which is the metal in the feed material, which is subjected to processes of electrochemical corrosion. When the biofilm loading becomes overgrown, the contact of the metal surface area with water decreases and the purification effect decreases. After regeneration of the load, the efficiency of phosphate removal increased to its previous level. Using the method of deep phosphate removal from domestic wastewater, with the help of reinforced feed material, at the tertiary treatment stage the required efficiency of phosphate removal can be achieved, however, there is a high consumption of metal in the feed material.

Separation and recovery of arsenic and alkali products during the treatment of antimony smelting residues

For the comprehensive utilization of antimony smelting arsenic-alkali residue, there are some problems such as the incomplete separation and low recoveries of arsenic and alkali, and the formation of arsenic-alkali mixed salts with secondary pollution. In order to solve these problems, the leaching solution of arsenic-alkali residue (arsenic-alkali solution) was used as a raw material in this study, and a novel process of twice alkali recovery with CO2, deep alkali removal with H2SO4, As(V) reduction with SO2 and evaporation concentration to recover arsenic was proposed to dispose of the arsenic-alkali solution. The total recovery of alkali was 87.8% by twice alkali recovery from the arsenic-alkali solution. After washing and thermal decomposition of crude NaHCO3, the obtained Na2CO3 product can be used as the reagent of arsenic removal in the refining process of crude antimony. In the process of deep alkali removal, compared with the direct treatment, the consumption of H2SO4 after twice alkali recovery was markedly reduced from the arsenic-alkali solution, and also no mirabilite was precipitated. The total recovery of arsenic was 80.6% in the process of arsenic recovery, and the purity of As2O3 in arsenic trioxide product reached 95.2% after washing, which meets the third grade standard of arsenic trioxide (GB 26721–2011). This process realizes the efficient separation and recovery of arsenic and alkali from the arsenic-alkali solution, and also no arsenic-alkali mixed salts are produced.

Rain-removing Algorithm for Image Based on Deep Learning

Aiming at the problem that the decrease of driver’s visual definition is affected by rainy weather, a new deep learning image rain removal algorithm is proposed. The network consists of a rainwater detection subnetwork and a rainwater removal subnetwork in series. The rainwater detection subnetwork adopts residual learning network, which can accurately learn the difference between rain images and non-rain images. The rain-removing subnetwork uses a U-shaped network with dense connections. On the one hand, it uses the U-shaped network to retain the details of the background, and on the other hand, the DenseNet is used to multiplex the lower layer features to higher layer features to improve the accuracy of rain removal, by combining them, it alleviates the contradiction between the loss of background details caused by excessive rain removal and the incomplete rain-removing. Experimental results show that this kind of deep rain-removing network can detect and remove the rainwater in the image well.

Preparation of High-Purity Lithium Carbonate Using Complexing Ion-Exchange Resins

Sorption of a series of alkaline earth and nonferrous metals (Ca, Mg, Cu, Ni, and Zn) from lithium hydrocarbonate and chloride solutions onto ion-exchange resins of various classes was studied. The highest values of the static exchange capacity were observed in sorption from a LiHCO3 solution onto imino carboxylic ion exchangers Amberlite IRC 748 (Rohm and Haas, the United States), Purolite S930 (Purolite, the United Kingdom), and AXIONIT 3S (AO Aksion RDM, Russia). In sorption from a LiCl solution with рН 1.4, the sorption capacity of all the sorbents tested is 3–7 lower. Sorption treatment of a LiHCO3 solution to remove Na, K, Са, Mg, Al, Si, Ti, Cr, Mn, Fe, Ni, Cu, and Zn impurities under dynamic conditions using AXIONIT 3S imino carboxylic sorbent was performed. The sorption ensures deep removal of Ca, Cu, and Zn impurities from a LiHCO3 solution. A procedure was suggested for preparing high-purity lithium carbonate by ion-exchange purification of a LiHCO3 solution on an imino carboxylic sorbent, followed by thermal decomposition of the purified solution at the boiling point to obtain a lithium carbonate precipitate. Lithium carbonate with the main substance content of 99.90 ± 0.05 wt % was obtained.

Design and proof of concept of a continuous pressurized multi-stage fluidized bed setup for deep sour gas removal using adsorption

Pressure swing adsorption (PSA) processes are frequently used in the (petro)chemical industry, but they suffer from ineffective use of the sorbent and slow heat transfer. A pressurized multi-stage fluidized bed (MSFB) for continuous PSA is proposed in this work to overcome these drawbacks. A one stage fluidized bed adsorber was used to determine minimum fluidization velocities of the used amine sorbent at various pressures up to 10 bara. The design of a pilot scale experimental setup is described, together with supporting experiments to show the proof of concept. Removal from 37,000 mol ppm CO2 to <10 mol ppm CO2 in a few seconds was demonstrated in the pressurized MSFB adsorber. The tray efficiencies were high: often larger than 0.85. Using a numerical particle model, it was concluded that the CO2 adsorption rate is controlled via intraparticle mass transfer.

Deep and high-efficiency removal of sulfate through a coupling system with sulfate-reducing and sulfur-oxidizing capacity under haloalkaliphilic condition.

Sulfide from anaerobic treatment of high-sulfate wastewater would always have some adverse effects on downstream processes. In this study, a coupling anaerobic/aerobic system was developed and operated under haloalkaliphilic condition to realize deep and high-efficiency removal of sulfate without production of sulfide. A haloalkaliphilic sulfur-oxidizing strain, Thioalkalivibrio versutus SOB306, was responsible for oxidation of sulfide. The anaerobic part was first operated at optimum condition based on a previous study. Then, its effluent with an average sulfide concentration of 674 ± 33mg·l-1 was further directly treated by a set of 1 l biofilter with SOB306 strain under aerobic condition. Finally, 100% removal rate of sulfide was achieved at aeration rate of 0.75l·l-1·min-1, ORP of -392mV and HRT of 4h. The average yield of elemental sulfur reached 79.1 ± 1.3% in the filter, and the CROS achieved a conversion rate of sulfate to sulfur beyond 54%. This study for the first time revealed the characteristics and performance of the haloalkaliphilic CROS in deep treatment of high-sulfate wastewater, whichpavedthewayforthedevelopmentandapplicationofthis method in the real world.

Process Control and Operation Optimization of PN-SAD Coupling Process Based on SBR-ABR

This study uses three different operating phases for a sequencing batch reactor (SBR) combined with an anaerobic baffled reactor (ABR) to determine the effect of deep nitrogen and carbon removal by the "partial nitrification-anaerobic ammonium oxidation combined denitrification" (termed PN-SAD) reaction. The effluent of the SBR (NO2--N/NH4+-N ratio range of 1-1.32) was accessed directly to the single compartment ABR anammox system in phase Ⅰ. The results showed that although the anammox reaction was stable, the combined process total nitrogen (TN) removal efficiency was<80%, and the TN concentration of effluent was~20 mg·L-1. In order to increase the denitrification function in the ABR, denitrifying sludge was added to the third compartment of the ABR in phase Ⅱ. We found that the TN removal efficiency of the coupling reaction was still low. An organic carbon source should be supplied in the latter stage of anammox if deep nitrogen removal is required. Therefore, in phase Ⅲ, the effluent of the SBR (NO2--N/NH4+-N ratio of ~5) was mixed with the partial raw water (mixed water NO2--N/NH4+-N ratio of ~1.4; C/N ratio of 2.5). The mixed water was connected to the single compartment of the ABR. The PN-SAD system not only achieved a good matrix ratio at the anammox stage, but also provided a good carbon source for denitrification. The chemical oxygen demand (COD) concentration of the effluent in the whole process was 50 mg·L-1, the TN concentration of the effluent was<6 mg·L-1, and the TN removal efficiency was 95%. We conclude that the stable operation of the combined PN-SAD reaction provides the basis for deep nitrogen and carbon removal using the combined SBR-ABR process.

Selenium migration behaviors in wet flue gas desulfurization slurry and an in-situ treatment approach

Excessive discharge of Se-containing wastewater from coal-fired power plants is a disaster for aquatic life, and it must be strictly controlled. However, conventional coagulation-precipitation technology cannot efficiently remove selenium from wastewater, owing to its complex species and high solubility. In this study, an innovative approach was proposed to realize the in-situ removal of selenium in desulfurization slurry, instead of treating it in wastewater. Firstly, the migration behaviors of selenium in slurry was studied. Among various ions, the ferric ion could significantly convert liquid selenite into solid phase by the formation insoluble ferric selenite. Then, several oxidizing factors were tested and the S2O82− showed obvious inhibition effect. A multi-component removal agent containing Fe3+/Mn2+ or Fe3+/Fe2+ successfully removed selenite from slurry in the presence of S2O82−, and the efficiency was as high as 96.5%. Furthermore, the in-situ removal agent was tested using a field slurry obtained from a full-scale coal-fired power plant, and the selenium concentration could be reduced to 38.4 μg/L. It is promising that the application of this technology in full-scale power plants will achieve better performance because the formation of troublesome selenate can be avoided. No complex system or process is needed for this in-situ selenium removal approach, and it can easily combine with other available advanced deep removal technologies, to build the double defense walls for controlling selenium discharge.

Recovery of alkali, selenium and arsenic from antimony smelting arsenic-alkali residue

Abstract Arsenic-alkali residue is a hazardous waste produced by the refining process of crude antimony in antimony smelting, and contains highly toxic sodium arsenate and a large number of residual alkali. In this study, aiming at the problems of the low recoveries and incomplete separation of arsenic and alkali, the secondary pollution of arsenic-alkali mixed salts and the insufficient utilization of valuable resources in the treatment process of arsenic-alkali residue, a new process of antimony enrichment with water leaching, twice alkali recovery with CO2, selenium recovery with acidification and arsenic recovery with SO2 reduction and evaporation concentration was proposed to dispose arsenic-alkali residue. The results showed that the leaching efficiencies of Sb, As, Se and alkali in arsenic-alkali residue were 1.8, 98.4, 97.9 and 100% by hot water leaching, respectively. Alkali was recovered with CO2 from arsenic-alkali solution and the direct recovery was 87.8%. In addition, the purity of Na2CO3 product was higher than 90% and As content in product was controlled below 0.2%. Deep alkali removal and efficient selenium recovery were achieved by acidification from the solution after alkali recovery, the direct recovery of Se was 80.6%, and the purity of crude selenium was 81.7%. Arsenic was recovered from the solution after selenium removal and the direct recovery was 79.4%, and the quality of As2O3 product reached the third grade standard of arsenic trioxide (GB 26721-2011). This process realizes the efficient recovery of alkali, selenium and arsenic in arsenic-alkali residue, and also does not produce arsenic-alkali mixed salts and wastewater.

Nitrogen removal performance of microbial fuel cell enhanced bioretention system

Abstract Bioretention cell (BRC) and an enhanced system combining bioretention cell with microbial fuel cell (BRC-MFC) were used to treat domestic wastewater. Nitrogen removal characteristics and permeation characteristics of two systems were investigated by adjusting influent carbon/nitrogen ratio (C/N = 2–20). Results showed that nitrification and denitrification performances were mainly influenced by organic matter and system combination, which further effected the nitrogen removal. When optimal operating parameters were: electrode space of 30 cm, hydraulic load of 1.0 m3/(m2·d) and inlet/reaction time of 1/8 in BRC-MFC system, chemical oxygen demand (COD), total nitrogen (TN) and NH4+ removal efficiencies still reached 97.63, 64, and 42.26%, respectively and achieved high removal efficiency of organic matter and nitrogen simultaneously compared to the BRC system. Efficient supply of electron and phylogenetic diversity of bacterial communities in BRC-MFC process was the main reason to achieve deep denitrification removal. After the V3-V4 variable region of 16S rRNA gene was sequenced by the Miseq high-throughput sequencing method, introduction of MFC enhancement technology affected the microbial community structure in the system. The presence of MFC contributed to an increase in community diversity (from 14 to 19 phyla). The results provide a simple method without kinetic energy for simultaneous denitrification and steady infiltration of bioretention.

Deep CO2 removal using high pressure membrane contactors with low liquid-to-gas ratio

Membrane contactor is a technology that intensifies conventional absorption column. However, liquid-to-gas ratios (L/G) of membrane contactor in existing reports are much higher compared to CO2 absorption column, which results in higher solvent circulation rate and higher consumption in heating energy. This makes the technology less attractive for deep CO2 removal. Direct reduction of liquid flow rate was not effective in lowering down L/G. Experimental results showed that 50% reduction in liquid flow rate could reduce L/G by 25%, but the reduction in CO2 flux (33%) was higher due to decrease in liquid phase mass transfer coefficient which was dependent on liquid velocity. An alternative method to reduce L/G through membrane module length increase was proven, where L/G was reduced 70% with only 16% flux reduction. The flux reduction was only observed when L/G dropped below 0.80L/mol and it was due to depletion of unreacted amine for CO2 absorption. The lowest L/G value obtained in this study was 36% lower than the conventional absorption column in liquefied natural gas (LNG) process, showing that membrane contactor technology is not only energy-viable and more compact for deep CO2 removal, but it also offers energy saving advantage.

Dissolution and mineralization behavior of metallic impurity content in diamond wire saw silicon powder during acid leaching

Metallic impurity removal is essential for the recovery and purification of silicon from diamond wire saw silicon powder during acid leaching process. However, the related dissolution and mineralization behavior are unclear, which are the two main factors governing the capacity of metallic impurity removal during the acid leaching process for silicon recovery from diamond wire saw silicon powder. Metallic impurities have different characteristics in diamond wire saw silicon powder, especially the mineralization hindering the deep removal of impurities. In this study, the dissolution behavior in out-field and mixed lixiviant assisted intensification acid leaching were investigated, respectively. Further, it is of interest in this study to search the root cause of the dissolution behavior from impurity sources with a unique insight, where related theory was used to explain both the mineralization behavior and dissolution behavior. Results revealed that the acid leaching dissolution occurred from the surface inwards, as well as the root cause, which is caused by mineralization behavior. Owing to the fact that the bare silicon surface developed on the amorphous SiO2 layer, the retention of metallic impurity was the result of the SiO2 layer obstacle. The dissolution behavior could be explained as the disintegrating corrosion of SiO2. For this reason, the 4 M HCl + 0.5 M HF mixture with a total removal efficiency of 99.28% outperformed out-field assisted leaching. This study can provide a suitable foundation for understanding the dissolution behavior and mineralization behavior for impurity removal, as well as contribute a roadmap for further silicon purification from diamond wire saw silicon powder.

Hydrogen peroxide coordination-calcium salt precipitation for deep phosphorus removal from crude sodium tungstate solution

In the traditional alkali smelting process of tungsten ore，a small amount of the associated phosphorus will enter the sodium tungstate solution. In order to produce a qualified tungsten product, phosphorus must be removed in depth. Conventional methods for removing phosphorus, such as magnesium salt precipitation, ion exchange, etc., are difficult to efficiently remove high concentrations of phosphorus from sodium tungstate solution. In this paper, a method for deep phosphorus removal from crude sodium tungstate solution by hydrogen peroxide coordination‑calcium salt precipitation is proposed due to the coordination ability of hydrogen peroxide with tungstate to form peroxytungstate which is difficult to be precipitated by calcium. The paper mainly explores the theoretical feasibility of this method, the influence of time, calcium addition, pH value, initial phosphorus concentration and other factors on P removal. The best phosphorus removal condition has been obtained: under the condition of adding hydrogen peroxide, when the reaction time is 10 min; the molar ratio of calcium to phosphorus added is 3; the pH value is 9.5, and the phosphorus concentration is higher than 1 g/L, the phosphorus removal effect has been basically stable. The phosphorus removal ratio can reach 99.9% which means that phosphorus concentration in solution is <10 ppm after phosphorus removal, and the tungsten loss is as low as 0.1%. This method can remove phosphorus deeply from sodium tungstate solution containing different initial phosphorus concentration.

Cooperative removal of SO2 and NO using a cost-efficient triple-area control method

Chlorite-induced oxidation reaction has been demonstrated to be an efficient approach for simultaneous removal of SO2 and NO, however the dosage of used chlorite is always high, which is unfavorable for economic operation and controlling the secondary environmental impact. The motivation of this work is to explore if it is possible to reduce the chlorite dosage meanwhile guaranteeing a good removal of NO by utilizing a triple-area control method. This reaction system consists of three parts: (1) a 0.9 mM NaClO2 solution at 60 °C, (2) a water layer at 50 °C, and (3) a 80 mM Na2SO3 solution. The water layer was used to capture the ClO2 emitted from the NaClO2 solution to conduct a deep removal of NO. Na2SO3 solution was used to remove the produced NO2 and the residual ClO2 via redox reactions. Co-presence of SO2 and O2 exhibited a great synergism in NO removal, but the presence of HCO3− remarkably suppressed the NO removal. According to the ion chromatography (IC) analysis, SO42− and NO3− were identified to be the main products, their concentration distributions in the triple-area were also revealed. The mechanisms of removal of SO2 and NO and the application prospective were proposed.

Analysis of Device-Related Infection after Deep Brain Stimulation Surgery

Device-related infection frequently becomes a serious problem after deep brain stimulation(DBS)surgery and DBS device removal is usually the only effective treatment option. In this study, we examined risk factors for infection related to DBS devices at our institution. We retrospectively investigated 80 DBS surgeries performed between March 2009 and September 2017 at our institution. We examined the relationship between DBS device-related infection and the following items:duration of electrode placement surgery, total number of tracks of microelectrode recordings(MER), period between surgeries, highest body temperature until implantable pulse generator(IPG)implantation, and patient background characteristics. Four(5.0%)patients developed device-related infection after DBS surgery. Three of them required device removal, whereas one improved following antibiotic treatment alone. We did not identify any specific trend or risk factor for infection. We perform DBS surgery in two stages. Patients were implanted with an IPG 2-3 days after electrode placement until August 2016, and at 6-8 days starting in September 2016. All cases of infection developed before September 2016, and no cases of infection have occurred since September 2016. We believe that lengthy surgical electrode placement affects the general status of patients and performing surgery before stabilization might confer a risk of infection. Device-related infection after DBS surgery does not seem to be associated with any risk factors. However, a shorter period between two-staged surgeries might affect infection rates.

Nutrient removal and microbial community structure variation in the two-sludge system treating low carbon/nitrogen domestic wastewater

A two-sludge system with separated phosphorus removal unit and nitrification unit was used to treat the actual municipal sewage deficient in organic carbon sources, with the carbon/nitrogen (C/N) ratio of 4.39. The system was first operated as anaerobic/oxic–nitrification (A/O–N) mode for 60 days (phase I), and then transformed into anaerobic/anoxic/oxic-nitrification (A/A/O–N) mode for the next following 80 days (phase II). Noteworthy, oxygen and nitrate acted as electronic acceptors for phosphorus removal in chronological order. Results indicated that deep phosphorus removal and complete nitrification were achieved at both phase I and phase II, and the system exhibited a higher microbial diversity. Microbial community abundance on genus level analysis indicated that Dechloromonas and Accumulibacter were respectively accumulated with 11.6 and 2.42% abundance (A/A/O sludge); and 9.31 and 1.29% Nitrospira and Nitrosomonas occupied the biofilm, and they performed denitrifying phosphorus removal (DNPR) and nitrification, respectively.

Results from an industrial size biogas-fed SOFC plant (the DEMOSOFC project)

The EU-funded DEMOSOFC project aims to demonstrate the technical and economic feasibility of operating a 174 kWe Solid Oxide Fuel Cell (SOFC) in a wastewater treatment plant. The fuel for the three SOFC modules (3 × 58 kWe) is biogas, which is available on-site from the anaerobic digestion of sludge collected from treated wastewater. The integrated biogas-SOFC plant includes three main units: 1) the biogas cleaning and compression section, 2) the three SOFC power modules, and 3) the heat recovery loop. Main advantages of the proposed layout are the net electric efficiency of the SOFC, which is in the range 50–55%, and the near-zero emissions. A specific focus of the demonstration project is the deep and reliable removal of harmful biogas contaminants. The presented work is related to the design of the SOFC system integrated into the wastewater treatment plant, followed by the analysis of the first results from the plant operation. We analyzed the biogas yearly profile to determine the optimal SOFC capacity to install that is 3 SOFC modules. The rational is to maintain high the capacity factor while minimizing the number of shutdown per year (due to biogas unavailability). First results from plant operation are also presented. The first SOFC module was activated in October 2017 and the second in October 2018. The measured SOFC efficiency from compressed biogas to AC power has always been higher than 50–52%, with peaks of 56%. Dedicated emissions measurements have been performed onsite during December 2017. Results on real biogas operation show NOx < 20 mg/m3, SO2 < 8 mg/m3 (detection limits for the instrument) and PM lower than ambient air values.

Simulated biomass tar removal mechanism by a Quench Coupled with ADsorption Technology (QCADT)

Abstract Tar removal is a bottleneck in the smooth commercialization of biomass gasification technology. Based on introducing adsorption process into Quench Coupled with ABsorption Technology (QCABT) previously proposed by the author's group, Quench Coupled with ADsorption Technology (QCADT) has been developed to narrow this gap. Additionally, benzene and naphthalene, which are more similar to the real tar for containing aromatic ring structures, were adopted as light and heavy simulated tar, respectively. Also their removal behavior by QCADT was investigated. The results show that the removal mechanism of QCADT is similar to that of QCABT, except for the higher overall tar removal rate due to adsorption effect. Adsorbents with both micro- and narrow mesopores exhibit a better benzene removal performance, while narrow mesopores play dominant roles in naphthalene removal. Penetration adsorption loading of benzene and naphthalene on AC-1 can reach 0.38 g·g−1 and 0.34 g·g−1, respectively. The sawdust hardly has any tar removal effect. Combined micro- and meso-pores, will benefit both deep tar removal and large adsorption rate, providing a high tar removal efficiency.

Modification of zeolite by metal and adsorption desulfurization of organic sulfide in natural gas

The metal modified zeolite was prepared by impregnation combined with roasting and the adsorption performance of organic sulfur in natural sulfur was evaluated. The zeolite type, ion concentration, calcination temperature, anion and cationic species all have effect on the desulfurization performance. Anions have a great influence on the performance of the zeolite modified by copper ions. Ag/13X had the highest adsorption capacity to methyl sulfide and the adsorption capacity increased by 1.6 times than that of the unmodified 13X zeolite. The order of adsorption capacity to sulfide by Cu/13X is ethyl mercaptan > methyl sulfide > dimethyl disulfide. And the adsorption capacity to the mixed sulfide is greater than that of the single sulfide, but less than the sum of the single sulfides. After regeneration by calcination, the adsorption capacity is basically recovered. Metal-modified zeolites are well suited for the deep removal of organic sulfur from natural gas.