Exhausted Resin Research Articles

Regeneration of a Fire‐Resistant Fluid‐Fouled Strong Base Anion Resin using a Caustic Solution with Citric Acid as a Surfactant

AbstractFire Resistant Fluid (FRF), used in turbine governing systems, transforms during operation, forming substituted phenol and phosphoric acid. The use of strong Base Anion Resin (SBA resin) to reduce the Total Acid Number (TAN) of FRF is widespread. However, the regeneration of these oil‐fouled resins is crucial due to their high cost and the challenges associated with their environmental disposal. In this study, we present a novel method for recovering exhausted resin by treating it with an aqueous solution of citric acid, followed by regeneration with a caustic soda solution. We optimized the recovery percentage in the ion exchange capacity by testing varying concentrations of the citric acid solution under different reaction conditions. The highest recovery of ion exchange capacity achieved was 55 % after soaking for 16 hours in a 5 % citric acid solution, followed by regeneration with a 5 % NaOH solution. The efficacy of citric acid in this research was further explored through a Density Functional Theory (DFT) study. This study is significant as it is the first to demonstrate the successful regeneration of oil‐fouled resins with high ion exchange capacity using citric acid, a more environmentally friendly and cost‐effective alternative.

Managing PFAS exhausted Ion-exchange resins through effective regeneration/electrochemical process

This study proposes an integrated approach that combines ion-exchange (IX) and electrochemical technologies to tackle problems associated with PFAS contamination. Our investigation centers on evaluating the recovery and efficiency of IX/electrochemical systems in the presence of five different salts, spanning dosages from 0.1 % to 8 %. The outcomes reveal a slight superiority for NaCl within the regeneration system, with sulfate and bicarbonate also showing comparable efficacy. Notably, the introduction of chloride ion (Cl−) into the electrochemical system results in substantial generation of undesirable chlorate (ClO3−) and perchlorate (ClO4−) by-products, accounting for ∼18 % and ∼81 % of the consumed Cl−, respectively. Several agents, including H2O2, KI, and Na2S2O3, exhibited effective mitigation of ClO3− and ClO4− formation. However, only H2O2 demonstrated a favorable influence on the degradation and defluorination of PFOA. The addition of 0.8 M H2O2 resulted in the near-complete removal of ClO3− and ClO4−, accompanied by 1.3 and 2.2-fold enhancements in the degradation and defluorination of PFOA, respectively. Furthermore, a comparative analysis of different salts in the electrochemical system reveals that Cl− and OH− ions exhibit slower performance, possibly due to competitive interactions with PFOA on the anode's reactive sites. In contrast, sulfate and bicarbonate salts consistently demonstrate robust decomposition efficiencies. Despite the notable enhancement in IX regeneration efficacy facilitated by the presence of methanol, particularly for PFAS-specific resins, this enhancement comes at the cost of reduced electrochemical decomposition of all PFAS. The average decay rate ratio of all PFAS in the presence of 50 % methanol, compared to its absence, falls within the range of 0.11–0.39. In conclusion, the use of 1 % Na2SO4 salt stands out as a favorable option for the integrated IX/electrochemical process. This choice not only eliminates the need to introduce an additional chemical (e.g., H2O2) into the wastewater stream, but also ensures both satisfactory regeneration recovery and efficiency in the decomposition process through electrochemical treatment.

AWWA Water Science Author Spotlight

Having recently published an article in AWWA Water Science, Levi Haupert answered questions from the publication's editor-in-chief, Kenneth L. Mercer, about the research. Avoiding Pitfalls When Modeling Removal of Per- and Polyfluoroalkyl Substances by Anion Exchange Levi M. Haupert, Jonathan G. Pressman, Thomas F. Speth, and David G. Wahman Levi Haupert and his younger son prepare to go climbing at the Cincinnati Zoo. Levi and his wife attend a friend's wedding in New Orleans. The traits I value most in myself as a researcher are my imagination and my resilience. Imagination is important because it allows researchers to construct and compare alternative theories and explanations for available data and experimental results. Without this trait, it is easy to miss important new information or get hung up on dead-end ideas. Resilience is also an essential trait because scientific research is an exploration of the unknown, and it is important for researchers to be able to respond gracefully to unexpected outcomes, whether they are setbacks or opportunities. On vacation in Florida, Levi and his family swam with a dolphin that used to be a movie star. The state of the science for understanding adsorption of PFAS on ion exchange resins is less developed overall than for adsorption of PFAS by granular activated carbon. Accordingly, most of the literature at the time we wrote the article discussed the performance of ion exchange resins in terms of generic adsorption concepts or using theory developed for activated carbon. Our goal was to assemble a collection of existing ion exchange theory and use it to lay the groundwork for building more detailed and specific models of PFAS treatment by ion exchange. Our hope is that the development of these models will allow more useful data to be extracted from laboratory and field experiments, both of which are very costly. I conduct my work in the service of EPA's mission to protect human health and the environment, a cause I am personally invested in. Specifically, several of my close friends and family members live in areas where PFAS contamination of drinking water is a serious concern. This personal connection is an important driving force behind my research. One shadow looming on the horizon is the need to effectively manage large waste streams from treatment of PFAS in drinking water. These waste streams include spent activated carbon, exhausted ion exchange resins, and reject water from membrane systems. Effective methods for storing or destroying these wastes are few, and the increased waste volume in the coming years will almost certainly strain existing capabilities. If the suggestions for modeling and research methodology made in the featured article are widely adopted, I believe that it will be possible to develop a deeper understanding of the mechanisms underpinning the adsorption of PFAS onto ion exchange resins. This improved understanding will in turn lead to more effective and efficient methods for removing PFAS from drinking water, which will have important public health benefits. Levi goes fishing with his older son. I prefer quiet, peaceful activities when I need to recharge from a stressful day. I enjoy hiking, fossil hunting, and bird watching. If the weather is unfavorable, I like to spend time painting with watercolors and practicing broad-pen calligraphy. I also enjoy playing cards and board games with my family. To learn more about Levi's research, visit the article, available online at https://doi.org/10.1002/aws2.1222.

Bioregeneration of sulfate-laden anion exchange resin

Ion exchange technology removes ionic compounds from waters effectively but treatment of the spent regenerant is expensive. The bioregeneration of sulfate-laden strong base anion exchange resin was successfully tested using both pure and mixed sulfate-reducing bacterial cultures. The resin was first used for removal of sulfate from neutral (pH 6.7 ± 0.5) synthetic sodium sulfate solutions, after which the spent resin was regenerated by incubating with a viable sulfate-reducing bacterial culture in batch and column modes. In the batch bioregeneration tests, the achieved bioregeneration was 36–95% of the original capacity of the fresh resin (112 mg SO42−/g) and it increased with regeneration time (1–14 days). The capacity achieved in the column tests during 24 hours of bioregeneration was 107 mg SO42−/g after the first regeneration cycle. During the bioregeneration, sulfate was mainly reduced by the sulfate-reducing bacteria (approx. 60%), but part of it was only detached from the resins (approx. 30%). The resin-attached sulfate was most likely replaced with ions present in the liquid sulfate-reducing bacterial culture (e.g., HCO3−, HS−, and Cl−). During the subsequent exhaustion cycles with the bioregenerated resin, the pH of the treated sodium sulfate solution increased from the original 6.7 ± 0.5 to around 9. The study showed that biological sulfate reduction could be used for sulfate removal in combination with ion exchange, and that the exhausted ion exchange resins could be regenerated using a liquid sulfate-reducing bacterial culture without producing any brine.

Thermal decomposition of perfluorinated carboxylic acids: Kinetic model and theoretical requirements for PFAS incineration

Thermal decomposition of high-fluorine content PFAS streams for the disposal of old generations of concentrates of firefighting foams, exhausted ion-exchanged resins and granular activated carbon, constitutes the preferred method for destruction of these materials. This contribution studies the thermal transformation of perfluoropentanoic acid (C4F9C(O)OH, PFPA), as a model PFAS species, in gas-phase reactions over broad ranges of temperature and residence time, which characterise incinerators and cement kilns. Our focus is only on gas-phase reactions, to formulate a gas-phase submodel that, in future, could be used in comprehensive simulation of thermal destruction of PFAS; such comprehensive models will need to comprise fluorine mineralisation on flyash and in clinker material. Our submodel consists of 56 reactions and 45 species, and includes new pathways that cover the initial decomposition channels of PFPA, including those that lead to the formation of the n-C4F9 radical, the abstraction of hydroxyl H by O/H radicals, the fragmentation of the n-C4F9 radical, reactions between HF and perfluoropentanoic acid, as well as between HF and heptafluorobutanoyl fluoride (C3F7COF), and the cyclisation reactions. The model illustrates the formation of a wide spectrum of small CnFm and CnHFm compounds in the temperature window of 800–1500 K, 2 and 25 s residence time in a plug flow reactor, providing theoretical estimates for the operating conditions of PFAS thermal destruction systems. The initiation reactions involve the loss of HF and formation of the transition α-lactone species that converts to C3F7COF, with C4F9C(O)OH completely decomposed at 1020 K for 2 s residence time. At 1500 K, we predict the emission of ꞉CF2 (biradical difluorocarbene), HF, CO2, CO, CF4, C2F6, and C2F4, but at < 1400 K, we note the formation of 1H-nonafluorobutane (C4HF9), phosgene (COF2), and heptafluorobutanoyl fluoride (C3F7COF), with 1-C4F8, 2-C4F8 and C3HF7 persisting to 1500 K. We demonstrate that, the gas-phase pyrolysis processes by themselves convert PFAS to HF and short-chain fluorocarbons, with similar product distribution for short (2 s) and long (25 s) residence times, as long as the treatment temperature exceeds 1500 K. These residence times reflect those encountered in incinerators and cement kilns, respectively. Thermokinetic and mechanistic insights revealed herein shall assist to innovate PFAS thermal disposal technologies, and, from a fundamental perspective, to accelerate research progress in modelling of gas/solid reactions that mineralise PFAS-derived fluorine.

Enhancing bio-hydrogen production from food waste in single-stage hybrid dark-photo fermentation by addition of two waste materials (exhausted resin and biochar)

Bio-hydrogen production from organic wastes is considered as one of the most promising alternatives for sustainable, green energy production. In this study, the effect of addition of Ca- and Mg-saturated resin and phosphate-laden biochar on single-stage hybrid dark-photo hydrogen fermentation from food waste was investigated. In the first step, fermentation was performed using different amounts of Ca- and Mg-saturated resin ranging from 2.5 to 20 g l-1 to analyze the effect of released calcium and magnesium on both the H2 production rate and the system pH. The addition of 5 g l-1 saturated resin resulted in an increase of hydrogen yield from 101.60 ± 2.4 to 164.4 ± 2.6 ml H2g−1 VS, and at the same time it prevented pH drop and improved bacterial function. In the second step, 5 g l-1 saturated resin combined with various amounts of phosphate-laden biochar were added to the reactor. The maximum accumulated hydrogen production (3130 ± 16.8 ml) and hydrogen yield (197.15 ± 2.9 mlg−1VS) was observed when 5 g l-1 resin and 0.5 g l-1 biochar was used. This corresponds to 94% increase in the yield compared with the control. The analysis of the fermentation products indicated that butyrate and acetate were the major by-products during hydrogen production. Moreover, the optimum concentrations of resin and biochar served to facilitate substrate degradation and shorten the lag phase from 8.19 ± 0.4 to 4.79 ± 0.5 h. Thus, the application of Ca- and Mg-saturated resin and phosphate-laden biochar in a single-stage hybrid dark-photo fermentation process enhanced the efficiency of the conversion of organic waste to hydrogen while maintaining the stability of the process.

Low energy consumption electrically regenerated ion-exchange for water desalination.

A new regeneration method of ion exchange resin named Adjacent Bed Electrically Regenerated Ion-exchange (ABERI) was proposed to eliminate the environmental impact of traditional chemical regeneration and improve the economy of replacing chemical regeneration with electrical regeneration. The desalting operation of ABERI was the same as the conventional mixed bed. When the resins were exhausted, anion and cation resins were separated and then packed in a dedicated regenerator adjacently. The resins were regenerated by the H+ and OH- ions produced from a pair of electrodes installed on both sides of the resin bed. By optimizing the regeneration time, current, and feed water flow rate, the energy consumption of ABERI was 0.38 kWh/m3 water; that is, 54% of that of another electrical regeneration technology, membrane-free electrodeionization (MFEDI). Compared with MFEDI, the quality and quantity of purified water produced after regeneration were improved. In ABERI, the average conductivity and the volume (times of bed volumes) of the purified water are 0.9 μS/cm and 109; that is, 75 and 133% of that of MFEDI, respectively. The preliminary economic analysis showed that ABERI offers the potential to regenerate ion exchange resin in an eco-friendly and cost-effective manner.

Recovery of non-regenerable exhausted resin by hydrothermal chlorination

Purpose Cationic resin is widely used in decolouring of textile wastewaters. Tonnes of resin are used in sector, and disposal of resin is being a second waste problem. The purpose of this paper is to investigate the adsorption behaviour of the methylene blue cationic dye from aqueous solution on the cation exchanger Lewatit CNP80 to understand the regenerability of cation exchanger resin from textile wastewaters. Design/methodology/approach Cationic resin was used as an alternative low-cost adsorbent for removing methylene blue dye from textile wastewaters. The adsorption study was carried out in the batch mode. Batch adsorption studies were carried out to examine the effect of parameters such as methylene blue concentration, temperature, pH, resin dose, shaking speed and contact time. Findings It was observed that dye-removal capacity of resin was reached from 17 mgg−1 to 19.4 mgg−1 at 25 °C temperature, pH 5 in 15 min. At the appropriate range of parameters, it was observed that more than 98% removal efficiency was achieved for methylene blue dye, and also, this study was focussed on whether the resin regenerates. In regeneration studies, our purpose was to recover of non-regenerable exhausted cationic resin by NaOCl. Regeneration of Lewatit CNP80 was performed in five cycles. After regeneration, the authors tried to determine whether the adsorption capacity was affected by regeneration. Originality/value In this study, the authors focussed on regeneration studies. The aim is to find easy, low-cost regeneration agent. In conclusion, the authors found that NaOCl is eligible for regeneration studies. The exhausted resin was recovered by NaOCl, and the authors also tested 5th regeneration cycles. Sodium hypochlorite is not a common regeneration agent for adsorption studies. Generally, resin is regenerated by HCl or other regeneration agent products. As a result of that, operational cost was reduced, and the other thing that the authors want to emphasise is textile industry wastewater based high temperature; therefore, this regeneration study can easily work with textile industries.

Fluoride removal from groundwater using Zirconium Impregnated Anion Exchange Resin

Drinking water containing excess fluoride is a major health concern across the globe. The present study reports the feasibility of zirconium impregnated hybrid anion exchange resin (HAIX-Zr) for treating fluoride contaminated groundwater. The HAIX-Zr resin was prepared by impregnating ZrO2 nanoparticles on polymeric anion exchanger resin. Fluoride uptake by HAIX-Zr was quite rapid, 60% removal was obtained within 30 min. Kinetics of fluoride uptake by HAIX-Zr resin followed the pseudo-second-order kinetic model and adsorption data fitted best to Freundlich adsorption isotherm model. Maximum fluoride uptake capacity was observed as 12.0 mg/g. The defluoridation capacity of the resin decreases with increase in solution pH. The co-existing anions like chloride, phosphate, bicarbonate, nitrate, and sulphate at 100 mg/L concentration significantly affected fluoride removal and bicarbonate showed the highest interference. Continuous flow packed bed experiments were performed with real groundwater. To maintain a lower pH, weak acid cation exchange resin (INDION-236) was used before HAIX-Zr. It was observed that reducing the pH of the sample water to 4–4.5, increased the number of treated bed volumes fifteen times. Regeneration of fluoride-containing resin was done by passing 3% NaOH and 3% NaCl solution through an exhausted resin bed. The results revealed that HAIX-Zr can effectively remove fluoride from groundwater.

Use of Ion Exchange Beads as a Bacterial Carrier for Biodenitrification

In this research, an exhausted ion exchange resin was used as a carrier of bacterial cells, and the resulting bio‐ion exchange resin beads were applied in batch and continuous‐flow experiments for monitoring nitrate removal. The continuous‐flow experiments investigated the effects of hydraulic retention times (HRTs) of 7–24 h on the course of denitrification; nitrate removal was achieved at HRTs longer than 9 h, with nitrate and organic removal efficiencies higher than 99 and 80%, respectively. Nitrate removal was then monitored continuously for 31 days. To investigate the influence of phosphate salts on denitrification performance, raw Cetina River water was used. The research also examined the effect of methanol addition on denitrification by decreasing the methanol‐to‐nitrogen mass ratio to 2.5:1. The obtained nitrate and organic removal efficiencies of 100 and 93%, respectively, suggest that the application of the resin beads was effective for continuous nitrate removal from surface water.

Radioactive wastes Conditioning. Optimization of operating parameters by the experience plan method

The conditioning of exhausted Resins Exchanging Ions (REI) (radioactive wastes generated by nuclear operations) was optimized using a full factorial experiments plan 24. Sixteen experiments with a suitable choice of four interpretable variables led to a mathematical model in the form of a first degree polynomial. After analysing the effects, this model showed that the most influential factor on the response (compression strength) is the water/cement ratio (W/C) with a positive effect of (+2.17), the second factor in order is the mixing time with a positive effect of (+1.54). The interaction between the (W/C) and the number of vibration and interaction between the (W/C) and the mixing time also have effects on the response.

Regeneration of a perchlorate-exhausted highly selective ion exchange resin: Kinetics study of adsorption and desorption processes

Perchlorate is a stable and soluble ion that can last for decades in the environment and can cause a number of environmental and health issues. Perchlorate is commonly removed using highly-selective ion-exchange resins that are replaced after exhaustion and incinerated or disposed in a landfill since there is no viable regeneration method. The major limitations in regeneration of single use resins is achieving complete desorption of perchlorate. The sustainability of treatment processes for perchlorate contaminated water can be achieved by regenerating the exhausted resin. As the first step of resin bioregeneration study, research on the adsorption and desorption kinetics of the perchlorate ion from a strong base anion exchange resin was conducted. Different chemical reaction and diffusion models were analyzed using experimental data. Both adsorption and desorption experimental data were best described by the Pseudo-second order model with adsorption rate constants of 2 × 10−3 ± 0.001 (g/mg/min) and desorption rate constants of 5 × 10−2 ± 0.01 (g/mg/min). These results suggest that the rate limiting stage for adsorption and desorption of perchlorate ion into the resin can be chemisorption.

Mathematical modelling and reactor design for multi-cycle bioregeneration of nitrate exhausted ion exchange resin

Nitrate contamination is one of the largest issues facing communities worldwide. One of the most common methods for nitrate removal from water is ion exchange using nitrate selective resin. Although these resins have a great capacity for nitrate removal, they are considered non regenerable. The sustainability of nitrate-contaminated water treatment processes can be achieved by regenerating the exhausted resin several times rather than replacing and incineration of exhausted resin. The use of multi-cycle exhaustion/bioregeneration of resin enclosed in a membrane has been shown to be an effective and innovative regeneration method.In this research, the mechanisms for bioregeneration of resin were studied and a mathematical model which incorporated physical desorption process with biological removal kinetics was developed. Regardless of the salt concentration of the solution, this specific resin is a pore-diffusion controlled process (XδD ¯CDr0(5+2α)<<1). Also, Thiele modulus was calculated to be between 4 and 12 depending on the temperature and salt concentration. High Thiele modulus (>3) shows that the bioregeneration process is controlled by reaction kinetics and is governed by biological removal of nitrate.The model was validated by comparison to experimental data; the average of R-squared values for cycle 1 to 5 of regeneration was 0.94 ± 0.06 which shows that the developed model predicted the experimental results very well. The model sensitivity for different parameters was evaluated and a model bioreactor design for bioregeneration of highly selective resins was also presented.

TREATMENT OF WASTEWATER FROM CHROME PLATING INDUSTRY BY ION EXCHANGE METHOD

In the present work an attempt has been made to evaluate the efficiency of removal Cr(VI) from chrome plating industry wastewater by using fresh and reconditioned strong base anion exchanger Tulsion A-27(MP). The Experimental data is evaluated by plotting breakthrough curves and by employing Bohart-Adams Model. The maximum removal (80%) of Cr(VI) from plating wastewater is obtained at 14cm column bed height and flowrate 1mL/min for 1144.39mg/L of influent Cr(VI) concentration. The breakthrough curves for reconditioned and fresh resins indicates that breakthrough occurs early with decrease in bed height, increase in flow rate and influent Cr(VI) concentration. Regeneration of exhausted resin is also studied by using 2M NaCl and 2M HCl.

Effect of temperature & salt concentration on salt tolerant nitrate-perchlorate reducing bacteria: Nitrate degradation kinetics

The sustainability of nitrate-contaminated water treatment using ion-exchange processes can be achieved by regenerating the exhausted resin several times. Our previous study shows that the use of multi-cycle bioregeneration of resin enclosed in membrane is an effective and innovative regeneration method. In this research, the effects of two independent factors (temperature and salt concentration) on the biological denitrification rate were studied. The results of this research along with the experimental results of the previous study on the effect of the same factors on nitrate desorption rate from the resin allow the optimization of the bioregeneration process.The results of nitrate denitrification rate study show that the biodegradation rate at different temperature and salt concentration is independent of the initial nitrate concentration. At each specific salt concentration, the nitrate removal rate increased with increasing temperature with the average value of 0.001110 ± 0.0000647 mg-nitrate/mg-VSS.h.°C. However, the effect of different salt concentrations was dependent on the temperature; there is a significant interaction between salt concentration and temperature; within each group of temperatures, the nitrate degradation rate decreased with increasing the salt concentration. The temperature affected the tolerance to salinity and culture was less tolerant to high concentration of salt at low temperature. Evidenced by the difference between the minimum and maximum nitrate degradation rate being greater at lower temperature. At 35 °C, a 32% reduction in the nitrate degradation rate was observed while at 12 °C this reduction was 69%. This is the first published study to examine the interaction of salt concentration and temperature during biological denitrification.

A New and Original Method to Produce Ca(OH)&amp;lt;SUB&amp;gt;2&amp;lt;/SUB&amp;gt; Nanoparticles by Using an Anion Exchange Resin

Ca(OH)2 nanoparticles in hydro-alcoholic dispersion (nanolime) were successfully employed in Cultural Heritage conservation, thanks to the ability to overcome the limiting aspects of traditional lime treatments. Nanolime were currently produced by chemical precipitation process, at high temperature, with long times of synthesis, and after several purification steps to remove undesired secondary phases. In this paper, an innovative, simple and original method for nanolime production was described. The method was based on an ion exchange process between an anionic resin and a calcium chloride aqueous solution, operating at room temperature. A pure Ca(OH)2 nanoparticles suspension can be rapidly obtained after separating the resin from suspension, and any purification step was necessary. The exhausted resins can be regenerated and reused for a cyclic nanolime production. Structural and morphological features of the produced nanolime were preliminarily characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Moreover, XRD measurements allowed estimating nanoparticles reactivity by following their carbonatation process in air, in relation to different water/alcohol ratios and medium or high relative humidity conditions. The produced Ca(OH)2 nanoparticles appeared hexagonally plated, with dimension less than 100 nm and, compared with those obtained by typical wet precipitation method, they proved to be more reactive.

Hexavalent chromium [Cr(VI)] removal by the electrochemical ion-exchange process

In the present investigation, the performance of a laboratory-scale plate and frame-type electrochemical ion-exchange (EIX) cell on removal of hexavalent chromium from synthetic wastewater containing 5 mg/l of Cr(VI) was evaluated under varying applied voltages. Ruthenium dioxide-coated titanium plate (RuO 2/Ti) was used as anode and stainless steel plates as cathode. The EIX cell was run at different hydraulic retention time (HRT). Before using in the electrochemical cell, the capacity of ion-exchange resin was evaluated through kinetic and isotherm equilibrium tests in batch mode. The batch kinetic study result showed that the equilibrium time for effective ion exchange with resin is 2 h. The isotherm equilibrium data fit well to both Freundlich and Langmuir isotherms. Maximum capacity (qm) of resin calculated from Langmuir isotherm was 71.42 mg/g. Up to 99% of chromium removal was noticed in the EIX cell containing fresh resin at applied voltages of 10 V and higher. Migration of chromium ion to anode chamber was not noticed while performing the experiment with fresh resin. As high as 50% removal of chromium was observed from the middle chamber containing exhausted resin at an applied voltage of 25 V when the influent flow rate was maintained at 45 min of HRT. The performance of the reactor was increased to 72% when the influent flow rate was decreased to maintain at 90 min of HRT. Build-up of chromium in the anode chamber took place when exhausted resin was used in the process.

Combined bio-regeneration and ion-exchange system for perchlorate removal

In order to prove that perchlorate-laden resins could be bio-regenerated through direct contact with perchlorate-reducing bacteria (PRB), a combined bio-regeneration and ion-exchange (IX) system was operated. Two kinds of perchlorate-laden resins, nitrate-selective A520E and perchlorate-selective A530E, were successfully regenerated by PRB cultivated under anaerobic conditions. The bio-regeneration efficiency of perchlorate-laden resins increased with the amount of flow passed through the IX column. When the fully exhausted resin was bio-regenerated for 10 days at the flow rate of 2 BV (bed volume)/min and mixed liquor suspended solids concentration of 80 mg/L, almost 100% of IX capacity was recovered. A520E resin had higher bio-regeneration efficiency than A530E under all conditions, probably due to the fact that the perchlorate ion is more strongly bonded to the functional group of perchlorate-selective A530E resin. Measurement of perchlorate concentrations in the column effluents also revealed that the amount of perchlorate eluted from A520E resin was higher than that from A530E resin. Since only 10-20% of perchlorate was eluted from the resin during 10 days of bio-regeneration, the main mechanism of bio-regeneration appears to be the direct reduction of perchlorate by PRB on the resin.

Denitrification of Spent Regenerated Brine Using Molasses

Spent BRINE from the regeneration of exhausted resins has to be properly treated before its disposal. The heterotrophic denitrification of regenerated brine was studied in present work. Molasses which served as a carbon source has until now not been applied during brine denitrification. The nitrate and nitrite consumptions were observed according to different ratios between total organic carbon and nitrate (TOC / NO3 ratios) and the influence of NaCl was studied during batch experiments. This work ascertained that molasses is a very good source of carbon, and no addition of other nutrients is necessary. The complete nitrate removal from regenerated brine could be achieved using molasses.

Combined magnetic ion exchange and cation exchange for removal of DOC and hardness

The overall goal of this research was to evaluate an innovative combined ion-exchange process for multi-contaminant treatment. Magnetically enhanced anion exchange resin and conventional cation exchange resin were used in a single completely mixed vessel for simultaneous removal of dissolved organic carbon (DOC) and hardness. Following treatment, exhausted anion exchange resin and cation exchange resin were regenerated together in a single completely mixed vessel using sodium chloride (NaCl). The performance of the combined ion-exchange process was evaluated using three groundwaters and two nanofiltration (NF) membrane concentrates. The test waters provided a wide range of water quality in terms of DOC (2.9–56mg/L), total hardness (300–1000mg/L as CaCO3), and sulfate (10–830mg/L). Combined ion-exchange treatment of groundwater achieved 76% DOC removal and 97% total hardness removal using a 20% (m/v) NaCl regeneration solution. Combined ion-exchange also achieved high removals of DOC (e.g., 83%) and total hardness (e.g., 86%) from NF concentrate using a 30% (m/v) NaCl regeneration solution. These results provide water treatment engineers with a new application of ion-exchange that can be used in place coagulation and precipitative softening or as an intermediate treatment step between primary and secondary NF or reverse osmosis membranes.