Treatment of industrial brine using capacitive deionization (CDI) towards zero liquid discharge - challenges and optimization.

Thermal-based Zero Liquid Discharge (ZLD) process has been used for managing industrial brine. However, conventional thermal ZLD process is very energy intensive. In view of this, pre-concentration techniques have been applied prior to thermal process to reduce energy consumption of ZLD systems. Capacitive Deionization (CDI) is an emerging desalination technique and has yet to be extensively explored for the treatment of industrial brine especially for ZLD applications. High concentration of total dissolved solids (TDS) and high fouling potential of industrial brine are two major challenges in CDI process. This paper reviews the possible factors for optimizing CDI process in industrial brine treatment, namely, cell architectures, strategies in operation and fouling control. Cell architectures of membrane CDI (MCDI) and flow-electrode CDI (CDI) are preferred options for treating industrial brine compared with classic CDI in terms of energy consumption and fouling propensity. There are other operational strategies that could enhance the feasibility of using CDI process for ZLD application. These include reversed voltage desorption, multi-stage operation, brine recirculation and fouling control. Fouling control methods comprise pretreatment, antifouling modification, antiscalant and chemical cleaning. These methods could be integrated to optimize fouling mitigation. In addition to providing insights on feasibility of using CDI to concentrate industrial brines, this review also proposed guidelines for optimizing CDI process applied to treat industrial brines for ZLD applications.

Water treatment residual: A critical review of its applications on pollutant removal from stormwater runoff and future perspectives.

In recent years, many studies have been conducted on using different filter media in bioretention systems for stormwater runoff treatment. This critical review paper provides a comprehensive review on the current state of water treatment residual (WTR), a recycled material that can be used as bioretention filter media for removals of key stormwater runoff pollutants (especially phosphorus) and future perspectives with innovative modification on WTR applied for pathogen removal from stormwater runoff. This review paper comprised (i) a brief summary of the reported WTR characteristics, (ii) a thorough evaluation of WTR performance on major pollutants removal from stormwater runoff (iii) a discussion on phosphorus removal mechanisms by WTR applied in the stormwater runoff treatment, and (iv) a review of the future perspectives of WTR for pathogen removal and other potential practical application in the field of stormwater treatment. As outlined in this review, WTR in stormwater runoff treatment has yet to be fully explored. The possible enhancements, especially metal surface modification on WTR are reviewed to bring about the widespread use of WTR in stormwater reuse practices.

Microbial community succession and its correlation with reactor performance in a sponge membrane bioreactor coupled with fiber-bundle anoxic bio-filter for treating saline mariculture wastewater.

The application of MBR in high saline wastewater treatment is mainly constrained by poor nitrogen removal and severe membrane fouling caused by high salinity stress. A novel carriers-enhanced MBR system was successfully developed for treating saline mariculture wastewater, which showed efficient TN removal (93.2%) and fouling control. High-throughput sequencing revealed the enhancement mechanism of bio-carriers under high saline condition. Bio-carriers substantially improved the community structure, representatively, nitrifiers abundance (Nitrosomonas, Nitrospira) increased from 2.18% to 9.57%, abundance of denitrifiers (Sulfurimonas, Thermogutta, etc.) also rose from 3.81% to 14.82%. Thereby, the nitrogen removal process was enhanced. Noteworthy, ammonia oxidizer (Nitrosomonas, 8.26%) was the absolute dominant nitrifiers compared with nitrite oxidizer (Nitrospira, 1.13%). This supported the finding of shortcut nitrification-denitrification process in hybrid system. Moreover, a series of biomacromolecule degraders (Lutibacterium, Cycloclasticus, etc.) were detected in bio-carriers, which could account for the mitigation of membrane fouling as result of EPS and SMP degradation.

Effect of ferric hydroxide on membrane fouling in membrane bioreactor treating pharmaceutical wastewater.

Membrane fouling is considered as a main drawback for MBR technology especially treating industrial wastewater. Therefore, this study aimed to investigate the effect of fouling in membrane bioreactor (MBR) treating pharmaceutical wastewater with the addition of ferric hydroxide. Two identical lab-scale MBRs, namely, a control MBR (Co-MBR) and an enhanced MBR dosed with ferric hydroxide (Fe-MBR), were operated in parallel. The results demonstrate membrane fouling was retarded by 35% with the addition of iron. Further exploration of membrane fouling mechanisms showed iron addition resulted in increase in biomass floc size, enhancement of bacteria activity and reduction of dissolved organic concentration, especially carbohydrate, biopolymer and low molecular weight compounds concentrations in mixed liquor. There was also lower abundance of bacterial associated with biofilm formation in the Fe-MBR compared with the Co-MBR. These findings collectively contributed to the positive impacts on membrane fouling mitigation.

Role of metal modified water treatment residual on removal of Escherichia coli from stormwater runoff.

Extensive studies have been conducted on bioretention filter media applied in best management practices for stormwater runoff treatment. To date, more reported studies are focused on pollutants elimination such as suspended solids and nutrients. There has been limited research on pathogen removal from stormwater runoff. More focused studies on pathogen removal are therefore required if the intended stormwater is harvested for indirect potable use. In this study, water treatment residuals (WTR), a recycled biofilter media was surface-modified with metals to assess its potential for E. coli removal from stormwater runoff. To achieve this goal, four types of modified WTRs, prepared using iron, copper, platinum, and silver as antibacterial agents, were tested in parallel batch tests. After the cost-effectiveness evaluation among the four modified WTRs for bacterial removal, Fe2O3- and CuO-WTRs were shortlisted for further mechanism and stability studies. Stable antibacterial performances (E. coli log removal of 0.58 ±â€¯0.04 and 0.90 ±â€¯0.04, respectively) were achieved using the Fe2O3- and CuO-WTRs under intermittent synthetic and natural stormwater runoff conditions. No significant metal leaching was observed over prolonged continuous treatment. The experimental results showed the bio-adsorption onto the surface modified Fe2O3- and CuO-WTR was a key mechanism for E. coli removal followed by E. coli inactivation at solid-liquid interface caused by the antibacterial effect of metal coatings (where CuO was reported to have higher biotoxicity than Fe2O3). These findings clearly suggested the potential of CuO-modified WTR for pathogen removal in stormwater treatment practices.

Combination of in situ preconcentration and on-site analysis for phosphate monitoring in fresh waters.

Excess nutrients of phosphorus and nitrogen would lead to adverse impacts on a water body. It is important that their concentrations in a dynamic water ecosystem are measured accurately and constantly for an early warning before occurrences of algal blooms and for environmental management. Nevertheless, on-site measurements by existing technologies are often limited by the inherent sensitivities. In this study, a portable system for dissolved phosphate monitoring in freshwater based on the diffusive gradients in thin films (DGT) technique was developed. A polydiallydimethylammonium chloride (PDA) aqueous solution and a dialysis membrane were used as a binding phase and a diffusive layer in this preconcentration device, respectively. The binding properties of the PDA solution were evaluated in solutions of different pH (3 to 9) and varying concentrations of anions (2.0-20 mM). The amount of phosphates preconcentrated in the devices was measured by ultraviolet-visible (UV) spectroscopy to obtain the concentrations in waters without elution steps. The devices were validated in synthetic river water with good agreement with the theoretical prediction and in natural river water. A system combining this preconcentration device and a compact detection chamber equipped with a pair of light emitting diodes (LED) was studied in lab synthetic solutions for on-site monitoring of phosphate concentrations and their fluctuations.

RO brine treatment and recovery by biological activated carbon and capacitive deionization process.

The generation of brine solutions from dense membrane (reverse osmosis, RO or nanofiltration, NF) water reclamation systems has been increasing worldwide, and the lack of cost effective disposal options is becoming a critical water resources management issue. In Singapore, NEWater is the product of a multiple barrier water reclamation process from secondary treated domestic effluent using MF/UF-RO and UV technologies. The RO brine (concentrates) accounts for more than 20% of the total flow treated. To increase the water recovery and treat the RO brine, a CDI based process with BAC as pretreatment was tested. The results show that ion concentrations in CDI product were low except SiO2 when compared with RO feed water. CDI product was passed through a RO and the RO permeate was of better quality including low SiO2 as compared to NEWater quality. It could be beneficial to use a dedicated RO operated at optimum conditions with better performance to recover the water. BAC was able to achieve 15-27% TOC removal of RO brine. CDI had been tested at a water recovery ranging from 71.6 to 92.3%. CDI based RO brine treatment could improve overall water recovery of NEWater production over 90%. It was found that calcium phosphate scaling and organic fouling was the major cause of CDI pressure increase. Ozone disinfection and sodium bisulfite dosing were able to reduce CDI fouling rate. For sustainable operation of CDI organic fouling control and effective organic fouling cleaning should be further studied.

Integrated pretreatment with capacitive deionization for reverse osmosis reject recovery from water reclamation plant.

Reverse osmosis (RO) reject recovery from the water reclamation process was demonstrated feasible using an integrated pretreatment scheme followed by the Capacitive Deionization (CDI) process. The RO reject had an average total dissolved solids (TDS) of 1276+/-166 mg/L. Water recovery of 85% with water quality comparable with the RO feed was achieved. Pretreatments using biological activated carbon (BAC) and BAC-ultrafiltration (UF) attained total organic carbon (TOC) removal efficiencies of 23.5+/-6.0% and 39.9+/-9.0%, respectively. Organics removal of RO reject was attributed to simultaneous adsorption and biodegradation in the BAC pretreatment, while further biodegradation in the submerged UF membrane tank provided additional organics removal. Membrane and CDI fouling was reduced by pH adjustment of the pretreated RO reject to approximately 6.5, which prolonged the CDI operation time by at least two times. The CDI process was able to achieve more than 88 and 87% TDS and ion removals, respectively, while PO(4)(3-) and TOC removals were at 52-81% and 50-63%, respectively.

Ozone-biological activated carbon as a pretreatment process for reverse osmosis brine treatment and recovery.

Ozonation was used in this study to improve biodegradability of RO brine from water reclamation facilities. An ozone dosage ranging from 3 to 10 mg O(3)/L and contact times of 10 and 20 min in batch studies were found to increase the biodegradability (BOD(5)/TOC ratio) of the RO brine by 1.8-3.5 times. At the same time, total organic carbon (TOC) removal was in the range of 5.3-24.5%. The lab-scale ozone-biological activated carbon (BAC) at an ozone dosage of 6.0mg O(3)/L with 20-min contact time was able to achieve 3 times higher TOC removal compared to using BAC alone. Further processing with Capacitive Deionization (CDI) process was able to generate a product water with better water quality than the RO feed water, i.e., with more than 80% ions removal and a lower TOC concentration. The ozone-BAC pretreatment has the potential of reducing fouling in the CDI process.

Alternative immunofluorescent labeling of Cryptosporidium parvum in water samples using semiconductor quantum dots.

The application of immunofluorescent labeling using quantum dots for detection of inactivated Cryptosporidium parvum oocysts in spiked water samples (reservoir water, treated wastewater effluent, permeate of a membrane bioreactor, and tap water) provided more consistent results compared with the organic fluorophores label. The varying degree of particles present in the different water samples (with turbidity ranging from 0.2 to 6.1 NTU) in nonconcentrated water samples had insignificant interference on the labeled counts (2-sample t-tests, p > 0.236) using the quantum dot label, while the quantum dot label provided an advantage of approximately 50% lower interference in concentrated water samples compared with the organic fluorophores label.

Effect of formaldehyde on biofilm activity and morphology in an ultracompact biofilm reactor for carbonaceous wastewater treatment.

The effects of formaldehyde on biofilm morphology and biomass activity were investigated in an ultracompact biofilm reactor (UCBR) for carbonaceous wastewater treatment. The wastewater contained a fixed amount of glucose (with a chemical oxygen demand concentration of 600 mg/L) and an increasing concentration of formaldehyde (ranging from 21.4 to 271.1 mg/L). An influent formaldehyde concentration higher than 75 mg/L could facilitate filamentous growth (on biofilm) control and lead to a higher biofilm density, which is desirable as it enhanced the UCBR performance stability. However, at an influent formaldehyde concentration higher than 214.4 mg/L, biomass production was inhibited and deteriorations of biofilm morphology and biomass activity were observed. This study showed that it was desirable to maintain an influent formaldehyde concentration lower than 202.2 mg/L, as this concentration could achieve a good biofilm morphology while not inhibiting its microbial activity.

Denitrification of nitrate wastewater using packed-bed columns.

Columnar packed-bed (PB) reactors with a specific surface area of 127 m2/m3 were investigated in this study for treating nitrate wastewater. This study demonstrated that a single-stage packed bed was able to achieve total nitrogen (TN) and chemical oxygen demand (COD) removal efficiencies higher than 83 and 75%, respectively. The highest achievable TN and COD removal rates were 47.2 g N/m2 x d and 158.0 g COD/m2 x d, respectively. The substrate removal rate in the PB column was found to follow half-order reaction kinetics, with a reaction coefficient, kappa, of 53.62 (mg/L)1/2/d. A dual-stage PB system was capable of achieving TN and COD removal efficiencies greater than 99 and 98%, respectively. Effluent TN and COD concentrations less than 6.5 mg NO3(-)-N/L and 50.0 mg COD/L, respectively, were obtained when the dual PB system was used.

Use of semiconductor quantum dots for photostable immunofluorescence labeling of Cryptosporidium parvum.

Cryptosporidium parvum is a waterborne pathogen that poses potential risk to drinking water consumers. The detection of Cryptosporidium oocysts, its transmissive stage, is used in the latest U.S. Environmental Protection Agency method 1622, which utilizes organic fluorophores such as fluorescein isothiocyanate (FITC) to label the oocysts by conjugation with anti-Cryptosporidium sp. monoclonal antibody (MAb). However, FITC exhibits low resistance to photodegradation. This property will inevitably limit the detection accuracy after a short period of continuous illumination. In view of this, the use of inorganic fluorophores, such as quantum dot (QD), which has a high photobleaching threshold, in place of the organic fluorophores could potentially enhance oocyst detection. In this study, QD605-streptavidin together with biotinylated MAb was used for C. parvum oocyst detection. The C. parvum oocyst detection sensitivity increased when the QD605-streptavidin concentration was increased from 5 to 15 nM and eventually leveled off at a saturation concentration of 20 nM and above. The minimum QD605-streptavidin saturation concentration for detecting up to 4,495 +/- 501 oocysts (mean +/- standard deviation) was determined to be 20 nM. The difference in the enumeration between 20 nM QD605-streptavidin with biotinylated MAb and FITC-MAb was insignificant (P > 0.126) when various C. parvum oocyst concentrations were used. The QD605 was highly photostable while the FITC intensity decreased to 19.5% +/- 5.6% of its initial intensity after 5 min of continuous illumination. The QD605-based technique was also shown to be sensitive for oocyst detection in reservoir water. This observation showed that the QD method developed in this study was able to provide a sensitive technique for detecting C. parvum oocysts with the advantage of having a high photobleaching threshold.