Nitrate adsorption and desorption during biological ion exchange

Impact of Cleaning on Membrane Performance during Surface Water Treatment: A Hybrid Process with Biological Ion Exchange and Gravity-Driven Membranes

In this study, the hybrid biological ion exchange (BIEX) resin and gravity-driven membrane (GDM) process was employed for the treatment of coloured and turbid river water. The primary objective was to investigate the impact of both physical and chemical cleaning methods on ceramic and polymeric membranes in terms of their stabilised flux, flux recovery after physical/chemical cleaning, and permeate quality. To address these objectives, two types of MF and UF membranes were utilised (M1 = polymeric MF, M2 = polymeric UF, M3 = ceramic UF, and M4 = lab-made ceramic MF). Throughout the extended operation, the resin functioned initially in the primary ion exchange (IEX) region (NOM displacement with pre-charged chloride) and progressed to a secondary IEX stage (NOM displacement with bicarbonate and sulphate), while membrane flux remained stable. Subsequently, physical cleaning involved air/water backwash with two different flows and pressures, and chemical cleaning utilised NaOH at concentrations of 20 and 40 mM, as well as NaOCl at concentrations of 250 and 500 mg Cl2/L. These processes were carried out to assess flux recovery and identify fouling reversibility. The results indicate an endpoint of 1728 bed volumes (BVs) for the primary IEX region, while the secondary IEX continued up to 6528 BV. At the end of the operation, DOC and UVA254 removal in the effluent of the BIEX columns were 68% and 81%, respectively, compared to influent water. This was followed by 30% and 57% DOC and UVA254 removal using M4 (ceramic MF). The stabilised flux remained approximately 3.8-5.2 LMH both before and after the cleaning process, suggesting that membrane materials do not play a pivotal role. The mean stabilised flux of polymeric membranes increased after cleaning, whereas that of the ceramics decreased. Enhanced air-water backwash flow and pressure resulted in an increased removal of hydraulic reversible fouling, which was identified as the dominant fouling type. Ceramic membranes exhibited a higher removal of reversible hydraulic fouling than polymeric membranes. Chemical cleaning had a low impact on flux recovery; therefore, we recommend solely employing physical cleaning.

Using selectivity to evaluate aqueous- and resin-phase denitrification during biological ion exchange

An increased fertilizer application for agricultural purposes has resulted in increased nitrate (NO3-) levels in surface water and groundwater around the globe, highlighting demand for a low-maintenance NO3- treatment technology that can be applied to nonpoint sources. Ion exchange (IEX) is an effective NO3- treatment technology and research has shown that bioregeneration of NO3- laden resins has the potential to minimize operational requirements and brine waste production that often prevents IEX application for decentralized treatment. In this work, batch denitrification experiments were conducted using solutions with low IEX selectivity capable of supporting the growth of denitrifying bacteria, while minimizing NO3- desorption from resins, encouraging resin-phase denitrification. Although only 15% of NO3- was desorbed by the low selectivity solution, this initial desorption started a cycle in which desorbed NO3- was biologically transformed to NO2-, which further desorbed NO3- that could be biotransformed. Denitrification experiments resulted in a 43% conversion rate of initially adsorbed NO3-, but biotransformations stopped at NO2- due to pH limitations. The balance between adsorption equilibria and biotransformation observed in this work was used to propose a continuous-flow reactor configuration where gradual NO3- desorption might allow for complete denitrification in the short retention times used for IEX systems.

Unraveling the roles of microporous and micro-mesoporous structures of carbon supports on iron oxide properties and As (V) removal performance in contaminated water

This study investigates the impact of microporous (SP-C) and micro-mesoporous carbon (DP-C) supports on the dispersion and phase transformation of iron oxides and their arsenic (V) removal efficiency. The research demonstrates that carbon-supported iron oxide sorbents exhibit superior As(V) uptake capacity compared to unsupported Fe2O3, attributed to reduced iron oxide crystallite sizes and As(V) adsorption on carbon supports. Maximum As(V) uptake capacities of 23.8 mg/g and 18.9 mg/g were achieved for Fe/SP-C and Fe/DP-C at 30 wt% and 50 wt% iron loading, respectively. The study reveals a nonlinear relationship between As(V) sorption capacity and iron oxide crystallite size after excluding As(V) adsorption capacity on carbon supports, suggesting the iron oxide phase (Fe3O4) plays a role in determining adsorption capacity. Iron oxide-loaded DP-C sorbents exhibit faster adsorption rates at low As(V) concentrations (5 mg/L) than SP-C sorbents due to their bimodal pore structure. Adsorption behavior varies at higher As(V) concentrations (45 mg/L), with Fe/DP-C reaching maximum capacity more slowly due to limited available adsorptive sites. All adsorbents maintained near-complete As(V) removal efficiency over five cycles. The findings provide insights for designing more efficient adsorbents for As(V) removal from contaminated water sources.

Enhanced denitrification performance of granular sludge for the treatment of waste brine from ion exchange resin process

Ion exchange resin process is a widely used process in wastewater treatment plants, but its waste brine is characterized by high salinity and nitrate concentration, leading to costly treatment. This study innovatively explored the use of an up-flow anaerobic sludge bed (USB) for the treatment of waste brine from ion exchange resin process, following a pilot-scale ion exchange resin process. Specifically, the D890 ion exchange resin was employed for nitrate removal from secondary effluent, with resin regeneration using 4% NaCl solution. The USB was inoculated with anaerobic granular sludge and acclimated under various single-factor conditions, which revealed the optimal pH range of 6.5-9, salt concentration of 2%, hydraulic retention time of 12 h, C/N ratio of 3.3, and up-flow velocity of 1.5 m/h for reactor operation. This study provides a novel approach for the cost-effective treatment of waste brine from ion exchange resin process. The study found that the denitrification efficiency was highest when the NO3--N concentration was around 200 mg/L, with NO3--N and TN removal rates exceeding 95% and 90%, respectively, under optimal operating conditions. Characterization of the granular sludge during different phases of the operation revealed a significant increase in proteobacteria and gradually became the dominant species over time. This study presents a novel, cost-effective approach to treat waste brine from ion exchange resin process, and the long-term stable operation of the reactor offers a reliable option for resin regeneration wastewater treatment.

Ion exchange for effective separation of 3-nitro-1,2,4-triazol-5-one (NTO) from wastewater

The explosive 3-nitro-1,2,4-triazol-5-one (NTO) presents a physiochemical challenge for treatment of munitions wastewater. Leveraging NTO's ionic character in neutral pH wastewater allows for expanded treatment options. Four commercial drinking water anion exchange resins specific for NO₃^- and ClO₄^- were evaluated for NTO adsorption extent, adsorption kinetics, and regeneration potential. Batch studies demonstrated NTO adsorption to all resins tested (max 690 mg NTO/g resin) and that resins were regenerable with 6% NaCl. Adsorption capacities (88-99%) and desorption efficiencies (80-85%) of NTO from the resins remained stable over three loading cycles. Perchlorate selective resins adsorbed more NTO, with larger desorption efficiencies, than nitrate selective resins. Kinetic experiments demonstrated that equilibrium adsorption between NTO and resins occurs within 120 min of exposure, following the pseudo second-order model (K₂ range 9.8 × 10^-5 to 15 × 10^-5 g resin/mg NTO/min). Intraparticle diffusion modeling suggested that boundary-layer diffusion was the predominant sorption mechanism in NTO adsorption to the resins compared to intraparticle diffusion. In synthetic wastewater mixtures of NTO, 2-4-dinitroanisole (DNAN), nitroguanidine (NQ), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), only NTO was exchanged to any great extent. This work suggests that perchlorate anion exchange resins may be a viable segregation technology for NTO from munitions wastewater as compared to activated carbon.