Assessment of zeolite and compost-zeolite mixture as permeable reactive materials for the removal of lead from a model acidic groundwater

Cyclic zinc capture and zeolite regeneration using a column method, mass transfer analysis of multi regenerated bed

Treatment of wastewater and reuse of purified water in an industrial process can provide an alternative source of fresh water as well as reduce pollution load by discharging a lower quantity of wastewater. When adsorption is used for treatment, the regeneration of the used adsorbent may also account for a large portion of the operational cost and cause secondary pollution. This problem may be solved by cyclic repetition of adsorption/regeneration cycles using a column method. In this paper, a total of nine successive cycles of zinc capture and zeolite bed regeneration using a column method have been investigated. The derived form of the breakthrough curve was used for analysing mass transfer in the column. For that purpose, the Dose-response, the Thomas, the Bohart-Adams, the Yoon-Nelson and the Wolborska models were used for modelling the breakthrough curve by nonlinear regression analysis. Simulation results and mathematical similarities between the models were discussed. This is the first study that used derived form of Dose-response model to analyse the inflection points of the breakthrough curve and mass transfer during nine consecutive sorption-regeneration cycles of zinc ions on natural zeolite. Obtained peak shape rate profiles were analysed for all cycles. Optimal operation conditions were evaluated with respect to the inflection point, the model parameters, and the residence time.

Application of zeolites in permeable reactive barriers (PRBs) for in-situ groundwater remediation: A critical review

Permeable reactive barrier (PRB) is one of the most promising in-situ groundwater remediation technologies due to its low costs and wide immobilization suitability for multiple contaminants. Reactive medium is a key component of PRBs and their selection needs to consider removal effectiveness as well as permeability. Zeolites have been extensively reported as reactive media owing to their high adsorption capacity, diverse pore structure and high stability. Moreover, the application of zeolites can reduce the PRBs fouling and clogging compared to reductants like zero-valence iron (ZVI) due to no formation of secondary precipitates, such as iron monosulfide, in spite of their reactivity to remove organics. This study gives a detailed review of lab-scale applications of zeolites in PRBs in terms of sorption characteristics, mechanisms, column performance and desorption features, as well as their field-scale applications to point out their application tendency in PRBs for contaminated groundwater remediation. On this basis, future prospects and suggestions for using zeolites in PRBs for groundwater remediation were put forward. This study provides a comprehensive and critical review of the lab-scale and field-scale applications of zeolites in PRBs and is expected to guide the future design and applications of adsorbents-based PRBs for groundwater remediation.

Evaluating low-cost permeable adsorptive barriers for the removal of benzene from groundwater: Laboratory experiments and numerical modelling

Permeable adsorptive barriers (PABs) consisting of individual (compost, zeolite, and brown coal) and composite (brown coal-compost and zeolite-compost) adsorbents were evaluated for their hydraulic performance and effectiveness in removing aqueous benzene using batch and column experiments. Different adsorption isotherms and kinetic models and different formulations of the equilibrium advection-dispersion equation (ADE) were evaluated for their capabilities to describe the benzene sorption in the media. The batch experiments showed that the adsorption of benzene by the adsorbents was favourable and could be adequately described by the Freundlich and Langmuir isotherms and the pseudo-second-order kinetic model. Particle attrition and structural reorganization occurred in the columns, possibly introducing preferential flow paths and resulting in slight changes in the final hydraulic conductivity values (4.3 × 10^-5 cm s^-1-1.7 × 10^-3 cm s^-1) relative to the initial values (4.2 × 10^-5 cm s^-1-2.14 × 10^-3 cm s^-1). Despite the fact that preferential flow appeared to have an impact on the performance of the investigated adsorbents, the brown coal-compost mixture proved to be the most effective adsorbent. It significantly delayed benzene breakthrough (R = 29), indicating that it can be applied as a low-cost effective adsorbent in PABs for sustainable remediation of benzene-contaminated groundwater. The formulated transport models could fairly describe the behaviour of benzene in the investigated media under dynamic flow conditions; however, model refinement and additional experimental studies are needed before pilot/full-scale applications to improve the fits and verify the benzene removal processes. Our results generally demonstrate how such studies can be useful in evaluating potential reactive barrier materials.

Experimental Study of Al-Modified Zeolite with Oxygen Nanobubbles in Repairing Black Odorous Sediments in River Channels

As an extreme phenomenon of water pollution, black odorous water not only causes ecological damage, but also severely restricts urban development. Presently, the in situ remediation technology for sediment from river channels is still undeveloped, and there are many bottlenecks in the key technologies for sediment pollution control and ecological restoration. In this study, three experimental tanks were used to explore the restoration effect of Al-modified zeolite with oxygen nanobubbles on black odorous sediment from the Shichuan River. One of the tanks housed Typha orientalis and Canna indica L. (TC), another tank housed the same plants and had Al-modified zeolite with oxygen nanobubbles (TC+AMZON), and the last tank was used as a comparison test (CS). The results show that the nitrogen (N) and phosphorus (P) in the sediment are violently released into the surrounding water. However, TC+AMZON could effectively inhibit the release of P. The released amount of soluble reactive phosphorus (SRP) from the pore water in the sediment reached its maximum at 40 d, and the amounts were 122.97% and 74.32% greater in TC and CS, respectively, than in TC+AMZON. However, the released amount of total phosphorus (TP) reached its maximum at 70 d, and the amounts were 260.14% and 218.23% greater in TC and CS, respectively, than in TC+AMZON. TC+AMZON significantly increased the dissolved oxygen (DO) and the oxidation-reduction potential (ORP) of pore water in the sediment in the early stages of the test. At 0 d, the DO content in TC+AMZON reached 10.6 mg/L, which is 112.0% and 178.95% greater than in TC and CS, respectively. The change law of ORP in the sediment is consistent with the DO. TC+AMZON significantly improved the transparency and reduced the content of chlorophylla in the upper water and could slightly reduce the N and P content in overlying water. The transparency of TC+AMZON increased by 130.76% and 58.73%, and chlorophylla decreased by 55.6% and 50.0% when compared to TC and CS, respectively.

Removal of Transition Metals from Contaminated Aquifers by PRB Technology: Performance Comparison among Reactive Materials

The most common reactive material used for the construction of a permeable reactive barrier (PRB) is zero valent iron (ZVI), however, its processing can generate corrosive effects that reduce the efficiency of the barrier. The present study makes a major contribution to understanding new reactive materials as natural and synthetic, easy to obtain, economical and environmentally friendly as possible substitutes for the traditional ZHV to be used as filters in the removal of three transition metals (Zn, Cu, Cd). To assess the ability to remove these pollutants, a series of batch and column tests were carried out at laboratory scale with these materials. Through BACH tests, four of seven substances with a removal percentage higher than 99% were prioritized (cabuya, natural clinoptilolite zeolites, sodium mordenite and mordenite). From this group of substances, column tests were performed where it is evidenced that cabuya fiber presents the lowest absorption time (≈189 h) while natural zeolite mordenite shows the highest time (≈833 h). The latter being the best option for the PRB design. The experimental values were also reproduced by the RETRASO code; through this program, the trend between the observed and simulated values with respect to the best reactive substance was corroborated.

Inhibitory effects of Ca2+ on ammonium exchange by zeolite in the long-term exchange and NaClO-NaCl regeneration process

The inhibitory effects of calcium ion (Ca²⁺) on ammonium (NH₄⁺) exchange by zeolite were investigated in the long-term exchange and sodium hypochlorite - sodium chloride (NaClO-NaCl) regeneration process, and alleviation measure was developed and validated in this study. The batch experiments indicated that NH₄⁺ removal efficiency, exchange kinetics and equilibrium isotherms were significantly dependent on the coexisting Ca²⁺. The exchange capacity decreased from 0.58 to 0.40 mg g^-1 by increasing initial Ca²⁺ concentration from 0 to 100 mg L^-1. The inhibitory effect of Ca²⁺ on NH₄⁺ exchange efficiency was fitted to the competitive inhibition Monod model with half-saturation rate constant of 134.7 mg L^-1. Ca²⁺ addition reduced the NH₄⁺ removal rate and lengthened the exchange equilibrium time of zeolite. Periodic precipitation of Ca²⁺ in the form of calcium carbonate from the used regenerant maintained the removal efficiency of NH₄⁺ commendably by alleviating inhibition effect of Ca²⁺ and extended the working life of zeolite. The major chemical compositions of natural and regenerated zeolite were basically unchanged. Compared to Bohart-Adams model and Thomas model, the Dose-Response model could predict the breakthrough curve well, and the fitted parameter further confirmed that NaClO-NaCl regeneration with periodic Ca²⁺ removal is an effective method to maintain efficient NH₄⁺ from wastewater by zeolite.

Selective Removal of As(V) Ions from Acid Mine Drainage Using Polymer Inclusion Membranes

Acid mine drainage (AMD) is globally recognized as one of the environmental pollutants of the priority concern due to high concentrations of toxic metals and sulfates. More rigorous environmental legislation requires exploitation of effective technologies to remove toxic metals from contaminated streams. In view of high selectivity, effectiveness, durability, and low energy demands, the separation of toxic metal ions using immobilized membranes with admixed extractants could ameliorate water quality. Cellulose triacetate based polymer inclusion membranes (PIMs), with extractant and plasticizer, were studied for their ability to transport of As(V) ions from synthetic aqueous leachates. The effects of the type and concentration of extractant, plasticizer content, and sulfuric acid concentration in source phase on the arsenic removal efficiency have been assessed. Under the best of applied conditions, PIM with Cyanex 921 as extractant and o-nitrophenyl octyl ether (o-NPOE) as plasticizer showed high repeatability and excellent transport activity for selective removal of As(V) from AMD.