Nitrate removal from aqueous solutions by γ-Al2O3 ultrafiltration membranes

Nitrates Removal from Simulated Groundwater Using Nano Zerovalent Iron Supported by Polystyrenic Gel

The main objectives of this present paper were to indicate the immobilization of nano zerovalent iron (nZVI) onto a polymeric material (Purolite A400) and the synthesis of the polymeric material (A400-nZVI) through sodium borohydride (NaBH4) reduction. The obtained polymeric material (A400-nZVI) was used for the nitrate ions removal from a simulated groundwater at different conditions. The polymeric materials, without and with nano zerovalent iron (A400 and A400-nZVI), were characterized trough the FTIR, SEM-EDAX, XRD, and TGA analysis. The analysis confirmed the presence of nano zerovalent iron (nZVI) onto the polymeric material (A400). The adsorption capacity of A400-nZVI, used as polymeric adsorbent, was evaluated by kinetic and thermodynamic studies. The obtained experimental results indicated that the nitrate ions reduction was fitted well by models: pseudo-second-order kinetic and Freundlich isotherm. According to the kinetic model results, a reaction mechanism could exist in the stage of reactions. The higher value of removal nitrate (>80%) was obtained under acidic condition. The results indicated that the obtained polymeric material (A400-nZVI) can be considered as a potential polymeric adsorbent for different pollutants from groundwater and wastewater.

Progress in alumina ceramic membranes for water purification: Status and prospects

Ceramic membranes have gained increasing attention in recent years for the removal of various contaminants from water. Alumina membrane is considered as one of the most important ceramic membranes, which plays important roles not only in separation processes such as microfiltration, ultrafiltration, and nanofiltration, but also in catalysis- and adsorption- enhanced separation applications in water purification and wastewater treatment. However, there is currently still lack of a comprehensive critical review about alumina membranes for water purification. In this review, we first discuss recent developments of alumina membranes, and then critically introduce the state-of-the-art strategies for lowering fabrication cost, improving membrane performances and mitigating membrane fouling. Especially, aiming to improve membrane performance, some emerging methods are summarized such as tailoring membrane structure, developing flexible membranes, designing nano-pores for precise separation, and enhancing multi-functionalities. In addition, engineering applications of alumina membranes for water purification are also briefly introduced. Finally, the prospects for future research on alumina membranes are proposed, such as economic preparation/application, challenging precise separation, enriching multi-functionalities, and clarifying separation mechanisms.

Strategic management of nitrate pollution from contaminated water using viable adsorbents: An economic assessment-based review with possible policy suggestions

Groundwater contaminated with nitrate has prompted a flurry of research studies around the world in the recent years to address this burning environmental issue. The common presence of nitrates in groundwater, wastewater, and surface waters has thrown an enormously critical challenge to the global research communities to provide safe and clean drinking water to municipalities. As per WHO, the maximum permissible limit of nitrate in drinking water is 10 mg/L and in groundwater is 50 mg/L; exceeding the limits, several human health problems are observed. Adsorption, ion-exchange processes, membrane-based approaches, electrochemical and chemical procedures, biological methods, filtration, nanoparticles, etc. have been well investigated and reviewed to reduce nitrate levels in water samples in the recent years. Process conditions, as well as the efficacy of various approaches, were discovered to influence different techniques for nitrate mitigation. But, because of low cost, simple operation, easy handling, and high removal effectiveness, adsorption has been found to be the most suitable and efficient approach. The main objectives of this review primarily focuses on the creation of a naturally abundant, cost-effective innovative abundant material, such as activated clay particles combined with iron oxide. Oxide-clay nanocomposite materials, effectively remove nitrate with higher removal efficiency along with recovery of nitrate concentrated sludge. Such methods stand out as flexible and economic ways for capturing stabilized nitrate in solid matrices to satisfy long-term operations. A techno-economic assessment along with suitable policy suggestions have been reported to justify the viability of the brighter processes. Indeed, this kind of analytical review appears ideal for municipal community recommendations on abatement of excess nitrate to supply of clean water.

Hydroxyapatite-based adsorbents: Applications in sequestering heavy metals and dyes

Hydroxyapatite (HAp) is a calcium phosphate material that was used primarily in bone regeneration and repair as a result of its chemical similarity with bone. However, HAp has emerged as a very promising adsorbent for sequestering contaminants like heavy metals, dyes, hydrocarbons as well as other emerging pollutants from wastewater as a result of its versatility and encouraging adsorptive properties. Contaminants like heavy metals and dyes have been a major source of environmental concern. Research studies involving the use of HAp as adsorbents for the adsorptive treatment of heavy metal- and dye-contaminated wastewater have become increasingly popular due to its eco-friendliness, easy synthesis, unique adsorption properties etc. Various methods are available for the synthesis of HAp and its composites with some of these methods used in combination with other methods to obtain more efficient HAp-based adsorbents. In this work, the adsorptive removal of heavy metals and dyes by HAp and its composites was extensively reviewed as well as the parametric effects of process factors like contact time, solution pH, temperature, solute concentration etc on the adsorption process. Kinetic, thermodynamic, and isotherm models for elucidating the adsorption process were also considered. Generally, from the works reviewed, HAp-based adsorbents were found to be very effective for sequestering heavy metals and dyes from solution and thus presents a low-cost option for adsorptive wastewater treatment.

Deposition of Thin Alumina Films Containing 3D Ordered Network of Nanopores on Porous Substrates

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensing.

Effect and mechanism of graphene structured palladized zero-valent iron nanocomposite (nZVI-Pd/NG) for water denitration

Nitrate reduction by zero-valent iron-based materials has been extensively studied. However, the aggregation of nanoparticles and the preference for unfavored ammonia products limit the application of this technology. To overcome this issue, this study introduced a novel synthesized nanoscale palladized zero-valent iron graphene composite (nZVI-Pd/NG) and explored its nitrate reduction efficiency. A nitrate removal rate of 97.0% was achieved after 120 min of reaction for an initial nitrate concentration of 100 mg N/L. The nitrogen gas selectivity was enhanced from 0.4% to 15.6% at the end point compared to nanoscale zero-valent iron (nZVI) particles under the same conditions. Further analyses revealed that zero-valent metal nanoparticles spread uniformly on the graphene surface, with a thin layer of iron (hydr)oxides dominated by magnetite. The nZVI-Pd/NG exhibited good catalytic activity with the associated activation energy of 17.6 kJ/mol being significantly lower than that with nZVI (42.8 kJ/mol). The acidic condition promoted a higher nZVI utilization rate, with the excess dosage of nZVI-Pd/NG ensuring a high nitrate removal rate for a wide pH range. This study demonstrates an improvement in nitrate reduction efficiency in a nZVI system by combining the exceptional properties of graphene and palladium.