Modified Grape Seeds: A Promising Alternative for Nitrate Removal from Water.

The aim of this work was to investigate grape seeds as a potential adsorbent for nitrate removal from water. Grape seeds were modified by quaternization and the applicability of the modified grape seeds (MGS) was evaluated in batch adsorption experiments. Fixed bed adsorption and regeneration studies were carried out to determine the regeneration capacity of MGS. The maximum adsorption capacity of 25.626 mg g-1 at native pH (6.3) for nitrate removal by MSG was comparable to that of the commercial anion exchange resin Relite A490 under similar conditions. The percent removal of nitrate from model nitrate solution was 86.47% and 93.25% for MGS, and Relite A490, respectively, and in synthetic wastewater 57.54% and 78.37%. Analysis of the batch adsorption data using isotherm models revealed that the Freundlich model provided a better fit to the data obtained than the Langmuir model, indicating multilayer adsorption. In kinetic terms, the results showed that the adsorption followed the pseudo-first order model. By investigating the adsorption mechanism, the results suggest that the intraparticle diffusion model was not the only process controlling the adsorption of nitrate on MGS. In column experiments (adsorption/desorption studies), three adsorption cycles were tested with minimal decrease in adsorption capacities, implying that this alternative adsorbent can be successfully regenerated and reused.

Characterization of multiple biomarker responses using flow cytometry to improve environmental hazard assessment with the green microalgae Raphidocelis subcapitata.

Microalgal toxicity tests using integrative endpoints as algal growth are regularly required to analyse the toxicity of potentially hazardous substances in the aquatic environment. However, these do not provide mechanistic information on the toxic mode of action by which contaminants may affect algae. Bottled waters can be used as a substitute for culturing media and should not impose any stress to the cultured organisms. However, certain chemical components can interfere with specific cell targets which are not revealed by general toxicity assays. The present study investigated the sensitivity of flow cytometry (FCM) to analyse sub-lethal effects of different bottled waters to the freshwater microalgae Raphidocelis subcapitata. Several endpoints were analysed including growth rate, natural pigments content, cell size, complexity, viability and cycle, Reactive Oxygen Species (ROS) formation, mitochondrial membrane potential and Lipid Peroxidation (LPO). Additionally, photosystem II (PSII) performance was analysed by PAM fluorometry, to provide further information on the absorption, distribution and use of energy in photosynthesis. Results indicated that the most sensitive endpoints were the oxidative stress related endpoints ROS formation and LPO, pigment content, morphological endpoints as cell size, complexity and cycle, with growth rate being one of the least sensitive. Although being essential macronutrients for algal growth, the chemical elements Ca, Na, Mg, and NH4 were identified as being primarily responsible for the observed toxicological effects to exposed algae. The applied methodology proved to be of high throughput, simultaneously assembling information on morphological, biochemical, and physiological status of algal cells. FCM also showed potential to reveal mechanistic information on the toxic mode of action of the bottled waters before any effects on algal growth was observed. The used approach demonstrated its potential for being integrated into future microalgal toxicity bioassays for testing chemicals to improve the hazard information obtained from currently approved internationally accepted test guidelines.

Water reclamation during drinking water treatments using polyamide nanofiltration membranes on a pilot scale.

The aim of this study was to investigate the performances of polyamide nanofiltration membranes during water reclamation. The study was conducted using nanofiltration concentrates obtained from two different nanofiltration drinking water treatment plants placed in the northern part of Serbia (Kikinda and Zrenjanin). Used nanofiltration concentrates contained high concentrations of arsenic (45 and 451 µg/L) and natural organic matter (43.1 and 224.40 mgKMnO4/L). Performances of polyamide nanofiltration membranes during water reclamation were investigated under various fluxes and transmembrane pressures in order to obtain drinking water from nanofiltration concentrates and, therefore, reduce the amount of produced concentrates and minimize the waste that has to be discharged in the environment. Applied polyamide nanofiltration membranes showed better removal efficiency during water reclamation when the concentrate with higher content of arsenic and natural organic matter was used while the obtained permeates were in accordance with European regulations. This study showed that total concentrate yield can be reduced to ~5 % of the optimum flux value, in both experiments. The obtained result for concentrate yield under the optimum flux presents considerable amount of reclaimed drinking water and valuable reduced quantity of produced wastewater.

Arsenic removal by nanoparticles: a review.

Contamination of natural waters with arsenic, which is both toxic and carcinogenic, is widespread. Among various technologies that have been employed for arsenic removal from water, such as coagulation, filtration, membrane separation, ion exchange, etc., adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities, and generally lower operation cost, but the need for technological innovation for water purification is gaining attention worldwide. Nanotechnology is considered to play a crucial role in providing clean and affordable water to meet human demands. This review presents an overview of nanoparticles and nanobased adsorbents and its efficiencies in arsenic removal from water. The paper highlights the application of nanomaterials and their properties, mechanisms, and advantages over conventional adsorbents for arsenic removal from contaminated water.

A Review on Adsorption of Fluoride from Aqueous Solution.

Fluoride is one of the anionic contaminants which is found in excess in surface or groundwater because of geochemical reactions or anthropogenic activities such as the disposal of industrial wastewaters. Among various methods used for defluoridation of water such as coagulation, precipitation, membrane processes, electrolytic treatment, ion-exchange, the adsorption process is widely used. It offers satisfactory results and seems to be a more attractive method for the removal of fluoride in terms of cost, simplicity of design and operation. Various conventional and non-conventional adsorbents have been assessed for the removal of fluoride from water. In this review, a list of various adsorbents (oxides and hydroxides, biosorbents, geomaterials, carbonaceous materials and industrial products and by-products) and its modifications from literature are surveyed and their adsorption capacities under various conditions are compared. The effect of other impurities on fluoride removal has also been discussed. This survey showed that various adsorbents, especially binary and trimetal oxides and hydroxides, have good potential for the fluoride removal from aquatic environments.