Synthesis of biosourced silica-Ag nanocomposites and amalgamation reaction with mercury in aqueous solutions

This paper focuses on the synthesis of a new silver nanocomposite adsorbent derived from rice husk as raw material. The synthesis is based on triethoxysilane chemistry and the reduction of silver without the aid of reductant chemicals. The derived AgNPs@SiO2 nanocomposites are fully characterized and then used for the removal of mercury (II) from aqueous solutions. The results demonstrated that the affinity of the composite for mercury is high and the removal mechanism is adsorption accompanied by a redox reaction between mercury and silver followed by the formation of calomel and amalgams between silver and mercury. The silver-mercury reaction is complex, and its stoichiometry seems to scale with the silver content. Besides the importance of the surface reactions, the successful implementation of biosourced silica for mercury removal from water is useful for the development of strategies for the valorization of agricultural waste and boosts the concept of circular economy and bioeconomy

Behaviour of aquaporin forward osmosis flat sheet membranes during the concentration of calcium-containing liquids

This study aims to examine the scaling and performance of flat sheet aquaporin FO membranes in the presence of calcium salts. Experiments showed that the application of calcium sulphate (CaSO4) resulted in an 8%–78% decline in the water flux. An increase in the cross-flow velocity from 3 to 12 cm/s reduced the decline in the flux by 16%. The deposition of salt crystals on the membrane surface led to the alteration in the membrane’s intrinsic properties. Microscopy, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and X-Ray fluorescence (XRF) analyses confirmed measurements of the zeta potential and contact angle. The use of a three-salt mixture yielded severe scaling as compared with the application of calcium sulphate dehydrate (CaSO4 × 2H2O), i.e., a result of two different crystallisation mechanisms. We found that the amount of sodium chloride (NaCl), saturation index, cross-flow velocity, and flow regime all play an important role in the scaling of aquaporin FO flat sheet membranes

Complex organic fouling and effect of silver nanoparticles on aquaporin forward osmosis membranes

Despite the negligible pressure used in forward osmosis (FO), the process still suffers from fouling. Recent studies demonstrated that this issue is common among all FO membrane types, including aquaporin-based filters. To address this problem, various approaches have been proposed. However, despite the biocidal effects of silver, no attempt has been made to apply silver for fouling mitigation in aquaporin FO membranes. Consequently, the present work focuses on the investigation of controlled combined organic fouling of aquaporin FO membranes and the effects of silver nanoparticles on the membrane performance and its properties. The obtained data show that in contrast with unaltered membranes, the membranes doped with silver nanoparticles are much more resistant to fouling. After the first filtration run, pristine membranes exhibited a flux decline of 50 %, while the flux decline of the modified membranes was limited to 10 %. Physical cleaning restored the flux of both membranes to 100 %. Analysis of the membranes showed that the membrane water flux was not affected by the covalent binding of the silver nanoparticles. Further, the membranes’ chemistry, zeta potential, contact angle, roughness, and antimicrobial resistance were altered

Tangential streaming potential, transmembrane flux, and chemical cleaning of ultrafiltration membranes

Transmembrane flux measurements are the only practical tools used to evaluate the degree of organic fouling and the efficiency of chemical cleaning of ultrafiltration membranes in situ. Tangential pH-streaming potential profiles may become a comprehensive in situ method to analyse cleaning efficiency versus potential membrane damage. A parallel implementation of the two methods was used to assist in tuning an efficient cleaning protocol for 300 kDa polyethersulfone membranes. The membranes were fouled with a mixture of organics and cleaned with nitric acid, acetic acid, caustic soda or liquid bleach, each at concentrations of 1, 5, or 10 mg/L. A modified Kolmogorov-Smirnov test for divergence in datasets clearly indicated cleaning with 5 mg/L NaOH or NaOCl. These findings were confirmed by atomic force microscopy surface contouring and infrared spectra recording. Tangential pH-streaming potential profiling is easy in terms of operation and maintenance, inexpensive, and may be conducted in situ. Implementation of two independent tests is instrumental in the validation of the cleaning agent efficiency, optimisation of the cleaning dose and pH, and assessment of membrane fouling potential by complex organic mixtures. A combination of transmembrane flux and tangential streaming potential tests may reduce the cost of chemical cleaning and suspend membrane ageing

The effect of caffeine, metronidazole, and ibuprofen on continuous flow activated sludge process

BACKGROUND: The aim of this work was to study the biological treatment of a synthetic wastewater containing emerging contaminants. The 95-day experiment was conducted in an 81 L continuous flow conventional activated sludge apparatus consisting of anoxic and aerobic reactors with internal recycling, and a clarifier with activated sludge recycling. Real activated sludge from the municipal wastewater treatment plant in the Nur-Sultan city was used. The degradation efficiencies of caffeine, metronidazole, and ibuprofen in the synthetic wastewater were studied either separately or in combination. RESULTS: When treated separately at the concentration of 30 mg/L, the degradation of caffeine and ibuprofen was up to 100%, while the degradation of metronidazole was in the range of 12–27%. Caffeine and ibuprofen inhibited the nitrification process, while the presence of metronidazole in the system suppressed the activity of denitrifying microorganisms. The biological treatment of the synthetic wastewater containing all three compounds (at the concentration of 10 mg/L each) resulted in degradation of caffeine and ibuprofen up to 100%, and 56% in the case of metronidazole. As both nitrification and denitrification processes were affected, the total nitrogen removal was significantly reduced from 53% to 22%. CONCLUSION: Complete degradation of caffeine and ibuprofen, and partial degradation of metronidazole were observed in a synthetic wastewater using the activated sludge process. As the presence of emerging pollutants in a wastewater affects the general efficiency of the wastewater treatment plants, other physical or chemical pre-treatment should be utilized to minimize the harmful effect of contaminants on the biological processes

Biological treatment, advanced oxidation and membrane separation for landfill leachate treatment : a review

Landfill leachate, especially when produced in old municipal solid waste landfills, is a challenging type of wastewater which contains a variety of toxic substances. The existence of pollutants in the landfill leachate is primarily due to inadequate solid waste separation at the source. Pretreatment on site is a must for the landfill leachate to be safely released into the environment. One-step treatment is insufficient since landfill leachate has a complex composition that spatially and temporally varies. Often, the landfill leachate and municipal wastewater are treated together. Biological treatment is a routine technique which is applied to landfill leachate less than five years old. The concentration of easily biodegradable organic matter in the young landfill leachate declines with time and, as a result, the application of physical and chemical treatment processes is required. The goal of the current work is to investigate the usefulness and capability of the most efficient and widely available technique/s for landfill leachate treatment, to identify the main challenges and strengths of each technology and seek the optimum solution

Understanding the interaction between biomacromolecules and their influence on forward osmosis process

Abstract This paper presents studies on the interactions and effects of biomacromolecules compounds on forward osmosis (FO) membrane performance. Individual components and a combination of various organic substances such as bovine serum albumin (BSA), dextran, sodium alginate and xanthan gum were used as model feeds and tested for their influences on FO performance with the active layer of the FO hollow fiber membrane facing the feed solution (AL-FS). The interactions between foulants were examined by using fluorescence spectroscopy, rotational rheometry and laser doppler micro-electrophoresis techniques. For a system containing combined organic foulants, it was found that viscosity was not the dominant factor governing FO membrane fouling as the decrease in viscosity did not always result in less fouling. The effect of divalent cations on the FO fouling behavior was also studied by adding CaCl2. The presence of calcium ions has exacerbated the flux decline, this occurred particularly for any combined organic foulants containing alginate, due to intermolecular bridging among alginate molecules. It is interesting to note that combined BSA+alginate caused moderate flux decline, while BSA and alginate alone did not cause any observable water flux loss. The (BSA+alginate) fouling became more severe with the presence of calcium ions

Anti-scaling and water flux enhancing effect of alginate in membrane distillation

This study focused on the effect of sodium alginate on the performance of direct contact membrane distillation (DCMD). The feed solution contained various combinations of sodium chloride, sodium sulfate and calcium chloride along with bovine serum albumin, xanthan gum and sodium alginate. Unlike findings from the majority of prior studies that suggested the presence of alginate in feed solution caused the deterioration of membrane process performance, our results indicated that sodium alginate exhibited anti-scaling properties and water flux enhancing effect. However, this interesting phenomenon was exhibited by sodium alginate under particular conditions only. Experiments performed with other organic foulants such as xanthan gum did not display the same trend. It is believed that the presence of a hydrophilic layer (calcium alginate gel), which is much less thermal conductive as compared to the PTFE membrane, on the top of the membrane could reduce the amount of heat dissipated due to evaporative cooling or reduce conductive heat loss in the membrane, thus enhancing the thermal efficiency of the system.Economic Development Board (EDB)Submitted/Accepted versionFunding support from Singapore Economic Development Board to Singapore Membrane Technology Centre is gratefully acknowledged

PHOTOCHEMICAL TREATMENT OF AN ACTUAL MUNICIPAL WASTEWATER BY MEANS OF UV, POTASSIUM PERSULFATE AND IRON

The photochemical treatment of an actual municipal wastewater (MWW) from wastewater treatment plant (WWTP) in Kazakhstan has been studied in the present work. The MWW has been taken after mechanical treatment stage and characterized. The photochemical treatment included the use of the photo-Fenton-like process in the batch photoreactor with a UV irradiation at 254 nm for 120 min. Experiments have been done without adjusting the initial pH of wastewater, which was around 7.7. Potassium persulfate (K2S2O8) was activated by means of UV and ferric ions, which led to generation of highly oxidative sulfate and peroxymonosulfate radicals. The concentration of Fe2+ ions ranged from 20 to 100 ppm, while the concentration of K2S2O8 was in between 5 and 25 mmol/L. 83% removal of total organic carbon (TOC) was achieved after 120 min of treatment using 15 mmol/L K2S2O8 and 20 ppm Fe2+, while 75% removal of total carbon (TC) was observed at 15 mmol/L K2S2O8 and 100 ppm Fe2+. As the carboxylic acids are common organic intermediates after photochemical treatment, the presence of formate and acetate anions in effluents were further detected on the ion chromatography