Hybrid ferrihydrite-MF/UF membrane filtration for the simultaneous removal of dissolved organic matter and phosphate

Novel Fe/Ca oxide co-embedded coconut shell biochar for phosphorus recovery from agricultural return flows

Efficient elimination and recovery of phosphorus from agricultural return flows are crucial for effective eutrophication management and phosphorus reuse. In this study, a neutral Fe/Ca oxide co-embedded biochar (FCBC) was synthesized using calcium peroxide and ferrous chloride as precursors for phosphate recovery from agricultural return flows. FCBC possesses a highly intricate pore structure and an abundance of surface-active groups. Fe/Ca oxides were loaded onto the biochar in the form of Ca2Fe2O5, Fe2O3, and CaCO3. FCBC demonstrated a broad pH tolerance range (pH = 6-12) in the aquatic environment. The maximum saturation adsorption capacity was 53.31 mg g-1. Phosphorus removal is influenced by Ca3(PO4)2 generation, intra-particle diffusion, and electrostatic attraction. The produced FCBC showed exceptional phosphorus removal efficiency in the presence of various anions, except for wastewater with high concentrations of SO4 2-, CO3 2-, HCO3 -, and F- (>500 mg L-1). FCBC can effectively remove phosphorus from agricultural return flows and reduce the risk of the water environment. Returning it to the field can also mitigate the depletion of phosphorus resources, effectively reduce carbon emissions from farmland, improve soil fertility, and realize multiple benefits.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Insights into graphene oxide/ferrihydrite adsorption as pretreatment during ultrafiltration: Membrane fouling mitigation and disinfection by-product control

In this study, a novel adsorbent of graphene oxide (GO) incorporated ferrihydrite (FH) was fabricated and integrated with ultrafiltration (UF) to remove natural organic matter (NOM), the crucial cause of membrane fouling and major precursor of disinfection by-products (DBPs). Compared with FH and powdered activated carbon (PAC), GO/FH exhibited superior removal for high molecular weight (HMW) humic- and fulvic-like substances and low molecular weight (LMW) protein. The cake layer formed by GO/FH alleviated the deposition of NOM on membrane surface or inside membrane pores. Therefore, GO/FH reduced 89% and 95% total fouling resistance and irreversible membrane resistance, respectively, together with the lowest increment of transmembrane pressure. Pearson correlation analysis indicated that DOC, rather than specific ultraviolet absorbance (SUVA) and UV₂₅₄, was significantly correlated to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) when SUVA was below 4 L/mg-C.m. Whilst the HMW NOM (1-20 kDa) was highly related to dibromochloromethane (DBCM) (r = 0.98-1), the LMW fraction (< 1 kDa) was correlated with dibromochloromethane (TCAA) and dichloroacetic acid (DCAA) (r = 0.88-0.98). Inspiringly, GO/FH-UF reduced 90% of carbonaceous DBPs, the concentrations of which well met the WHO Guidelines. In summary, GO/FH-UF substantially alleviated membrane fouling and dramatically reduced DBP formation potential.

Retarding performance of the vadose zone for nitrogen pollutants derived from municipal solid waste landfills in the red bed zone

Nitrogen pollutants such as ammonia and nitrates cause soil and groundwater contamination at municipal solid waste landfill (MSWL) sites due to leachate leakage. Here, the migration of nitrogen pollutants in the vadose zone of the red bed (VZRB) at a MSWL site was studied by static adsorption batch experiments and one-dimensional simulated migration experiments. The results indicated that the soil in the red bed did not adsorb nitrates. Chemical adsorption and monolayer adsorption of the soil played dominant roles during ammonia adsorption in the VZRB, which was best fitted by the pseudo-second-order kinetic equation ( [Formula: see text] = 0.99) and the Langmuir model. The ammonia adsorption capacity of the soil was the highest (Q_m = 2.041 mg·g^-1) at 318 K. It was due to the endothermic and non-spontaneous chemical adsorption of ammonia, whose enthalpy change (ΔH) reached 20.995 kJ·mol^-1 and Gibbs free energy ranged from 8.469 to 8.706 kJ·mol^-1. Chloride penetration tests indicated that the diffusion coefficient and migration speed reached 0.0515 cm²·h^-1 and 0.0833 cm·h^-1, respectively, in the clay layer under the MSWL sites. The average hysteresis diffusion coefficients of ammonia in the simulated soil columns leached by ammonium chloride solution (SSCAC) and by the leachate from MSWL (SSCL) were 1.129 and 1.400, respectively. After the leaching experiments, the clay pore structure was saturated, and the specific surface area decreased. The absorption peak intensities of clay functional groups, including carboxyl, alkyne, and hydroxyl groups, were reduced. The ammonia content in the soil of SSCAC decreased from the top (14.51 mg·kg^-1) to the bottom (3.14 mg·kg^-1) and in the SSCL from 24.96 mg·kg^-1 to 5.05 mg·kg^-1, respectively. Thus, the impermeable clay layer and VZRB helped in retardation of ammonia leakage from MSWL sites. This was due to the blockage of seepage, ammonia mechanical filtration, ammonia monolayer chemical adsorption, and the reaction between the functional groups and ammonia in the VZRB underneath the MSWL sites.

Effects of Chemical Cleaning on the Ageing of Polyvinylidene Fluoride Microfiltration and Ultrafiltration Membranes Fouled with Organic and Inorganic Matter

Herein, the effects of cleaning with sodium hydroxide and citric acid solutions as cleaning reagents on the changes in the properties of two hollow-fiber PVDF microfiltration (MF) and ultrafiltration (UF) membranes fouled with organic and inorganic matter were investigated. Accelerated membrane ageing was induced by use of high concentrations of tannic acid and iron oxide (Fe₂O₃) particles in the feed water; these conditions were kept with different membrane soaking times to observe temporal effects. It was found that tannic acid molecules adsorb onto the membrane surface that results in changes in surface characteristics, particularly surface functional groups that are responsible for enhancing membrane’s hydrophilicity. Experimental results demonstrate that NaOH had a stronger effect on the tensile strength and surface chemistry of the fouled MF and UF membranes than citric acid. Prediction of lifetime by an exponential (decay) model confirmed that the UF membrane cleaned with NaOH would be aged within about 1.8 years and the MF membrane after about 5 years, at cleaning every 15 days, downtime 2 h per cleaning, when a 10% tensile strength decrease against the original membrane is allowed.

Extracellular electron transfer influences the transport and retention of ferrihydrite nanoparticles in quartz sand coated with Shewanella oneidensis biofilm

Microbial biofilm has been found to impact the mobility of nanoparticles in saturated porous media by altering physicochemical properties of collector surface. However, little is known about the influence of biofilm's biological activity on nanoparticle transport and retention. Here, the transport of ferrihydrite nanoparticles (FhNPs) was studied in quartz sands coated with biofilm of Shewanella oneidensis MR-1 that is capable of reducing Fe(III) through extracellular electron transfer (EET). It was found that MR-1 biofilm coating enhanced FhNPs' deposition under different pH/ionic strength conditions and humic acid concentrations. More importantly, when the influent electron donor (glucose) concentration was increased to promote biofilm's EET activity, the breakthrough of FhNPs in biofilm-coated sands was inhibited. A lack of continuous and stable supply of electron donor, on the contrary, led to remobilization and release of the originally retained FhNPs. Column experiments with biofilm of EET-deficient MR-1 mutants (ΔomcA/ΔmtrC and ΔcymA) further indicated that the impairment of EET activity decreased the retention of FhNPs. It is proposed that the effective surface binding and adhesion of FhNPs that is required by direct EET cannot be neglected when evaluating the transport of FhNPs in sands coated with electroactive biofilm.

Fe(III) loaded chitosan-biochar composite fibers for the removal of phosphate from water

Excess phosphorous (P) in aquatic systems causes adverse environmental impacts including eutrophication. This study fabricated Fe(III) loaded chitosan-biochar composite fibers (FBC-N and FBC-C) from paper mill sludge biochar produced under N₂ (BC-N) and CO₂ (BC-C) conditions at 600 °C for adsorptive removal of phosphate from water. Investigations using SEM/EDX, XPS, Raman spectroscopy, and specific surface area measurement revealed the morphological and physico-chemical characteristics of the adsorbent. The Freundlich isotherm model well described the phosphate adsorption on BC-N, while the Redlich-Peterson model best fitted the data of three other adsorbents. The maximum adsorption capacities were 9.63, 8.56, 16.43, and 19.24 mg P g^-1 for BC-N, BC-C, FBC-N, and FBC-C, respectively, indicating better adsorption by Fe(III) loaded chitosan-biochar composite fibers (FBCs) than pristine biochars. The pseudo-first-order kinetic model suitably explained the phosphate adsorption on BC-C and BC-N, while data of FBC-N and FBC-C followed the pseudo-second-order and Elovich model, respectively. Molecular level observations of the P K-edge XANES spectra confirmed that phosphate associated with iron (Fe) minerals (Fe-P) were the primary species in all the adsorbents. This study suggests that FBCs hold high potential as inexpensive and green adsorbents for remediating phosphate in contaminated water, and encourage resource recovery via bio-based management of hazardous waste.

Effects of Ferrihydrite-Impregnated Powdered Activated Carbon on Phosphate Removal and Biofouling of Ultrafiltration Membrane

The presence of multiple contaminant species in surface waters makes surface water treatment difficult to accomplish through a single process. Herein, we evaluated the ability of an integrated adsorption/ultrafiltration (UF) membrane filtration system to simultaneously remove phosphates and dissolved organic matter (DOM). When bare powdered activated carbon (PAC) and PAC impregnated with amorphous ferrihydrite (FHPAC) adsorbents were compared, FHPAC showed a greater adsorption rate and capacity for phosphate. FHPAC had a phosphate adsorption capacity of 2.32 mg PO43−/g FHPAC, even when DOM was present as a competing adsorbate. In a lab-scale hybrid FHPAC-UF system (i.e. integrated adsorption by FHPAC with UF membrane filtration), irreversible membrane fouling was ca. three times lower than that in a PAC-UF system. When membrane fouling in the PAC-UF system was described with pore blockage models, we found that the main cause of fouling was bacterial deposition on the membrane surface. CLSM analysis determined that the chemical composition of foulants in the PAC-UF system included higher proportions of proteins, nucleic acids, and alpha-polysaccharides than that in the FHPAC-UF system. Overall, FHPAC’s ability to undergo ligand exchanges with DOM helped to reduce the nutrients and bacteria that cause biofouling to accumulate on the membrane surface.

Dissolved organic nitrogen in wastewater treatment processes: Transformation, biosynthesis and ecological impacts

With the upgrade of wastewater treatment plants (WWTPs) to meet more stringent discharge limits for nutrients, dissolved organic nitrogen (DON) is present at an increasing percentage (up to 85%) in the effluent. Discharged DON is of great environmental concern due to its potentials in stimulating algal growth and forming toxic nitrogenous disinfection by-products (N-DBPs). This article systematically reviewed the characteristics, transformation and ecological impacts of wastewater DON. Proteins, amino acids and humic substances are the abundant DON compounds, but a large fraction (nearly 50%) of DON remains uncharacterized. Biological treatment processes play a dominant role in DON transformation (65-90%), where DON serves as both nutrient and energy sources. Despite of the above progress, critical knowledge gaps remain in DON functional duality, relationship with dissolved inorganic nitrogen (DIN) species, and coupling/decoupling with the dissolved organic carbon (DOC) pool. Development of more rapid and accurate quantification methods, modeling transformation processes, and assessing DON-associated eutrophication and N-DBP formation risks should be given priority in further investigations.

Comparison between ferrihydrite adsorption and full-scale advanced drinking water treatment processes for controlling bacterial regrowth potential

Bacterial regrowth in drinking water systems is a threat to public health. In this study, ferrihydrite (Fh) adsorption was compared with advanced drinking water treatment processes (ADWTP) during one and a half years of sampling to test the reduction in assimilable organic carbon (AOC) and bacterial regrowth potential (BRP). Dissolved organic matter (DOM) was removed by Fh through ligand exchange and electrostatic interaction. The DOM removal was higher below pH 6 due to protonation of Fh surfaces. The ADWTP exhibited higher removal rates of DOM than Fh and lower phosphate removal rates than Fh. Excitation-emission matrix (EEM) and size exclusion chromatography (SEC) revealed that Fh removed aromatic DOM larger than 1000 Da, while the biological activated carbon (BAC) of ADWTP could remove DOM smaller than 1000 Da. These differences of organic compositions resulted in the lowest AOC of BAC treated water, and the lowest BRP of Fh-treated water, indicating that it was the most biostable water. Phosphate addition experiments illustrated that phosphorus was the primary rate limiting nutrient, indicating that the higher phosphate removal of Fh made it possible to produce waters with lower BRP than ADWTP. Therefore, BRP is considered to be a better indicator of bacterial regrowth than AOC when phosphorus is a rate-limiting nutrient, as is the case with the Fh treatment.

Development of nanoscale zirconium molybdate embedded anion exchange resin for selective removal of phosphate

Development of a selective adsorbent with an enhanced removal efficiency for phosphate from wastewater is urgently needed. Here, a hybrid adsorbent of nanoscale zirconium molybdate embedded in a macroporous anion exchange resin (ZMAE) is proposed for the selective removal of phosphate. The ZMAE consists of a low agglomeration of zirconium molybdate nanoparticles (ZM NPs) dispersed within the structure of the anion exchange (AE) resin. As major results, the phosphate adsorption capacity of the ZMAE (26.1 mg-P/g) in the presence of excess sulfate (5 mM) is superior to that of the pristine AE resin (1.8 mg-P/g) although their phosphate uptake capacity was similar in the absence of sulfate and these results were supported by the high selectivity coefficient of the ZMAE toward phosphate over sulfate (S_PO4/SO4) more than 100 times compared to the pristine AE resin. This superior selective performance of the ZMAE for phosphate in the presence of sulfate ions is well explained by the role of the ZM NPs that contributed to 69% of the phosphate capacity which is based on an observation that the phosphate adsorption capacity of the ZM NPs is not affected by the presence of sulfate. In addition, the behavior of the selective phosphate removal by the ZMAE was well demonstrated by not only in the batch mode experiment with simulated Mekong river water and representative wastewater effluent but also in a column test.

Enhanced transport of ferrihydrite colloid by chain-shaped humic acid colloid in saturated porous media

Both humic acid and colloid particle size effectively regulate colloid transport. However, little is known about effect of particle size and configuration of humic acid colloid (HA_colloid) on enhanced-transport of ferrihydrite colloid (FH_colloid) in porous media. Co-transport of HA_colloid and FH_colloid at different pH was systematically investigated by monitoring breakthrough curves (BTCs) in saturated sand columns. The colloid transport model and the (X)DLVO theory were used to reveal the mechanism of HA_colloid-enhanced FH_colloid transport in the columns. Results showed that HA_colloid enhanced FH_colloid transport in neutral and alkaline conditions. In neutral conditions, small HA_colloid (F-HA_colloid) with chain-shaped structure enhanced FH_colloid transport more prominently than pristine granular HA_colloid. The chain-shaped F-HA_colloid caused osmotic repulsion and elastic-steric repulsion between colloids and sand, leading to enhanced transport. However, the granular HA_colloid readily occurred as deposition due to attachment and straining, which decreased the enhanced transport of FH_colloid. In alkaline conditions, both HA_colloid and F-HA_colloid were chain-shaped, with longer chains of HA_colloid than F-HA_colloid. Ferrihydrite colloid transport was enhanced by HA_colloid more significantly than F-HA_colloid due to stronger repulsion between mixed HA_colloid-FH_colloid and sand. It suggested that regulation of particle size and morphology of HA_colloid would enhance FH_colloid transport and further help in understanding FH_colloid-facilitated contaminants transport in porous media.

Reducing ultrafiltration membrane fouling during potable water reuse using pre-ozonation

Wastewater reclamation has increasingly become popular to secure potable water supply. Low-pressure membrane processes such as microfiltration (MF) and ultrafiltration (UF) play imperative roles as a barrier of macromolecules for such purpose, but are often limited by membrane fouling. Effluent organic matter (EfOM), including biopolymers and particulates, in secondary wastewater effluents have been known to be major foulants in low-pressure membrane processes. Hence, the primary aim of this study was to investigate the effects of pre-ozonation as a pre-treatment for UF on the membrane fouling caused by EfOM in secondary wastewater effluents for hydrophilic regenerated cellulose (RC) and hydrophobic polyethersulfone (PES) UF membranes. It was found that greater fouling reduction was achieved by pre-ozonation for the hydrophilic RC membrane than the hydrophobic PES membrane at increasing ozone doses. In addition, the physicochemical property changes of EfOM, including biopolymer fractions, by pre-ozonation were systemically investigated. The classical pore blocking model and the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theories were employed to scrutinize the fouling alleviation mechanism by pre-ozonation. As a result, the overarching mechanisms of fouling reduction were attributed to the following key reasons: (1) Ozone degraded macromolecules such as biopolymers like proteins and polysaccharides into smaller fractions, thereby increasing free energy of cohesion of EfOM and rendering them more hydrophilic and stable; (2) pre-ozonation augmented the interfacial free energy of adhesion between foulants and the RC/PES membranes, leading to the increase of repulsions and/or the decrease of attractions; and (3) pre-ozonation prolonged the transition from pore blocking to cake filtration that was a dominant fouling mechanism, thereby reducing fouling.

Analysis of adsorption processes of dissolved organic matter (DOM) on ferrihydrite using surrogate organic compounds

Ferrihydrite (Fh) has been recently used in water treatment for removing dissolved organic matter (DOM), but its governing interactions with low-molecular weight DOM are largely unknown. This study aimed to elucidate the influence of chemical structure of DOM on the interactions between functional groups of DOM and Fh using various surrogates representing DOM in natural waters. We tested four surrogate compounds: L-glutamic acid, resorcinol, L-serine, and tannic acid, which represent the main chemical groups of carboxylic and hydroxyl groups; and the Suwannee River NOM (SRNOM) that represents the composition of DOM in natural aquatic systems. Batch adsorption experiments revealed that the DOM adsorption onto Fh was significantly influenced by the steric arrangements of -COOH and -OH functional groups. Both L-serine with α-carboxyl group and resorcinol with hydroxyl groups in meta-position were marginally removed by Fh, indicating that the adsorption of DOM on Fh was determined by their chemical structures and the relative positions of carboxylate and hydroxyl groups. The adsorption of L-glutamic acid was controlled by the pH-dependent ligand exchange of γ-carboxyl groups, which was similar to the SRNOM adsorption. In contrast, adsorption of tannic acid was not affected by pH, which can be explained by a two-step adsorption, namely, ligand exchange followed by multi-layer adsorption to the partitioning phase. The results of kinetic experiments demonstrated that adsorption of DOM by Fh was significant and rapid. The kinetic adsorption data can be expressed by the pseudo-second-order equation, indicating that the adsorption step might be the rate-limiting step.

Phosphate adsorption on novel hydrogel beads with interpenetrating network (IPN) structure in aqueous solutions: kinetics, isotherms and regeneration

Adsorption has attracted much attention for its effectiveness, low cost and the possibility of regeneration among many phosphorus removal methods.

Study on mechanism of algal inactivation and pollution removal by Fe-ACF electro Fenton-like process

Algae inactivation and algal metabolic pollutant removal of Chlorella and Duneliella salina from seawater by the Fe-ACF electro Fenton-like process has been studied. The experiments were conducted at neutral condition of pH 8.3 (raw water) and 6.2 to break through the limit of strong acidic conditions. Experimental results indicated that the Fe-ACF electro Fenton-like process has a good effect for algae inactivation and for pollutant removal in neutral conditions, and pH has no obvious effect for the inactivation of algae. At optimum conditions, the inactivation efficiency for algae could reach up to 98%. A pH of 8.3 is more favorable for pollutant removal. Under neutral pH conditions, the coupling effect of indirect oxidation of •OH, direct oxidation of free chlorine and coagulation and adsorption of ferric and ferrous hydroxy complexes in the electro Fenton-like process was achieved, and the coupling effect promotes the inactivation of algae and the removal of metabolic pollutants.