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.

Mathematical modeling of arsenic(V) adsorption onto iron oxyhydroxides in an adsorption-submerged membrane hybrid system

The adsorption of arsenic (V), As(V), on two porous iron oxyhydroxide-based adsorbents, namely, micro-sized tetravalent manganese feroxyhyte (μTMF) and granular ferric hydroxide (μGFH), applied in a submerged microfiltration membrane hybrid system has been investigated and modeled. Batch adsorption tests were carried out to determine adsorption equilibrium and kinetics parameters of As(V) in a bench-scale slurry reactor setup. A mathematical model has been developed to describe the kinetic data as well as to predict the As(V) breakthrough curves in the hybrid system based on the homogeneous surface diffusion model (HSDM) and the corresponding solute mass balance equation. The kinetic parameters describing the mass transfer resistance due to intraparticle surface diffusion (D_s) involved in the HSDM was determined. The fitted D_s values for the smaller (1-63 μm) and larger (1-250 μm) diameter particles of μGFH and μTMF were estimated to be 1.09 × 10^-18 m²/s and 1.53 × 10^-16 m²/s, and 2.26 × 10^-18 m²/s and 1.01 × 10^-16 m²/s, respectively. The estimated values of mass transfer coefficient/ kinetic parameters are then applied in the developed model to predict the As(V) concentration profiles in the effluent of the hybrid membrane system. The predicted results were compared with experimental data for As(V) removal and showed an excellent agreement. After validation at varying adsorbent doses and membrane fluxes, the developed mathematical model was used to predict the influence of different operation conditions on As(V) effluent concentration profile. The model simulations also exhibit that the hybrid system benefits from increasing the amount of adsorbent initially dosed and from decreasing the membrane flux (increasing the contact time).

Polymer-based spherical activated carbon - ultrafiltration (UF-PBSAC) for the adsorption of steroid hormones from water: Material characteristics and process configuration

The European Union has proposed the value of 1 ng L^-1 as a drinking water quality standard for estradiol. With conventional technologies only partially removing estradiol, the investigation of novel alternatives is more than ever required. Tagliavini and Schäfer proposed that the use of a thin activated carbon layer combined with a membrane is worth considering. In this work, the process was further advanced through a systematic investigation of the role of activated carbon size, activation and surface chemistry on the removal of estradiol. The use of smaller carbon particles allows reaching the ambitious target value of 1 ng L^-1 in a millimetric layer. Further, adsorption kinetic enhancement by increasing the oxygen content on the carbon improves the removal from 96 to 99 % (for a layer of 2 mm) for OH-containing pollutants such as estradiol. High removal, together with low pressure and no by-product formation, are characteristics that make the UF-PBSAC a promising and competitive approach.

Drinking water treatment using a submerged internal-circulation membrane coagulation reactor coupled with permanganate oxidation

A submerged internal circulating membrane coagulation reactor (MCR) was used to treat surface water to produce drinking water. Polyaluminum chloride (PACl) was used as coagulant, and a hydrophilic polyvinylidene fluoride (PVDF) submerged hollow fiber microfiltration membrane was employed. The influences of trans-membrane pressure (TMP), zeta potential (ZP) of the suspended particles in raw water, and KMnO₄ dosing on water flux and the removal of turbidity and organic matter were systematically investigated. Continuous bench-scale experiments showed that the permeate quality of the MCR satisfied the requirement for a centralized water supply, according to the Standards for Drinking Water Quality of China (GB 5749-2006), as evaluated by turbidity (<1 NTU) and total organic carbon (TOC) (<5mg/L) measurements. Besides water flux, the removal of turbidity, TOC and dissolved organic carbon (DOC) in the raw water also increased with increasing TMP in the range of 0.01-0.05MPa. High ZP induced by PACl, such as 5-9mV, led to an increase in the number of fine and total particles in the MCR, and consequently caused serious membrane fouling and high permeate turbidity. However, the removal of TOC and DOC increased with increasing ZP. A slightly positive ZP, such as 1-2mV, corresponding to charge neutralization coagulation, was favorable for membrane fouling control. Moreover, dosing with KMnO₄ could further improve the removal of turbidity and DOC, thereby mitigating membrane fouling. The results are helpful for the application of the MCR in producing drinking water and also beneficial to the research and application of other coagulation and membrane separation hybrid processes.

Performance of biological magnetic powdered activated carbon for drinking water purification

Combining the high adsorption capacity of powdered activated carbon (PAC) with magnetic properties of iron oxide nanoparticles (NPs) leads to a promising composite material, magnetic PAC or MPAC, which can be separated from water using magnetic separators. We propose MPAC as an alternative adsorbent in the biological hybrid membrane process and demonstrate that PAC covered with magnetic NPs is suitable as growth support for heterotrophic and nitrifying bacteria. MPAC with mass fractions of 0; 23; 38 and 54% maghemite was colonized in small bioreactors for over 90 days. Although the bacterial community composition (16s rRNA analysis) was different on MPAC compared to PAC, NPs neither inhibited dissolved organic carbon and ammonia biological removals nor contributed to significant adsorption of these compounds. The same amount of active heterotrophic biomass (48 μg C/cm(3)) developed on MPAC with a mass fraction of 54% NPs as on the non-magnetic PAC control. While X-ray diffraction confirmed that size and type of iron oxides did not change over the study period, a loss in magnetization between 10% and 34% was recorded.

Ammonia removal in the carbon contactor of a hybrid membrane process

The hybrid membrane process (HMP) coupling powdered activated carbon (PAC) and low-pressure membrane filtration is emerging as a promising new option to remove dissolved contaminants from drinking water. Yet, defining optimal HMP operating conditions has not been confirmed. In this study, ammonia removal occurring in the PAC contactor of an HMP was simulated at lab-scale. Kinetics were monitored using three PAC concentrations (1-5-10 g L(-1)), three PAC ages (0-10-60 days), two temperatures (7-22 °C), in ambient influent condition (100 μg N-NH4 L(-1)) as well as with a simulated peak pollution scenario (1000 μg N-NH4L(-1)). The following conclusions were drawn: i) Using a colonized PAC in the HMP is essential to reach complete ammonia removal, ii) an older PAC offers a higher resilience to temperature decrease as well as lower operating costs; ii) PAC concentration inside the HMP reactor is not a key operating parameter as under the conditions tested, PAC colonization was not limited by the available surface; iii) ammonia flux limited biomass growth and iv) hydraulic retention time was a critical parameter. In the case of a peak pollution, the process was most probably phosphate-limited but a mixed adsorption/nitrification still allowed reaching a 50% ammonia removal. Finally, a kinetic model based on these experiments is proposed to predict ammonia removal occurring in the PAC reactor of the HMP. The model determines the relative importance of the adsorption and biological oxidation of ammonia on colonized PAC, and demonstrates the combined role of nitrification and residual adsorption capacity of colonized PAC.

Removal of emerging contaminants by simultaneous application of membrane ultrafiltration, activated carbon adsorption, and ultrasound irradiation

Advanced wastewater treatment is necessary to effectively remove emerging contaminants (ECs) with chronic toxicity, endocrine disrupting effects, and the capability to induce the proliferation of highly resistant microbial strains in the environment from before wastewater disposal or reuse. This paper investigates the efficiency of a novel hybrid process that applies membrane ultrafiltration, activated carbon adsorption, and ultrasound irradiation simultaneously to remove ECs. Diclofenac, carbamazepine, and amoxicillin are chosen for this investigation because of their assessed significant environmental risks. Removal mechanisms and enhancement effects are analysed in single and combined processes. The influence of adsorbent dose and ultrasonic frequency to EC removal are also investigated. Results suggest that adsorption is probably the main removal mechanism and is affected by the nature of ECs and the presence of other components in the mixture. Almost complete removals are achieved in the hybrid process for all ECs.