Effect of powdered activated carbon type on the performance of an adsorption-microfiltration submerged hollow fiber membrane hybrid system

Submerged membrane/adsorption hybrid process in water reclamation and concentrate management-a mini review

Clean water shortage is a major global problem due to escalating demand resulting from increasing human population growth and industrial activities, decreasing freshwater resources and persistent droughts. Recycling and reuse of wastewater by adopting efficient reclamation techniques can help solve this problem. However, wastewater contains a wide range of pollutants, which require removal before it may be reused. Adsorption and membrane processes are two successful treatments used to remove most of these pollutants. Their efficiency increases when these processes are integrated as observed, for example in a submerged membrane adsorption hybrid system (SMAHS). It uses coarse air bubbling/sparging to produce local shear which minimises reversible membrane fouling, improves performance and extends the life of the membrane. Additionally, the adsorbent acts as a buoyant media that produces an extra shearing effect on the membrane surface, reduces membrane resistance and increases flux. In addition, it adsorbs the organics that would otherwise deposit on and cause fouling of the membrane. The use of activated carbon (AC) adsorbent in SMAHS is very effective in removing most pollutants including natural organic matter (NOM) and organic micropollutants (OMPs) from wastewaters and membrane concentrate wastes, the latter being a serious problem in practical applications of the reverse osmosis process. However, certain NOM fractions and OMPs (i.e. hydrophilic and negatively charged ones) are not efficiently removed by AC. Other adsorbents need to be explored for their effective removal.

Algal fouling and extracellular organic matter removal in powdered activated carbon-submerged hollow fiber ultrafiltration membrane systems

In this work, the effect of powdered activated carbon (PAC) on fouling by algal solution during ultrafiltration using two different PAC dosing strategies: pre-depositing PAC onto the membrane surfaces or the conventional addition of PAC to the bulk feed. The addition of PAC by either mode improved the removal of extracellular organic matter (EOM) from the algal solution. However, for the pre-deposition mode, increasing the PAC amount from 0 to 2.1 g caused a steady increase in the membrane fouling rate (from 0.4 to 1.4 kPa/h), whereas the opposite result (from 0.4 down to 0.1 kPa/h) was found for the conventional PAC dosing mode. This is likely due to the differences in the initial arrangement of algal cells and PAC along the cake layer depths. The pre-deposited PAC avoided contact between cells and membranes, but aggravated the deformation of the cells and hindered their back-transport to the bulk solution. Furthermore, although the effect of PAC on the EOM fouling was marginal, there were highly synergistic effects when cells and EOM were present together in the PAC pre-deposition mode. Changes in the PAC dosing mode also altered the PAC-membrane interactions, inducing a higher cleaning efficiency of backwash for the conventionally-dosed PAC from membrane surfaces than that for the pre-deposited PAC.

Technical feasibility study of a low-cost hybrid PAC-UF system for wastewater reclamation and reuse: a focus on feedwater production for low-pressure boilers

This study has applied the concept of the hybrid PAC-UF process in the treatment of the final effluent of the palm oil industry for reuse as feedwater for low-pressure boilers. In a bench-scale set-up, a low-cost empty fruit bunch-based powdered activated carbon (PAC) was employed for upstream adsorption of biotreated palm oil mill effluent (BPOME) with the process conditions: 60 g/L dose of PAC, 68 min of mixing time and 200 rpm of mixing speed, to reduce the feedwater strength, alleviate probable fouling of the membranes and thus improve the process flux (productivity). Three polyethersulfone ultrafiltration membranes of molecular weight cut-off (MWCO) of 1, 5 and 10 kDa were investigated in a cross-flow filtration mode, and under constant transmembrane pressures of 40, 80, and 120 kPa. The permeate qualities of the hybrid processes were evaluated, and it was found that the integrated process with the 1 kDa MWCO UF membrane yielded the best water quality that falls within the US EPA reuse standard for boiler-feed and cooling water. It was also observed that the permeate quality is fit for extended reuse as process water in the cement, petroleum and coal industries. In addition, the hybrid system's operation consumed 37.13 Wh m^-3 of energy at the highest applied pressure of 120 kPa, which is far lesser than the typical energy requirement range (0.8-1.0 kWh m^-3) for such wastewater reclamation.

A hybrid froth flotation-filtration system as a pretreatment for oil sands tailings pond recycle water management: Bench- and pilot-scale studies

Through sustainable water management, oil sands companies are working to reduce their reliance on fresh water by minimizing the amount of water required for their operations and by recycling water from tailings ponds. This study was the first pilot-scale testing of a hybrid technology consisting of froth flotation combined with filtration through precoated submerged stainless steel membranes used to treat recycle water from an oil sands facility. The results indicated that the most important factor affecting the performance of the hybrid system was the influent water quality. Any rise in the levels of suspended solids or total organic carbon of the feed water resulted in changes of chemical consumption rates, flux rates, and operating cycle durations. The selections of chemical type and dosing rates were critical in achieving optimal performance. In particular, the froth application rate heavily affected the overall recovery of the hybrid system as well as the performance of the flotation process. Optimum surfactant usage to generate froth (per liter of treated water) was 0.25 mL/L at approximately 2000 NTU of influent turbidity and 0.015 mL/L at approximately 200 NTU of influent turbidity. At the tested conditions, the optimal coagulant dose was 80 mg/L (as Al) at approximately 2000 NTU of influent turbidity and <40 mg/L (as Al) at approximately 200 NTU of influent turbidity. Precoat loading per unit membrane surface area tested during the pilot study was approximately 30 g/m(2). The results of this study indicated that this hybrid technology can potentially be considered as a pre-treatment step for reverse osmosis treatment of recycle water.

Submerged microfiltration membrane coupled with alum coagulation/powdered activated carbon adsorption for complete decolorization of reactive dyes

Even the presence of very low concentrations of dyes (1mgL(-1)) in the effluent is highly visible and is considered aesthetically undesirable. It must be removed from wastewater completely. This study systematically evaluates the performance of adsorption (three kinds of powdered activated carbons), coagulation (AlCl3.6H2O) and membrane (submerged hollow fiber microfiltration) processes individually in treating two kinds of reactive dyes (Orange 16 and Black 5) and then using a hybrid process with combined coagulation-adsorption-membrane treatment system. Adsorption capacity and kinetics of Orange 16 were much higher and faster than those of Black 5. The dye removal efficiency by coagulation was highly dependent on dye concentration and solution pH. The hybrid process performance was far more superior that individual process in removing both kinds of dyes. It was evident that the combined coagulation-adsorption-membrane process has a great potential application for complete reactive dye removal, production of high-quality treated water and allows the reduction in the use of coagulant and adsorbent.