Transmembrane Pressure Build-up Research Articles

고율하수처리를 위한 생물막여과와 분리막 연계시스템 구성

Compared with the conventional MBR, granular sludge MBR due to the reactor compact design, outstanding settleability, and the ability of granules to withstand high organic loading rate has emerged with strong potential to overcome membrane fouling. The objective of this study is to configure an high-rate system using granular sludge sequencing batch reactor (GSSBR) and granular media filter (GMF) using sand and granular activated carbon (GAC)) coupled with membrane for enhancing membrane filtration performance and reducing membrane fouling in treating wastewater. As a result, GSSBR/GMF/MF configured system achieved higher efficiency than GSSBR-MBR and GSSBR/MF systems in reducing total organic carbon (TOC), total nitrogen (T-N) and total phosphorus (T-P), respectively. For transmembrane pressure (TMP), the GSSBR/GMP/MF developed much lower than that of GSSBR-MBR. In particular, the GSSBR/sand filter/MF system achieved lower TMP build-up than that of the GSSBR/GAC filter/MF system The above results indicate the GSSBR-MF coupled with GMF is more effective than conventional MBR using activated sludge in mitigating membrane fouling. The food/microorganism (F/M) ratio in the GSSBR and the biofilm growth in the GMF play an important role to reduce contaminants and TMP build-up.

Membrane photoreactor treatment of 1,4-dioxane-containing textile wastewater effluent: Performance, modeling, and fouling control

A membrane photoreactor (MPR) system was investigated for the purification of textile wastewater effluent containing 1,4-dioxane for potential reuse. The effects of TiO2 dosage, alkalinity, particulate matter, and sunlight radiation on the removal of 1,4-dioxane from the effluent were evaluated. The photocatalytic 1,4-dioxane degradation followed pseudo–first order reaction kinetics. A considerably large dose of TiO2 catalyst (5 g/L) was required for maximal 1,4-dioxane degradation by MPR. The high alkalinity (∼550 mg/L) of the textile wastewater effluent negatively affected the 1,4-dioxane degradation rate, whereas 1,4-dioxane degradation was not impacted by the presence of particulate matter. Solar photocatalysis of 1,4-dioxane was as effective as that achieved with UV lamps in the MPR, which could lead to energy savings. Continuous flow MPR was effective for continuous degradation of 1,4-dioxane; the unsteady- and steady-state performances were well-predicted at various hydraulic residence times (HRTs). The quality of the MPR product obtained at an HRT of 8.57 h satisfied the drinking water guidelines. The transmembrane pressure (TMP) buildup, which is indicative of fouling, was dependent on the TiO2 dose and permeate flux. The TMP buildup was marginal at low flux, but increased dramatically beyond a flux level of >60 L/m2-h. However, the fouling layer could be sufficiently removed by periodic backwashing, even at an extremely high flux of 100 L/m2-h. The membrane permeability was sustained without any sign of irreversible fouling during MPR treatment of textile wastewater effluents.

Hydraulically irreversible membrane fouling during coagulation–microfiltration and its control by using high-basicity polyaluminum chloride

The extent of hydraulically irreversible membrane fouling in a coagulation–filtration system depends on several factors, including properties of the coagulant. Effects of polyaluminum chloride (PACl) coagulant properties, specifically basicity and sulfation, were investigated by conducting long-term direct filtration experiments. Elemental analysis determined Al and Si to be the major foulants, though the Si/Al ratios of the foulants differed from those of coagulated floc particles. While floc particle size depended on the concentrations of sulfate ions and polymeric species in the PACls, floc-size changes did not affect transmembrane pressure (TMP) buildup and thus did not affect irreversible fouling. Differences in PACl basicity, which affected the distribution of aluminum species, resulted in changes to the degree of irreversible fouling.Pretreatment with high-basicity (71%) PACl was superior to pretreatment with normal-basicity (51%) PACl in reducing irreversible fouling and attenuating TMP buildup during filtration. Higher basicities resulted in less Al breakthrough and a decrease in the Si/Al ratio of the foulants. However, TMP buildup was the same for PACls with basicities of 71% and 90%; therefore, TMP buildup is not simply related to Al breakthrough and deposition. Increasing the basicity of PACls would be an effective way to reduce the amount of foulant deposited on the membrane by decreasing the amount of aluminum that passes through the membrane.

Control of fouling formation in membrane ultrafiltration by ultrasound irradiation

The increasing application of membrane filtration in water and wastewater treatment necessitates techniques to improve performance, especially in fouling control. Ultrasound is one promising technology for this purpose as cavitational effects facilitate continuous cleaning of the membrane. This research studied the ultrafiltration of lake water in systems with constant permeate flux under medium frequency (45 kHz) ultrasound irradiation. Fouling was investigated by monitoring transmembrane pressure (TMP) using continuous or intermittent ultrasound irradiation and dead-end or crossflow operation. Best performance was observed with continuous ultrasound irradiation in crossflow mode. Intermittent irradiation reduced the rate of TMP build-up but nevertheless allowed irreversible fouling to develop.

Membrane bioreactor (MBR) for wastewater treatment: Filtration performance evaluation of low cost polymeric and ceramic membranes

This work compares the filtration performance of low cost filters for wastewater treatment in a submerged MBR. Two filters viz. commercial nylon mesh of 30 μm pore size and 2–6 μm macroporous ceramic filters prepared from bagasse fly ash were investigated. Critical flux was measured by flux stepping method, and the MBR filtration performance was monitored in terms of flux, transmembrane pressure (TMP) build-up and permeate quality. It was observed that both the nylon mesh and the ash filter are good solid–liquid separators with low TMP build-up. However, the ash filter displayed higher critical flux that was comparable to commercial microporous membranes; it also does not require the formation of a secondary filtration layer to ensure consistently high suspended solids retention.

Effects of super-powdered activated carbon pretreatment on coagulation and trans-membrane pressure buildup during microfiltration

As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment.

Evaluating submicron-sized activated carbon adsorption for microfiltration pretreatment

Submicron powdered activated carbon (PAC) rapidly adsorbed natural organic matter (NOM) fromwater samples: a batch test of the adsorption kinetics showed that the NOM concentration dropped substantially within 15 s and then leveled off. In a tubular flow reactor test, NOM removal after a 15 s contact time was almost the same as removal values attained at longer contact times. Laboratory-scale and bench-scale pilotplant ceramic microfiltration (MF) experiments with submicron PAC adsorption pretreatment were conducted to evaluate NOM removal and to examine the effect of the PAC on filterability. The laboratory scale MF experiment revealed that PAC adsorption pretreatment could be accomplished with a detention (2.4 s) that was much shorter than the time expected from the adsorption kinetics test. This result suggests that adsorption pretreatment for MF could be accomplished by adding the submicron PAC directly into the feed line to the membrane and that installation of a special PAC contactor before the membrane unit is unnecessary. Although micron PAC rather than submicron PAC was used unintentionally in the pilot plant experiment, these PAC showed much better NOM removal than normal PAC, and no adverse effects, such as transmembrane pressure buildup and reversible or irreversible membrane fouling, were observed.

Enhancing an adsorption-membrane hybrid system with microground activated carbon

The effects of particle size and mixing method of adsorbent during pretreatment in a microfiltration system were investigated. Micrometre-size powdered activated carbons (PACs) obtained by pulverization of an as-received PAC removed natural organic matter (NOM) from water much more efficiently than the as-received PAC, without additional membrane fouling and trans-membrane pressure buildup. The dosage of micrometre-size PAC required for pretreatment was one-sixth the equipollent dosage of the as-received PAC. The coagulant – PAC dosing sequence did not affect the extent of NOM removal, suggesting that the reduction of PAC-pore-blocking macromolecules by coagulation before PAC adsorption was not a key factor in improving the final extent of NOM removal. The mechanism of the enhanced adsorption by micrometre-size PAC seems to involve increases in the adsorption capacity itself, as well as increases in adsorption kinetics.