Application of coagulation‐ultrafiltration‐nanofiltration in a pilot study for Tai Lake water treatment

Abstract

In this study, the inline coagulation was combined with ultrafiltration and nanofiltration (UF‐NF) in a pilot study for Tai Lake water treatment. The results showed that the combination process was very effective for Tai Lake water treatment in terms of organic removal and membrane fouling control. With inline coagulation, no irreversible membrane fouling was observed for either UF or NF at fluxes of 65–90 and 22–26 L/(m2 hr), respectively. The membrane foulants were analyzed, and the results indicated that the low molecular weight fractions in the feed were main membrane fouling contributors for both UF and NF, where hydrophilic substances and proteins, as well as neutral substances and humic acids with polycarboxyl groups, contributed significantly to UF and NF membrane fouling, respectively. Compared with direct UF‐NF filtration without coagulation, the coagulants could aggregate organic micromolecules for cake formation. With inline coagulation, the moving flocs could generate shear stress to scrub the membrane surface for fouling control of UF. Moreover, with inline coagulation, the organics removal efficiency could be further increased by 10%–20%. With NF, the permeate had a TOC concentration of less than 0.5 mg/L, satisfying the drinking water quality. Therefore, the coagulation‐UF‐NF is very useful for Tai Lake water treatment. Practitioner points Inline coagulation‐UF‐NF for Tai Lake Water treatment is implemented. Inline coagulation can aggregate hydrophilic substances to reduce membrane fouling. Moving flocs produce shear stress for fouling control of UF‐NF. Superior quality of permeate is achieved with the combined coagulation‐UF‐NF process.

Application of Coagulation–Membrane Rotation to Improve Ultrafiltration Performance in Drinking Water Treatment

“…Besides membrane vibration, coagulation is widely used in drinking water treatment to reduce UF membrane fouling and enhance organic removal [ 18 , 34 ]. In the coagulation process, coagulants, such as Al (III) and Fe (III) compounds, were added to the influent.…”

“…The colloids, usually with a negative charge, can be combined with the positive trivalent ions to form flocs, which can reduce its stability and settle down in the subsequent sedimentation process. With the reduction of the colloid in the coagulation process, the influent DOM concentration for the followed UF thus can be much lowered [ 34 ]. In the coagulation process, the dosage amount is a very important parameter since insufficient coagulant dosage cannot aggregate the DOM to form flocs, while too many coagulants could make the colloid stable again and cannot induce effective precipitation resulting in a reduced organic removal.…”

“…Generally, large flocs had an efficient precipitation ability, while small flocs were difficult to settle down. In addition to the coagulant dosage amount, the hydrodynamic condition is also an important issue for effective coagulation [ 34 , 35 ]. The flocs were easy to precipitate in a relatively stable environment, while they may be broken down in an environment with strong fluid motion since flocs are relatively loose [ 34 ].…”

“…The combination of membrane vibration and coagulation thus can be a potentially useful technique for UF pretreatment. The coagulation could aggregate the DOM to form large particle flocs while the membrane vibration could produce a high shear force to eliminate the particle flocs [ 34 , 35 ]. However, the flocs may be destroyed when too much shear stress was applied, resulting in the ineffectiveness of the membrane fouling control and the deterioration of effluent quality.…”

Insights into the roles of membrane pore size and feed foulant concentration in ultrafiltration membrane fouling based on collision‐attachment theory

“…Ultrafiltration (UF) technology is widely used in water and wastewater treatment (Bu, Gao, Shen, Wang, & Yue, 2019; Huang, Lv, Zhou, Hu, & Dong, 2019; Jiang et al., 2018; Li et al., 2020). However, membrane fouling is still the bottleneck problem in membrane promotion and application as fouling can not only increase the operation cost, but also shorten the service life of membrane (Gao et al., 2011; Shi, Tal, Hankins, & Gitis, 2014).…”