Combined effect of air and mechanical scouring of membranes for fouling reduction in submerged membrane reactor

This study investigated the combined effect of air flow and use of granular support medium in suspension in a submerged membrane reactor to reduce membrane fouling. Lower membrane fouling and a slower rise in transmembrane pressure (TMP) were noticed when a higher air flow rate was used for membrane scouring. Further fouling reduction was achieved by adding a granular medium in the reactor. The results showed that in the absence of the granular medium, when air flow was tripled (from 600 to 1800L/h/m 2), the TMP development was decreased by 60%. TMP further dropped to 85% with the addition of granular medium (for the same air flow rate). The doubling of the air flow rate (from 600 to 1200L/h/m 2), without granular medium, led to a 32% reduction in TMP development at 10L/m 2 h. The same result was obtained at a lower air flow rate of 600L/h/m 2 with the granular medium. This result shows that the same reduction of TMP can be obtained by adding granular medium instead of doubling air flow rate. Therefore adding granular medium in the suspension (mechanical scouring) with air flow (air scouring) could be a sustainable alternative to applying high air flow in submerged membrane systems. © 2011 Elsevier B.V

Pre-flocculation of secondary treated wastewater in enhancing the performance of microfiltration

In this study, a new design of static floating medium flocculator was examined for its ability to remove suspended solids, organics and phosphorus. The floating medium flocculator also produced uniform microflocs, which could be removed easily by cross flow microfiltration. Flocs formed enhanced the permeate flux of microfiltration. The floating medium flocculator was able to be operated at high velocities of up to 40 m/h, producing filterable flocs of around 20 μm. Using a filter bed depth of 1m, the floating medium flocculator was able to remove 45% of suspended solids, to as low as 1.3 mg/L; 83% of turbidity, achieving values <1 NTU; 97% of phosphorus, reducing orthophosphate to 0.07 mg/L and 45% of organics, to as low as 1.02 ppm C total organic carbon (TOC). A periodic backwash for duration of 1 min every 90 min enabled the floating medium flocculator to run continuously without termination. A series of experiments was conducted with a combined system of flocculation-microfiltration to assess its capability in removing solids and organics. The improvement of flux by the pre-flocculation was also investigated. The purpose of the floating medium flocculator was to produce filterable flocs and also removal of solids and organics. The critical flux of kaolin clay suspension of 10-100 mg/L was measured with a 0.2 μm membrane, in the presence of 0-4 mg/L of fulvic acid. The pretreatment of flocculation leads to 50% removal of organics, while producing uniform microflocs of 13-16 μm. It enhanced the critical flux by 70% and resulted in a further 30-70% removal of organics by microfiltration

Membrane-flocculation-adsorption hybrid system in wastewater treatment: Micro and nano size organic matter removal

Cross flow microfiltration with in-line flocculation reduces the fouling of membranes thus leading to high quality product water. A detailed experimental study conducted with an artificial suspension (particle size distribution similar to that of surface water) revealed that the filtration rate can be increased by several times by adopting in-line flocculation. In-line flocculation-microfiltration is therefore an attractive technique to reduce internal clogging while improving the permeate flux significantly. A detailed ultrafiltration (UF) study was conducted with biologically treated sewage effluent with pretreatment by flocculation and powdered activated carbon adsorption. The TOC removal by the NTR 7410 UF membrane alone was 43.6%. The TOC removal increased significantly by the use of pretreatment: 69.3% by flocculation and 91% by flocculation followed by adsorption. The organic colloidal portion (between 3,500 dalton and 0.45 μm) in the biologically treated effluent was removed up to more than 65% by the pretreatment of flocculation. The molecular weight of the biologically treated effluent ranged from 250 to about 3,573 dalton with the highest fraction in the range of 250-845 dalton. By the incorporation of pretreatment, the majority of both large and small molecular weight organic matter was removed. This hybrid system led to practically no filtration flux decline in membrane filtration. © 2004 IWA Publishing and the authors