Influence of mechanical mixing rates on sludge characteristics and membrane fouling in MBRs

The influence of shear intensity (G) induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in membrane bioreactors (MBRs) was investigated. Four MBRs were operated at different mechanical mixing conditions. The control reactor (MBR0) was operated with aeration only supplemented by mechanical stirring at 150, 300, and 450 rpm in MBR150, MBR300, and MBR450, respectively. It was found that the MBR300 demonstrated minimum rate of membrane fouling. The fouling potential of the MBR300 mixed liquor was lowest characterized by the specific cake resistance and the normalized capillary suction time (CSTN). Moreover, it was found that the mean particle size reduced with an increase in the shear intensity. These results reveal that membrane fouling can be significantly mitigated by appropriate shear stress on membrane fibers induced by mechanical mixing condition.

Powdered activated carbon for fouling reduction of membrane in a pilot-scale recirculation aquaculture system

Recirculating aquaculture systems (RAS) are essential for the reduction in fresh water usage as well as the discharge of nutrients along with aquaculture effluents. A RAS consisting of an anoxic reactor, a membrane bioreactor (MBR) and a UV-disinfection unit was used to process 10,000 L/d of aquaculture effluent providing high-quality treated water for recirculation to a Barramundi fish culture. The system maintained low levels of nitrate (<20 mg/L), nitrite (<3 mg/L) and ammonia (<0.6 mg/L) in the fish tank. Permeate from the membrane that was recirculated to the fish tank contained <21 mg/L of nitrate, <2 mg/L of nitrite and 0 mg/L of ammonia. However, the rate of fouling of the membrane in the MBR was around 1.47 kPa/d, and the membrane in the MBR required cleaning due to fouling after 16 days. Cleaning of the membrane was initiated when the TMP reached around 25 to 30 kPa. In order to reduce the rate of fouling, 500 mg of powdered activated carbon (PAC) per litre of MBR volume was introduced, which decreased the rate of fouling to 0.90 kPa/d. Cleaning of membrane was needed only after 31 days of operation while maintaining the treated effluent quality. Thus the frequency of cleaning could be halved due to the introduction of PAC into the MBR.

Application of a hybrid MBR system to treat herbicides from agricultural runoffs

Agricultural discharge of herbicides to the Great Barrier Reef (GBR) poses significant threat to the marine ecosystem. This study evaluates the performance of a hybrid treatment system consists of a membrane bioreactor (MBR), UV disinfection unit and a granular activated carbon (GAC) column in treating Ametryn which is one of the major herbicides in agricultural discharges. While the MBR alone removes only 40% of Ametryn at a hydraulic retention time of 7.8 hours, the hybrid system removed Ametryn to below detection levels.

Treatment of ametryn in wastewater by a hybrid MBR system : a lab-scale study

Agricultural discharge of herbicides to the Great Barrier Reef (GBR) poses significant threat to the marine ecosystem. This study evaluates the performance of a hybrid treatment system consists of a membrane bioreactor (MBR), UV disinfection unit and a granular activated carbon (GAC) column in treating ametryn which is one of the major herbicides in agricultural discharges. While the MBR alone removes only 40% of ametryn at a hydraulic retention time of 7.8 h, the hybrid system removed ametryn to below detection levels.

Reuse of car wash wastewater by chemical coagulation and membrane bioreactor treatment processes

Car wash wastewater contains significant concentrations of contaminants such as nutrients, organics, particulate matter, sand, oil, grease, diesel detergents and so on. A range of treatment processes such as a membrane bioreactor (MBR), coagulation and ozonation were investigated to treat car wash wastewater. Ozonation was effective in removing the chemicals and suspended solids; the removal efficiency was greater than the coagulation process. Once the MBR system was acclimatised, 100% of suspended solids, 99.2% of COD, 97.3% of TOC and 41% of ammonia were removed. This study demonstrates that MBR is a potentially promising treatment system for recycling car wash wastewater which could be reused in the same car wash station.

Performance of reverse osmosis (RO) for water recovery from permeates of membrane bio-reactor (MBR)

In this study, permeate from a hollow fiber polyethylene (PE) membrane bio-reactor (MBR) system treating synthetic agricultural wastewater was fed into a cellulose acetate brackish water reverse osmosis (BWRO30 2540) membrane system; three different trans-membranes pressures (TMPs) of 1000, 2500, and 4000 kPa were selected to evaluate the system performance in terms of general operating parameters as well as the removal of chosen important potential fouling water quality parameters. The results showed that highest corrected permeate flux rate was at a TMP of 2500 kPa, whereas lowest recorded at a TMP of 4000 kPa. Similar situation prevailed in water recovery rate. But temperature corrected specific fluxes decreased as the applied TMPs increased. In all selected TMPs, more than 96% of salinity was removed. Permeate from MBR as feed to reverse osmosis required frequent chemical cleaning than the microfiltration/ultrafiltration (MF/UF) permeates and granular media filter (GMF) filtered in order to maintain the required rate of product water. One of the reasons for this frequent chemical cleaning is due to higher total organic carbon as well as total nitrogen (TN) in the MBR permeate. This result needs to be further evaluated through field trials.

Evaluation of pre-treatments for minimizing membrane fouling in water recovery

 RO membrane major foulants were reviewed. Among available pre-treatment technologies four pre-treatments namely; MF, UF, MBR membranes and GMF are qualitatively ranked as best. Further, experiments and fouling mathematical models showed suitability of UF and MF membrane as pre-treatments, based on their higher permeability and lower fouling potentiality than others.

Application of enhanced membrane bioreactor (eMBR) to treat dye wastewater

An enhanced membrane bioreactor (eMBR) consisting of two anoxic bioreactors (ARs) followed by an aerated membrane bioreactor (AMBR), UV-unit and a granular activated carbon (GAC) filter was employed to treat 50-100 mg/L of remazol blue BR dye. The COD of the feed was 2334 mg/L and COD:TN:TP in the feed was 119:1.87:1. A feed flow rate of 5 L/d was maintained when the dye concentration was 50 mg/L; 10 L/d of return activated sludge was recirculated to each AR from the AMBR. Once the biological system is acclimatised, 95% of dye, 99% of COD, 97% of nitrogen and 73% of phosphorus were removed at a retention time of 74.4 h. When the effluent from the AMBR was drawn at a flux rate of 6.5 L/m(2)h, the trans-membrane pressure reached 40 kPa in every 10 days. AMBR effluent was passed through the UV-unit and GAC filter to remove the dye completely.

Effect of membrane stress on surface roughness changes in sheet forming

Friction plays an important role in sheet metal forming (SMF) and the roughness of the surface of the sheet is a major factor that influences friction. In finite element method (FEM) models of metal forming, the roughness has usually been assumed to be constant; even though it is commonly observed that sheet drawn under tension over a tool radius results in the surface becoming shiny, indicating a major change in surface morphology. An elastic–plastic FEM model for micro-contact between a flat surface and a single roughness peak has been developed. The model was used to investigate the effect of the membrane stress in the sheet on the deformation of an artificial roughness peak. From the simulation results, the change in asperity, or deformation of the local peak, for a given nominal tool contact stress is significantly influenced by the local substrate stress. The height of the asperity decreases with increasing substrate stress and the local pressure is much higher than the nominal pressure. In addition, the local contact stress decreases with an increase in the substrate stress levels.

A novel polymer membrane for extraction applications

In this study, a new type of Aliquat 336/PVC membrane has been made for extraction experiments. This new membrane is capable of holding more Aliquat 336 than previously developed extraction membranes, hence overcoming a major problem that has confronted many researchers for a long time. The new membrane has been used to investigate the rate of extraction for the Cd(II) ion in 2.0 M HCl solution and the effect of membrane thickness on the rate of extraction. The experimental results have shown this new membrane has a promising future in relevant industrial applications. A new method is also used in this study to qualitatively identify the oily substance on the surface of membrane after the extraction experiment was completed. This oily substance has been found to be Aliquat 336.