Effects of a novel bimetallic catalytic biofilter-based pretreatment technique on the form of ultrafiltration membrane fouling

Pretreatments of influents using bimetallic catalytic biofilter(BC-biofilter)can help reduce transmembrane pressures.For ultrafiltration membranes coupled with a conventional biofilter pretreatment,the cake layer resistance accounts for 25.0%of the total resistance.However,for those coupled with BC-biofilter pretreatment,the cake layer resistance accounts only for 12.5%of the total resistance.Confocal laser scanning microscopy is employed to determine the porosity of cake layer.It is found that ultrafiltration membranes with BC-biofilter pretreatment show a cake layer porosity of up to 0.56 or greater,whereas those with a conventional biofilter pretreatment exhibit a cake layer porosity of only 0.36.This is because micro-flocculation occurs in the effluents of BC-biofilter.The flocs generated through flocculation deposit on membrane surfaces to create highly porous cake layer.Moreover,catalytic reduction can increase the zeta potentials of the biofilter effluents.This makes the deposition of colloidal particles and flocs on membrane surfaces difficult under electrostatic repulsion.Simultaneously,micro-flocculation after BC-biofilter pretreatment can remove colloidal particles with particle sizes of200–350 nm in water.This can effectively prevent the blockage of ultrafiltration membrane pores.Furthermore,compared to conventional biofilter,BC-biofilter pretreatment can more effectively reduce the number of colloidal particles and the van der Waals forces of ultrafiltration membranes.They can also change the action directions of electric double layers and thereby mitigate ultrafiltration membrane fouling.

Physicochemical interaction and its influence on deep bed filtration process

The capillary model was used to analyze the hydraulic conditions in the deep bed filtration process. The physicochemical interaction forces between the filter media and suspended particles and their influence on deep bed filtration process were also studied theoretically. Through the comparison of the hydraulic and physicochemical forces, the key influencing factors on the filtration process were proposed and investigated. Pilot study of the micro-flocculation deep bed filtration was carried out in the No. 9 Potable Water Treatment Plant of Beijing, and the experimental results of hydraulic head loss, particle distribution and entrapment were presented. The theoretical prediction was reasonably consistent with the experimental results under different conditions, which indicated that the regulation and control of micro-flocculation and deep bed filtration could be realized by the evaluation of the physicochemical interactions. Further theoretical and experimental research should be carried out to investigate the interaction mechanism and its application in the deep bed filtration and other cases.

An Innovative Process to Improve Turbidity and Organics Removal by BAC Filters

The turbidity criterion for the product water of a WTP according to the State Project ‘863’ on the safeguard technology of drinking water in the southern areas of China is 0.1 NTU. The turbidity removal in the activated carbon filter was analyzed in a pilot-scale test and an innovative technology to improve the turbidity removal in a biologically activated carbon (BAC) filter was put forward in order to meet the criterion. Experimental results showed that the enhanced filtration by adding polymerized aluminium chloride (PAC) into the BAC filter was quite effective in turbidity control. The effluent turbidity was kept at a stable level (mean) of 0.033 NTU with a high removal of about 80% for influent turbidity of 0.110-0.240 NTU with an addition of PAC at 0.05 mg L -1, meeting the requirement for filtrate turbidity equal to or less than 0.1NTUC totally. In addition, the larger the PAC dosage was, the lower the effluent turbidity was. However, further improvement of turbidity removal was not obvious for PAC dosages beyond 0.10 mg L -1, and an optimal PAC dosage in the range of 0.]05-0.10 mg L -1 was proposed.

Effect of the Design Parameters on the Performance of Inner-Recycling Continuous Sand Filter

A novel integrated water treatment facility, inner-recycling continuous sand filter, is discussed. The theory of micro-flocculation is applied in the sand-washing circulation system with continuous filtration and backwashing. The design and operation parameters, which affect the performance of the filter, are discussed. The key design parameters are provided as follows: diameter of filter material is 0.7 to 1.0 mm, depth of filter bed is 0.6 m, filtration velocity is less than 12 m/h, ratio of gas to water is 9:11 and sand recycling rate is 2 to 4 mm/min.

Pilot Study on Powder Active Carbon / Flotation/Microflocculation / Ultrafiltration Combined Process for Treatment of Reservoir Water

[Objective] The study aimed to discover the effects of powder active carbon（ PAC） /flotation /micro-flocculation /ultrafiltration combined process on the treatment of reservoir water. [Method]Taken the water from a mountainous reservoir for the initial samples,the parameters such as turbidity,COD Mn,chlorophyll-a and methylisobormeol（ MIB） of water samples were monitored before and after treated with combined processes of micro-flocculation /ultrafiltration, flotation /micro-flocculation /ultrafiltration, PAC /flotation /micro-flocculation /ultrafiltration. [Result] The results showed that the removal rates of turbidity of water samples by the above three processes were 97. 5%,98. 0% and 98. 6%,respectively. The removal rates of COD Mn were 30. 9%,35. 0% and 52. 0%. The removal rates of chlorophyll-a were 80. 6%,91. 0% and 99. 0%. The removal rates of MIB were 17. 0%,34. 2% and 97. 0%. [Conclusion]The PAC /flotation /micro-flocculation ultrafiltration combined process can be flexibly combined based on the characteristics of algae and odor in water,and is suitable for water plant construction or reconstruction.