Summary Hiking of crude oil prices and diesel fuel shortage is incentive for the researchers to develop bioenergy sources. Biodiesel has environmental beneficial attributes, and its production processes are worthy of continued studies. Many biodiesel production processes are available but, most of them are not on a commercial scale. Biodiesel production using solid catalysts involved fewer unit operations compared with homogeneous catalyzed processes. Many heterogeneous catalysts have been extensively investigated in the recent years and well established. Researchers' focus is how to obtain active and more stable silicates catalyst that can be recycled for several times in the process. Silicates catalyst activity and stability are critically discussed in this work to assess their industrial application, as excessive purification steps could be avoided. This review provides a brief overview on semi‐novel heterogeneous catalyst types ‘silicates’ used in the transesterification of vegetable oils for biodiesel production. Process conditions and leaching out of catalyst active sites are also highlighted. Product quality analysis is presented, in addition to concluded remarks regarding silicates as a selected catalyst. A preliminary economic assessment of biodiesel production catalyzed by the suggested catalyst ‘silicates’ compared with potassium hydroxide (KOH) and lime (CaO) is performed. Copyright © 2016 John Wiley & Sons, Ltd.

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a b s t r ac tThis research highlighted the ability of sludge membrane filters (SMF) as an alternative technique for processing wastewater treatment. The sludge ash based membranes were prepared by blending cellulose acetate (CA) with sewage sludge ash (SSA) from wastewater by dry-wet phase inversion method in various proportions of CA/SSA (100/0, 90/10, 80/20 and 50/50 wt%). Characterization of prepared membranes was performed such as water content, X-ray diffraction analysis and mechanical strength. Also, the possibility of solute rejection of nickel ions from wastewater using SMF was evaluated. Effects of organic additives concentration such as polyethylene glycol (PEG 600) in the casting solution were studied in range of 0-10 wt%. Results reported that the best performance of CA/SSA blend membranes was at 50/50 wt% Furthermore, investigation of SMF in reducing the water turbidity, COD, BOD, TSS and total dissolved solids of effluent wastewater from Abu Rawash plant was depicted.