# Shifting from Conventional to Organic Filter Media in Wastewater Biofiltration Treatment: A Review
## 3 Filter Media Selection on the Efficiency of Biofililtration
### Characteristics of Organic Filter Media Compared to Conventional Filter Media  
[PERSON] et al. [57] stated that organic filter materials should contain favorable characteristics such as larger surface area, higher porosity, physiologically stable (presence of hemicellulose/lignin content), non-toxic, higher adsorption ability, and contain functional groups (i.e., phenolic hydroxyls, carboxylic or methoxyl). Recently, plant-based wastes are widely utilized by various researchers as support materials for biofilm formation due to advantages such as cost-effectiveness, environmentally friendly, higher specific surface area, higher void fraction, lower bulk density, higher microbial population density, and higher resistance towards biodegradation due to their cellulose, hemicellulose, and lignin contents [31; 58]. Some successful applications of organic materials as biofilm supporting media include Brewer's spent grains, peanut shells, wood chips, wheat straws, rice straws, coconut husk, _Lofofah, Agave_ fibers, and _Arundo donax_[30; 31; 57; 59; 60; 61; 62]  
Most of the organic biofilm supporting materials are characterized by their cellulose, hemicellulose, and lignin contents. [PERSON] et al. [63] identified that high cellulosic and lignin contents increase the strength, durability, and toughness of the plant fibers, which in turn provides the organic media with physicochemical stability, as the structural units of oxyphenylpropanol present in the lignin polymer are relatively hard to be hydrolyzed. Furthermore, these lignocellulosic compounds contain polar functional groups such as phenol and carboxyl groups, which tend to increase the adsorption ability, thus promoting the attachment of the biofilm to the organic filter media. The presence of a hydrophilic group on the filter media aids in increasing the water adsorption which enhances the attachment and growth of the biofilm [64]. These chemical properties are similar to those of GAC, which is one of the efficient filter media that contains several functional groups such as carboxylic, alcoholic, and ether groups [65]. Other than that, it was observed that efficient organic filter media commonly show high porosity, i.e., between 74.0 and 84.0% [29; 31; 57]. The porosity of the organic media is higher compared to that of the conventional media such as anthracite (52.9%) and activated carbon (66.7%) [66]. Higher porosity helps in the prevention of the compaction of the support material in the bioreactor, increases the spaces for fluid circulation, and at the same time, the presence of pores and micropores favorably enhances the conditions of the attachment site for the biofilm [29; 31]. Another important parameter of a potential organic media is the surface area of the organic materials. [PERSON] et al. [63] demonstrated that the specific surface area of coconut fiber is up to 5.63 m\({}^{2}\)/g while that of oil palm fibers is up to 2.68 m\({}^{2}\)/g. These values are higher compared to the specific surface area of anthracite (1.68 m\({}^{2}\)/g) but lower compared to activated carbon (122.75 m\({}^{2}\)/g) as reported by [PERSON] et al. [66]. The superior performance of GAC compared to other media is due to its larger specific surface area in providing more space for the development of a microbial community, which enhances the biofilm formation and improves the biodegradation process [67]. Other than that, the cost of the filter materials is also one of the important parameters influencing the investment andoperational cost of biofilters. Most of the organic filter materials are characterized by their low cost as these organic materials are usually waste or agricultural by-products. It was reported by [PERSON] et al. [30] that the cost of wood chips and wheat straws are 2.37 US$S/m3 and 2.5 US$S/m3, respectively, which is much lower compared to the cost of anthracite and GAC at approximately 9.46 US$/m3 and 43.35-47.29 US$S/m3 [68], respectively. [PERSON] et al.