Waste biomass surfactants

Surfactants Obtained from Biological TYansformation of Waste Biomass... 

The term biosurfactant is typically reserved for surface-active agents (surfactants) that are produced by microorganisms, as part of their metabolism [3-8]. However, it is necessary to clarify that there are other surfactants - such as lung surfactants - that are secreted by other species and could also be called biosurfactants. In this part of the chapter we will concentrate on the conventional definition of biosurfactants and the use of microbes to degrade waste biomass to secrete potentially usefiil biosurfactants. 

The efforts in reducing the production costs for biosurfactants have taken three basic routes the use of less expensive carbon sources, the genetic modification of strains to improve surfactant yield and the improvement in the method of separation of the surfactant from the cell culture [19], We will describe in more detail the efforts made in using waste biomass as the source of carbon and nutrients for the synthesis of biosurfactants. 

It is important to recall that the research into bio-based surfactants extracted by chemical methods from waste biomass is still in its early days. As such, the production technology that will be described in the next section is still quite close to laboratory protocols and not industrial processes. As will be described in more detail, the quality of these surfactants is inferior to the quality of the biosurfactants produced (higher CMC, higher surface tension after CMC). However, the potential for high throughput, abundance of the biomass and the current economics of wastewater biosolid handling make this an interesting alternative for some applications that will be described later in this chapter. 

Figure 9.10 Surface tension-surfactant concentration curves for alkaline extracts from waste biomass. The data from Garcia-Becerra was obtained in an electrolyte solution containing 1 g NaCI/IOOml. The sodium dodecyl benzene sulfonate data (SDBS) was obtained at a pH of 6 [43, 661...

A considerable number of standardized OECD and International Organization for Standardization (ISO) methods for measuring the biodegradability of surfactants are available. Table 22.4 gives an overview of such methods. ISO 7827 and OECD 301 A are used to determine the ultimate biodegradability in the aquatic environment. This is achieved via the measurement of dissolved organic carbon (DOC) at an incubation period of 28 days. The widely used Zahn-Wellens Test (OECD 302 B) is also a static method but works with a substantially higher biomass and substrate concentration (50-400 mg/1). This corresponds more to the situation in a real waste-water treatment plant. 

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