**4.4 Biopolymers and biodegradable plastics**

Exopolysaccharides (EPSs) often show clearly identified properties that form the basis for a wide range of applications in food, pharmaceuticals, petroleum, and other industries. The production of these microbial polymers using OMWW as a low-cost fermentation substrate has been proposed (Ramos-Cormenzana et al. 1995). This approach could reduce the cost of polymer production because the substrate is often the first limiting factor. Moreover, OMWW contains free sugars, organic acids, proteins and other compounds such as phenolics that could serve as the carbon source for polymer production, if the chosen microorganism is able to metabolize these compounds (Fiorentino et al. 2004).

Xanthan gum, an extracellular heteropolysaccharide produced by the bacterium *Xanthomonas campestris* has been obtained from OMWW. Growth and xanthan production on dilute OMWW as a sole source of nutrients were obtained. Addition of nitrogen and/or salts led to significantly increased xanthan yields with a maximum of 7.7g/l (Lopez and Ramos-Cormenzana 1996).

The fungus *Botryospheria rhodina* has been used for the production of β-glucan from OMWW with yield of 17.2 g/l and a partial dephenolisation of the substrate (Crognale et al. 2003). A metal-binding EPS produced by *Paenibacillus jamilae* from OMWs. Maximum EPS production (5.1 g/l) was reached in batch culture experiments with a concentration of 80% of OMWW as fermentation substrate (Morillo et al. 2007).

Polyhydroxyalkanoates (PHAs) are reserve polyesters that are accumulated as intracellular granules in a variety of bacteria. Of these polymers, poly-β-hydroxybutyrate (PHB) is the most common. Since the physical properties of PHAs are similar to those of some conventional plastics, the commercial production of PHAs is of interest. However, these biodegradable and biocompatible 'plastics' are not priced competitively at the present, mainly because the sugars (i.e. glucose) used as fermentation feed-stocks are expensive. Finding a less expensive substrate is, therefore, a major need for a wide commercialisation of these products. Large amounts of biopolymers containing β-hydroxybutyrate (PHB) and copolymers containing β-hydroxyvalerate (P[HB-co-HV]) are produced by *Azotobacter chroococcum* in culture media amended with alpechin (wastewater from olive oil mills) as the sole carbon source (Pozo et al. 2002).

#### **4.5 Biosurfactants**

Rhamnolipids, typical biosurfactants produced by *Pseudomonas aeruginosa*, consist of either one or two rhamnose molecules, linked to one or two fatty acids of saturated or unsaturated alkyl chain between C8 and C12. The *P. aeruginosa* 47 T2 produced two main rhamnolipid

using dry matter of TPOMW. The results showed that yeasts could effectively ferment TPOMW without nutrient addition, resulting in a maximum ethanol production of 11.2 g/l and revealing the tolerance of yeast to TPOMW toxicity (Georgieva and Ahring 2007).

Anaerobic digestion is a biological process in which organic material is broken down by microorganisms. Unlike composting, the process occurs in the absence of air. Anaerobic digestion is a practical alternative for the treatment of TPOMW, which produces biogas. The TPOMW is biodegradable by anaerobic digestion at mesophilic temperatures in stirred tank reactors, with COD removal efficiencies in the range of 72–89% and an average methane yield coefficient of 0.31 dm3 CH4 per gramme COD removed. Hydrogen production was coupled with a subsequent step for methane production, giving the potential for production

The OMW used as a sole substrate for the production of hydrogen gas with *Rhodobacter sphaeroides* O.U.001. The bacterium was grown in diluted OMW media, containing OMW concentrations between 20% and 1% in a glass column photobioreactor at 32°C. The released gas was nearly pure hydrogen, which can be utilized in electricity producing systems, such as fuel cells. The maximum hydrogen yield (145 ml) was obtained with 3% and 4% OMW concentrations. However, as well as hydrogen production, COD, BOD and phenol reduction

Biodiesel, a fuel that can be made from renewable biological sources such as vegetable oils or animals fats, has been recognized recently as an environment friendly alternative fuel for diesel engines. Among liquid biofuels, biodiesel derived from vegetable oils is gaining ground and market share as diesel fuel in Europe and the USA. A mixture of frying olive oil and sunflower oil for the production of methyl esters that can be used as biodiesel (Encinar

As far as agronomic use of the waste is concerned, the idea of re-using microbially treated OMWW as fertiliser has been also proposed. An acidogenic fungus strain *Aspergillus niger* was grown in either free or immobilised form on OMWW with rock phosphate added in order to solubilise it. It was found that at optimized process conditions (moisture 70%; corn steep liquor as a nitrogen source; inoculum size of 3-4 ml; presence of slow release phosphate), the filamentous fungal culture was able to produce 58 U phytase/g dry substrate and 31 mg soluble phosphate per flask (Vassilev et al. 1997; Vassilev et al. 2007).

Already 50 years ago, the production of yeast biomass using OMWW in a chemostat for use in industrial applications was reported. The microbial biomass produced from OMW fermentations either as an additive to animal feed or to improve its agronomic use. For example, an intense degradation of most polluting substances of OMWW and the production of biomass could be used as an animal feed integrator using a chemical–

Seven strains of *Penicillium* isolated from OMWW disposal ponds were tested for biomass production and biodegradation of undiluted OMWW. Best results were obtained by using

of 1.6 mmol H2 per gramme of TPOMW (Borja et al. 2006).

from OMW were recorded (Eroglu et al. 2004).

et al. 2005).

**4.9 Biofertilizers** 

**4.10 Biomass** 

biological method (Morillo et al. 2009).

homologs, (Rha-C10-C10) and (Rha-Rha-C10-C10), when grown in olive oil waste water or in waste frying oils consisting from olive/sunflower (Pantazaki et al. 2010).
