Coproduct recovery in vegetable oil processing

Home Based Recycling Business

Make Money in the Recycling Business

Get Instant Access

As stated before, vegetable wastewater can be considered as an important source of valuable products, i.e. carbohydrates, phenols, lecithin, vitamin E, sterols and proteins. Visioli et al. (1999), in view of the need for upgrading by-products at all stages of the olive oil industry, investigated different procedures for the recovery of the active components of OMWW and compared the antioxidant and biological activities of various extracts.

20.3.1 Sugars

Glucose is the main soluble sugar present in olive pulp together with smaller quantities of sucrose and fructose and a significant amount of the polyol called mannitol. The insoluble polysaccharides in the cell wall of olive fruit are composed of pectin, hemicellulose and cellulose. The hemicelluloses are mainly rich in acid xylan and xyloglucan. Therefore, this by-product may be utilized as a chemical feedstock for the production of fermentable sugar as a source of mannitol. Furthermore, due to cleavage of the hemicel-lulose by the steam treatment, a wide variety of xylo-oligomers with different molecular fragments might be obtained. Carbohydrates are not only ideal energy substrates for the majority of microorganisms, but also the main carbon sources for biotechnological production processes. Biotransformation of hexoses to gluconic acid, itaconic acid, citric acid and lactic acid is performed on a large scale to produce basic ingredients for laundry detergents, glues, preservatives and polylactides, respectively. Polylactides are polymers of lactic acid with a molecular mass of 40 000300 000 Da. The lactic acid is produced with lactobacilli. The recovery of lactic acid from alfalfa or soya fibres that were enzymatically digested with cellulases and pectinases, and fermented with lactobacilli, was 32-46 g per 100 g of fibres (Sreenath et al., 2001). The properties of polylactides depend on the proportion and the distribution of d(-) and l(+)-lactic acid isomers in the polymer. Poly-l-lactic acid and poly-d-lactic acid are crystalline polymers, whereas poly-d,l-lactic acid with a regularly alternating d- and l-isomer array is an amorphous polymer and poly-d,l-lactic acid with statistically distributed d- and l-isomers is an amorphous to crystalline polymer (Richter et al., 1999).

An important polysaccharide obtainable from OMWW is xanthan, which is composed of the sugars glucose, mannose and glucuronic acid. Xanthan is widely used as a thickener or viscosifier in both the food and nonfood industries. Xanthan is extracellulary produced by the bacterium Xanthomonas campestris, and has become the focus of a great deal of interest on account of its physical properties. Xanthan production from OMWW can be achieved at reasonable levels after optimising several nutrients in culture media. López et al. (2001) studied the effect of OMWW variability on xanthan production. The authors determined that factors affecting wastewater composition - namely waste storage, time of olive harvesting and method for oil extraction - influenced xanthan production in shake-flask cultures. Specifically, they found a maximum xanthan production of 4 g L-1 with 50% OMWW as the sole source of nutrients. OMWW storage decreased effluent quality for xanthan production. The range of effluent concentration for Xanthomonas campestris growth and xanthan production varied depending on the OMWW extraction method. Wastewaters from press and two-phase production varied depending on the OMWW extraction method. Wastewaters from press and two-phase extraction methods required higher dilution rates (<10%) than those from the three-phase extraction method (50%). Nitrogen supplementation improved xanthan production in press and two-phase OMWW. Conditions for xanthan production from OMWW should be optimized in accordance with the nature of the waste material. The time of olive harvesting and milling was also found to influence the quality of the substrate for xanthan production. OMWW from late harvesting were found to be more beneficial for xanthan production than OMWW from early harvesting. The main differences between the samples used are the olive ripeness and probably the storage period prior to milling. This results in changes in fruit composition that may affect effluent quality. Guillén et al. (1993) reported a drop in fruit sugars during maturation. Such variations led to increases in xanthan production. Results indicated that xanthan production varied greatly depending on the type of effluent used. The main factor influencing waste quality for xanthan production was the method of extraction. Effluents with lower organic matter content such as three-phase system OMWW and two-phase system OMWW can be included in media at 50%. More concentrated effluents, such as those from press and aqueous extracts resulting from two-phase systems, should be diluted tenfold. Nitrogen supplementation results in a C/N balance that allows growth and xanthan production at higher effluent concentration levels than in media where the effluent becomes the only source of nutrients.

20.3.2 Sugar alcohol

Another important product obtainable from oil waste waters is mannitol, which is a sugar alcohol that is used as an excipient in the pharmaceutical industry and as an anti-caking and free-flow agent, lubricant, stabilizer, thickener and low-caloric sweetener in the food industry. Due to its physi-cochemical properties, it is predominantly used in chewing gum and in bread products for diabetics. Xylo-oligosaccharides can be used as a food additive due to their favourable effect on the intestinal flora. Non-digestible oligosaccharides are usually considered to enhance the growth of bifido-bacteria and lactic acid bacteria in the human large intestine, with certain evidence of a preventive effect against colon cancer and other intestinal dysfunctions. Recently Fernandez-Bolanos et al. (2002) optimized and integrated a process for alperujo that allows compounds of high added value to be obtained from the water-soluble fraction, leaving a solid residue enriched in cellulose, and residual oil that can be valorized by further processing. They established the operating conditions that govern the auto-hydrolysis process (temperature and time) in order to evaluate this byproduct as a source of fermentable sugar, mannitol and oligomers. The use of sulphuric and phosphoric acids as catalysts during steam treatment and its implication on the isolation of some of these compounds can be effective and the further purification and crystallization of mannitol are also possible.

20.3.3 Polymer building blocks

Vegetable oils are a potential feedstock for polymers because their fatty acid molecules can be modified to serve as polymer building blocks (Fig. 20.2). Several projects exist to develop catalyst systems for chemistries such as hydroformylation to convert the vegetable oils to polyaldehydes and subsequent chemistry to convert the polyaldehydes to polyols, polyacids and polyamines. By adding functional groups to the vegetable oil molecules, the reactivity of the vegetable oil is increased creating the potential

Vegetable oil

Vegetable oil y

Polyaldehyde

CH=OcH=O

CH=O

Hydroformylation

Oxidation

Reductive amination

Hydroformylation y

Polyaldehyde

CH=OcH=O

CH=O

Reduction

Polyol (Primary alcohol)

CH2OH CH2OH

ch2oh

Polycarboxylic acid

COOH

COOHCOOH

COOH Polyamine

COOH Polyamine

Fig. 20.2 Catalyst system for the formation of polyaldehydes, polyols, polyacids and polyamines.

Fig. 20.2 Catalyst system for the formation of polyaldehydes, polyols, polyacids and polyamines.

for polymerizing the modified vegetable oil. These processes were originally developed for fossil feedstocks that are less viscous than vegetable oils and easier to separate from the catalyst at the end of the reaction. Researchers are developing new catalyst systems that have high efficiencies for the conversion of vegetable oils such as soy oil and allow efficient catalyst recovery and easy product separation from the vegetable oil derivatives.

546 Handbook of waste management and co-product recovery 20.3.4 Polymerins

Other authors have studied the possibility of obtaining useful polymeric products from OMWW. Arienzo and Capasso (2000) obtained a dark polymeric organic fraction using precipitation of the organic polymeric fraction (opf) by cold methanol. The chemical nature of the opf binding the metal cations was analyzed and its size in terms of relative molecular mass was also investigated by combining the ultraviolet (UV)-visible spectroscopic analysis with ultra-filtration experiments. The COD/BOD values of the obtained fractions were also determined to verify whether the proposed treatment (i.e. cold methanol precipitation) reduced the organic load of the initial raw material and its related environmental risks, and to evaluate the potential for use of these fractions as a soil amendment and in environmental biotechnology processes. Results indicated that most of the metal cations were bound to the OMWW opf composed of polysaccharides, phenol polymers and proteins to which K and Na are essentially bound by single electrostatic bonding, whereas all other ions are more strongly bound - even in chelated form - by means of anionic functional groups. Opf molecular mass was substantially estimated in the range 1000-30 000 Da for ~75% and in the range 30 000-100 000 Da for ~25%. Thus, the polymeric product was revealed to be rich in K and was named polymerin, in fact K was the most abundant metal, followed, in decreasing order, by Ca, Mg, Na, Zn, Fe and Cu. The free residual cations pool proved to be neutralized by the inorganic counter-anions (Tables 20.2 and 20.3). These findings were in agreement with those shown by other authors, who revealed that non-living biomass materials have a high potential in binding metals. Metal ion uptake is believed to occur through interactions with functional groups such as car-boxyl, amino, sulphydryl, phenolic or hydroxyl moieties. These proved to be native to the proteins, lipids and carbohydrates that make up the cell

Table 20.2 Metal cation and inorganic anion concentrations determined in raw OMWW (adapted from Arienzo et al., 2000)

Total cations

Inorganic anions

Cation

Concentration

Concentration

Anion

Concentration

Concentration

(g L-1)

(meq L-1)

(g L-1)

(meq L-1)

K+

17.1

437.2

Cl-

1.63

45.9

Mg2+

2.72

223.8

H3PO4-

1.07

11.0

Ca2+

2.24

111.8

F-

0.57

30.0

Na+

0.40

17.4

SO42-

0.53

10.8

Fe2+

0.12

4.6

NO3-

0.023

0.37

Zn2+

0.06

1.9

Mn2+

0.014

0.5

Cu2+

0.086

0.2

Z = 797.5

Z = 98.07

Table 20.3 Concentrations of metal cations bound to the opf in OMWW (adapted from Arienzo et al.,

2000)

Table 20.3 Concentrations of metal cations bound to the opf in OMWW (adapted from Arienzo et al.,

2000)

(g L-1)

Concentration (mequiv L-1)

K+

13.2

337.5

Mg2+

2.51

206.4

Ca2+

2.11

105.3

Na+

0.373

16.2

Fe2+

0.105

3.8

Zn2+

0.059

1.8

Mn2+

0.0113

0.4

Cu2+

0.0058

0.2

Z = 671.6

walls. All cations, except K, are >90% bound to opf. K was 78% bound to opf and 22% was free in solution. Except for K and Na, cations are bivalent and possess strong chelating properties. The relative abundance of negatively charged sites of the opf explains the consistent binding of K to the opf. In the case of sodium, 99.1% of the metal was bound to opf, thus competing with K, which has a smaller ionic ray, 0.95 and 1.53 A, respectively. This difference should make the Na more reactive towards the negative sites of opf than K. The opf that resulted was mainly formed by polysaccharides, polymeric polyphenols and proteins. In addition, the COD and BOD of this biomaterial markedly decreased in comparison with those of the raw OMWW. These findings prompted the recovery of the metal polymeric organic fraction, which was named polymerin, with the aim of studying its possible recycling in agriculture and use in environmental technology processes. The potential employment of this biomaterial in agriculture as a bioamendment and/or metal bio-integrator is motivated by its humic acid-like nature and its richness in macro- and micronutrients such as K and to a lesser extent Ca, Mg, Fe and Zn. Capasso et al. (2002) described the production of metal polymerins obtained separately by saturation of polymerin with various micronutrients (Cu, Zn, Mn and Fe) and other metals of interest (Na and Al). They also studied the production of the metal Cu, Zn, Mn, Fe and Al salts of deglycosylated polymerin (Me-SDpolymerins), obtained separately by saturation of a K salt of deglycosyl-ated polymerin (K-SDpolymerin). In view of the possible application of these biomaterials, their effects on tomato cuttings were studied compared with the effect of raw OMWW. Saturated metal polymerins were characterized by diffuse reflectance infrared Fourier transform spectroscopy, and atomic absorption and atomic absorption spectrometry. Tests on tomato plants of the various polymerins showed that only the soluble polymerin, K-SDpolymerin and the insoluble Mn-SDpolymerin were significantly toxic. The toxic effects of OMWW on tomato at the original concentration and diluted 1 : 10 were much stronger than those of any polymerin. The soluble polymerin and its derivative K-SDpolymerin and the insoluble Mn-SDpolymerin were only significantly toxic. The wilting effect of the soluble polymerins was attributed to a mechanical obstruction of the xylem pathways of the tomato, whereas that of Mn-SDpolymerin was related to interference with the plant metabolism. The strong phytotoxicity of OMWW on tomato observed at both original and diluted 1 : 1 concentrations was ascribed primarily to a synergistic effect of polyphenols, which act on plant metabolism, and secondarily to the polymeric fraction, which acts through a mechanical obstruction and is visible only at high concentrations. The authors also found that the COD and BOD of the OMWW polymeric fraction was strongly reduced with respect to the whole wastewaters. The low toxicity of polymerins, their humic acid characteristics, and the abundance of macronutrients (K, Mg and Ca) and micronutrients (Cu, Zn, Fe and Mn) suggest their promising exploitation as bio-amendments and/or metal-bio-integrators. However, the use of Me-polymerins with respect to Me-SDpolymerins is of great interest because of the simpler and cheaper production process.

The detoxification of agro-industrial effluents using superabsorbent polymers is a new and innovative process. The high metal-binding capacity of opf represents a potential industrial tool for the extraction of toxic metal ions from wastewaters and mining effluents. The single-step chemical OMWW treatment can in fact offer an opportunity to mitigate waste disposal problems, to reduce the costs of chemical by-processes and to aid in the development of a filtration system to remove and recover metal ions from contaminated waters.

Veglio et al. (2003) conducted a study on olive mill residues (OMR) as a copper-adsorbing material. A rough characterization of the waste material was performed by microanalysis and scanning electron microscopy pictures. Sorption tests with suspended OMR resulted in copper removal from solution, of about 60%. The COD release in the solution was also monitored during biosorption. Before biosorption OMR were washed with water. In this case the COD release in the solution was reduced to less than 600 mg L-1 after two washings, while the OMR metal sorption properties did not change. Residues regenerated by acid solutions gave a copper removal of about 40% in the same experimental conditions as the first adsorption test: regeneration with ethylenediaminetetraacetic acid (EDTA) at different concentrations suggested that it damages adsorption active sites. On the other hand, the use of HCl and CaCl2 led to a complete regeneration of the biosorbent material. Tests were also performed with a column filled with 80 g of OMR and the breakpoint was demonstrated to take place after about 1 L of solution was treated. Regeneration tests demonstrated that a concentration factor of about 2 can be obtained in non-optimised conditions, highlighting the possibility of using OMR for the treatment of metal-bearing effluents. The main advantages of the process would be the 'low-cost' biosorbing material, considering that it is a waste from olive oil production. Various parameters that characterize OMWW were evaluated after absorption in two different superabsorbent polymers (SAP1 and SAP2). The organic matter was equally distributed in both phases, while there was a concentration of protein and sodium in solution. The K : Na ratio decreased from 70 : 1 to 2 : 1. the polyphenol desorption from the gel into solution was found to follow Fick's law. The mass transfer coefficients were 0.147 min-1 and 0.0085 min-1 for SAP1 and SAP2, respectively. Phytotoxicity tests were carried out with SAP2. OMWW in SAP2 with polyphenol concentrations up to 200 mg L-1 revealed no phytotoxicity, and even stimulated Lepidium sativum growth, while OMWW without the superabsorbent polymer revealed growth inhibition for all concentrations tested. Caffeic acid degradation by the immobilized biomass followed zero-order kinetics. Degradation constants of 0.087 L-1 min-1 (g SAP2)-1 and 1.156 mg L-1 min-1 (g SAP2)-1 were found. Fungi that developed in the plant growth medium were identified as Aspergillus sp. and Penicillium sp.

Was this article helpful?

0 0
Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook


Post a comment