**4. AOP applications in food industry wastewater treatment**

Food industry wastewaters can generally be treated biologically, in both aerobic and anaerobic reactors. However, as a consequence of diverse consumption, the forming effluents may contain compounds which are poisonous to the micro-organisms in the biological treatment plant. The pre-treatment of the effluent by chemical oxidation, especially with AOPs, can oxidise biorefractory pollutants into a more easily biodegradably form. In the following Sections, there are several examples of AOP applications in different sectors of food industry wastewater treatment.

#### **4.1 Winery and distillery wastewater**

The winery industry generates strong organic wastewater whose quality is highly dependent on the production activities. A typical COD value of the effluent containing sugars, ethanol, organic acids, aldehydes, other microbial fermentation products, soaps and detergents, is between 800 and 1200 mg L-1 but can easily increase to over 25000 mg L-1. Winery wastewater is quite acidic (pH 3-4) and it usually contains large amounts of phosphorus, but not nitrogen and other trace minerals, which are important for biological treatment (Oller et al., 2010).

There are some studies that have considered the ozonation of winery wastewaters. Lucas et al. (2009a) for example, have treated winery wastewaters by ozonation in a bubble column reactor. During a three hour reaction period the degradation of aromatic and polyphenol content was found to be significant, thus the biodegradability of the wastewater was improved and therefore the ozonation may be considered as pre-treatment to further biological treatment. In addition, Beltrán et al. (1999) have noticed the same BOD/COD enhancement in winery effluent after ozonation whereas Lucas et al. (2010) have combined UV and UV/H2O2 with ozone. According to the results, O3/UV/H2O2 combination was identified as the most economical process compared with O3 and O3/UV to the treated winery wastewater.

Winery wastewaters were also treated by solar photo-Fenton integrated with activated sludge treatment in a pilot-plant scale (Mosteo et. al., 2008) and by UV and UV/TiO2 at labscale (Agustina et. al., 2008). With both techniques the efficient removal of organics was successfully achieved whereas photo-Fenton combined with biological treatment showed higher mineralisation rates and a significant toxicity decrease of the treated effluent.

Sources of distillery wastewater, much in common with winery wastewater, are stillage, fermenter and condenser cooling water, and fermenter wastewater. These effluents contain high concentrations of organic material (COD 100-150 g L-1 and BOD 40-200 g L-1) and fertilisers such as potassium, phosphorus and nitrogen. In addition, the molasses wastewater from ethanol fermentation has a typical brown colour which is difficult to remove by traditional biological treatment (Oller et al., 2010).

Several AOP methods have been studied in the treatment of distillery wastewaters. Beltrán et al. (1997b), Benitez et al. (1999; 2003), Sangave et al. (2007) and Sreethawong & Chavadej (2008) have all used ozonation and its combination with UV, H2O2 or Fe-catalyst in the degradation of organics from distillery wastewaters. All these researchers agree that the removal of organic matter improved with the simultaneous presence of UV radiation, hydrogen peroxide or Fe-catalyst in addition to ozone, due to the contribution of hydroxyl radicals generated in these combined processes. In addition, the combined process of ozone pre-treatment followed by an activated sludge step provides enhancement in the removal of substrate obtained in relation to that obtained in the single aerobic treatment without ozonation, i.e. from 28% to 39 % (Benitez et al., 1999; 2003). The integrated process (ozone pre-treatment-aerobic biological oxidation-ozone post-treatment) achieved almost 80% COD reduction in the treatment of distillery wastewater along with the decolouration of the effluent compared with 35% COD removal for non-ozonated samples (Sangave et al., 2007). UV/H2O2 (Beltrán et al., 1997a) and electro-Fenton (Yavuz, 2007) processes have also been used for the treatment of distillery wastewaters. The EF process (Yavuz, 2007) seems to be a promising technique with the COD removal over 90% compared with a UV radiation and hydrogen peroxide combination whose COD reduction is only 38% (Beltrán et al., 1997a). Belkacemi et al. (1999; 2000) investigated wet oxidation and catalytic wet oxidation for the removal of organics from distillery liquors. The initial TOC of the effluent was 22500 mg L-1 while in the AOPs described earlier the total organic carbon was 10 or even 100 times lower. In the temperature and oxygen partial ranges of 180-250 °C and 5-25 bar respectively, the highest TOC removal (around 60%) was achieved with Mn/Ce oxides and Cu(II)NaY catalysts. These catalysts were found to be very effective for short contact times, while for prolonged exposures catalysts deactivation by fouling carbonaceous deposit was shown to be the prime factor responsible for the loss of catalysts activity (Belkacemi et al., 2000). In the supercritical water oxidation of alcohol distillery wastewater (Goto et al., 1998) almost complete colour, odour and TOC removal was attained when more than stoichiometric amount (over 100%) of oxidant (H2O2) was used in temperatures between 200-600 °C.

#### **4.2 Olive industry wastewater**

326 Food Industrial Processes – Methods and Equipment

Food industry wastewaters can generally be treated biologically, in both aerobic and anaerobic reactors. However, as a consequence of diverse consumption, the forming effluents may contain compounds which are poisonous to the micro-organisms in the biological treatment plant. The pre-treatment of the effluent by chemical oxidation, especially with AOPs, can oxidise biorefractory pollutants into a more easily biodegradably form. In the following Sections, there are several examples of AOP applications in different

The winery industry generates strong organic wastewater whose quality is highly dependent on the production activities. A typical COD value of the effluent containing sugars, ethanol, organic acids, aldehydes, other microbial fermentation products, soaps and detergents, is between 800 and 1200 mg L-1 but can easily increase to over 25000 mg L-1. Winery wastewater is quite acidic (pH 3-4) and it usually contains large amounts of phosphorus, but not nitrogen and other trace minerals, which are important for biological

There are some studies that have considered the ozonation of winery wastewaters. Lucas et al. (2009a) for example, have treated winery wastewaters by ozonation in a bubble column reactor. During a three hour reaction period the degradation of aromatic and polyphenol content was found to be significant, thus the biodegradability of the wastewater was improved and therefore the ozonation may be considered as pre-treatment to further biological treatment. In addition, Beltrán et al. (1999) have noticed the same BOD/COD enhancement in winery effluent after ozonation whereas Lucas et al. (2010) have combined UV and UV/H2O2 with ozone. According to the results, O3/UV/H2O2 combination was identified as the most economical process compared with O3 and O3/UV to the treated

Winery wastewaters were also treated by solar photo-Fenton integrated with activated sludge treatment in a pilot-plant scale (Mosteo et. al., 2008) and by UV and UV/TiO2 at labscale (Agustina et. al., 2008). With both techniques the efficient removal of organics was successfully achieved whereas photo-Fenton combined with biological treatment showed

Sources of distillery wastewater, much in common with winery wastewater, are stillage, fermenter and condenser cooling water, and fermenter wastewater. These effluents contain high concentrations of organic material (COD 100-150 g L-1 and BOD 40-200 g L-1) and fertilisers such as potassium, phosphorus and nitrogen. In addition, the molasses wastewater from ethanol fermentation has a typical brown colour which is difficult to

Several AOP methods have been studied in the treatment of distillery wastewaters. Beltrán et al. (1997b), Benitez et al. (1999; 2003), Sangave et al. (2007) and Sreethawong & Chavadej (2008) have all used ozonation and its combination with UV, H2O2 or Fe-catalyst in the degradation of organics from distillery wastewaters. All these researchers agree that the removal of organic matter improved with the simultaneous presence of UV radiation, hydrogen peroxide or Fe-catalyst in addition to ozone, due to the contribution of hydroxyl radicals generated in these combined processes. In addition, the combined process of ozone

higher mineralisation rates and a significant toxicity decrease of the treated effluent.

remove by traditional biological treatment (Oller et al., 2010).

**4. AOP applications in food industry wastewater treatment** 

sectors of food industry wastewater treatment.

**4.1 Winery and distillery wastewater** 

treatment (Oller et al., 2010).

winery wastewater.

Wastewaters from olive oil extraction plants, also called olive mill wastewaters, and wastewaters generated by table olive production, contain high concentration of phenolic compounds. In olive oil production, an oily juice is extracted from the fruit through milling or centrifugation. Table olive production requires the same treatment in order to eliminate the bitterness of the fruit, due to the presence of polyphenolic compounds (Bautista et al., 2008).

Olive mill wastewater contains polysaccharides, sugars, polyphenols, polyalcohols, proteins, organic acids, oil etc. and therefore, the COD of the effluent may be as high as 220 g L-1 and even 190 g L-1 for the amount of suspended solids (Oller et al., 2010).

For several years, olive mill wastewater has been the most polluting and troublesome waste produced by olive mills in all the countries surrounding the Mediterranean. Thus, the management of this liquid residue has been investigated extensively and the efficiency of AOPs for treating olive mill effluents has been studied widely (Mantzavinos & Kalogerakis, 2005). Many researchers have also investigated Fenton processes in the treatment of olive mill effluents (Table 6).

Olive mill wastewater has also been treated by several other AOPs such as ozonation or ozone/UV (Lafi et al., 2009) which have increased the biodegradability of the effluent. Minh et al. (2008) and Gomes et al. (2007) have been successful in decreasing the TOC and phenolic content of olive mill wastewater by CWAO. At reaction conditions of 190 °C and 70 bar of air using Pt and Ru supported on titania and zirconia carriers, the toxicity and phytotoxicity of the effluent decreased to a suitable level for anaerobic treatment (Minh et al., 2008). Gomes et al. (2007) reported that with the carbon supported Pt catalyst TOC and the colour of olive mill wastewater were completely removed after 8 h of reaction at 200 °C

organic matter removal from table olive processing wastewaters (Beltran-Heredia et al.,

323

Meat processing industry wastewaters constitute one of the greatest concerns of the agroindustrial sector, as approximately 62 Mm3/year of water is used worldwide. However, only a small amount of this becomes a component of the final product. Meat processing industry wastewater contains high concentrations of fat, dry waste, sediments and total suspended matter as well as nitrogen and chlorides whilst possessing high biological and chemical oxygen demand (Sroka et al., 2004). Traditionally, meat processing industry wastewaters are treated by anaerobic or aerobic biological systems (Johns, 1995) but recently few studies concerning AOPs have been published. In the publication of Sena et al (2009), dissolved air flotation (DAF) followed by photo-peroxidation (UV/H2O2) and photo-Fenton reactions were evaluated in the treatment of meat processing industry wastewater. According to the results, DAF connected with photo-Fenton treatment achieved the best removals of COD, colour, turbidity and total solids of the treated effluent. WAO have also been used for the removal of organic compounds from meat processing industry wastewater (Heponiemi et al., 2009). After catalytic wet air oxidation treatment, the biodegradability of

Various factors, such as seasonal and source variations, unit operations etc. affect the composition of vegetable and fruit processing industry wastewater. Typically, this effluent contains high organic loads, e.g. from peeling and blanching, cleaning agents and suspended solids such as fibres, dissolved solids, salts, nutrients etc. Furthermore, residual pesticides, which are difficult to degrade during wastewater treatment, may be a concern (EC, 2006). In some studies, AOPs have been used for the removal of organics from fruit and vegetable processing industry wastewaters. In the research of Beltran et al. (1997a, b), wastewater from a tomato processing plant was treated by UV, UV/H2O2, O3, O3/H2O2 and O3/UV. According to results, an ozone-UV radiation system achieved the highest degradation rates (90% removal of COD). Due to the improved biodegradability of the treated effluent, Beltran et al. (1997a, b) recommended the combination of this process with biological oxidation. Caudo et al. (2008) have studied copper-pillared clays catalysed wet peroxide oxidation of citrus juice production wastewater. This effluent contains various phenolic compounds with a chemical oxygen demand of over 4000 mg L-1. After 4 h of oxidation reaction, the TOC had decreased 50% and the biodegradability of the effluent

Coffee industry wastewater is another example of a highly polluted food industry wastewater. The coffee industry uses large amounts (around 40-45 L per kilogram of coffee) of water during the various stages of the production process. The forming effluent contains e.g. caffeine, fat and peptic substances, as well as many different macromolecules such as lignins, tannins and humic acids, which are difficult to handle by conventional biological treatment processes. Recently, Zayas et al. (2007) studied the combination of the chemical

2000; Benitez et al., 2001a, b; Rivas et al., 2000, 2001).

**4.3 Meat processing industry wastewater** 

the wastewater sample has improved.

**4.4 Vegetable and fruit processing wastewater** 

(BOD5/COD index) had increased from 0.05 to 0.4.

**4.5 Miscellaneous wastewater** 

at 6.9 bar of O2. Caudo et al. (2008) have also tested copper-pillared clays as catalysts in wet hydrogen peroxide catalytic oxidation (WHPCO) of olive mill wastewater. According to the research, copper pillared clays are effective and stable catalysts for WHPCO of wastes in water whilst this treatment decreases the toxicity of the olive mill wastewater.


Table 6. Fenton processes for the treatment of olive mill wastewater.

The organic content of wastewater from a table olive process is quite similar to olive mill wastewater containing phenols, polyphenols, sugars, acids, tannins, pectins and oil residues, with a COD of several grams per litre. The inorganic fraction consists of high concentrations of NaCl and NaOH which are used for debittering and fermentation, as well as trace amounts of various metals. As a consequence of the complexity of these effluents, they are unsuitable for conventional aerobic and anaerobic processes (Oller et al., 2010). Recently, it has been possible to enhance the biodegradability of the table olive processing wastewater by different AOPs. Kyriacou et al. (2005) have scaled this treatment method up from a labscale to a pilot-scale for green table olive processing wastewater, which combines biological treatment with an electro-Fenton system. In the pilot plant, 75% COD removal was achieved and the post-treatment by coagulation finally gave an overall 98% COD removal for the treated effluent. Photocatalytic treatment and WAO alone (Chatzisymeon et al., 2008; Katsoni et al., 2008) as well as O3, O3/H2O2, O3/UV, UV, UV/H2O2, Fenton, photo-Fenton and WAO processes combined with aerobic biological treatment have been studied for organic matter removal from table olive processing wastewaters (Beltran-Heredia et al., 2000; Benitez et al., 2001a, b; Rivas et al., 2000, 2001).

#### **4.3 Meat processing industry wastewater**

328 Food Industrial Processes – Methods and Equipment

at 6.9 bar of O2. Caudo et al. (2008) have also tested copper-pillared clays as catalysts in wet hydrogen peroxide catalytic oxidation (WHPCO) of olive mill wastewater. According to the research, copper pillared clays are effective and stable catalysts for WHPCO of wastes in

**Fenton process Conclusions References** 

flocculation-Fenton COD removal 60% and decrease of phytotoxicity Ginos et al.

Considered as a pre-treatment (COD removal 75- 20%) before classical biological process

degradation even 100%

66%) before anaerobic digestion

Considered as a pre-treatment (COD removal 53%) before anaerobic digestion and ultrafiltration resulting in a complete detoxify of effluent. Pilot plant.

The organic content of wastewater from a table olive process is quite similar to olive mill wastewater containing phenols, polyphenols, sugars, acids, tannins, pectins and oil residues, with a COD of several grams per litre. The inorganic fraction consists of high concentrations of NaCl and NaOH which are used for debittering and fermentation, as well as trace amounts of various metals. As a consequence of the complexity of these effluents, they are unsuitable for conventional aerobic and anaerobic processes (Oller et al., 2010). Recently, it has been possible to enhance the biodegradability of the table olive processing wastewater by different AOPs. Kyriacou et al. (2005) have scaled this treatment method up from a labscale to a pilot-scale for green table olive processing wastewater, which combines biological treatment with an electro-Fenton system. In the pilot plant, 75% COD removal was achieved and the post-treatment by coagulation finally gave an overall 98% COD removal for the treated effluent. Photocatalytic treatment and WAO alone (Chatzisymeon et al., 2008; Katsoni et al., 2008) as well as O3, O3/H2O2, O3/UV, UV, UV/H2O2, Fenton, photo-Fenton and WAO processes combined with aerobic biological treatment have been studied for

treatment

Considered as a pre-treatment (COD removal 40- 50%)

COD and aromatics removal 40% Ahmadi et al.

COD removal 70% Lucas &

COD removal 85% by F and 95% by PF Rizzo et al.

Bressan et al. (2004)

(2005)

Dogruel et al. (2009)

Peres (2009b)

(2008)

(2006)

Kallel et al. (2009)

Gernjak et al. (2004)

Khoufi et al. (2006)

Khoufi et al. (2009)

water whilst this treatment decreases the toxicity of the olive mill wastewater.

Fenton COD removal 80-90%, followed by biological

Solar photo-Fenton COD removal 85%, phenolic compounds

Electro-Fenton Considered as a pre-treatment (COD removal

Table 6. Fenton processes for the treatment of olive mill wastewater.

Coagulation and Fenton/photo-Fenton

Fenton with zero-

Coagulation-

valent iron

Meat processing industry wastewaters constitute one of the greatest concerns of the agroindustrial sector, as approximately 62 Mm3/year of water is used worldwide. However, only a small amount of this becomes a component of the final product. Meat processing industry wastewater contains high concentrations of fat, dry waste, sediments and total suspended matter as well as nitrogen and chlorides whilst possessing high biological and chemical oxygen demand (Sroka et al., 2004). Traditionally, meat processing industry wastewaters are treated by anaerobic or aerobic biological systems (Johns, 1995) but recently few studies concerning AOPs have been published. In the publication of Sena et al (2009), dissolved air flotation (DAF) followed by photo-peroxidation (UV/H2O2) and photo-Fenton reactions were evaluated in the treatment of meat processing industry wastewater. According to the results, DAF connected with photo-Fenton treatment achieved the best removals of COD, colour, turbidity and total solids of the treated effluent. WAO have also been used for the removal of organic compounds from meat processing industry wastewater (Heponiemi et al., 2009). After catalytic wet air oxidation treatment, the biodegradability of the wastewater sample has improved.

#### **4.4 Vegetable and fruit processing wastewater**

Various factors, such as seasonal and source variations, unit operations etc. affect the composition of vegetable and fruit processing industry wastewater. Typically, this effluent contains high organic loads, e.g. from peeling and blanching, cleaning agents and suspended solids such as fibres, dissolved solids, salts, nutrients etc. Furthermore, residual pesticides, which are difficult to degrade during wastewater treatment, may be a concern (EC, 2006). In some studies, AOPs have been used for the removal of organics from fruit and vegetable processing industry wastewaters. In the research of Beltran et al. (1997a, b), wastewater from a tomato processing plant was treated by UV, UV/H2O2, O3, O3/H2O2 and O3/UV. According to results, an ozone-UV radiation system achieved the highest degradation rates (90% removal of COD). Due to the improved biodegradability of the treated effluent, Beltran et al. (1997a, b) recommended the combination of this process with biological oxidation. Caudo et al. (2008) have studied copper-pillared clays catalysed wet peroxide oxidation of citrus juice production wastewater. This effluent contains various phenolic compounds with a chemical oxygen demand of over 4000 mg L-1. After 4 h of oxidation reaction, the TOC had decreased 50% and the biodegradability of the effluent (BOD5/COD index) had increased from 0.05 to 0.4.

#### **4.5 Miscellaneous wastewater**

Coffee industry wastewater is another example of a highly polluted food industry wastewater. The coffee industry uses large amounts (around 40-45 L per kilogram of coffee) of water during the various stages of the production process. The forming effluent contains e.g. caffeine, fat and peptic substances, as well as many different macromolecules such as lignins, tannins and humic acids, which are difficult to handle by conventional biological treatment processes. Recently, Zayas et al. (2007) studied the combination of the chemical

**6. Acknowledgements** 

0304-3894

0268-2575

ISSN 0888-5885

ISSN 0920-5861

pp. 812-819, ISSN 0038-092X

199-209, ISSN 0926-860X

**7. References** 

This review has been carried out with the financial support of the Maj and Tor Nessling Foundation and the Finnish Funding Agency for Technology and Innovation (within project

Abdo, M.S.E.; Shaban, H. & Bader, M.S.H. (1988) Decolorization by ozone of direct dyes in

Ahmadi, M.; Vahabzadeh, F.; Bonakdarpour, B.; Mofarrah, E. & Mehranian, M. (2005)

Andreozzi, R.; Caprio, V.; Insola, A. & Marotta, R. (1999) Advanced oxidation processes

Andreozzi, R.; Caprio, V.; Marotta, R. & Radovnikov, A. (2003). Ozonation and H2O2/UV

APHA (1998) Standard Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, Washington, D.C, USA, ISSN 55-1979 Babu, B.R.; Meera, K.S.; Venkatesan, P. & Sunandha, D. (2010) Removal of fatty acids from

*Water, Air, and Soil Pollution,* Vol. 211, No. 1-4, pp. 203-210, ISSN 0049-6979 Banu, J.R.; Anandan, S.; Kaliappan, S. & Yeom, I.-T. (2008) Treatment of dairy wastewater

Bautista, P.; Mohedano, A.F.; Casas, J.A.; Zazo, J.A. & Rodriguez, J.J. (2008) Review An

Belkacemi, K.; Larachi, F.; Hamoudi, S. & Sayari, A. (2000) Catalytic wet oxidation of high-

Belkacemi, K.; Larachi, F.; Hamoudi, S.; Turcotte, G. & Sayari, A. (1999) Inhibition and

Beltrán, F.J.; Encinar, J.M. & González, J.F. (1997b) Industrial wastewater advanced

Beltrán, F.J.; García-Araya, J. & Álvarez, P.M. (1999) Wine distillery wastewater degradation.

*Research,* Vol.31, No.10, pp. 2415-2428, ISSN 0043-1354

*Materials,* Vol. 103, No.3, pp. 233-246, ISSN 0304-3894

presence of some catalysts. *Journal of Environmental Science and Health. Part A,* Vol.

325

Application of the central composite design and response surface methodology to the advanced treatment of olive oil processing wastewater using Fenton's peroxidation. *Journal of Hazardous Materials,* Vol. 123, No. 1-3, pp. 187-195, ISSN

(AOP) for water purification and recovery. *Catalysis Today,* Vol. 53, No, 1, pp. 51-59,

treatment of clorifibric in water: a kinetic investigation. *Journal of Hazardous* 

palm oil effluent by combined electro-Fenton and biological oxidation process.

using ananerobic and solar photocatalytics methods. *Solar Energy,* Vol. 82, No. 9,

overview of the application of Fenton oxidation to industrial wastewater treatment. *Journal of Chemical Technology and Biotechnology,* Vol. 83, No. 10, pp. 1323-1338, ISSN

strength alcohol-distillery liquors. *Applied Catalysis A: General,* Vol.199, No. 2, pp.

deactivation effects in catalytic wet oxidation of high-strength alcohol-distillery liquors. *Industrial & Engineering Chemistry Research,* Vol. 38, No. 6, pp. 2268-2274,

oxidation. Part 2. Ozone combined with hydrogen peroxide or UV radiation. *Water* 

1. Oxidative treatment using ozone and its effect on the wastewater

70023/08) from the European Regional Development Fund.

23, No. 7, pp. 697-710, ISSN 1077-1204

coagulation-flocculation process with various advanced oxidation processes (UV/H2O2, UV/O3, UV/H2O2/O3) for the treatment of coffee industry wastewater. Among the AOPs tested, UV/H2O2/O3 process was the most effective in the reduction of COD, colour and turbidity of the treated effluent.

Baker´s yeast is a commercial product of molasses (the end product of sugar manufacture) which constitutes a solution of sugar, organic and inorganic material in water. Baker`s yeast industry wastewater has a high BOD and COD values which contains significant amount of nitrogen and non-biodegradable organic pollutants. In addition, the effluent has a typical dark colour and, therefore the possible decolourisation of the effluent has been investigated by the Fenton process (Pala & Erden, 2005). Fenton oxidation was applied to the biologically pre-treated baker´s yeast industry wastewater. In the optimum operating conditions, 99% colour removal and 88% COD reduction was achieved. Photo-Fenton and UV/H2O2 processes have also been studied in the removal of colour and organics from baker´s yeast effluents (Çatalkaya & Şengül, 2006).

Palm oil effluent is a colloidal dispersion of biological origin which has a typical unpleasant odour. The total solids content of the effluent is 5-7% and it constitutes of dissolved, organic and inorganic solids, a reason why it is extremely difficult to treat by conventional wastewater treatment methods (Zinatizadeh et al., 2006). In the study of Babu et al. (2010) a palm oil effluent was treated by a combined electro-Fenton-biological oxidation process. After 2 h of EF and 5 d of biological treatment 86% COD removal was achieved. The treated water can be reused for general purpose in an industrial application.

Dairy industry wastewater has a typical white colour and a high nutrient level as well as organic matter content. It is usually treated by biological methods such as the activated sludge process and anaerobic filters although aerobic biological processes have high energy requirements whilst anaerobic biological methods require additional treatment (Kushwaha et al., 2010). Recently, solar photocatalytic oxidation has been used after anaerobic sludge blanket reactor for the removal of COD from dairy industry wastewater (Banu et al., 2008). The combination of anaerobic process and solar photocatalytic oxidation using TiO2 as a catalyst resulted in 95% removal of COD from dairy industry wastewater. This integrated system may be a promising alternative for the treatment of dairy industry effluents. In addition, Inamdar & Singh (2008) have applied photocatalysis in the treatment of dairy industry effluent.

#### **5. Conclusion**

The characteristics and treatment of food industry wastewaters by different advanced oxidation processes were considered. Typically, the amount and composition of the effluent varies considerably. The high organic matter content is a basic problem in food industry wastewaters but the organic compounds are usually easily biodegradable and the effluents can be treated by conventional anaerobic or aerobic biological methods. However, as a consequence of diverse consumption, the forming effluents may contain compounds which are poisonous to micro-organisms in the biological treatment plant. The pre-treatment of the effluent by chemical oxidation, especially with AOPs, can oxidise biorefractory pollutants to a more easily biodegradable form. Thus, the combination of AOP and biological treatment may be a possible solution for the treatment of variable food industry wastewaters.
