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A review in Reuse of water in dairy companies: Possible Solutions

1. INTRODUCTION................................................................. 12 . WASTEWATER OF MILK PRODUCTS................................. 1 2.1. USE OF WATER............................................................. 3 2.2.CHARACTERISTICS OF DAIRY WASTEWATER................. 3 2.3 WASTEWATER TREATMENT.......................................... 4 2.3.1.. PHYSICAL TREATMENT............................................. 4 2.3.2. CHEMICAL TREATMENT............................................ 4 2.3.3. BIOLOGICAL TREATMENT......................................... 5 2.3.4 ALTERNATIVES........................................................... 53. WASTERWATER OF CHEESE COMPANIES.......................... 7 3.1. INDUSTRIAL STRATEGIES FOR LIQUID WHEY............... 8 3.2 CHEESE WHEY WASTEWATER TREATMENTS............... 11 3.2.1. BIOLOGICAL TREATMENT........................................ 11 3.2.2 PHYSICOCHEMICAL TREATMENT.............................. 11 3.2.3 CONSTRUCTED WETLANGS...................................... 124. REUSE OF WATER ........................................................... 12 4.1. NANOFILTRATION...................................................... 14 4.2. REVERSE OSMOSIS..................................................... 15 4.3. COMBINATION OF METHODS.................................... 165. REFERENCES.................................................................... 19

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1. INTRODUCTION

Ever increasing industrialization and rapid urbanization have considerably increased the rate of water pollution. The dwindling supplies of natural resources of water have made this a serious constraint for industrial growth and for a reasonable standard of urban living. The environmental protection agencies have imposed more stringent regulatory prohibitions and they have started more strict vigil along with some non governmental organizations to protect the environment. This has made the water treatment more expensive and to comply with the discharge quality standard itself, is becoming a huge burden for the industries. It was therefore felt that the possibilities of reuse of the wastewater for various purposes should be investigated. The recycling or reuse of water for similar duties mainly depends on availability of suitable process technology for water purification. Due to wide fluctuations in industrial effluent quality, this becomes more challenging. With the advent of membrane technology and significant improvements in efficiency and cost effectiveness, the competitiveness of recycling over discharge has greatly increased. In dairy industries, water has been a key processing medium. Water is used throughout all steps of the dairy industry including cleaning, sanitization, heating, cooling and floor washing — and naturally the requirement of water is huge. Dairy wastewater is distinguished by the high BOD and COD contents, high levels of dissolved or suspended solids including fats, oils and grease, nutrients such as ammonia or minerals and phosphates and therefore require proper attention before disposal. Researchers have shifted their interests in possibilities of reuse or recycling of industrial wastewaters. Dairy wastewater does not contain toxic chemicals but it has high concentration of dissolved organic components like whey proteins, lactose, fat and minerals and the decomposition of some of the contaminants causes discomfort to the surrounding population. A suitable technology for recycling or reuse at least a reasonable quantity of the wastewater produced in the plant is needed.

2. WASTEWATER OF MILK PRODUCTS

Dairy plants are found all over the world, but because their sizes and the types of manufactured products vary tremendously, it is hard to give general characteristics. The dairy industry can be divided into several production sectors. Each division produces wastewater of a characteristic composition, depending on the kind of product that is produced (milk, cheese, butter, milkpowder, condensate). Wastewater from dairy industry may originate from the following sources: (Carawan, Chambers, Zall, 1979)

1) The washing and cleaning out of product remaining in the tank trucks, cans, piping, tanks, and other equipment is performed routinely after every processing cycle.

2) Spillage is produced by leaks, overflow, freezing-on, boiling over, equipment malfunction, or careless handling.

3) Processing losses include: a) Sludge discharges from CIP clarifiers b) Product wasted during HTST pasteurized start-up, shut-down, and product change-over c) Evaporator entrainment d) Discharges from bottle and case washers e) Splashing and container breakage in automatic packaging equipment f) Product change-over in filling machines.

4) Spoiled products, returned products, or by-products such as whey are wasted.5) Detergents and other compounds are used in the washing and sanitizing solutions that

are discharged as waste.6) Entrainment of lubricants from conveyors, stackers and other equipment appear in the

wastewater from cleaning operations.7) Routine operation of toilets, washrooms, and restaurant facilities at the plant contribute

waste.8) Waste constituents may be contained in the raw water which ultimately goes to waste.

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Uncontaminated water from coolers and refrigeration systems, which does not come in contact with the product, is not considered process wastewater. Such water is recycled in many plants. If wasted, it increases the volume of the effluent and affects the size of the piping and treatment system needed for disposal.

FIGURE 1. MILK PROCESSING

EPA assembled available information on the dairy industry. That included two major studies of the industry, one by a private research firm, the other by a university. Those studies provided basic data about the industry and virtually all available information on the technology of dairy products processing. Out of this extensive study emerged this picture:1) The more than 5,000 dairy plants in the United States discharge about 53 billion gallons of wastewater each year - about 31 billion gallons into municipal treatment plants, and 22 billion gallons directly into water bodies.2) That the typical wastewater stream from a dairy plant has the following characteristics Typical Waste Stream from a Dairy Plant a) BOD - 2300 mg/l b) SS- 1500 mg/l c) FOG - 700 mg/l3) The major pollutant in waste discharges from dairy plants is organic material. Breaking down the organic pollution, the micro-organisms consume oxygen in the water. A measurement of pollutants that consume oxygen in water is called "biochemical oxygen demand," or BOD. Water with high BOD contains a large amount of decomposing organic matter.4) Another major pollutant in dairy plant discharges is suspended solid waste, such as coagulated milk, particles of cheese curd, and in ice cream plants, pieces of fruits and nuts. The measurement of this pollutant is called "total suspended solids," or TSS.

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MILK

RECEIVING

STORAGE TANKS

CLARIFICATIONN

PASTEURIZATION

MILK HOMOGENIZATION CHEESE MANUFACTURE BUTTER: CHURNING MILK POWDER: DRYING CONDENSATE: CONDENSING

PACKAGING

STORAGE

SHIPPING

CLEANING AND SANITATION SOLUTIONS

WASHWATER

STEAN COOLING WATER

MILKCHEESE WHEY/BUTTERBUTTERMILK POWDERCONDENSATE

EFFLUENT

TO DRAIN

STEAM COOLING WATER

WASTEWATER

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5) Raw wastes from dairy plants contain excessive amounts of organic materials and suspended solids.6) Other identified pollutants in dairy plant wastes are phosphorus, nitrogen, chlorides, and heat. 7) Another consideration is the acid or alkali content of liquid wastes. The pH of many individual wastes within a dairy plant fall outside the acceptable range for direct steam discharge.8) Finally, research also has revealed that wastes from most dairy plants can be successfully treated by municipal treatment plants and pose no dangers to the municipal plants. However, in some situations, a byproduct cheese-manufacturing - whey - may create problems in some municipal treatment plants.2.1. Use of water Water is used for a number of purposes in a dairy plant. For example, water is used for washing trucks, cooling products, make-up for products, as a cooling tower medium, for washing and sanitizing and for employee drinking and restrooms. Relatively clean water from condensers, refrigeration and air compressors and air conditioning systems can be a substantial part of the water use in a dairy plant (Carawan, Chambers, Zall, 1979).Depending on the type of installation and the cleaning system and its management, the total quantity of water consumed in the process can reach several times the volume of milk processed. Consumption is usually 1.3-3.2 litres of water/kilo of milk received, but can reach as much as 10 litres of water/kilo of milk received. Nonetheless, it is possible to optimize this consumption at 0.8-1.0 litre of water/kilo milk received using advanced equipment and proper management (UNEP, 2000). As indicated in table 1, the greatest consumption of water occurs during secondary operations, particularly in the cleaning and disinfection where 25-40 per cent of the total is consumed.TABLE 1: WATER CONSUMPTION IN THE DAIRY INDUSTRY (CARAWAN, CHAMBERS, ZALL, 1979)

Productive processes

Level Of consuption

Operations with highest

water consumption

Observations

Milk Low Heat treatmentPackaging

Cream and Butter

Low Pasteurization of cream churning

Rinsing of buttermilk before churning

Yogurt Low - Mainly secondary in operationsCheese Medium Salting Salting using brine

Secondary operations

High Cleaning and disinfection

Generation of steam

Refrigeration

Consumption of water is the greatest during these operations

2.2. Characteristics of the dairy wastewater Dairy effluent contains soluble organics, suspended solids, trace organics. All these components contribute largely towards their high biological oxygen demand (BODS) and chemical oxygen demand (COD). Dairy wastes are white in colour and usually slightly alkaline in nature and become acidic quite rapidly due to the fermentation of milk sugar to lactic acid. The suspended matter content of milk waste is considerable mainly due to fine curd found in cheese waste. The pollution effect of dairy waste is attributed to the immediate and high oxygen demand. Decomposition of casein leading to the formation of heavy black sludge’s and strong

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butyric acid odors and characterize milk waste pollution. The characteristics of a dairy effluent contain temperature, Color, PH (6.5-8.0), DO, BOD, COD, dissolved solids, suspended solids, chlorides, sulphate, oil & grease. It depends largely on the quantity of milk processed and type of product manufactured. The waste water of dairy contains large quantities of milk constituents such as casein, inorganic salts, besides detergents and sanitizers used for washing. It has high sodium content from the use of caustic soda for cleaning.Dairy effluents contain dissolved sugars and proteins, fats, and possibly residues of additives. The key parameters are biochemical oxygen demand (BOD), with an average ranging from 0.8 to 2.5 kilograms per metric ton (kg/t) of milk in the untreated effluent; chemical oxygen demand (COD), which is normally about 1.5 times the BOD level; total suspended solids, at 100–1,000 milligrams per liter (mg/l); total dissolved solids: phosphorus (10–100 mg/l), and nitrogen (about 6% of the BOD level). Cream, butter, cheese, and whey production are major sources of BOD in wastewater. The waste load equivalents of specific milk constituents are: 1 kg of milk fat = 3 kg COD; 1 kg of lactose = 1.13 kg COD; and 1 kg protein = 1.36 kg COD. The wastewater may contain pathogens from contaminated materials or production processes. A dairy often generates odors and, in some cases, dust, which need to be controlled. Most of the solid wastes can be processed into other products and byproducts. (Patil et al., 2014)

2.3. Waste water treatment Common techniques for treating dairy industry wastewaters include grease traps, oil water separators for separation of floatable solids, equalization of flow, and clarifiers to remove SS. Biological treatment consists of the aerobic and anaerobic process. Sometimes anaerobic treatment followed by aerobic treatment is employed for the reduction of soluble organic matter (BOD) and biological nutrient removal (BNR) is employed for the reduction of nitrogen and phosphorus. Aerobic biological treatment involves microbial degradation and oxidation of waste in the presence of oxygen. Conventional treatment of dairy wastewater by aerobic processes includes processes such as activated sludge, trickling filters, aerated lagoons, or a combination of these. But there are more advanced techniques which will be beneficial to us by providing energy generation and reuse and because energy conservation have become the words of the day and anaerobic processes have emerged. As described previously, dairy processing wastewaters contain substantial quantities of organic matter, nitrogen and phosphorus. If excessive concentrations of these enter waterways, oxygen depletion and plant growth in the waterways may reach nuisance proportions.The following methods can be used in appropriate combination to achieve the effluent treatment objectives. 2.3.1 Physical treatment Solid and suspended matter can be separated from the effluent stream by use of equipment and separation methods such as dissolved air flotation, centrifugation and micro-filtration.Wastewater, usually passes through screens to remove debris and solids. In addition, solids that are heavier than water will settle out from wastewater by gravity. Particles with entrapped air float to the top of water and can also be removed. These physical processes are employed in many modern wastewater treatment facilities today.This type of treatment will not only reduce sludge duild up in lagoons and wear on pumps, but also should be a rapid way of reducing BOD concentration in effluent prior to disposal or reuse (Carawan, Chambers, Zall, 1979). 2.3.2. Chemical treatmentChemicals can be used to enhance treatment characteristics, such as settling of solids by PH correction, and to improve treatment performance or suitability for land application. Care should be taken to ensure that concentrations of any trace elements such as copper or cadmium, which may be present as impurities, do not have adverse residual impact on organisms in the treatment and disposal systems and in the general environment. Chemical methods of phosphorus removal utilize the low solubility of metal phosphates. Both ferric and aluminium phosphates show minimum solubility between pH 5 and 6. A variety of different calcium phosphates exist and these show minimum solubility at high pH values (usually greater than 9).

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Reports exist in the literature on the use of iron (both ferrous and ferric ions), aluminium and calcium salts for chemical phosphate precipitation. It has been found that about twice the molar ratio of metal ion to phosphorus is required for effective phosphate precipitation. With milk processing wastes even higher metal to phosphate ratios are required, and that calcium ions are not very effective at removing phosphates. It is assumed that this is in some way related to the proteins that are present in milk wastes and that they compete with phosphates for bonding to the metal ions. Typical treatment efficiencies for phosphate precipitation using ferric, ferrous and aluminium salts results in phosphorus concentrations in the effluent of less than 1 g m-3. Treatment to this degree will result in insufficient phosphorus being available for subsequent biological treatment. Chemical precipitation of phosphorus will be most effective after biological treatment (Carawan, Chambers, Zall, 1979). 2.3.3. Biological treatment The dairy industry uses aerobic or anaerobic treatment, or a combination of both, to treat the wastewater. Aerobic systems require an energy source to provide the oxygen required to assimilate the organic matter in the wastewater and hence are more suited to low to moderate strength wastewaters, since the higher the organic content the greater the oxygen demand and the greater the costs. Anaerobic systems have been developed for their ability to treat high strength wastes and the utilization of the methane gas. In aerobic treatment systems, bacteria, in the presence of oxygen, convert the organic components of the waste to carbon dioxide,water and bacterial biomass. All aerobic treatment systems have the potential to cause odours if operated incorrectly. The industry worldwide has tried many forms of aerobic treatment. These have included trickling filters, rotating biological contactors and various forms of mechanically aerated lagoon systems. In New Zealand only extended aeration activated sludge systems are used. Typical treatment parameters for an activated sludge plant treating dairy plant wastewater are 94% COD, 99% BOD5 70% TKN and 50% total phosphorus removal (Carawan, Chambers, Zall, 1979). Considerable experimental work has been undertaken on the anaerobic digestion of whey from casein and cheese plants. Various forms of high rate anaerobic digestion systems have been investigated with whey. In an anaerobic digester, anaerobic bacteria, acting in the absence of oxygen, convert the organic components in the wastewater to methane, carbon dioxide and water. Organic forms of nitrogen are converted to the ammonium nitrogen form. Anaerobic digestion may be carried out in low rate lagoon systems or in high rate reactors. The advantages of anaerobic digestion are: production of a valuable byproduct (methane), that can be recovered and utilized as a fuel , removal substantial quantities of BOD5 and COD without the input of mechanical energy for aeration, produce less sludge than aerobic systems. 2.3.4 Alternatives A step away from pretreatment of dairy process wastewaters is its total treatment and discharge to a tributary stream. Usually economic and political considerations move the processor toward treating his own wastewater. As treatment alternatives are considered, there are two systems which have received wide acceptance. These systems use either land application techniques or the aeration lagoon - stabilization pond system. Both systems depend on land availability and are applicable to rurally-operated plants. These systems offer a simplistic approach to minimizing manpower requirements and operational logistics. A third alternative for the treatment of-dairy process wastewaters is the extended aeration system which includes the oxidation ditch operating mode. This type system is an activated sludge system which can treat the wastewater within a 24 to 30 hour time frame. The extended aeration system maintains the wastewater under aerobic conditions for the entire detention time of treatment. The operation of this system requires a high level of operator skill and knowledge. This activated sludge system is quite susceptible to "bulking" and requires close attention on a daily basis. Considerable monitoring of the system is required to maintain the system at its peak performance. The activated sludge process is a more sophisticated system to operate but is probably the more efficient and effective form of treating dairy wastewaters. Again, cost considerations must be determined when selecting an activated sludge system of this type. (Carawan, Chambers, Zall, 1979).

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Even at BOD5 reduction efficiency above 90%, biological treatment systems will generally discharge BOD5 and suspended solids at concentrations above 20 mg/l. To achieve zero discharge, systems such as reverse osmosis and ion exchange would have to be used to reduce inorganic and organic solids that are not affected by the biological process. The following is a brief description of various tertiary treatment systems that could have application in aiming at total recycling of dairy wastewater. (Carawan, Chambers, Zall, 1979).

FIGURE 2. DAIRY PROCESSING EFFLUENT TREATMENT AND DISCHARGE OPTIONS (CARAWAN, CHAMBERS, ZALL, 1979)

Sand filtration involves the passage of water through a packed bed of sand on gravel where the suspended solids are removed from the water by filling the bed interstices. When the pressure drop across the bed reaches a partial limiting value, the bed is taken out of service and backwashed to release entrapped suspended particles. In lieu of backwashing, the bed may be taken out of service and the first few inches of sand removed and replaced with fresh sand. To increase solids and colloidal removal, chemicals may be added ahead of the sand filter. Activated carbon adsorption is a process wherein trace organics present in wastewater are adsorbed physically into the pores of the carbon. After the surface is saturated, the granular carbon is regenerated for reuse by thermal combustion. The organics are oxidized and released as gases off the surface pores. Activated carbon adsorption is ideal for removal of refractory organics and color from biological effluent. (Carawan, Chambers, Zall, 1979). Lime precipitation clarification process is primarily used for removal of soluble phosphates by precipitating the phosphate with the calcium of lime to produce insoluble calcium phosphate. Lime is added usually as a slurry (10%-15% solution), rapidly mixed by flocculating paddles to enhance the size of the floc, then allowed to settle as sludge. Besides precipitation of soluble phosphates, suspended solids and colloidal materials are also removed, resulting in a reduction of BOD, COD and other associated matter. With treated sewage waste having a phosphorus

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content of 2 to 8 mg/l, lime dosages of approximately 200 to 500 mg/l, as CaO, reduced phosphorus content to about 0.5 mg/l. (Carawan, Chambers, Zall, 1979). Ion-exchange operates on the principle of exchanging specific anions and cations in the wastewater with non-pollutant ions on the resin bed. After exhaustion, the resin is regenerated for reuse by passing through it a solution having the ion removed by wastewater. Ion-exchange is used primarily for recovery of valuable constituents and to reduce specific inorganic salt concentrations. Reverse osmosis process is based on the principle of applying a pressure greater than the osmotic pressure level to force water solvents through a suitable membrane. Under these conditions, water with a small amount of dissolved solids passes through the membrane. Since reverse osmosis removes organic matter, viruses, and bacteria, and lowers dissolved inorganic solids levels, application of this process for total water recycles has very attractive prospects. Ammonia air stripping involves spraying wastewater down a column with enforced air blowing upwards. The air strips the relatively volatile ammonia from the water. Ammonia air stripping works more efficiently at high pH levels and during hot weather conditions. A recycling system utilizing tertiary treatment systems that could be used for treatment of secondary wastewater for complete recycle would include a combination of the preceeding in the following order: secondary treatment, lime precipitate-clarification, ammonia stripping, recarbonation, sand filtration, reverse osmosis, and activated carbon filtration (Carawan, Chambers, Zall, 1979). Besides the secondary biological sludge, excess sludge from the tertiary systems specifically the lime precipitation clarification process would have to be disposed of. Sludge from sand filtering backwash is recycled back to biological system. Organic particles, entrapped in the activated carbon pores, are combusted in the carbon regenerating hearths. Thus, recycle of water in dairy processing may be theoretically possible but the management and operational costs would be prohibitive not even considering the high capital outlay needed for such an elaborate system.

3. WASTEWATER OF CHEESE COMPANIES

According to FAO (Food and Agricultural Organization) cheese is one of the main agricultural products worldwide. Whatever type of cheese (Parmesan, Mozzarella, Gouda, Danish blue, Brie, Camembert, Feta, Serpa, etc.), the making factories generate effluents that represent a significant environmental impact. Cheese effluents exhibit COD values in the interval 0.8–102 g L−1 and BOD values in the range 0.6–60 g L−1 leading to a high consumption of dissolved oxygen in water bodies. The lactose and fat contents can be considered as the main responsible for COD and BOD and because of their very high concentration of organic matter, these effluents may create serious problems of organic burden on the local municipal sewage treatment systems (Janczukowicz et al., 2008). This effluent has a low pH, although basic pH's have also been reported in the wide interval 3.3–9.0. Suspended solids, TKN, and total phosphorus oscillate in the intervals (g L−1 ) 0.1–22.0, 0.01–1.7 and 0.006–0.5, respectively. Furthermore, the ammonium nitrogen (NH4 +-N) value ranging from 60 to 270 mg L−1 can also cause toxic effects to aquatic life (Farizoglu et al., 2007). In addition, cheese effluent composition can be approached to the following ratio for carbon, nitrogen and phosphorus C/N/ P≈200/3.5/1 which may be considered as deficient in terms of nitrogen components for aerobic or anaerobic processes. The cheese manufacturing industry is responsible for the three main types of effluents; cheese whey (resulting from cheese production), second cheese whey (resulting from cottage cheese production) and the washing water of pipelines, storage and tanks that generates a wastewater called cheese whey wastewater (CWW). This effluent also contains CW and SCW (Janczukowicz et al., 2008). The whey is a by-product from the cheese or casein manufacturing. This effluent is a greenish-yellow liquid and can be considered as milk free of casein and fat. Casein precipitation leads to the formation of two whey types. Acidic whey (pH<5) is obtained after fermentation or addition of organic or mineral acids. Sweet whey (pH= 6–7) is obtained by addition of proteolytic enzymes like chymosin. The milk type used in the cheese production (cow, goat,

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sheep, buffalo and other mammals) also influences the characteristics of the produced cheese whey. From the valorization point of view, cheese whey has a high nutritional added value. Acid coagulation occurs close to the isoelectric pH of casein (pH 4.6), as a consequence, more milk protein precipitates. Acid whey has a limited use due to the acidic taste and high salt content. Calcium (1.2– 1.6 g L−1 ) concentrations in acidic whey are approximately 2 times higher than the values observed in sweet whey. Thus, in the acidic coagulation, colloidal calcium contained in the casein micelles is solubilized and partitioned into the whey (Panesar et al., 2007). The lactose level is higher in sweet whey than in acidic whey. Cheese whey is considered the most important pollutant in dairy wastewaters, not only because of the high organic load, but also for the volume generated. Cheese whey has a biological oxygen demand in the range 27–60 g L−1 and a chemical oxygen demand in the interval 50–102 g L−1. The BOD/COD ratio is normally above 0.5 constituting a substrate easily biodegradable by anaerobic or aerobic digestions. The high CW salinity (conductivity in the proximity of 8 mS cm−1 ) is the consequence of the type of whey produced in the process and NaCl addition during cheese production. Additionally, other minor components such as citric and lactic acids (0.02–0.05%), non-proteinic nitrogen compounds (urea and uric acid), and vitamins (B group), can also be found in CW. Acidic pH favors the filamentous biomass growth. The low buffering capacity of CW is responsible for the rapid acidification in biological treatments. The main mineral components (>50%) are NaCl, KCl and calcium salts. The high sodium content of CW can cause problems when operating biological digesters. Lactose is the main responsible of the organic load, and an extensive number of microorganisms cannot directly use it as a carbon source. When cheese whey is used in cottage cheese production, it generates the second cheese whey (SCW). Second cheese whey has about 60% of the dry matter content of the original cheese whey (Pereira et al., 2002). This effluent maintains a significant organic matter content (COD values up to 80 g L−1 ) and high salinity (7–23 mS cm−1 ). This high salinity comes from the second addition of salts like calcium chloride in the cottage cheese production. Once more, lactose (around 50 g L−1 ) is the principal constituent responsible of the high COD values (>70%). The SCW has acidic characteristics with pH values within the range 3–6. A biodegradability value close to 0.5 makes these effluents suitable to undergo biological degradation. Protein (≈0.5–8gL−1 ), total solids (≈6.8 g L−1 ) and total nitrogen (2 g L−1 ) contents are similar to those reported for CW. The values of COD (60–80 g L−1 ), BOD (≈30 g L−1 ), fats (0.5–8gL−1 ) and total suspend solids (≈8.0 g L−1 ) are normally below the maximum values observed in CW. These lower values are the consequence of the second flocculation carried out to obtain the cottage cheese. SCW keeps a high lactose concentration similar to that observed in CW. SCW is normally free of amino acids and vitamins (Minhalma et al., 2007). Cheese whey wastewater presents characteristics similar to CW. Cheese whey wastewater generally presents acidic characteristics; however basic pHs have also been reported. This parameter is logically affected by the volume of alkaline reagents used in washing stages. In general, CWW has an elevated concentration of organic matter, however values in a wide range from 0.8 to 77 (COD) and 0.6 to 16 g L−1 (BOD) can be found. The high biodegradability index (BOD/COD≈0.46–0.80) suggests the suitability of biological process application. Lactose, protein and fat contents average concentrations of 45, 34 and 6 g L−1 , respectively (Yang et al., 2003). The low values of lactose and protein can be explained by the tendency to acidification due to the fermentation of lactose to lactic acid. As a result, the lowering of the initial pH causes the casein precipitation and a disagreeable odor of butyric acid. Additionally, the CWW fat content can bring about sludge floatation and the washout of active microbial biomass in biological processes. The level of total suspended solids is reported to be in the range 0.1–5.0 g L−1 while total solids average values of roughly 65 g L−1 (Yang et al., 2003; Janczukowicz et al., 2008).

3.1. Industrial strategies for liquid whey Whey concentration traditionally takes place under vacuum in a falling-film evaporator with two or more stages. Evaporators with up to seven stages have been used since the mid-seventies to compensate for increasing energy costs. Mechanical and thermal vapour compression have

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been introduced in most evaporators to reduce evaporation costs still further. RO (reverse osmosis) plants of tubular design have also been installed in many plants for preconcentration before the whey is sent back to the farmers and before being evaporated to final concentration.Concentrated whey is a supersaturated lactose solution and, under certain conditions of temperature and concentration, the lactose can sometimes crystallise before the whey leaves the evaporator. At concentrations above a DM content of 65% the product can become so viscous that it no longer flows. Whey concentration by reverse osmosis (RO) is frequently used to reduce volumes and increase solids content prior to transportation or further processing. Preconcentration of sweet whey before evaporation allows for more energy efficient removal of water at lower solids and increased capacity of existing evaporators. Total solids (TS) levels of 10-25% can be obtained in an efficient, practical manner. Reverse Osmosis membranes are used to remove water and will not alter the relative composition of the sweet whey components. Permeate quality from RO systems depends on the quality and composition of the feed and the level of concentration. The higher the TS, the greater the amount of constituents in the permeate. Typically, RO permeate will contain small (but measurable) amounts of organic solids. The process performance is greatly affected by operating parameters such as feed flow rate, pressure, temperature, pH and micro-biological quality of feed stream, feed concentration and fouling characteristics of the membrane for various components. Advantages of RO are the reduction salt content and dissolved matter content in brackish water, reduction in heavy metals, reduction in nitrates and sulphates, reduction in colour, tannins and turbidity, softens hard water, chemical-free e.g. needs no salt or chemicals during operation, high retention for salts and particular univalent ions (up to >99%), disinfection, including viruses. Disadvantages of RO are the higher operating costs, high energy costs, high discharge volumes, high concentrate volume, high operating pressure than NF, requires supply water to be treated (pre-filtration 0.1 - 20 microns), reverse osmosis normally provides water with aggressive pH level (in other words, a low or high pH in water with few ions), membranes sensitive to free chlorine. Whey proteins were originally isolated through the use of various precipitation techniques, but nowadays membrane separation (fractionation) and chromatographic processes are used in addition to both precipitation and complexing techniques. The process that has been most extensively used for separation of whey proteins from whey serum is heat denaturation. Theprecipitated protein formed by this process is either insoluble or sparingly soluble depending on the conditions prevailing at denaturation: it is called heat-precipitated whey protein (HPWP).Native protein concentrates have a very good amino acid profile with high proportions of available lysine and cysteine. Whey protein concentrates (WPC) are powders made by drying the retentates from ultrafiltration of whey. They are described in terms of their protein content, % protein in dry matter, ranging from 35% to 85%. To make a 35% protein product the liquid whey is concentrated about 6-fold to an approximate total dry solids content of 9%. To obtain an 85% protein concentrate the liquid whey is first concentrated 20 – 30-fold by direct ultrafiltration to a solids content of approximatively 25%; this is regarded as the maximum for economic operation. It is then necessary to diafilter the concentrate to remove more of the lactose and ash and raise the concentration of protein relative to the total dry matter.Diafiltration is a procedure in which water is added to the feed as filtration proceeds in order to wash out low molecular components which will pass through the membranes, basically lactose and minerals. About 95% of the whey is collected as permeate, and protein concentrationsas high as 80 – 85% (calculated on the DM content) can be obtained in the dried product. Advantages of ultrafiltration are the high throughput of production,it is economical, easy to clean and operate, easy to scale up. Possible disadvantages of UF are that only removes suspended matter and bacteria, is sensitive to oxidative chemicals, NaOCl exposure determines the life-span of the membrane and is typically 150.000 to 500.000 ppm and pH dependent. Damage may occur when trying to prevent hard and sharp particles > 0.1 mm, membrane damage at pressure > 3 bar.Defatted WPC powder containing 80 – 85% protein dry matter is a very interesting option for some applications, e.g. as a replacement for white of egg in whipped products such as meringues and as a valuable ingedient in various foods and fruit beverages. Treatment of the

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whey retentate from a UF plant in a microfiltration (MF) plant can reduce the fat content of 80 – 85% WPC powder from 7.2% to less than 0.4%. Microfiltration also concentrates fat globule membranes and most of the bacteria in the MF retentate, which is collected and disposedof separately. The defatted MF permeate is routed to a second UF plant for further concentration; this stage also includes diafiltration. The resulting WPC with about 20 –25% DM is then spray-dried to reduce the moisture content to a maximum of 4% before bagging. The advantages of MF are the low operating pressure required, low energy consumption for semi dead-end set-up, compared to nano-filtration or reverse osmosis, few manual actions required, relatively cheap, no energy-consuming phase transfer needed, such as e.g. evaporation techniques, quality of the produced permeate is not determined by the management. Possible disadvantages of MF are that only suspended matter and bacteria removed (~log 5 removal), sensitive to oxidative chemicals (e.g. nitric acid, sulphuric acid, peroxide and persulphate in  high concentrations), damage can be caused by hard and sharp particles > 0.1 mm, whereby pre-filtration is necessary, membrane damage if re-rinsed at pressure in excess of 1 bar. As whey has a fairly high salt content, about 8 – 12% calculated on dry weight, its usefulness as an ingredient in human foods is limited. By having the whey demineralised, various fields of application can however be found for whey which is partially (25 – 30%) or highly (90 – 95%) demineralised. Demineralisation involves removal of inorganic salts together with somereduction in the content of organic ions such as lactates and citrates. The partial demineralisation is mainly based on utilisation of cross-flow membranes specially designed to “leak” particle species that have radii in the nanometer (10–9 m) range. This type of filtration is called nanofiltration (NF). Here are a few specific advantages and disadvantages of NF. Advantages: Lower discharge volumes, lower retentate concentrations than RO for low value salts, reduction salt content and dissolved matter content (TDS) in brackish water, reduction in heavy metals, reduction in nitrates and sulphates, reduction in colour, tannins and turbidity, softens hard water when specific softening membranes are used, chemical-free e.g. needs no salt or chemicals during operation, pH of water after nano-filtration is normally non-aggressive, disinfection. Disadvantages: Higher energy consumption than UF and MF (0.3 to 1 kWh/m³), pre-treatment is needed for some heavily polluted waters (pre-filtration 0.1 - 20 microns), limited retention for salts and univalent ions, nano-filtration membranes are a little more expensive than reverse osmosis membranes, membranes are sensitive to concentrations, free chlorine (life-span of 1000 ppmh), an active carbon filter or a bi-sulphite treatment is recommended for high chlorine concentrations.The high degree desalination is based on either of two techniques:• Electrodialysis: Electrodialysis is defined as the transport of ions through non-selectivesemi-permeable membranes under the driving force of a direct current (DC) and an applied potential. The membranes used have both anion and cation exchange functions, making the electrodialysis process capable of reducing the mineral content of a process liquid, for example seawater or whey. A major limiting factor for using electrodialysis in dairy processing is the cost of replacing membranes, spacers and electrodes, which constitutes 35 –40% of the total running costs in the plant. Replacement is necessary due to fouling of the membranes, which in turn is caused by precipitation of calcium phosphate on the cation exchange membranesurfaces and deposition of protein on the anion exchange membrane surfaces.Electrodialysis is best for demineralisation levels below 70%, where it isvery competitive compared to ion exchange.• Ion exchange: In contrast to electrodialysis, the process which removes ionisable solidsfrom solutions on a continuous electro-chemical basis, an ion exchange process employs resin beads to adsorb minerals from solution, in exchange for other ionic species. The resins have a finite capacity for this, so that when they are completely saturated, the adsorbed minerals must be removed and the resins regenerated before reuse. Normally the resins are used in fixed columns of suitable design. Ion exchange resins are macromolecular porous plastic materials,formed into beads with diameters in the range of 0.3 to 1.2 mm for technical applications. Chemically they act as insoluble acids or bases which, when converted into salts, remain insoluble. The main characteristic of ion exchange resins is their capacity to exchange the

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mobile ions they contain for ions of the same charge sign, contained in the solution to be treated. There are various types of resin, which often have a specific impact on particular ions. This enables effective selectivity.  It also enables particular heavy metals to be re-used.Ion exchangers are quickly polluted, which considerably reduces the exchange capacity. Another disadvantage is the relatively high operational costs for, among other things, the regeneration fluid. After use, this regeneration fluid forms a major concentrate flow that needs to be disposed of.

3.2. Cheese whey wastewater treatments3.2.1. Biological treatmentsAnaerobic digestion: The conventional treatments of CWW effluents are based on anaerobic and aerobic digestion processes. A number of researchers have claimed that the anaerobic processes are essentially the only viable method of wastewater treatment with high organic load from cheese making-plants. Accordingly, the majority of studies have been conducted under anaerobic conditions using Upflow Anaerobic Sludge Blanket (UASB) reactors applied to raw CWW. (Gutiérrez et al., 1991; Gavala et al., 1999) and diluted CWW (Gavala et al., 1999). COD removal values in the interval 81–99% (raw CWW) and 85–98% (diluted CWW) have been reported. Despite the significant COD removal obtained by the anaerobic digestion of raw CWW, in some cases, the residual COD of the effluent still presents unacceptable values as high. The required HRT seems to be highly dependent on initial COD concentration. Thus, COD values above 5 g L−1 require more than 2 days of digestion reaching up to 13 days. Due to their highly flocculation capacity with elevated sludge settling and compaction, the use of the up flow anaerobic sludge blanket (UASB) reactors to treat CWW has been recommended. The continuously stirred tank reactors (CSTR) and vertically moving biofilm system (VMBS) configurations have been used to treat diluted (Yang et al., 2003) and synthetic (Rodgers et al., 2004) CWW, respectively. A food amount of methane in the biogas is achieved with this method. Disadvantages of the anaerobic digestion are that the biological degradation of CWW is characterized by unstable operation, when the CWW has a high content of CW, the production of volatile acids by acetogenic bacteria is faster than the consumption by the methanogenic bacteria which causes a reduction of the pH and COD elimination extent (Rodgers et al., 2004), difficulty of granular sludge formation when acidification occurs (Yang et al., 2003).Aerobic digestion: Some studies have been carried out under aerobic conditions to treat raw CWW, mainly by activated sludge (Fang, 1991; Martins and Quinta-Ferreira, 2010; Rivas et al., 2010; Rivas et al., 2011) with high eliminations of the principal contaminant indicators. In the majority of cases the process has been conducted by using high HRTs (8 days). Fang (1991), reported a reduced HRT (≈19.8 h) by using a low initial COD cheese wastewater. This author completed some activated sludge experiments in three stages achieving a residual BOD lower than the value legally permitted for direct discharge. The aerobic digestion achieved an 89% of COD elimination. The consecutive anaerobic+ aerobic digestions were tested thereafter. This sequence led to COD removals close to 99% and an effluent in accordance with the legal limit value. Similar results were reported by Frigon et al. (2009), when treating a reconstituted CW in a SBR system. The COD reduction was 98% and the residual COD was only 33 mg L−1 . However the initial COD of the reconstituted CW (2.0 g L−1 ) does not approximate to the actual organic load of typical CWW. Normally, the aerobic biodegradation is limited by excessive sludge formation (Gutiérrez et al., 1991); however Rivas et al. (2010), minimized this effect when applying the aerobic digestion to a precoagulated CW.3.2.2. Physicochemical treatmentsOxidation processes:. Oxidation is suggested to perform better as a post-treatment process, after biodegradation (Martins and Quinta-Ferreira, 2010). Thus, the Fenton oxidation, as a post-treatment process presents leads to a significant COD removal (final COD=20 mg L−1 ) using a high concentration of hydrogen peroxide, 0.5 M and 2 g/L of Fe3+ and a pretreated effluent with low COD, 00.5 g/L. This need for high reactants concentration leads to the high operational costs. The single ozonation and catalytic ozonation have also been tested, as pos-treatment,

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allowing a very good COD removal. Oxidation processes are not recommended when dealing with raw CWW.Coagulation/flocculation and precipitation: Among the different physicochemical processes coagulation–flocculation is likely the most simple and economical system. A high COD removal has been reported by using FeSO4 at pH 8.5 than FeCl3 utilized at pH 4.5 (Rivas et al., 2010). The supernatant after coagulation/flocculation/precipitation is highly biodegradable and present an odorless colourless aspect. The high salinity is the limiting factor for agricultural use. It can be used as fertilizer in fertigation, after the correct addition with irrigation water, according to crop tolerance and nutrient needs. 3.3.3. Constructed wetlands Typically the small and medium cheese factories are isolated from centralized wastewater treatment facilities, and in some cases, located next to ecologically sensitive areas, which exacerbates environmental risks. Land application is often the only viable option for wastewater disposal. The presence of suspended solids and high salinity content might affect the physical and chemical structures of soils and eventually pollute the groundwater. Constructed wetlands are an emerging technology which uses plants and microbial communities from the rhizosphere to eliminate various organic and/or inorganic chemical contaminants. Theoretically, this technology could be a good environmental-friendly solution. The technology does not need a full time monitoring strategy, presents low construction and operating costs with good ecological and landscape integration. Thus, this wastewater needs a pre-treatment for previous fat removal (Comino et al., 2011), or even fat removal plus dilution with domestic wastewater (Farnet et al., 2008). Chemical pretreatment with lime (Rivas et al., 2010; Prazeres et al., 2012) can be a solution to allow the use of wetlands in the CWW treatment.

4. REUSE OF WATER

Increasing prices of water supply and disposal, the availability and quality of water, and strict legal environmental controls have increased concerns about sustainable development and thepreservation of the public image of companies. It has therefore been advised that industries internally reclaim and reuse process waters in order to reduce water consumption and effluent production. Dairy factories are characterised by high consumption of water, generating from 0.2 to 10 L of effluent per litre of treated milk (Balannec et al, 2005). Washing, rinsing, cleaning-in-place (CIP), pasteurising, ultra-high temperature (UHT) processes, chilling, cooling, steam production, etc. are the main processes in which large amounts of water are consumed. The wastewater streams of this type of industry show variable composition, often containing different concentrations of organic matter (proteins, carbohydrates and lipids), suspended solids and oils/fats. According to the levels of these contaminants, the wastewater is considered to be a low-, medium- or highpollution stream. The heterogenity of dairy industry wastewaters is one of the problems with treating these effluents. (Suarez and Riera, 2015). Several techniques have been assayed to reduce the pollutant load of wastewaters generatedby food industries in general, and dairy industries in particular: flocculation, deep filtration, coagulation, etc. Membrane technologies (MTs), ranging from microfiltration (MF) to reverse osmosis (RO), are among the most promising techniques due to their consideration as “clean technologies” (Riera, Suarez, Muro, 2013). One-step ultrafiltration (UF) experiments were performed but obtained permeates did not fulfil the quality levels to reuse the water. (Riera et al., 2013). UF processes only reject proteins, passing lactose and other small molecules through the membrane, which leads to high values of COD in dairy wastewater permeates. In other cases, a combination of different technologies has been adopted to obtain higher quality water. One of the aspects to bear in mind when selecting the type of membrane treatment is that of deciding on the desired quality of the permeate, as this affects both the technology and the process conditions used (effect of pressure, feed concentration, pH, etc., on membrane selectivity). Different water specifications depending on its end use can be seen in Table 2. The highest possible water quality is required when the aim is to reuse water to produce steam. Its main properties must include a lowCa2+ content as well as low conductivity and a low

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concentration of soluble solids. Water for boilers is only obtained using RO, combining two NF steps or sequences of NF and RO. The characteristics of water that is to be used in cleaning and watering are less restrictive and, in these cases, simple processes can be sufficient to achieve the purpose. Bacteriological control is of paramount importance when the reused water may come into contact with food (heat exchangers, etc.).

TABLE 2. WATER SPECIFICATIONS ACCORDING TO END USES (RIERA, SUAREZ, MURO, 2013)

Parameter Boiling water

Cooling/Heating water

Water for cleaning

Process Other uses

PH 7-10 6.9-9.0 6.5-9.0 6.5-9.5 6-9Conductivity (25 oC) μS/cm

<40 1000 <200 2500 (20 °C) /

COD, mg O2/L <10 75 / <5 43TOC, mg O2/L <4 14 <4 <4 16BOD5, mg O2/L 1-50 25 / / 30Ca2+, mg/L <0.4 240 <1 <400 /Total suspended solids,mg/L

0.5-10 100 35 / <20

Turbidity, NTU

/ 50 / <5 <10

Colony count/1 mL

/ / <100 <100 /

E. Coli/100ml / / ND ND <200Coliform bacteria/100 mL

/ / ND ND <200

Water used in the industry for production processes, equipment cleaning, heatexchangers,etc., which could be in contact with food (must be drinking quality water).

Segregating wastewater streams or “in situ” wastewater treatment before mixing with other currents can be a wise practice. It has the advantages of optimizing water use and the treatments to reuse the water produced by MT, adapting the water composition to the most suitable technology to obtain a certain water quality. Automatic online monitoring of each stream for pH, conductivity and turbidity is recommended to control and isolate water streams with a similar composition which could be processed using similar technology (Riera et al., 2013). Membrane technologies (MTs), mainly nanofiltration (NF) and reverse osmosis (RO), have shown satisfactory behaviour and are promising techniques due to their advantages as “clean technologies”. The good quality of water obtained with these techniques, the high recovery rates, space savings, chemical dosage savings, continuous and simple operation without phase changes, easy transportation and reduced cost are important advantages. However, MTsundergo a decline in permeate flux due to the problems of particle blocking, concentration polarisation and fouling after continuous long-term operation. Biofouling problems can cause frequent shutdowns and are related to the discontinuity of production cycles. Several researchers have used MTs to produce water of different qualities using single or combination membrane stages (with or without pre- and post-treatments), which include onestep processes such as ultrafiltration (UF), NF or RO, and combinations of UF +NF, NF+NF, NF+RO or RO+RO (Suarez and Riera, 2015).

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4.1. Nanofiltration The nanofiltration membrane allows permeates be obtained that can be reused in the industry with high permeate flow rates (Riera et al., 2013). Riera et al. (2013), used flash cooler condensates from a dairy factory . Condensates from evaporation and drying may be considered low pollutant waters, while end pipe wastewaters need intense treatment to obtain clean water. Flash cooler condensates from a dairy factory (1.5·106 L processed per day) were characterised and then processed using a nanofiltration membrane (molecular weight cut-off (MWCO) 200 Da) in a single step pilot plant (1.6 m2 surface area) to study the effect of the main process parameters (pressure, temperature, recovery rate) on the quality of the permeate thus obtained. The effluent used in this study was taken from a Spanish dairy factory. The wastewater source was collected at the output of four FCs used in a direct UHT process. A commercial spiral wound SelRO MPS-34 2540 B2X (Koch Membrane Systems, USA) NF membrane was used. The membrane was first characterised with prefiltered tap water. After stabilization, the permeate flow rate was plotted versus temperature, TMP and time. Condensates from industrial FCs were nanofiltered at pressures between 15 and 30 bar and temperatures between 30 and 50 °C. Feed flow rates varied between 3.5 and 5 m3/h. The permeate flow rate was measured continuously and permeate samples were analyzed each hour.

FIGURE 3. SCHEME OF THE NF(RIERA ET. AL, 2013)

According to the final results and of the sudy and bearing in mind the limitations of their end use, the generated permeates could be used first for indirect heating purposes, taking advantage of the thermal potential of condensates. A subsequent secondary reuse would also be possible in other miscellaneous services. A NF plant has been proposed (171 and 185.4 m2 theoretical andreal membrane areas, respectively) to treat 20 m3/h of condensates with 87.5% water recovery (Riera et al, 2013). A study evaluated the application of MBR as secondary treatment and NF as tertiary treatment for the reuse of dairy wastewater. Emphasis was placed on evaluating the best NF operating conditions that would generate a better quality permeate and provide less membrane fouling (Andrade et al., 2014). The wastewater that was fed into the MBR came from a large dairy industry located in the state of Minas Gerais, Brazil, whose manufactured products are UHT milk, yogurt, cheese, cottage cheese and petit suisse. The wastewater was collected from the industry wastewater treatment station, following the stages of sieving and flotation with compressed air. The bench scale membrane bioreactor used to conduct the tests was built by PAM Membranas Seletivas Ltda (Rio de Janeiro Brazil). The MBR had one module of hollow fiber, submerged microfiltration membranes (polyetherimide, average pore size of 0.5 lm, membrane area of 0.044 m2, packing density of 500 m2/m3). MBR showed high removal efficiency for COD (mean of 98%) and nutrients (86% total nitrogen and 89% phosphorus).

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However, the concentration of dissolved solids in the permeate still prevented its reuse. For NF testing, an NF90 commercial membrane from Dow–Filmtec was used. The membrane was cut properly and inserted into an 8.9 cm diameter stainless steel cell, providing a 62 cm2 filtration area, which simulated a procedure with a flat membrane. Cross-flow velocity of 7.8 m/s was selected as the most suitable for the NF of the MBR permeate, once this condition led to increased turbulence and, therefore, less fouling and better permeate quality. It is observed that the quality of the NF permeate meets all the standards for cooling water and water for low pressure steam generation, proving that it may be reused for these applications as well as for washing floors, external areas and trucks, that require a lower quality water. The COD concentration of 73 mg L-1 not only meets the discharge parameters of environmental legislation in effect in the state of Minas Gerais, Brazil (180 mgCOD L-1), but is also well below this standard, thus contributing to the release of better quality effluent and to the preservation of water bodies. Vourch et al. (2005) used NF to treat a synthetic dairy wastewater, comprising whole milk, skim milk and milk whey, with COD concentration of 8200 mg L-1and conductivity of 700 lS cm-1. The NF permeate had a COD concentration of 87 mg L-1, conductivity of 637 lS cm-1 and calcium concentration of 3.2 mg L-1. Fernandez et al.(2010) evaluated the operation of a pilot NF unit used for the recovery of clean in place (CIP) solution consumed in the dairy industry. The feed solution had a COD concentration between 3000 and 10,000, total dry extract between 1.0% and 2.0%, and conductivity of 15 mS cm_1; while the permeate had 1500–2500 mgCOD L-1, conductivity of 15–20 mS cm-1 and total dry extract of 0.9–1.0%. The concentrations of the permeate obtained in the study of Andrade et al. (2013) were found to be lower, which is probably due to the contribution of the high removal of pollutants in the MBR in order to generate a final permeate with high quality.

4.2. Reverse Osmosis Suarez and Riera (2015) used low-pollution flash cooler (FC) condensates from the direct heat treatment of milk and milk-based products in order to treat them by means of reverse osmosis (RO) to obtain high-quality water for use in boilers. Boiler water specifications (pH 7–10, conductivity (25 oC) <40mS/cm, COD <10mg O2/L, total organic carbon (TOC) <4mg O2/L, biological oxygen demand after 5 days (BOD5) 1–50mg O2/L, Ca2+ <0.4 mg/L and total suspended solids (TSS) 0.5–10 mg/L) are the most restrictive reuse parameters of all these possibilities (Suarez and Riera, 2015). The water treated in their study was the effluent from some of the FCs operating in a direct UHT process at a Spanish dairy factory. For the RO experiments, a spiral-wound thin-film Duratherm HWS 4040 HR membrane was recommended by the manufacturer (GE Water & Process Technologies, USA) to treat this type of effluent. The treated condensates did not fulfil the characteristics of water if they are to be reused in boilers. But high-quality water with low conductivity (up to 17.5 lS/cm) and COD (up to 10 mgO2/L) can be obtained after discontinuous RO (Duratherm HF membranes) of low-pollutant direct UHT milk condensates (156.2–285.0 lS/cm conductivity and 5–89 mgO2/LCOD). Reductions up to 98.2% and 97.8% in conductivity and COD, respectively, were achieved. Permeate conductivities and CODs lower than 40 lS/ cm and 10 mgO2/L, respectively, were obtained by single RO couple with an activated carbon column when working in continuous modem (Suarez et al., 2014). Reverse osmosis water similar to available vapour condensates (produced in drying processes) can be achieved allowing this water to be reused for heating, cleaning and cooling purposes. (Vourch et al., 2008). The objective of Vourch et al., (2008) study was to use RO units for the treatment of several selected wastewaters from dairy plants for water reuse purposes. The study also showed that RO operation gave better water quality than NF, as NF did not provide a better permeate flux. These selected wastewaters of eleven French companies were mainly mixtures of milk, whey and cream with dry matter (DM) ranging from 0.4 g.L-1 to 71 g.L-1, fat content (0 to 22%) and heat treatment (no heat treatment to high heat treatment: 130 oC, 20 min). A commercially available RO spiral-wound membrane was used in this study, a TFC HR SW2540 (provided by KOCH Membrane Systems) with a NaCl rejection of 99.5%. It is a thin film

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composite (TFC) membrane with polyamide active layer and an effective filtration area of2.5 m2. Inspection of data illustrated that RO operation can reach a water recovery of 90 to 95 % with TOC of purified water lower than 7 mg.L-1. The removal efficiency for RO membrane was high for all the compounds: organic matter removal was very high (>99.8 % for TOC and > 99.5% for lactose), nitrogenous matter removal was around 96% and conductivity removal was about 97% (higher than 95% for multivalent ions and 87% for monovalent ions). RO treatment of the selected wastewaters was carried out until 90–95% water recovery was achieved with an average permeate flux around 11 L.h-1.m-2. TOC of purified water was lower than 7 mg.L-1and came mainly from lactose (76–100%). Purified water was low mineralised: conductivity <50 μS.cm-1 corresponding essentially to monovalent ions (Na+, K+ and Cl-). Quality of purified water was similar to vapour condensates, so it can be reused for the same applications as heating, cleaning and cooling. Pretreated dairy waste water using coagulation adsorption and membrane separation was passed through a cross flow reverse osmosis membrane system and the permeate water was found to have very good quality (Sarkar et al. 2006). Raw wastewater was collected from A.P. Dairy, Hyderabad, India and was pretreated with different types of coagulants like inorganic (alum and ferric chloride), polymeric (polyaluminium chloride) and natural organic (sodium arboxymethyl cellulose commonly known as Na-CMC, alginic acid, and chitosan). Cellulose acetate flat sheet membranes of 44 cm2 surface area having 10,000 Da and 1,000 Da molecular weight cut off were supplied by Millipore Corporation, MA, USA. Permionics Pvt.Ltd., Vadodara, India had supplied nanofiltration membrane of 300 Da molecular weight cut off (MWCO) and RO flat sheet membrane as complimentary samples. The membranes were polyamide on non oven polyester. The ceramic microfiltration membrane having 0.45 micron pore size used in pilot plant was purchased from Orelis, France. It is having tubular configuration with 19 channels and 0.167 m2 surface area. Spiral wound RO membrane with 2 m2 surface area was procured from Osmonics, USA. The membrane is made up of cellulose acetate and having more than 99% NaCl rejection. The nanofiltration/reverse osmosis experiments were done in a stainless steel test cell of dead-end type having maximum pressure limit of 50 bar. After coagulant and PAC (Powdered activated charcoal) treatment the pH of the water was adjusted to 6.5 and was passed through UF and RO membranes separately. Pilot scale experiment using spiral wound RO membrane yields better water quality compared to flat sheet membranes used in bench scale experiments. The quality of water after reverse osmosis was found to be comparable to that of process water used in the Dairy and can be recycled back.

TABLE 3. COMPARISON OF RO WATER WITH DAIRY PROCESS WATER (SARKAR ET. AL., 2006)

Process water RO permeatepH 7.3 6.5

Conductivity, μS/cm 242 40Turbidity, NTU 0.2 0.0TDS, mg/L 128 33Hardness, mg/L 88 3FOG, mg/L Nil NilChloride, mg/L 58 16COD, mg/L 24.7 16.5

4.3. Combination of methods Vourch et al., (2005) treated waste wasters of 10 French industrial dairy plants using two-stage membrane treatments (NF + RO and RO + RO). Two commercially available spiral-woundmembranes were used in this study: one NF membrane (Desal5-DL, Osmonics) with a 150-300 g.mol-1 molecular weight cut-off and one RO membrane (TFC HR, Koch) with a NaCI rejection of 99.5%. Membranes are thin-film composite (TFC) with an active polyamide layer. The filtration area of the spiral wound modules is 2.5 m2. Deionised water membrane permeabilities (at 25°C) were 3.3 and 7.3 L.h-l.m-2.bar-1 for Koch TFC HR and Desal-5 DL,

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respectively. A two-stage NF+RO treatment of process waters, purified water was produced with roughly the same quality as with the single RO stage: TOC <3.3 mg.L-1 and conductivity <9/~S.cm-1. For the process waters processed by RO+RO operation, purified water was quite significantly demineralised (conductivity <3/tS.cm -1) and TOC was <2.5 mg.L -1. Three qualities of water could be produced: the poorest quality by a single NF, good quality for reuse in dairy plants by single-stage RO or by a two-stage NF+RO process, and very pure water by a two-stage RO+RO. The quality of these purified waters is similar to the quality of vapourcondensate produced by the dairy industry. For water used for cleaning in place: preparationof dilute acid or alkaline solutions, pre- and intermediate rinsing, for washing floors and theoutside of plant and vehicles, for heating and cooling applications. For such applications purified water produced by a single RO operation or by two-stage operations (NF+RO or RO+RO) can be reused as well as vapour condensates. For applications where unexpected contact between milk products and water can occur, when there is a risk of leakage, drinking water quality is required (TOC <2 mg.L (Vourch et al., 2005). A two-stage ultrafiltration and nanofiltration (UF/NF) process for the treatment of model dairy wastewater was investigated to recycle nutrients and water from the wastewater.(Luo et al., 2011). A model effluent was prepared from commercial whole milk (Sanyuan pure milk, Capital Agribusiness Group, China), skimmed by a refrigerated centrifuge (4k-15, Sigma, Germany) at 4 C for 20 min (10,000 rpm, 10,733g). Then the skim milk was diluted with deionized water. Three commercial UF membranes (UP005P, UH030P, Ultracel PLGC) and five NF membranes (NF270, NF90, Nanomax50, Desal-5 DL, Desal-5 DK) were tested in this study. As UF permeate of dairy wastewater with the Ultracel PLGC membrane contains lactose and cleaning chemicals at low concentration, nanofiltration could be applied to obtain dischargeable or reusable water. From the five NF membranes the NF270 membrane would have higher productivity and lower operating cost in NF operation. Therefore, NF270 could be considered as the most suitable membrane for the NF step in terms of its solutes rejection and low TMP. The Ultracel PLGC membrane was suitable to concentrate proteins and lipids in wastewater in the first stage because of its excellent antifouling performance and high transmission of lactose and inorganic salt. The NF270 membrane was suitable to treat the UF permeate in the second stage to obtain lactose in retentate and reusable water in permeate due to its high permeability and high lactose rejection as well as the low retention of salts.

FIGURE4. SCHEMATIC DIAGRAM OF A TWO-STEP UF/NF PROCESS FOR DAIRY WASTEWATER TREATMENT AND UTILIZATION FOR BIOENERGY PRODUCTION. (LUO ET. AL., 2011)

Dairy wastewaterBiodiesel

Protein Lipid Biofuel UF permeate

Lactose Biogas

Reusable Water

17

NF

Algaecultivation

Lipid extraction

Transesterification

Starch + celluloseFermentation

Anaerobic digestion

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Balannec et al.,(2002) compared membranes used for NF and RO in order to study their ability to reject milk components. The effluent model solution was 1/3 diluted skimmed milk. The following membranes were studied: in dead-end NF (Desal5-DL and Desa15-DK,150-300 Da, Osmonics NF45 and the NF, 200 Da, FilmTec TFC S, Koch), in dead-end RO (Desal3-SE Osmonics BW30, FilmTec TFC HR, Koch), in crossflow NF (Desal5 DL, Osmonics and Nanomax 50, 400 Da, Millipore), in crossflow RO (TFC HR, Koch and Nanomax 95, 100 Da, Millipore). Dead-end filtration experiments were carried out in a stainless steel cylindrical cell installed on an anti-vibrating table in a thermostatic controlled room at 25°C. Crossflow filtration experiments were conducted with spiral wound organic membranes at 25 or 50°C. As expected, concentrations in permeate were higher with NF membranes than with RO ones. Permeate COD ranged from 173 to 1095 mg O2.L-1 for NF. With RO membranes, COD rejection was very high (99.88-99.96%) and permeate COD was low, in the range 45 to 120 mg O2. L-1. In NF rejection of multivalent ions (Ca2+ ,Mg2+, citrate, phosphate) ranged from 92.4 to 99.9%, while for Na+ and K+ it was in the range 50-84% conversely, rejection of Cl- was negative in some cases. The best COD rejection for NF was obtained with FilmTec new available NF and Desa15 DL membranes. In RO, rejection of monovalent ions was higher than 93.8% and multivalent ions were almost totally rejected (>99.6%). The best COD rejection for RO was obtained with Desal3-SF and TFCHR membranes. Balannec et al., showed that one single membrane operation is insufficient for producing water of compositioncomplying with the requirements for drinking water, but purified water in the dairy plant can be produced if finishing step (membrane, other) is added.

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5. References

A.M. Farnet, P. Prudent, M. Cigna, R. Gros, Soil microbial activities in a construted soil reed-bed under cheese-dairy farm effluents. Bioresour Technol 2008;99:6198–260

A.R. Prazeres, F. Carvalho, F.J. Rivas, Cheese whey management: a review. J Environ Manage 2012;110:48–68

A. Suarez, F. A. Riera, Production of high-quality water by reverse osmosis of milk dairy condensates. Journal of Industrial and Engineering Chemistry 21 (2015) 1340–1349

A. Suarez, T. Fidalgo, F. Riera, Recovery of dairy industry wastewaters by reverse osmosis. Production of boiler water. Separation and Purification Technology 133 (2014) 204–211

B. Balannec, G.G. Guiziou, B. Chaufer, M.R. Baudry, G. Daufin, Treatment of dairy process waters by membrane operations for water reuse and milk constituents concentration. Desalination 147 (2002) 89-94

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