Water treatment

Water is the largest in gre di ent in reconstituted or ange juice and or ange-based drinks, cor re - spond ing to 80–85 % of the fi nal juice. The qual i ty of re con sti tu tion water signifi cantly in fl u enc es the fi nal prod uct. The wa ter re moved from the juice when it is concentrated is in prin ci ple dis tilled or “pure” wa ter. But dis tilled wa ter is not nor mal ly

used for re con sti tu tion. Water from mu nic i pal sup plies or from pri vate wells nor mal ly needs fur ther on-site treat ment to make it suit a ble for re con sti tu tion of good qual i ty juic es.

7.3.1 WATER QUALITY

There are no regulatory stand ards specifying water quality for beverage production other than that it should ful fi l individual national standards for drink ing water or those of the WHO (the World Health Or gan i sa tion run by

the United Nations). Council Directive 98/83/ EC provides legislation on water quality for human consumption for the European Union. How ev er, al though water may be of accept- able drinking qual i ty, it may be un ac cept a ble as reconstitution water, giving rise, for ex- am ple, to off-fl avours in reconstituted juice. A list of some recommended specifi cations for wa ter used in bev er age pro duc tion, also re ferred to as prod uct wa ter, is in Table 7.2. The effects of various water impurities on juice quality are discussed in sub sec tion 4.1.1.

Water hardness is an important qual i ty pa- ram e ter. It is caused by dis solved cal ci um and mag ne si um salts. Tem po rary hard ness re sults from calcium and magnesium bicarbonates, permanent hardness results from chlorides and sul phates. To- tal hard ness, the sum of tem po rary and per ma nent hard ness, may be ex pressed in dif fer ent ways.

In North America it is expressed as cal ci um car bon ate, CaCO3, in wa ter (i.e. the con cen tra tion

of dif fer ent salts cal cu lat ed as the cor re spond ing quan ti ty of CaCO3). In Eu rope the ex pres sion

°dH, de grees Ger man hard ness, is com mon ly used along with °f (France). The con cen tra tion of ions in water (ex pressed as meq/l) is often used in East

In everyday language, water hard ness is sim ply de scribed as soft or hard water. How ev er, the ranges from soft to hard vary be tween coun tries. Typ i cal rang es ex pressed in dif fer ent units are giv en in Table 7.3. Water for juice pro duc tion should be soft, <6 °dH.

TABLE 7.2 SOME

SPECIFICATIONS FOR WATER USED IN BEVERAGE PRODUCTION

Smell none

Taste none

Colour none

Turbidity 1 unit or less

Dry matter, mg/l <500 Total hardness (as CaCO3), mg/l <100 Alkalinity (as CaCO3), mg/l <50 Chlorine, mg/l <0.05 Iron, mg/l <0.1 Manganese, mg/l <0.1 Trihalomethane (THM) none

Source: Tetra Pak

7.3 Water treatment

TABLE 7.3 WATER HARDNESS Degrees Millequi-

German valent CaCO3 hardness /litre

mg/l °dH meq/l Very soft <50 2.8 1 Soft 50–100 2.8–5.6 1–2 Moderately hard 100–200 5.6–11 2–4 Hard 200–400 11–22 4–8 Very hard >400 >22 >8 Conversion factors: 1 °dH = 17.9 CaCO3 mg/l 1 meq/l = 50.0 CaCO3 mg/l 1 °f = 10.0 CaCO3 mg/l 1 ° Clark = 14.3 CaCO3 mg/l

1 grain/US gal = 17.1 CaCO3 mg/l

Product water to storage

Buffer storage Bag/cartridge fi lter Softening

Raw water

Reverse osmosis Ultraviolet light

Activated carbon fi lter

Fig. 7.5 A typical water treatment system used in a juice packing plant.

7.3.2 WATER TREATMENT METHODS

The quality of incoming water de ter mines the types of water treatment car ried out at the juice packer. To fulfi l wa ter quality rec om men da tions, on-site wa ter treatment should aim at:

• removing organic matter • reducing hardness • removing salts • removing chlorine

• removing iron and manganese com pounds • destroying all microorganisms

• maintaining a consistent pH value

Several com mon water treat ment meth ods are de scribed be low. Some treat ments such as ion-ex- change, reverse osmosis and nanofi ltration tech- niques may be used on a par tial stream fol lowed by blend ing with the rest of the water stream to achieve the de sired water quality pa ram e ters.

Figure 7.5 shows a com bi na tion of treat ment steps for prod uct water. However, de pend ing on water qual i ty and juice packer pref er ence, sev er al alternative combinations may be worked out. Flocculation

A method for removing suspended particles, such as organic matter and humic acids from water. The ad di tion of ap pro pri ate chem i cals (fl occulants) to in com ing water ag gre gates the par ti cles to form fl ocs which settle on the bot tom of the reaction tank. Flocculants commonly used are alu min i um sulphate and iron sulphate.

Flocculation is normally not needed for a mu nic i pal water supply because organic mat- ter has already been removed in the municipal wa ter works.

Sand fi ltration

This involves passing water through a sand fi l ter held in a tank to remove insoluble solids. A sand fi l ter consists of several layers of sand which vary in coarseness. It may be used as fi nal fi ltering after fl occulation or iron-man ga nese oxidation. Iron and manganese removal

Under appropriate conditions, iron compounds in wa ter form fl ocs when oxidised by air. The fl ocs are sub se quent ly removed in a sand fi lter. Manganese and iron compounds are re moved by a com bi na tion of ox i da tion and fi l tra tion through a sand fi l ter with a “man ga nese-treat ed” fi l ter bed. The lat ter is re- gen er at ed by po tas si um per man ga nate.

Dealkalisation by ion-exchange

A method used to reduce the alkalinity of water. This may be required as high al ka lin i ty neu tral is es the acid i ty of fruit juices. The presence of carbon- ates and hy drox ides, e.g. of calcium and magne- sium, in wa ter makes it al ka line (pH >7). These are removed by an ion-exchange process. When water is passed through a resin bed (con sist ing of small beads of ap pro pri ate polymer) the calcium and magnesium ions attach to the resin, and water and carbon di ox ide are pro duced. Reducing al ka lin i ty also reduces the hard ness of the water.

Softening by ion-exchange

In this method, calcium and magnesium ions are re placed by sodium ions by passing water through a bed of resin in a similar way to dealkalisation. The hardness of the softened wa ter is virtually zero. Of ten only part of the water is softened so that when it is blended back with the main water stream the de sired hardness is obtained.

Reverse osmosis

A membrane fi ltration system for re mov ing small dis solved molecules including salts. It pro duc es vir tu al ly pure water (>95 % of dis solved salts and >99 % of or gan ic matter are re moved). Despite higher costs, the reverse os mo sis method, which also reduces bi car bo nate con tent, is sometimes preferred to dealkalisation by ion-exchange. Nanofi ltration

A membrane fi ltration system having slight ly larg er pores than those used for re verse os mo sis. It removes par ti cles larger than 1 nanometer (0.000 001 mm). This means that hard ness and col our are removed to geth er with >90 % of dis- solved salts and >99 % or gan ic matter. Nano- and ultrafi ltration are being in creas ing ly used as al ter - na tive methods to fl occulation. (Microfi ltration and ul tra fi l tra tion meth ods in cor po rate mem- branes with cor re spond ing ly larg er pore siz es.) Chlorination

Chlorine is the most widely used sterilant for wa ter. Nevertheless, it should not be added to water con tain ing hu m ic organic matter because trihalomethanes (THMs) are formed. Chlorine is most effi cient as a dis in fect ant at pH <4. As it re acts with several sub stanc es in water, suf- fi cient chlorine must be added to ensure enough is avail a ble to de stroy any mi cro or gan isms. The chlo rin a tion step must be followed by the re mov al of residual chlorine.

Chlorination is normally not needed for mu- nic i pal waters. However, residual chlorine left in the wa ter should be removed as it will otherwise react with or ange fl avour and result in reconsti- tuted juice with a fl at taste.

Activated carbon fi lter

Activated carbon is a highly porous material with a very high adsorbent capacity. Filtering water through activated carbon removes colour and odour. When there is a risk of mi cro bi al con tam i- na tion of fi lters, UV treat ment on the outlet fl ow is rec om mend ed as a safe guard. An al ter na tive is to equip the fi l ters for steam ster i li sa tion, al though

Ultraviolet light

Passing water under ultraviolet (UV) light is a meth od of destroying microorganisms in water. It is a rel a tive ly simple technique of low energy us- age. UV light effectively kills all mi cro or gan isms, but ul tra vi o let radiation is impeded by in sol u ble material in water. It should therefore only be ap- plied to clar i fi ed water.

Ozone treatment

A method of water sterilisation using ozone gas. Be ing a very strong oxidising agent, ozone may also be used to remove off-taste, colour and iron and man ga nese compounds. Ozone is generated on-site from air. Control of the system includes converting re sid u al ozone gas to oxygen by heat, activated carbon or ultraviolet light.

Particle fi lters

Safety fi lters used for incoming water to protect down stream equipment. They are typically bag or car tridge fi lters of 5–10 µm pore size.

7.3.3 IN-PLANT DISTRIBUTION OF PRODUCT WATER

From the water treatment section, product water is dis trib ut ed through pipes to the point of use in the plant. Short but intensive periods of water usage may occur si mul ta ne ous ly at several out- let points, ex ceed ing the out put from the water treatment plant. Buffer storage of treated water is therefore recommended with a volume typ i cal ly cor re spond ing to two hours’ water pro duc tion. It is advisable to recirculate water in the stor- age tank through a UV disinfectant unit to lim it bacterial growth.

The water distribution sys tem must be ca pa ble of han dling high peaks of water con sump tion while main tain ing high water supply pres sure. An increase of production capacity in the juice

packing plant may make the water dis tri bu tion sys tem inadequate. In this case, a pres su rised tank of a few m3 _{can over come the prob lem of}

drop in supply pres sure during pe ri ods of peak water consumption.

7.3.4 DEAERATION OF WATER

The amount of air – or more precisely the ox y gen con tent – in water greatly infl uences the ox y gen con tent of re con sti tut ed juice. Treated product water may contain both free and dis solved air. Free air (bub bles) may be re leased by holding the water in a buffer tank for a certain time, but the removal of dis solved ox y gen re quires a de- aeration process.

Dissolved oxygen levels in cold water are typ i cal ly 10–12 ppm, depending on temperature and pres sure. The solubility of oxygen in water is shown in subsection 4.2.

Provided that the concentrate has been han dled care ful ly (without mixing in air) and that blend ing with water is done in the absence of air, re con sti - tut ing with deaerated water results in a packaged juice with very low oxygen content.

There are several different water deaeration sys tems intended for preheated water or water at am bi ent tem per a ture. Figure 7.6 illustrates a deaeration sys tem working under vacuum suit a ble for both preheated water and water at am bi ent temperature. Water pass es down through a col umn with internal packing. The large con tact area be- tween water and va pour phase makes it easier for the dis solved ox y gen to leave the wa ter. Dis solved ox y gen in the out go ing water is about 0.5 ppm.

Water deaeration is common practice in brew- er ies and carbonated soft-drink pro duc tion, as it fa cil i tates the subsequent car bon a tion step. It is not yet so common in juice pro duc tion, where juice deaerators dominate. In juice packing plants today, the equipment used upstream of pasteurisa- tion often allows the product to come into contact with air. Oxygen is thereby reintroduced into al- ready deaerated prod uct.