Food wastewater production and characteristics

A typical characteristic of the food industry is the great variability in the length of the processing season and the amount of material processed. Also associated with this industry is the wide variation in both the amount of water used for processing and the waste loading from process plant to process plant. In general, wastes from the food industry contain biodegradable organic matter in the form of both dissolved and suspended solids, fats, oils and greases. Therefore, typical pollutant parameters of importance to the food industry are BOD, COD, TSS, fats, oils and greases (FOG) as well as nutrients (nitrogen and phosphorus). Other important parameters include the levels of salt or chlorine (for example in the seafood industry), or proteins (produced, for example, by the meat and dairy industries). Recently, attention has also focused on a number of micropollutants including hormones, pesticides and surfactants.

When considering the literature dealing with food wastewaters it is clear that the quantity and quality of wastewaters produced in the food industry are dramatically different from process to process. In general, processing of food from raw materials requires large volumes of high-grade water which then generate large amounts of wastewater. Table 21.1 shows some typical examples of wastewater production per tonne of treated material. Generally, as an average, some 10-20 m3 of wastewaters are produced per tonne of product. These are also characterised by very different pollutant profiles. For example, vegetable washing generates waters with high loads of particulate matter and some dissolved organics; they may also contain surfactants. Animal slaughter and processing produces very strong organic waste from body fluids, such as blood, and gastrointestinal contents. This wastewater is frequently contaminated by significant levels of antibiotics and growth hormones from the animals and by a variety of pesticides used to control external parasites. Insecticide residues in fleeces are a particular problem in treating waters generated during processing of wool. Processing food for beer produces wastes generated from cooking which are often rich in plant organic material and may also contain salt, flavourings, colouring material and acids or alkalis. Very significant quantities of oil or fats may also be present. So, it is evident

Table 21.1 Wastewater production in the food processing industry (adapted from Johns, 1995; and Metcalf & Eddy, 2002)

Industry, activity

Range of flow (m3/tonne of product)

Cannery

Green beans Peaches and pears Fruits and vegetables (general)

Food and beverage

Bread

Meat packing

Slaughterhouses, USA

Slaughterhouses, Europe

Milk products

Beer

Whisky

Wine

4-17

that different processes for food treatment produce a broad range of wastewaters with different characteristics. Table 21.2 summarises some of the data reported in the literature; this provides an overview of the range of wastewater compositions from the different food-industry sectors. The data also show clearly that inside any one sector the ranges of pollutant concentrations are very wide. In fact, if one examines any single kind of food processing wastewater, the situation is seen to be even more complex. Table 21.3 shows the values of the main parameters for some different kind of wastewaters produced in the dairy industry alone (from Demirel et al, 2005).

The variability of these wastewaters obviously affects the choice of the correct train of processes for wastewater treatment. In order to design the correct treatment process, it is imperative that a truly representative sample of the stream effluent is obtained for characterisation. Not only may samples be required for the 24-hour effluent loads, but it is necessary that peak load concentrations, the duration of peak loads and the occurrence of variation throughout the day are determined (Metcalf & Eddy, 2002). All these elements are of tremendous importance when designing the WWTP for these wastewaters and obviously orient the choices of the designer among different process options.

Table 21.2 Characteristics of food processing wastewater

Parameter

Soluble

nh4 no3

Salinity

References

Dairy

Winery

Fishery

900-7000 530-4700

Slaughter house

Olive oil 20 400-77 200 mill

500-5000 100-2 500 255-830 400-2000 220-2100 16 000-36 000

7130-27200 5805-12700

600-1400

130-170

6 000-66 000

Beverage 2500-22000 1660-6000

Vegetable 250-15 000 7 000 125-4700 103-3 960

50-270 40-230 500-800

4 600-57 000 4100-6500 520

3-70 604

10-300 6-34

5200 4000

25-53 0-45

0-13

7 000-12 000

1280-2990

460-738

20-150

Demirel et al.

Scioli et al. (1997); Becker et al. (1999); Inan et al.

(2005); Yuerekli et al. (1999) Andreottola et al. (2005), Beck et al. (2005), Colin et al. (2005), Eusebio et al. (2005), Brucculeri et al., 2005 Aspé et al. (1997),

Uttamangkabovorn et al. (2005), Austermann-Haun et al. (1997, 1999) Mohammadi et al. (2004), Azbar Yonar (2004), Mishra et al. (2004), Burgoon et al. (1999), Beltrán et al. (1997)

TVS, total volatile solids; N-NH4, ammonia as nitrogen; TKN, total Kjeldhal nitrogen; TP, total phosphorous.

Table 21.3 Characteristics of dairy waste effluents (adapted from Demirel et al., 2005)

Effluent type

COD

bod5

pH

Alkalinity

SS

VSS

TKN

TP

(mg/l)

(mg/l)

(mgCaCO3/l)

(mg/l)

(mg/l)

(mg/l)

(mg/l)

Creamery

2 000-6 000

1200-4000

8-11

150-300

350-1000

330-940

50-60

Cheese whey

68 814

1462

379

Cheese

1000-7500

588-5000

5.5-9.5

500-2500

Fresh milk

4 656

6.9

Milk powder/butter

1 908

5.8

Fluid milk

950-2400

500-1300

5-9.5

90-450

Mixed milk wastewaters

980-7500

680-4500

4.4-9.4

90-450

Mixed dairy

processing wastewaters

1150-9200

6-11

320-970

340-1730

255-830

14-272

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