Aerated lagoon treatment

Aerated lagoons are generally used where there is not sufficient land available for seasonal retention or land application, and economics do not justify

Table 21.6 Efficiency of the activated sludge process for different food processing wastewaters

Wastewater

removal

BOD5 removal

removal

N-NH4 removal

removal

Reference

(%)

(%)

(%)

(%)

(%)

Winery

89-97

96

5G-71

85

88

Chudoba

and Pujol, 1996 Houbron et al., 1998 Brucculeri et al., 2005

Egg processing

88

99

Olsson et al., 1997

Slaughterhouse

62

9G

Johnson et al., 2000

Dairy effluent

86

Liu et al. , 2004

Pet food

70-92

Liu et al. , 2004

Confectionery

86.7

85.9

El-Gohary et al., 1999

Potato-chips

84

86

El-Gohary et al., 1999

an anaerobic or activated sludge system. Efficient biological treatment can be achieved by the use of the aerated lagoon system (Fonade et al., 2000). Air is applied to these ponds by fixed or floating mechanical aerators or by compressors through air diffusers located on the bottom of the pond between 2.5 and 5 m deep. Operating with 2-10 days retention time facilitates a reduction in BOD5 of 55-90%. Table 21.7 reports some results found in literature dealing with the application of aerated lagoons for treatment of food processing wastewaters. From the data reported one can see that a partial removal of nitrogen can be obtained because of the simultaneous nitrification/denitrification processes. There are two types of aerated lagoons in common use: completely mixed (all solids are kept in suspension and aerobic oxidation takes place) and facultative-aerated lagoons (the contents of the pond are only partially mixed and suspended solids settle to depths where anaerobic decomposition occurs). Loading rates for aerated lagoons vary considerably, however aerated lagoons achieve good BOD5 removal. Levels of suspended solids in the effluent are

Table 21.7 Efficiency of aerated lagoons for different food processing wastewaters w t t COD BOD5 TN N-NH4 TP „ ,

Wastewater , , , 4, , Reference removal removal removal removal removal

Dairy

Meat industry 63-69 32-41 22-47 15-47

Potato 61-72

processing

19-27

0-27

Baick et al., 1992 van Oostrom, 1995 Kadlec et al., 1997

usually high and therefore aerated lagoons are usually followed by quiescent settling to reduce the concentration of solids.

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