56 Organic waste recycling: technology and management
Table 2.21 Pollution loads in effluents from water blanching of vegetablesa (U.S.EPA 1971)
Vegetable
Effluent
flow (L/hr)
BOD 5
(kg/ton)COD
(kg/ton)SS
(kg/ton)Beets (and peelers) 3,013 88(85)b 147(83) 109(55)
Carrots (and peelers) 1,937 44(65) 90(67) 153(64)
Corn 523 11.2(16) 14(18) 3(12)
Peas 294 3,500 ppm
in effluent
Potatoes 580 24 26 21
Potatoes (and peelers) 2,118 84(89) 127(86) 82(37)
aBOD 5 , COD, and SS in kg per ton of raw product except as noted
bPercent of total effluent pollution load in ().
(COHNS) + anaerobic bacteria + energy ĺ C 5 H 7 O 2 N
(new bacterial cells) (2.4)Note: C 5 H 7 O 2 N is a common chemical formula used to represent bacterial
cells.
In the absence of organic matter, the bacteria will undergo endogenous
respiration or self-oxidation, using its own cell tissue as substrate:
C 5 H 7 O 2 N + 5O 2 ĺ 5CO 2 + NH 3 +2H 2 O + energy (2.5)The compounds CO 2 and NH 3 are nutrients for algae. With sufficient
sunlight, algal photosynthesis will occur (Oswald and Gotaas 1955):
NH 3 + 7.62CO 2 + 2.53H 2 Oĺ C7.62 H8.06 O2.53 N+ 7.62 O 2
(new algal cells) (2.6)Another equation to incorporate P compound in the algal photosynthesis is
(Oswald 1988):
106CO 2 + 236H 2 O + 16NH 4 + + HPO 4 2- ĺ C 106 H 181 O 45 N 16 P + 118O 2 +
171H 2 O + 14H+ (2.7)In a natural water course receiving low organic loading, the oxygen produced in
Equation 2.6 can be used by the bacteria in Equations 2.1 and 2.2, and the cycle is
repeated. This cycle, called ‘algal-bacterial symbiosis’, is a natural phenomenon
occurring in a water body that receives a low organic loading, and these algal-
bacterial reactions are in a state of dynamic equilibrium. Parts of the algal and
Sunlight
AlgaeSunlightAlgae