54 Organic waste recycling: technology and management
Waste generation by unit operations
Much of the total waste flows from many commodities, especially from citrus,
come from relatively clean water used in cooling, condensing, and
concentrating. The segregation of this water for reuse is practised to some extent
and should become almost universal. Other large waste flows are from washing
tomatoes, peeling potatoes, peeling peaches, washing potatoes, cutting corn,
cutting and pitting peaches, washing corn, and blanching corn. Large quantities
of BOD 5 are generated in those processes. Citrus by-products recovery also
generates very large amounts of BOD 5 and SS. Other large sources of SS are
peeling potatoes, cutting corn, and washing tomatoes.
Peeling: Table 2.20 shows a summary of estimated pollution loads in the
effluent from peeling fruits and vegetables reported by various investigators.
Peel wastes comprise a high percentage of the total pollution loads in the
effluent of fruit and vegetable plants.
Blanching: Table 2.21 shows examples of losses from vegetables during
blanching expressed in BOD 5 , COD, and SS. The volume of effluent from
blanchers is generally relatively small, but the concentrations of suspended and
total solids can be high. These wastewaters contain a high organic content (in terms
of BOD 5 and COD) which can be treated or recycled by biological processes.
2.4 Pollution caused by human wastes and other wastewaters
Because human, animal and agricultural wastes are organic in nature, when
being discharged into a stream or lake, they will serve as food for heterotrophic
bacteria. Bacterial reactions will decompose the organic compounds to simple,
inorganic end-products with the production of energy for cell synthesis as
shown in Equations 2.1 and 2.2 (Metcalf and Eddy Inc. 2003):
Oxidation or dissimilatory process(COHNS) + O 2 + aerobic bacteria ĺ CO 2 + NH 3 + other end products
+ energy (2.1)Synthesis or assimilatory process(COHNS) + O 2 + aerobic bacteria + energy ĺ C 5 H 7 O 2 N
(new bacterial cells) (2.2)