A General Bakery Waste:
It's Characteristics and Treatability
BRYAN YIM, Graduate Student
REGINALD H.F. YOUNG, Associate Professor
NATHAN C. BURBANK, JR., Professor
GORDON DUGAN, Associate Professor
School of Civil Engineering
University of Hawaii
Honolulu, Hawaii 96822
INTRODUCTION
The disposal of a bakery's wastewaters is a difficult problem, not only for the bakery,
but for the community in which it is located. The type of bakery products, methods of
production, and cleaning operations determine the pollutional load of a bakery's discharge.
Bread plants and similar dry baking operations produce wastewaters of low strength with
the main contaminants being flour and grease. Such wastewaters generally result from plant
cleanup operations and include floor washings and specialized machine washings. Bread
crumbs and other dry materials are swept off the floor and treated as solid waste. Cake,
sweet goods, doughnut, and pie shop operations generate the highest strength liquid wastes.
Pans and trays must be washed and greased after each baking, resulting in a discharge
containing large quantities of grease, sugar, flour, fruit-filling materials, and detergents.
In Honolulu, bakeries are generally located in densely populated areas and are small-
scale operations. Previously, as with most other local industries, the municipal sewer system
was utilized to dispose of their wastewaters with no strict compliance to sewer ordinances
and no cost incurred by the industry. The City and County of Honolulu will implement a
user charge system in 1974 (Table I), an assessment on both the general public and the
industries on Oahu, in order to comply with PL 92-500 and enable the municipality to be
eligible for federal assistance for publicly-owned treatment facilities.
For industries, the user charge will be based both on quantity and quality of their
wastewater discharge. As a preliminary investigation for establishing guidelines for the user
charge, each industry is being required to submit an analysis of their discharge to the
Division of Sewers of the City and County of Honolulu with periodic reports to that office
being mandatory in the near future. This study was performed to assist a major Honolulu
bakery with the characterization of its wastewaters prior to discharge into the municipal
sewer system. A study of the treatability of the wastewaters was also conducted, with
specific emphasis on reducing the BOD, SS, and grease in order to meet acceptable levels
specified in the local ordinance (Table I). Treatment methods assayed in this preliminary
study were chemical coagulation, pressure flotation, chlorine dioxide oxidation, and
ozonation.
PREVIOUS STUDIES
Reports on the characterization and treatment processes for bakery wastes are limited
in the literature probably since most bakeries are located near densely populated areas and
the wastes are mixed and treated with domestic wastes in municipal facilities.
1049