34    ANAEROBIC PRETREATMENT OF
DAIRY LIQUID EFFLUENTS
Bruno Coraucci Filho, Associate Professor
Roberto Feijo de Figueiredo, Professor
Edson Aparecido Abdul Nour, Associate Professor
University of Campinas - UNICAMP
School of Civil Engineering
Dept. of Hydraulics and Sanitary Engineering
Universidade Estadual de Campinas
Faculdade de Engenharia Civil
Bairro Barao Geraldo—Caixa Postal 6021
INTRODUCTION
Industrial wastewater treatment plants sometimes get overloaded when situations such as
these occur: increase in seasonal peak production, changes in production processes, or accidental
discharges. An adequate effluent treatment plant design may anticipate such a situation, but those
designed systems have certain limits. When the upper limits are exceeded, by overloading, for
instance, the existing treatment units have to be redesigned or the whole system has to be upgraded by adding new units.
The dairy industry in Brazil is subject to a dramatic seasonal production variation as it depends
on a seasonal milk supply. In the case of the studied industry a set of factors, like a greater
cheese and butter production, development of new products, including milk sweet paste and, evidently, more milk being received and processed, has contributed to industrial effluent flowrate
increase, with increasing organic matter concentration. The increased industrial production was
not accompanied by process and equipment modernization. That has led to a greater number of
accidental spills, resulting in frequent unstable conditions in the existing wastewater treatment
plants.
To improve the existing plants, instead of enlarging the pond system, a less costly solution was
tried by readapting an existing tank, formerly a dissolved air flotation unit, into an upflow anaerobic reactor, then called a pretreatment unit. Adaptation on the tank was minimal, and was made
in a short time. The pretreatment unit was located ahead of the ponds, right after preliminary
treatment, as seen in Figure 1.
The objective of this work was to evaluate efficiency of the pretreatment unit to partially remove organic matter of liquid effluents from the dairy industry. Chemical oxygen demand was
the major analyzed parameter, and it was verified by its variation with organic loading rate and
hydraulic detention time.
ANAEROBIC PROCESS
Search for new systems applicable to treat industrial and/or sanitary liquid effluents at a low
cost and low operational and maintenance levels, had a great impulse in the 1970s. Among the
studied systems, those that utilize anaerobic process had good acceptance. Although the anaerobic process has been well known for a long time, and has a history of treating biological sludges,
or biosolids, its utilization to treat liquid effluents is recent.
Anaerobic organisms degrade organic matter in several steps like the hydrolitic step, acetogenic step, homoacetogenic step, and methanogenic step, each one achieved by a specialized set
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
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