Section 13. DAIRY WASTES
DAIRY PROCESSING WASTEWATER BIOAUGMENTATION-
AN EVALUATION OF EFFECTIVENESS
John H. Martin, Jr., Research Associate
Department of Agricultural Engineering
Robert R. Zall, Professor
Department of Food Science
Cornell University
Ithaca, New York 14853
INTRODUCTION
As noted by Harper et al. [1], it is a common misconception that biological treatment of dairy
processing wastewaters is a relatively simple task particularly in comparison to the treatment of municipal wastewaters. As industry experiences have demonstrated, it is in fact, far more difficult. In
an analysis of the performance of 20 dairy processing wastewater treatment plants, Harper et al.
found that the efficiency of these facilities was less than 70% for more than 25% of time.
Although relatively low influent suspended solids concentrations eliminate the need for primary
treatment, the highly variable nature of flows and the characteristics of dairy processing wastewaters
have made the realization of consistently high levels of treatment efficiency exceedingly difficult. For
the activated sludge process, the occurrence of bulking is probably the most frequently cited problem
in treating these wastewaters [1,2,3],
Bulking is the term that is used to describe activated sludge that settles and compacts poorly.
When bulking occurs, the ability to produce a well-clarified effluent and a concentrated return sludge
is impaired. Ultimately, process failure can occur due to excessive losses of activated sludge solids
in secondary clarifier effluent and high recycle ratios required due to the dilute nature of secondary
clarifier underflow.
Sezgin et al. [4] have suggested that many of the settling, compaction, and dewatering problems
associated with the activated sludge process are related to the relative numbers of filamentous and
zoogleal microorganisms present. Excessive numbers of filamentous microorganisms are characteristic of bulking sludges. In contrast, the absence of filamentous organisms or their presence in low
numbers result in small, weak floes that settle rapidly but produce a turbid effluent. This is due to
the presence of small "pin point" floes that do not settle. This led Sezgin et al. to conclude that a
balanced population of filamentous and zoogleal microorganisms is necessary to produce activated
sludge floes that settle and compact readily and produce a well clarified effluent. It is the role of the
filaments to provide a strong rigid structure to which the zoogleal organisms can attach.
The frequent occurrence of bulking in the treatment of dairy processing wastewaters using the
activated sludge process led Chambers [3] to question the validity of what was described as the "Ubiquity Principle" as applied to the biological treatment of these wastes. Citing the abundance of filamentous bacteria and fungi that are common to bulking sludges, Chambers suggested that microbial
populations that develop naturally in these biological waste treatment systems are not necessarily
composed of those species that will provide the most effective degree of treatment. This led to Chamber's proposal that more effective microbial populations can be established via the practice of bioaug-
mentation.
In support of this hypothesis, case histories of three industry-operated, full-scale dairy processing
wastewater treatment systems were presented. For each treatment system involved in the study: an
extended aeration system, an aerated lagoon, and an oxidation ditch, marked improvement in system
performance was reported to have occurred following the implementation of a program of bioaug-
mentation. Unfortunately, because information regarding waste characteristics and flows before and
after bioaugmentation as well as other important details were omitted, the data presented did not
conclusively demonstrate that bioaugmentation was solely responsible for the improvements noted.
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