88    BATCH REACTOR TREATMENT OF DAIRY
WASTEWATERS: A CASE HISTORY
Mervyn C. Goronszy, Vice President
Transfield, Inc.
Irvine, California 92715
INTRODUCTION
Recent changes to Federal and State funding policies for publicly owned treatment works (POTWs)
will eventually lead to increased user fees for industrial dischargers. Relatively recent activated sludge
batch reactor technological advances are now available for the treatment of a number of wastewaters
which have historically been regarded as difficult. High strength predominantly soluble carbohydrate
type wastewaters, such as those from the food and allied processing industries including those from
the dairy industry, are typical of this category. This chapter describes the use of a two basin Cyclic
Activated Sludge System (CASS™) for the treatment of wastewaters generated from the Mid Valley
Dairy fluid milk manufacturing facility in California. This facility which is regarded as one of the
most advanced computer integrated fluid milk manufacturing plants in the United States,1 receives 26
million pounds of raw milk per month via road tankers and operates with a six day processing week
with two shifts totalling 20 hours operation per day. Production includes three million gallons per
month of milk, 80,000 gallons per month of sweetened orange juice, 60,000 gallons per month of
drinks and 50,000 gallons per month of bottled water. Historical records indicated a wastewater
generation of about 140,000 gallons per day, characterized by wide variations in both hydraulic and
organic loading parameters. The data base showed excursions of 800-8000 mg/L COD, 110-5400
mg/L BOD, 80-2600 mg/L total suspended solids which is quite typical for a fluid milk handling
facility (Figure 1).
SYSTEM DEVELOPMENT
Early studies on full-scale fed-batch reactors treating municipal wastes2 showed effective nutrient
removal and suppression of low F/M filamentous sludge bulking through oxic/anoxic/anaerobic
cycling of the biomass through interrupted mixing and aeration sequences. Captive selectors were first
introduced into the fed-batch reactor configuration in 1977 by the author. In early plants the initial
selector was positioned to form two unequal connected volumes with an approximate 1:10 volumetric
ratio and to operate at a mean initial design organic loading of 5 day1. Back-flow during the aeration
sequence provided for the replenishment of biomass into the initial selector zone3 for contacting with
influent wastewaters. This arrangement proved effective in controlling the growth of filamentous
microorganisms and in reducing BOD in dairy wastewater from around 1500 mg/L to less than 30
mg/L using two cycles each of 12 hours per day. Studies on this facility showed substantial depletion
of mixed liquor solids from the initial reaction volume during non-reaction sequences (2 hours per
cycle) and during aeration sequences caused by influent hydraulic interchange. Extension of this
principle to provide two initial zones in a fed-batch reactor proved effective in reducing the BOD of
dairy wastewater from around 3000 mg/L to less than 30 mg/L using 3x8 hour cycles per day. The
initial selector volume was designed to operate on a loading of l/day.4 While suitable for small
systems designed to operate on a low organic loading (less than 0.08 day1) and long aeration cycles
(6-10 hours/cycle) this approach did not provide sufficiently defined reaction conditions for larger
applications operating at higher loadings (0.2+ day1) and short aeration cycles of 6 or less hours.
More defined initial reaction conditions have been simply provided through positive direction of
biomass to the initial zone to establish appropriate floc-loading reaction conditions5"9 to promote
enzymatic removal of soluble substrate, coupled with the interruption of flow of influent during the
effluent removal sequence of operation. While compartmented fed-batch reactors essentially operate
as a sequencing batch reactor, the initial captive selector permits the use of reduced basin volumes by
comparison with other batch and fed-batch reactor facilities. Anoxic mixing and reaction sequences
can also be included into the sequence of operation to enhance the efficacy of treatment of specific
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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