79    TREATMENT OF DAIRY WASTEWATER BY CHEMICAL
COAGULATION
Frederic C. Blanc, Professor
Rita Navia, Graduate Student
Department of Civil Engineering
Northeastern University
Boston, Massachusetts, 02115
INTRODUCTION
Industrial dairy wastewaters are generally high strength wastes containing soluble, colloidal and
suspended solids with a high concentration of BOD. The more than 5,000 industrial dairy plants in
this country have a large waste load to treat and dispose of. If discharged into the municipal sewer
system, such wastewaters often produce a high pollution load which is unacceptable to the Publically
Owned Treatment Works [POTW]. This then results in a requirement for industrial pretreatment of
such wastes before discharge to the collection system. Chemical coagulation-flocculation followed by
sedimentation, which plays an important role in many solid liquid separation schemes and is widely
used in water and wastewater treatment may be used in the pretreatment of dairy wastewaters in some
instances. This method can remove BOD, COD and suspended solids from the waste stream and may
be economically feasible for some of the industrial dairy product facilities which are located in urban
areas.
In this study a laboratory investigation of chemical coagulation treatment of dairy processing
wastewater using alum, ferric chloride, or ferrous sulfide together with lime was performed. Extensive
testing to determine chemical requirements and combinations for various removal efficiencies was
conducted. Following the laboratory studies, a cost analysis was performed evaluating treatment
benefits and pretreatment process economics based on costs of local sewer user surcharges.
BACKGROUND
Dairy wastes are generated by disposing of residues, wasting of by-product, process equipment
cleaning and leakage or spills. The main organic constituents in dairy wastewaters consist of fats,
proteins and carbohydrates in various proportions which are associated with milk. Other organics
found in some dairy industry wastewaters may come from processing companion products such as
orange juice, other fruit juices, or ice cream and sherbet additives such as fruits, nuts, coloring
substances or sugar. The BOD strength of dairy wastewaters varies depending on the type of production process. This parameter has been reported to vary from as low as 40 mg/L to as high as 10,000
mg/L, with a mean of 2,300 mg/L.' Suspended solids, which are mostly organic, are typically present
in concentrations up to 2,000 mg/L.' COD values range from 80 mg/L to 95,000 mg/L with a typical
mean of 4,500 mg/L for various types of dairy plants.2 Phosphorus, which comes from milk and
cleaning compounds is typically present in a mean concentration of 49 mg/L.2 The reported values of
pH range from 4.5 to 9.2.3
The treatment objectives for dairy wastewaters are described by the Environmental Protection
Agency in Effluent Guidelines and Standards for Dairy Products.4 Treatment or pretreatment processes for dairy wastewaters are usually the biological type with the most common being: activated
sludge, trickling filters, rotating biological contactors, lagooning, land treatment, and anaerobic
reactors. Anaerobic processes as described by Sobkowicz5 for the treatment of cheese production
wastewaters or Backman6 for treating dairy wastewater have the capability of handling high organic
loadings in a pretreatment application. Table I depicts the range of treatment efficiency for various
biological treatment processes treating dairy wastewaters.
Chemical treatment or pretreatment of dairy wastewaters is not practiced to a great extent. There
are not many reports of chemical treatment in the wastewater treatment literature. A physical-
chemical pretreatment system was described by Bough and Swientek with reported cost savings.8
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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