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Dairy Products Wastewater Treatment
System
Process Description
The dairy industry involves processing raw
milk into products including milk, butter, cheese, yogurt, using
processes such as chilling, pasteurization, and homogenization.
Typical by-products include buttermilk, whey, and their derivatives.
Huge amounts of water are used during the process producing
effluents containing dissolved sugars and proteins, fats, and
possibly residues of additives. These effluents have the following
characteristics
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Biochemical oxygen demand (BOD), with an
average ranging from 0.8 to 2.5 kilograms per metric ton (kg/t)
of milk in the untreated effluent
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Chemical oxygen demand (COD), which is
normally about 1.5 times the BOD level
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Total suspended solids (TSS), at 100–1,000
milligrams per liter (mg/l)
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Total dissolved solids (TDS): phosphorus
(10–100 mg/l), and nitrogen (about 6% of the BOD level).
Cream, butter, cheese, and whey production are
major sources of BOD in wastewater. The waste load equivalents of
specific milk constituents are: 1 kg of milk fat = 3 kg COD; 1 kg of
lactose = 1.13 kg COD; and 1 kg protein = 1.36 kg COD. The
wastewater may contain pathogens from contaminated materials or
production processes. A dairy often generates odors and, in some
cases, dust, which also need to be controlled.
Hydro-Flo engineers and builds complete
solutions to efficiently manage the wastewater treatment and odor
control requirements of the dairy industry. Our solution includes
the following benefits:
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Optimization of use of water and cleaning
chemicals with option for recirculation of cooling waters.
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Segregation of effluents from sanitary
installations, processing, and cooling (including condensation)
systems; this would facilitate ability to recycle the
wastewater.
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Energy recovery through use of heat
exchangers for cooling and condensing.
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Use of high-pressure nozzles to minimize
water usage.
Dairy wastewater is treated by adjusting pH
and using strong coagulant chemistry to break any emulsions caused
by cleaning agents and sanitizers and to precipitate solids and
fats. The chemicals are added to cause de-emulsification,
precipitation, coagulation, and flocculation.
The reuse of wastewater from the dairy
industry can also be provided for by usage of adsorption and
membrane separation among other processes. The color and the odor
may be removed completely after activated carbon treatment. The
pretreated water can be passed through a cross flow reverse osmosis
membrane system and the permeate water can then be reused.
The typical method to treat Dairy Processing
wastewater is as follows:
Stage 1 Emulsion Cracking/pH Adjustment/Precipitation and
Coagulation:
pH is raised (or lowered) to ~8.5 with the pH controller using
caustic (or acid). A coagulant de-emulsifier is added to break any
emulsion and cause precipitation of the solids. A “pin floc” is
developed indicating the emulsion and the suspended solids are
precipitated.
Stage 2 - Flash Mix:
The wastewater with it’s precipitated pin floc is introduced to the
flash mix zone where a polymer flocculent is added. This stage
maximizes flocculent dispersion throughout the coagulated
wastewater.
Stage 3 - Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate
the floc into larger particles suitable to be enmeshed with the air
bubbles.
Clarifier, Dissolved Air Flotation (DAF):
The flocculated wastewater is introduced into the DAF inlet where
the floc particles are comingled with a pressurized dissolved fine
bubble recycle stream. The floc particles attach to the bubbles and
float to the surface where they are mechanically skimmed into the
float scum sludge chamber. The clarified treated water then exits
the end of the DAF and flows downstream to sewer or further
treatment if necessary. The DAF system bubbles come from a Recycle
Air Dissolving system that takes a portion of treated effluent,
pressurizes it and introduces air to be dissolved. The dissolved
air comes out of solution and forms a fine bubble stream when the
pressure is released at the DAF entrance in the presence of floc
wastewater.
DAF
Sludge Handling:
The resulting DAF waste scum/sludge is removed from the DAF
automatically as the scum accumulates and is pumped to the sludge
holding tank where it further thickens and accumulates a batch for
disposal or processing in a filter press. The sludge is mixed and
conditioned with a filter aid such as DE to improve porosity and
filterability which will improve cake dryness and prevent premature
blinding of the filter cloths.
Sludge Dewatering:
The thickened DAF scum/sludge is allowed to accumulate sufficiently
to provide a full batch for the Filter Press. The filter press is
pumped with the sludge until it is full. The filter press is then
emptied of the “cake” which is a semi solid of approximately 20-35 %
solids. Sludge cake is high in solids and should be disposed of
according to environmental regulations.
APPLICATIONS:
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