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Industrial Laundry Wastewater Treatment
System
Process Description
Uniforms worn by
manufacturing personnel, hospital employees, and meat packers; shop
towels used by service stations, printing companies, and bakers; and
floor mats from offices, stores and schools are all items that are
washed on a daily basis by industrial laundries.
The wastewater
generated from industrial washers contains sand and grit, lint, free
and emulsified oil and grease, heavy metals and volatile organic
compounds (VOC’s).
The treatment of
these waste streams involves multiple stages. Lint removal is
accomplished through screening, grit removal requires sedimentation,
oils and greases are de-emulsified, coagulated and flocculated
through chemical conditioning, solubilized metals are precipitated
by pH adjustment, and VOC’s can be removed with activated carbon
treatment.
The typical method to treat Oil Recycling
Facility wastewater is as follows:
Stage 1 Emulsion Cracking/pH Adjustment:
pH is lowered (or raised) to ~3.5 with the pH controller using acid
(or caustic). A coagulant de-emulsifier is added to break any
emulsion.
Stage 2 pH Adjustment/Precipitation and Coagulation:
pH is adjusted to ~8.5 using caustic and a coagulant is added such
as Alum or PAC to cause further de-emulsification and 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.
Sludge Dewatering:
The thickened DAF scum/sludge is allowed to accumulate sufficiently
to provide a full batch for the Filter Press. First a precoat
slurry is circulated thru the filter press to coat the cloths with
DE to prevent blinding of the cloth and aid in easy cake removal.
The filter press is then pumped with sludge until it is full. The
press is emptied of the “cake” which is a semi solid of
approximately 20-35 % solids. Sludge cake is high in fats and
greases and solids and should be disposed of according to
environmental regulations.
NOTE:
These operations
can be performed with screening, microfiltration, dissolved air
flotation and/or clarification. All of these treatments produce a
thickened slurry or sludge that may require additional conditioning
before being processed with a filter press. Precoating of the
filter cloth may be required to reduce cloth blinding and cleaning
problems.
APPLICATIONS:
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