|
Bulk
Transport Tanker Cleaning (Washout)
Wastewater Treatment System
Process Description
Tanker washout wastewater is from tanker
cleaning facilities where an extremely wide variety of transported
liquid products are washed from the tankers in preparation for the
tanker receiving the next load. Tanker cleaning falls into several
categories; Food Grade, Chemical Grade, and Specialty Grade. Tankers
carry everything from corn syrup to paint pigment.
Tanker cleaning wastewater is difficult to
treat mostly because the wastewater strength and composition
regularly changes depending on the mix of tankers being washed that
day. Add to that the detergents, sanitizers and in the case of
chemical grade, various solvents are often used.
The wastewater typically contains an emulsion
that must be broken, followed by precipitation, coagulation,
flocculation and flotation separation. A mixed/aerated equalization
tank ahead of the wastewater treatment system is necessary to store
and homogenize the wastewater which will smooth out the operation of
the system.
The typical method to treat Tanker Cleaning
Washout wastewater is as follows:
%20Wastewater%20System%20Process%20Description.jpg)
Stage 1 Emulsion Cracking/Acidification:
pH is lowered to ~3.5 with the pH controller using acid to break any
emulsion.
Stage 2 Precipitation and Coagulation/pH Adjust:
pH is raised to 8.5 with the pH controller using caustic while
adding a coagulant such as alum or a PAC. A “pin floc” is developed
indicating the emulsion and the suspended solids are precipitated.
Stage 3 - 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 4 - 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 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 various contaminants and should be
disposed of according to environmental regulations.
APPLICATIONS:
|
