SLUDGE DEWATERING BOX THEORY AND OPERATION
For many years, liquid waste generators have been
drying sludge using Drying Bed and Belt Press Technology
or others. Over the years many generators have found the
advantages of using a Gravity Separator – more commonly
known as a Sludge Dewatering System. These units are superior
to drying beds and have advantages over other technologies
as well.
DEWATERING
SYSTEM OPERATION
Liquid sludge is pumped through an
in-line static mixer where it is blended with polymer.
From there, the sludge/polymer mixture continues
into the Sludge Dewatering Unit. The same pump is
utilized since mixing occurs on the fly and in-line.
Once in the Dewatering Unit, solids are dewatered
in a predetermined period of time. In a properly
designed Dewatering System, 60-70 percent of free
water should have drained within a matter of minutes
if flow rate, polymer, and filter media are properly
mated during the design phase. In many applications,
solids will reach a dryness of 12-20 percent within
18-24 hours. Solids of this dryness should easily
pass the Paint Filter Test.
Once dried to the operator’s satisfaction,
the Dewatering Unit is picked up by a standard
Roll-on/Roll-off truck and taken to the local
beneficial use site or landfill. Options to the
Roll-on/Roll-off Dewatering Unit include:
- Trailer Mounted Units- these are typically
self-dumping units and are limited to 20 yard
capacity
- Pedestal Mounted Stationary Units –
these are hydraulic self-dumping units with
sizes ranging from 10 – 40 cu yards.
For further drying, solids can be dumped into
an existing drying bed or composting area as part
of the Pathogen Kill process.
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THE
SPECIFICS OF GOOD DEWATERING BOX TECHNOLOGY AND
DESIGN
Currently the most innovative dewatering systems
utilize “fixed in place,” reusable filter
media in the interior of the container. A
properly designed Dewatering System should also
include a full height center divider wall with sufficient
width (no more than 4 inches) to allow for free
flow of the filtrate. This center divider
wall should be full height to the side walls to
provide the most efficient dewatering possible.
The center divider wall serves two purposes. First,
to add more total filter area to the unit, and secondly,
to dewater the “slug” of moisture that
will get trapped in the center of the sludge “loaf”
if a center divider wall is not used. Since the
Dewatering Unit operates on gravity only, water
will flow downward to the floor. If
no filter media is used in the floor of the Dewatering
Unit, the water will simply sit in the bottom of
the unit causing a wet, thick, mess. Simply put,
water will not flow through a steel floor; a bottom
screen must be used for proper dewatering.
This is only logical since we are talking about
a “Gravity Dewatering Unit.” SMART designed
systems utilize filter media on the floor as well
as the outside, front and middle walls of the container. |
THE
DRYING PROCESS
Once the free liquid is removed, the solids will
begin to peel away from the walls and “roll
in” to form what looks like a split-top “loaf”
of bread. Dewatering is aided by the weight of the
“loaf” of solids pressing down and squeezing
out the remaining water. With no media, or improper
media, in the floor, “complete” dewatering
cannot take place. This is the difference between
a “Sludge Holding Box” and a “Sludge
Dewatering Unit.” The filter media must be
chosen properly for each application, ONE
TYPE FILTER MEDIA DOES NOT FIT ALL APPLICATIONS.
Solids, and therefore, the sludge from one generator
to another will vary greatly. Only SMART, LP currently
engineer’s their dewatering systems in this
way.
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SUMMARIZING
DEWATERING UNIT DESIGN
Engineering the proper Dewatering System for the
application is CRITICAL. A Sludge Dewatering System
is a carefully engineered combination of polymer
selection, polymer activation and distribution
system, a high efficiency static mixer to insure
proper polymer/water/sludge interface, proper
filter media selection and exceptional Start Up,
Troubleshooting, and Customer Service after the
sale.
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Written By:
John Jetelina
President
SMART, LP
210.269.3910
Contact SMART by clicking here |
