Methods and apparatus for sludge collection

Sludge collection and removal systems are disclosed. The present invention provides methods and apparatus that include piping system of headers and laterals selectively provided with flow from a central point so that sludge can be removed from areas where it accumulates most rapidly. The adaptable nature of the piping system additionally permits the number of collection laterals and orifices to be varied to suit the sludge accumulation characteristics of the sludge basin. Additionally, improved multiple port valves are disclosed that permit the selective connection of the flow among sections in preferred embodiments of the sludge collection systems.

The present invention is directed to methods and apparatus for removing 
sludge byproducts that are created by water filtration processes from 
settling basins and tanks commonly found in water and wastewater treatment 
plants. 
BACKGROUND OF THE INVENTION 
The settling basins in water and wastewater treatment plants are typically 
circular or rectangular concrete structures that have sloped bottoms that 
collect and store sludge. The basins are periodically drained and the 
sludge that has accumulated is flushed out through drains in the basin 
floor. Removal of the accumulated sludge is an important part of the 
overall treatment process, particularly since anaerobic bacterial activity 
may develop in the collected sludge over time. Therefore, in an ideal 
situation, the sludge is drained or removed without disturbing the 
material through excavation or manual removal. Moreover, it is further 
desirable from a cost and efficiency standpoint to be able to effectively 
remove the sludge from the basin when accumulation requires its removal. 
Methods of removing sludge on a more or less continuous basis have been 
developed in an effort to reduce the need to completely drain and flush 
the basin. Techniques such as header and lateral piping systems, scraper 
mechanisms and vacuum or suction removal systems have been tried, without 
complete success. 
Sludge removal systems are known where a moving apparatus is directed 
across the floor of the basin to remove the sludge in its path. The unit 
can be guided by rails and may use static head or eduction to remove the 
sludge. In some variations, the sludge collection basin is cone-shaped and 
the sludge collection apparatus moves along a circular or spiral path over 
the surface of the cone. Such systems are cumbersome and expensive and 
require a complex system of moving parts and precision machinery prone to 
breakdown in the gritty environment of a sludge bed. 
In other systems, the inherent problems of moving equipment are avoided by 
providing a series of fixed pipes to remove the sludge. The pipes are 
selected so that a number of perforated pipes of small diameter are 
connected to larger diameter pipes, which are in turn connected to a 
lesser number of larger diameter pipes, and so on, until ultimately, the 
piping "tree" meets at a single header pipe of relatively large diameter 
that is controlled by a single collection valve. The single valve is 
opened to flush sludge into drains by means of the static head of water in 
the basin. In order for fixed grid sludge collection systems to collect 
evenly, it is critical that the flow capacity of the grid be compatible 
with the flow capacity of the downstream piping including the header, 
valve and basin outlet. Therefore, it is necessary to either use a very 
large valve and basin outlet in combination with a grid covering the 
entire basin or to use multiple valves and basin outlets in combination 
with smaller grids. 
Another limitation to fixed sludge collection systems is that sludge is 
often not efficiently removed because the water in the basin tends to flow 
around the sludge and into the collection system. Typically, sludge may 
flow into the collection system when the valve first opens, creating a 
hole or depression in the sludge. This depression is known as a "rat 
hole." Once this depression exposes the collection orifice, water enters 
the collection system rather than sludge. Fixed collection systems that 
have valves open for extended periods of time usually collect more water 
than sludge. The tendency toward "rat holing" is dependent upon certain 
characteristics of the sludge such as its composition, concentration, 
viscosity, and compressibility. Sludge found in water treatment processes 
may have different compositions, varying amounts of suspended solids, and 
therefore different characteristics. For example, alum sludge will have 
different characteristics than ferric sludge or lime sludge. 
A limitation to systems using single large outlets is that the system must 
be operated to remove sludge from the entire basin as soon as one area 
exhibits significant sludge accumulation. This type of operation is 
inherently inefficient and either wastes water unnecessarily or allows 
sludge to accumulate more heavily than is optimal for the process. A 
limitation to systems using the multiple basin outlets is the expense of 
the outlets and the difficulty in retrofitting the basin. 
Finally, sludge removal is also sometimes attempted by providing systems 
that float and skim the sludge from the water overlying the bottom of the 
basin. However, such systems are inefficient, expensive and require 
complex systems of piping and suction, the latter of which are prone to 
breakdown since a gritty slurry of sludge and water must be skimmed and 
pumped. 
Additionally, all of the known systems discussed above are difficult if not 
impossible to retrofit into existing sludge collection basins. 
Therefore, it would be desirable to provide a sludge collection system that 
is simple and reliable, while still effectively removing sludge. 
Additionally, it would be desirable to permit the amount of removal 
applied to various areas of the bed to be adjusted or varied based upon 
sludge accumulation patterns. Finally, such a system would ideally be 
adaptable for both new construction and retrofit applications. 
SUMMARY OF THE INVENTION 
The present invention provides a sludge collection system that is comprised 
of a manifold having a plurality of manifold inlets and a manifold outlet, 
a plurality of collection laterals, for collecting sludge, that are in 
fluid communication with the manifold by way of the manifold inlets, a 
drain, in fluid communication with the manifold outlet for removing sludge 
from the manifold, and one or more collection valves that selectively 
permit flow of sludge from the collection laterals through the manifold 
inlets and through the manifold. 
The specialized piping of the sludge collection system of the present 
invention provides improved hydraulic characteristics. One advantage of 
the sludge collection system disclosed is that the performance of the 
system can be regulated and adjusted to meet the requirements of the 
filtration system. Another advantage of this invention is the ability to 
effectively remove sludge through smaller or fewer basin outlets than 
conventional fixed grid designs. The disclosed system is thereby more cost 
effective for retrofitting into existing basins. 
The present invention uses the static head of the water in the basin to 
push sludge and water into a sludge collection grid, through a valve, 
through main drain piping and out of the basin. Each sludge collection 
basin is divided into a number of collection zones, and each zone may be 
sized and independently operated to allow the hydraulic characteristics of 
the system to be optimized. Optimization is preferably obtained by 
matching the flow rates of each zone to the capacity of the piping system 
used to remove the sludge from the basin. 
The flow rate from each zone is dependent on the available static head and 
the diameter and number of the orifices in the zone. The flow rate can be 
optimized by varying the diameter and/or the number of orifices in the 
collection grid. In addition, the laterals may be spaced at varying 
pitches to provide further flexibility. The zones allow the system to 
provide the required amount of removal capacity in each area of the basin. 
In most basins, sludge tends to collect more rapidly in one area, and the 
removal capacity of each zone is thus preferably tailored to the 
anticipated sludge accumulation rate. The spacing of the orifices and the 
laterals can also be optimized for the collection of various types of 
sludge in order to reduce the effect of "rat holing." As a result, the 
present invention is more cost effective and efficient than previous 
systems. 
In a preferred embodiment, the sludge collection system of the present 
invention comprises one or more header and lateral piping systems 
installed on the bottom of the basin that together create a sludge grid 
disposed within a zone. The header piping from each zone is connected to a 
valve and the valve selectively allows water and sludge from one or more 
selected sections to flow into a main drain pipe, and out of the basin for 
further processing. For example, the collected sludge can then be 
transferred to a holding tank or clarifier. The sludge may then be 
dewatered by one of several available methods and the supernatant returned 
to the head of the plant or otherwise carried away. 
In various preferred embodiments, the sludge collection system of the 
present invention can be provided with either automated or manual 
controls. These controls preferably allow the operator to control the 
frequency and the duration of the operation of the valves within each zone 
independent of the other zones. In this manner, sludge can be removed from 
a particular zone or zones as necessary. The optimal frequency of 
withdrawal is dependent on site specific factors such as the condition of 
the raw water, chemical feeds, sludge characteristics, and the plant's 
capacity to handle concentrated sludge and unfinished water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, a plan view of a sludge collection system 100 made 
in accordance with the present invention is illustrated. It will be 
understood that the embodiment shown in FIG. 1 is a representative 
installation and that the present invention is by its nature, modular, 
flexible and adaptable to a variety of sludge collection basins, both 
existing and those under construction. In FIG. 1, the sludge basin 50 is 
rectangular and is divided into three equal zones 52,54,56 along its 
length. 
In other embodiments, as explained below, the zones need not be equal, or 
arrayed along a central axis. Each zone includes a multiple inlet manifold 
10, from which four main collection conduits 12 extend. As shown in FIG. 
1, each manifold 10 is situated in the interior of each zone rather than 
on the periphery, near the wall of the sludge basin 50. In one embodiment 
of the invention, the multiple inlet manifold 10 is a central collection 
hub. Thus, each zone, 52,54,56 is in turn, sub-divided into four sections. 
In other embodiments, less than four sections or more than four sections 
can be provided, and the sections themselves can be of unequal sizes or be 
asymmetrically arrayed about the multiple inlet manifold 10. Connected to 
each main collection conduit 12 is a spreader conduit 14, and extending 
from each spreader conduit 14 are a plurality of collection laterals 16. 
The main collection conduit 12 and the spreader conduit 14 are preferably 
of approximately equal diameter, while the collection laterals 16 are of a 
smaller diameter than the spreader conduit 14. As illustrated in FIG. 1, 
the pitch of the collection laterals along the length of the spreader 
conduit 14 can be varied. The left hand zone 52 has a smaller pitch, and 
thus a higher number of collection laterals 16. The laterals in zone 52 
may also have a higher number of orifices and/or larger diameter orifices 
than in the adjacent zones. In application, this is because this area 52 
of the basin 50 accumulates sludge at a higher rate than the adjacent 
zones 54,56. In conjunction with the other aspects of varying the sizes 
and configurations of the zones, it will be readily appreciated how the 
geometry of the sludge collection system of the present invention can be 
infinitely varied to suit the conditions of the collection basin 50. 
A side elevation view of two zones 52,54 of the sludge collection system 
illustrated in FIG. 1 is shown in FIG. 2. In this view it can be seen how 
the main collection conduits 12 and spreader conduits 14 extend from the 
multiple inlet manifold 10. This view further illustrates the multiple 
inlet manifold 10 and the main drain conduit 20 that is selectively opened 
in conjunction with the operation of the multiple inlet manifold 10. FIG. 
2A and FIG. 3 each further illustrate one of the alternate preferred 
embodiments of the present invention. As shown in FIG. 2A, the manifold 10 
has multiple manifold inlets 11 that provide for the flow of sludge from 
the main collection conduits 12 into the manifold 10. FIG. 3 is an end 
elevation view of the sludge collection system 100 illustrated in FIG. 2A. 
The drain 20, shown in FIG. 3, which is in fluid communication with the 
manifold outlet is a single central drain that is perpendicular to the 
drains illustrated in FIG. 2. The arrows, shown in FIG. 3, depict the 
direction of the flow of sludge S through the collection grid by means of 
the static head of water in the basin. The varying level of water W in the 
basin is also shown in FIG. 3. 
The piping layout described above, in conjunction with the other aspects of 
the present invention set forth below, permits sludge to be collected at 
varying cycles. In the illustrated preferred embodiment, approximately 70% 
of the sludge collects in the first zone 52, and the four sections of this 
zone can be flushed as often as necessary, for example, once an hour. The 
center zone 54 collects about 20% of the sludge and needs to be flushed 
daily, or at another frequency usually determined empirically. Finally, 
since the remaining sludge gravitates to the farthest zone 56, it may be 
necessary to flush these four sections as infrequently as once a week. It 
should be understood that the cycling can be accomplished in any order, 
with any frequency, simply by controlling valves using known manual, 
semi-automatic or automatic controls. In certain embodiments, if the 
valves are opened and closed in a dynamic sequence, the sludge can be 
moved or "swept" into a particular zone or area for collection in a more 
efficient manner. 
Those of skill in the art will realize, however, that the size, shape and 
location of the zones are dependent on a number of factors. The available 
static head of water in the basin and the available capacity of the outlet 
or outlets to handle the flow of sludge and water will to some extent 
dictate the ability of the system to be flushed, and will thus influence 
the number and size of the collection zones. For example, if a relatively 
low static head is available or if the outlets are of relatively small 
size, the number of zones must be greater, i.e., the area of each zone 
must be smaller or the number and/or size of collection orifices must be 
reduced. Sludge tends to settle at a greater rate in certain areas of a 
basin, depending upon a number of factors, including basin layout, process 
flow and sludge characteristics. In areas where sludge accumulates 
rapidly, a greater number of collection zones is preferably provided so 
that the overall amount of sludge that accumulates per zone is 
approximately equal. Similarly, the physical dimensions of the settling 
basin and the presence or absence of sloped floors, trenches, supporting 
structures and other obstructions in the basin will influence the sludge 
profile and will thus dictate to some extent the sizing and placement of 
the piping that defines the collection zones. 
One aspect of the present invention is the provision of a collection valve 
or valves that selectively interconnect one or more of the collection 
zones and the drainage system. Preferably, any single zone can be drained 
at any given time. However, embodiments of the present invention are 
envisioned where more than one zone is drained at a time, or where zones 
are partially drained or drained in alternating sequences. For example, 
FIG. 4 shows one preferred embodiment that uses an actuated disc valve 132 
or mud valve enclosed in a canister 114 or vessel. Transfer piping or the 
main collection conduits 12 from each of the sections is connected to the 
vessel 114, through the top or its sides, and the bottom zone of the 
vessel is connected to a drain pipe. With this disc valve 132, the main 
collection conduits 12 from all the sections of that particular zone are 
actuated, all at the same time, to collect sludge or not. 
FIG. 5A shows a preferred embodiment of a multiple port valve 110, 
illustrated as a four-port valve, for collecting sludge at one section of 
a zone independently from the other sections of that zone. A connecting 
pipe 116 is moveable between four ports 118. When the valve 110 is 
actuated, the static head of water pushes sludge S, along with the 
flushing water, through all of the interconnected sections, through the 
transfer piping 12, through the valve 110 and into the drain pipe 20 by 
means of the manifold outlet 15. The illustrated embodiment is connected 
to four sections and thus has four openings 118. In other embodiments, a 
greater number or a lesser number of sections could be serviced, with a 
commensurate number of openings 118 being required. In certain 
embodiments, the connecting pipe 116 can be actuated to continuously sweep 
the surface of the top of the canister 114 and thus systematically pass 
over each of the openings 118. By varying the rate of the sweep and/or 
building in dwell points, the connecting pipe 116 may reside over one or 
more openings 118 for a set period of time. Thus, it can be appreciated 
that this valve design adds another degree of flexibility and selectivity 
to the sludge collection system of the present invention. 
An alternate embodiment of a valve that is used in certain preferred 
embodiments of the present invention is illustrated in FIG. 5B. This 
configuration is a multiple port valve 120 and again is preferably used in 
collecting sludge in one section of a zone independent from the other 
sections of that zone. Transfer piping from each zone is connected to one 
of the valve ports 128, and a center port 126 is connected to a drain 
pipe. A rotating valve bonnet 122 rotates around the valve body 124 and at 
each position the bonnet 122 interconnects a different port 128, allowing 
sludge from each section to flow into the main drain piping (20 in FIG. 
2). 
In either of the preferred valve configurations illustrated and described 
above, air should be prevented from entering the system through the drain 
pipe 20. If air were to become trapped in the transfer piping, valve 
canister or drain piping, it would likely inhibit the flow of sludge and 
water and also cause excessive vibration. It is further important to 
slowly open and close the valves and to prevent water hammer, which could 
also damage the system. 
As noted above, a drawback of many prior art systems is that the sludge 
collection systems needed to be designed and installed when the sludge 
collection basin was constructed. This is often difficult, and even if 
accomplished, over time and changing conditions, the sludge collection 
characteristics of the basin are likely to change. Sludge collection 
characteristics may change, for example, when there is a change in the 
chemical coagulant that is used or when there is a change in the overall 
flow rate of the plant. Thus, an important advantage of the present 
invention, in addition to the ability to selectively remove sludge from a 
zone, is that the piping and valving system described above can be 
retrofitted into existing sludge collection basins, and even after being 
installed, can be modified if the sludge collection parameters dictate. 
Those skilled in the art will appreciate that numerous changes and 
modifications may be made to the preferred embodiments of the invention 
and that such changes and modifications may be made without departing from 
the spirit of the invention. It is therefore intended that the appended 
claims cover all such equivalent variations as fall within the true spirit 
and scope of the invention.