Liquid purification or separation – With heater or heat exchanger – With treating fluid addition
Reexamination Certificate
1999-12-08
2002-03-12
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
With heater or heat exchanger
With treating fluid addition
C062S238300, C062S335000, C062S476000, C210S180000, C210S188000, C210S220000, C261S129000, C261S157000, C261S161000
Reexamination Certificate
active
06355162
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to wastewater treatment, and, in particular, to an apparatus that introduces oxygen into the wastewater to increase the flocculation rate of suspended solids.
Sewage treatment by means of flocculation removes dissolved and suspended solids from wastewater. Such treatment frequently takes place at a wastewater treatment facility in a rectangular secondary tank downstream from the primary treated wastewater, which tank may be continuously seeded with bacteria-laden activated sludge to augment growth of the bacteria that oxidizes the organics and inorganics in the wastewater to achieve flocculation of the waste. Flocculate of activated sludge depends upon gravitational effects and settles on the tank bottom from where it is scraped off and pumped to another tank or digester for a subsequent anaerobic treatment or disposal. The flocculation rate depends upon the biological aspect of the solids being treated, and the environment and life supporting habitat within the wastewater for the bacteria that in effect devours the organic carbon and other suspended solids.
In particular, in order to increase the rate of flocculation of the activated sludge, wastewater treatment processes frequently involve aeration to provide oxygen for the growth of the bacteria seedings. The provided oxygen is diffused into the wastewater and in combination with the dissolved oxygen provides life support for the bacteria that produces the flocculation of the waste. The replenishment of suspended oxygen along with the dissolved oxygen fosters the respiration of the bacteria that impacts the retention time needed for flocculation, which time is based upon numerous other factors including the characteristics of the sewage being treated, hydrostatic head, compressed air discharge temperatures, and net diffuser discharge pressure.
One known wastewater aeration system is diagrammatically shown in FIG.
1
. Concrete reservoirs or baths
10
, each of which may be one of many in a series of similarly constructed baths, each holds a quantity of wastewater
12
, such as domestic sewage, being treated. Air supply pipes
18
include at their respective downstream ends a diffuser section
16
submerged within the wastewater
12
. The diffuser sections
16
include a multitude of small orifices through which air is output or bubbled into the wastewater. Although only one supply pipe and diffuser for each reservoir is shown in
FIG. 1
for illustration purposes, multiple pipes and/or diffusers may be used to provide an adequate amount and distribution of aerating air. Each of the air supply pipes
18
is connected to a distribution manifold
20
connected to a large diameter duct
22
that is supplied with pressurized air from a blower or centrifugal compressor
24
. A filtered intake duct
26
that ports or opens to the outside where ambient air is connected to compressor
24
.
During operation, compressor
24
draws ambient air into duct
26
, which air then passes in sequence through compressor
24
, duct
22
, manifold
20
, and supply pipes
18
. The blower conveyed air continues out through diffuser sections
16
in the form of bubbles, shown at
30
, that bubble or percolate upward through wastewater
12
to provide oxygen for the respiration of the bacteria within the wastewater.
While the prior art aeration system shown in
FIG. 1
does on occasion provide some benefit, its effectiveness at treating the wastewater is sometimes limited. Specifically, the respiration of the bacteria in the wastewater is at optimum in a habitat of around 68° F. (20° C.) to a high of around 140° F. (60° C.).
Except for some rare heat resistant strains of bacteria, higher temperatures may harm or kill the bacteria within a short period of time. However, in the prior art of
FIG. 1
, the heat of compression incidentally applied to the aerating air by the blower may, depending on ambient air conditions, increase the temperature of the air reaching the diffuser and the wastewater to undesirably high levels at which bacteria respiration is hindered, or the bacteria is killed, and the solubility of dissolved oxygen is diminished. For example, in some situations and blower configurations, air output from the diffuser will have a dry bulb temperature of in excess of 155° F. when ambient air has a dry bulb temperature of as low as 70° F. Although such diffuser output temperatures may not measurably change the overall temperature in the tank so as to adversely affect all the bacteria therein, bacteria passing near the diffusers will be subjected to thermal shock.
Another shortcoming of existing aeration systems is related to the net diffuser discharge pressure, which is the difference between the discharge pressure at the diffuser orifices and the wastewater hydrostatic pressure. The pressure delivered by a centrifugal blower is dependent on the intake ambient air mixture density and specific humidity, which density is a function of the temperature and humidity of the ambient air. Under some ambient conditions, such as high temperature with high humidity, pressure losses due to high temperatures and vapor condensation downstream of the blower result in the net diffuser discharge pressure being insufficient to produce bubbles or to prevent wastewater from clogging the air distribution pipes. Under certain other ambient conditions, the net diffuser discharge pressure is so high that the diameter of the diffused air bubbles are too large and the wastewater is made too turbulent for efficient absorption of oxygen into the wastewater.
Still another shortcoming of existing aeration systems is related to the fact that classical adiabatic blowers ingest air at constant volumes. Because the density of air varies with temperature, the mass of air conveyed by the blower varies with temperature. As the temperature and relative humidity of air inlet to the blower increases, the mass of air and therefore oxygen delivered to the diffuser for introduction into the wastewater for use by the bacteria undesirably decreases. And, although the horsepower required to compress this less dense mass flow is reduced, its rate of decline is much less than that of the mass flow.
Thus, it would be desirable to provide a wastewater aeration system that overcomes these and other shortcomings of the prior art.
SUMMARY OF THE INVENTION
The present invention provides a wastewater aeration system that improves the flocculation rate of suspended solids within the wastewater by conditioning an intake air flow prior to its introduction into the compressor of the aeration system. The intake air is conditioned by a vapor condensing heat exchanger within the air stream that de-hydrates and cools the air to a desired level. Another and optional heat exchanger positioned within the air stream more downstream of the vapor condensing heat exchanger will secondarily sensibly cool the air stream upstream from the bell-mouth of the compressor. The inventive heat exchangers may also be configured to heat the air stream when ambient conditions are cooler than desired.
In one form thereof, the present invention provides a wastewater treatment system for a bath of wastewater, including a conduit having an outlet opening into the bath of wastewater, an air duct having an inlet in flow communication with a source of air, at least one blower in flow communication with the air duct and the conduit and operable to cause air to pass through the air duct and through the conduit to be output through the conduit outlet into the bath of wastewater, and a heat exchanger installed in the air duct and adapted to condition air passing through the air duct.
In another form thereof, the present invention provides a wastewater aerating system including a conduit having at least one outlet submerged within a bath of wastewater to be treated, an air duct having an inlet in flow communication with a source of ambient air, at least one blower in flow communication with an air duct outlet and a conduit inlet and operable to cause air to pass through the air
Baker & Daniels
Hruskoci Peter A.
RWI
LandOfFree
Apparatus for increasing the flocculation rate of suspended... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for increasing the flocculation rate of suspended..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for increasing the flocculation rate of suspended... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2881311