Anaerobic method of treating high-strength waste-water

Method for treating a fluid containing anaerobically digestible nutrients and organic substrates wherein a plurality of individual anaerobic microorganisms are established upon rotatable discs mounted within an enclosed housing and a stream of treatable fluid is passed through the housing to wet more than fifty percent of the disc surfaces. The discs are rotated through the fluid whereby the microorganisms are able to feed upon the nutrients and substrates in the fluid and expel a process gas into the atmosphere maintained over the fluid. To further enhance both the feeding of the microorganisms and the expulsion of gas, the housing is divided into a number of individual compartments or stages and the pressure is reduced below atmospheric pressure in each compartment.

BACKGROUND OF THE INVENTION 
This invention relates to an anaerobic treatment method for rapidly and 
effeciently treating a fluid containing anaerobic digestible nutrients and 
primarily organic substrates. 
The most pertinent art known to the Applicants at the time of filing this 
application is embodied in the following United States Patents: 
______________________________________ 
2,029,702 3,941,691 
2,899,385 3,943,055 
3,105,014 3,994,780 
3,598,726 4,043,936 
3,724,542 
______________________________________ 
Heretofore most anaerobic treatment processes have been carried out in 
either relatively large holding tanks, lagoons or in packed columns. In 
either case, an anaerobic biomass is generally immersed within a fluid 
material that is being treated. These prior art devices thus operate under 
flooded conditions so that the microorganisms are forced to both feed and 
exhaust process gases while underwater. As a consequence, the 
microorganisms become highly saturated with process gases which are either 
inhibitory or toxic to the microorganisms and thus experience a relatively 
high resistance when they attempt to function in this environment. A 
natural resistance to efficient metabolism and substrate utilization is 
therefore inherently present in all flooded aerobic treatment systems 
which therefore inherently require relatively long mean cell detention 
times relative to anaerobic treatment. Even with retention periods of 
between 30 and 50 days the quality of the effluent is sometimes poor. 
Similarly, because of the typically low growth rate for most anaerobic 
microorganisms large volume holding or treatment tanks are required which 
necessitate large capital expenditures for both land and equipment. 
Oftentimes, because of the complexity of the equipment involved, 
operational difficulties are encountered which compound the existing time 
and money problems normally associated with many anaerobic processes. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to improve anaerobic 
treatment methods. 
A further object of the present invention is to shorten the amount of time 
required to anaerobically treat high strength wastewaters. 
A still further object of the present invention is to increase the 
efficiency of anaerobic treatment processes to provide for the production 
of high quality effluents. 
Yet another object of the present invention is to overcome the natural gas 
transfer resistance present in most flooded anaerobic treatment systems. 
Yet a still further object of the present invention is to provide a 
relatively inexpensive anaerobic treatment process. 
These and other objects of the present invention are attained by passing a 
fluid containing anaerobically treatable nutrients and primarily organic 
substrates through an enclosed housing and alternatingly immersing 
anaerobic colonies into the fluid for a first period of time to permit the 
microorganisms to feed upon the nutrients and substrates in the fluid and 
then exposing the microorganisms to the closed atmosphere maintained above 
the fluid for a second period of time whereby the microorganisms can expel 
the process gas produced by anaerobic fermentation directly into the 
atmosphere thereby considerably reducing resistance to the natural 
anaerobic process.

DESCRIPTION OF THE INVENTION 
The present invention basically involves an anaerobic process that is 
ideally well suited for treating concentrated organic wastewaters. 
However, as will become apparent from the disclosure below, the process 
and the apparatus used to carry out the process can be equally as well 
utilized in treating any type of fluid containing nutrients and/or 
substrates upon which anaerobic microorganisms may feed. The term 
anaerobic, as herein used, refers to the metabolism by a large variety of 
microorganisms of organic substrates and nutrients that are contained 
either in a fluid or an atmosphere that is devoid of free oxygen. 
Substrate materials may include but are not limited to carbohydrates, 
fats, proteins, alcohol and acids that are either soluble or insoluble in 
a fluid and which can exist alone or in combination with other substrates 
and/or nutrients. One application of further importance involves the 
production of process gases by bioconversion which can be used as raw 
materials in the production of fuels and fertilizers. 
With reference to the drawings, the present process is carried out within 
an airtight and fluidtight housing that is generally referenced 10. The 
housing is partitioned into a number of individual compartments that 
include a mixing chamber 11 and a plurality of processing or treatment 
stages 12--12. In this particular embodiment of the invention there are 
five separate treatment stages. However, the number of stages may be 
varied without departing from the teachings of the present invention. In 
operation, influent is initially delivered into the mixing chamber and 
from there passed seriatim through each of the treatment stages. 
A horizontally aligned drive shaft 16 is centrally positioned within the 
housing and is journalled for rotation in the two end walls 17, 18 via 
bearing 20--20. The right hand end of the shaft, as viewed in FIG. 1, 
passed through wall 18 and is coupled to a variable speed drive motor 23. 
In operation, influent is delivered into the mixing chamber by means of an 
inlet line 25. An impellor wheel 26 is secured to the drive shaft within 
the chamber that functions to thoroughly blend or mix the constituents 
contained in the fluid. After mixing, the fluid is passed directly into 
the first treatment stage. 
Each treatment stage contains a number of circular discs 30--30 that are 
uniformly spaced along the drive shaft. The discs are affixed in a 
vertical position upon the shaft so as to turn with the shaft as it is 
driven by motor 23. As will be explained in greater detail below, a colony 
of anaerobic microorganisms is established upon the surface of each disc. 
The discs, in operation, are partially submerged within the process fluid 
so that the colony is sequentially immersed in the fluid and then exposed 
to the atmosphere above the fluid. The biomass thus feeds upon the 
nutrients and substrates for a portion of each revolution and can expel 
process gases generated by bioconversion directly into the housing 
atmosphere. The rotating discs also provide added mixing of the process 
fluid and serve to strip gas from the fluid. 
As best seen in FIG. 1, the mixing chamber and the treatment stages are 
separated by a series of baffles 32--32. As further shown in FIG. 3, each 
baffle contains a series of horizontal holes 35--35 for exchanging process 
fluid or wastewater between stages. The holes are located below the axial 
centerline of the shaft. The liquid level 37 in the housing, on the other 
hand, is maintained above the shaft bearings to wet about 70% of the 
surface area of each disc. The process fluid is thus used as a fluid seal 
to isolate the atmosphere in each stage from ambient air. An exhaust line 
36 passes out of the last stage in the series through the end wall 18. The 
exhaust line is at a lower elevation than the inlet line whereby it can 
carry effluent from the housing under natural flow conditions. 
In the anaerobic process, a relatively large amount of the food consumed by 
the organisms is converted to a process gas rather than going into cell 
mass. However, in most flooded anaerobic systems, where the biomass 
remains submerged in the process fluid, a built-in resistance is present 
which tends to slow down the bioconversion process. It is believed that 
when the process gases are discharged directly into the process fluid, the 
fluid first becomes saturated with gas before the gas can be released into 
the atmosphere. The effect of this fluid resistance in the flooded system 
is reflected in the long retention times required to bring the process to 
completion. Retention time of between 30 and 50 days are typical for 
unmixed systems and 10 to 20 day retention times for mixed systems. 
In the present invention, retention periods which previously have been 
measured in days have been reduced to hours. This is achieved by providing 
a dynamic living environment for the biomass wherein anaeobic 
microorganisms can feed upon the wastewater for a prescribed period of 
time and, upon digestion of the food, are allowed to discharge the 
converted process gas directly into a controlled oxygen-free atmosphere. 
As should be evident from the present disclosure, by establishing colonies 
on the surfaces of the discs, the microorganisms in the colony are drawn 
through the wastewater for a portion of each shaft revolution and exposed 
to the anoxic atmosphere over the fluid for the remaining portion thereof. 
This creates a controlled feeding cycle within the system which overcomes 
much of the resistance encountered in a flooded system. This controlled 
feeding cycle is also believed to speed up the biomass digestive process 
thereby permitting each colony to perform relatively more work. 
In many systems, the present invention will inherently control the pH 
within desired or optimum operating boundaries. Most anaerobic systems 
produce quantities of carbon dioxide, particularly when used to treat high 
strength industrial waste. If the gas is allowed to saturate the process 
fluid, carbonic acid can be formed, thereby driving down the pH of the 
effluent. By discharging the process gases directly into the atmosphere 
saturation of the process fluids with carbon dioxide is avoided and the pH 
of the fluid will remain generally stable. 
Referring once again to FIG. 1, a gas discharge line 40 is connected to 
each of the treatment stages and is adapted to a single main outlet line 
43 for carrying the gases out of the system. An automatic control valve 45 
is operatively positioned in line 43 for regulating the flow of gas from 
the housing. A negative pressure, that is, a pressure somewhat below 
atmospheric pressure, may be maintained in the atmosphere over the fluid. 
Although not shown, a vacuum pump or any other suitable exhaust system 
attached to line 43 can be used to draw a negative pressure within the 
housing. By lowering the operating pressure of the system, resistance to 
the anaerobic process is further reduced and the speed and efficiency of 
the system is thus increased. 
As noted, each treatment stage is isolated by means of the baffling 
arrangement whereby the concentration of nutrients and substrates 
contained in the wastewater is lowered in steps as the wastewater moves 
through the housing. Progressive lowering of the concentration gradient 
promotes good substrate removal while utilizing a minimal amount of space. 
To extend the operational capacity of the present apparatus under certain 
load conditions, an auxiliary influent delivery system is provided which 
is able to introduce raw influent independently into each of the treatment 
stages. A bypass line 37 is arranged to divert a portion of the influent 
from inlet line 25 and direct it below each of the treatment stages as 
shown in FIG. 1. The bypass line is connected into each stage via a feed 
line 38 that passes upwardly through the bottom wall of the stage. A 
control valve 39 is connected into each feed line. The valves can be 
adjusted to regulate the amount of raw influent that is introduced into 
each treatment stage. Although the auxiliary fluid is not premixed, the 
rotating discs contained in each stage will provide sufficient fluid 
mixing and gas stripping to effectively handle the added load. 
The invention will now be explained in greater detail with reference to the 
following examples: 
EXAMPLE 1 
A synthetic wastewater was prepared containing sucrose (C.sub.12 H.sub.22 
O.sub.11) and the nutrients of nitrogen, phosphorus, magnesium, potassium, 
iron, cobalt, calcium, sodium and sulfur. Additional trace nutrients were 
supplied by adding tap water to the influent. Sodium bicarbonate was also 
added to provide a buffer for volatile acid formations and to maintain a 
pH in the system within a 6 to 8 range. The wastewater constituents were 
continually mixed and delivered to a treatment housing similar to that 
described above that was maintained in a control room at a temperature of 
about 35.degree. C. 
The treatment housing contained four uniform sized stages and a smaller 
size mixing chamber. All components were constructed of a clear plastic so 
that visual observations of the interior of the housing could be made. 
Eleven discs, each having a 5" diameter, were rotatably mounted upon a 
common shaft within each stage with about 70% of the total surface area of 
each disc being submerged in the process fluid. Drain ports were provided 
in each stage through which fluid samples could be drawn. Gas produced in 
each stage was collected and passed through a wet test gas meter. 
At start-up, the housing was seeded with about a one liter mixture of 
biomass water containing organic and inorganic material taken from 
effluents of existing anaerobic treatment systems. The biomass was fed a 
mixture of methanol and sucrose. Seed was periodically added to the system 
when the color of the fluid changed from a healthy black to a lighter 
brownish color. Microorganisms found in the effluent were pumped back into 
the stages in varying amounts. After about 27 days, colonies of 
microorganisms were observed growing on the discs and start-up was deemed 
completed. Synthetic wastewater, prepared as noted above, was pumped 
through the housing at varying rates and the results noted. 
A total organic carbon (TOC) analysis was performed upon liquid samples of 
both the influent and effluent as well as samples drawn from each of the 
four treatment stages. All samples were passed through a 0.45 .mu.m 
membrane filter. The process gases were collected and the percent methane 
and carbon dioxide contained therein were recorded. Alkalinity, pH and 
volatile acids were measured and recorded in the effluent, influent and 
fluid samples drawn from each stage. Alkalinity was based upon the amount 
of equivalent calcium carbonate present in each sample. The amount of 
solids present in the effluent were also determined and recorded using a 
Reeve Angel type 934A filter. Additional data collected included the total 
amount of solids present as well as total volatile solids, total 
filterable solids and total volatile filterable solids. Readings were 
taken for various flow rates, while holding the shaft speed constant. The 
results are tabulated in the following tables where e represents final 
effluent values. 
______________________________________ 
Fluid Flow = 0.30 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 1050 .congruent.7 
-- 
Stage 1 192 7.12 1680 
Stage 2 110 7.27 1680 
Stage 3 44 7.32 1810 
Stage 4 44 7.80 1750 
Effluent 32 8.17 1680 
RPM = 12 
TS.sub.e = 2990 mg/l 
TVS.sub.e = 940 mg/l 
TFS.sub.e = 340 mg/l 
VFS.sub.e = 290 mg/l 
Gas Flow = 0.631/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
______________________________________ 
Fluid Flow = 0.60 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 1050 .congruent.7 
-- 
Stage 1 345 7.20 1560 
Stage 2 262 7.37 1590 
Stage 3 130 7.50 1440 
Stage 4 55 7.80 1280 
Effluent 53 8.01 1590 
RPM = 12 
TS.sub.e = 2910 mg/l 
TVS.sub.e = 815 mg/l 
TFS.sub.e = 480 mg/l 
VFS.sub.e = 345 mg/l 
Gas Flow = 1.1 l/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
______________________________________ 
Fluid Flow = 1.20 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 1102 .congruent.7 
-- 
Stage 1 812 6.34 1123 
Stage 2 573 6.29 1298 
Stage 3 474 6.56 1373 
Stage 4 326 6.64 1435 
Effluent 229 6.45 1123 
RPM = 12 
TS.sub.e = 2960 mg/l 
TVS.sub.e = 1010 mg/l 
TFS.sub.e = 220 mg/l 
VFS.sub.e = 220 mg/l 
Gas Flow = 1.6 l/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
______________________________________ 
Fluid Flow = 2.40 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 1102 .congruent.7 
-- 
Stage 1 858 6.36 1190 
Stage 2 700 6.30 1250 
Stage 3 696 6.15 1120 
Stage 4 597 6.24 1250 
Effluent 532 6.82 1590 
RPM = 12 
TS.sub.e = 3200 mg/l 
TVS.sub.e = 1300 mg/l 
TFS.sub.e = 300 mg/l 
VFS.sub.e = 300 mg/l 
Gas Flow = 2.9 l/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
The results set forth in the above-noted tables indicate that a high 
percentage of substrate and nutrients are removed from the influent in a 
relatively short period of time and that the volume of usable gas produced 
increases as the loading rate increases. 
EXAMPLE 2 
A synthetic organic wastewater slurry was manufactured to test the system's 
ability to produce both methane and carbon dioxide from many plentiful 
waste materials such as agricultural, industrial, municipal and domestic 
wastewaters as well as wastewater treatment plant sludges and other 
organic plant and animal waste materials. Basically the feed stock used 
sucrose as the primary constituent. 
The treatment housing was set up as noted in Example 1 and the amount of 
gas produced for a regulated influent flow was recorded. The results are 
as follows: 
______________________________________ 
Fluid Flow = 0.30 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 2320 .congruent.7 
-- 
Stage 1 628 7.07 3410 
Stage 2 391 7.27 3410 
Stage 3 162 7.45 3480 
Stage 4 68 7.42 3320 
Effluent 56 7.99 3410 
RPM = 12 
TS.sub.e = 5210 mg/l 
TVS.sub.e = 1490 mg/l 
TFS.sub.e = 450 mg/l 
VFS.sub.e = 450 mg/l 
Gas Flow = 1.3 l/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
______________________________________ 
Fluid Flow = 0.60 l/hr. 
TOC Alkalinity 
Sample mg/l pH mg/l CaCO.sub.3 
______________________________________ 
Influent 2320 .congruent.7 
-- 
Stage 1 1233 6.90 3000 
Stage 2 777 7.08 3350 
Stage 3 749 7.27 3320 
Stage 4 498 7.24 3350 
Effluent 454 7.55 3450 
RPM = 12 
TS.sub.e = 5630 mg/l 
TVS.sub.e = 2190 mg/l 
TFS.sub.e = 560 mg/l 
VFS.sub.e = 560 mg/l 
Gas Flow = 2.1 l/hr. 
% CH.sub.4 of Gas .congruent. 50% 
% CO.sub.2 of Gas .congruent. 50% 
Temp = 35.degree. C. 
______________________________________ 
As can be seen, as the flow rate of wastewater through the system increases 
the amount of bioconverted gas also increases. These tests were conducted 
at a constant shaft speed under atmospheric conditions. Increasingly the 
shaft speed, while decreasing the housing pressure, will further increase 
the rate of gas production. 
While this invention has been described with reference to the method 
disclosed above, it is not confined to the details as set forth and this 
application is intended to cover any modifications or changes that may 
come within the scope of the following claims.