Untitled record

<img file="AT277895B_D0001.tif" />

AUSTRIAN

Class: 85 c 14/09

PATENT OFFICE

Int. Cl .:

C 02 c 3/00

PATENT NUMBER NO. 277895

12th January 1970

DORR-OLIVER INCORPORATED IN STAMFORD (USA)

Method for concentrating biological solids in reaction systems

Registered on September 5, 1967 (A 8115/67); Priority of the application in the United States of America of September 9, 1966 (578374) claimed.

Beginning of the patent period: April 15, 1969.

The invention relates to a method for concentrating biological solids in liquid media using selective permeable membranes to separate the biologicals from the carrier liquid. Such membranes and their preparation are described in detail in the journal Chemical Engineering, March 28, 1966, by Friedlander and Rickles. The invention finds particular application for the concentration of biological solids or Liquids used in plants and processes used to treat urban wastewater and industrial wastewater. Such systems have previously been used in the treatment of wastewater, for example, activated sludge systems in which aerobic biological living matter is the metabolic conversion agent. However, these systems are limited to relatively ineffective or adverse operating conditions, which are determined by the phase separation device, which is usually a clarifier, and which separates solids, ie, the biological matter with the adsorbed sewage nutrients, from the effluent water.

A practical size clarifier for wastewater treatment plants can handle a feed with a maximum solids concentration in the range of 0.5 to 1.0%, and most of these so-called secondary clarifiers in activated sludge plants operate at a 0.3 to 0 feed , 5% solids. To obtain these dilute feeds, primary clarifiers are used to prevent the easily settling nutrient solids in the raw sewage from entering the biological process system, thus increasing the load on the secondary clarifier. As a further measure, the reaction system with activated sludge, which receives the outflow of the former clarifier, operated so that a build-up of biological solids above the maximum specified above is prevented. This limitation with respect to the concentration in conventional systems with activated sludge leads to various disadvantageous results:

1. larger units in the biological stage of the plant and / or lower treatment times,

Second more dilute and therefore more voluminous sewage sludge from the system with activated sludge,

Third the requirement of a primary clarifier,

4th larger quantities of solids in the sludge discharge of the entire plant, since the primary sludge is not metabolized, and

5th a tendency to provide secondary effluent of questionable quality when the values ​​of the Be30 sediment concentration for the secondary clarifier are shifted to the maximum in an attempt to alleviate the problems caused by these drawbacks. In addition, clarifiers are not capable of dissolved solids that have not been metabolized or not by the biological living2

No. 277895

Substances were absorbed, separate.

Accordingly, it is a primary object of the invention to provide treatment systems and processes with biological processes that overcome the disadvantages of the prior art.

To achieve this aim, the invention provides two larger assemblies, the first of which is a biological reaction container containing biological living matter in a liquid carrier. The reaction vessel is adapted to receive a nutrient stream, such as raw sewage, and, in the case of aerobic biological matter, oxygenation to provide metabolic conversion of the nutrients through the biological matter. A stream of the contents of the biological reaction vessel is withdrawn and directed to the second major system component, a membrane separation device. This separator has a selectively permeable membrane or membranes to permit transport of the carrier liquid through the membrane while preventing the flow of biological matter through the membrane.

In applying the invention to wastewater treatment, the membrane preferably retains not only the biologicals but also the large-molecule, bulky or slowly biodegradable organic nutrients so that there is ample opportunity and time for the metabolic conversion of these nutrients. In certain uses for wastewater treatment, it may be desirable to use a membrane which passes dissolved, non-biodegradable inorganic materials into the effluent. In other applications of the invention, the biological living matter can provide a valuable product, and in that case it may be desirable for this product to pass through the membrane for subsequent recovery.

Since the separations occurring in the invention are membrane, reverse osmosis and ultrafiltration, a pressurized feed to the membrane separation apparatus is used to obtain the required pressure drop across the membrane. The carrier liquid passes through the membrane and leaves the membrane separator as an effluent stream. The biological living matter and the majority of the carrier liquid are retained on the feed side of the membrane and leave the membrane separator as a so-called concentrate stream. This concentrate stream is recirculated to the membrane to allow further separation on the membrane. This circulation is carried out by direct return and / or return circulation guide through the biological reaction vessel. In addition, provision is made for biological solids to be removed from the system to allow control of the solids concentration and / or recovery of a valuable biological product.

Because of the specific size separation of semi-permeable membranes, effluent quality is not adversely affected by the concentration of feed to the separator. Therefore, the biological reaction systems of the invention can operate at much higher solids concentrations than heretofore possible. Thus, when applied to wastewater treatment systems, the invention allows the biological reaction vessel to directly receive raw sewage, eliminating the need for a primary clarifier. This leads to a metabolic conversion of the entire wastewater nutrient stream, thus reducing the total amount of sludge solids to be discharged. In addition, the effluent solids withdrawn from the biological reaction system are more concentrated and therefore less bulky. Furthermore, in the invention, the individual components of the reaction system are smaller because of the higher permissible solids concentrations. Finally, the effluent of the plant does not contain any biological solids, despite the high solids concentrations, and is of exceptionally high quality and contains no bacteria and no known viruses. Accordingly, it is not necessary to chlorinate the effluent of the plant before it is discharged to a receiving water.

Accordingly, the invention provides a method of concentrating biological solids in reaction systems with a biological reaction vessel which contains nutrients for the liquid biological living matter in the system and wherein conditions for the metabolic conversion of the nutrients are maintained. This process is characterized by passing the stream containing biological living substances along one side of a semipermeable membrane selected to retain the biological matter on that one side of the membrane while allowing the carrier liquid to pass through, thereby rendering the biological fluid concentrates the life of biological living substances, and at least part of the concentrated, containing the biological livers current flowing past this one side of the membrane, recirculated and allowed to flow past the membrane again to repeatedly concentrate the biological livers containing stream on the membrane.

<img file="AT277895B_D0002.tif" />

Nr.277895

In terms of apparatus, the invention provides a biological reaction system characterized in that it comprises a reaction vessel containing biological fluids supported by a fluid capable of reacting nutrients, said reaction vessel having a membrane separation device with a selectively permeable membrane which is capable of transporting carrier liquid through the membrane, while preventing the biological matter from passing, and means for circulating the bioluminescent liquid from the reaction vessel to the membrane separation device and back to the reaction vessel.

For a clearer understanding and ease of explanation of the effect, the invention will now be described by way of example with reference to the drawings. In the drawings: Fig. 1 is a schematic flow diagram showing the novel system of the invention comprising a biological reaction vessel and a membrane separation device for ultrafiltration and reverse osmosis. 2 Fig. 3 is a schematic flow diagram showing a modified arrangement of the invention, wherein a biological reaction vessel operating under ambient pressure is used, and Fig. 4 is a schematic flow diagram showing a flowchart of the present invention another embodiment of the invention wherein a two-stage membrane is used to separate the effluent of the first stage into fractions.

Fig. 1 shows a pressurized biological reaction vessel -10- which contains a liquid -12-, which carries the biological living substances in itself. The biological living substances are obtained by nutrients, which are supplied by pump -14- and line -16-. In the application of the invention for wastewater treatment, preferably a comminution or milling device is incorporated into the nutrient supply line to reduce the particle size of the solids of the raw sewage and thus to facilitate its metabolic conversion and to prevent oversize particles from entering the sewage system Block flow in the system, especially in the membrane separator.

For those applications where the biological living matter in the reaction vessel is aerobic, a manifold -20- is installed in the reaction vessel and connected to a suitable source of compressed air or oxygen -22- to provide the oxygen required for the metabolic conversion of the nutrient stream , The reaction vessel also has a vent with suitable regulation means, such as a valve 26, to permit the escape of gases.

A stream of the contents of the reaction vessel is withdrawn through a discharge line -28- and fed by means of a pump -30- through a feed line -32- to a membrane separation device -40--. The separator has a suitable housing -42- which is separated by a selectively permeable membrane or membranes -44- into a feed through-space -46- and an outflow space -48-. The properties of membranes -44- are selected to provide reverse osmosis and ultrafiltration separation, with the bioavailables retained on the feed side of the membrane. Since a pressure differential must be maintained across the membrane to effect reverse osmosis and ultrafiltration, a perforated membrane support plate -45- is provided on the outflow side of the membrane. The housing -42- is provided with a Ausflußauslaß -50-, which is connected to the Ausflußraum --48-. The carrier liquid passing through the semi-permeable membrane -44- is collected in the outflow space -48- and leaves the separator as effluent stream -52-.

The material retained on the feed side of the membrane -44- and enclosing the bulk of the carrier liquid as well as the biological matter flows out of the feed space -46- through line -54- as a somewhat concentrated stream. The concentrate line -54- leads back to the inlet side of the circulation pump so that at least a portion of the concentrate stream is recirculated through feed line -32- to again pass the membrane.

In order to maintain the desired concentration of biological living matter in the reaction vessel -10-, a portion of the combined stream of pumped-off concentrate discharged from the reaction vessel is recirculated through the reaction vessel by means of a recirculation line -56-. The distribution of the flow delivered by the pump to return line -56 and feed line -32- is regulated by valves -58 and 60-in the respective lines.

As the continued growth of biological living matter in the system of this system 4

No. 277895 can be overloaded with biological living solids, a withdrawal line -62- with a control valve -64- is installed in the circulation line of the separation device.

The system illustrated in Fig. 2 is generally similar to that of Fig. 1, and the same reference numerals are used herein for identical components. The main differences between the systems of Figures 1 and 2 are in the circulation arrangement. Thus, in Fig. 2, a stream of the contents of the reaction vessel -10-is withdrawn through a discharge line-80 and recirculated by means of a pump -82- through a feed line -84- in the membrane separation device. A portion of the concentrate exiting the membrane feed space -46- through a concentrate line -86- is recirculated through the reaction vessel 10 -10 with the aid of a recycle line 88, and another part is recirculated directly through a recycle line. or secondary line -87- to the separator. The splitting between the recirculated portion and the directly circulated portion of the concentrate stream is regulated by valves -90 and 92- which are turned on in the return line -88- and the circulating line -87-, respectively.

The system of Fig. 3 is generally similar to that of Fig. 2, and accordingly like reference numerals are used for identical elements. The main difference between these figures is that in Fig. 3, a biological reaction vessel-100 operating at ambient pressure is used. The reaction vessel -100- contains a liquid -102- in which the biological living matter is contained, and is supplied with nutrients via a nutrient line. A stream of the contents of reaction vessel -100- is withdrawn through line -106- and introduced into the pressurized side of the system by means of a pump -108-.

The system illustrated in Fig. 4 is generally similar to that of Fig. 2, and the same reference numerals are used for identical elements. However, in Fig. 4, the membrane separation device -40- is the first of two separation stages. The separator - 40 - has a relatively loose membrane -120- which is selected to retain the biological matter on its feed side and reject not only the carrier liquid but also certain molecules smaller than that of the biological living matter. When applied to wastewater treatment, these molecules may be, for example, the inorganic nutrients or non-biodegradable substances contained in the wastewater stream supplied to the reaction vessel. Alternatively, these molecules can also be a valuable product resulting from the metabolic transformation. In any event, effluent stream -122- containing these substances is discharged from separator -40- and fed to the second stage -124- of the separator by means of a pump -126- through a feed line -128-.

The separator -124- has a membrane or membranes -130-, a membrane support body 132 -and corresponding outlet ports connected to a discharge line -134 and a concentrate line -136-. The concentrate line returns to the inlet side of the circulation pump -126- for direct recirculation of the concentrate past the membrane. The membrane -130- is a relatively dense membrane which retains molecules of the inorganic nutrients or the metabolic products while allowing passage of the carrier liquid. In this way, the repeated recirculation of the feed to the second stage membrane provides a concentration of effluent from the first stage. Periodically or continuously, a portion of this concentrated stream is withdrawn through the valved line -137- to a recovery or extraction unit -138- which removes from the removed portion the solids therein from the carrier liquid. For example, plant-138 may operate under direct precipitation, adsorption precipitation, ion exchange, solvent extraction or distillation. The separated fractions are discharged from the system -138- through corresponding lines -140 and 142-.

For example, to give a specific example of the use of the systems and methods described above, the application of the invention to wastewater treatment will now be described in detail in conjunction with the flow sheet of FIG. Typical domestic raw sewage from a municipality is directly used for treatment by the present system. Such raw sewage is a very dilute hydrous mass with a low solids content in solution and a greater proportion of solid constituents suspended in the water. This raw sewage is comminuted in the grinder -18- to obtain a maximum particle size of about 0.8 mm, and is then pumped into the biological reaction vessel, which is maintained substantially below the pressure required on the feed side of the membrane (in the range from 1.4 to 7.0 kg / cm²).

No. 277895

The reaction vessel contains typical water slurried aerobic biologics such as are commonly used in activated sludge sewage systems. The reaction vessel contents are aerated with sufficient air to ensure the metabolic conversion of the nutrient material in the raw sewage and the gases resulting from the metabolic conversion, principally CO₂, and other exhaust gases are allowed to escape from the pressurized reaction vessel through the control valve -26-. The reaction vessel is sufficiently large and the withdrawal and recycle streams are chosen to give a residence time in the reaction vessel in the range of 10 to 30 minutes. The discharge of biological solids through the downcomer line is adjusted to maintain the system at a high concentration of living biological solids, such as 3%, with the ratio of biological oxygen demand to biological solids on the order of .03 to 0 , 3 is.

The membrane in separator -40- was selected in this example to give a release size corresponding to molecular weights on the order of 200 to 400. Such a membrane retains the biological matter and substantially all of the unadsorbed or unmetabolized organic molecules or suspended particles from the raw sewage while permitting the transport of water and dissolved inorganic matter such as salts. The separation size of the membrane is preferably chosen to be well below the size of the retained material and well above the size of the material which is to pass through the membrane, thus avoiding a reduction in the rate of flow through the membrane due to clogging.

To consider the factors that affect the desired volumetric flow rates in this example of the invention, the waste feed to the reaction vessel is assigned the volumetric flow unit value Q. The flow in the recycle loop of the system is determined by the need to avoid depletion of the biological organisms in the reaction vessel. Since, under steady-state operating conditions, the rate of removal from the reaction vessel exceeds the recycle rate to the reaction vessel by 1 Q, and because the reflux to the reaction vessel is about more concentrated than the withdrawn stream, biodegradation of the biological organisms can be enhanced by such increase in recycle Reaction vessel can be avoided that the excess of the take-off speed is compensated by IQ. In this example of the invention, it was found that a feedback loop factor of 20Q was sufficient to obey the conditions given above. Therefore, the take-off flow in line is -28- 20 Q and the recycle flow to the reaction vessel through line is -56- 20 Q.

The determining factors that influence the desired flow rates in the separator are due to the membrane itself. To reduce the adverse effects of concentration slopes, which tend to build up across the surface of the membrane as the charge advances along that surface, turbulent flow across the membranes is preferred to minimize these increases in concentration. In addition, higher flow rates and corresponding turbulence along the membranes promote a leaching effect to inhibit the build-up or deposition of solids or a cake on the surfaces of the membranes. Therefore, for effective membrane operation, the feed rate to the separator should be high relative to the outflow rate, for example, in the range of 100 times for a particular type and for a particular arrangement of the membrane surfaces of the separator. Since the effluent flow from the separator is substantially 1 Q under steady state conditions, the feed rate in line -32- may be 101 ° C and the concentrate flow in line -54- may be 100 ° C.

Desirable upper limits of flow through the separator are determined by the fact that the membranes can be destroyed by erosion at excessively high speeds and / or that the membranes -44- of the support structures -45- can be physically peeled off. In addition, it will be appreciated that from the standpoint of pump strength, recycle through the reaction vessel and direct recycle of the concentrate are desirably kept to a minimum that is possible in view of the flow requirements mentioned above.

As best understood with reference to the flow sheet of Figure 2, the split between the reflux flow in line -88- and the direct circuit flow in line -87 "

No. 277895 can somehow be varied between the extremes of 100% recirculation and 100% direct recycle by appropriate adjustment of valves -90 and 92-. Assuming that the flow requirements described above indicate that the flow through the membrane separation device should be at least 100 Q and the reflux to the reaction vessel at least 20 Q, it will be understood that these minima are accomplished by recycling all of the 100 Q of concentrate flow from the separation device to the reaction vessel without direct circulation or diversion by line -87- "can be achieved. However, one can achieve a reduction in pumping strength while maintaining the desired flow minimum when recirculating 80Q through bypass line -87- and returning 20Q through line -88-.

Further, if it is desired to increase the concentration of biosolids in the separator loop of the cycle system, for example in the production of solids to be removed, the return valve -90- may be closed. (This corresponds to closing the return valve -58- in FIG. 1, under which conditions the two flowcharts are identical.) This results in depletion of biological solids in the reaction vessel and converts them into the recycle flow in the separator loop such that the solids concentration therein is increased. In plants where the volume of the separator loop is small relative to that of the reaction vessel, this concentration in the separator loop may be accomplished without corresponding reduction of the biological material concentration in the reaction vessel.

In the exemplified use of the invention for wastewater treatment, the effluent from the membrane device is of very high quality. Specifically, the biological oxygen demand of the effluent is on the order of 3 mg / l, the chemical oxygen demand on the order of 20 mg / l without bacteria or known viruses. This high quality of effluents is due to the retention of the slowly biodegradable molecules as well as the bacteria and viruses through the membrane. Effluent of this quality is capable of being discharged into receiving waters without further treatment, and therefore the invention eliminates the need to chlorinate the effluent prior to delivery to the receiving waters.

It is a further advantage that the present membrane separation device can operate effectively at very high levels of biological solids. Although a 3% concentration of biological solids was used in the example, the separator can work effectively even at concentrations of 7 to 12%. The factors that limit these maximum concentrations are

1. excessive viscosity, which requires higher pumping strength and causes problems of flow distribution in the membrane separation device, and

Second the unwanted competition between such thick sludges and the membranes for the available water. In other words, above the maximum concentration limits, the membrane can not effectively draw water from the feed sludge, although the pressure drop across the membrane.

The ability of the membrane separation device to operate on these thick slurries of high concentration of biological solids is a significant difference over known wastewater treatment plants, where the biological reaction vessel is usually at solids concentrations of about 0.3 to 0.5% because of the limitations of the art secondary clarifier works. Thus, at these higher permissible levels of live biological material, the size of the reaction vessel may be reduced although it allows for complete adsorption of the wastewater nutrients by the biological matter in the reaction vessel.

Another advantage that results from operating the system at high solids concentration is that the periodic decrease in excess of live biological material occurs at these higher concentrations. Therefore, the sewage sludge has a much lower volume per unit weight of solids, and this eliminates the need for a thickening step that has been commonly used in known activated sludge systems.

Finally, because of the ability of this phase separation device of the invention to operate at a very high solids concentration, the need for a conventional, known primary clarifier is eliminated and, in the invention, raw sewage can be fed directly to the biological reaction vessel. Not only does this result in cost savings, it also means that all of the nutrient feed in the raw sewage is subject to metabolic conversion, thereby reducing the total weight of solids for processing.

Nr.277895