JPH03114591A - Dynamic fixed bed bioreactor - Google Patents

Abstract

PURPOSE:To reconcile the enhancement of the concn. of bacterial cells and the suppression of clogging/offset flow by connecting carrier layers for bonding a microbial membrane every other layer and integrally shaking the connected layers. CONSTITUTION:Carrier layers A1, A2, A3... are fixed while carrier layers B1, B2, B3... are mutually connected and bacterial cells or SS are adhered and accumulated to the surface of the carrier A-group or B-group (fermentation tank activity period) and, when a tank is filled with the carrier groups and water passing resistance increases (closure period), the connected carrier B-group is moved so as to be shifted (water permeability recovery period). When the alternately connected layers are shaken in parallel to the surfaces of said layers at the point of time when crosslinkage due to bacteria propagated sludge is developed, the crosslinkage between all of the layers is cut and the closure of a water channel is opened. Since a water passing shortcircuit part is not selectively expanded, offset flow is also eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fixed bed fermenter equipped with two partially movable carriers for increasing the efficiency of a fermenter that passes a large amount of liquid, such as for water treatment.

Conventional technology and its problemsFixed beds help accelerate the desired reaction by retaining a large amount of fermentation bacteria in the bioreactor and increasing their concentration, and they also prevent bacterial cells from being washed out and prevent sludge from being returned. This contributes to the stabilization of the bioreactor by keeping the bacterial cell concentration at a higher level. Furthermore, as a filter bed, it has been highly evaluated for its ability to promote water purification by capturing and adsorbing a portion of solids and soluble substances, and its use has recently become popular.

In particular, for bacterial species with low growth rates such as methane-fermenting bacteria,
There is a risk that the amount of bacteria produced by the method will exceed the amount of bacterial growth, resulting in washing and deactivation.
To prevent this, bioreactors tend to grow large. Therefore, by immobilizing the bacterial cells, water retention time (F(RT)
) and the solids residence time (SRT), and by extending only the SRT, it is possible to downsize the device. By ordering a waste film through the adhesion and propagation of bacterial cells to the carrier, and by capturing and retaining floating bacteria in the gaps between the carriers, it is possible to retain 10 to 100 times the amount of bacterial cells in the bioreactor compared to a general floating bed.

However, the fixed bed system has the disadvantage that it inevitably tends to cause clogging because the surface area of the carrier to which it adheres is expanded and the microbial film thickens in order to increase the amount of bacteria attached.

Local clogging causes dead volume within the bioreactor, reducing the effective reaction space and causing inactivation and deactivation of bacterial cells in the clogging area.
cause death. At the same time, the flow is biased to other parts, causing short bathing and channeling of the waterway, resulting in outflow of untreated liquid and increased local flow velocity, resulting in detachment of biofilm and washing out of bacteria. In classical fixed beds, the dead space often reaches as much as 1/3 and is clogged with solid suspended matter, so packed beds are not suitable for rSS.
(J,
C.

Youug, “The Anaerobic Filt”
er for Waste Treat-ment''
, Proc, 22nd, lnd, Waste Con
f, Purdne Univ.

No, 129. p. 559.1987).

Complete clogging increases the water flow resistance of the bioreactor, leading to pressure loss during operation, and eventually leading to blockage of the bioreactor.

Technical Issues The most fundamental technical issue for fixed-bed bioreactors is to achieve both high bacterial cell concentration and suppression of clogging and drift.

In the packed bed shown in FIG. 1, crosslinking due to microbial growth sludge is likely to occur, resulting in clogging. The causal relationship is shown as follows.

These various measures and their technical challenges are listed below.

(b) There is little flexibility in adjusting the filling rate and taking measures based on the filling rate or porosity. Normally, a fixed bed with a porosity of 50±10% is standard for single-stone ceramic fillers, and a porosity of around 95% for plastic fillers that are easily formed into flakes or hollow molding. If it is made more sparse than this, it will resemble a floating bed and the risk of sticking to the floor will be reduced, but the bacterial membrane area will be insufficient. vice versa,
In order to enhance the advantage of a fixed bed, which is the improvement in bacterial cell density, if the bed is made denser, it becomes more likely to cause blockage.

In any case, if the distance between the carriers approaches 1 to 3 mm or less, adhesion and occlusion are likely to occur as the bacterial cell membrane grows, and this becomes a limiting factor and determines the packing density. In order to increase the amount of bacteria retained and at the same time ensure water permeability,
It can be said that the trick to maximizing the treatment efficiency of fixed beds is to ``operate in a state just before clogging.''

(b) Adjustment by the shape of the filler, the shape of the filler may be spherical or
There have been various attempts such as floating balls, honeycomb shapes, plate shapes, perforated plates, net shapes, cloth shapes, string shapes, shell shapes, irregular shapes, etc., and although there are considerable differences in solid matter trapping ability, the above-mentioned contradiction has been overcome. I haven't reached the point where I can. As for the solid matter trapping ability, experiments were carried out to measure the solid matter separation ability using inclined plates having various tilt angles with respect to 1 gravity or inertial force due to water flow (Naohiro Shirakami et al., Kako Ronshuu).

1987.1. p, 86), the inclination angle is 0°〈20
It is known that the separation becomes better as the angle increases from °<30°<45°. In addition, water treatment experiments using filter beds using packing materials with different inclination angles (T, Richards et al., J
W CF, 58.7°774, 1986),
Due to the flow of water, the amount of deposits increases in right-angled materials, and at the same time, short circuits occur frequently, and partial vortices occur in random filling materials distributed at an inclination angle of 0 to 90°, resulting in a shortened SRT and 45% for both. The BOD removal ability was lower than that of the tilted material at 60° to 60°.

From these results, the opposite phenomena of water flow blockage and uneven flow short circuit tend to occur together, so how can we create uniform water flow conditions and obtain a fixed bed that is difficult to block even with a high concentration of retained bacteria? is the issue.

(c) Parallel beds: If the packed bed is a honeycomb-shaped parallel bed (FIG. 2), clogging is reduced and drifting is also suppressed. However, the ability to retain bacteria is significantly reduced, resulting in performance similar to that of a one-through floating bed, and the advantages of a fixed bed, such as fermentation stability due to high bacterial density and no need to return sludge, are lost.

(d) Adjustment by water flow rate 1. It is possible to destroy bacterial cell bridges and regenerate water channels by changing the water flow rate. In an anaerobic fixed bed, the upward flow is generally 0.2 to 1 m/hour, but if the flow is further accelerated, bacterial flocs in the voids will escape, and then the bacterial membrane will peel off. Incidentally, the SS sedimentation speed of the sewage primary sedimentation tank is approximately less than 10 m/hour.

Breaking the blockage using intermittent flow, pulsating flow, etc. is a technique that can naturally be attempted. However, the flow rate of membranes such as bacterial cell separation membranes (for stripping and cleaning the surface) is 1 m/sec or more, which is several orders of magnitude higher than the general water flow rate. At such high speeds, there is a high possibility of fixed bed failure, and in fact, intermittent water flow acceleration inevitably has the disadvantage of selectively expanding water flow short circuits rather than breaking through blockages.

(e) Fluidized bed: By adjusting the density and particle size of the carrier, the flow rate of the fluidized bed can be set to 15 to 30 m/hour, making it possible to create conditions that prevent clogging even at fairly high concentrations. In an anaerobic fluidized bed, the critical flow rate to avoid detachment of bacterial membranes is approximately 10
m/time (L, G, M, Gorris, eta
l, +Biotechno1. Bioeng, +33
+687+1989). In addition, the UASB method, which is a type of fluidized bed using the bacterial cells themselves as carriers (approximately 1
(upward flow of about 0.2 m/hour for floc type) has also been quite successful in increasing bacterial cell concentration.

However, the fluidized bed has low filter performance and is difficult to expect to capture floating microbial cells and SS. Furthermore, in methane fermentation, the generated air bubbles adhere to the carrier and bacterial membrane, reducing the total specific gravity of the carrier.
This also tends to cause the carrier to float up and escape. When the flow rate is lowered to suppress outflow, carrier particles cause sticking (plugging). Therefore, if the flow velocity is increased, local blow-throughs are likely to occur before the lumps dissolve. In order to increase treatment efficiency, it is desired that the amount of retained bacterial cells be 30 KgVSS/m3 or more, so this type of adhesion problem is likely to occur frequently.

Part of the fixed bed can be moved to prevent blockages.
A method of performing anaerobic fermentation by suspending a large number of plastic strips in a tank (Shukai 304734 and Nasai 372)
8031.1989) has also been proposed, but the porosity is large and the amount of carrier adhesion is at a low level.

(f) Gas lift can contribute to agitation of the fermenter, destruction of bridges, and restoration of water permeability, but in general, gas masses selectively pass through large waterways, which is undesirable as it rather promotes short circuits and drifting.

(g) Stirring by stirring blades has little effect on the fixed bed section, which is about to become clogged, and rather has a strong local shearing force, which is undesirable because it only promotes the disintegration and emulsification of bacterial flocs in the drifting section.

As mentioned above, it is difficult to solve the problem using conventional techniques, and it is desirable to create a fixed bed that partially incorporates the advantages of a fluidized bed to break only the blockage while maintaining the high load on the verge of blockage.

Features of the countermeasure technology of the present invention Therefore, as an ideal fermenter, (1) a carrier that can hold more bacteria and has a large effective surface area to which bacteria can attach;
(carrier with a large inclination angle to the water flow direction to capture as much processable substances as possible (including SS)), ■ hard to cause blockage or water flow short circuit (many and uniform voids), ■ immediately before blockage. What is desired is a method that satisfies the following requirements: 1. The removal means does not destroy the bridge and selectively expand the water flow short-circuit.

In the present invention, we focused on (1) and (2) and devised means to more fully satisfy these needs. In other words, in a bioreactor constructed by stacking carriers for attaching microbial membranes in layers or membranes, the carriers are connected every other layer and the connected layers are agitated as a unit, so that the area between the eyebrows can be removed. It destroys the crosslinked parts all at once and restores water permeability.

When the crosslinks caused by the microorganism-proliferated sludge have developed, if this alternating connection layer is shaken parallel to the layer plane, all the crosslinks between the eyebrows will be severed and the blockage of the waterway will be overcome. Unbalanced flow is also eliminated because the water flow short-circuit portion is not selectively expanded.

FIG. 3 shows a simple carrier arrangement. Carrier layer A11. A
2, A3, ... are fixed, and the carrier layers B8, B2
, B3, ... are interconnected, and bacterial cells and SS are attached and deposited on the surface of carrier group 4 and B group (fermenter active phase)
When the space between the seeds is eventually filled and the resistance to water passage increases (occlusion area), the group of connecting carriers 758 is moved to shift (water permeability recovery period).

The moving distance may be 1 to 3 times the A-B layer spacing, and even if the distance is moved larger than that, the effect of breaking the crosslinking will be the same. The direction in which the connected carrier layer group B is agitated may be parallel to the water flow direction or perpendicular to the water flow direction, but in order to quickly discharge the solid matter liberated by the agitation, it is better to move it along the water flow direction. More preferred.

It is sufficient that the number of agitation is 1 to 3 times, and even if the number of agitation is increased, the effect of breaking the crosslinking will be the same. The water flow rate during the agitation period can be freely set between 0 and 10 m/hour, but to enhance the washing effect, the water flow rate should be set at 1 to 10 m/hour compared to the water flow rate under normal fixed bed operation.
A range of 2 times is preferred.

The carrier may be anything that can form a layer or film. The same applies to any carrier that can provide a sufficient surface to which microbial cells can adhere, such as cloth, nonwoven fabric, mesh, wire mesh, perforated plate, thread stretched over a frame, and lattice frame. However, it must have the strength to withstand mechanical vibration.

Effects of the Invention This invention breaks the blockage between the carriers and restores water permeability by moving the aggregate of the carriers at the time of blockage, so that the fermenter can be operated stably.

In addition, in order to increase the amount of bacterial cells and SS retained, it is necessary to increase the effective surface of the carrier (the specific surface area of the carrier is usually about 60 m2).
/m3, and the ratio of surface-attached bacteria to interstitial floating bacteria is approximately 50-50.

The specific surface area of the carrier can be up to 200 to 300 m2/m3, and the ratio of bacteria adhering to the surface becomes overwhelming); however, the larger the specific surface area, the more likely it is to be blocked by the development of a bacterial cell membrane. Conventionally, the specific surface area of the carrier has been limited due to obstruction, but the present invention eliminates this limitation.

During operation of a fixed bed fermenter, the activity gradually increases at the start of operation, and after the activity reaches its limit with the development of bacterial membranes and the accumulation of SS to be treated, water flow resistance increases, partial blockage, and uneven flow develop. Along with this, the activity of the fermenter decreases. By applying the present invention, it becomes possible to always maintain the fermenter in an operating state near the maximum activity.

Examples Example 1 As a fermentation tank, 20 frames covered with polyvinyl chloride W4 (for insect repellent net) were layered, and every other frame was connected to a frame (layer A) fixed to the tank to make it movable. (B layer)
It was constructed by connecting several square glass vessels measuring 00xlOOxlO00 (length x width x height). Inflow water has a BOD of 250
ppm, S S Using model sewage of 400 ppm, it was sent upward at a rate of about 0.3 m/hour along with anaerobic species sludge.
The animals were acclimated for one month at 35°C.

The BOD removal rate of the treated water at a water retention time (HRT) of 12 hours gradually increased and reached 60χ, but the blockage was so severe that water could not be passed. Observing the situation inside the tank at the time of blockage,
The voids are mostly filled with bacterial cells and SS, and gas pockets appear here and there.

In this state, when Layer B was shaken up and down by 10 mm three times, the water channels in the voids were regenerated, gas pockets disappeared, water permeability was restored, and treatment capacity was restored. The quality of the treated water temporarily becomes thick due to the discharged sludge, but it quickly returns to a high BOD removal rate. The discharged sludge is allowed to settle and solids are disposed of.
The supernatant liquid was returned to the influent water for treatment.

Example 2 A fermentation tank was constructed by laminating and arranging ten 7 mm thick plates made of foamed polyurethane reinforced with polyester nonwoven fabric in the same manner as in Example 1. SS-free model wastewater prepared with a peptone-glucose solution (B OD 900 ppm) was used as the inflow water, and the animals were acclimatized for two weeks in the same manner as in Example 1.

After 6 hours of HRT, the BOD removal rate of the treated water gradually increased and reached 90χ, but the blockage was so severe that it became impossible to pass water after 15 days.

In this state, when Layer B was shaken up and down seven times and twice, the water channels in the voids were regenerated, water permeability was restored, and treatment capacity was restored.

Example 3 A 10 mm thick polypropylene corrugated plate whose surface was roughened with polishing sand
A fermenter was constructed by stacking 25 perforated plates with holes of 3 mm in diameter at intervals in the same manner as in Example 1. The inflow liquid is a high SS liquid obtained by crushing kitchen waste (B OD 4000 ppm) into particles with a particle size of 1 mm or less. At first, only the juice without SS was supplied to the rats, and they were acclimatized for 3 weeks in the same manner as in Example 1. When full-wave HRT supply starts in 3 days, treated water B
The OD removal rate reached 60χ, but after 4 days it became clogged and water could not pass through.

In this state, when Layer B was shaken up and down by 10 mm three times, the water channels in the voids were regenerated and water permeability was restored, but they were blocked after half a day. Therefore, by repeating the agitation process once every half day, we were able to maintain a processing capacity with a BOD removal rate of 60χ.

[Brief explanation of drawings]

Figure 1 Packed bed, which is a conventional fixed bed 1: Inlet pipe 2: Drain pipe 3: Exhaust gas pipe Diagram 2 Parallel floor. 5: Honeycomb tube Figure 3 Partially movable fixed floor A1, A2, A3: Fixed carrier layer B2, B3: Movable carrier layer 4: Filling

Claims (1)

[Claims] In a bioreactor that uses a carrier to which a microbial film is attached as a fixed bed, and in a bioreactor that is constructed by laminating layered carriers, the carriers are connected every other layer and the connected layers are agitated as a unit. Fixed bed bioreactor.