WO2016033625A1

WO2016033625A1 - Method and device for biological wastewater purification

Info

Publication number: WO2016033625A1
Application number: PCT/AT2015/050208
Authority: WO
Inventors: Kurt Ingerle
Original assignee: Kurt Ingerle
Priority date: 2014-09-03
Filing date: 2015-09-01
Publication date: 2016-03-10

Abstract

A method for carrying out biological purification of wastewater with the aid of activated sludge, in which the wastewater is first introduced into an activated sludge tank that can be ventilated (referred to hereinafter as the B tank) and then, in alternation, into one of a number of sedimentation and recirculation tanks (referred to hereinafter as SU tanks) continuously connected hydraulically to the B tank and in which a number of operating cycles are carried out over the course of a day. The SU tanks are all situated on one side of the B tank, to allow for positioning additional SU tanks on the opposite side of the already existing SU tanks.

Description

METHOD AND DEVICE FOR BIOLOGICAL WASTEWATER PURIFICATION

The present invention relates to a method for carrying out biological purification of communal or similar wastewater with the aid of activated sludge according to the preamble of claim 1, and to a device for carrying out this method. A method for biological purification of wastewater with the aid of activated sludge, in which the wastewater is first introduced into an activated sludge tank that can be ventilated and then into a sedimentation tank, in which activated sludge and treated water are separated and, after the separation process, activated sludge is fed back into the activated sludge tank and treated water is drawn off, is known from European patent EP 0 851 844. A number of operating cycles are carried out in the sedimentation tank over the course of a day and comprise a stirring phase U, a pre-sedimentation phase V and a draw-off phase A, wherein, in the stirring phase, the activated sludge is again mixed with the water, in the pre-sedimentation phase the activated sludge is sedimented, and in the draw-off phase treated water is drawn off. In accordance with the method disclosed in this document, the purification process takes place in a biological twin-tank system that is to say in the activated sludge tank and in the sedimentation tank, with continuous inflow and intermittent outflow. During the period of no outflow, the water level increases as a result of the inflow (filling principle) . The patent claim of this method is based on the fact that sedimented activated sludge is returned to the activated sludge tank of the "twin-tank system with filling operation" after the pre- sedimentation phase and before the stirring phase. In the stirring phase, the contents of the B tank (activated sludge tank) are mixed with the contents of the SU tank (sedimentation tank) until a largely constant dry substance concentration is obtained. Both tanks border one another and are continuously interconnected hydraulically in the base region. A similar method is known from international patent application WO 2001 046075 A2 (PCT/ATOO/00322 ) , in which sedimented, thickened activated sludge is returned from the SU tanks into the B tank after the V phases, but before the U phases. The B tank is continuously connected hydraulically to two SU tanks by one or more openings in the central region of the tank (figure 1), and the cycle times are selected to be approximately 140 minutes (S phase approximately 5 min; U phase approximately 5 min; V phase approximately 60 min; A phase approximately 70 min, A=(S+U+V) ) . In the S phase, thickened sludge is conveyed from the base of the SU tanks into the upper region (close to the surface) of the B tank, and the contents of the B tank thus displaced are returned via the openings in the central region of the tank. In the U phase, the contents of the SU tank are swirled and homogenized, without generation of a circulating flow via the B tank. In the A phase, there is a flow from the B tank into the SU tank, likewise through the openings in the central region. The stirring in the SU tanks (U phase) is achieved by blowing in air.

Another similar method is known from international patent application WO 2011 091452 Al (PCT/AT2011/000001) , wherein the object is to improve or complement the method described in the introduction for biological wastewater purification in such a way that an application for medium and large wastewater treatment plants is also made possible due to the use of the module principle, without development of short- circuiting flows of the thickened activated sludge (S phase) in the B tank and of the crude wastewater introduced continuously into the B tank. The module system is applied in large wastewater treatment plants. A relatively large number of modules, consisting of a B tank and two SU tanks arranged on the opposite sides of the B tank are combined to form a wastewater treatment system path. By combining up to 10 modules (and possibly more), a very long and narrow B tank is created, in which there is a risk that short-circuiting flows of the thickened activated sludge may develop in the S ph3. S Θ _f 3. S well as short-circuiting flows of the wastewater fed continuously for purification. One aspect of the international patent application WO 2011/091452 Al lies in solving the problem of returning the thickened activated sludge Q_s from the SU tank into the B tank (S phase) in such a way that there is no short-circuiting flow. After entry into the B tank, the thickened sludge cannot arrive back in the SU tank over a short path, since the sludge return would otherwise be disturbed, the dry substance in the B tank would fall sharply and purification would no longer be efficient. In accordance with this aspect, the solution to this problem lies according to WO 2011/091452 Al in the arrangement of two ventilation fields 1 and 2 (mostly fine bubble ventilation) in the B tank, at the edges bordering the SU tanks, said ventilation fields being operable together or separately depending on the requirements of the process. A ventilation-free region (approximately one third of the tank width) remains in the centre of the tank. In accordance with PCT/AT2011/000001, merely the ventilation field which borders the SU tank in which the S phase takes place is operated during the S phase. A vertical hydraulic flow, which guides the thickened sludge Q_s coming from the SU tanks into the opposite half of the B tank and thus prevents a short-circuiting flow, thus develops in the B tank.

Yet another aspect of WO 2011/091452 Al concerns the problem of introducing the wastewater to be purified Q into the B tank in such a way that there is no drifting of the wastewater to be purified Q, which is still purified insufficiently, into the SU tanks, the B tank and all modules are subject to equal hydraulic load, and constant conditions are obtained in the two SU tank units of a module. Care should also be taken to ensure that the flow conditions in the S phase (large vertical hydraulic flow) are not disturbed and that there is no constant depositing of activated sludge Q_s in the unventilated region of the B tank. In accordance with this aspect of WO 2011/091452 Al, in order to solve this problem, the wastewater to be purified Q is fed via one or more horizontal pipelines, which extend in the longitudinal direction of the B tank, are situated in the centre of the tank at approximately half the water depth or at the base and have openings. The openings will preferably be arranged in such a way that an escape horizontally in both directions and uniform coating of the B tank and modules is possible. The object of the present invention is to improve and/or complement the method described in the introduction for biological wastewater purification according to WO 2011/091452 Al in such a way, that costs can be saved in specified cases. This object is met by the features of the characterizing part of claim 1.

At present, two treatment methods for the purification of wastewater are placed into the foreground:

- For the "simultaneous aerobic sludge stabilisation" without primary treatment (first construction step ) a large B-tank is needed, because in addition to the large organic ( BOD₅=6 Og/PE ) load the long sludge age (long sludge age refers to sludge having an age of t_TS = 15 to 25 days depending on the temperature of the sludge, preferably t_TS = 25 days with a sludge temperature of 10°C) for the sludge stabilisation is to be considered. -The "activated sludge process (second construction step) with primary treatment combined with separate sludge stabilisation needs only a B-tank with the half volume of the first method.

The organic load of the primary treatment reduces the organic load of the B-tank (BOD₅=40g/PE personal equivalent) and short sludge age (short sludge age refers to sludge having an age of t_TS = 5 to 10 days depending on the temperature of the sludge, preferably t_TS = 10 days with a sludge temperature of 10°C) contributes to a reduction of the volume of the B-tank. The stabilisation of the surplus sludge will be treated with digestion or incineration.

For the first construction step, the required volume of the B-tank is more than two times higher than for the second construction step. Therefore, it is possible to start with the first construction step and pass after years later to the second construction step.

The capacity of the treatment plant enlarges thus to the double size (i.e. to the doubled capacity) with only doubling the SU-tanks. The second construction step has the advantage to use the digester gas of a digestion for producing energy. For the first construction step all SU-tanks will be situated on one side of the B-tank and for the second construction step the B-tank remains the same as before and additional added SU-tanks will be provided on the opposite side (see reference sign "1" in Fig. la) of the already existing SU-tanks. In the second construction step the sum of the SU-tanks preferably have at least the doubled volume of the sum of the SU-tanks in the first construction step.

In developing countries sometimes the sewerage channels are still incomplete and therefore it is economical very advantageous to start with the first construction step and enlarge later to the second construction step. It is important that already for the first construction step the wall of the B-tank on the opposite side of the already existing SU-tanks receives all required equipment for the later expansion to the second construction step (openings, shaft for airlifts, platform, etc.) . These openings will be closed till the expansion: for example with stainless steel plates. During the expansion of the treatment plant to the second construction step the operation of the plant will be completely maintained.

A large treatment plant (a large treatment plant refers to a treatment plant in the range of roughly 500 000 PE or more for instance) consists of many modules. It is therefore very difficult to distribute exactly the inflow into the B-tank in such a manner, that every module gets the same amount (identical quantity) of wastewater. Several pipes with large diameters in the longitudinal direction of the B-tank impair the flow conditions and should be avoided. It is better to arrange these pipes under the bottom of the B-tank. An advantageous solution is given in the distribution for two modules with one pipe and only two openings (see Fig. 2c) . To get the same amount of wastewater into each pipe a sufficient large compensating tank with a horizontal water level is necessary. After the passing of this tank the wastewater flows over a flat slide (preferably in stainless steel, openable and closable) and then in the pipe. The wastewater will be introduced in the surface of the B-tank and in this middle area. The outflow of the treated wastewater is of high relevance for treatment plants. The increase of the water level in the SU-tanks may be low, situations occurring in the winter term (frost) are to consider and floating sludge may not reach or not enter a discharge device. A number of horizontal arranged openings with an area of approximately 0,6 to 2,0 dm² are openable and closable by a system consisting of horizontally displaceable slides (for example plates, slide chain) . Maintenance services can be easily performed on the system. The lower edges of the openings determine the minimal water level in the SU- tanks .

For large treatment plants (for example 1 Mio PE, 4 lines with 12 modules per line) it is advantageous to construct an "infrastructure street" with all necessary installations: influx of waste-water, efflux of the treated Clearwater, divert of the excess-sludge, approach road to the lines, devices providing compressed air, supply of the electricity power control cables etc.. The wastewater flows through a closed main channel into a distribution tank to divide the waste water into the four lines and finally into the 48 modules. Every module has to get the same amount of wastewater. The water levels in this tank are preferably horizontal. This can be reached with a slow velocity of flow (v equals roughly 0,3 m/s) . To avoid the settling of sludge, the distribution tank will be aerated in determined periods. The wastewater flows from this tank over flat slides into the different pipes 2 (see Fig. la) . Fig. 4 shows an outline of the infrastructure street.

While setting up the first construction step the infrastructure street may be designed in a manner that is already prepared for the second step.

Figure la and lb show a schematic illustration of a wastewater treatment system in the exemplary embodiment, consisting of three lines with two modules per line,

a) simultaneous aerobic sludge stabilisation (62500 PE, 8000 m³/d) without primary treatment, b) activated sludge process (125000 PE, 16000 m³/d) with primary treatment and separate sludge stabilisation .

Figure 2a, 2b and 2c show the inflow of wastewater to be purified into the B-tank below the bottom thereof, c) outline, a) vertical section 1, b) vertical section 2.

Figure 3 shows the outflow of the treated water with horizontal designed outflow openings by horizontal moving flat slide chain.

Figure 4 shows the outline of the infrastructure street of a large treatment plant (1 Mio PE, consisting of foure lines with 12 modules per line) . The wastewater flows through a main channel 3 into the distribution tank 4 into the inflow system 5, into the B-tank 6, into the outflow system 7 (with slide chain) and into the outflow channel 8.

Claims

1. A method for carrying out biological purification of wastewater with the aid of activated sludge, in which the wastewater is first introduced into an activated sludge tank that can be ventilated (referred to hereinafter as the B tank) and then, in alternation, into one of a number of sedimentation and recirculation tanks (referred to hereinafter as SU tanks) continuously connected hydraulically to the B tank and in which a number of operating cycles are carried out over the course of a day, including a sludge return phase, a recirculation phase, a pre-sedimentation phase and a draw-off phase (referred to hereinafter as the S phase, U phase, V phase, and A phase respectively) , wherein consecutively, in the S phase, the thickened sludge is returned in succession from the SU tanks into the B tank, in the U phase the activated sludge is again mixed with the water, in the V phase the activated sludge is sedimented, and in the A phase treated water is drawn off, wherein in the SU tanks the cycles are phase-shifted in relation to one another, the A phases border one another, a flow passes through the SU tanks merely in the A phases, an approximately constant water level is provided, wherein a wastewater treatment system discharge corresponds to the wastewater treatment system supply ("continuous flow" principle), wherein in the B tank, at least two ventilation fields are used, wherein, in the S phases, only the ventilation field bordering the SU tank in which the S phase has just taken place is operated alone, at least for the most part, and in the U and V phases the two ventilation fields are used together or intermittently, characterized in that, for a first construction step a "simultaneous aerobic sludge stabilisation" without primary treatment and with a long sludge age will is selected, wherein all SU-tanks are situated on one side of the B-tank to allow for a second construction step to follow the first construction step, wherein in said second construction step an "activated sludge process" with primary treatment and with a short sludge age is selected, wherein the B-tank remains the same as before and additional SU-tanks are positioned on the opposite side of the already existent SU-tanks.

The method according to claim 1, characterised in that in the first construction step the wall of the B-tank on the opposite side of the wall with the SU-tanks receives all required equipment for the later expansion in the second construction step, wherein the equipment comprises openings, a shaft for airlifts, and a platform, wherein these openings will be closed temporary, preferably with stainless steel plates, till expansion to the second construction step.

The method according to claim 1 or 2, characterised in that during the expansion from the first construction step to the second construction step the purification of the wastewater is not hindered.

The method according to any of the preceding claims, characterised in that the wastewater to be purified flows into the B-tank via one or more horizontal pipes, which extend in the longitudinal direction of the B-tank below the bottom thereof, coming from an influent distributor, preferably from a distribution tank, with basically horizontal water level and with an aeration for whirling up settled sediments, passing overflow with a flat slide, flowing through the pipe and then out in the B-tank on different places, preferably only on two places.

The method according to any of the preceding claims, characterised in that the outflow of the treated wastewater soil is made with a number of horizontal arranged openings with a surface (area) of 0,6 to 2,0 dm², wherein the openings are openable and closeable by a system comprising horizontally displaceable slides or slide chains, and with a plunge plate to avoid the flowing off of floating sludge.

The method according to any of the preceding claims, characterised in that for a large treatment plant (a large treatment plant refers to a treatment plant in the range of roughly 500 000 PE or more for instance) an infrastructure street with all necessary installations for the operation of the treatment plant, comprising an influx of the wastewater, an efflux of the treated clearwater, a divert of the excess-sludge, connecting roads to the lines, production of compressed air, a supply of the electricity and control cables, is designed, comprising in particular a distribution tank with aeration, to divide up the waste water, so that all modules get the same quantity of waste water. 7. A wastewater purification device for carrying out the method according to one of the preceding claims .