METHOD FOR OPTIMIZING THE DRAINAGE OF MICROORGANISM-CONTAINING SLUDGE

Description

[0001] The invention relates to a method for optimizing the dewatering of sludge containing microorganisms from a biological purification process, in particular from wastewater treatment, which is fed to a dewatering device.

[0002] Wastewater treatment uses activated sludge processes, in which microorganisms are used, for example, to degrade organic carbon and nitrogen compounds, remove phosphates, and thus generally purify contaminated water. In addition to this biological treatment, chemical treatment stages are also used to remove phosphorus or other problematic substances such as heavy metals from the wastewater.

[0003] Basically, large quantities of sludge are produced, the volume and mass of which must be reduced for further recycling or supply.

[0004] A method for optimizing the dewatering of biogenic sludge is already known from WO2009065509. In a first process step, the sludge is treated with ultrasound to disintegrate, i.e., destroy the microorganisms. Afterward, a flocculant containing polymers is added to the sludge in a second process step. The sludge can then be dewatered using a filter press. A disadvantage of this method, however, is that wastewater and the resulting sludge can vary greatly, which is why previously known optimization methods lead to sludge with widely varying residual water contents. This lack of reproducibility poses a problem for logistics and general advance planning for sludge disposal.Until now, an approximately constant or continuous result could only be achieved through permanent manual readjustment of, for example, the wastewater flow rate, the aggregate power and the precipitant quantity.

[0005] EP3539932 A1 describes a method for optimising the dewatering of sludge from a biological treatment process, wherein the sludge is treated with ultrasound and before, during and / or after which a conditioning agent is added to the sludge.

[0006] The invention is therefore based on the object of proposing a resource-saving method for dewatering sludge and a device for carrying out the method, which enables improved and, above all, reproducible dewatering of the sludge regardless of the nature of the initial sludge.

[0007] The invention solves the problem by the method defined in claim 1.

[0008] The sludge preconditioner, a solution of calcium salt, citric acid, and iron dichloride, is used to precondition the sludge. Preconditioning in this context means preparing the sludge surface for subsequent charge equalization with a flocculant. It has been found that particularly good preconditioning, with regard to sludge floc structure and stability, is achieved when the sludge is ultrasonically treated during or after the addition of the sludge preconditioner.

[0009] According to the invention, the ultrasound parameters, such as frequency and power, are selected so that the microorganisms are not destroyed. The ultrasound is therefore not used to disintegrate the microorganisms, but rather to precondition the sludge, with the effect of the ultrasound being enhanced by the sludge preconditioning agent. Surprisingly, the combination of cell-nondestructive ultrasound treatment and the addition of the sludge preconditioning agent achieves a greatly improved charge balance between the sludge flocs and the polymer-containing flocculant added in the final step, which allows the required amount of flocculant to be significantly reduced.Through efficient sludge preconditioning, a nearly constant charge balance between sludge flocs and the flocculant can be achieved, regardless of the nature of the source sludge. This ensures reproducible dewatering results and improves the efficiency compared to previously available methods. Typically, the disposal costs of sludge, which is burned in incineration plants, for example, increase with its mass. By reducing the water content, both transport and incineration costs can be reduced. Another advantage is that the process is more cost-effective due to the lower amount of flocculant required.It probably goes without saying that after adding the flocculant, the sludge treated according to the invention must be fed to a dewatering device known from the prior art, such as a screw press or centrifuge.

[0010] A particularly efficient treatment of the sludge without damaging the microorganisms is achieved when the sludge is treated with an ultrasound frequency between 20 and 100 kHz, in particular with a frequency of 25 kHz.

[0011] In order to achieve a permanently reproducible dewatering of the sludge without significantly increasing the operating costs, the sludge is sonicated with a specific power of 5 to 50 W / kg of solids contained in the sludge.

[0012] The sludge to be dewatered can be treated in full or partial flow. The measures according to the invention make it possible to create virtually consistent dewatering conditions despite varying conditions, such as different seasons. Furthermore, the consistent conditions significantly increase the adjustment intervals for fine-tuning the ultrasound parameters, the addition of the sludge preconditioning agent, and the flocculant. The process thus requires significantly less maintenance and is more reliable. With the proposed optimization, the dewatering results of sewage sludge, for example, can be improved by up to 20%.

[0013] The method according to the invention can be carried out in a device with a flocculant dosing device arranged between an ultrasonic system and a dewatering device, wherein a sludge preconditioning agent dosing device is arranged in addition to and / or upstream of the ultrasonic system.

[0014] The drawing shows an example of an apparatus for carrying out the method according to the invention.

[0015] A device for dewatering sludge 1 containing microorganisms from a biological purification process comprises a sludge preconditioning agent dosing device 3 located upstream of an ultrasonic system 2 for dosing a sludge preconditioning agent 4. Further downstream of the ultrasonic system 2 is a flocculant dosing device 5, through which the sludge 1 can be treated with a flocculant 6 before the sludge 1 is fed to the dewatering device 7. In the dewatering device 7, the thus pretreated sludge 1 is dewatered, and the liquid phase 8 is separated from the solid phase 9 of the sludge 1. The sludge preconditioning agent 4 can also be added via the ultrasonic system 2.

Claims

1. Method for optimising the dewatering of sludge (1) containing microorganisms from a biological purification process, in particular from waste water treatment, which sludge (1) is fed to a dewatering device (7), characterised in that a solution of calcium salt, citric acid and iron dichloride is added to the sludge (1) as a sludge preconditioning agent (4), after which or wherein the sludge (1) is sonicated with ultrasound, the parameters of the ultrasound being selected such that cell walls of the microorganisms remain intact, and in that a flocculant (6) comprising polymers is then added to the sludge (1) before the latter is fed to the dewatering device (7), wherein the sludge (1) is sonicated with a specific power of 5 to 50 W / kg of solids contained in the sludge (1).

2. Method according to claim 1, characterised in that the sludge (1) is sonicated with a frequency as a parameter of the ultrasound between 20 and 100 kHz, in particular with a frequency of 25 kHz.