DE3840123A1 - Aerobic biological waste-water purification - Google Patents

Abstract

Fine-grained anthracite is used for aerobic biological waste-water purification.

Description

It is known to dispose of sewage sludge thermally. To be a self-sufficient ver to enable combustion or the dried sewage sludge as economic A carbon carrier is added to the sewage sludge to make good use.

When it comes to biological wastewater treatment, in addition to the low The following problem areas:

• - suitable carrier material
• - Improvement of the sedimentation properties of the sludge
• - Avoiding bulking and swimming mud
• - drainage aid
• - drying aid
• - nitrification and denitrification.

The object of the invention is to increase the calorific value to give wastewater treatment a supporting function. this will achieved by using finely ground anthracite dust.

It is state of the art that through additional growth area in the Aeration tanks of aerobic biological wastewater treatment plants the spatial material sales performance can be increased. This results in the planning new aeration systems have smaller activation tanks (cost advantages) or if they exist the cleaning capacity can be improved in the overloaded systems, so that the limit values required for discharge into the receiving water can be guaranteed.

Additional growth area can be provided by permanently installed internals (e.g. cross-linked moldings, plastic cords) or by floating growth body (e.g. sand, fly ash, plastic cubes, activated carbon, activated coke) be created. The previously known methods have the following shortcomings:

Fixed installations tend to become blocked, particularly due to the build-up unsuspended solids. They also form a hydraulic one Resistance, so that additional energy expenditure is required. Often undesirable anaerobic zones occur.  

Due to the smooth surface of sand, the formation of a biofilm difficult, since this the shear forces of the particles with different Relative speeds is exposed. The relatively high density of the sand this negative effect also favors premature sedimentation tion of individual particles.

The high fine fraction of fly ash has an effect on premature sedimentation opposite. With the eluates of the ash, however, the wastewater becomes additional charged.

Both when using sand and ashes, it comes with the thermal treatment of sewage sludge to a disproportionate increase of the combustion residues to be landfilled and in addition to one Reduction in calorific value. Both aspects are becoming increasingly important as a result the only sensible solution for sewage sludge disposal in the future thermal recovery will be if composting or the Ver bringing into agriculture is not possible.

Porous elastic cubes made of polyurethane foam have proven unsuitable proven. The effective surface is relatively small. Inside the cube there are anaerobic zones and inactive biomass, since only the outer one Biofilm is actively involved in the implementation of the substrate. The activity of the activated sludge is already around with a layer thickness of approx. 0.1 mm Half back. At 0.5 mm it is still about a tenth.

With activated carbon and activated coke the very high specific upper is often area highlighted. The surface consists almost entirely of inside surface in the form of meso- and micropores, whose diameter is smaller than the microorganisms and are therefore no longer a growth area. The the effective surface area is therefore limited to the outer surface Surface.

For reasons of cost, activated carbon is only used in special cases. Active As a rule, coke has a rough grain distribution, so that compared to fine dust little outer surface is available. The rough ones Particles sediment prematurely, so that they also serve as growth areas omitted. The percentage of these particles is not insignificant.  

A requirement profile for results from the disadvantages listed above an ideal carrier material:

• - very high proportion of the outer surface
• - high grain size to avoid premature sedimentation or low energy requirements for the required buoyancy
• - Chemical purity to avoid additional loads
• - Organic substance to increase the calorific value and at the same time Minimization of combustion residues
• - low cost of the economics of the process.

Another property, not yet mentioned, is imperative dig. The species-specific adsorption behavior of the microorganisms must also match the surface of the carrier material.

When calling for an organic fine dust inevitably Safety aspects related to self-igniting and exploitation risk of the respective carrier material to be checked, as this is their own the safety and economy of the process determine.

Finely ground anthracite dust meets all of these requirements ideal carrier material. The grain distribution is as follows fixed:

Because of the positive experiences so far with the use of feinge ground anthracite dust as a carrier material also results in the following Utility functions:

• - sedimentation aid
• - Avoiding bulking and swimming mud
• - drainage scaffolding and improved drying properties of the filter cake
• - Increase in the calorific value of the filter cake.

In addition, finely ground anthracite dust is an ideal carrier material for intermittent and / or simultaneous nitrification and denitrification.

Studies with mixed bacterial cultures have shown that under different microorganisms show a species-specific adsorption behavior As a decisive factor for the adhesion of microorganisms the charge and hydrophobicity of the cell surface poses. Hydrophilic carrier materials are suitable for municipal waste water well proven. The hydrophilic properties of finely ground anthracite additionally favor the wetting behavior, so that an unproblematic clean, dust-free metering into the inlet of the Aeration tank can take place.

The hydrophilic properties are achieved as follows: Anthracite sludge with a moisture content between 15% and 25% water is used as the raw product. This product is directly dried in a mill drying system and ground to the required fineness. The volatile components are between 8% and 10%. The ash content ( wf ) differs between 17 and 23%. The finished product has a residual moisture of less than 1%.

The quantities to be dosed are determined as follows:
Minimum amount: 5% based on the solids content
Maximum amount: 50% based on the solids content.

Due to the above-mentioned high grain size, anthracite dust has a wide range of outer surfaces. The small density difference of anthracite (approx. 1.4 g / cm ³ ) to the waste water combined with the fineness leads to the following advantages:

• - Low energy requirement for the necessary buoyancy
• - no premature sedimentation in hydraulically dead zones of the Be life basin
• - no hydraulic losses and anaerobic zones as with fixed ones Internals for the immobilization of the microorganisms
• - low shear forces due to small masses, therefore better Flake stability
• - homogeneous distribution in the aeration tank leads to an improved Efficiency in organic degradation of the substrate.

The special suitability of finely ground anthracite dust as a growth area was detected by scanning electron microscope.

Anthracite is chemically harmless, so that u. a. for filtering Drinking and mineral water can be used. The eluate has a pH Value of approx. 8.

The harmlessness with regard to the risk of explosion and spontaneous combustion during transport, pneumatic conveying and storage certified by an expert, so that no special safety precautions must be taken.

The special flat grain distribution of the anthracite dust according to the invention (see above) contains a relatively high proportion of fines. These fine particles preferentially attach to the filiform microorganisms. The The product can therefore also be used to suppress expanded sludge.

Using microscopic images, it can be shown that even larger ones Particles (approx. 100 µm) should be built into the mud floc. The bio Film on the surface of the carbon particles favors this process. On sedimented due to the high average density of the "loaded" mud flake this faster. The anthracite dust causes an increased sludge concentration tion and an improved sludge index.  

Sewage sludge is difficult to dewater. For this reason often added solids to increase the dry matter content. Play grain size, grain distribution and the wettability of the solid an important role here.

In several test series on a large wastewater treatment plant it could be shown that very good results were achieved with finely ground anthracite dust. When adding 10% anthracite dust, based on the solid share, an increase in the TS content of around 18% was found will.

With the generally customary addition of the solid as a support There is a certain inhomogeneity in the drainage before the filter presses do not avoid. The anthracite dust is added more expediently point in the inlet of the aeration tank, so that a very homogeneous one the dust is mixed into the sludge to be dewatered. Hereby A procedural advantage results from the following Example is confirmed.

When operating a larger sludge drying system, the Mixing of finely ground anthracite into the sewage sludge is essential Drying efficiency improvements. The homogeneous interference and favor the larger outer surface of finely ground anthracite dust a crumb structure so that the hot gases get more contact when drying have areas and the entire process is much more efficient.

By adding finely ground anthracite dust, the pump could also Ability of the sludge to be improved, so that the drive power and the pressures for the slurry pumps were reduced.

When finely ground anthracite dust is added, the calorific value becomes increase in the sludge to be dewatered determined by two factors:

• - Due to the respective mixing ratio, the Calorific value based on the dry matter.
• - With a disproportionate drainage rate ( see above), heat of vaporization is saved.

The limit values prescribed by law for the nitrate content lead especially for a number of existing sewage treatment plants problems. There are a variety of nitri and Denitrification, most of which are for economic reasons omitted.

The procedures of intermittent and simultaneous denitrification because it has no major structural Effort can also be practiced on existing systems.

The aeration tank is time for intermittent denitrification wise under aerobic (nitrification) and sometimes under anaerobic conditions conditions operated (denitrification). Those that become free with nitrification Hydrogen ions enable the implementation of the Nitrate in molecular nitrogen.

With simultaneous denitrification, the aeration is carried out in a circulation tank designed so that in one or more areas under aerobic conditions nitrified and denitrified in anaerobic areas becomes.

A requirement for both processes is an increased sludge concentration and a higher mud age. As the growth rates of the Nitri fikanten (Nitrosomonas, Nitrobacter) by approx distinguish heterotrophic bacteria, it must be ensured that the Nitrificants cannot be overgrown by these.

Throttling the growth rate of heterotrophic bacteria can only be achieved by reducing the BOD5 sludge load. This results in an increase in sludge age, which in turn increases creates necessary growth conditions for the nitrificants.

Finely ground anthracite dust favors this process in two ways Wise.

The individual particles initially act as a carrier material, so that over a Increasing the sludge concentration reaches the required sludge age becomes.  

Denitrification releases molecular nitrogen, which is similar to a Flotation process that floats mud flakes. This undesirable te swimming mud is another problem caused by use of anthracite dust can be largely avoided. The additional Loading the flake with anthracite dust acts as a boost to the nitrogen bubbles towards it so that it sediments.

Claims (2)

Aerobic biological wastewater treatment in which finely ground coal is used, characterized in that anthracite is used as coal, the anthracite being

• - carrier material and / or
• - sedimentation aid and / or
• - Help with swelling and swimming sludge suppression and / or
• - drainage aid and / or
• - drying aid and / or
• - Aid for nitrification and denitrification

with a grain size of 90% less than 40 µm to max. 120 µm and in quantities of at least 5% and at most 50% based on the solids content of the Sewage sludge is used.