WO1987005592A1

WO1987005592A1 - The use of hydrophobic zeolites as adsorption material at the biological purification of wastewater

Info

Publication number: WO1987005592A1
Application number: PCT/SE1987/000126
Authority: WO
Inventors: Nils Ludvig Molin; Thomas Gunnar Welander; Lars Olof FÄLTH; Sten Eskil Andersson
Original assignee: Anox Aktiebolag; Zeol Aktiebolag
Priority date: 1986-03-13
Filing date: 1987-03-12
Publication date: 1987-09-24
Also published as: SE8601177D0; SE456087B; AU7124787A; SE8601177L

Abstract

A method at the biological purification of wastewater containing substances toxic for the bacteria cultures used. In order to reduce the content of the toxic substances, the wastewater is treated in a pre-treatment step containing a zeolite as adsorption material, which zeolite has such a composition that the mole ratio Si:Al exceeds 15.

Description

The use of hydrophobic zeolites as adsorption material at the biological purification of wastewater

This invention relates to the use of hydrophobic zeolites as adsorption material at the biological purification of w-ste water.

Due to the ever increasing severity of environmental requirements, biological purification of wastewater has gained in importance as an alternative purification method in recent years. An intensive research and development work has been spent on finding specific methods adapted to different types of wastewater. A special problem is involved with such wastewater, which contains substances toxic for the bacteria cultures used.

Several proposals have been made previously to remove, convert or immobilize the toxic substances prior to the biological breakdown. One proposal suggests that the wastewater in a pre-treatment step is brought into contact with an adsorption agent, which binds the toxic material. It is especially this type of treatment methods which is of interest in the present context.

At one previously known method, which also is applied commercially, the toxic substances are adsorbed on active carbon. The active carbon is used in granulate state in an intermittent ("fixed bed") or continuous process. It has also been proposed to use the active carbon in pulverous state, in which case it is supplied to the activated sludge basin.

In literature proposals have been made previously at the biological purification of water to use zeolites, a.o. as carriers of the bacteria culture or for the adsorption of phosphorous and/or nitrogen compounds.

It is previously known through the international patent application with the publication number WO 85/04390 to use hydrophilic zeolites at the biological treatment of wastewater. It is stated there that such waters often contain metal ions, which have a toxic effect on the bacteria cultures, and that these ions can be removed by selective ion exchange by means of hydrophilic zeolite material.

It,thus,has been proposed previously to use hydrophilic zeolites at the biological purification of water. At the research and development work, on which the present invention is based, it was found that the use of hydrophobic zeolites at the biological purification of water opens entirely new possibilities. According to the invention, the zeolite shall have a mole ratio between silicon and aluminium which is greater than 20. Especially good results were obtained when said ratio was greater than 30.

According to a particularly expedient embodiment of the use according to the invention, the zeolite shall have pore openings of the magnitude 1-10 Å, preferably 5-10 Å.

The invention is described in greater detail in the following by way of some embodiments and with reference to the accompanying drawing, in which Fig. 1 shows a plant with a pre-treatment step according to the invention, Fig. 2 shows an arrangement for the regeneration of the adsorotion material, and Fig. 3 shows a plant comprising two adsorption beds.

At experiments with the plant according to Fig. 1 wastewater containing 3 g/1 phenol was supplied through the conduit 22 to a container 1 comprising a filter with the zeolit material 9 used according to the invention. Due to the arrangement of such an adsorption step before the activated sludge plant, the phenol content of the wastewater could be reduced to 20 mg/1. This pre-treated wastewater was then transferred to the activated sludge plant 5, into which air was injected through pipe systems arranged in the container bottom, which systems are schematically indicated in the Figure by the reference numeral 11. After the cleaning in the container 5 the water was transferred through the conduit 13 to a septic tank 6, and cleaned water then could be taken out by an overflow through the conduit 16. In the cleaned water no phenol was found. The septic tank 6 was provided in a usual manner with a pipe 12 at its bottom for rendering it possible to recycle sludge to the activated sludge plant 5.

Due to the removal of the greater amount of phenol in the zeolite filter 9 , the remaining part could be consumed completely by the bacteria in the activated sludge plant 5. The staying time of the wastewater in the zeolite filter 9 was about 15 minutes and in the activated sludge plant about 2 hours.

The zeolite filter, after some time of use, will be saturated with phenol. The filter then must be taken out of operation and be regenerated. This can easily be arranged by a plant shown in Fig. 1, for example in the way as shown in Fig. 2.

By arranging, as shown in Fig. 2, a special conduit 17 from the overflow of the septic tank 17 to the zeolite filter 2 and simultaneously disconnecting the supply of wastewater, purified water can be caused to flow through the filter and thereby bring about a regeneration. The clean water supplied to the filter bed takes up phenol from the zeolite material and supplies it to the activated sludge plant in such an amount per time unit, that the bacteria culture in the plan 5 is capable to break down the phenol.After the water has been circulated through the conduits 14 and 17 for a time sufficiently long for effecting the cleaning of the zeolite material, the procedure is stopped and the purification of the wastewater according to the arrangement shown in Fig. 1 is re-started.

The plant shown in Fig. 2 is provided with air injection through the conduit 11 and sludge recycling through the conduit 12 in the same way as in Fig. 1.

By using plants as illustrated in Figs. 1 and 2 purification of wastewater containing toxic substances can be carried out in a simple way. When, however, it is desired to make the treatment still more effective, a continuous method can be used. Examples of such a method are shown in Fig. 3.

According to Fig. 3 two zeolite filters 3 and, respectively, 4 are used. The wastewater to be purified is led to the zeolite bed 4 through the conduit 23. The experiment was also in this case carried out with water containing the toxic substance phenol, in this case in an amount of 3 g/1. The water, after having flown through the zeolite bed 10, is passed through the conduit 20 to an activated sludge plant 5. An analysis of the water showed that after the zeolite bed it contained less than 20 mg phenol per litre. In the same way as described with reference to Figs. 1 and 2, the cleaned water was passed through the conduit 15 to a septic tank 8. The purified water coming from the septic tank partially was taken out through the conduit 19 as completely treated water and partially was passed through the conduit 18 to the zeolite bed 9 in the container 3 for regenerating the material. The discharge from the container 3 then was returned to the plant 5 through the conduit 5. The plant 5 also in this case is provided with air injection 11. and sludge recycling 12 from the septic tank 8. The zeolite material in the container 4 has been given in Fig. 3 the reference numeral 10. By using a hydrophobic zeolite according to the present invention, a substantially improved purification of a toxic wastewater is obtained. The system gets a high resistance level to poisons and to changes in the composition of the water. At the same time it is possible thereby to utilize a greater selection of biological processes and to achieve a system at optimum from an economic point of view.

The invention is not restricted to the embodiments described, but can be varied within the scope of the invention idea. It is , thus, also possible to use the zeolite in a fluidized bed or as a coating on surfaces .

Claims

C l a i m

The use of a hydrofobic zeolite material as adsorbent at biological purification of wastewater, which material has such a composition, that the mole ratio Si:Al is greater than 20, preferably greater than 30, and has a pore opening of 1 - 10 A, preferably 5 - 10 A.