GB1567467A

GB1567467A - Method of heating water

Info

Publication number: GB1567467A
Application number: GB45545/76A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-11-19
Filing date: 1976-11-02
Publication date: 1980-05-14
Also published as: FR2332236A1; CH630323A5; FR2332236B3; DE2551902C2; IT1063813B; AT357950B; NL7611903A; ATA850376A; DE2551902A1

Abstract

The water proceeds sequentially through a plurality of aeration stages of which each is connected to a delay and/or reaction chamber. After the aeration, the water remains in the delay and/or reaction chamber for establishment of equilibrium and, possibly, reaction with added agents and/or biological oxidation. This treatment is repeated in the following identical stages. Precipitation or reaction products are taken off from the delay and/or reaction chambers. In the apparatus for carrying out the process, the treatment stages are arranged one above the other and are connected together by branch pipes in such a manner that the water can run first through all odd-numbered and then through the even-numbered aeration stages and reaction chambers. A pump makes intensive treatment possible by connecting one after the other the odd and even treatment stages. The pump can be bypassed by gate valves and the throughput can be doubled by parallel operation of the odd and even treatment stages. Process and apparatus make possible softening to any desired degree of hardness, deacidification, biological oxidation and nitrification independently of variations in the throughput in volume per unit of time.

Description

(54) A METHOD OF TREATING WATER (71) I, KLAUS HABERER, a Citizen of the Federal Republic of Germany, of Nussbaumstrasse 4, 6200 Wiesbaden, The Federal Republic of Germany do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of treating water by the removal of carbonate hardness.

In some known methods, calcium carbonate is precipitated or there is an ion exchange. In view of the large water throughputs, these methods produce large amounts of solid or liquid waste substances which cause difficulties. It is particularly difficult to eliminate liquid waste, and even the removal of calcium carbonate sludge is complicated and expensive.

Calcium carbonate is precipitated in water treatment in accordance with the equation: Ca(HCO3)2 + Ca(OH)2 = 2 CaCO3 + 2H2O by adding an equal quantity of calcium in hydroxide form. In order to reduce the hardness of the water by 2 mmol/l (11.2"d) at a throughput of 1000 m3/h; 3.6 tons of Ca(OH)2 is required and 9.6 tons of CaCO3 is precipitated daily. In order to reduce the waste problem, it is known for the calcium carbonate to be burnt in large furnaces and partly recycled. In a more recent method, Ca(OH)2 is replaced by caustic soda, which is usually more expensive.

Only half the amount of calcium carbonate is precipitated, but sodium ions enter the water (46 mg/e in the above example, if 3.9 tons/day of NaOH is added). But clearly the removal of organic substances from water is a prime concern in waste-water purification and in the treatment of surface water to produce drinking water. If the organic substances are biologically decomposable, they can be removed by biological methods. Such methods, however, are efficient only with an adequate oxygen supply, and they are therefore adversely affected by other oxygen-consuming processes such as the biological nitrification of ammonium ions, which uses a large amount of oxygen. If natural or man-produced organic substances are present, e.g. in surface water and underground water containing humic acid, conventional break-point chlorination for oxidizing ammonium ions results in the formation of chlorine compounds which are difficult to decompose and in some cases are a danger to health.

Attempts are therefore being made to oxidize ammonium ions biologically. However, ammonium oxidation by bacteria in biologically active filters comes to an end when the atmospheric oxygen is used up. The solubility of oxygen in water is very limited and the saturation concentration is about 10 mg/e. Biological nitrifications is frequently interfered with by organic substances in the water, which are preferentially decomposed by the micro-organisms. Organic substances which cannot be decomposed by biological means can be removed from the water by adsorption agents. Finally, many substances which are difficult to decompose can be converted into a more easily decomposable form by using stronger oxidizing agents.

According to the present invention I provide a method of treating water in which it passes alternately through an aeration stage and a reaction chamber, in the aeration stage the water is intensively aerated and in the reaction chamber the water is softened by removal of calcium carbonate together with the biological oxidation of organic substances and/or the biological oxidation of ammonium ions in the water.

During the intensive aeration for the purpose of calcium carbonate softening by carbonate hardness removal, the water is converted into a state where it is supersaturated with calcium carbonate. In its unstable state, the water is given the opportunity to precipitate calcium carbonate, thus again liberating carbon dioxide. The processes are then carried out again and repeated until the desired softening is obtained. For this purpose the water must be conveyed through reaction chambers after the aeration stage. Advantageously the calcium carbonate precipitation is accelerated by suitable methods, e.g. by providing catalysts. More particularly, substances can be added for use as crystal nuclei.

Organic substances and ammonium ions can be adsorbed by the successive use of different adsorption agents having different efficiency with respect to individual classes of substances, and also by using porous substances to which micro-organisms adhere and can grow. By means of a multi-stage suspended bed arrangement, pressure losses may be reduced to a minimum. The adsorption agents can be continuously withdrawn and replaced bv measured amounts of traditional adsorption agents, to ensure uniform quality of the product If the same adsorption agent is used in a number of stages, it can be supplied to the next higher stage and thus conveyed in counter-current to the water.

Intensive aeration also greatly assists the removal of volatile organic substances.

In order to improve the adsorption and biological decomposition. the pH in the initial stages can be advantageously altered by adding acid or alkali. Organic substances which are difficult to decompose can, if required, be converted into a biologically more decomposable form by adding suitable oxidizing agents. It may also be advantageous to use suitable catalysts.

The invention also provides devices for performing the method, characterised in that aeration stages and reaction chambers are disposed in economic and space-saving manner, so that a number of aeration and reaction stages are flowed through in free fall.

More particularly, the processes can be combined and suitably extended so as to be completely adapted to different processing requirements, depending on the quality of the water. and can also be supplemented by flocculation processes. There are also the following detailed advantages.

Undesired gases (excess CO. and HrS) and easily volatile organic substances (evilsmelling substances) are directly removed by intensive aeration. Multiple intensive aeration results in partial softening by removal of carbonate hardness and reduces the buffering of the water. At the same time iron and manganese are precipitated. If the water is made strongly alkaline with (a) alkali or (b) anion exchangers in the OH- form, naturally present magnesium is precipitated as the hydroxide, which has excellent flocculating properties. In case (b) anions (e.g. chloride) are additionally withdrawn. The withdrawal of organic substances by adsorption can be increased to a maximum by using various adsorption agents having different properties. The multiple intensive aeration facilitates the biological decomposition of organic substances and also enables higher amounts of ammonia to be nitrified.

The invention will be explained in detail with reference to the accompanying drawings. in which: Figure 1 shows a device particularly suitable for softening by removal of carbonate hardness: Figure 2 is a graph illustrating the calcium content. which decreases in the separate stages Figure 3 is a diagrammatic side view of a device which is particularly suitable for oxidation. and Figure 4 is a view in oblique perspective of the device in Figure 3.

The device in Figure 1 comprises individual aeration stages in a multistage reaction tower comprising suitable packing elements. Air enters each aeration stage at the top end and it is discharged at the bottom end. Reaction chambers are provided between the aeration stages; water enters the reaction chamber after leaving one aeration stage and before entering the next aeration stage.

In another feature of the invention, the water for treatment in an aeration column flows from the first aeration stage into a third and thence into the other odd-number stages with interposed reactors, after which the water flows through the even-number aeration stages, i.e. the second, fourth stage etc.. with interposed reactors, and the odd-number and even-number aeration stages are flowed through either in parallel or in sequence, after a single pumping operation.

In the device in Figure 1, raw water for softening is supplied by a raw-water pipe line 1 to an aeration tower 2 and flows through a distribution tray 3 into a first aeration stage BI, where air is sucked in through lateral aeration slots (not shown) and forms a large, constantly-changing boundary layer with water in aeration element 4 and produces a gas exchange. After travelling through each aeration element 4, the used-up air is liberated and the water, depleted in carbon dioxide and rich in oxygen, is discharged through a pipe line 6 into a separation reactor 7. More particularly, after travelling through the first aeration stage Bl, the water flows into the separation reactor Al, where calcium carbonate is deposited from the supersaturated solution and carbon dioxide is simultaneously liberated.

After being freed from supersaturated material, the water is returned from reactor 7 via return pipe lines 8 in the aeration tower 2. so that more carbon dioxide can be remove The water flows from reactor Al into aeration stage B111 and then through reactors A111, Av.

Avll through the subsequent odd-number aeration stages Bv, 13vl1 and Blx. 'Ihé cven-number stages Blx with reactor All, Blv with reactor Alv etc. can either be supplied with the same water subsequently, or else the installation can be operated so that the even-number aeration stages Bull, Blv etc. are supplied in parallel by the raw-water supply pipe line 1. This greatly reduces the softening effect by removal of carbonate hardness but doubles the throughput. The water flowing through the parallel-operating groups of aeration stages and reactors then enters a collecting vessel 13 and is then discharged via a pure-water pipe line 14.

The substances deposited in the individual reactors Al, All etc. are discharged through the sludge lines after opening the associated gate valves and, if required, are given sludge treatment. In this manner, depending on requirements, the water for softening by removal of carbonate hardness can be conveyed through the required number of aeration stages and reactors and thus brought to the required degree of hardness.

Figure 2 is a graph in which the free CO2 (in mg/f) is plotted against the carbonate hardness (in memo1/4).

Normally, the water for softening by removal of carbonate hardness is in a state represented by the equilibrium curve 20. Starting from a point 21, carbon dioxide is removed by aeration and, assuming an easily-attainable gasification efficiency of n = 40% per stage. the water reaches an unstable stage represented by point 22. After calcium carbonate has been separated and equimolar quantities of CO2 have simultaneously formed, the water returns to a new equilibrium state denoted by point 23 i.e. is again in a state described hv the equilibrium curve but contains less calcium carbonate. By means of the individual aer'ltion stages, this process is repeated a number of time until the desired final state at 24 is reached.

This method of softening by removal of carbonate hardness cannot give very soft water, but excessively soft drinking water is thought by the World Health Organisation to be undesirable for health reasons.

The device shown in Figure 3 has perforated trays disposed one above the other, through which air from a blower is conveyed upwards. According to the invention the water on the trays flows at an angle to the air flow and then travels through reaction chambers before being supplied to the next perforated tray and downstream reaction chamber, so that it flows in a zig-zag through the entire installation. Separation, sedimentation, adsorption and flocculation processes can also occur in the reaction chambers; in the latter case, the solids are where possible held in a fluidized bed.

The device shown in Figure 3 is made up of similar elements each comprising a porous perforated aeration plate 31, and an adjacent reaction chamber having tapered walls 32. If required. two separation chambers can be placed in series.

A number of such elements (between four and twelve depending on the required output) is disposed one above the other so that the aeration plates are horizontal and spaced vertically at equal intervals apart, whereas the adjoining separation chambers are offset by a right angle from one stage to another. The aeration plates are sealed to produce a multi-stage closed column 34. The resulting aeration tower is sealed by surge tanks at the water inlet and outlet, so that no air can escape laterally. As shown in Figure 4 one outer separation chamber has a lateral overflow edge 35 adjacent a small channel 36 supplying water to the perforated plate of the stage that is below it.

A bell vessel (Figure 3) having an outlet 37 is disposed above the top aeration plate.

Water flows horizontally over the plates. and a large excess of air is blown in from below by a compressor through a distribution chamber 38. and this flows through the porous plates and out at the top outlet 37.

As a result of the cross-current aeration, an intensive gas exchange occurs with formation of a foam layer at each plate. oxygen being absorbed and carbon dioxide being liberated.

The water travels through a foam trap and then enters reaction chamber 32 and then, if required, enters reaction chamber 33 where the reactions occur, measured amounts of substances being added if required. The reaction products are discharged laterally.

The following processes can occur in the multi-stage reactor.

In the case of relatively hard water, calcium carbonate is deposited, resulting in partial softening by removal of carbonate hardness, in the upper stages, crystal nuclei such as fine sand being added if required after the CO2 has been discharged. After travelling through the first-stage reactor, the water is supplied to the aeration plate of the stage below, so that carbon dioxide can be discharged and calcium carbonate can be subsequently separated as often as required.

In the case of softer water or water partially softened by removal of carbonate hardness, the lower stages can be used for flocculation, exchange or adsorption processes or biological oxidation. For this purpose, flocculating agents, flocculating auxiliary agents, active carbon having various degrees of activity, other adsorption agents and other substances having a porous structure on which micro-organisms adhere and can grow, are placed in the inlet channels to the aeration plates or in the reaction chambers themselves. Acids or alkalis or cation and anion exchangers in the H+ or OH forms can be added so as to alter the conditions of the water medium in the optimum manner for the required processes. In the last mentioned case, there is a simultaneous reduction of cations, or anoins (i.e. calcium or chloride ions). Agents, having a relatively intensive oxidizing effect e.g. KMnO4, H2O2 and ozone, can convert organic substances which are difficult to decompose into a form in which they can be biologically decomposed.

Operation in a fluidized bed in an upward stream of water eliminates high resistances and enables the throughput to be increased and the added chemicals to be more efficiently used.

Normally, the process is not critically affected if small residues of reaction products penetrate into the downstream stages. For increased efficiency, it may even be advantageous for small proportions of adsorption agents, flocs and other substances to be carried directly into the downstream stages, whereas most of the industrial auxiliary substances and reaction products are withdrawn directly, either continuously or periodically, from the individual stages. In addition, a low-power pump can be used to introduce the adsorbing or biologically active substances in the opposite direction to the flow of water in the reaction stage above and thus produce a counter-current effect, whereby the fresh adsorption agent is first supplied to the last stage, in which the water has been most completly processed, and then, as it becomes increasingly charged, makes contact with increasingly contaminated water.

The entire processing operation occurs in free fall without intermediate pumps, and needs to be followed only by a filtration step. The quality of the product can be kept constant, since substances can be added or discharged continuously or in small steps.

WHAT I CLAIM IS: 1. A method of treating water in which it passes alternately through an aeration stage and a reaction chamber, in the aeration stage the water is intensively aerated and in the reaction chamber the water is softened by removal of calcium carbonate together with the biological oxidation of organic substances and/or the biological oxidation of ammonium ions in the water.

2. The method according to claim 1, characterised in that the water is intensively aerated and converted into a state in which it is supersaturated with calcium carbonate; the water in its unstable state is given the opportunity to precipitate calcium carbonate, and the method is repeated until the desired softening is obtained.

3. The method according to claim 1, characterised in that the separation of calcium carbonate is accelerated by catalysts that are nucleating agents.

4. The method according to any preceeding claim, characterised in that adsorption processes are simultaneously carried out.

5. The method according to claim 4, characterised in that use is made of adsorption agents having different partial selectivity or of porous substances to which micro-organisms adhere and can grow.

6. The method according to claim 5, characterised in that the adsorption agents or porous substances are held in an upward flowing stream in a suspended bed.

7. The method according to claims 4 to 6. characterised in that the pH of the medium is altered between the individual aeration stages.

8. The method according to any of claims 1 to 7, characterised in that the reaction products or the loaded adsorbents are continuously or periodically withdrawn.

9. The method according to claims 4 or 7. characterised in that an adsorption agent is supplied in the opposite direction to the water, to achieve a counter-current effect.

10. The method according to any of claims 1 to 9. characterised in that flocculation agents, auxiliary flocculation agents, acids, alkalis or oxidizing agents are also supplied.

11. The method according to any one of claims 7 to 9, characterised in that the pH of the medium is altered by adding ion exchangers in the H+ or OH form.

12. A device for performing the method according to any of the preceding claims, characterised in that the aeration stages and reaction chambers are disposed in economic and space-saving manner so that a number of aeration and reaction stages are flowed through in free fall and repeated pumping is avoided.

13. The device according to claim 12, characterised in that the individual aeration stages

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

the first-stage reactor, the water is supplied to the aeration plate of the stage below, so that carbon dioxide can be discharged and calcium carbonate can be subsequently separated as often as required.

In the case of softer water or water partially softened by removal of carbonate hardness, the lower stages can be used for flocculation, exchange or adsorption processes or biological oxidation. For this purpose, flocculating agents, flocculating auxiliary agents, active carbon having various degrees of activity, other adsorption agents and other substances having a porous structure on which micro-organisms adhere and can grow, are placed in the inlet channels to the aeration plates or in the reaction chambers themselves. Acids or alkalis or cation and anion exchangers in the H+ or OH forms can be added so as to alter the conditions of the water medium in the optimum manner for the required processes. In the last mentioned case, there is a simultaneous reduction of cations, or anoins (i.e. calcium or chloride ions). Agents, having a relatively intensive oxidizing effect e.g. KMnO4, H2O2 and ozone, can convert organic substances which are difficult to decompose into a form in which they can be biologically decomposed.

Operation in a fluidized bed in an upward stream of water eliminates high resistances and enables the throughput to be increased and the added chemicals to be more efficiently used.

Normally, the process is not critically affected if small residues of reaction products penetrate into the downstream stages. For increased efficiency, it may even be advantageous for small proportions of adsorption agents, flocs and other substances to be carried directly into the downstream stages, whereas most of the industrial auxiliary substances and reaction products are withdrawn directly, either continuously or periodically, from the individual stages. In addition, a low-power pump can be used to introduce the adsorbing or biologically active substances in the opposite direction to the flow of water in the reaction stage above and thus produce a counter-current effect, whereby the fresh adsorption agent is first supplied to the last stage, in which the water has been most completly processed, and then, as it becomes increasingly charged, makes contact with increasingly contaminated water.

The entire processing operation occurs in free fall without intermediate pumps, and needs to be followed only by a filtration step. The quality of the product can be kept constant, since substances can be added or discharged continuously or in small steps.

WHAT I CLAIM IS:

1. A method of treating water in which it passes alternately through an aeration stage and a reaction chamber, in the aeration stage the water is intensively aerated and in the reaction chamber the water is softened by removal of calcium carbonate together with the biological oxidation of organic substances and/or the biological oxidation of ammonium ions in the water.

2. The method according to claim 1, characterised in that the water is intensively aerated and converted into a state in which it is supersaturated with calcium carbonate; the water in its unstable state is given the opportunity to precipitate calcium carbonate, and the method is repeated until the desired softening is obtained.

3. The method according to claim 1, characterised in that the separation of calcium carbonate is accelerated by catalysts that are nucleating agents.

4. The method according to any preceeding claim, characterised in that adsorption processes are simultaneously carried out.

5. The method according to claim 4, characterised in that use is made of adsorption agents having different partial selectivity or of porous substances to which micro-organisms adhere and can grow.

6. The method according to claim 5, characterised in that the adsorption agents or porous substances are held in an upward flowing stream in a suspended bed.

7. The method according to claims 4 to 6. characterised in that the pH of the medium is altered between the individual aeration stages.

8. The method according to any of claims 1 to 7, characterised in that the reaction products or the loaded adsorbents are continuously or periodically withdrawn.

9. The method according to claims 4 or 7. characterised in that an adsorption agent is supplied in the opposite direction to the water, to achieve a counter-current effect.

10. The method according to any of claims 1 to 9. characterised in that flocculation agents, auxiliary flocculation agents, acids, alkalis or oxidizing agents are also supplied.

11. The method according to any one of claims 7 to 9, characterised in that the pH of the medium is altered by adding ion exchangers in the H+ or OH form.

12. A device for performing the method according to any of the preceding claims, characterised in that the aeration stages and reaction chambers are disposed in economic and space-saving manner so that a number of aeration and reaction stages are flowed through in free fall and repeated pumping is avoided.

13. The device according to claim 12, characterised in that the individual aeration stages

are disposed in an aeration tower comprising packing elements, or larger aeration elements.

14. The device according to claim 13, characterised in that gate valves are provided for the purpose of parallel operation between odd-number and even-number aeration stages.

15. The device according to claim 13 or claim 14, characterised in that all the separating reaclors are provided with valves whereby sludge can be evacuated through common sludge lines A method of alternately softening water ond/or biological oxidation and nitrification of water substantially as described herein and shown in the figures of the accompanying drawings.

17. A device for carrying out the method of claim I constructed and adapted to operate substantillly as described herein and shown in the figures of the accompanying drawings.