WO2002044094A1

WO2002044094A1 - Process for enhancing the efficiency of wastewaster purification and decreasing the demand of reagent

Info

Publication number: WO2002044094A1
Application number: PCT/HU2001/000122
Authority: WO
Inventors: Dénes KALLÓ; József OLÁH; Péter PRINCZ; Kirk Hatfield; Scot E. Smith
Original assignee: Élo Bolygó Környezetvédelmi Kft.
Priority date: 2000-11-28
Filing date: 2001-11-27
Publication date: 2002-06-06
Also published as: AU2002220933A1; HU0004740D0; HUP0004740A2; HU223798B1; WO2002044094B1; WO2002044094A8

Abstract

Process for enhancing the efficiency and decreasing the time and reagent demand of biochemical and/or physico-chemical decontamination technologies used to remove the dissolved and insoluble, organic or inorganic contaminating materials or combinations thereof from waters. The main feature of the process is that one or more artificial or natural materials containing at least 1 weight % crystalline alumino-hydrosilicate having a three-dimensional crystal lattice comprising a pore structure of molecular size, preferably one or more types of rock granules containing clinoptilolite, mordenite and/or other zeolites are added to the water to be treated or to the activated sludge, and macromolecules comprising a large number of positively charged groups, preferably cation-active polymers are bonded previously to the said materials by physical-chemical bonds so that free positively charged groups still remain on the bonded macromolecules. The bond between the solid material and the organic macromolecules is formed in a one- or two-step process.

Description

PROCESS FOR ENHANCING THE EFFICIENCY OF WASTEWATER PURIFICATION AND DECREASING THE DEMAND OF REAGENT

The invention relates to the enhancing of the efficiency of biochemical and/or physico-chemical purification technologies used to remove dissolved and insoluble organic and/or inorganic contaminating materials from waters and to decrease the time and reagent demand of treatment.

It is known that the most widespread sewage treatment method in the world is the biological sewage purification by activated sludge whose effectiveness can significantly decrease due to industrial contamination, i.e., the quality of the purified water can deteriorate. Considering the high investment and operation costs of this sewage purification method, a part of the sewage purification plants is biologically overloaded which also results in unsatisfactory water quality.

During the past 70 years a number of technological developments have been carried out in order to enhance the efficiency of the traditional process using activated sludge and to increase the effectiveness of the sewage purification plants; these can be summarized by the following terms:

• total oxidation system;

• semi-continuous aerobic system;

• application of selectors;

• use of pure oxygen; • two-step active sludge technology;

• application of bio-filters;

• addition of bacterium substrates on powdered adsorbents.

One of the most promising methods of those mentioned above is based on the recognition that tectosilicates having three-dimensional crystal structure including pores of molecular size in regular steric arrangement which occur as constituents of some rocks in nature - hereinafter zeolites - or zeolites activated by treatment with reagent or mixtures thereof are added to the sewage to be purified in order to enhance efficiency. It was in Hungary where natural zeolites were first used for sewage purification by activated sludge. During the patented process known in the field as "Zeoflocc" [Kiss, J., Hosszύ, A., Deak, B., Kallό, D., Papp, J., Meszarosne Kiss, A., Mucsy, G., Olah, J., Urbanyi, G., Gal, T., Aprό, I., Czepek, G., Tδrδcsik, F. and Lo- vas, A. (1984) Process and equipment for removal of suspended material, biogenetic nutrients and dissolved metal compounds from sewage contaminated with organic and/or inorganic substances: Hungarian Pat. No. 193 550, EP 0177 543; (1988) Process for preparing an agricultural fertilizer from sewage: U.S. Pat. No. 4,772,307], a rhyolite tuff containing zeolite clinoptilolite and having a particle size from 10 to 180 μm and a concentration from 35 to 100 mg/L was added to the sew- age fed into the biological reactor [Olah, J., Papp, J., Kallό, D. (1991): Upgrading the efficiency of biological sewage treatment with zeolites. Hidrolόgiai Kδzlδny 72(2), p. 70-76].

The application and effects of zeolites in activated sludge systems (quality improvement of the purified sewage, improvement of sludge settling, effective re- moval of phosphorus) and the mechanism of zeolitic action have been reviewed by Papp [Papp, J. (1992): Einsatzmδglichkeiten von Zeolith in der Abwassertechnik: Abwassertechnik 43(2), p. 44-47]. According to this review, the insoluble iron phosphate is quickly and effectively precipitated on the large surface of the zeolite particles due to iron(III) ions. The iron phosphate and zeolite particles improve sludge settling as they bond to the sludge floes.

According to the process developed by Holman and Hopping, a synthetic type "A" zeolite (in an amount of 20 weight% related to the floating substance concentration) was added to the activated sludge and it was found that the settling rate of the sludge doubled. The water releasing capability of the sludge also increased [Holman, W. F. and Hopping, W. D. (1980): Treatability of Type A Zeolite in

Wastewater - Part II. Journ. Wat. Pollut. Cont. Fed. 52, 2887-2905]. According to the Hungarian experience, the settling of the activated sludge is significantly improved by natural zeolites and zeolites activated with iron(III) ions. The settling ca- pability expressed by Mohlman index decreases from 200 to 300 mL/g to 80 to 100 mL/g due to zeolite addition [Olah, J., Papp, J., Meszaros-Kiss, A., Mucsy, Gy., Kallό, D. (1989): Simultaneous Separation of Suspended Solids, Ammonium and Phosphate Ions from Waste by Modified Clinoptilolite. Zeolites as Catalysts, Sorb- ents and Detergent Builders, 46, p. 711-719, Elsevier Science Publishers B.N., Am- sterdam].

The fact that the zeolite addition improves sludge settling is also described by Charuckyj [Charuckyj, L. (1997, 1998): Brisbane Water Zeoflocc Performance Report; Zeofiocc Process Selected by Queensland Government; Zeolite Australia Limited]. In the Fairfield sewage plant working in the area of Brisbane Water Authori- ties, a sludge volume index of 200 mL/g decreased below 100 mL/g due to zeolite addition. According to the author, this improvement of the purified sewage quality can essentially be attributed to the fact that the bonding of the zeolite particles to the sludge floes improves the settling of the activated sludge and decreases the amount of the sludge leaving the secondary settling tank. However, in spite of their several advantages, the activated sludge technologies based on zeolite addition have not been widely used. Now only 350 thousand m³ sewage per day is treated by a zeolitic process in the world. This can be mainly attributed to the fact that bacteria decomposing sewage contaminants settle slowly on zeolites, so zeolites can exert their favorable effects in the biological decomposi- tion of organic materials only after a longer period of time, i.e., after three to five days. If the sewage purification plant is affected by toxic impulses this period of time can further increase (four to six weeks) and the favorable effect cannot even happen.

In order to accelerate the development of the favorable effects of zeolite ad- dition, Heinzel uses a preliminary microbiological and/or enzymatic and/or substrate addition [Heinzel, K., IPUS GmbH. (2000): Zeolite based bioactive product; the corresponding Hungarian patent application number is P0000604]. However, the method according to the referred patent application slightly decreases the time re- quirement of the process. This can be explained by the fact that although the bacteria (Nitrosonomas, Nitrobacters, etc.) brought into contact with the zeolite in an aqueous suspension or an aerosol provide a high bacterium concentration on the external zeolite surface, between the bacteria and the zeolite particles stable bond is not formed. Therefore, in aqueous solutions a significant part of the bacteria is re- moved from the zeolite surface due to the frictions occurring in the biological reactor. The accelerating effect can be essentially explained by the excess microorganisms added into the reactor though they have to be adapted to the given sewage. The enzyme content of the zeolite with enzyme additives functions as a substrate under the conditions of sewage purification by activated sludge, and, similarly to the zeolites treated with substrates, it can mainly exert its favorable effects in systems with insufficient nutrients. The accelerating effect is not significant in this case either, which can be explained by the fact that the limiting factor of the favorable effects of the zeolite addition is rather the adsorption time of the bacteria on the zeolite surface than the time required for the zeolite-substrate adsorption. It follows from the foregoing that the object of the process according to the invention is to find an appropriate method for treating the zeolite-containing materials to enable the bacteria to settle on the zeolite surface quickly and to induce the prompt appearance of the favorable effects of the zeolite and the development of additional favorable effects. The process according to the invention is based on the following discoveries:

• Natural zeolites dissociate in aqueous media due to their ion exchange properties resulting in fOOOree negative lattice charges on their surface (see the following reaction equation). Positively charged ions and particles in the aqueous phase begin to compete for the negatively charged sites of the zeolite lattice. Meⁿ⁺ _2/n[Al₂O₃-xSi0₂]-yH₂0 + H₂0 _<= > [Al₂0₃-xSi0₂]²- yH₂0 +2H⁺ +

+ 2/nMeⁿ⁺ + 20H^"

• The surface charge of the bacteria is also negative in the aqueous phase. It is well known that particles of similar charge repulse each other, therefore, it can be eas- ily seen that the adsorption of the bacteria on the zeolite surface is hindered. The fact that the zeolite-bacterium bond is formed can be attributed to the extracellular polymers (ECP) produced by the bacteria since the ECP molecules support positive charges and can bridge the bacteria and the zeolite surface. However, the biopolymer production is a slow process and is hindered by toxic effects. • If positively charged cation-active polymers (CAP) are bonded to the zeolite particles having negative surface charges, the CAP molecules are able to bind the bacterium floes to themselves and to bind to the zeolites in a prompt reaction by their remaining free positively charged groups.

When a CAP-modified zeolite is used a large number of zeolite-bacterium floes are formed in the activated sludge tank due to positively charged bacteria which are bound to the CAP covered zeolite particles, therefore, the zeolite can exert its favorable effects in a few minutes.

Thus, the process according to the invention is based on the idea that zeolites with CAP-treated surfaces have to be added to the water to be purified in order to accelerate the immobilization of the bacteria on the zeolite surface and to increase the bacterium concentration on the surface. This means that, according to the invention, the slow and uncertain biopolymer production of the bacteria is not allowed to control the fixation of bacteria on zeolite.

During the treatment of the zeolites with cation-active polymers the follow- ing points should be considered:

• If a natural zeolite is treated with a CAP, the zeolite-CAP bond can be formed only on the external surface of the zeolite crystal since large organic molecules cannot be accommodated in the (inner) pores of the zeolite (the pore diameters are between 6 and 10 A). It can generally be stated that the external surface charge of the zeolites is about 8 to 10% of the total charge or the total ion- exchange capacity (IEC).

• Low molecular weight CAP compounds comprise less monomer units and thus lower number of positive charges, therefore, they can be bound weaker to the zeolite particles and are capable to immobilize lower number of bacteria than high molecular weight CAP. In the case of high molecular weight CAP compounds, it can be difficult to form stable zeolite-CAP bonds with mechanical resistance due to the significant molecular length. It follows that the modification has a certain preferable molecular weight range which is between 5,000 and 250,000 according to the experience of the applicants.

• If the negatively charged lattice sites of the zeolite particles which can be accessed by the CAP molecules are in excess of the positive charges represented by the CAP molecules, the remaining free positive charges on the CAP molecules may not be enough to bond the bacteria. If the CAP is used in a considerable ex- cess, the individual CAP molecules will probably be bound to the zeolite particles only at a few points so a weak zeolite-CAP binding will form. It follows that the favorable effects can be achieved by choosing an appropriate zeolite/CAP mixing ratio for the modification. As a starting point, the determination of the mixing ratios can be suitably based on the external surface cation-exchange capacity (IEC₀) of the zeolite and the equivalent weight (E) of the CAP molecules. According to our investigations, the CAP can be used preferably in a 5 to 10% excess of the theoretical value. The favorable effects occur also at a lower CAP amount but they do not reach their maximum. Increasing the CAP amount the positive effects are not decreased, but the CAP excess is removed from the zeolite which may unnecessarily increase the water treatment costs. The CAP excess can be removed by washing the modified zeolite with water.

• In order to bind chemically the CAP molecules to the zeolite particles in the case of natural zeolites which contain generally Na, K, Ca or Mg in cationic sites, i.e., zeolites in Na-, K-, Mg-, Ca-forms, the zeolite is first to be converted to H- or NH -form or the pH of the aqueous solution of the CAP used for modification is to be decreased below 5. Note that the natural free and bound water content of the zeolites can also be considered as water. In order to convert the zeolite to an H- or NH₄-form, the pulverized rhyolite tuff is suspended in a two- to threefold amount of a HC1 or ammonium salt solution of about 0.1 normal concentration.

In order to perform the ion-exchange, the treated zeolite is agitated for one to two hours. The suspension is settled and decanted. The dense suspension remaining after decantation is washed with tap-water until the pH of the rinsing water reaches 6 or it becomes ammonium-free. Thus, the main feature of the process according to the invention is that, in order to enhance the efficiency and to decrease the time and reagent requirements of biochemical and/or physico-chemical purification technologies used to remove the dissolved and insoluble, organic or inorganic contaminating materials or combinations thereof from waters, one or more artificial or natural materials containing at least 1 weight% crystalline alumino-hydrosilicates having a three-dimensional crystal lattice comprising a pore structure of molecular size, preferably one or more types of rock granules containing clinoptilolite, mordenite and/or other zeolites are added to the water to be treated or to the activated sludge, and macromolecules comprising a large number of positively charged groups, preferably cation-active polymers are bonded previously to the said materials by physical-chemical bonds so that free positively charged groups still remain on the bonded macromolecules.

Crystalline alkaline or alkaline earth alumino-hydrosilicates having a three- dimensional crystal lattice or mixtures thereof having a grain size below 200 μm can be used, for example, as rock granules. According to the invention, organic macromolecules with quaternary nitrogen atoms, having a molecular weight above 5,000, are bonded as cation-active polymers to the said rock granules before adding them to the water to be purified.

According to the invention, the bond between the said materials is formed by mixing the rock granules, converted in a hydrogen or ammonium form by an acidic or ammonium salt treatment, with the aqueous solution of a cation-active polymer.

According to an other possible embodiment of the invention, the bond between the materials is formed by mixing the rock granules with the aqueous solution of the cation-active polymer having a pH below 5. The additive produced as described above is mixed, preferably in a concentration of 10 to 200 mg/L, into the water to be purified by a biochemical and/or physico-chemical method, or it is added to the activated sludge decomposing the organic substances, preferably in an amount of 1 to 20 weight%. The preferable embodiments of the process according to the invention are illustrated with the follow- ing examples to facilitate understanding but without limiting the invention. Unless otherwise indicated, the percentage values mean weight%.

Example 1

100 kg rhyolite tuff originating from the area of Ratka/Hungary and contain- ing 50 to 55% zeolite is pulverized. 200 mL of the 50% aqueous solution of a poly- acrylamine type /poly-2-(hydroxypropyl)-N,N-dimethyl ammonium chloride/ cation- active polymer having a molecular weight of 50,000 is mixed to 18 to 19 liters tap- water and then the pH of the solution is set to 2.2 by the addition of hydrochloric acid. After mixing it for half an hour, when the cation-active polymer molecules are already bound to the tuff particles, the suspension is used to purify sewage. The suspension is fed into the sewage to be purified continuously or in batch mode. The appropriate suspension/sewage ratio is determined by laboratory experiments. During the experiments, the sewage to be purified is subjected to biological decomposition investigations, in continuous or batch mode, and the suspension/sewage ratio is varied from measurement to measurement. The suspension/sewage ratio leading to the best water quality according to the laboratory experiments is used during the sewage treatment on a large scale. The suspension/sewage ratio is expressed then in gzeoiite/gdry activated sludge units. The preferable gzeoiite dr activated sl dge ratio can be expected to fall between 2 and 15%. Example 2

100 kg rhyolite tuff originating from the area of Ratka/Hungary and containing 50 to 55%) zeolite is pulverized. 10 kg of the grain fraction between 30 and 50 μm of the ground tuff is suspended in 40 liters 0,5 normal HC1 solution. The suspension is mixed for 3 to 4 hours at ambient temperature and the aqueous phase is decanted from the tuff after 10 minutes settling. The tuff is filtered and thoroughly washed with distilled water until the pH of the filtrate increases to 6. The filtered, washed tuff is added to 8 to 19 liters tap-water in which the aqueous solution of 1 liter 50%> polyacrylamine /poly-2-(hydroxypropyl)-N,N-dimethyl ammonium chloride/ having a molecular weight of 50,000 has been mixed previously. The suspension is mixed for 2 hours and after settling it is decanted and filtered. The filtered, surface-treated tuff is washed with tap-water until the total organic carbon content of the filtrate decreases below 2 mg/L. The modified tuff freed from the CAP excess is used for water purification according to Example 1.

Example 3

100 kg rhyolite tuff originating from the area of Ratka/Hungary and containing 50 to 55% zeolite is pulverized. 10 kg of the grain fraction between 30 and 50 μm of the ground tuff is suspended in 40 liters 0,5 normal NH₄C1 solution. The suspension is mixed for 3 to 4 hours at ambient temperature and the aqueous phase is decanted from the tuff after 10 minutes settling. The tuff is filtered and thoroughly washed with distilled water until the ammonium content of the filtrate decreases below 0.1 mg/L. The filtered, washed tuff is added to 8 to 19 liters tap-water in which the aqueous solution of 1 liter 50% polyacrylamine /poly-2-(hydroxypropyl)- N,N-dimethyl ammonium chloride/ having a molecular weight of 50,000 has been mixed previously. The suspension is mixed for 2 hours and after settling it is decanted and filtered. The filtered, surface-treated tuff is washed with tap-water until the total organic carbon content of the filtrate decreases below 2 mg/L. The modi- fied tuff freed from the CAP excess is used for water purification according to Example 1.

The favorable effects of the process according to the invention can be sum- marized as follows:

• The chemical bond between the zeolite particles and bacterium floes is formed within a few minutes, therefore, after adding the modified zeolite, the effective decomposition of the organic materials practically immediately occurs and the settling of the insoluble impurities is improved. • The decomposition rate of the organic material increases by 20 to 25 percent (expressed in COD).

• The nitrification and denitrification rate increase by 50 to 100 percent.

• The biological decomposition rate of the organic nitrogen-containing compounds increases by 30 to 50 percent. • The floating substance content of the purified water decreases by 10 to 30 percent.

• The value of the Mohlmann index characterizing the settling rate of the sludge decreases below 100 mL/g.

• The consumption of polyelectrolyte used to dehydrate the sewage sludge dis- charged from the biological purification system decreases by 15 to 20 percent.

Claims

1. A process for enhancing the efficiency and decreasing the time and reagent requirements of biochemical and/or physico-chemical purification technologies used to remove the dissolved and insoluble, organic or inorganic contaminating materials or combinations thereof from waters, wherein one or more artificial or natural materials containing at least 1 weight% crystalline alumino-hydrosilicate having a three- dimensional crystal lattice comprising a pore structure of molecular size, preferably one or more types of rock granules containing clinoptilolite, mordenite and/or other zeolites are added to the water to be treated or to the activated sludge, and macromolecules comprising a large number of positively charged groups, preferably cation-active polymers are bonded previously to the said materials by physical- chemical bonds so that free positively charged groups still remain on the bonded macromolecules .

2. The process according to Claim 1, wherein crystalline alkaline or alkaline earth alumino-hydrosilicates having a three-dimensional crystal lattice comprising a pore structure of molecular size or mixtures thereof with a grain size below 200 μm are used as rock granules.

3. The process according to Claim 1, wherein organic macromolecules with quaternary nitrogen atoms, having a molecular weight above 5,000, are bonded as cation-active polymers to the rock granules according to Claim 2 before adding them to the water to be purified.

4. The process according to Claim 1, wherein the bond between the materials according to Claims 2 and 3 is formed by mixing the rock granules according to Claim 2, which are converted in a hydrogen or ammonium form by an acid or ammonium salt treatment, with the aqueous solution of the cation-active polymer according to Claim 3.

5. The process according to Claim 1, wherein the bond between the materials according to Claims 2 and 3 is formed by mixing the rock granules according to Claim 2 with the aqueous solution of the cation-active polymer according to Claim 3 having a pH below 5.

6. The process according to Claim 1, wherein the additive produced according to any one of Claims 4 and 5 is mixed, preferably in a concentration of 10 to 200 mg/L, into the water to be purified by a biochemical and/or physico-chemical method, or it is added to the activated sludge decomposing the organic substances, preferably in a concentration of 1 to 20 weight% related to the amount of the dry sludge.