WO2007019588A1

WO2007019588A1 - Treatment method of water containing humic substances and arsenic for the production of drinking water using inorganic polymers of aluminium and silica as coagulants

Info

Publication number: WO2007019588A1
Application number: PCT/YU2006/000017
Authority: WO
Inventors: Mileta Perisic
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-08-08
Filing date: 2006-07-20
Publication date: 2007-02-15
Anticipated expiration: 2008-02-08
Also published as: EP1919832A1; EA200800568A1

Abstract

The invention relates to the removal of humic matter and arsenic from natural waters with inorganic polymers of aluminum and silica in the field of raw waters with extreme humic mater and arsenic content and outstanding negative purification conditions such as high ionic strength and distinctly negative temperature conditions. With the innovated, enhanced, purification technology defined by this procedure removal of humic matter and arsenic such that even in the phase of coagulation and flock separation give drinking water quality standard is achieved, under conditions of extremely high humic matter content like the raw water of Zrenjanin type with KMnO4 consumption over 50 mg/dm3 and total As over 0.100 mg/dm3. Presence of high content of different arsenic forms in raw water, solely or together with high content of humic matter demands their removal by the most suitable techno economic and ecologic way. By application of innovative technology the best conditions for simultaneous removal of both pollution types from raw water have been produced. The method itself consists in optimization of purification conditions: by neutralization of the charge of humic molecules, provision of optimal pH and inorganic polymer doses and their ratios with appropriate energetic conditions for flock formation, and than application of different separation processes, whether classical separation schemes (sedimentation or flotation by sand filtration) or membrane separation processes.

Description

TREATMENT METHOD OF WATER CONTAINING HUMIC SUBSTANCES AND ARSENIC _FOR THE PRODUCTION OF DRINKING WATER USING INORGANIC POLYMERS OF ALUMINIUM AND _SIL_ICA AS COAGULANTS

a) Technical field

This innovation belongs to the field of water treatment, closer to the field of drinking water treatment, and it refers to the method for humic substances removal from raw waters which is the most wide spread organic pollution of natural waters on broad area, as well as arsenic which appears in surface and ground water as primary pollution or together with humic substances.

Coagulation and separation processes, as one of the more representing methods for removal of humic matter from natural water are realized today by using different coagulants with partial success. The main problems are in the domain of treatment of soft and hold waters with humic matter which are very vide spread.

According to the international clasification of the patents (ICP) object of inovation is indicated with basic classification symbols Cl. C 02Fl /52.

Background Art

By solution given with application PCT/YU01/000012 the best effects of purification of raw water with humic matter by coagulation is achieved. For achievement of the best effects in presentation of the essence of innovation conditions for purification are defined: pH value and ratio OfAl₂O₃ : SiO₂ concentrations. Enhancement of purification effects by this technology in relation with the existing technical state is exceptionally high (two times in relation to the USEPA demands defined for TOC removal by enhanced coagulation, 1998.)

However by using PCT/YUO 1/000012 drinking water quality standards in extremely unfavorable condition of application cannot be provided: very high content of humic substances in raw water (over 30 mg/1 KMnO₄ consumption) and with high ionic content (CaCO₃ over 120 mg/dm³). Smaller shortage is in the demand, that even at lower humic and ionic content, especially under low temperatures, pH adjustment in the range defined by patent clams must be provided for the achievement of the best results.

New task is demand for removal of high content of arsenic which frequently appears in ground and surface water as dominant pollution or common with humic substances. On the enhancement of purification of raw water which contains excessive concentration of arsenic are lots of activities today. Numerous purification methods are in practice but reaching of leading standards needs high investment and exploitation costs. For purification of raw water with humic substances and arsenic does not exist suitable techno economic and ecological solution.

By solution given with application PCT/YUO 1/000012 for a part of raw water of natural organic mater (NOM) removal to provide drinking water quality standard (consumption KMnθ₄ below 8.0 mg/dm³) and for other part of raw water with higher organic content NOM removal must be achieved with new investment, new phase of purification, but with lower scope compared with conventional coagulation processes.

New enhancement of humic substances removal from raw water with the most unpleasant characteristics and supplying drinking water quality standard was a part of problem which must be solved in next phase. Other segment of this problem is concerned with enhancement effects of arsenic removal from raw water, especially in the conditions of simultaneous high content of humic substances and arsenic. This problem for a long time exists in searching of solution of purification of raw water for Zrenjanin town.

Activities on the problem of removal of arsenic from raw water are very intensive. Here are defined numerous technologies with corresponding purification effects. Solutions cover all of spectra of methods for purification raw water existing in practice starting with conventional solution of coagulation to absorption, ionic exchange, membrane processes, even ground oxidation and removal with Fe salts. However, here priority is given to coagulation as the most rational purification technology with application of Fe and Si salts, and this is advancing practice in purification of waters with arsenic. A specific problem is removal OfAs³⁺ where for most methods applied in practice is necessary to oxidize to As⁵⁺ state. In our practice are applied solutions for removal of part of arsenic simultaneously with Fe oxidation in the phase of sedimentation, and/or filtration. Bat this procedure cannot provide demanded purification effects with highly loaded natural waters with arsenic.

According to mentioned increased efficiency of humic substances removal from raw water a task is that water with high organic load even after coagulation and flock separation of organic mater content is put with in the range of dinking water quality standards. Since that in some ground water with humic mater, or without them high arsenic content also appears additional task is simultaneous removal of it to values defined by contemporary drinking water quality standards from 0.050 to 0.010 with the aim to 0.005 mg/dm³. Disclosure of the Invention

In the patent application PCT/YUO 1/000012 by presented experimental results conditions for reaching best purification effects are defined. In the presentation of the essence of invention obtained effects are explain by mutual effects of two inorganic polymers in the defined pH range with the simultaneously established ratio OfAl₂O₃ : SiO₂ concentration for different types of raw water in the value range 6 : 1 to 3 : 1.

Concentrations OfAl₂O₃ and SiO₂ as well as their ratio are defined in patent Clams at the level which was found by the experiments upon which the claim was based. Such AI₂O₃ and SiO₂ concentration ratios under conditions of inorganic Al polymer and activated SiO₂ use the first time exist in the practice of water supply. Suitable ratio of these two polymers with creation of structures for binding of humic substances molecules enables significant increase of humic matter removal with the decrease of Al coagulant consumption, decrease of residual Al in purified water and decrease of Al emission to environment in relation to all previous methods. Enhancement of purification effects by this technology, by use of PCT/YUOl/000012 in comparison to the state of technique is very high. However by it drinking water quality standard under extreme application conditions be achieved: very high content of humic matter in raw water (over 30 mg/dm³ KMnO₄ consumption) with high ionic content (CaCO₃ over 120 mg/dm³). Problem partly appears under conditions of extremely low temperature where decreased kinetics of flock formation demands increased dimensions of plants. Lesser shortages of this method are also necessity for adjusting pH in the range 5.5 - 6.5 which additional demands new water alkalization.

Under the scope of analysis for this complex is also removal of increased arsenic content from raw water which has been defined in ground water from Zrenjanin town and surface water of the Jablanica river for the Topola town water supply.

Basic investigations on the enhancement of coagulation effects are directed towards provision of more stable flock Al and Si polymers with more complete binding of humic macromolecules and sorption of arsenate on formed flocks. Even by changing of these two polymers ratio increase of Al participation, considerable enhancement in all elements that defines purification effects are obtained: better coagulation with almost quantitative binding of humic substances in flock, better flock characteristics with farther enhancement of water purification under extremely low temperatures, and smaller residual Al in drinking water. Better purification effects of raw water with smaller ionic content (alkalinity < 120 mg CaC(VcIm³) under extremely low temperature are obtained also in a wide pH range 5.5 - 8.0 giving drinking water quality standard. This was found in laboratory experiments in the case of water purification by coagulation under extremely low temperature at Kopaonk. Properties of flock: period of flock forming, flock stability and density are of a specific significance both for purification effects and dimensions of installation for removal of humic matter and arsenic from raw water with unfavorable characteristics.

Experiments included a significant number of raw waters with different characteristics. Since it has been known that waters with even greater organic load exist, that were not included in these investigations, correlation between humic matter content in raw water and dosage of coagulant was established, Fig. 9. For Al polymer it is given explicitly, while Si was defined as a ratio of these two polymers.

In the next phase of enhancement of waters with humic matter purification process and effects of purification of water with excessive arsenic content need for process optimization was found in accordance with significant enhancement of purification effects that were found by changing inorganic polymers Al and SiO₂ ratio.

By patent application PCT/YUO 1/000012 problems of arsenic (As³⁺, As⁵⁺ and organic bounded As) removal were not included and this appears as a problem with simultaneous purification of raw waters which have increased concentrations humic matter and arsenic. By application of conditions of enhanced coagulation given by PCT/YUO 1/000012 for the case of Zrenjanin ground water purification effects which provide drinking water quality standards were not obtained for neither of set tasks: reduction of humic matter content and removal of arsenic.

With establishment of new two polymers ratio conditions for farther enhancement of the effects of humic matter and arsenic removal were established, by which even in the phase of coagulation and sedimentation drinking water quality standard was achieved (KMnO₄ consumption below 8,00 mg/dm³ and As content lower than 0,010 mg/dm³.

The essence of enhancement is connected to change of inorganic polymers ratio, and the result is a high increase of purification effect. This increase is founded on creation of aluminum silicate complex with quantitative incorporation of Al and Si polymers which provides creation of flock even in extremely clean water. In the coagulation phase, during creation of aluminum silicate complex, quantitative binding of humic substances macromolecules and incorporation of arsenic in flock happen. As a result high effects of raw water purification are achieved, residual content of components significantly decreases in purified water and negative effects on environment especially connected by aluminum emission decrease. pH adjustment, if necessary, is done by procedure defined in PCT7YU01/000012. Dosage of coagulants, Al polymer and activated SiO₂ is done in the phase of intensive mixing and subsequent pH correction (if necessary) is made after flock separation. Inorganic polymer of Al is dosed without dilution or a dilution range which is permitted by producer for concentrated or hard product.

Dosage of polymers Al and activated SiO₂ is determined for concrete purification conditions. Dose of inorganic polymers is determined on the basis established correlation of uv- extinction, or KMnO₄ consumption, and dose of Al (Fig. 9), and dose Of SiO₂ from established ratio of these two polymers. Doses of coagulants depending on the type of water vary in range, for Al polymer from 2 to 25 mg/dm³ Al₂O₃ and activated SiO₂ from 0.5 to over 15.0 mg/dm³. Inorganic polymer Al and activated SiO₂ are added to raw water by previously adjusted pH value: for water with low alkalinity (CaCO₃ concentration lower than 100 mg/dm³) to app. 5.5 to 7.9 (if water is not of such pH at water source) and for water with high alkalinity (CaCO₃ concentration above 100 mg/dm³) in the range 5.5 to 6.5, it passes process of fast and slow mixing, and then separation by sedimentation is performed for app. 30 min. which is usual procedure of laboratory jar test. In industrial conditions investigations are limited to construction characteristics of the installation. Adjustment of the pH, realized according PCT/YUOl/000012, for the raw waters with low mineralization adjustment is realized with some of mineral acids : H₂SO4 or HCl, but for waters with high bufer capacity where exist possibility for degradation of ionic content and water quality this realized by use of H⁺ cationic resin. For optimal effects of purification is realized on the begining of the process. Posible later corections, adjustment to range defined by drinking water standards and improvement water stability is realized after sedimentation, but before phase of filtration.

Innovation and invention step in relation to PCT/YUOl/000012 is in provision of conditions for formation of stable complexes from metastable Al₂O₃ state and amorphous SiO₂ with formation of alumosilicate with exceptionally small solubility, that gives to this step exceptional application character. Best results are obtained with ratio of these two polymers

Al₂O₃ : SiO₂ = 3 : Ho 2 : 1.5.

Inorganic polymers Al and Si are in instable states at dosing that are quickly transformed with formation of stable complexes. According to literature data (Stumm & Morgan, Aquatic Chemistry, 1970) created alumosilicates have very small solubility 10^"8 M Al(OtTb at changeable concentrations Of H₄SiO₄ from 10^"10 - 10^"5 and with minimal solubility of Al from l(r⁹ to l(r¹⁰ at pH 6.0.

Application of inorganic polymers of Al and activated SiO₂ as accessory coagulant with pH control) in optimal ratio provides high enhancement of coagulation process and overall purification effects in comparison with PCT/YUO 1/000012 for water with high ionic content, humic matter and arsenic content in domains of:

- removal of organic matters especially humic substances from water phase (expressed by KMnO₄ consumption around 90%), - removal of high percentage organic matter which show uv-extinction, which is especially significant since these substances are main precursors of halogen organics substances (effects of uv-extinction removal are in some cases greater than 90%),

- coagulation and separation processes are intensified even at extremely low temperature (process of coagulation and sedimentations at Kopaonik by this process is made independent of temperature and it is realized in a wide pH range 5.5 - 8.0.

- content of THM precursors (Trichalomethanes, sum: CHCl₃, CHCl₂Br, CHClBr₂, CHBr₃) - in purified water, often to the level lower than MCL (maximum permissible concentration) in drinking water (PTHM is reduced to around 90%,

- especially significant results are achieved in decrease of color even over 95%, - especially significant results are achieved in As and organically bounded As removal even over 90%,

- exceptionally low concentration of residual Al in drinking water is achieved (with correct performance of the process Al concentration is smaller than 0.050 mg/dm³, by which even most strict drinking water quality standards are provided, - effects of mud from drinking water purification plants on environment, consumption and emission of Al is reduced for 50 - 80 %. Pollution with reactive Al is reduced by creation of insoluble aluminum silicates too.

Brief Description of Drawings Investigations in laboratory conditions were realized with standard methodology, by jar test with propeller mixer changeable speed from 10 - 200 r/min., which provided realization of experiments in defined conditions: rapid and slow mixing. For investigation different commercial polymer: PAC, Megafloc and Koaflok were used. Mostly experiment was realized with Koaflok and new Al polymer Alkoflok (P-2005/0801).

Process of purification of raw water by coagulation with separation flock on the installation has phases given in the scheme 1: Adjustment of the pH (if it is necessary), dosing of the coagulants (Al polymer and activated SiC>2) with mixing phases (rapid and slow mixing) and finally sedimentation and filtration. Adjustment of the pH before phase of coagulation (if it is necessary) is realized by dozing of mineral acids or by filtration of some part of the water flow

(about 15 % and more present, depending on expected pH and type of water) trough column with H+ resin. Water for acidification is taken from basic flow, row water, or after sedimentation of filtration phases protecting H+ resin pollution. Neutralization of treated water is realized before filtration phases.

The method permits other purification schemes. This is related to existing installations, for example these with coagulation/direct filtration. In this case effects of the process are dependant on concentration of humic matter, or coagulant doses, because the filter run is dependant on these parameters.

Best Modes for Carrying Out of the Invention

Although significantly increased effects of water with high content of organic matter of Kikinda and Zrenanin type are increased by PCT/YUOl/000012 procedure in the phase of coagulation and flock separation drinking water quality standards cannot be obtained, consumption KMnO₄ below 8.00 mg/dm³.

By the new enhancement even with purification of raw water with extreme organic load, high alkalinity and extreme arsenic content, drinking water quality standard can be provided as it is shown by examples 1 and 2. Even in the phase of coagulation and sedimentation (in decanted water) under new conditions that are defined by this optimization, drinking water quality standards are provided and it is shown by examples 1 and 2 and Fig. 2, 3, 4 and 5. Example 1. Results of laboratory investigations purification effects of ground water in Kikinda.

Row water has following characteristics: turbidity = 1.0 NTU, color = 48 mgPt/dm3, uv- extinction = 0.260 I/cm, consumption of KMnO₄ = 26 mg/1, TOC = 8,0 mg/dm3, Na = 220 mg/dm3, As = 0.009 mg/dm3.

Purification of raw water from Kikinda source was carried out as follows: adjustment of pH was achieved by passing definite quantity of water which was to be purified through ionic resin H⁺ type, than mixing it with equivalent quantity of raw water. In that way, obtained water had pH around 6.5. Farther acidification to pH around 5.8 was done by addition of 0.20 ml 1 :3 H₂SO₄. To this water different doses of Al polymer and activated SiO₂ in quantities which correspond to the ratio AI₂O₃ : SiO₂ = 2 : 1,2 (which was defined in the application PCT/YUO 1/000012 to the value 3 : 1). Enhancement of raw water from Kikinda source purification effects (removal of organic matter: KMnθ₄ consumption and uv-extinction) with the change in the ratio of inorganic polymers Al and SiO₂ is shown in Fig. 2 and 3.

In comparison with obtained purification effects given in application PCT/YUO 1/000012 here high enhancement of purification effects of coagulated and decanted water was obtained: turbidity = 0.1 NTU, color = 4 mgPt/dm3, uv- extinction = 0.047 I/cm, consumption of KMnθ4 = 5.10 mg/1, TOC = 1.8 mg/dm3, Na = 112 mg/dm3, As = 0.001 mg/dm3.

Example 2. Raw water, ground water from Zrenjanin source is with following characteristics: turbidity = 1.8 NTU, color = 120 mgPt/dm³, uv- extinction = 0.510 I/cm, consumption of KMnO₄ = 53.00 mg/ dm³, TOC = 11.5 mg/ dm³, Na = 260 mg/ dm³, As = 0.103 mg/ dm³.

Purification of raw water from Zrenjanin source was carried out as follows: adjustment of pH was achieved by passing definite quantity of water which was to be purified through ionic resin H⁺ type, than mixing it with equivalent quantity of raw water. In that way, obtained water had pH around 6.5. Farther acidification to pH around 5.8 was done by addition of 0.25 ml 1 :3 H₂SO₄. To this water different doses of Al polymer and activated SiO₂ in quantities which correspond to the ratio AI₂O₃ : SiO₂ - 2 : 1,2 (which was defined in the application PCT/YUO 1/000012 to the value 3 : 1). Enhancement of raw water from Zrenjanin source purification effects (removal of organic matter: KMnO₄ consumption and uv-extinction) with the change in the ratio of inorganic polymers Al and SiO₂ is shown in Fig. 4 and 5.

In comparison with obtained purification effects given in application PCT/YUOl/000012 here high enhancement of purification effects of coagulated and decanted water was obtained: turbidity = 0.1 NTU, color = 6 mgPt/ dm³, uv- extinction = 0.056 I/cm, consumption of KMnθ4 = 5.80 mg/ dm³, TOC = 2.1 mg/ dm³, Na = 132 mg/ dm³, As = 0.006 mg/ dm³.

According to the results of the experiments with excessively loaded natural waters, data on •the results of Zrenjanin ground water purification where high participation of humic matter in organic load were proved, it was found that the best results of organic matter removal (KMnO₄ consumption and uv-extinction) are obtained with the ratio of these two polymers which correspond to values AI₂O3 : SiO₂ = 2 : 1.2 which is shown in Fig. 6 and Fig. 7. This ratio closely corresponds to molar contents Al and Si in aluminum silicate of kaolinite. For conditions of these contents, concentration ratio, the most stable flock is obtained and forming of sediment with minimal water content.

Example 3. Purification of raw water of small ionic strength with increased content of humic matter undeλ- extremely low temperatures at Kopaonik was carried out successfully according to PCT/YUOl/000012 in pH range 5.5 - 6.5. Under conditions of changed doses of coagulants with the increase of SiO₂ part same effects are successfully obtained without pH adjustment.

According to this, farther adjustment pH by alkalization is not necessary. Raw water was purified at 3⁰C at the installation with the same temperature during experiments. Raw water had following characteristics: turbidity = 1.2 NTU, color = 25 mgPt/ dm³, pH = 7.9, consumption of KMnO₄ = 15.25 mg/ dm³, uv- extinction = 0.136 I/cm.

By standard procedure of the jar test (fast and slow mixing) with dosing of coagulants in the new optimal ratio 3.5 mgAkCVcm³ and 1 mgSiO₂/dm³ flock with high effects of humic matter removal was obtained. Purification of raw water by this method guarantee stable supply of drinking water quality standard: turbidity = 0.2 NTU, color = 2.0 mgPt/dm3, pH = 7.7, consumption of KMnθ4 = 5.5 mg/dm3, uv- extinction = 0.016 I/cm.

Under new conditions of coagulation, by change of inorganic polymers ratio effective purification without pH correction has been obtained. It is evident that even at pH 7.9 required purification effects are obtained that in practice of drinking water purification significantly facilitate work. Removal of arsenic by enhanced coagulation

In the example 2, purification of Zrenjanin drinking water enhancement of arsenic removal effects with change in the Al and SiO₂ ratio was also analyzed.

The best effects of humic matter removal, KMnO₄ consumption and uv-extinction, were obtained with the ratio Al₂O₃ : SiO₂ = 2 : 1.15. With the change of coagulation conditions, at is was given in the PCT/YUOl/000012 supplement in the same time high enhancement of purification effects for As⁵⁺ and organic As is also achieved, Fig. 8.

Best effects of arsenic removal from raw water of Zrenjanin source are obtained with doses of Al salts around 25 mgAl₂O₃/cm³ and with ratio Al₂O₃ : SiO₂ = 2 : 1.15. Best effects of humic macromolecules and arsenic binding by inorganic polymers Al and

SiO₂ are obtained with pH values 5.5 - 6.5, Al₂O₃ doses of 2 - 25 mgAl₂O₃/cm³ and SiO₂ doses from 1.0 - 12.5 mgSiO₂/cm³. Ratio AI₂O₃ : SiO₂ = 2 ; 1.2 provides almost quantitative binding Al and Si in macro complex and by this minimal residual of Al in purified water.

According to established enhancement of purification conditions are created that, without supplementary purification phases, by techno economics and ecologically best means drinking water quality standard is provided in the waters where it was not possible to be done without application of the most complex technological purification schemes.

Adjustment pH by strong acid cationic resin enables decrease in excessive Na content and in ionic strength, while with application of Al polymer SO₄ ^2" content increase is excluded, which is present in the case with application Al sulfate, so by this procedure multiplied effects on drinking water quality enhancement are obtained, decrease in organic matter content and water mineralization.

Example 4. Removal of arsenic with small organic matter content and turbidity, the Jasenica river as water source for Topola. The Jasenica river springs from Rudnik mountain, which is known for lead and zinc mine. Water of the river Jasenica is with increased As content of 0.025 - 0.060 mgAs/dm³. Since raw water of the Jasenica is transparent with low organic matter content removal of As by classical coagulation would demand dosing of suspensions that would enable this process. Dosing of Al polymer and activated SiO₂ in concentration that give weight ratio 2 : 1,2 provides effective flock formation with high arsenic removal effect.

Raw water used in experiments had composition: turbidity = 0.55 NTU, color = 3.5 mgPt/dm³, pH = 7.5, consumption Of KMnO₄ = 8.4mg/dm³, As = 0.047 mg/dm³.

By standard jar test procedure (fast and slow mixing) with coagulants dosing in new optimal ratio mgAliOs/cm³ and mgSiO₂/cm³ flock with high raw water purification effects is obtained, especially for arsenic, and that guarantee drinking water quality standard all the time: turbidity = 0.25 NTU, color

As = 0.002 mg/dm³.

Industrial Applicability

Method given in application PCT/YUO 1/000012 is in usage in the Lebane (Serbia) drinking water treatment plant from 2003. with excellent results. According to the fact that new enhancement is realized in the same conditions as previous, Fig. 8., this method can be realized on the different industrial schemes from conventional flock separation to new membrane technology.

Claims

CLAMS

Enhancement of the method of water with high humic matter and arsenic contents purification in comparison with method of enhanced coagulation given in application PCT/YUOl/000012 consist in a) maintaining pH in the optimum range between 5.5 to 6.5, according to type of water, is achieved: for raw waters with low mineralization, as required according to raw water pH, by mineral acid dosage; for raw waters where the possibility for degradation of ionic content and water quality exists, by passage of a part of the water through H⁺ resin, b) selection of optimum doses of coagulants is carried out in the application phase, the optimum doses of coagulants ranging between 2-25 mgAljOs/dm³ for Al polymer and activated SiO₂ by weight ratio to Al₂O₃, the weight ratio AI₂O₃ : SiO₂ being between 6:1 and 3: 1 and a posteriori pH correction is realized by adding Ca(OH)₂, with or without CO₂, as usually applied by conventional methods for this control in water supply practice, even with the most unfavorable raw water purification conditions: high mineralization, high humic matter and arsenic content in water and extremely low temperature with providing drinking water quality standards characterized by

- to provide the best mass ratio of two inorganic polymers by widening range in the domain Al₂O₃ : SiO₂ = from 3 : 1 to 2 : 1.5

- that for the case of extreme humic matter content Al dose ought to be increased even over 25 mgAl₂O₃/dm³ depending on the increase of organic matter content (correlation of these two polymers given in the procedure) and than established by experiments,

- that in the case of purification of water with small ionic strength and with high organic matter content and extremely low temperature pH value is not necessary to be corrected if in raw water it is lower than 7.9, - removal of arsenic is done simultaneously with humic matter in the process of coagulation and separation of flock only in the case OfAs³⁺ it ought to be previously oxidized, while in the case of As removal from raw water without organic matter Fe is dosed in 5 times greater concentration than As content.