FI124493B - Procedure for removing humus from raw water - Google Patents

Description

METHOD FOR REMOVING HUMAN FROM RAW WATER FIELD OF THE INVENTION

The invention relates to a method for removing humus from raw water and to a system for removing humus.

BACKGROUND OF THE INVENTION

The quality of hot water is largely determined by the quality of the water used as raw water. Household water can be prepared from surface water and groundwater.

Surface water quality is influenced by the quality and quantity of rainwater, land use such as drainage of marshes, runoff substances, various wastewater and biological activity of waterways. Finnish surface waters are characterized by 15 high concentrations of humus, which appear as a brown color in the water. Humus consists largely of negatively charged colloidal particles.

Coagulation allows the removal of suspended impurities and colloidal size in water purification from water. The purpose of coagulation is to neutralize the surface charge and zeta potential of negatively charged colloids, such as humus colloids, by removing the electrostatic repulsion forces acting between them and allowing the formation of flocs. The colloidal particles then grow into larger particles, co T microns, into logs.

o, the microblocks generated by coagulation are further grown into larger particles, macroclaves, by flocculation. In flocculation, particle size increase occurs by external forces and embarrassment.

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ns. Final removal of impurities o occurs by sedimentation or flotation and filtration m £ 2, o c \ j 35 The coagulant used neutralizes the charge of the colloidal particle. The coagulant must also precipitate out of the water itself at the pH range to be treated. Typical coagulants include e.g. iron sulfate and ferric chloride.

Ineffective humus removal at the beginning of the water treatment process causes load on industrial desalination stages, and dirt and corrosion of tanks and equipment. The problem with the use of iron coagulants is their difficult handling due to their corrosivity and, in particular, the fouling and corrosion hazards caused by residual iron. In addition, the effect of UV-disinfection used in water purification is impaired by ice-iron. In addition, the high cost of iron coagulants can be considered as a disadvantage.

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PURPOSE OF THE INVENTION

It is an object of the invention to provide a new type of method for the removal of humus from raw water which enhances the coagulation, flocculation and clarification steps and a system for its implementation. Another object of the invention is to improve the microbiological safety of water. In particular, it is an object of the invention to alleviate the above problems.

SUMMARY OF THE INVENTION

For the process of the invention, hummus

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The extraction of ε from raw water is characterized by what is set forth in claim 1.

The system for removing humus δ 30 from raw water according to the invention is characterized in what is set forth in claim 9.

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The invention is based on the research work carried out which was intended to enhance the removal of humus

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and reduce the use of coagulant chemicals. Surprisingly, in this study, it was found that peroxides such as peracetic acid and hydrogen peroxide are excellent 3 for efficiently removing humus from raw water when using an iron-based coagulant for coagulation and flocculation. The method according to the invention is based on the combined use of oxidizing and limiting agents.

5 Raw water here refers to the water used by the water abstraction and industrial plants for the production of hot water. Raw water can be taken from either surface water, groundwater or other water supplies.

In the method of the invention for removing humus from raw water, the iron-based coagulant is added to the raw water before clarification, the raw water is mixed to form humus silks, and the raw water is clarified by settling or flotation to remove the humus. The method involves adding peroxide to the raw water before, after or simultaneously with the addition of the iron-based coagulant, and adjusting the peroxide addition so that the charged humus particles in the clarified raw water are close to neutral or neutral.

Iron-based coagulant and peroxide are added to the raw water to neutralize the surface charge and / or zeta potential of the humus particles. The efficacy of coagulation and flocculation may be affected by coagulant and peroxide and their dosage.

The peroxide used in the process of the invention may be any compound containing a peroxide group [0-0]. Peroxide to be used in the method

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is preferably a mixture of peracetic acid, hydrogen peroxide or n-CM.

In one embodiment of the invention, the addition of o peroxide is adjusted to

The surface charges of humus particles in raw water are

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10 peq / l to 15 peq / l, preferably -5 peq / l to 5 peq / l and most preferably about 0 peq / l

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In another embodiment of the invention, the addition of ω c peroxide is adjusted so that the clarified humus particles of the raw water have a zeta potential of -10 to 40 mV, preferably -1 to 1 mV.

In one embodiment of the process of the invention, the iron-based coagulant is ferric sulfate-5 and / or ferric chloride.

By mixing, colloids and large and dense flocs can be formed. In the coagulation step, mixing occurs rapidly and in the flocculation step, mixing is slow.

Peroxide, such as peracetic acid or hydrogen peroxide, used as a humus removal enhancer, is a potent oxidant whose oxidative action of humus and other organic compounds promotes humus removal.

The amount of peroxide added to the raw water is 0.1 to 15 ppm. Preferably, 0.25-0.7 ppm peroxide is added. Any strength of peroxide can be used in the process of the invention. Preferably, the peroxide used is 3-15 wt%, preferably 5-12 wt%, and most preferably 5 wt% of the peroxide solution.

After agitation, i.e. the rapid and slow agitation steps, the coagulated and flocculated humic matter in the water is removed by clarification. Raw water can be clarified by flotation in which particles rise to the surface of the pool due to the presence of small air bubbles. The particles can also be lighter than water and naturally rise to the surface. Raw water can also be clarified by settling, whereupon the particles to be separated are heavier than water and sink to the bottom of the clarification basin due to gravity.

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? In one embodiment of the process of the invention, the peroxide is added to the raw water simultaneously with the iron-based coagulant.

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In another embodiment of the method of the invention, the peroxide is added to an iron-based coagulant.

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After the addition of 35 lbs, the efficiency of coagulation and flocculation can be affected by adjusting the pH of the water. In one embodiment of the process of the invention, the base of raw water is added before or after the addition of the iron-based coagulant so that the pH of the raw water in the coagulation step, i.e. the pi-5 mixing step, is 4.3 to 4.8, preferably 4.5 to 4.8. The base to be used is usually calcium hydroxide Ca (OH) 2, soda Na 2 CO 3, alkaline NaOH or a mixture thereof.

Water temperature also affects the efficiency of coagulation and flocculation.

In one embodiment of the invention, filtration is used to complement the settling and flotation processes. During filtration, solid impurities are removed by filtration of clarified water through a sand filter, a fine-grained film, activated carbon and / or any other filter commonly used in water purification. The filtration steps may be one or more in succession. In one embodiment of the invention, sand filtration and then activated carbon filtration are used first.

In one embodiment of the invention, disinfection is used to supplement the purification of filtered raw water. Any disinfectant commonly used in water purification can be added to clarified raw water or treated with UV light, for example.

In the method according to the invention, the charge ω £ of the clarified raw water humus particles can be measured and it adjusts the amount of peroxide to be dosed so that optimum humification c \ hum is achieved. 30 with the smallest effective amount of iron-containing coagulant.

Er Measurement of humic particle charge

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of raw water, the peroxide dosage parameter o is a clear and workable analytical method. This measurement m £ 2 35 also serves as a measure of the dosage of the iron-containing coagulant. Much anomalous negative charge indicates a deficient neutralization of the particles, leaving the coagulation step deficient. If the dosage of the coagulant chemical and peroxide is too high, the charge will turn positive, resulting in defective joy formation.

The measurement can be performed before, during and after the addition of coagulant chemicals and peroxide. Preferably, the measurement is made after the clarification, which is a good representation of the clarification power.

Prior to the addition of coagulant chemicals and peroxide, the measurement describes the quality of the raw water to be treated and such measurement can be used as a starting point for determining and optimizing the amount of iron-containing coagulant and peroxide.

In one embodiment of the invention, the surface charges of humus par-15 particles were determined by the Particle charge detection (PCD) method.

Surface charge information is also obtained by determining the zeta potential of humus particles. Methods for electrophoretic light scattering and / or other methods suitable for the determination of zeta potential may be used to determine the zeta potential.

The flow of raw water can also be measured in the method of the invention. The flow of raw water 25 is measured before or after the addition of the iron-containing coagulant and peroxide, or before or during the coagulation and / or flocculation step.

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^ or after clarification. The flow of raw water is preferably measured before the chemicals are added.

c5 S5 In one embodiment of the invention, the iron-containing properties required for neutralization were first determined.

The amount of Er coagulant added by measuring humus particles

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reservation. Subsequently, the peroxide addition is adjusted to obtain optimal humus removal at > 2 with the lowest effective amount of iron containing coagulant.

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The method according to one embodiment of the invention is continuous.

The system for removing humus according to the invention comprises an iron coagulant dispenser, a peroxide dispenser, means for forming colloids and flocs, means for humus silk removal by clarification, an analyzer for measuring the charge of humus particles.

The iron coagulant and peroxide dispensers comprise means for adjusting the dispenser.

Containers equipped with mixers suitable for rapid and slow mixing may be used as means for forming colloids and flocs.

A sedimentation basin or flotator may be used as a means of removing humus silks.

Any known meter for measuring particle charge can be used as a humus particle charge analyzer.

One embodiment of the system of the invention comprises a flow meter for measuring water flow. Any known water flow meter may be used as a flowmeter. One embodiment of the system of the invention comprises a base dispenser and means for adjusting the pH to

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S5 30 for measuring.

o The humid system of the method according to the invention is a simple to install, inexpensive and lightweight Q_ solution that can easily be installed in a raw water purification process either as a continuous part or m £ 2 35 for emergency use. o cm The method of the invention improves the quality 8 for the amount of organic matter. The method enhances the removal of humus and further enhances the microbiological safety of water. By the method of the invention, it is possible to reduce the microbial load already at the purification stage to a level that meets the criteria for domestic water. In addition, the dosage of the iron-based coagulant chemical can be reduced by about 20-50%, which reduces the iron-based coagulant chemical residues and the chemical-induced fouling and corrosion damage. At the same time, the cost of purchasing a coagulant chemical and a base is reduced. In addition, the method reduces the amount of humus-iron slurry and allows e.g. slimming of sand filters and activated charcoal washing and activated charcoal regeneration intervals;

LIST OF FIGURES

Figure 1 is a flow chart of a method according to the invention.

Figure 2 shows the molecular distributions of raw water and clarified waters in a surface water plant.

Figure 3 shows the molecular distributions of raw water and clarified water in a mill water plant.

Figure 4 shows the molecular distributions of raw water and clarified water from a second plant water plant 25.

Figure 5 shows the molecular distributions of raw water and clarified waters of the water plant of another mill.

Figure 6 shows the water plant of another plant

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cvj the molecular weight of raw water and clarified waters at 30 different doses of hydrogen peroxide.

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| DETAILED DESCRIPTION OF THE INVENTION

O) In the process according to the invention shown in Fig. 1, humus is precipitated by feeding an iron coagulant, usually ferric sulphate, an iron coagulant dosing vessel (2) and peroxide such as peracetic acid (peroxide) into raw water feed channel (1). Ferrisulphate is usually added before peracetic acid, but the addition can also be done simultaneously. The dosing of Perok-5 binder is performed in such a way that mixing is as immediate as possible.

The peroxide, such as peracetic acid, is administered in fresh water at 0.1 to 1.0 ppm, and more preferably 0.25 to 0.7 ppm. The raw water, to which ferric sulfate and peracetic acid 10 have been added, is introduced into a mixing tank (5) where it is rapidly mixed so that the humus particles form colloids. After rapid mixing, the raw water is led to a second tank (6) where the water is slowly stirred and flocculated. The speed gradient is <1000 l / s for fast mixing and <100 l / s for slow mixing. After flocculation, the raw water is led to a clarification tank (7). The clarification can be effected by flotation, whereby air is introduced into the pool, the air bubbles of which adhere to the flocs and lift them to the surface of the pool. From the surface, the flocs are separated into a sludge basin (8).

The solids in the clarified water are then filtered through a sand filter (9). The water can then be led to activated carbon filtration (10) 25 and UV disinfection (11).

The acidity of the raw water to be treated can be adjusted, if desired, by supplying the base from the dosing base (4) of the base prior to the coagulation step. Usually, lye is used as the base. The pH of the raw water is adjusted

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? 30 preferably 4.5 to 4.8.

δ The method according to the invention measures the charge of the humus particles of clarified raw water. blood

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Samples for the measurement of humus particles can be taken or derived from the clarification tank. A water sample can be

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35 also takes or directs the raw water from the canal for clarification o cvj thereafter. The humus particle charge is measured, for example, with the Particle charge detection (PCD) analyzer and the peracetic acid dispenser (2) is adjusted so that the humus particle charge of the clarified raw water is close to neutral or neutral. In addition, the flow of raw water can be measured with a flow meter (12) and the peracetic acid dispenser (2) can be adjusted in relation to the flow change. However, the dispenser (2) is also adjusted at the same time so that the charges of the clarified raw water humus particles are close to neutral or neutral.

10 Measurements can be made continuously or at intervals. According to one embodiment of the invention, measurements are made at 30 minute intervals. Measurements can also be made at, for example, hourly intervals, or longer or shorter intervals.

Further, the elimination of microbes, mainly during or after the clarification step, by peracetic acid enhances the effect of the next sand or other biological filtration in the process, since the microbes living in the filter can utilize the biological material already dead. Further, sand or other biological filtration in the process enhances the effectiveness of peracetic acid.

In one embodiment of the invention, the addition of peracetic acid is, after clarification, prior to biological filtration of water, activated carbon filtration and / or sand filtration.

In the process illustrated in Figure 1, hydrogen peroxide or a mixture of peracetic acid and hydrogen peroxide can also be used as the peroxide.

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Example 1

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The experiment investigated the effect of peracetic acid (PAA)

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o the removal of humus compounds ΙΓ) £ 2 35 from the surface water plant. The HPSEC method was used to determine the molecular size distribution of humus, which separates humus compounds on a column based on their size characteristics. In the pictures, the X-axis has time (min) and the greater the time, the smaller the humus compound. In the conventional process, larger drug compounds can be more easily removed by precipitation 5 and other process steps. The Y-axis represents the intensity (concentration) of the drug compounds.

Precipitation tests were carried out with raw water used by the water plant. A water sample from the water plant (after flotation) was used as a reference. Iron sulfate (PIX-322) was used as the coagulant chemical. The dose of the coagulant chemical in the control experiment was about 140 g / m 3 and the pH was> 5.

In experiments where peracetic acid was used as a precipitation enhancer, the increases of the coagulant chemical an-15 were 140 g / m 3, 100 g / m 3 and 70 g / m 3 and pH

was 4.8 and the dosage of peracetic acid was 0.25 g / m3.

The result of the experiment is shown in Figure 2. Figure 2 shows the molecular size distributions of raw water, plant clarified, and humus from precipitation experiments. The use of Pe-20 acetic acid dosage with the initial plant coagulant dose (140 g / m3 PIX-322) did not improve humus reduction. . At doses of 70 and 100 g / m 3 of coagulant chemicals, PAA improved humus reduction. The figure shows that PAA improves humus reduction with 25 up to 50% lower coagulant chemical doses.

The microbiological purity of raw water and flotation (iron coagulant + co-PAA) and post-filtration raw water was analyzed. The results are summarized in Tables 1 to 5.

δ _Table 1 ___

Analysis Method Raw Water Raw Water Unit filtration

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o after ID ----- £ 2 Coliform * Colliert 2000 <1 mpn / 100 o cvj bacteria Quanti ml __Tray____ 12

Escherichia * Colliert 65 <1 mpn / 100 inch Quanti ml __Tray____

Enterococci * SFS-EN 43 0 ρπιμ / 100 ISO 7899- ml __2: 2000 ____ CODMn value, * SFS 1.7 mg / 1 chemical 3036: 1981 oxygen consumption_____

Chlorophyll * SFS 50 <0.1 pg / l __5772: 1993 ____ TOC, or- * SFS-EN 3.8 mg / l total 1484: 1997 total carbon ___ * sample tested by accredited method

Example 2 The effect of peracetic acid on enhancing humus removal was investigated at the mill's water plant. In addition, corrosion measurements were performed. The mill has two separate water systems: raw water production and cooling water circulation. Of these, the flow of raw water production 10 is about 100 m3 / h. Iron sulfate was used in the preparation of the raw water to precipitate the humus.

Experiments were performed using PAA solution,

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£ with 5% PAA, pumping system and monitoring and data acquisition equipment. The pumps were connected to the subfloor c / o 15 and connected via tissue reinforced pvc hoses to the process. The PAA was fed into the water system of the limb through a mixing tank. Everything

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backgrounds and controls were delivered through modules to a data-co § acquisition and control PC program where m was built.

flow averages (hourly moving average); and the control algorithms needed at a later stage (slow integration). Initially, the pumps were switched to manual setting by pumping approximately 0.5 kg / h into the raw water system, corresponding to a concentration of about 0.25 mg / L PAA. Test runs were conducted for two months.

The precipitation process / flotation optimization to-5 was carried out in stages.

Steps: 1. PAA (0.25 ppm) was dosed for humus removal a. No dosing of iron coagulant chemical (PIX-115) (dose 150 10 ml / m3) b. PH maintained (4.8) 2. PAA dose 0.25 ppm a. Dose of iron-containing coagulant chemical dropped over 30% (100 100 ml / m3) b. pH remained constant (4.8) no NaOH addition required

Before and during the experiments, 20 samples of raw water and water were taken after flotation and after sand filtration. Samples were analyzed for KMnO4, Fe and Humus. In addition, particle surface charge (PCD) was analyzed for raw water and water from the flotation pool and after flotation.

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Score:

Water quality improved:

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^ KMnO 4 below limit value (11 ppm) ^ Humus reduction improved C \ 1 9 30 Residual iron below detection limit o Savings: ir Precipitation chemical dosage over 30% lower

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Reduced NaOH dosing, 50 m3 / year savings o Hypochlorite no dosing required, savings 60 10 $ 2 35% o cm Indirect savings:

Corrosion and waste decreased 14

Optimization of the precipitation process had a positive effect on the quality of raw water.

Figure 3 shows the molecular size distributions of raw water and humus from precipitation experiments.

The use of peracetic acid (PAA) improved humus reduction when dosages of the plant iron-coagulant chemical were used (ca 170 ml / m3 PIX).

Example 3

The effect of the iron-containing coagulant chemical and peracetic acid and hydrogen peroxide on the removal of the humus compounds in the raw water was studied at the water plant of another plant. The experiments were performed in two steps on 15 laboratory scale a) and on an institutional scale b).

Peracetic acid (a) Initially, laboratory scale precipitation experiments were performed on JAR equipment (Lovibond ET 740). In laboratory experiments, optimal dosages of 20 iron-containing coagulant chemicals (PIX-322) were sought. Precipitation experiments were carried out at pH 4.55. Doses of 110 to 135 ppm of coagulant chemicals gave all similar humus reductions.

A dose of coagulant chemical at 145 ppm slightly enhanced humus reduction. Higher doses of PIX-322 were at risk of iron escaping.

Thereafter, precipitation experiments were performed with PIX-322 co-chemical Ha peracetic acid. Based on PIX-322 ^ precipitation tests, PAA precipitation tests

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? 30 were performed with PIX-322 at doses of 120, 125, and 130 ppm at pH 4.55 and 4.7. The dosages for PAA were 0.25 ppm and 0.5 ppm. Hummus Q of JAR experiments.

based on molecular size distributions (HPSEC: HPLC Waters 2695), the reduction of humus is best when the PIX-322 ΙΓ) ≤250 dose was 130 ppm and the PAA dose was 0.25 ppm o c at pH 4.55. In addition, hormone reduction is better at lower pH (4.55) based on JAR experiments at 125 ppm for PIX-322 and 0.25 and 0.5 for PAA. Humus reduction is not significantly enhanced by higher PAA dosage.

b) The dosage of the PIX-5 322 iron coagulant chemical was adjusted to 140 ppm at pH 4.56.

The post-flotation water sample had a PCD value of + 30 peq / l, indicating an excessive chemical dose. Based on JAR experiments, the dose of the coagulant chemical was set at 130 to 10 ppm. The precipitation pH was maintained between 4.5 and 4.6. The PCD value was close to neutral (-4 peq / l). Two and a half hours later, the PIX-322 dosage was raised to 144 ppm. Based on JAR experiments, PIX-322 dosing (130 vs. 144 ppm) did not have a significant effect on humus reduction.

Subsequently, based on the results of the JAR experiments, the dosage of PIX-322 was adjusted to 130 ppm at pH 4.56 and the dosage of PAA to 0.25 ppm. After about 3 hours, the flotation PCD value was close to 20 neutrals (-7 peq / l). Figure 4 shows the molecular size distributions of humus in raw water, flotation and outgoing water.

Comparison of precipitation processes

Figure 5 compares the factory 25 precipitation process, the coagulant chemical PIX-322 iron and the coagulant chemical PIX-322 and peracetic acid according to the invention. The mill precipitation process yields 93 cc of 30% humus reduction. With PIX-322, the amount of residual humus o is 14% lower compared to the factory method.

The amount of residual humus in PAA precipitation is 35% PIX-322

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precipitation and 45% lower compared to mill o precipitation.

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Hydrogen Peroxide S Assays were performed as above.

Precipitation experiments were performed on a laboratory scale using a JAR-16 apparatus (Lovibond ET 740). The duration of the rapid mixing step was about 2 min and the slow mixing step was 15 min. The settling time was 30 min. The same optimal dosage of 130 ppm iron-coagulant chemical 5 (PIX-322) was used in the experiments. Precipitation experiments were carried out at pH 4.5 - 4.62.

Hydrogen peroxide dosages were 0.25 ppm, 0.35 ppm, 0.5 ppm and 1.0 ppm. The PCD value was close to neutral in all experiments (5 peq / l, 8 peq / l, 5 10 peq / l and 11 peq / l,). Based on the molecular size distributions of the hummus in the JAR experiments, the reduction of the hummus is best with a dose of 130 ppm PIX-322 and a dose of 0.5 ppm hydrogen peroxide at pH 4.5. Humus reduction is not enhanced by higher doses of hydrogen peroxide. Figure 6 shows the molecular size distributions of water humus at different doses of hydrogen peroxide.

The invention is not limited to the above-described embodiment examples only, but many modifications are possible within the scope of the inventive idea defined by the claims.

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Claims (11)

A process for removing humus from raw water, comprising the steps of: adding an iron-based coagulant to the raw water before clarification; Mixing raw water to form humus flocs; clarifying raw water by settling or flotation to remove humus; characterized in that the method further comprises the steps of adding peroxide to the raw water before or after the addition of iron-based coagulant 10, measuring the charge of the clarified raw water humus particles and adjusting the peroxide charge so that the clarified raw water humus particles are close to neutral or neutral. Process according to claim 1, characterized in that the peroxide is peracetic acid, hydrogen peroxide or a mixture thereof. Process according to Claim 1 or 2, characterized in that the clarified raw water humus particles have a charge of -10 peq / l to 15 peq / l, preferably -5 peq / l to -5 peq / l and most preferably about 0 peq / l. Method according to claim 1 or 2, characterized in that the clarified raw water humus particles have a zeta potential of -10 to 40 mV, preferably -1 to 1 mV. A process according to any one of the preceding claims, characterized in that the peroxide is added to the fresh water at 0.1 to 1.0 ppm, preferably 0.25 to 0.7 ppm. Process according to any one of the preceding claims, characterized in that the iron-containing coagulant is ferric sulfate and / or ferric chloride. C \ J A process according to any one of the preceding claims, characterized in that a base such as Ca (OH) 2 calcium hydroxide, Na 2 CO 3 soda, NaOH brine is added to the raw water before or after the addition of the iron-based coagulant so that the pH of the raw water prior to mixing is 4.3 to 4.8, preferably 4.5 to 4.8. Method according to one of the preceding claims, characterized in that the clarified raw water is filtered and / or UV-disinfected. A system for removing humus from raw water, comprising: a dispenser (2) for adding an iron-containing coagulant to the raw water prior to clarification, means (5, 6) for mixing the raw water to form humus flocs and means (7) for clarifying the raw water by settling or flotation that the system further comprises a dispenser (3) for adding peroxide to the raw water before or after the addition of the iron-containing coagulant, an analyzer for measuring the charge of humus particles from the clarified raw water and means for adjusting the peroxide dispenser (3) or neutral. System according to claim 8, characterized in that the system comprises a water flow meter (12). System according to claim 8 or 9, characterized in that the system comprises a base dispenser (4) and means for measuring the pH. 't δ c \ j C \ l O CD CM X cc CL CD O) O LO CD O CM