WO2015198279A1

WO2015198279A1 - Method and facility for the biological treatment of the sulphides and sulphur compounds in wastewater

Info

Publication number: WO2015198279A1
Application number: PCT/IB2015/054823
Authority: WO
Inventors: Philippe Ginestet
Original assignee: Degremont
Priority date: 2014-06-26
Filing date: 2015-06-26
Publication date: 2015-12-30

Abstract

A method for the biological treatment of sulphides and sulphur compounds in municipal and industrial wastewater, according to which the water undergoes a pretreatment, followed by a free-culture biological treatment, then a clarification operation, characterised in that the raw water is mixed at or upstream from the pretreatment with desulphurising biological sludge, and facility for implementing said treatment.

Description

METHOD AND PLANT FOR BIOLOGICALLY TREATING SULFIDES AND SULFUR COMPOUNDS IN WASTEWATER. The invention relates to a process for the biological treatment of sulphides and sulfur compounds in waste water, according to which the water is subjected to a pretreatment (passage in a degreaser or in a grit chamber), followed by biological treatment with culture free, the water then being subjected to a clarification operation.

The treatment of domestic or industrial wastewater is generally dedicated to the treatment of particulate, organic nitrogen and phosphorus pollution. However, other compounds such as sulphides in wastewater must also be treated.

Indeed, sulphides are problematic at the level of sanitation systems (networks and purification stations) in several ways:

- the dissolved sulphides can be volatilized in the form of H ₂ S gaseous generating odors, on the one hand, and presenting a significant risk for health (acute toxicity). The proportion of sulphides in the raw water likely to volatilize is very low (1-2%), but this very small fraction is sufficient to create the disorders mentioned above. The emission of gaseous sulphides causing significant ventilation and odor treatment needs is of the order of 200 to 4000 mg / h / m ² depending on the concentration of sulphides in the water and the type of structure. considered (pumping station, canal, spillway, screening, sand trap, degreaser ...),

the sulphides can be oxidized to sulphates generating acids responsible for the corrosion of metals and concretes,

- Sulphides when they arrive in the aerated biological treatment favor the development of certain filamentous organisms (Thiothrix, Microthrix, Beggiatoa, Type021 N ...), which lead to malfunctions (foam development, reduction of sludge settlability). .).

Sulphides sometimes present in wastewater (1 - 40 mg of sulphide / L or more) are produced by anaerobic fermentation of the organic matter during the transport of waste water. In general, the temperature, the presence of deposits and biofilm and the residence time in the network are factors that will favor the presence of sulphides in the wastewater at the station entrance. The sulphide concentration at the station entrance can vary significantly during the day. In general, it is considered that the maximum sulphide concentration corresponds with long residence times in the network, therefore at a low flow rate. Conversely, when the flow rate is high, the residence time is short, the anaerobic fermentation in the network is limited, which lowers the concentration of sulphides in the raw water.

For the reasons mentioned above, the designer and operator of the station (and the network) are often forced to implement a number of means of control.

There are means without treatment dedicated to sulphides and means with dedicated treatment for sulphides.

1. In the absence of dedicated treatment of sulphides

The risks associated with the presence of H ₂ S in the air, odors and corrosion of the materials are very important, the designer is then forced to set up a major ventilation of the premises, treatment systems of the stale air (deodorization) and special protection of structures and equipment.

The lack of dedicated treatment of sulphides leads de facto:

- a greater health risk for the operating staff related to the toxicity of H ₂ S,

- significant olfactory nuisances for operators and residents,

the need for oversizing the ventilation flow of larger structures and premises,

- an over-dimensioning of the deodorization (stale air treatment works),

- overconsumption of reagents in deodorization and

- the need to take precautions / provide remedies for the risk of filamentous growth (chlorination of sludge, larger dimensioning of secondary clarifiers ...). 2. Establishment of dedicated treatments for sulphides

2.1. Injection of oxidants / electron acceptors The (often preventive) fight against sulphides consists of the injection of oxygen, nitrate salts or even hydrogen peroxide.

2.1.1. Compressed air injection

The principle is to provide dissolved oxygen to inhibit the formation of sulphides. This is a preventive action that can be carried out on discharge pipes with a diameter of less than 300 mm. The amount of oxygen supplied is very small, and insufficient to oxidize sulphides already present (approximately 1 mg of O ₂ transferred per L of water).

This solution is limited in its application to the case of small discharge pipes of limited geometry (topographic profile, slope, diameter, length).

2.1.2. Pure oxygen

This solution consists of the injection of pure oxygen. This curative treatment should theoretically consume 8.5 g of 0 ₂ / g of sulphides. Without taking into account the real transfer (50-80%), it is necessary to count 130 g of 0 ₂ / m ³ of water.

This expensive solution also requires pure oxygen storage and is hardly ever used.

2.1.3. Hydrogen peroxide

Hydrogen peroxide can be used in preventive treatment of sulphides, as in curative. The doses are important: 4-10 gH ₂ 0 ₂ to 35% / g of sulphides. In addition, a reaction time of 30 minutes to a few hours is necessary.

This solution is excessively expensive and the reaction time of 30 minutes to a few hours limits its application potential. It is hardly ever used.

2.1.4. Salts of nitrates

This solution makes it possible to maintain anoxic conditions inhibiting the production of sulphides (preventive) and also allowing the treatment of sulphides formed (curative). If the theoretical input was 0.7 g of N-nitrates / g of S-sulfides, the contribution in practice is of the order of 10 to 20 g of calcium nitrate per g of sulphides (ie 1.7 to 3.4 g of N-nitrates / g of S-sulphides).

This solution is expensive (consumption of reagent), and leads to a significant consumption of easily biodegradable organic matter that will no longer be available for the removal of nitrogen (denitrification) and phosphate (biological dephosphatation) at the station. The consumption of easily biodegradable DBO is 2.86 g / gN added. For 15 mgS / L in raw water, theoretically 10 mgN / L will be required and nearly 30 mg / L of readily biodegradable BOD will be consumed. This carbon deficit will penalize the performance of the station (risk of non-compliance with the rejection standard: 10 mgN-N0 ₃ - / L more to be eliminated) and / or require oversizing of the treatment process, or even even in some cases to force the addition of external organic matter (methanol, acetic acid). Similarly, the effect on biological dephosphatation will induce excess consumption of ferric chloride to compensate for 3 to 6 mgP / L which will not be eliminated by the dephosphating bacteria.

2.2. Setting up catalytic desulphurisation The principle of catalytic desulphurisation is to add small amounts of iron (or manganese) in a stirred and aerated reactor at the top of the treatment. These structures are an investment (30 minutes of contact time, mechanical mixing and ventilation) expensive and significant consumption of metal reagents and air.

This solution involves the consumption of reagents (metal salts) and energy (air injection) as well as the installation of a dedicated treatment facility (heavier investment).

2.3. Precipitation by iron salts

The sulphides formed are precipitated by the addition of iron salts II

(ferrous sulphate, ferrous chloride) and III (ferric chloride, ferric chlorosulfate ...). Injection at the elevation stations and at the station inlet is done with a theoretical stoichiometry of between 1.1 and 1.8 g of Fe / g of sulphides. In practice, larger doses are encountered. This technique induces a large sludge production that can be estimated (without taking account of parasitic reactions also producing sludge) at least between 2.2 and 2.8 g / g of sulphide.

This solution has the disadvantage of a significant consumption of metal salts. At the theoretical minimum, 1 mole of iron per mole of sulfide is required, ie 1.75 gFe / gS. Thus, for 15 mg / L of sulphides, 26 mgFe / L is required, which is much greater than the quantity of Fe injected in general to ensure the physicochemical elimination of phosphorus (7-20 m g Fe / L).

This technique also has the disadvantage of a significant sludge production that can be estimated (without taking into account parasitic reactions also producing sludge) at least between 2.2 and 2.8 g / gS. Thus for 15 mgS / L in raw water, excess sludge production will be of the order of 40 mg / L, ie almost 15% of the sludge production of the station (hypothesis of 1 g sludge / g BOD incoming and 250 mgDBO / L in raw water).

Thus all these solutions are generally expensive both in investment and operation.

The patent application US Pat. No. 5,529,693 describes a method for treating waters containing sulfur compounds, as well as an installation implementing said method, comprising a pH adjustment of the water in a reservoir at or upstream of the biological treatment so as to to maintain an alkaline pH at all points within the biological water treatment tank.

The patent application US 2003/0201227 describes a method of pretreatment with alkanes in order to remedy the unpleasant odors associated with certain chemicals such as sulphides.

The patent application FR 2913234 describes a method for treating sulphide and ammonium-containing wastewater, as well as an installation implementing said method, comprising an anoxic reactor in which the recirculated sludge makes it possible to treat the incoming carbon and denitrify the surplus of nitrates.

There is therefore a need to make available to the operator effective solutions for the removal of sulphides and sulfur compounds which are inexpensive both in investment and operation and require neither the addition of reagents, nor that of oxygen.

However, the inventors have surprisingly discovered that in a biological dephosphatation system such as that described in application FR 2992639 in which the pretreated raw water is mixed with the recirculation of the clarifier sludge before the dephosphatation, the sulphides disappear very rapidly. and that no sulphide is detected from the first biological treatment zones.

Also, in contrast to the state of the art which recommends a pretreatment of the raw water, in particular by a screen, a grit or a degreaser, before its biological treatment, the invention recommends the addition of biological sludge at the level or upstream of the pretreatment to biologically remove the sulphides. In other words, the desulfurization biological treatment processes according to the state of the art are made without recirculated sludge.

The subject of the invention is therefore a process for the biological treatment of sulphides and sulfur compounds in municipal or industrial waste water, according to which the water is subjected to a pretreatment, followed by a free culture biological treatment and then an operation. clarifier, characterized in that the raw water is mixed at or upstream of the pretreatment with biological desulfurizing sludges.

According to the invention, desulfurizing biological sludges:

- come directly from any point in the biological basin,

- or are recirculated sludges from the secondary clarification operation downstream of the biological treatment,

or are excess sludge extracted from the water line, in particular in the case of primary settling.

According to the invention, the desulfurizing biological sludge can come directly from the biological basin; in this case they are provided at the level of the pretreatment or upstream of the pretreatment by any means known to those skilled in the art, for example by recirculation pipes and mixed with the raw water at the same time as the pretreatment or before the preprocessing is performed. They may also be recirculated sludges from the secondary clarification operation, the last step of the water treatment process; in this case they are made at the pretreatment level by a recirculation loop from the clarifier and then mixed with the raw water before the pretreatment is performed or at the same time as the pretreatment. In the case of a primary settling, the intake of desulphurising sludge is carried out by the excess biological sludge extracted from the water line which integrates the sludge treatment channel via the primary sludge. This avoids the definitive trapping of the sludge in the primary clarifier.

In the context of the invention, the free culture biological treatment can be carried out by any technique known to those skilled in the art, in particular by activated sludge, sequenced batch reactors, membrane bioreactors or mixed IFAS-type cultures ( Integrated Fixed-film Activated Sludge); the treatment is preferably nitrifying and denitrifying.

According to the invention, the desulphurising sludges are added:

- either directly in the pretreatment work, as for example in pumping tarpaulins, at the level of screening channels, grit removal or de-oiling works,

- either in a storage structure located upstream of the pretreatment such as a buffer pool fed in line,

- either in a dedicated structure located upstream of the pretreatment such as a catalytic desulfurization zone,

When recirculated sludge is used, the recirculation rate of the sludge is between 5 and 30%, advantageously equal to 20% of the flow rate of raw water to be treated.

After mixing with the water to be treated, the desulphurising sludge content is between 0.1 and 2 g / l. This quantity is sufficient to allow the biological elimination of sulphides. However, in the case of primary settling, the sludge concentration is very low (approximately 0.1 - 0.2 g / L) and the removal efficiency of the sulphides is lower. The contact time between the desulphurizing sludge and the water to be treated is a function of the concentration of the sludge and is between 10 and 40 minutes, advantageously between 20 and 40 minutes, times which allow a sulphide removal efficiency of between 80 and 40 minutes. and 100%, advantageously 85% and remain compatible with conventional average residence times in pre-treatment works.

The invention also relates to a biological wastewater desulfurization installation comprising:

a system for supplying desulphurizing biological sludge at or upstream of the pre-treatment structure (s) by screening or desanding or de-oiling,

a system for treating the raw water with the desulphurising sludge at or upstream of the pretreatment works by screening or desanding or de-oiling,

- a system of regulation of this input and

a system for measuring the sulphide content of the raw water / desulfurizing sludge mixture and a desulphurized water outlet system to the biological treatment system.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with regard to embodiments described with reference to the accompanying drawings, but which are not in no way limiting. On these drawings:

Fig 1 is a diagram of an installation implementing the method of the invention.

FIG. 2 is a graph modeling the elimination in% of sulphides carried on the ordinate as a function of the contact time carried on the abscissa in minutes for different contents of sludge in the water to be treated, that is to say in quantity of matter volatile in suspension in water expressed in g / L.

Fig 3 is a graph illustrating

the sulphide concentration expressed in milligrams of sulphides per liter measured on the ordinates as a function of water (raw and pretreated) and treatment conditions (preanaerobic, aerobic and anoxic) values plotted on the abscissa and the comparison of said measurements with a model,

the cumulative reduction in sulphide% plotted on the y-axis according to the water (raw and pretreated) and treatment conditions (pre-aerobic, aerobic and anoxic) plotted on the abscissa and the comparison of these measurements to a model Fig 4 is a graph illustrating

the sulphide concentration expressed in milligrams of sulphides per liter measured on the ordinates as a function of water (raw and pretreated) and treatment conditions

(preanaerobic, aerobic and anoxic) values plotted on the abscissa and the comparison of said measurements with a model

the cumulative sulphide% abatement, plotted against the water (gross and pretreated) and treatment conditions (pre-aerobic, aerobic and anoxic) on the abscissa and the comparison of those measurements to a model Referring to Fig 1, we can see the diagram of a biological desulphurization plant of wastewater according to the invention, which includes a zone R lifting and pre-treatment (screening, grit removal, deoiling, ...). The zone R is fed with waste water to be treated by a pipe 1. Upstream of the zone R or at this zone, a pipe 2 is used to supply biological sludge from a clarifier 3. Surprisingly, Effective desulphurization is achieved without sludge input upstream or in the pretreatment zone R adversely affecting the biological treatment itself. If the supply of biological sludge was carried out, not upstream or in the pretreatment zone R but downstream of this zone and upstream of the biological treatment zone B, then the drawbacks related to the presence of sulphides or compounds sulfur would not be removed as early. On the other hand, early initiation of denitrification and biological dephosphatation reactions is a potential gain for downstream biological treatment facilities.

The water leaving the zone R is brought by a pipe 4 to the zone B of biological treatment and then are directed by a pipe 5 to the clarifier 3.

The sludge deposited in the bottom of the clarifier 3 is recirculated, at least in part, by a pipe 6 to the inlet of the biological treatment B. A three-way solenoid valve 7 is installed on the pipe 6 and the pipe 2 is connected to an output of this solenoid valve 7 to ensure the supply of biological sludge upstream or at the level of the pretreatment R. The adjustment of the biological sludge inflow rate can be ensured by control of the valve 7. The flow of the contribution of the Sludge, via line 2, is advantageously equal to 20% of the raw water flow rate to be treated.

A device 8 for measuring the sulphide content of the desulphurized water may be installed on the pipe 4 upstream of the biological treatment system. The signal provided by said device 8, representative of the sulfide content, is sent to a programmable controller 9 or a computer, which controls the valve 7 which regulates sludge input from the clarifier.

This device for measuring the sulphide content of the desulfurized water makes it possible to determine whether the desulfurized water still contains sulphides. If a moderate presence of sulphides is detected, (2 mg S / L for example), the biological treatment is carried out without further treatment of the sulphides upstream of the installation, and without injection of metal salts, in particular ferric chloride. The importance of equipment is thus reduced, as are the costs of production.

The analysis of the sulphides can also be carried out in the ambient atmosphere of the pretreatment rooms.

The operating results on a test facility showed excellent removal of sulphides and sulfur compounds without the addition of oxygen or other reagents such as nitrate salts, hydrogen peroxide or alkanes. According to the process according to the invention it is not necessary to adjust the pH during the water treatment.

The modeling of these results is given in FIG. 2 which is a graph illustrating the elimination expressed in% of sulphides carried on the ordinate as a function of the contact time carried on the abscissa and expressed in terms of minutes, at a temperature of 20 ° C. The modeling of the sulphide elimination is obtained according to a kinetics of order 1 type Eckenfelder of coefficient k and dependent on the concentration of sludge {[MVS]) and of the temperature, where k = 12 ^* 1, 04 ^{T "20} (in Lh ^"1 .g ^{" 1} _M vs) ■ The solid upper curve corresponds to a water whose content of MVS (volatile matter in suspension) is 2 g / L, the dashed curve corresponds to a water of which the MVS content is 0.8 g / L, the dotted line curve corresponds to a water with an MVS content of 0.5 g / L, the lower solid curve corresponds to a water with a content of MVS is 0.2 g / L for different contents of water sludge that is to say in amount of volatile matter suspended in water expressed in g / L.

The sulphide removal efficiency is a function of the concentration of desulphurizing biological sludge in the water and the contact time between said sludge and the water; if the supply of desulfurizing biological sludge results in a concentration of MVS in water of 0.8 g / l and a residence time of 20 minutes, the removal efficiency of the sulfides is 85%.

Several samples were taken along the water treatment line of an installation according to the invention at different temperatures. The results obtained are given and compared with the model, described above, in FIGS. 3 and 4 which illustrate:

- the concentration of sulphides expressed in milligrams of sulphides per liter measured on the ordinates as a function of water (gross and pretreated) and treatment conditions (pre-aerobic, aerobic and anoxic), as abscissa,

- the cumulative reduction in sulphide percentages on the y-axis according to the water (raw and pretreated) and treatment conditions (pre-aerobic, aerobic and anoxic) on the abscissa, at temperatures of 35 ° C and 28 ° C C, respectively.

The results were obtained according to known techniques for the analysis of sulphides in water.

The cumulative sulphide% reduction is the difference between the sulphide content of incoming and outgoing water. Other says:

the sulphide content measured in the raw water was obtained from the sample taken in line 1 with reference to FIG.

the sulphide content measured in the treated water was obtained from the sample taken at the outlet of zone R with reference to FIG.

the sulphide content measured under the various treatment conditions (preanaerobic, aerobic and anoxic) was obtained from the sampling made at different points in zone B with reference to FIG. 1. The invention is therefore applicable to any type urban or industrial effluents containing sulphides.

Applications of the invention

The invention allows:

the reduction of the consumption of reagents dedicated to the preventive and / or curative treatment of sulphides (iron salts, nitrates, hydrogen peroxide, oxygen, etc.),

- the reduction of sulphide emissions from the station, especially at the pre-treatment level, involving a reduction in the ventilation rate and deodorization structures, olfactory nuisance and toxicity risks,

- the reduction of the consumption of reagents of the stale air treatment works,

- the reduction of the risks of corrosion related to sulphides and

- the reduction of the risks of biological dysfunction related to sulphides.

Claims

1. Process for the biological treatment of sulphides and sulfur compounds in municipal or industrial waste water, according to which the water is subjected to pretreatment by screening or desandering or de-oiling, followed by free-culture biological treatment followed by a clarification operation, characterized in that the raw water is mixed at or upstream of the pretreatment with biological desulfurizing sludges.

Process according to Claim 1, characterized in that the desulphurising biological sludges:

- come directly from any point in the biological basin,

- or are excess sludge extracted from the water line.

3. Method according to claim 1 or 2 characterized in that the biological treatment is a nitrifying and denitrifying treatment.

Process according to any one of the preceding claims, characterized in that the desulphurising sludges are added:

- either directly in the pre-treatment work,

- either in a storage structure located upstream of the pre-treatment,

- either in a dedicated structure located upstream of the pre-treatment.

Process according to any one of the preceding claims, characterized in that, when recirculated sludge is used, the sludge recirculation rate is equal to 20% of the raw water flow to be treated.

6. Method according to any one of the preceding claims, characterized in that the MVS content of the water to be treated is between 0.1 and 2 g / L.

Process according to any one of the preceding claims, characterized in that the contact time between the desulfurizing sludge and the water to be treated is between 10 and 40 minutes, advantageously between 20 and 40 minutes.

Biological wastewater desulphurization plant comprising:

a system for supplying desulphurizing biological sludge at or upstream of the pretreatment works by screening or desanding or deoiling,

- a system of regulation of this input and

Installation according to claim 8, comprising:

a pretreatment zone R supplied with water to be treated by a pipe 1,

a pipe 2 upstream of the zone R or at this zone allowing a supply of biological sludge coming from a clarifier 3,

a pipe 4 bringing the water leaving the zone R towards the zone B of biological treatment,

a pipe 5 directing treated water leaving zone B to clarifier 3,

a pipe 6 bringing, at least in part, the sludge which is deposited in the bottom of the clarifier 3, towards the entrance of the biological treatment B, a three-way solenoid valve 7, installed on line 6, line 2 being connected to an outlet of this solenoid valve 7 to ensure the supply of biological sludge upstream or at the level of pretreatment R.