FR2771728A1 - Treatment of waste water containing oxidising agents - Google Patents

Abstract

Treatment of domestic or industrial waste waters, especially washing, bleaching or disinfection liquors containing oxidising agents, comprises passing the waste water over a catalyst bed comprising magnesium and/or transition metal(s). The transition metals are selected from Fe, Cr, Ni, Mn and Cu. The catalyst comprises the metal(s) and/or salts, oxides and/or hydroxides thereof.

Description

 The present invention relates to a method for activating and / or self-cleaning of domestic or industrial effluents, in particular washing, bleaching or disinfection baths, containing oxidizing agents.

 Many household and industrial processes involve baths containing sometimes significant quantities of oxidizing agents (chlorites, hypochlorites, mineral or organic peroxides, ...) which can be recovered (closed loop circulation) or simply rejected at taste.

 By way of non-limiting example of such processes, mention may be made of the bleaching of linen (laundry, textile industry) of paper (paper industry) as well as the washing and disinfection processes based on oxidizing agents (dishes, agro- food), both industrially and in terms of the individual user.

 In their context, these processes generally involve ionic-type reactions, which has the corollary of a relatively low reactivity (potential aspect) and a low speed (kinetic aspect); as a result, significant amounts of oxidizing agents may be present in the streams leaving the reactor.

 These residues cause various drawbacks affecting, in particular, the field of environmental protection: in fact, effluents loaded with oxidizing agents are toxic and polluting and cannot be directly discharged into the sewer, all the more that they are not very biodegradable.

 I1 should also be noted that it can be inconvenient to reuse, in certain phases of a closed loop process, solutions containing oxidizing agents, even in trace amounts.

 The object of the invention is to provide a method for activating and / or self-purifying domestic or industrial effluents containing oxidizing agents capable of remedying these drawbacks.

 To this end, it relates to a process of the aforementioned type, characterized in that the flow to be treated is passed over a catalytic bed containing at least one metal chosen from magnesium and the transition metals, so as to generate within of this flow of very reactive radical species capable of partially neutralizing it and reducing its polluting character.

 According to the invention, the metal (s) (ux) can be in metallic form and / or in the form of salts and / or metal oxides and / or hydroxides.

 Such a process can schematically be compared to the self-purification of exhaust gases from motor vehicles thanks to the interposition of a catalytic converter which transforms toxic gases into carbon dioxide and water: the principle of such a device consists, in effect, in passing the gas stream to be treated over a finely divided catalytic bed so as to carry out the oxidation of the CC to CO 2, the combustion of unburnt hydrocarbons and the reduction of nitrogen oxides.

 In accordance with the invention, the catalytic bed however acts on a flow not gaseous but liquid, and must therefore be adapted accordingly.

 As a general rule, we opt for a leaching type contact; of course, the geometry and the volume of the apparatus used as well as the quantity of catalyst depend, in each case, on the kinetics of the reaction (flow temperature, desired contact time, etc.) as well as the flow rate and of the load of the effluents to be treated.

 It should be noted that, in accordance with the invention, the catalytic bed can be located outside the washing reactor.

 The idea underlying the invention is therefore to activate the oxidizing agents present in the effluents to be treated so as to pass from an ionic type process to a radical type process in which the reactivity is much higher. the appearance of free radicals with an extremely short lifespan.

 Within the framework of a closed-loop process, the radical species thus created can be put back into circulation so as to raise the level of reactivity, this however taking into account the risks which may be inherent in a higher reactivity associated with more kinetics. fast.

 In accordance with the invention, the radical oxidizing species combine in all cases almost instantaneously with the oxidizable organic materials present in the effluents; this results in at least partial oxidation of these to carbon oxides, which has the advantage of causing a reduction in the COD (Chemical Oxygen Demand) present in the flow as well as associated financial charges.

 We have been able to verify that the presence of radical species leads in parallel to a reduction in bacterial populations and other micro-organisms and therefore in microbiological elements.

More specifically, the radical reactions which occur within the effluents to be treated in accordance with the invention can be diagrammed as follows
catalyst
ROO

RO- + O * n O + + (CH2) m

n / 2 C02 + n H + + (CH2) min / 2
Consequently, these reactions are accompanied by an evolution of CO 2 and a release of H + ions; this leads to neutralization of the effluents since, in accordance with the invention, they generally have an alkaline pH.

 As a result, the effluents thus treated can be more easily reused or discharged into the sewer.

 It should also be noted that when the content of oxidizing agents is increased, the quantities present in the discharges are increased in parallel, and consequently the COD and therefore the polluting character of the discharges are reduced, this which is particularly advantageous.

 In accordance with the invention, the transition metal (s), used in the catalytic bed, is (are) a function of the nature of the effluents to be treated, it can advantageously be chosen in the group formed by iron, chromium, nickel, manganese or copper.

 Preferably, the catalyst is in a physical form which makes it possible to obtain large contact surfaces without however being too finely divided in order to avoid as much as possible the risk of clogging by a charged fluid.

The characteristics of the activation and / or self-purification process which is the subject of the invention will be described in more detail with reference to the examples below.
Example l
Effluents were passed through from a hospital center whose COD load was initially around 1300 mg / l over metallic manganese; after a few minutes of contact, it was possible to reduce this charge to a value of the order of 100 to 150 mg / l, which corresponds to one tenth of the initial charge.

Claims (2)

CLAIMS 1 ") A process for the self-purification of domestic or industrial effluents, in particular washing, bleaching or disinfection baths, containing oxidizing agents, characterized in that the flow to be treated is passed over a catalytic bed containing at least one metal chosen from magnesium and transition metals, so as to generate within the flow very reactive radical species capable of partially neutralizing it and reducing its polluting character. 20) Method according to claim 1, characterized in that the transition metal (s) is (are) selected from the group formed by iron, chromium, nickel, manganese or copper. 30) Method according to any one of claims 1 and 2, characterized in that the metal (s) (ux) are in metallic form and / or in the form of salts and / or oxides and / or metal hydroxides .