GB2279070A

GB2279070A - Process for the treatment of sewage

Info

Publication number: GB2279070A
Application number: GB9411002A
Authority: GB
Inventors: Frederic Mabire; Gerard Barbaras
Original assignee: Francaise Hoechst Ste
Current assignee: Sanofi Aventis France
Priority date: 1993-06-03
Filing date: 1994-06-02
Publication date: 1994-12-21
Anticipated expiration: 2014-06-02
Also published as: BE1007195A3; FR2705957A1; CH687704A5; GB9411002D0; FR2705957B1; ITTO940409A0; ES2066740A1; ES2066740B1; IT1265966B1; GB2279070B; ITTO940409A1

Abstract

Process of the reduction of unpleasant odours normally generated in a sewage plant, said process comprising continously introducing an aqueous solution of glyoxal having a pH of less than 3 into aqueous effluent passing from sedimentation tanks into consolidation tanks in the sewage plant.

Description

PROCESS FOR THE TREATMENT OF SEWAGE The present invention relates to a process for the treatment of sewage in a sewage plant for the purpose of reducing unpleasant odours (olfactory pollution) which emanate from the sewage plant.

The treatment of urban and/or industrial sewage in sewage plants frequently generates foul-smelling gases such as hydrogen sulphide (H2S), which on occasions are even toxic, and which, in the majority of cases, are released in a diluted state into the atmosphere; this creates a serious pollution hazard for personnel and for the waterside environment of these sewage plants.

Moreover, the hydrogen sulphide as well as the various salts and esters dissolved in the waters and sludges during treatment encourages the development of bacteria of the Thiotrix genus which disturbs the efficient operation of the sewage plant by impeding the decantation of sludges.

The treatment of sludges originating from sewage plants with glyoxal absorbed on an inert and water-insoluble mineral solid support such as kieselguhr is known from JP-A-58 (83)-112 098. A process for reducing the concentration of hydrogen sulphide in an aqueous medium containing it, while avoiding the formation of sulphurated derivatives which are insoluble in water, is also known from US-A-4 680 127. This document describes treating the said aqueous medium which has been adjusted to a neutral or alkaline pH beforehand, advantageously to a pH = 9, with an effective quantity of glyoxal, usually in a glyoxal/hydrogen sulphide molar ratio comprised between 1/1 and 2.5/1 and advantageously in a molar ratio of 2.07/1.

Finally, the use of an aqueous solution of glyoxal adjusted to a pH comprised between 5 and 9 for the elimination of odours created by excremental materials and by the products of their treatment, is also known from Japanese Patent Application No. 48-098042. Adjustment of the pH to between 5 and 9 is imperative as aqueous solutions of commercial glyoxal having a pH between 1 and 3 have practically no deodorizing effect, and in addition, they lead to the destruction of microorganisms.

Although the first of the processes described above may avoid the release of hydrogen sulphides by the sludges, it does not resolve the problem caused by the release of hydrogen sulphide from the various water treatment tanks in the sewage plant. As regards the other two processes described above, they require the alkalinization of the water to be treated to a neutral or alkaline pH, which is extremely expensive for a sewage plant treating several thousand cubic metres of water per day.

The present invention provides a process for reducing unpleasant odours in a sewage plant thereby counteracting olfactory pollution which normally occurs, which process comprises introducing an aqueous solution of glyoxal having a pH of less than 3 into a stream of aqueous effluent which passes from sedimentation tanks to consolidation tanks in the said sewage plant.

The process according to the invention is preferably performed by using a commercial aqueous solution of glyoxal, having a pH of less than 3, which is continuously introduced into the aqueous effluents which pass from sedimentation tanks in the sewage plant to so-called consolidation tanks in the sewage plant.

Under further preferred conditions for implementing the invention, the process described above is carried out using: glyoxal in a commercial aqueous solution at 40% by weight, having a pH of about 2; 1 to 24 moles of glyoxal per mole of hydrogen sulphide dissolved in the aqueous effluent to be treated, i.e. 1.7 to 40 g of glyoxal per gram of hydrogen sulphide.

Under even more preferred conditions for implementing the invention, the process described above is carried out using 2.6 + 0.7 moles of glyoxal per mole of hydrogen sulphide dissolved in the aqueous effluent to be treated, i.e. about 4.4 + 1.2 g of glyoxal per gram of hydrogen sulphide.

The process according to the present invention allows on the one hand olfactory pollution of the plant both for the personnel and the waterside environment to be considerably reduced and, on the other hand, the proliferation of filamenteous bacteria of the Thiotrix genus to be avoided without however interfering with the efficient operation of the plant. This last result is surprising as it is known that glyoxal is a powerful bactericide, which is all the more effective when it is used in a pH region below 5.

The present invention will now be illustrated in more detail by the following Example.

EXAMPLE In a sewage plant for urban sewage water treating 24,000 m3/day of sewage, analysis of the air above the consolidation tanks downstream from the sedimentation tanks shows a level of 1,000 vpm (volume per million) of hydrogen sulphide and analysis of the aqueous effluent supplying the consolidation tanks indicates an amount of 21 mg of hydrogen sulphide per litre for a flow of 540 m3/day.

At the start of the process, 0.190 g of a commercial aqueous solution of glyoxal at 40% by weight, having a pH of 2 + 0.5, per litre of aqueous effluent is introduced over a period of 24 hours into the ducts, such as channels or conduits, which supply the said aqueous effluent to the consolidation tanks, i.e. 76 mg (1.31 mmole) of glyoxal, which represents 41 kg (707 moles) of glyoxal, is introduced over a 24 hour period.

At this stage, analysis of the air above the consolidation tanks shows a level of 1 vpm of hydrogen sulphide. The introduction of glyoxal solution (i.e. 0.19 g of a commercial aqueous solution of glyoxal at 40% by weight, having a pH of 2 + 0.5, per litre of aqueous effluent) into the ducts supplying the consolidation tanks is then continued.

After 15 days of treatment, analysis of the air above the consolidation tanks shows a level of less than 1 vpm of hydrogen sulphide. It was also noted that within the plant as a whole, foul-smelling odours no longer existed. In addition, the sludges issuing from the plant, both during their storage and then their distribution, no longer release foul-smelling odours. Moreover, the operation of the plant is not adversely affected by the proliferation of filamentous bacteria of the Thiotrix genus.

This result is obtained, in continuous operation, by a daily consumption of 29.5 mmoles (about 1.71 g) of glyoxal per m3 of sewage arriving at the sewage plant, i.e. a daily consumption of about 102.6 kg of a commercial aqueous solution of glyoxal at 40% by weight, having a pH of 2 + 0.5, for the 3 treatment of 24,000 m3 of sewage.

Claims

1. Process for reducing unpleasant odours in a sewage plant, which process comprises introducing an aqueous solution of glyoxal having a pH of less than 3 into a stream of aqueous effluent which passes from sedimentation tanks to consolidation tanks in the said sewage plant.

2. A process according to claim 1, wherein the amount of glyoxal used is such that 1 to 24 moles of glyoxal are introduced into the said aqueous effluent per mole of hydrogen sulphide present in the said aqueous effluent.

3. A process according to claim 2, wherein the amount of glyoxal used is such that 2.6 + 0.7 moles of glyoxal are introduced into the said aqueous effluent per mole of hydrogen sulphide present in the said aqueous effluent.

4. A process according to claim 1 substantially as described in the foregoing Example.