CA2010741A1

CA2010741A1 - Method for treating sediment

Info

Publication number: CA2010741A1
Application number: CA002010741A
Authority: CA
Inventors: Marinus P. Quaak
Original assignee: VOLKER STEVIN BAGGERMAATSCHAPPIJ NEDERLAND BV
Current assignee: VOLKER STEVIN BAGGERMAATSCHAPPIJ NEDERLAND BV
Priority date: 1990-02-22
Filing date: 1990-02-22
Publication date: 1991-08-22

Abstract

ABSTRACT OF THE DISCLOSURE A method for treating sediment, in particular phosphate containing sediment, which has deposited on the bottom of a water region, in which method a treatment agent is injected directly into the sediment, said treatment agent comprising non-gaseous components.

Description

Method for treating_sediment The invention relates to a method for treatlng ~ediment which has deposited on the bottom of a water region, in which method a treatment agent is injected directly into the sediment.
A method of this ~ype is known from the ~uropean Patent Application EP A-0,275~317. In the latter, ~ediment is treated underwater from 8 vessel. A mixture of oxy~en and water is injected in~o the sediment. The ob~ect of this is to provide low-oxygen sedimentation with oxygen. In order to make ~n optimum oxygen absorption possible, mixing chambers for gas and water are fitted immediately in front of the nozzles of the known apparatus.
The water may contain che~ical additives.
From the book entitled "Lake and Reservoir Restoration" by G.
Dennis Cooke et al. (1986), pages 133~138, it is known that, to oxidise secliments under water, a solution of cslcium nitrate is injected into the sediment in order to stimulate the denitrification. This publication also reports the use of iron chloride and calcium hydroxide to remove hydrogen sulphide and phosphorus snd to adjust the pH in order to achieve an optimum pH
for the microbial denitrification. The treatment solution is pumped to the bottom via a "harrow-like" apparatus from reservoirs situated on the bank. SPid harrow-like apparatus is provided with flexible tubes which penetrate the sediment. 1~e vertical posi~ion of the harrow-like apparatus on the bottom is adjusted by re~ulating the injection of compressed air through the said tubes.
The harrow is pulled along the bottom with th~ aid of a winch which is sited on a raft or on the bottom. In this process, sediment is loosened to a depth of approxima~ely 20 cm and the chemical solutions are injected via the tubes.
This known method hss certain disadvantages. Thus, the construction of the harrow-like appsratus having flexible tubes is complicated snd fragile. The vertical po~ition o~ the harrow has to be regulated by injecting compressed air, and this represents a 2 2~
complic~ting factor. A disadvantage of injectin~ air and/or oxygen into th~ sediment is that sludge particles adhere to the rising air bubbles, and this results in a ~erious and persistent turbidity of the surface water situated above. In addition, the effeetiveness of an operation of this type is limited to a relatively short time.
According to the prior art, it is also possible to remove the wat2r bottom sediment by dredging it away or by overing the sediment with B layer of clean material. These known ~ethods are expensive. In addition, in the case of dredging, it $s a great problem to find a suitable dumping location for the sediment.
It is an object of the present invention to provide a novel method which obviate~ or mitigates at least some of the disadvanta~es associated with the prior art.
i5 Accordingly, the present invention provides a method f~r treating sediment which has deposited on the bottom of a water region, in which method a treatment agent is injected directl~ into the sedimént, characterized in that a treatment agent is used which is composed of non-gaseous components.
The invention provides a method with which sediment can be treated in a very simple and cheap manner.
Preferably, the nozzles are diret:ted downwards.
In the method &ccordin~ ~o the invention, the treatmen~ is preferably carried out from a vessel provided with a tube which can be lowered onto the bottom and is directed transversely to the sailing direction and in which the nozzles are fitted. Ex~mples of apparstuses which are suitable for carrying out the method accord-ing to the invention are described in the Dutch Patent Applications 83.00990 and 86.00941. In the method according to Dutch Application 83.ooggo, a tube provided with outlet openings is used in order to inject water into the layer to be processed, as a result of which said layer temporarily starts to behave as a heavy liquid.
In the method according to the invention, depending on the composition of the sediment, a particular outlet opening of the nozzles and the flpw of the liquid treatment agent can be adjusted in order to obtain a desired penetration depth. Over the penetration depth, the injected ~et of liquid breaks up the cohesion between the sediment particles, as a re~cult of which a so-called sludge cloud i9 formed. During the formation of said sludge cloud, the sediment particles sre brought into intimate contact with the injected liquid and the treatment agent contained therein, 8S a result of the turbulent nature of the flows around the outlet openings. In general, the treatment agent will be injected to a dep~h of 10-40 cm.
In particular, the method according to the invention is suitable for treating the so-called "live" layer Or underwater flora And underwater fauna. This live layer is $n general approximately 2Q cm thick.
In the method according ot ~he lnvention, a solution or dispersion in water o~ at least one substance or micro-organicm which renders a pollutant harmless is used as treatment ~gent.
When combating phosphate, use may be made, for ex&mple, of substances such as iron(III~chloride or iron(III)sulphate snd/or pH-regulating sgent.
The pH of sediment si~uated underwater can be increased, for example, by supplying lime.
The methods described above are used, in particular, for combating eutrophication due to phosphate in ~ater bottom sediments, excellent results being obtained if ~ solution of a dispersion of a phosphate-binding agent such as an iron salt is injected directly into the ~ediment Yi~ nozzles.
I~ has been found that, after carrying out the method according to the invention, a layer Or sediment remains behind which is very stable as regards chemicalt physico-chemical binding 3 0 of the treated or immobilised pollutant because DO noxious substances are released therefrom over a long period.
It must be understood that the invention is not limited to the abovementioned prefered embodiments but that many variants are possible without departing from the inventive idea.

Claims

1. A method for treating sediment which has deposited on the bottom of a water region, in which method a treatment agent is injected directly into the sediment, characterized in that a treatment agent is used which is composed of non-gaseous components.

2. The method according to Claim 1, characterized in that the nozzles are directed downwards.

3. The method according to Claim 1 or 2, characterized in that the treatment is carried out from a vessel provided with a tube which can, be lowered onto the bottom and is directed tranversely to the sailing direction and in which the nozzles are fitted.

4. The method according to one of the preceding Claims, characterized in that the treatment agent is injected into the sediment to a depth of 10-40 cm.

5. The method according to one of the preceding Claims, characterized in that a solution or dispersion in water of at least one substance or micro-organism which renders a pollutant harmless is used as treatment agent.

6. The method according to Claim 5, characterized in that an iron salt such as iron(III) chloride or iron(III) sulphate and/or a pH-regulating agent are/is used.

7. A method for combating eutrophication due to phosphate in water bottom sediments according to one of the preceding claims, characterized in that a solution or dispersion of R phosphate-binding agent such as an iron salt is injected directly into the sediment via nozzles.

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