METHOD FOR TREATING SEDIMENT

METHODE DE TRAITEMENT DE SEDIMENTS

English 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.

Claims

WE CLAIM:
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.
*****

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.