GB2044240A

GB2044240A - Method of and apparatus for sewage treatment

Info

Publication number: GB2044240A
Application number: GB8005205A
Authority: GB
Original assignee: LE T KHOLODIL PROMYSH
Current assignee: LE T KHOLODIL PROMYSH
Priority date: 1979-03-21
Filing date: 1980-02-15
Publication date: 1980-10-15
Also published as: FR2451897A1; GB2044240B; FR2451897B1; DE3010748C2; FI74695C; FI800816A; SE440642B; SE8002019L; DE3010748A1; FI74695B

Abstract

A method of treating sewage comprises separating solids (3) from the sewage (1), accumulating and averaging the separated sewage (5), and further subjecting averaged sewage (7) to electrochemical treatment so as to produce a foam layer (9), forming in the resulting foam layer (9) air counterflows by means of rarefaction provided by a pump (10) at the solids separation stage such that the flows of air (11) and foam are directed from the peripheral areas of the foam layer (9) towards the central portion thereof and further onto the solids separation stage, while treated liquid (14) is directed towards the area underlying the central portion of the foam layer (9) and subsequently withdrawn therefrom. <IMAGE>

Description

SPECIFICATION Method of and apparatus for sewage treatment The present invention is concerned generally with environmental pollution control, and in more specific terms relates to methods of an apparatus for sewage treatment.

It is a matter of common knowledge that the prob lem of terrestrial biosphere pollution prevention has nowadays assumed geniunely worldwide implica tions. The contamination of reservoirs, rivers, seas and oceans with sewage is recognized to occupy a singularly notorious place in the biosphere pollution problem. The term "sewage" is to be defined and understood herein as water that has been utilized for living or production necessities and therefore has acquired in the process a variety of extraneous impurities (contaminants) causing a change in its chemical composition or physical properties. Marine sewage generated on a vessel as a result of vital functions of its crew represents a class in itself among such polluted effluents.In view of the fact that marine vessels are highly mobile transportation means there is always present an imminent hazard of transferring contaminants to various regions of the world and, consequently, of carrying therewith diverse contagious diseases and epidemics.

For precisely this reason many nations of the world are known to undertake considerable efforts directed at the preclusion of ships lacking sewage treatment and decontamination facilities from their territorial waters.

Under the regulations of the International Convention of 1973, treated sewage water has to meet certain requirements regarding the content of suspended materials and chole-bacteria included therein as well as biochemical oxygen demand. This treated sewage water should also display the following characteristic values with reference to the indexes in question: - content of suspended material ............................. 50 mg/l (in onshore testing); .......................... 100 mg/l (in on-board testing); content of chole-bacteria ................................................... 250 c-b/100 ml; biochemical oxygen demand ............................................................... 50 mg/l.

At the present time the development of marine sewage treatment hardware incorporating various treatment processes and giving due consideration to its particular on-board application features is well under way.

Marine sewage tends to show a number of distinctive properties, the major of them being an extensive variation in the supply of effluents, high concentrations of impurities and the presence of large4raction impurities contained in these effluents which are practically not capable to undergo any physicochemical changes due to the insufficient extent of marine sewage systems.

According to the invention there is proposed a method of sewage treatment, comprising processing sewage in a number of sequential stages, the first stage being intended to separate solids contained in the sewage and to collect said solids, the next stage being intended to accumulate the sewage treated at the previous stage, to average the same over its volumetric loading and physico-chemical composition and then to accomplish electrochemical treatment of a flow of said average sewage resulting in the isolation of impurities and purified water, wherein, according to the invention, said electrochemical treatment is conducted at a rate of the average sewage flow sufficient to produce a surface foam layer in which air counterflows are subsequently formed by means of developing rarefaction at the solids separation stage, said rarefaction being provided to direct said air flows and form from the peripheral portions of said foam layertowardsthe central portion thereof and further onto the solids separation stage where the foam is mixed with the solids separated from the sewage, and said purified water, towards the area underlying the central portion of said foam layer, wherefrom said purified water is then removed.

An apparatus for practicing the above-described method comprising a unit for separating solids from sewage, a tank for accumulating and averaging sewage connected to said unit by way of a pipe line, an electrochemical treatment unit containing liquid with electrodes submerged therein, provided with liquid inlet and outlet means and connected to said unit for accumulating and averaging sewage by way of a pressure pipe line, wherein, according to the invention, said unit for separating solids from sewage accommodates a rarefield tank provided with a duct having a lower end thereof submerged in the liquid permanently available within the unit for separating solids from sewage and connected by way of a pipe line to said electrochemical treatment unit provided with an air-operated device for removing foam generated in the electrochemical treatment process.

The formation of air counterflows in the foam layer of the electrochemical treatment unit, which direct the foam from the peripheral zones of the foam layerto the central part there of, as well as directing the treated liquid towards the area underlying the central part of the foam layer enables to col lectthefoam and treated liquid atthat portion of the electrochemical treatment unit where they are exposed to the least vertical displacements and practically do not change in volume with sideways motions of the sewage treatment apparatus induced by listing and rolling of the vessel equipped with such an apparatus. This factor is conducive to the timely and effective removing of the foam and treated water from the electrochemical treatment unit.

Rarefaction provided at the solids separation stage (in the unit for separating solids from sewage) and passed at the sewage electrochemical treatment stage (to the electrochemical treatment unit) allows both the formation of air counterflows in the upper section of the electrochemical treatment unit and the conveyance of the foam from the electrochemical treatment unit to the unit for separating solids from sewage, which considerably simplifies the process of sewage treatment and the structure for its effectuation.

Electrochemical treatment performed at average sewage flow rates sufficient to provide a surface foam layer in the electrochemical treatment unit permits to make use of electrochemical flotation phenomena for the purpose of forcing impurities to the surface of the liquid being treated.

Mixing of the foam with the solids extracted from the sewage at the first stage in the solids separation unit makes it possible to remove both the solids and the impurities yielded in the electrochemical treatment process from one and the same area, which essentially simplifies the flow chart of the process and the structure of the apparatus incorporating this process.

An assembly interconnection pattern of the apparatus devised for the solids separation unit, the electrochemical treatment unit and the sewage accumulation and averaging tank enables to minimize the number of valves required for the apparatus, which to a tangible extent simplifies its structure and operation and improves apparatus operational reliability.

What is more, such an apparatus unit interconnection pattern allows to effectuate the treatment process without mixing of the flows of treated and untreated liquids, which leads to a further increase in the efficiency of treatment and in the sewage handling capacity of the apparatus. While processing sewage in the electrochemical treatment unit, use is made of electrochemical flotation phenomena for removal of impurities from the sewage, this removal owing to the rational interconnection pattern between the electrochemical treatment unit and the solids separation unit being achieved by the simplest possible technique according to which suspended impurities together with the foam produced in the electrochemical treatment unit are passed via a pipe line to the solids separation unit and subsequently withdrawn therefrom.Removal of the hydrogen generated in the electrochemical treatment unit and ventilation of the apparatus proceed concurrently therewith.

Provision of the tank accommodated with the solids separation unit with the duct having its lower end submerged in the liquid permanently available in the solids separation unit and supplied thereto in the process of separating solids together with the impurities isolated in the process of electrochemical treatment provides an effective means of removal and extinguishment of the foam and also results in mixing of the impurities isolated in the electrochemical treatment unit and in the solids separation unit.

Thus, the sewage treatment apparatus of the present invention offers a number of constructional and operational features allowing to utilize it beneficially and highly efficiently for carrying out sewage treatment in shipboard conditions, i.e. in the conditions abounding in constant vibrations, listing and rolling of a vessel.

According to one of the embodiments of the method of sewage treatment it is expedient that prior to mixing the foam with the solids the latter be separated by means of filtering sewage through a tapered filtering surface, effecting a supply of the sewage to the apex thereof followed by removing the solids accumulated on the filtering surface with the aid of centrifugal forces and the action of a medium leading to a decrease in the adhesion of the impurities to the filtering surface and applied under pressure to the inner side of this surface opposite to the side where the sewage is supplied.

Sewage filtration through the tapered filtering sure face combined with sewage flow feeding to its apex promotes optimum distribution of the sewage over the filtering surface, which results in the high efficiency of sewage solids separation and leads to the contamination of the filtering surface showing a uniform and gradual increase towards the base of the taper. At a subsequent stage the latter contributes to a rise in the effectiveness of filtering surface cleaning done by means of centrifugal forces whose magnitude is also increasing towards the taper base of the filtering surface.

The effect produced upon the impurities accumulated on the filtering surface by a medium reducing the adhesion of the impurities to the filtering surface and applied under pressure to the inner side of this surface opposite to the side to which the sewage is supplied assists greatly in cleaning of the filtering surface, since the above is accompanied by loosening, melting and dissolving of the impurites deposited on the filtering surface as well as by washing of this surface by the flow of an adhesion-reducing medium oppositely directed in relation to the flow of sewage. At the same time, by virtue of the fact that this medium is delivered under pressure penetration of the impurities to the inner side of the filtering surface is excluded, which, in turn, equally excludes penetration of the impurities from the filtering surface into the liquid being treated.

According to one of the embodiments of the method of sewage treatment it is expedient that said medium reducing the adhesion of the impurities to the filtering surface be provided not untill 50-60% of the total filtering surface area is clogged.

Such an embodiment of the method permits to check penetration of the sewage to the accumulated solids and to gain an increase in the efficiency of filtering by means of provision of optimum hydraulic resistance in the filtering surface.

According to another embodiment of the method of sewage treatment it is expedient that hot water be employed as the medium reducing the adhesion of the impurities to the filtering surface.

Hot water applied under pressure to the inside of the filtering surface loosens the fatty depositions sticking together with the fibrous impurities to form conglomerations, which are later readily removable from the filtering surface by the action of centrifugal forces. Furthermore, with hot water being applied in the above-specified manner the fibrous impurities located on the filtering surface become loosened, which also results in the improved effectiveness of filtering surface cleaning by means of centrifugal forces.

According to still another embodiment of the method of sewage treatment it is expedient that a mixture of steam and water be employed as the medium reducing the adhesion of the impurities to the filtering surface.

With such a mixture of steam and water being employed as the adhesion-reducing medium, the solids removed from the filtering surface are exposed to a lesser degree of flooding and a lesser amount of water penetrates into the solids when the latter are being gathered.

According to still another embodiment of the method of sewage treatment it is expedient that a mixture of water and detergents, e.g. surface-active substances, be employed as the medium reducing the adhesion of the impurities to the filtering surface.

With such detergents being added to the water, the effect of reducing the adhesion of the fatty impurities to the filtering surface is still more augmented as the strength of the adhesion of the fibrous impurities thereto is concurrently diminished, which enables to gain a further decrease in the amount of water used for filtering surface cleaning.

According to yet another embodiment of the method of sewage treatment it is expedient that steam be employed as the medium reducing the adhesion ofthe.impurities to the filtering surface.

The use of steam as the adhesion-reducing medium permits to lower flooding of the solids from the filtering surface and to lessen the amount of water penetrating into the solids when they are being collected.

According to yet another embodiment of the method of sewage treatment it is expedient that hot air be employed as the medium reducing the adhesion of the impurities to the filtering surface.

The use of hot air as the adhesion-reducing medium allows not only to obviate excessive flooding of the solids deposited on the filtering surface, but also to profuce a certain drying effect upon these solids, which facilitates further processing of the impurities removed from the filtering surface.

According to one of the embodiments of the apparatus for practicing the above method of sewage treatment it is expedient that the electrochemical treatment unit incorporated in the apparatus be fabricated in the form of a sectional tank provided with a centrally arranged tube for treated liquid reception having a vertical position and connected hydraulically to the liquid outlet means and to the section of the tank wherein the sewage is finally disinfected, the upper end of said tube for treated liquid reception being preferably fabricated so as to project over the liquid level in said tank.

A sectional configuration of the electrochemical treatment unit makes it possible to purify and decontaminate the liquid treated with better fullness and efficiency by means of consequitive transferences of the liquid from one section to the other, and also allows to minimize hydraulic impacts incidental to the listing and rolling motions of the apparatus.

A central arrangement of the tube for treated liquid the reception tank and connection of this tube only to that section of the tank in which the sewage is finally decontaminated enable to prevent in shipboard conditions the mixing of treated and untreated liquids since the area located in the centre of the tank is characterized by a constant volume of the liquid and minimum vertical displacements of the latter in listing and rolling of a vessel.

The above circumstance leads to a stabilized quality of purification of the liquid processed in the electrochemical treatment unit prevents the liquid from spilling out of the tank and excludes the possibility of electrodes exposure.

Fabrication of the tube for purified liquid reception so that its upper end is made to project over the liquid level in the tank prevents the untreated liquid and foam from flowing to the tank for treated water and further to overboard water.

According to another embodiment of the apparatus for sewage treatment the air-operated device for foam removal comprises an air duct mounted along the upper edge of the electrochemical treatment unit and provided with air outlet holes located on the surfaces facing the interior of the electrochemical treatment assembly, and with air inlet holes, and also a foam receiver positioned in the centre of the electrochemical treatment unit above the upper boundary of the liquid level therein and connected to a ventilator providing rarefaction in the tank accommodated within the solids separation unit, in the foam receiver and in the space confined by the surface of the liquid contained in the electrochemical treatment unit, by the cover of this assembly and the air duct The siting of the air duct with the air inlet and outlet holes along the upper edge of the electrochemical treatment unit permits to attain the rational dispensation of air around the entire perimeter of the upper edge of the electrochemical treatment unit. As this takes place, the currents of air urge the foam from the peripheral portions of the electrochemical treatment unit towards the centre thereof where the liquid and the foam layer are sub elected to minimum displacements.Under severe sideways motions of the apparatus caused by listing, rolling or vibrations of the vessel carrying this apparatus, the volume of purified water and foam in the central part of the electrochemical treatment unit practically does not change, which forwards the timely and effective removal of the foam from the unit to the foam receiver.

Positioning of the foam receiver in the centre of the tank permits to accumulate the foam within the area of electrochemical treatment where the liquid and the foam experience minimum vertical displacements, which also facilitates removal of the foam from the electrochemical treatment unit.

Positioning of the foam receiver above the upper boundary of the liquid level in the electrochemical treatment unit prevents the liquid treated from penetrating into the foam receiver.

A connecting link provided between the foam receiver and the ventilator developing rarefaction in the tank arranged in the upper portion of the solids separation unit, in the foam receiver itself and in the space confined by the surface of the liquid contained in the electrochemical treatment unit, by the cover of the unit and the air duct makes it possible in a concurrent fashion to dispense through the outlet holes the air sucked in via the inlet holes of the air duct, to convey the foam from the electrochemical treatment unit to the solids separation unit and to ventilate the apparatus by means of a single device, i.e. the ventilator, in other words, results both in the simplified structure of the apparatus and in the simplified technological links between the treatment assemblies thereof.

According to still another embodiment of the apparatus for sewage treatment it is expedient that vertical partitions be erected in the space confined by the outer surface of the foam receiver and the inner surface of the air duct so as to divide said space into sections.

Such a structure allows to preclude the intersection of air flows, which leads to that they move in a more rational manner and, consequently, the foam in the electrochemical treatment unit is outsed also more effectively.

According to yet another embodiment of the apparatus for sewage treatment it is expedient that the vertical partitions be erected so that their lower edges are sumberged in the liquid available in the electrochemical treatment unit, whereas their upper edges reach up, at least, to the upper edge of the air duct.

Such a structure of the partitions prevents the air flows from travelling above or below said partitions, which enablesforthe air flows to travel in optimum conditions and, therefore, assits in forcing out the foam in the required direction.

According to still another embodiment of the apparatus for practicing the above method of sewage treatment the solids separation unit comprises a sewage inlet duct, under the outlet hole of which there is provided a shaft carrying a taper filter whose lateral surface is turned back towards the apex, adjacent to which is a shield mounted on said shaft, with the base of the filter taper having thereunder a receiving funnel for separated sewage with an outlet duct, whereas at a distance from the base of the filter taper exceeding the maximum dimensions of the solids separated there is provided an apron mounted coaxially to the shaft and shaped as a cylinder of elastic material.

The shaft-mounted taper filter having a shield adjacentto the apex of the taper permits to smoothly distribute the flows of the liquid treated over the filtering surface and to prevent the solids from accumulating near the centre of rotation where the centrifugal forces arising in rotation of the taper filter are insignificant. The latter allows to reduce the speed of filter shaft rotation, which is of the utmost importance when employing the filter in shipboard conditions.

The uniform distribution of sewage flows overthe surface of the taper filter conduces to the improved efficiency in purification of its filtering surface and the liquid being treated.

Provision of the outlet hole in the inlet duct above the apex of the filter taper affords the uniform distribution of the liquid treated over the surface of the taper filter and, therefore, favours the uniform contamination of the filtering surface, which upgrades the efficiency of purification of the polluted liquid and the filtering surface of the taper filter.

Provision of the taper filter with its lateral surface turned back towards the apex bars the penetration of the sewage flowing down the outside of the taper filter into the tank for solids collection, i.e. enables to obtain separated solids with a minimum amount of water therein as well as to increase the efficiency of polluted liquid treatment. Such a structure of the lateral surface assists in the accumulation of the solids in the vicinity of the filter taper base, which, in turn, - - improves the efficiency of cleaning of the filtering surface of the taper filter owing to the fact that the centrifugal forces acting on the impurities are higher in the area close to the base of the filter taper than at the apex thereof.

The elastic apron mounted coaxially to the shaft having the taper filter attached thereto inhibits the adhesion of the impurities to the walls of the filter frame and the erosion of these walls as well. It should be also pointed outthatthe presence of the apron does not prevent in any way the penetration of the solids into the lower part of the solids separation unit, but is does prevent the repeated penetration of the impurities onto the filtering surface due to the elasticity inherent in the apron.

According to still another embodiment of the apparatus for practicing the method of sewage treatment it is expedient that the lateral surface of the filter be turned back at an obtuse angle.

With such a structure of the lateral surface no blind pockets are formed in the taper filter, which aids both in raising the efficiency of cleaning of the filtering surface of the filter and in improving the efficiency of contaminated liquid treatment.

According to yet another embodiment of the apparatus for practicing the method of sewage treatment it is expedient that the apron be mounted so that its lower edge reach up, at least, to the level of the taper filter base.

Positioning of the filter as described above affords improved protection of the walls of the filter frame from the solid impurities sticking thereto and, therefore, inhibits the erosion of the frame walls.

According to yet another embodiment of the apparatus for practicing the method of sewage treatment it is expedient that in the treated sewage reception funnel along its upper edge facing the filter taper base be mounted an annular tube provided with holes made on the surface of the tube facing the inner surface of the taper filter, and connected via a pressure regulator to the source of the medium reducing the adhesion of the impurites to the filtering surface.

The incorporation in the treated sewage reception funnel of the annular tube provided with holes and connected via the pressure regulator to the source of the medium reducing the ahdesion of the impurities to the filtering surface makes it possible to apply under pressure the liquid or gaseous adhesion reducing medium to the inner side of the filtering surface which by acting upon the depositions located on the filtering surface tends to mitigate the degree of their adherence to the surface in question and, thus, conduces to better cleaning of the filter ing surface and to more effective use of the centrifugal forces stemming from rotation of the filter during its cleaning.

The holes provided in the tube through which the above medium is applied to the inner surface of the filter are arranged so that the jets of the adhesionreducing medium coming out of the holes overlap the entire inner side of the filtering surface of the taper filter.

Effected under pressure by means of the pressure regulator, the application of the medium reducing the adhesion of the impurities to the filtering surface of the filter favours the exclusion of the impurities from the inner filtering surface, which, in turn, prevents the impu rites from finding their way from the filtering surface into the liquid treated.

According to still another embodiment of the apparatus for practicing the method of sewage treatment it is expedient that the holes provided in the annular tube be made expanding towards the outer wall thereof.

Such a structure of the holes permits to take full advantage of the kinetics of the jet of the outflowing medium reducing the adhesion of the impurities to the filtering surface.

According to still another embodiment of the apparatus for practicing the method of sewage treatment it is expedient that the holes in the annular tube be provided with conically diverging nozzles.

Such a structure of the holes through a slight constructural complication enables to take even fuller advantage of the kinetics of the nozzle-discharge jets of the medium abating the adhesion of the impurities to the filtering surface.

The present invention will be further disclosed in the following detailed description of its practical embodiment with reference being made to the accompanying drawings, in which: FIG. I is a flow chart illustrating the method of sewage treatment, according to the invention; FIG 2 is a block diagram of the electrochemical treatment unit illustrating the position of liquid and foam layer under severe sideways motions of the, according to the invention; FIG. 3 is a graph of hydraulic resistances of the filtering surfaces versus its surface blocking degrees, according to the invention; FIG. 4 is a block diagram of the apparatus for practicing the method of sewage treatment, according to the invention; FIG. 5 is a top view of Fig. 4; FIG. 6 is a general view of FIG. 4;; FIG. 7 illustrates the electrochemical treatment unit of FIG. 4, 5 and 6 presented in section on an enlarged scale, according to the invention; FIG. 8 is a top view of FIG. 7; FIG. 9 illustrates FIG. 7 in section along the line IX-IX; FIG. 10 is another embodiment of the electrochemical treatment unit of Fig. 4, 5 and 6 presented in section on an enlarged scale, according to the invention; FIG. 11 is a section along the line Xl-Xl of Fig. 10; FIG. 12 is another embodiment of the electrochemical treatment unit of FIG. 4, 5 and 6 presented in section on an enlarged scale, according to the invention; FIG. 13 is a section along the line XIII-XIII of FIG. 5 on an enlarged scale; FIG. 14 is an axonometric view of the air duct of Fig. 4, 5 and 6 presented on an enlarged scale (hexahedral form); FIG. 15 illustrates the same as in FIG. 14 (round form);; FIG. 16 illustrates the same as in FIG. 14 with the electrochemical treatment unit of cylindrical form; FIG. 17 is the unit for separating solids from sewage, illustrated in FIG. 4 and 6 and presented in section on an enlarged scale with a taper filter mounted thereon, according to the invention; FIG. 18 is a top view of the annular tube illustrated in FIG. 17 presented on an enlarged scale, according to the invention; FIG. 19 is section along the line XIX-XIX of Fig. 18; FIG. 20 illustrates unit D of Fig. 19; FIG. 21 is a graph characterizing operation of the apparatus illustrated in Figs. 4, 5 and 6, according to the invention; The method of sewage treatment is illustrated by the chart shown in FIG. I.Polluted liquid treatment is accomplished in a number of sequential stages, among which the first stage is intended to filter sewage I through a tapered filtering surface 2, with solids 3 being separated from the liquid of the sewage I, accumulated in the lower part of unit 4 for separation of the solids 3 from the sewage I and then passed for disposal or utilization, whereas cleaned sewage 5 being accumulated and average over volumetric loading and physico-chemical composition in a tank 6. Averaged sewage 7 is subjected to electrochemical treatment in a unit 8 of electrochemical treatment. In the course of electrochemical treatment there is effected coagulation of colloid particles, flotation of the coagulated colloid particles by the bubbles of hydrogen being generated in the electrolysis and disinfection of the sewage.

Depending on the content of chlorides, electrochemical disinfection of the sewage can be carried out with chlorine (at a substantial chlorine content), hydrogen peroxide and ozone (at a small chloride content). As this takes place, the amount of chlorine, hydrogen peroxide and ozone produced in the electrolysis of the sewage with different chloride concentrations is liable to change, maintaining constant the total amount of the above disinfectants in the sewage treated.

Electrochemical treatment is conducted at a rate of the flow of the averaged sewage 7 sufficient to produce a foam layer 9. During this process in the foam layer 9 under the action of rarefaction developed by a ventilator 10 in the unit 4 for separation of the solid 3 from the sewage I and, hence, in the electrochemical treatment unit 8 connected thereto there are formed air counterflows II forcing the foam from the peripheral regions of the foam layer 9 towards its central portion designated in the chart of FIG. I by a dotted rectangle, wherefrom impurities 12 suspended in foam are passed to the unit4 for separation of the solids 3 from the sewage I by the action of the same above-mentioned rarefaction.Then the impurities 12 are mixed with the solids 3 separated from the sewage I in the unit 4 and their mixture 13 is directed from the unit 4 for separation of the solids 3 from the sewage I for disposal or utilization.

Treated water 14 is directed to the area underlying the central portion of the foam layer 9 designated in the chart by a dotted rectangle, wherefrom it is removed to a collection tank to be used later or dumped overboard.

The formation of the air counterflows II in the foam layer 9 during the process of electrochemical treat mentforcing the foam from the peripheral regions of the foam layer 9 towards its central portion as well as urging the treated water 14 to the area underlying the central portion of the foam layer 9 enables to collect the foam and the treated water 14 within the zone where they are exposed to minimum vertical displacements and do not change practically their volumes under severe sideways motions of the electrochemical treatment unit 8 arising from listing and rolling of the vessel incorporating the assembly. This is illustrated by a block diagram (FIG. 2) of the electrochemical treatment unit 8 showing the position of the liquid and the foam layer 9 under severe sideways motions of the assembly.

As can be seen from the diagram, under heavy tilting of the electrochemical treatment unit 8 the boundary of the foam layer 9 and the water contained in the electrochemical treatment unit 8 may extend, for example, along lines A or B. In this case only in the central portion of the foam layer 9 and the water volume adjacent thereto, say at point C, the levels of the water and the foam layer 9 remain constant and, therefore, the volumes of the foam and water located close to point C remain also constant.

Thus, is appears expedient to force the foam and the treated water to the area located near the centre of the foam layer 9 when employing the above method of sewage treatment in apparatus designed for marine operation, i.e. in the conditions of constant vibrations, listing and rolling of a vessel.

The method is also characterized by that the sewage I (FIG. I) is supplied to the tapered filtering surface 2 towards its apex, which helps to achieve the optimum distribution of the sewage I over the filtering surface 2. In turn, this circumstance leads to the high efficiency offered by separation of the solids 3 from the sewage I and to the clogging of the filtering surface 2 showing a uniform and gradual increase towards the taper base thereof. The solids 3 accumulated on the filtering surface 2 are removed therefrom by the action of centrifugal forces arising in rotation of the taper filtering surface 2 and also by the action exerted on them by a medium 15 reducing the adhesion of the solids 3 to the filtering surface 2 and applied under pressure to the inner side of the filtering surface 2 opposite to the side where the sewage I is supplied.

Application to the solids 3 accumulated on the filtering surface 2 of the medium 15 reducing the adhesion of the impurities to the filtering surface 3 contributes to improved cleaning of the filtering surface 2 since the process is accompanied by loosening, melting and dissolving of the impurities deposited on the filtering surface 2. Due to the fact that the above medium 15 is applied under pressure there is excluded the penetration of the impurities to the inner side of the filtering surface 2, which in turn, prevents the impurities from penetrating from the filtering surface 2 into the separated sewage 5.

The pressure under which the medium 15 reducing the adhesion of the contaminants to the filtering surface 2 is to be applied thereto is apt to vary within a broad range and is largely dependent on a number of factors, the major of them being as follows: the kind of the adhesion-reducing medium 15, which can be in a liquid or gaseous state, or else represent a mixture of liquid and gas; the temperature of the medium 15 employed; the nature of the depositions located on the filtering surface 2 and so on and so forth.

It appears to be most advisable that the pressure chosen forthe liquid medium 15 be equal to 1 + 2 atm. (1 .~2.1 05Pel:), for the gaseous medium -3 . 5 atm. (3+5.1 05Pa), for a mixture of the liquid and gaseous medium -2.5-3 atm (2.2 .3.105Per).

It should be noted that the application of the medium 15 reducing the adhesion of the impurities to the filtering surface 2 produces a benificial effect on the action of centrifugal forces, which are the principle means for removal of the impurites from the filtering surface 2. On having decreased the extent of their adherence to the filtering surface, the impurities are readily removable therefrom by the action of centrifugal forces, said centrifugal forces action being provided either concurrently with or after the application of the adhesion-reducing medium 15.

The application of the medium 15 reducing the adhesion of the impurites to the filtering surface 2 is effected not untill 50-60% of the total area of the filtering surface 2 has been clogged. The above-stated limit is dictated by an increase in the hydraulic resistance of the filtering surface 2 as a result of blocking of the filtering surface with large impurities (paper, cotton wool, etc.) Such an increase in the hydraulic resistance interrelated with the blocking degree of the filtering surface exhibits an exponential character, as shown in the graph of FIG. 2. In this graph values of the hydraulic resistance of the soiled filtering surface 2 are plotted on the Y-axis without allowance made for the hydraulic resistance of the clean filtering surface 2.Values of the blocking degrees of the filtering surface 2 are plotted on the X-axis in percentage with respect to the total area of the filtering surface 2. It follows from the graph that with 50-60% covering the surface the hydraulic resistance of the filtering surface 2 remains within an optimum range. With values in excess of those specific hereinabove there is observed a marked rise in hydraulic resistances bringing about an increase in the penetration of the liquid component of the sewage 1.

into the unit 4 (FIG. 1) for separation of the solids 3.

When applying the adhesion-reducing medium 15 with the soil covering degree of the filtering surface less than 50-60%, this medium is consumed in large amounts and the efficiency of cleaning is also dropping due to the losses of time required for frequent recoveries of the filtering surface 2.

A variety of substance or mixtures thereof, both in a liquid and gaseous state, can be adapted for use as the medium 15 reducing the adhesion of the impurities to the filtering surface 2. Most preferred among such substances employed as the medium reducing the adhesion of the contaminants to the filtering surface are hot water, a mixture of steam and water, a mixture of water and detergents, such as surface-active substances, steam, hot air, etc.

Hereinbelow are given by way of example practical embodiments of cleaning of the filtering surface 2 from the solids 3 deposited thereon by means of centrifugal forces combined with the application to the inner side of the filtering surface 2 of various media 15 reducing the adhesion of the contaminants to the filtering surface 2.

EXAMPLE 1 To exemplify one of the embodiments of the method of sewage treatment let us consider the case of cleaning of the filtering surface 2 soiled with fatty and fibrous depositions by means of centrifugal forces in combination with the application of hot water to the inner side thereof.

300 litres of the sewage 1 having a temperature of 20 C and containing an average of 650 mg/l of impurities comprised of an averaged of 0.1 g/l of fatty contaminants and 0.05 g/l of fibrous contaminants were passed through the filtering surface 2. The filtering surface 2 intercepted 27 g of fatty and 12 g of fibrous impurities. Recovery of the filtering surface 2 was conducted with the surface rotating at a speed of 1000 r.p.m. and 60 litres of water at a temperature of 500C and a pressure of 1 atm (1.105Pa) being applied to the inner side thereof.

When using hot water with a temperature of 500C for washing of the filtering surface it was found that the fatty impurities stick together with the fibrous ones forming conglomerations, which are readily removable under the action of centrifugal forces.

Eleven experiments were performed in which hot water was used for washing of the filtering surface 2 and the same number of experiments with the use of centrifugal forces alone. Experimental data are presented in the table below. It transpires from the table that the efficiency of cleaning of the filtering surface 2 with resort made to the combined action (of centrifugal forces and hot water) exerted on the impurities is increasing through the improved efficiency of the centrifugal method of cleaning of the filtering surface 2 resulting from a reduction in the forces of adhesion between the impurities and the filtering surface 2 when the former are exposed to the action of hot water.

It is expedient to make use of hot water with a temperature up to 500C for cleaning ofthefilterin surface 2 on large passenger vessels which are abundantly supplied with hot water of such a temperature to satisfy the needs of a crew and passengers.

EXAMPLE 2 To exemplify another embodiment of the method it is considered the case of cleaning of the filtering surface 2 by means of centrifugal forces combined with the application to its inner side of hot water whose temperature exceeds a melting temperature Removal of fatty and fibrous impurities from the filtering surface by means of centrifugal forces alone and by means of centrifugal forces com bined with hot water washing of the filtering sur face.

No. Weight of impurities Weight of impurities Weight of impurities checked by the left on the filtering left on the filtering filtering surface surface after its surface after its cleaning by centrifugal cleaning by centrifugal forces forces combined with hot water washing of the filtering surface fatty fibrous fatty fibrous fatty fibrous 9 9 9 9 g 9 1 27 12 0.5 1 fatty inclu- 10-3 sions are not 2. 20 8 0.3 0.6 detected visually. 2.10-3 3. 28 4 0.8 0.4 Solvent washing 1.10-3 attended by fat extraction 4. 15 10 0.1 0.9 showed only 5.10-3 slight traces 5. 17 5 0.09 0.1 offatty 1.10-3 6. 23 14 0.4 0.12 impurities 6.10-3 7. 12 9 0.8 0.08 1.10-3 8. 16 12 0.25 0.13 1.10-3 9. 22 7 0.4 0.2 8.10-3 10. 21 9 0.18 0.12 1.5.10-3 11. 13 4 0.6 0.26 4.10-3 of the fatty depositions on the filtering surface 2. 300 litres of the sewage having a temperature of 200C and containing an average 650 mg/l of impurities comprising an average of 0.1 gll of fatty impurities and 0.05 g/l of fibrous impurities were passed through the filtering surface. The filtering surface 2 intercepted 26 g of fatty and 13 g of fibrous impurities.Recovery of filtering surface 2 was conducted with the surface rotating at a speed of 1000 r.p.m. and a hot water having a temperature of 700C being applied at its inner side, said temperature exceeding the melting point of the fatty impurities, at a pressure of 1 atm (1.1 05Pa). To achieve the same degree of cleaning of the filtering surface 2 as in above-considered Example 1 it took a considerably lesser amount of hot water, all in all 36 litres, i.e. 24 litres less than while using water with a temperature of 500C.

Hence, the use of this "hot" alternative embodiment of the method allows to effect a saving in hot washing water and it can be advantageously employed on small vessels carrying limited supplies of hot water.

EXAMPLE 3 Another embodiment of the method will be exemplified by the case of cleaning of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application of a mixture of steam and water to the inner side thereof.

300 litres of the sewage having a temperature of 200C and containing an average of 650 mg/I of impurities comprising an average of 0.1 g/l of fatty impurities and 0.05 g/I of fibrous impurities were passed through the filtering surface 2. The filtering surface 2 intercepted 24 9 of fatty and 12 of fibrous impurities. Recovery of the filtering surface 2 was conducted with the surface rotating at a speed of 1000 r.p.m. and a mixture of steam and water at a pressure o 2.5 atm (2.5.1 05Pa) being applied to the inner side thereof.

At a temperature of the steam equal to 1270C, the steam-water mixture ratio amounted to 2 kg of steam per 0.8 kg of water. The washing took 21 litres of water.

This alternative embodiment of the method is particularly suitable for use on vessels provided with a centralized steam supplying system.

EXAMPLE 4 Still another embodiment of the method will be exemplified by the case of cleaning of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application of a mixture of steam and water to the inner side thereof.

The amount of sewage equal to that of Example 3 and having the same average impurities concentrations was passed through the filtering surface 2. As it took place, the filtering surface intercepted 28 g of fatty and 10 g of fibrous impurities. Recovery of the filtering surface 2 was conducted with the surface rotating at a speed of 1000 r.p.m. and a mixture of steam and water being applied at a pressure of 3 atm 3.1 05Pa to the inner side thereof, the steam had a temperature of 134 C. The steam-water mixture ratio amounted to 1 kg of steam per 0.6 kg of water. The washing took 16 litres of water.

With a rise in temperature and pressure of the steam in use, the consumption of water required for recovery of the filtering surface 2 decreases and, as a consequence, the water content of the solids 3 being removed from the sewage 1 on the filtering surface 2 also decreases.

EXAMPLE 5 Yet another embodiment of the method will be exemplified by the case of cleaning of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application to the inner side thereof hot water with addition of a detergent thereto.

300 litres of the sewage having a temperature of 20 C and containing an average of 650 mg/l of impurities comprised of an average of 0.1 g/l of fatty contaminants and an average of 0.05 g/I of fibrous impurities were passed through the filtering surface in much the same manner as described in the preceeding examples. The filtering surface intercepted 27 g of fatty and 12 g of fibrous impurities. Recovery of the filtering surface 2 was conducted with the surface rotating at a speed of 1000 r.p.m. and hot water at a temperature of 500C and a pressure of 1 atm (1.1O"Pa) with a detergent of disodium monoalkylsulfosuccinate added thereto in a concentration of 0.5% being applied to the inner side thereof.

To achieve the same degree of cleaning of the filtering surface 2 as in Example lit took a significantly lesser amount of hot water, all in all 20 litres, i.e. 40 litres less than with the use of hot water alone at a temperature of 50 C.

The above-stated alternative embodiment can be well adapted for use on small vessels with restricted supplies of hot water and further compulsory treatment and decontamination of the sewage passed through the filtering surface.

It is should be noted that other surface-active materials can be also employed as detergents.

EXAMPLE 6 Yet another embodiment of the method will be exemplified by the case of cleaning of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application to the inner side thereof of hot water with addition of a detergent thereto. Both sewage treatment and filtering surface cleaning conditions were the same as in Example 4, but the water had a temperature of 70 C.

To achieve the same degree of cleaning of the filtering surface 2 as in Example 4 considered hereinabove a total of 14 litres was all that it took, i.e.

a lesser amount of hot water as compared to the case in question.

Thus, when available supplies of water abroad are in limited amounts it is advisable in using this alternative embodiment of the method to raise its temperature.

EXAMPLE 7 A still further embodiment of the method will be exemplified by the case of cleaning of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application of steam to the inner side thereof.

Similarly to the preceeding examples, 300 litres of the sewage having a temperature of 20 C and containing an average of 650 mg/l of impurities comprised of an average of 0.1 g/l of fatty impurities and an average of 0.05 g/l of fibrous impurities were passed through the filtering surface. The filtering surface 2 intercepted 24 g of fatty and 13 g of fibrous impurities. Recovery of the filtering surface 2 was conducted with the latter rotating at a speed of 1000 r.p.m. and steam at a temperature of 1 20 C and a pressure of 2 atm being applied to the inner side thereof.

To achieve the same degree of cleaning of the filtering surface 2 as in the above-considered examples a total of 2.8 litres of water was all that penetrated as a result of steam condensation into the impurities removed from the filtering surface.

Upon further processing of the impurities, for instance, while treating them thermally, the reduced water concentration of the impurities attained through the use of steam for filtering surface cleaning enables to essentially curtail the consumption of fuel expanded for thermal treatment.

It is advisable to employ this alternative embodiment of the method on vessels provided with steam generating sources.

Elevation in the temperature of steam as well as in the pressure under which the steam is being applied to the filtering surface 2 leads to the improved filtering surface cleaning effect, but the choice of these parameters should be appropriately matched with technical expedience and the nature of depositions on the filtering surface.

EXAMPLE 8 To exemplify still another embodiment of the method, consider now the case of clening of the filtering surface soiled with fatty and fibrous depositions by means of centrifugal forces combined with the application of hot air to the inner side thereof.

Similarly to the preceeding examples, 300 litres of the sewage having a temperature of 20 C and containing an average of 650 mg/l of impurities comprised of an average of 0.1 g/l of fatty impurities and an average of 0.05 g/l of fibrous impurities were passed through the filtering surface 2. The filtering surface intercepted 24 g of fatty and 13 g of fibrous contaminants. Recovery of the filtering surface 2 was conducted with the latter rotating at a speed of 1000 r.p.m. and hot air at a temperature of 250 C and a pressure of 2 atm (2.1 08pea) being applied to the inner side thereof.

To achieve the same degree of cleaning of the filtering surface 2 as in the above-considered examples, the water content of the impurities removed from the filtering surface 2 was reduced by 20% (initial water content of the impurities amounted to 92-98%).

Upon further processing of the impurities, for instance, while treating them thermally, drying of the impurities in the process of their removal from the filtering surface 2 allows to gain a substantial decrease in the consumption of fuel expended for thermal treatment.

It is advisable to employ this alternative embodiment of the method whenever there is an incinerator for solids incineration available in the proximity of the sewage treatment apparatus, which considerably simplifies solids transporation to the incinerator, and also when the vessel is provided with a hot gas source, for instance, on oil-carrying vessels equippped with inert gas generators.

From the above-presented specific embodiments of the method of the present invention disclosed in the specification thereof it becomes apparent to those skilled in the art that the objects of the invention can be readily fulfilled within the scope defined by the appended claims. However, it is not intended that the invention be limited by any of the particularly embodiments thereof described and given hereinabove solely for the purpose of illustration.

In practicing the method it is also perfectly evident that further inessential modifications and variations may suggest themselves for introduction into operating conditions, parameters and specific means thereof without substantially departing from the spirit of the invention.

For the sake of better lucidity the aboveconsidered particular embodiments of the invention have been described with recourse being made to the narrow specialized nomenclature, but is to be understood that each of the terms thereof is meant to cover all available equivalent elements functioning in a similar manner and used to accomplish the same objects as those of the present invention.

An apparatus for practicing the above method of sewage treatment as described hereinabove comprises a unit 4 (FIG. 4) for separating the solids 3 from the sewage 1 connected by way of a pipe line 16 to a tank 6 for accumulating and averaging the solids separated by the unit4, an electrochemical treatment unit 8 connected by way of a pressure pipe line 17 to the sewage accumulating and averaging tank 6. Between the sewage accumulating and averaging tank 6 and the averaged sewage treatment unit 8 there is provided a pump 18 for pumping averaged sewage from the sewage accumulating and averaging tank 6 to the averaged sewage electrochemical treatment unit 8. The average sewage electrochemical treatment unit 8 by way of a pipe line 19 is connected to a tank 20 for holding the tre- ated water 14. The tank 20 for holding the treated water 14 is connected by way of a pipe line 21 to a pump 22 serving for pumping of the treated water overboard.

The sewage solids separating unit4 is connected by way of a pipe line 23 to a pump 24 sewing for removal of the mixture 13 of the solids 3 and the impurities 12 extracted in the process of electrochemical treatment from the sewage solids separating unit 4.

The pump 24 by way of the pipe line 23 and pipe lines 25 and 26 is connected to the separated sewage accumulating and averaging tank 6 by way of the pipe line 23,25 and pipe lines 27,28,29 and 30 is connected to the averaged sewage electrochemical treatment unit 8 and by way of the pipe lines 23,25, 27 and a pipe line 31 to the sewage solids separating unit 4.

Valves 32 and 33 are provided for drying of the averaged sewage electrochemical treatment unit 8; a valve 34 is provided for drying of the sewage accumulating and averaging tank 6 and a valve 35 is provided for drying of the sewage solids separating unit4. When required, a crushed 36 is incorporated between the sewage solids separating unit 4 and the pump 24. Connection and disconnection of the crusher 36 is accomplished by a valve 37. The sewage accumulating and averaging tank 6 is furnished with a recycle pipe line 38 designed for washing away of the deposits formed in the sewage accumulating and averaging tank and for controlling the rate of average sewage feeding to the electrochemical treatment unit 8.The averaged sewage electrochemical treatment unit 8 is connected by way of a pipe line 39 to a tank 40 arranged in the sewage solids separating unit 4 and placed under rarefaction developed by a ventilator 10. The tank 40 is provided with a sleeve 41 having its lower end submerged in the liquid constantly located in the lower portion of the sewage solids separating unit 4 and penetrating thereto in the process of solids separation and together with the contaminants isolated in the process of electrochemical treatment. Furth ermore, the tank 40 is provided with a hole42 serving for ventilation of the sewage solids separating unit 4. Within the sewage solids separating unit 4 there is an inlet sleeve 43 under whose outlet hole is located a taper filter 45 mounted on a shaft 44.Under the base of the taper filter 45 is provided a reception funnel 46 for separated sewage (a drive of the taper filter 45 is not shown in the drawing).

The sewage solids separating unit 4 (FIGs. 5 and 6), the averaged sewage electrochemical treatment unit 8, the sewage accumulating and averaging tank 6 (FIG. 5), the tank 20 (FIGS. and 6) for holding the treated liquid are compact in size and mounted on a common platform 47. At the centre of the averaged sewage electrochemical treatment unit 8 (FIG. 5) there is provided a hole 48 serving for air intake.

There may be provided more such air intake holes 48. The sleeve 43 (FIGS. 5 and 6) connects the apparatus to the source of marine sewage (not shown in the drawing). A power pack 49 is disposed on the housing of the sewage solids separating unit.

The averaged sewage electrochemical treatment unit 8 is disposed on the tanks 6 (FIG. 5) and 20 (FIGs.

5 and 6). The sewage solids separating unit 4 is disposed on the platform 47. Such an arrangement of the tanks 6 and 20 and of the units 4 and 8 of the apparatus has been found beneficial for its improved structural rigidity and reduced overall dimensions.

Along the upper edge of the averaged sewage electrochemical treatment unit 8 there is mounted an air-operated device 50 (FIGS. 4, 5 and 6) for removal of the foam generated in the averaged sewage electrochemical treatment unit 8. The ventilator 10 has an electric motor drive 51 (FIG. 5), the pump 24 is driven by an electric motor 52, the pump 18, from an electric motor 53 and the pump 22, from an electric motor 54.

The sewage solids separating unit 4, the sewage accumulating and averaging tank 6 and the averaged sewage electrochemical treatment unit 8 are provided with bottoms having a slant towards the pipe lines 31 (FIGS. 4 and 5), 26,29, and 30 respectively.

The averaged sewage electrochemical treatment unit 8 (FIG. 7) is manufactured in the form of a sectional tank 55 divided by partitions 56, 57 and 58 (FIG. 8) At the centre of the sectional tank 55 (FIG. 7) there is arranged a treated liquid receiver pipe 59 positioned vertically and connected hydraulically to a liquid outlet means 60 made in the form of a discharge pipe, and to a section 61 of the tank 55 serving for final sewage disinfection. The upper end of the treated liquid receiver pipe 59 is disposed so as to protrude above the liquid level in the tank 55.

A section 62 accommodates active aluminium electrodes 63, a section 64 incorporates inert graphite electrodes 65, the section 61 includes inert graphite electrodes 66. The electrodes 63, 65 and 66 are connected in parallel to the power pack 49 (FIGS.

5 and 6) so that with a break in the electrodes feeding circuit or with electrodes damage in any of the sections of the electrochemical treatment unit 8 the current continues to be maintained between the electrodes in other sections.

Furthermore, to prevent the passivation of the electrodes by oxides and insoluble compounds generated by electrolysis there is provided an automatic change in the polarity of the electrodes.

A section 67 (FIG. 7) is designed for removal from the sewage of gas bubbles and coagulated colloid impurities.

The air-operated device 50 incorporates an air duct 68 disposed along the upper edge of the averaged sewage electrochemical assembly 8 and provided with air outlet holes 69 arranged on the surfaces of the air duct 68 facing the inside of the electrochemical treatment unit 8.

To ensure the uniform discharge of the air from the holes 69 the upper portion of the air duct 68 is provided with blinds 70.

The walls of the air duct 68 also have a hole 48 with a sleeve 71 serving for atmospheric air intake.

Under the sleeve 71 inside the air duct 68 there is erected a partition 72 (FIG. 8) which serves for the uniform distribution of the air between the two halves of the air duct 68. At the corners of the air duct 68 there are mounted splitters 73 designed for lowering the turbulence of air flows and for eliminating stagnation zones at the corners of the air duct 68.

Behind each of the air outlet holes 69 there are provided cutoffs 74 which are designed for cutting off and directing a portion of the air towards the centre of the space defined by the air duct 68, the surface of the liquid located in the electrochemical treatment unit 8 and the cover (not shown in the drawing) of this unit. The air duct 68 on the side opposite to the sleeve 71 has a partition 75 which serves for the prevention of mixing of the air counterflows in the air duct 68. The partition 72 and 75 also preclude the overflow of the liquid treated upon tilting of the apparatus from one half of the air duct 68 to the other.

At the centre of the electrochemical treatment unit 8 above the upper boundary of the liquid level therein is mounted a foam receiver 76 (FIG. 7) connected to the ventilator 10 (FIGS. 4, and 6) providing rarefaction in the tank 40 disposed in the sewage solids separating unit 4, in the foam receiver 76 (FIG. 7) and in the space confined by the surface of the liquid located in the electrochemical treatment unit 8, by the cover of the above-mentioned assembly and the air duct 68.The foam including impurities suspended therein is passed from the foam receiver 76 by way of a pipe line 77 and further via the pipe line 39 (FIGS.4,5 and 6) to the tank 40, wherefrom it is supplied to the sewage solids separating unit 4 in which the foam is mixed with the solids and removed from this unit by means of the pump 24. In the space between the outer surface of the foam receiver 76 (FIG. 8) and the inner surface of the air duct 68 there are erected vertical partitions 78 serving for dividing said space into sections, the partitions 78 being disposed so that the lower edges thereof are submerged in the liquid located in the average sewage electrochemical treatment unit 8, whereas the upper edges thereof reach, at least, the upper edge of the air duct 68 and reach the cover of the averaged sewage electrochemical unit 8.These partitions 78 can be as well arranged above the upper edge of the air duct 68 and reach the cover of the averaged sewage electrochemical treatment unit 8. The partitions 78, by dividing into sections the space defined by the air duct and the surface of the liquid located in the averaged sewage electrochemical treatment unit 8, prevent mixing of the air flows being directed from each of the halves of the air duct 68 toward the centre of this space. The abovementioned partitions 78 also assist in transferring the foam to the receiver 76.With a view to the prevention of moving of the air flows above or below the partitions 78, the partitions have their lower edge submerged in the liquid available in the averaged sewage electrochemical treatment unit 8, while their upper edge is disposed at least in line with the upper edge of the air duct 68 (in cases when the cover of the averaged sewage electrochemical unit8 is adjacent to the upper edge of the air duct 68). If the cover of the averaged sewage electrochemical treatment unit 8 has a clearance between the cover and the upper edge of the air duct 68, then the upper edge of the partitions 78 must be in contact with the cover of the averaged sewage electrochemical treatment unit 8.

The electrochemical treatment unit 8 is provided with the pressure pipe line 17 (FIGS. and 8) for feeding thereto of the averaged sewage. The withdrawal of treated and decontaminated sewage is effected from the section 61 (FIG. 7) by way of a double bottom 79 (FIGS. 7 and 9), a hole 80 in the treated liquid receiver pipe 59, the liquid output means 60 made in the form of a discharge pipe and via the pipe line 19 (FIG. 5) to the treated sewage holding tank 20.

Connection of the section 61 to the treated liquid receiver pipe can be effected through a pipe 81 (FIGS. 10 and 11).

The treated liquid output means 60 may be arranged inside the treated liquid receiver pipe 59, as shown in FIG. 12. In this case the sewage is removed through the bottom of the electrochemical treatment unit 8.

FIG. 13 shows connection of the foam receiver 76 disposed at the centre of the electrochemical treatment unit 8 above the upper boundary of the liquid level therein, to the ventilator 10 providing rarefaction in the tank 40 of the sewage solids separating assembly, in the foam receiver 76 and in the space defined by the surface of the liquid available in the electrochemical treatment unit 8, the cover of the above-mentioned unit 8 and the air duct 68. The tank 40 is provided with a partition 82 for separating foam from the air.

FIGS. 14, 15 and 16 are axonometric views of different embodiments of the air duct 68.

The air duct 68 shown in Fig. 14 is fabricated in the form of a hexagon (in plan), in FIG. 15, in the form of a circumference, in FIG. 16, in the form of a hexagon with the cylindrical electrochemical treatment unit 8.

In FIG. 17 there is shown the solids separating assembly 4 incorporating therein the taper filter 45.

The taper filter 45 having its lateral surface 83 turned back towards the apex thereof is mounted on the shaft 44 under the outlet hole of the sleeve 43 of the sewage solids separating unit 4.

The lateral surface 83 of the taper filter 45 is fabricated in the form of a smoothly interlaced mesh.

A shield 84 is mounted on the shaft 44 at the apex of the taper filter 45. Under the base of the taper filter 45 there is arranged the separated sewage reception funnel 46 with the outlet sleeve 16 connected to the tank 6, while an apron 85 made in the form of a cylinder of elastic material, e.g. rubber, is mounted coaxially to the shaft 44 at a distance from the base of the taperfilter45 exceeding the maximum size of the solids separated.

The lateral surface 83 of the taper filter 45 is turned back at an obtuse angle. The apron 85 is positioned so that the lower edge thereof reaches at least the level of the base of the taper filter 45, but it can be positioned lower than this level as well.

In the treated sewage reception funnel 46 along the upper edge thereof facing the taper base of the filter 45 is mounted an annular tube 86 with holes 87 (FIGS. 18 and 19) made on the surface of the tube facing the inside of the taper filter 45 (FIG. 17). The annulartube 86 is connected by way of a pressure regulator (not shown in the drawing) to the source (not shown in the drawing) of the medium 15 reducing the adhesion of the impurities to the filtering surface of the filter 45.

The holes 87 (FIG. 19) in the annular tube 86 can be made expanding towards the outer wall thereof or provided with conically diverging nozzles 88 (FIG 20).

The pipe 16 of the solids separating unit4 (FIG. 17) is furnished with an emergency overflow meshed sleeve 89 maintaining the apparatus in operative condition should the taper filter 45 fail. For visual checking of the lateral surface 83 of the taper filter 45 there is provided an inspection hole 90.

The sewage treatment apparatus operates as follows. Sewage from the marine sanitation equipment by way of the sleeve 43 (FIG. 4) is supplied to the taperfilter45 where large-fraction impurities (paper, cotton wool, food refuse, etc.) are removed from the sewage. The partially purified sewage is passed to the reception funnel 45 and by way of the pipe 16 is forwarded to the separated sewage accumulating and averaging tank 6.

The averaged sewage is collected in the tank 6.

When the sewage reaches a specified level, a transducer (not shown in the drawing) arranged in the tank 6 is brought to action, upon which is initiated power feed to the electrodes 63, 65, 66 (FIG. 7) and to the ventilator 10 (FIG. 4). The pump 18 pumping the averaged sewage by way of the pipe line 17 to the electrochemical treatment unit8 is actuated concurrently therewith. A part of the liquid is passed by way of the pipe line 38 back to the sewage accumulating and averaging tank 6 washing away the deposit accumulated in the tank 6, mixing the sewage therein for the purpose of averaging the physicochemical composition of the sewage and ensuring the required flow rate of the averaged sewage being directed to the electrochemical treatment unit 8 by means of recycling a part of the liquid through the pipe line 38.

By way of the pipe line 17 (FIG. 8) the sewage is fed to the lower portion of the section 62 (FIG. 7) of the electrochemical treatment unit 8. The section 62 accommodates the active aluminium electrodes 63 disposed in parallel, in the clearances between electrodes is circulated the sewage processed. As this occurs, the colloid impurities included in the sewage are coagulated under the action of the electric field and the ions of aluminium passing over to the solution underthe action of the former. This is accompanied by the process of hydrogen release on the electrodes serving as the cathodes. The hydrogen thus released forms gaseous microbubbles which are carried to the surface of the liquid by the coagulated and suspended fine-dispersion impurities generating foam on the surface of the liquid treated.

Then the liquid by-passing the partition 56 is fed from the top downwards into the section 64 incorporating a parallel set of the graphite inert electrodes 65. Upon the flow of current running through the graphite inert electrodes 65 there electrodes also generate hydrogen removing the impurities from the liquid processed by flotation. This process is attended by the release of decontaminating substances on the anodes, i.e. chlorine, hydrogen pyroxide and ozone. From the lower portion of the section 64 the liquid processed flows under the partition 58 (FIGS. 8, 9) to the section 67 (FIG. 7), where the impurities comprising the smallest hydrogen bubbles entrained by the downcoming liquid flow from the section 64 are removed from the liquid treated.

From the section 64 the liquid flows into the section 61 incorporating the graphite electrodes 66 arranged in parallel to each other. The remainder of the impurities left in the liquid treated is removed and finally decontaminated in the section 61. The finally treated liquid from the lower portion of the section 61 either under the double bottom 79 (FIGS. 7, 9 12) of by way of the pipe 81 (FIGS. 10,11) is supplied to the treated liquid receiver pipe 59 (FIG. 7) wherefrom by way of the treated liquid output means 60 made in the form of a pipe the liquid is passed via the pipe line 19 (FIGS. 4, 5, 6) to the treated liquid holding tank 20 and thence by means of the pump 22 directed along the pipe line 21 either for further use or for overboard discharging.

The withdrawal of the treated water from the electrochemical treatment unit 8 can be accomplished through the means 60 (FIG. 12) made in the form of a pipe arranged inside the treated liquid receiver tube 59. In this case the withdrawal of the sewage is accomplished through the bottom of the electrochemical treatment unit 8. Such an arrangement also enables to improve the fabrication properties of the electrochemical treatment unit 8.

Upon electrochemical treatment of the sewage, the coagulated and fine-grained impurities carried to the surface of the liquid being processed by the bubbles of electrolysis released hydrogen produce the foam layer 9 (FIGS. 1,8) on the surface of the liquid.

To remove the foam in the process of sewage electrochemical treatment, the ventilator 10 (FIGS.4,5, 6) provides rarefaction in the tank 49 (FIGS, 4, 5,6, 13) imparted by way of the pipe line 77 (FIG. 13) to the foam receiver 76 and to the space defined by the surface of the liquid located in the electrochemical treatment unit 8, by the cover of the abovementioned unit 8 and the air duct 68. As a result of the rarefaction developed, atmospheric air by way of the sleeve 71 through the hole 48 penetrates into the air duct 68, wherefrom via the holes 69 forming the direction of air counterflows it enters the foam receiver 47 entraining the foam therewith.

Captured by the flows of atmospheric air, the foam from the foam receiver 76 is passed by way of the pipe line 77 to the tank40 arranged in the solids separating unit 4. This is followed by extinguishment of the foam resulting from an abrupt variation in the rates and direction of foam and air propagation in the pipe line 77 and the tank 40. The resultant suspension is chaneled by way of the sleeve 41 to the lower portion of the sewage solids separating unit 4, wherein it is mixed with the solids separated from the sewage by the taper filter 45 (FIGS. 4,6,17).

The air and hydrogen separated from the foam by the ventilator 10 are vented to the atmosphere. The partition 82 (FIG. 13) serves for separation of the liquid drops entrapped by the air flows.

The solid impurities of the sewage intercepted on the lateral surface 83 (FIG. of the the ofthetaperfilter45 are removed therefrom by periodic rotations of the taper filter 45 from a driving means (not shown in the drawing).

To obtain a more uniform distribution of the sewage over the lateral surface 83 of the taper filter 45, the sewage is supplied to the taper apex of the filter 45, the smoothly surfaces screen 84 also promotes a still better distribution of the impurities over the lateral surface 83. Because of that the impurities are deposited on the lateral surface 83 predominantly at such a distance from the rotation axis of the taper filter 45 which enables for the centrifugal forces arising in the rotation thereof to develop a magnitude sufficient for removal of the impurities from this surface.

In order to reduce the amount of water penetrating together with the impurities into the lower portion of the solids separating unit 4, the lateral surface 83 is deflected towards the apex of the taper filter 45 at an obtuse angle for checking the sewage flowing down the lateral surface 83.

With a sharp increase in the load imposed on the taper filter 45, the water not yet filtered by the lateral surface 83 is retained by its deflected rim.

Furthermore, the impurities thus retained by the deflected lateral surface 83 are subsequently readily removed from this surface upon its recovery, which is attributable to the magnitude of a deflection angle of this surface and to the adequate distance of the impurities from the rotation axis of the taper filter 45.

The apron 85 arranged in the solids separating unit 4 serves for mitigating the speed of the solids rebounding from the lateral surface 83 in the process of sewage filtration and also in recovery of the filtering surface of the taper filter 45 by the action of centrifugal forces developed during its periodic rotations. Moreover, the above-specified apron 85 serves to prevent the solids from sticking to the walls of the solids separating unit 4 and to protect them from erosion.

Recovery of the lateral surface 83 of the taper filter 45 is performed automatically. Upon the passage of a specified amount of sewage through the lateral surface 83, level sensing devices (not shown in the drawing) positioned in the sewage accumulating and averaging tank 6 energize the drive of the shaft 44. The operational interval of the drive is preset by a time switch (not shown in the drawing). Prior to rotating the taper filter45, the medium reducing the adhesion of impurities to the filtering surface of the filter 45 is applied through the annular tube 86 to the filter inner surface. The application of this medium is interrupted at the moment when the driving means is brought to a stop.The application of the medium reducing the adhesion of impurities to the filtering surface of the taper filter 45 may be effected before the taper filter45 has commenced to rotate and be terminated at the instant when its driving means is being actuated.

The first case of applying the medium which reduces the adhesion of impurities to the filtering surface of the taper filter 45 is recommended for use when processing only black water, whereas the second case of applying this medium is recommended for use when processing all of the sewage being generated on a vessel.

When the sewage treatment apparatus is functioning in an automatic mode, a specified pressure is adopted under which the above adhesion-reducing medium is being applied to the inner surface of the taperfilter45. However, if the conditions of filtration are deteriorating due to the penetration of very large or strongly adhesive impurities to the lateral surface 83, the pressure of this medium can be considerably increased.

The medium 15 (FIG. 17) reducing the adhesion of impurities to the lateral surface 83 is applied through the hole 87 (FIG. 19) orthe nozzles 88 (FIG. 20) in the annulartube86 being made so that the jets ofthe medium effluxing therefrom overlap uniformly the entire inner surface of the taper filter 45.

The holes 87 (FIG. 19) are made in the annular tube 86 so that they expand towards the outer side thereof and thereby provide optimum hydrodynamic conditions for efflux of the medium reducing the adhesion of impurities to the filtering surface of the taper filter 45. The provision of the above-indicated holes 87 with the nozzles 88 (FIG. 20) is also conducive to this.

When performing scheduled maintenance, suspended operation of the apparatus or eliminating malfunctions, the sewage solids separating unit 4 (FIG. 4), the sewage electrochemical treatment unit 8 and the sewage accumulating and averaging tank 6 are dried up by means of the pump 24.

The above-mentioned units and tank can be dried both simultaneously and separately as well. In simultaneous drying, the valve 37 is closed while the valves 32,33, 34 and 35 are opened. In separate drying, the valve 37 is shut down while the valve associated with the respective unit is opened.

To facilitate both transportation of the solids through the piping system and destruction of these solids in a marine furnace specially designed for this purpose (incinerator) the solids are disintegrated by the crusher 36 (FIGS. 4,5,6).

The ventilator 10, apart from the functions of foam transportation and hydrogen removal, also ventilates the units and the tanks maintaining small rarefaction in the apparatus and preventing the penetration of malodours into the compartments of a vessel.

The graphs shown in FIG. 21 present apparatus performance test data acquired in a period of 90 days, wherein on the Y-axis are plotted the values of suspended substances concentrations (C) and biochemical oxygen demand (BODs), the content of chole bacteria being equal In untreated sewage to 101o#1014 pcs/l, in treated sewage to 20 pcs/l. The graph E illustrates a variation in the characteristics of the untreated sewage (curve G'- suspended substances and curve H1 - BODs).

The characteristics of the sewage processed in the apparatus of the present invention are given in the graph F, from which it is evident that the suspended substances concentration (curve G) and the BOD, (curve H) fulfill the requirements of the International Convention of 1973 for Marine Pollution Prevention.

Thus, the proposed method of and apparatus for sewage treatment can find an extensive range of application on vessels of any type and class providing an exceptidnaily high level of operational and processing efficiency.

Claims

1. A method of treatment of sewage including a number of successive stages, the initial stage comprising separating of solid components from the sewage water and collecting said solid components, the succeeding stage comprising accumulating the sewage water separated at the previous stage and averaging same over volumetric load and physicochemical composition, and further performing electrochemical treatment of a flow of the averaged sewage water with the resultant isolation of impurities and treated water, wherein aforesaid electrochemical treatment is conducted at a flow rate of the average sewage water being sufficient to produce a surface foam layer, in which air counterflows are formed thereupon by means of rarefaction provided at the sewage solids separation stage, aforesaid rarefaction acting upon the flows of air and foam so as to directthem from the peripheral areas of said foam layer towards the central portion thereof, and further onto the solids separation stage where the foam is mixed with the solid components separated from the sewage water, while the treated water is directed towards the area underlying the central portion of aforesaid foam layer and subsequently withdrawn therefrom.

2. A method set forth in Claim 1, wherein prior to mixing the foam with the solid components, the latter are separated by filtering the sewage water through a taper filtering surface, with the sewage water being supplied to the apex thereof and the solid components accumulated on the filtering surface being removed therefrom by means of centrifugal forces in combination with the action upon same of a medium reducing the adhesion of impurities to the filtering surface being applied under pressure to the inner side of said surface opposing the side onto which the sewage water is supplied.

3. A method set forth in Claim 2, wherein the application of an adhesion-reducing medium is effected upon 50-60% covering the total area of the filtering surface.

4. A method set forth in Claim 2, wherein hot water is used as an adhesion-reducing medium.

5. A method set forth in Claim 2, wherein a mixture of steam and water is used as an adhesionreducing medium.

6. A method set forth in Claim 2, wherein of water and detergents, e.g. surface-active substances is used as an adhesion-reducing medium.

7. A method set forth in Claim 2, wherein steam is used as an adhesion-reducing medium.

8. A method set forth in Claim 2, wherein hot air is used as an adhesion-reducing medium.

9. An apparatus embodying the method of Claim 1 comprising a sewage solids separation unit, a sewage accumulation and averaging tank connected by way of a pipe line to aforesaid unit, an electrochemical treatment unit containing liquid with electrodes immersed therein, provided with liquid inlet and outlet means, and connected by way of a pressure pipe line to aforesaid sewage accumulation and averaging tank, wherein the sewage solids separation unit accommodates a rarefied tank provided with a sleeve having the lower end thereof immersed in the liquid permanently available within the sewage solids separation unit, and connected by way of a pipe line to the electrochemical treatment unit provided with an air-operated device for removal of foam being generated in electrochemical treatment.

10. An apparatus set forth in Claim 9, wherein the electrochemical treatment unit is fabricated in the form of a sectional tank incorporating at the centre thereof a treated liquid reception tube positioned vertically and connected hydraulically to the liquid output means and to a section of the tank designed for final sewage water decontamination, the upper end of the treated liquid reception tubecbeing arranged so as to project above the liquid level in aforesaid tank.

11. An apparatus set forth in Claim 9, wherein the air-operated foam removing device comprises an air duct mounted along the upper edge of the electrochemical treatment unit and provided with air outlet holes disposed on the surfaces facing the inside of the electrochemical treatment unit and with air intake holes, and also a foam receiver arranged at the centre of the electrochemical treatment unit above the upper boundary of the liquid level therein and connected to a ventilator developing rarefaction in the tank mounted in the sewage solids separation unit, in the foam receiver and in the space confined by the surface of the liquid available in the electrochemical treatment unit, the cover of aforesaid unit, and the air duct.

12. An apparatus set forth in Claim 11, wherein the space confined by the outer surface of the foam receiver and the inner surface of the air duct is provided with vertical partitions being erected for division of aforesaid space into sections.

13. An apparatus set forth in Claim 12, wherein the vertical partitions are erected so that the loweredges thereof are immersed in liquid, whereas the upper edges thereof, at least, the upper edge of the air duct.

14. An apparatus embodying the method of Claim 2, wherein the sewage solids separation unit comprises a sewage inlet sleeve, under the outlet hole of which installed on a shaft is a taper filter having the lateral surface thereof deflected towards the taper apex where a screen being adjacent thereto is mounted on aforesaid shaft, with a separated sewage reception funnel provided with an outlet sleeve being arranged below the filter taper base, whereas an apron structure made in the form of a cylinder of elastic material being arranged coaxially to the shaft at a distance from the filter taper base exceeding the maximum dimensions of the solid impurities separated.

15. An apparatus set forth in Claim 14, wherein the lateral surface of the taper filter is deflected at an obtuse angle.

16. An apparatus set forth in Claim 14, wherein the apron structure is arranged so that the lower edge thereof reaches, at least, the level of the base of the taper filter.

17. An apparatus set forth in Claim 14, wherein in the separated sewage reception funnel along the upper edge thereof facing the tiltertaper base is mounted an annular tube provided with holes made on the surface of the tube facing the inner surface of the taper filter, and connected via a pressure reg ulator to the source of a medium reducing the adhesion of impurities to the filtering surface of the filter.

18. An apparatus set forth in Claim 17, wherein the holes provided in the annular tube are made expanding towards the outer wall thereof.

19. An apparatus set forth in Claim 17, wherein the holes provided in the annular tube are furnished with conically diverging nozzles.

20. A method of sewage treatment being carried out substantially as described hereinabove with reference to the accompanying drawings.

21. An apparatus embodying the method of sewage treatment substantially as described hereinabove with reference to the accompanying drawings.