FR2473036A1 - Reclaiming sludge from filtration plants - esp. from water treatment plants, where sludge is used as make=up water in concrete mixts. - Google Patents

Abstract

The filter is washed with rinsing water to remove solid matter, and the water is then held so that the solids settle to form a sludge, which is used as make-up water in concrete mixts. The concrete mixt. is pref. moistened with water, followed by adding the sludge to obtain a water/cement ratio (W/C) of 0.35 to 0.7. The sludge pref. contains aluminium salts and/or iron salts. Used pref. for the cleaning of filters for mains water, drinking water, or technical water. By using the filter sludge in concrete mixts., the problems of its disposal, and its pollution of the environment are avoided. The salts in the sludge may arise from materials added to the filter to increase filtration speed.

Description

 The present invention relates to the field of the protection of the environment against pollution, and particularly relates to a method of using the residue of cleaning water filtering facilities.

 This is the first time that such a process can be proposed that can be applied to the distribution of greywater, drinking water and industrial wastewater treatment plants, both surface and bottom sources, whose mainly contain aluminum and iron salts, respectively. On the other hand, the present invention can advantageously be used in the building materials industry for the manufacture of concrete.

 From the days when ancient Egyptians made use of potash alums in order to clarify bedrock surface springs, it became necessary to remove the residue observed in barrels after evacuation of the water decanted. However, the amount of this residue did not yet pose serious problems for humanity.

 Subsequently, slow water filters in which the water was purified by biological processes in the surface film appeared in the water purification technology, the regeneration of the filter consisting in removing the thick filter layer from the water. at 10 mm.

 Since this regeneration process did not involve the use of cleaning water, the problem of residues did not arise yet.

 With the advent of rapid filtration, we began to subject the filter load, having retained, during filtering, the various impurities, a regeneration by an updraft of water, which created a problem of water treatment cleaning and, above all, the treatment and use of waste water residues.

 According to the current water purification technology, a water treatment plant with a capacity of 1000000 m3 per day consumes about 50000 m3 / day of cleaning water.

 These cleaning waters contain nearly 2500 m3 of residues.

 Most of the water supply plants in the various countries of the world drain wastewater, with the residue they contain, into nearby water basins, which are often the same as those used as water sources. water. This causes serious environmental pollution, especially in the case where the water plants are cascaded along the banks of large rivers and when the downstream station not only purifies the water but also a significant percentage of the residue released by the previous station.

 Less frequently, the cleaning water is decanted and is either recycled in the purification process or used, adding a certain percentage of pure water, to wash the filters.

 Currently, there is a fairly large number of processes for treating the wastewater residue.

 As a general rule, wastewater residues are thickened by decanting them for several days, filtering them with vacuum filtrates, or centrifuging them.

 However, the high specific resistance of the residue does not remove the moisture and, consequently, its thickening, which makes its filtration and centrifugation inefficient.

 For the same reason, current efforts to prevent environmental pollution from wastewater residues include reducing the volume of the residue by subjecting it to thermal drying or freezing.

 The freezing of the residue, as well as its thermal drying, make it possible to reduce by several tens of times the volume of the residue and to raise its concentration at the same time.

 It is known in particular a method for treating the wastewater residue, described in US Pat. No. 3,720,608, consisting in dehydrating the residues by means of thermal drying.

 Also proposed in a study published in the American journal "Water and Sewage Works", Vol 112, No. 11, 1965, pp 401-406, a method of treating the wastewater residue, which consists in dehydrating the residue by means of a heat treatment preceded by the freezing and deicing of said residue for the destruction of its structure and, thereby, the increase in the efficiency of dehydration.

 There is furthermore known a method of treating residues described in the American journal "AWWA", vol. 61, No. 10, 1966, pp. 541-566, according to which the residue is dehydrated by freezing followed by vacuum filtration.

 All the residue treatment methods mentioned above make it possible to reduce the volume of the residue by several tens of times and at the same time to increase its concentration. However, all these processes are extremely difficult, since they require the use of specialized equipment and consume a lot of energy.

In addition, they do not solve the problems of environmental protection against pollution by residues, since a dehydrated residue by any process is always transported to a roadway where it is dissolved by rain, meltwater and floodwater and re-enters the water basins and aquifers.

 In this way, despite a significant increase in the cost of waste treatment processes, which in some cases is higher than the cost of the treatment of greywater and drinking water, current technology does not prevent the pollution of the wastewater. environment by wastewater residues that have never been used.

 Only the use of cleaning water or the residue contained therein, from this point of view, resolves in a radical way the problem of the protection of the environment so that it complies with the requirements imposed by maintaining the ecological balance.

 Although the problem of environmental protection against wastewater pollution from wastewater has long been a problem, it is not solved at present because of the lack of processes for using such waste.

 The present invention therefore relates to a method of using the wastewater residue, the implementation of which would make it possible to use said residue in a sufficiently effective manner and to avoid environmental pollution by such residues.

 For this purpose, there is provided a method of using the residue, obtained by decantation, of the cleaning water of a filtering installation, in which according to the invention, the residue of the cleaning water is incorporated in a mixture for the preparation of concrete as a mixing agent.

 The incorporation of the wastewater residue in said mixtures makes it possible, for the first time in the art, to use said residue and prevent it from polluting the environment.

It is useful, if the residue of the cleaning water contains mainly aluminum salts, that the amount of residue introduced into the concrete preparation mixture is chosen so as to ensure a water / cement ratio within the limits of 0, 35 to 0.70, said residue being incorporated into a mixture of previously moistened concrete
Incorporation of such amounts of residue, essentially containing aluminum salts, into a pre-moistened concrete preparation mixture, in addition to allowing it to be used and thereby preventing environmental pollution, present the advantage of allowing to obtain a concrete which, by its resistance characteristics, corresponds to that which is strained with tap water, the incorporation of the residue in quantities ensuring a water / cement ratio lower than 0.35 significantly affects the strength characteristics of the concrete, due to insufficient humidification of the concrete mix, and complicates the compaction process of the concrete.

Incorporation of the residue in amounts that provide a water / cement ratio greater than 0.7 at night adversely affects the strength characteristics of the concrete due to excessive humidification of the mixture. The latter must be submitted beforehand to humidification, otherwise the aluminum salts can destroy the crystalline structure of the concrete formed.

 It is also useful, if the residue of the cleaning water contains mainly iron salts, it is added to the concrete preparation mixture in amounts providing a water / cement ratio ranging from 0.35 to 0.70.

 Incorporation of such amounts of residue containing essentially iron salts not only makes it possible to use said residue and thereby prevent pollution of the environment, but also has the advantage of allowing a concrete to be obtained. having higher strength characteristics than concrete tempered with tap water. The achievement of these high strength characteristics of the concrete is due not to the increase of its weight, but to the creation of stronger structures due to the interaction between the precipitates containing iron and the cement. addition of residues in quantities providing a water / cement ratio of less than 0.35, seriously affects the strength characteristics of the concrete, given the insufficient humidification of the concrete mix, and complicates the concrete compaction process. The introduction of the residue in amounts providing a water / cement ratio greater than 0.7 also impairs the concrete's strength characteristics as a result of excessive wetness of the concrete mix.

 The invention will be better understood and other objects, details and advantages thereof will appear better in the light of the explanatory description, which follows, preferred modes and non-limiting implementation of the method, object of the invention.

 The method of using the residue, obtained by decanting the cleaning water of the filtering installations, comprises incorporating said residue into a mixture of concrete preparation as a mixing agent.

Said residue of cleaning water coming from surface sources, when it contains mainly aluminum salts, is incorporated in quantities providing a water / cement ratio of between 0.35 and 0.7, said mixture being moistened before introducing said residue. As for the residue of cleaning water from underground sources, which contains mainly iron salts, it is added in quantities ensuring a water / cement ratio between 0.35 and 0.7.

On an experimental basis, a dry mixture of concrete preparation was prepared, the composition of which was the same in all the tests. To prepare the mixture, the following materials were used: Portland cement type 100 passed through a sieve of 0.9 mm quartz sand quartz size of 0.14 to 5 mm, containing up to 0 , 5, harmful impurities; broken granite with particle sizes of 5 to 30 mm, containing up to 0.5% of harmful impurities
The dry mixture was prepared in a room at a temperature of 18 to 200C. Before preparing the mixture the aggregates were subjected to a treatment in a drying oven at a temperature of 1050C until a constant weight was obtained.

 The components were dosed using a scale, with a dosing accuracy of up to 1%. The dry mixture was prepared as follows. In a weighed quantity of sand, cement was introduced according to the calculations, the mixture thus obtained was stirred until a homogeneous color was obtained, then coarse aggregate was added and the whole stirring was carried out. dry mixture until it is distributed evenly throughout the mass.

 The weight ratio of cement, sand and broken granite in the dry mixture thus prepared was 1: 2: 3.

 Two series of tests were conducted. In the first series of tests, a pre-wetted concrete mix was tempered using a cleaning water residue containing aluminum salts.

 In the second series, a dry mix was run using a cleaning water residue containing iron salts.

 To make the samples, the following procedure was followed: The mixture was thoroughly stirred until the necessary homogeneity was obtained. The duration of the brewing (from the moment when the addition of the gassing agent) was from 1 to 5 minutes.

 As a control, a mixture was mixed with tap water. In all tests, concrete cubes with dimensions of 100 x 100 x 100 mm were manufactured.

 The samples were made as follows.

 The freshly prepared concrete mix was poured into metal molds and installed on a vibrating table with oscillations of 2800 per minute. For mixtures in which the water / cement ratio was less than 0.45, vibrocharging was applied by vibrocharging by subjecting the surface to a specific pressure of 50 g / cm 2. Upon vibroteration of the completed concrete mix, the remnants of the mixture from the mold surface were removed by means of a steel ruler and the exposed top surface of the mixture was smoothed by trowel. The samples thus prepared were then held in a normal curing chamber at a temperature of 20 to 250 ° C and a relative humidity of 90 to 95%.

 When testing concrete samples, the main criteria adopted were exterior appearance and compressive strength.

 During the external examination of the samples, the surface condition, the color, the humidity, the presence of cracks and voids were checked. The samples from each series were then subjected to compressive strength tests on a hydraulic press after 7, 28 and 365 days.

 For the sake of clarity, concrete but non-limiting examples of implementation of the method which is the subject of the invention are described below.

Example 1
A dry mixture of concrete preparation was moistened with tap water until a water / cement ratio of 0.3 was reached, and after thorough stirring, a residue of the water from the cleaning plant was introduced. filtering, containing aluminum hydroxide. When the concrete is made with a water / cement ratio of less than 0.35, there is a noticeable reduction in the strength of the concrete, due to insufficient moisture in the mixture, and a complication of the concrete compaction process.

 The amount of incorporated residue was chosen so that the total amount of water added during mixing in the mixture was 0.35 0.40, respectively; 0.50; 0,60-; 0.70. The manufacture of the mixture with a water ratio of more than 0.7 causes a decrease in the strength characteristics of the concrete prepared from such a superhumidified mixture.

The composition of the residue incorporated in the concrete was characterized by the following data
Humidity 99.5%
Solid phase content 0.5 96
Density of the residue 2.35 g / cm3
Allium content reported to
Al2O3 after calcination 21.45%
Iron content reported at Fe203
after calcination 0.24 No
Hard salt content reported in
CaO + MgO 0.79 5 '
(salts causing hardness of water) 15,16 5 '
sulphate content
Chloride content 5.27 5 '
Silicon oxide content
reported to SiO2 7.39%
Organic impurity content 50.7%
For each of the water / cement ratios, a series of samples, nine in number, were prepared.

 The results of the compressive strength tests are given in Table 1. Table 2 compares the results of the compressive strength tests for the control samples mixed with tap water.

 As can be seen from the comparison of Tables 1 and 2, the concrete tempered with the residue of cleaning water containing aluminum salts, with a water / cement ratio within the limits of 0.35 to 0.70, corresponds, by its characteristics of resistance, to that which is wasted with tap water.

Example 2
A dry mixture of concrete was mixed with a wastewater residue containing iron salts.

 Concrete production with a water / cement ratio of less than 0.35 compromises the strength of the concrete due to insufficient moisture in the concrete mix and the complication of the concrete settling process. The amount of incorporated residue was chosen so that the amount of water added during the mixing of the mixture is-respectively 0.35; 0.40; 0.50 0.60; 0.70. When the mixture is manufactured with a water / cement ratio higher than 0.7, there is a reduction in the strength characteristics of the concrete prepared from such a superhumidified mixture.

 The composition of the residue was characterized by the following data.

Humidity 99.3 96
Density of dry residue 2.7 g / cm2
Solid phase content 0.7 46
Iron content reported to
Fe203 after calcination 84 9s
Hard salt content reported
at CaO + MgO 15.1%
Content of organic impurities
(humines) 0.63%
Content of non-impurities
identified 0.2 46
For each of the water / cement ratios, a series of samples, nine in number, were prepared. The results of the compressive strength tests are given in Table 3.

 By comparing Tables 2 and 3 it can be seen that the concrete tempered by wastewater residue containing mainly iron salts has higher strength characteristics. These strength characteristics are obtained not because of the increased weight of the samples, but due to the creation of higher strength structures as a result of the interaction between the iron-containing residue and the cement, whereas in the processes Known for use in the manufacture of high-strength concrete, the increase in strength is due to the incorporation into the concrete of high-strength aggregates (magnetite, hematite, waste or "scrap") of high unit weight.

 Consequently, the implementation of the method, subject of the invention, providing for the use of wastewater residue containing iron oxides for spoiling concrete, makes it possible not only to use said residue, but also to manufacture a high strength concrete without increasing its weight.

 The application examples described above demonstrate the possibility of achieving all the objects and advantages of the present invention within the scope of the invention defined by the claims. it is also obvious that modifications can be made to the various operations of the proposed method, without departing from the scope of the invention.

 The advantages of the present invention are that, for the first time in the art, a method is proposed for using the wastewater residue and thereby avoiding environmental pollution.

In addition, the use which is thus made of said residue is sufficiently effective. The concrete that is made by mixing with the residue of cleaning water containing mainly aluminum salts is similar in its resistance characteristics to conventional concrete mixed with tap water. The concrete that is made by mixing with the wastewater residue, which contains mainly iron salts, has higher strength characteristics than conventional concrete mixed with tap water, and is similar to special high-strength concretes, while having a lower specific weight than the latter. The implementation of the method, object of the invention, is very inexpensive because it does not require any specialized equipment.

Of course, the invention is not limited to the embodiments described which have been given by way of example. In particular, it includes all means constituting technical equivalents of the means described and their combinations if they are executed according to its spirit and implemented in the context of the protection as claimed. TABLE 1

n <SEP> of <SEP> the <SEP> report <SEP> aspect <SEP> Resistance <SEP> to <SEP> the <SEP> compression,
<tb> series <SEP> water / cement <SEP> outside <SEP> 7 <SEP> Days <SEP> 28 <SEP> Days <SEP> 365 <SEP> Days
<tb><SEP> Values <SEP> Value <SEP> Values <SEP> Value <SEP> Values <SEP> Value
<tb><SEP> average particle size <SEP> average <SEP> particle size <SEP> average particle size <SEP>
<tb><SEP> lières <SEP> lières <SEP> lières
<tb><SEP> 1 <SEP> 0.35 <SEP> Surface <SEP> 256 <SEP> 259 <SEP> 324 <SEP> 328 <SEP> 363 <SEP> 369
<tb><SEP> Smooth, <SEP> 259 <SEP> 305 <SEP> 383
<tb><SEP> Color <SEP> 261 <SEP> 358 <SEP> 362
<tb><SEP> gray
<SEP> clear
<tb><SEP> 2 <SEP> 0.40 <SEP>"<SEP>"<SEP> 237 <SEP> 254 <SEP> 391 <SE> 338 <SEP> 352 <SEP> 354
<tb><SEP> 270 <SEP> 340 <SEP> 335
<tb><SEP> 256 <SEP> 342 <SEP> 376
<tb><SEP> 3 <SEP> 0.50 <SEP>"<SEP>"<SEP> 153 <SEP> 154 <SEP> 248 <SEP> 253 <SEP> 252 <SEP> 253
<tb><SEP> 151 <SEP> 250 <SEP> 244
<tb><SEP> 157 <SEP> 262 <SEP> 263
<tb><SEP> 4 <SEP> 0.60 <SEP> Surface <SEP> 105 <SEP> 103 <SEP> 167 <SEP> 177 <SEP> 218 <SEP> 223
<tb><SEP> mate, <SEP> 80 <SEQ> 176 <SEP> 226
<tb><SEP> color <SEP> 124 <SEP> 188 <SEP> 224
<tb><SEP> gray
<tb><SEP> 5 <SEP> 0.70 <SEP> Surface <SEP> mate, <SEP> 81 <SEP> 76 <SEP> 111 <SEP> 103 <SEP> 131 <SEP> 132
<tb><SEP> color <SEP> gray <SEP> 71 <SEP> 101 <SEP> 127
<tb><SEP> with <SEP> of <SEP> ta- <SEP> 77 <SEP> 97 <SEP> 139
<tb><SEP> ches <SEP> brunettes
<tb> TABLE 2

n <SEP> of <SEP> the <SEP> report <SEP> aspect <SEP> Resistance <SEP> to <SEP> the <SEP> compression, <SEP> kg / cm
<tb> series <SEP> water / cement <SEP> outside <SEP> 7 <SEP> Days <SEP> 28 <SEP> Days <SEP> 365 <SEP> Days
<tb><SEP> Values <SEP> Value <SEP> Values <SEP> Value <SEP> Values <SEP> Value
<tb><SEP> average particle size <SEP> average <SEP> particle size <SEP> average particle size <SEP>
<tb><SEP> lières <SEP> lières <SEP> lières
<tb><SEP> 1 <SEP> 0.35 <SEP> Surface <SEP> 247 <SEP> 251 <SEP> 331 <SEP> 336 <SEP> 372 <SEP> 366
<tb><SEP> smooth, <SEP> 265 <SEP> 329 <SEP> 357
<tb><SEP> color <SEP> 250 <SEP> 348 <SEP> 373
<tb><SEP> gray
<SEP> clear
<tb><SEP> 2 <SEP> 0.40 <SEP>"<SEP>"<SEP> 229 <SEP> 237 <SEP> 338 <SEP> 333 <SEP> 381 <SEP> 360
<tb><SEP> 236 <SEP> 286 <SEP> 370
<tb><SEP> 246 <SEP> 396 <SEP> 320
<tb><SEP> 3 <SEP> 0.50 <SEP>"<SEP>"<SEP> 145 <SEP> 158 <SEP> 232 <SEP> 251 <SEP> 231 <SEP> 259
<tb><SEP> 152 <SEP> 250 <SEP> 252
<tb><SEP> 176 <SEP> 270 <SEP> 275
<tb><SEP> 4 <SEP> 0.60 <SEP> Surface <SEP> mate <SEP> 101 <SEP> 98 <SEP> 179 <SEP> 185 <SEP> 228 <SEP> 228
<tb><SEP> color <SEP> 102 <SEP> 196 <SEP> 230
<tb><SEP> gray <SEP> 92 <SEP> 180 <SEP> 220
<tb><SEP> 5 <SEP> 0.70 <SEP>"<SEP>"<SEP> 83 <SEP> 74 <SEP> 101 <SEP> 108 <SEP> 125 <SEP> 137
<tb><SEP> 75 <SEP> 113 <SEP> 138
<tb><SEP> 63 <SEP> 109 <SEP> 149
<tb> TABLE 3

n <SEP> of <SEP> the <SEP> report <SEP> aspect <SEP> Resistance <SEP> to <SEP> the <SEP> compression, <SEP> kg / cm
<tb> series <SEP> water / cement <SEP> outside <SEP> 7 <SEP> Days <SEP> 28 <SEP> Days <SEP> 365 <SEP> Days
<tb><SEP> Values <SEP> Value <SEP> Values <SEP> Value <SEP> Values <SEP> Value
<tb><SEP> average particle size <SEP> average <SEP> particle size <SEP> average particle size <SEP>
<tb><SEP> lières <SEP> lières <SEP> lières
<tb><SEP> 1 <SEP> 0.35 <SEP> Surface <SEP> 235 <SEP> 241 <SEP> 334 <SEP> 327 <SEP> 400 <SEP> 409
<tb><SEP> smooth, <SEP> 247 <SEP> 327 <SEP> 411
<tb><SEP> color <SEP> 241 <SEP> 320 <SEP> 415
<tb><SEP> gray
<SEP> clear
<tb><SEP> 2 <SEP> 0.40 <SEP>"<SEP>"<SEP> 260 <SEP> 236 <SEP> 343 <SEP> 330 <SEP> 401 <SEP> 413
<tb><SEP> 232 <SEP> 314 <SEP> 422
<tb><SEP> 220 <SEP> 332 <SEP> 416
<tb><SEP> 3 <SEP> 0.50 <SEP> Surface <SEP> 170 <SEP> 162 <SEP> 253 <SEP> 267 <SEP> 275 <SEP> 301
<tb><SEP> smooth, <SEP> 156 <SEP> 260 <SEP> 280
<tb><SEP> Color <SEP> 160 <SEP> 290 <SEP> 348
<tb><SEP> brown
<tb><SEP> clear
<tb><SEP> 4 <SEP> 0.60 <SEP>"<SEP>"<SEP> 113 <SEP> 124 <SEP> 196 <SEP> 203 <SEP> 268 <SEP> 277
<tb><SEP> 120 <SEP> 203 <SEP> 278
<tb><SEP> 138 <SEP> 210 <SEP> 286
<tb><SEP> 5 <SEP> 0.70 <SEP> Surface <SEP> mate, <SEP> 61 <SEP> 69 <SEP> 105 <SEP> 104 <SEP> 151 <SEP> 144
<tb><SEP> color <SEP> 82 <SEP> 107 <SEP> 138
<tb><SEP> brown <SEP> 64 <SEP> 101 <SEP> 143
<tb><SEP> clear
<Tb>

Claims (3)

 1.Process of using the residue of the cleaning water of filtration plants obtained by decantation, characterized in that incorporates the wastewater residue in a mixture for the preparation of concrete as a mixing agent.  2. Method according to claim 1, characterized in that, in the case of a residue containing substantially aluminum salts, the amount of residue to be introduced into the concrete preparation mixture is chosen so that the ratio water / cement in said mixture is within the range of 0.35 to 0.70, said mixture being moistened prior to introduction of said residue.  3. Process according to claim 1, characterized in that in the case of a residue containing mainly iron salts, the amount of residue to be introduced into the concrete preparation mixture is chosen so that the water / cement ratio in said mixture is within the range of 0.35 to 0.70.  4o Concrete, characterized in that it is obtained by application of the method forming the subject of one of claims 1, 2 and 3.