IMPROVED PROCESS AND EQUIPMENT FOR PURIFYING TREATMENT AND UTILIZATION OF WASTE-WATERS FROM THE DAIRY INDUSTRY

Abstract: Process for the purifying treatment of waste-waters from the dairy industry through the coagulation of the fat and protein content by treatment with chemicals and through the removal, in given case through the re-processing of economic utilization purpose of the forming waste sludge as well as an equipment for the effectuation of the process. The essence of the process consists in that the waste-water is destabilized for a definitive time in presence of a suitable bacterial flora between the formation and the chemical treatment and the destabilization is accelerated expediently by measures augmenting the contacting surface, in given case increasing the intensity of the contacting. The forming waste sludge or its solid content can be utilized by being burnt in furnace, being added to fodder or my ameliorating fertilization. The pre-purified waste-water can be advantageously after-purified by additionally applying an aero-biological (active-sludge) procedural phase.

Description: _ _ IMPROVED PROCESS AND EQUIPMENT FOR PURIFYING TREATMENT AND UTILIZATION OF WASTE-WATERS FROM THE DAIRY INDUSTRY Technical Field The invention relates to an improved process for purifying treatment of waste-waters produced by a dairy plant through the coagulation of the fat and protein content by treatment with chemicals and through the removal, in a given case the reprocessing of utilization purpose of the nascent waste sludge. The subject matter of the invention is.further on an equipment suitable for the realization of the process. Background Art It is a well known fact that with the progress of the urbanization the milk-processing is concentrated world¬ wide in the towns. Due to the development of the professional milk processing the production volume of plant increased to the multiple. The wastage of plants coming into the waste-water increased proportionally thereto, constituting a serious load to the communal sewage treatment plant overcharged at any rate of the towns. The average specific water consumption of the milk processing makes out 1 to 2 cu.m. for 1 cu. . processed milk. This may, however, show up considerable divergences depending on the type, the size, the age of the plant and on several other factors. In the course of the cleaning operations necessary for the maintenance of the hygienic standards, about 2 per cent of the basic material come into the waste-water. In case of draining off the whey, this value is much higher, the whey carries with namely about the half of the dry substance content of the milk in 85 per cent of the original volume. With full knowledge of the composition of milk, the quantity and the quality of the contamination can be calculated. The average composition of the milk is as follows: Milkfat 3-8 (38 g/1) Casein 2.7 # (27 g/D Albumin, globulin 0.6 % ( 6 g 1) Lactose .6 # ( 6 g/1) Mineral salts 0.8 # ( 8 g/1) Total solids 12.5 £ (125 g D With a processing loss of 2 per cent, 760 g fat, 660 g protein, and 920 g lactose come into the waste-water counted for each cu.m. of the processed milk. In the practice these values are generally higher because also the whey comes into the waste-water, from 65 kg/cu.m. of the solid content of which 4-5 kg are lactose, 6 kg are protein, 1 to 3 kg are fat, the remainder is made out by the lactic acid and mineral salts. The excess loading of the sewage works caused by the dairy industry is easy to see. The biological oxigen demand of the unskimmed milk is 11000 mg/1, that of the whey, however, 40000 mg/1. Taking the average processing loss of 2 per cent into consideration, the wastage coming into the waste-water being counted to 1 cu.m * of the processed milk, 2.2 kg biological oxygen demand loads the public sewage conduit and through it the communal sewage treatment plant if the dairy does not carry out some kind of pre-purification. The contamination caused by each cubic meter of the processed milk corresponds to 41 inhabitant equivalent (ΣE) (IE » 54 g biological oxygen demand per day) . The drained whey and buttermilk mean further 740 inhabitant equivalents per cubic meter. Taking the daily processing into consideration, the proportion of a dairy plant in the loading of the communal sewage treatment plant can be easily calculated. In respect of the waste-water purification both in the plant and in the communal sewage treatment plant the demand arises as a real necessity that the dairy plants reduce the contamination of their effluent waste-water by the so-called pre-purification just within the plant. In several countries, this is stimulated by a fine system as well as by the fact that the recovery and utilization of fat, protein and carbonhydrate corresponding to about 2 per cent of the raw material may be hoped. A perfect solution would be, of course, the evaporation of the waste-water whereby the complete elimination of the drained waste-water and the recovery of the dry substances could be achieved. This solution would be, however, highly power-consuming and expensive, therefore its application in the industry is out of question. The putrefaction, desiccation and evaporation of the waste-water in lakes must not be carried through either, though in spite of the entire loss of useful materials this would be the least expensive method. Its primary impediment is the economic or environment-protectional aspect: no sewage treatment plant must be established in the neighbourhood of the town whereas the transportation of the waste-water at great distances would be very expensive. Numerous papers contain the description of the industrially acceptable known methods (e.g. Ξemmings, M.L.: Dairy Industries International, 4 , 23-28 /1980/; Bull, M.A. , Sterritt, R.M., Lester, J.N.: J. Chem. Tecimol. Biotechnol., 51, 579-583 (1981) . The anaerobic putrefaction of the waste-water is a rather general pre-purifying method. As a result of the microbiological processes accompanied by methane and carbon dioxide formation, the biological oxygen demand of the waste-water considerably reduces. The drawback of such processes is the demand on huge storage capacity. No use can be made of the forming sludge, its placing causes further expenses. Moreover, the control of the plβnt requires also a high accuracy. The pH of the water must be continuously watched and care must be taken of its value not to sink below 6,8, since in this case the fermentation stops. Fat traps shall be built before the anaerobic step since other¬ wise the once separated fat will dissolve again. The different physical-chemical purification methods are recently gaining ground by the application of which the utilizable components of the waste-water can be recovered purely and with good efficiency. Such methods are the ultra- filtration and the reversed osmosis. (Muers, M.M.: Wat. Poll. Control, 6 , 644 /1968/; Kosikawaski, F.V.: J. Dairy Sci., 61, 41 /1979/) . The drawback of these methods consists in that they require a highly careful operation and they are very sensitive to the unstable loading. Their further drawback is that the costs of their investment amount to 10 per cent of the total volume of investments and their operation consumes 5 per cent of the entire operating costs. (H. Deodens, Deutsche Milchwirtschaft, 2£, /V?/ 454-458 /197V) . The decomposition of the emulsion by chemical methods and the segregation of the separated fat and protein constitute a practically scarcely applied pre-purifying method in case of waste-waters of the dairy industry, due to the limited efficiency and primarily due to the operational problems. A publication introducing such possibilities, being by far the most complete one, summarizing both the theoretical and research aspects is the work of Ildikδ Toδkos issued in 1983 (Acta Alimentaria, 1983, 12 /3/ 163-84) . On the strength of her continuous research works carried out with waste-water from the dairy industry partly in intermittent, partly in laboratory equipment and on the basis of the relative international professional literature, her fundamental statements are, as regards the efficiency of the flotation and precipitation, as follows: - essential differences are observable between the dwelling times necessary for the achievement of the same quantity of suspended matter in the draining water in the mentioned types of the equipment. The loadability or the capacity of the flotation machine is higher, in general cases about the fivefold of that of the precipi ator, - under identical coagulation conditions the quality of the purified water flowing off from both types of water purifier is identical and - the flotation provides for a radically more stable operation. As the examinations show, in case of the sewage purifier of the dairy plant of Vesaprέm, 41 to 55 per cent reduction of the chemical oxygen demand and 83 to 90 per cent reduction of the fat content was characteristically achievable on the basis of a series of measurements carried out in a month, by jointly using 400 mg/1 aluminium sulfate and pol electrolyte, applying phase separation by means of ICI electric flotation machine (Pintέr, L.: Examination of the Purification of Waste-waters of Dairy Plants. Dissertation for taking the university degree. Chemical University of Veszprem, 1982) , which is somewhat in erior as regards the chemical oxygen demand to the laboratory data of I. Toόkos, wheres the fat separation is just the same as with I. Toδkos (1982) . Without the use of coagulant good results can be achieved even with the more efficient flotation method of dissolved air only in case of the precise adjustment of the isoelectric point which means by itself a considerable acid consumption. Moreover, the process is highly sensitive to the adjustment of the narrow pH-range of the isoelectric poii which is by itself dependent on the composition of the waste- water and is constantly varying, the continuous adjustment of its working point is an almost impossible technical task. This fact explains in all likelihood the extremely poor capacity of the other flotation purifiers in Hungary. The flotation with dispersed air cannot be used in the dairy industry due to the low mechanical stability of the precipitate. On the other hand, the considerable drawback of the flotation methods of higher efficiency (dissolved air flotation, and electroflotation, respectively) is caused by the high costs of investment and operation. 20 to 0 per cent of the discharging purified water shall be saturated with air at a pressure of 4 to 6 bars and recycled to the input of the flotation machine. The suitable surplus flotation space, the costs of building in the electrodes, the expenses of the air compressors and recirculating pumps, and the costs of the electric power demand, the replacement of electrodes and the costs of the maintenance are extremely high. On the strength of the operating experience, a further drawback of the flotation is that with the industrial waste-water the formation of more or less sludge depositing under the electrodes is inevitable. This depositing sludge quantity increases especially if the flotation is carried out in an alkaline pH-range being more advantageous with respect to the stability of the precipitate. Although the sludge quantity forming in this way being discharged below can be combined with the flotated sludge, its removal requires the special construction and operation of the flotation machine. The suspended matter content of the draining water is also considerably greater in such a case than with the unambiguous - unidirectional - phase selection. The average solid content of the sludge achieves the values stated in the above cited paper (I. Toδkos) only after further precipitation and desiccation The similarly unfavourable experience made with the known waste-water purification methods carried out by means of chemicals is the fact mentioned and introduced in the above cited comprehensive work that the efficiency of the purification, i.e. the extent of the reduction of chemical oxygen demand is subject to significant variation depending on the type and composition of the waste-water and may reduce even by 20 to 30 per cent. Such a substantial reduction may be expected mainly in case of the drainage of whey when the proportion of lactose and lactic acid, against which the chemicals are ineffective, is disproportionately high. The aim of the invention is the elaboration of a process, and of an equipment, free of the above particularize drawbacks and deficiencies of the hitherto known and applied processes which renders possible the considerable and economic pre-purification of the waste-waters from the dairy industry and also the purification of full value completed also with after-purification. The invention is based on the recognition that the model solutions containing 1 to 4 per cent milk as well as other fresh waste-waters of industrial origin behave still similarly in respect of various chemical purification, whereas after standing for a few hours they behave highly differently. While the efficiency of the acidic-chemical purification of the general industrial waste-water, i.e. not that from the dairy plant, rapidly declines with the increase of the period between the formation of the waste- water and the precipitation with chemicals (even with the highly thorough adjustment of the isoelectic point) , in the course of our experiments the unambiguous experience has been made that in case of waste-waters from the dairy industry the efficiency of precipitation provisionally increases by leaps in the pH-range between 7 and 14 without any considerable change in the composition of the raw waste-water. It was stated that this phenomenon is caused by the activity of the bacterial flora settling in the waste pipes of the dairy plants, being rather resistent to the usual detergents and desinfectants. This flora multiplying in the waste-water considerably changes the colloidal structure thereof in a short time (e.g. a few hours) and suddenly reduces the stability of the emulsion against the usual precipitating agents such as the various ferric and luminium salts, and hydroxides, respectively (sodium aluminate) , more difficultly soluble alkali-earth metal oxides and hydroxides, and their other salts, respectively, mineral precipitation intermediates, such as earth silicon, bentonites, zeolites. In case of such coagulation the effect furthering the flocculation (precipitation of flocculent solids) of polyelectrolytes is more pronounced. The precipitate originating in this way can be quickly and efficaceously settled without the formation of ascending part. The fat and protein content o the waste-water biologically destabilized in this way can b precipitated almost quantitatively in alkaline agent by means of the above chemicals and surprisingly, even a part of the lactose can be removed. The method can be applied both for milky and wheyish waste-waters. Sterile milky . solutions inoculated with such baterial flora behave similarly. Disclosure of the Invention On the basis of the foregoing, the set aim can be achieved by the development and application of an improved new waste-water purifying treatment process according to which as a pre-treatment, the emulsion of milk appearing as waste-water being contacted with a biomass between the formation and the chemical treatment and simultaneously aerated, is biologically destabilized by the surface trans¬ formation of the protein case of the emulsified particles. As a biomass, advantageously the active sludge containing bacterial flora suitably resistent - as experienced - to the usual detergents and desinfectants, taken preferably from the sewage of the dairy industry is used, the dwelling time in the destabilizer of which is adjusted to 1 - 30 days, preferably to 5 - 15 days by the sludge retention. During the destabilizing contacting of the milk emulsion with the biomass, the aeration is varied preferably by stirring, in proportion to the current waste-water output. The biological destabilization constituting the surface transformation of the protein case of the emulsified particles is carried out by contacting the milk emulsion with the biomass for 0.5 to 48 hours, expediently for 1 to 24 hours, while the process may be accelerated by contact-surface increasing measures, in particular case by measures enhancing also the intensity of contact. The essence of the highly simple and inexpensive equipment suitable for carrying out the process according to the invention, built up of units known by themselves in the chemical industry consists in that it contains at least one active-sludge destabilizer inserted between the waste- water drain(s) and the precipitator operating with chemical intermixer suitable for the intermixing of chemical coagulating agents, provided with sludge retaining and aerating structural elements, and, resp. units, where the total volume of the destabilizer(s) is developed so as to be 2 to 0.01-fold, advantageously 1 to 0.05-fold of the daily waste-water output. The destabilizer may be a sludge- retaining structural unit consisting preferably of pipe and/or channel and/or tank and/or of their multiple and/or of their combination, especially of cascade construction, developed in given case with increased internal contacting surfaces. Since the active sludge containing the appropriate bacterial flora is present or can be settled in the majority of the dairy sewerage systems, for the purification according to the invention of adequate efficiency only such an equipment is necessary in operational respect which provides for an average dwelling time of 0.5 to 48 hours necessary for the destabilization of the emulsion before the chemical treatment. As for its construction, it may be a pipe, a channel, a tank or of cascade structure. In the destabilizer the necessary dwelling time can be reduced to 0.5 to 24 hours, moreover, to 0.5 to 12 hours by the forma¬ tion of large contacting surfaces suitable for the settlement of bacteria, by slow stirring, or by the re- circulation of a part of the forming sludge and/or of the through-flowing water. One of the essential features of the process according to the invention consists in the chemical pre-purification carried out by means of the usually applied precipitating agents, anticipated by a biological destabilization of relatively short dwelling time. The main operational steps of the phase of pre- purifying character of the process according to the invention are as follows: The collected technological waste-water of the plant comes into the destabilizer the volume of which is chosen so as to provide for a dwelling time of 0.5 to 48 hours, preferably of 2 to 12 hours. From here, the waste-water comes to one or more combined chemical intermixing units where one or more precipitating agents enumerated above are added jointly or subsequently in solution or in solid state in a quantity which ensures their concentration in the sewage to be 0.5 to 15 mole/cu.m. From here, the waste-water flows into the precipitator the bottom of which is developed so as to be suitable for the collection and outlet of the sludge, whereas the upper part for those of the purified water. The nascent precipitate coagulates well, it flocculates quickly in the precipitator itself and in case of a dwelling time of about 10 to 15 minutes, it settles appropriately out of the system. The precipitate thickness to less than 1/10 of the entire volume and can be easily removed from the bottom of the precipitator. The obtained purified water scarcely contains any suspended matter, its fat content is insigni icant, its chemical oxygen demand reduces by 70 to 80 per cent. Although better results were reported from time to time in the public tions, the data have to be accepted with the proper criticism because the lactose and lactic acid content of the milk, end of the waste-water, respectively, cannot be eliminated with the applied acidic-chemical purifying methods and this fact imposes an absolute restriction to the extent of the reduction of chemical oxyge demand. The reduction of the chemical oxygen demand achieved exclusively by the application of the above pre-purifying i process exceeds the value calculated from the degree of the elimination of protein and fat. This can be attributed to the fact that, as a result of the processes taking place in the destabilizer, a part of the lactose gets surprisingly also into the precipitate. The process according to the invention eliminates the essential drawbacks of the previous chemical pre-purifying methods so far industrially applied or suggested in publications and patents, and its technical and economic efficiency is superior to them. With the application of the process according to the invention only precipitating sludge arises which settles completely even without the use of a preflocculator from the water, in 15 to 20 minutes. The process, and the adding of chemicals, respectively, do not require the precise adjustment or regulation of pH. The costs of the chemicals for the purification are low: the 70 to 80 per cent reductio of the chemical oxygen demand and the almost complete elimination of the fat content do not require higher costs of chemicals than the half or one fifth of the costs of the present industrial solutions of approximate efficiency or those proposed by reason of laboratory experiments. The extremely short precipitation dwelling time require the building out of a lower phase separation volume which, due to its direct discharge construction saves a considerab sum of the costs of investment and operation, as compared to whatever suggested flotation methods. The precipitate thickens spontaneously until a solid content of 3 to 3«5 per cent and, if necessary, it can be advantageously further thickened by simple physical separation. By the application of the process according to the invention, 5 to 7 kg sludge of 60 to 70 per cent moisture content can be expected from each cubic meter of the dairy waste-water of average composition, containing inorganic compounds in a quantity corresponding to 1 to 1.5 kg precipitant, 0.3 to 0.5 kg milkfat, and in the residual part protein and the decomposition products of protein. The sludge can be extensively utilized. Its protein content is high; after neutralization and desiccation, it can be used as the mixing component of fodder. The use for energetic purposes of the sludge is also advantageous. Being mixed with the combustible of coal- fired furnace, it increases the quantity of the energy carrier, whereas its metal content improves the efficiency of the combustion and reduces the quantity of the furnace black and of the nitrogeneous combustion products. The sludge can be well emulsified in fuel oil and in gas oil by adding a small quantity of detergent. 10 kg sludge being emulsified in 1 cu.m. oil, the efficiency of the combustion increases by 2 per cent, the black- and C0-content of the flue gas reduces. If the sludge is not utilized, the process has even in this case the advantage that due to the high concentration of the sludge, its transportation requires only negligible costs. The plants which deliver the flotation sludge by tank vehicles to the sewage treatment plant, could spare 80 per cent of the transport charges by the application of the process according to the invention. Due to the high nitrogen, phosphorus and other advantageous precipitant content, the sludge is excellently utilizable for the fertilization of arable soil and for the soil-amelioration either directly or in compost form. The purification process phase particularized above according to the invention can be completed well and advantageously by an aero-biological after-purification phase known by itself, by means of which water not harmful to the environment is obtained which can be returned in the living natural waterways or surface waters without environme damaging consequences. For this purpose, communal sludge is used as active sludge on which optional bacterial flora is introduced and cultivated. Practically no sludge removal occurs because in the course of the consumption of the bacterial flora the sludge itself is processed. The dimensioning should ensure 0.1 to 0.4 kg inorganic substance to be eliminated (lactose, lactic acid and protein) to 1 kg sludge. In order to increase the efficiency of the process, air injection is preferably also used. For the purpose of the after-purification, two or more parallel tanks to be alternately coupled can be used in which the dwelling time of the pre-purified waste-water is adjusted to about 24 hours. As an alternative solution, the cascade scheme of seveis series-connected small tanks may be used where the general dwelling time is the same as with the construction of inter- ittent operation and where the air injection is throughout maintained. In case of surplus sludge, the sludge is recirculated from the end to the fore-part. The use of tank of successively increasing volume proved expedient. The joint application of the pre-purification and after purification is especially advantageous because during the aero-biological purification the reaction of the waste-water to be treated will be acidic since the lactose content decomposes in the first step to lactic acid. This process takes place relatively quickly and the reaction of the waste water changes over to be acidic. The dairy waste-water pre- purified with the process according to the invention enters the biological after-purifier while having high, about 9 pH i.e. being alkaline (the . lime salt, i.e. calcium salt of the lactic acid enters the after-purifier) , therefore the reaction of the waste-water to be after-purified remains for a relatively long time in the range of neutral reaction and the calcium salts bound to various organic acids remain in the solution still a good while. They precipitate only when the most part of the organic matter is already consumed and thus, they precipitate as carbonate salt (lime stone) , i.e. as inorganic matter. This latter infiltrates into the sludge, making it thus heavier so that the sludge settles quickly and thereby the decantability of the liquid increases even in case of relatively small dimensions of the treatment space. The pre-purifying process according to the invention removes in a relatively small volume so much organic matters from the waste-water that the purification of the water to b biologically after-purified requires only about one third of the necessary capacity of the traditional biological purifie used in cases devoid of pre-purification. In some instances, to the biological after-purification a small quantity of P- and N-containing compound (e.g. urea) shall be mixed as nutrient substance for the sustentation of the bacterial flora. The process according to the invention, especially through the insertion of the pre-purification, has broken through the professional prejudice according to which thin sugary waters cannot be well purified biologically because the phenomenon of the so-called sludge-swelling takes place and the sludge swims off. The pre-purified water having alkaline reaction due to the pre-purification according to the invention can be after-purified with high efficiency and in small-volume equipment as a result of the above mentioned effect mechanism, in aero-biological way using active sludge and air injection. Modes of Carrying out the Invention The process and equipment according to the invention will be now introduced by way of example in the following embodiments: Example 1 The pre-purification of the waste-water of a dairy pla was carried out in a continuous experimental equipment of 12 cu.m./day capacity. The water flowing in the fat trap w conducted first in the destabilizer developed as a mixed channel of 1.5 cu.m. capacity where the average dwelling time of the waste-water amounted to 3 hours. The chemical oxygen demand of the flowing-in waste-water was 3200 mg/1, its fat-oil-content to be extracted 570 mg/1 taken in the weekly average. The destabilized waste-water was conducted from here to two series-connected chemical intermixers of 0.05 cu.m. capacity, of direct discharge. A suspension corresponding to 0.5 - 0.8 g/1 magnesium hydroxide dosage was continuously added to the waste-water in the first intermixer, whereas a solution corresponding to 0.15 - 0.25 g/1 ferric sulfate dosage in the second one. The homogeneous mixing was ensured in these units by stirring. Now, the mixture was conducted in a precipitator of 0.5 cu. capacity, developed concially below where the phase separation occurred. The purified water discharged through the overflow ring developed above, whereas the sludge was removed through the locking mechanism developed below. The colourless, turbidity-free purified water containe in addition to the lactose and the lactic acid, a small quantity of decomposition product which however, meant from the point of view of the further quick biological de¬ composition a more advantageous contamination than the proteins and fats. Corresponding to its appearance, it contained a minimum quantity of suspended matter, and extractable fat, respectively. The quantity of the latter varied between 20 and 30 mg/1. The chemical oxygen demand of the discharging purified water showed a value between 700 and 900 mg/1 in the course of the examination. As for the efficiency of the process, the above values corresponde to a 72 to 78 per cent chemical oxygen demand and to a 92 t 95 per cent fat-removal efficiency. The sludge removed from the bottom of the precipitator contained averagely 35 per cent dry substance and the possibility of its further dehydration proved also advantageous. In the course of the informative experiments carried out with a screw decanter, the solid content of the sludge succeeded to be increased to 20 - 28 per cent. The purity of the aqueous phase flowing out of the decanter corresponded to that of the purified water flowing out of th precipitator. On the basis of the examinations carried out following the desiccation of the sludge samples, in the average 20 to 30 per cent of their solid content were protein, and 30 to 0 per cent extractable fat. If the waste-water was conducted from the fat trap to the chemical intermixer and then to the precipitator by disconnecting the destabilizer, the double amount of the abc quantity of chemicals was necessary for the acceptable coagulation and flocculation. In this latter case, the efficiency of the precipitator fell considerably behind the former one, the dwelling time proved to be short and there¬ fore, the discharging water contained also 100 to 150 mg/1 finely dispersed suspended matter. This increased at the time proportionally the values of the chemical oxygen demand and of the extractable fat content which varied in such a case between 1100 and 1400 mg/1, and between 60 and 100 mg/1 respectively. This notable reduction of the efficiency means the overstepping of the channel level values currently valid in Hungary and involves the obligation of the plant to pay a fine for waste-water as compared to the process proposed by the invention. Example 2 The procedure is the same as in Example 1 with the difference that calcium oxide and magnesium chloride were used as precipitants. In the first chemical intermixer 0.4 g CaO, whereas in the second chemical intermixed 0.25 g gCl2 solution was fed reckoned to 1 litre of the waste- water. The chemical oxygen demand of the discharging water varied between 800 and 1000 mg/1, its fat content between 40 to 50 mg/1. This meant an efficiency of 69 to 75 per cent chemical oxygen demand and of 86 to 89 per cent at removal. The possibility of dehydration of the sludge was the same as in Example 1. Example The steps described in Example 1 were carried out but only one single chemical intermixer was used. " In the chemical intermixer the solution of 0.25 g/1 l^SO^ and such a quantity of NaOH were pamH.elly added which rendered the solution alkaline. * The chemical oxygen demand of the water varied between 750 and 950 mg/1, whereas its fat content between 30 and 40 mg/1. This meant a 70 to 76 per cent reduction of the chemical oxygen demand and a 89 to 92 per cent reduction of the fat content and corresponded to the prescriptions relating to the communal channel. Feeding polyelectrolyte of Praestol 411 K trade name in a quantity of 1 mgTl into the waste-water before the precipitation, the efficiency of the purification improved in case of both characteristics by 1 to 3 per cent. The possibility of dehydration of the sludge worsened as compared to Examples 1 and 2: the solid content achievabl in the decanter did not exceed 20 to 25 per cent. Example 4 The purification of waste-water was carried out as described in Example 1 with the difference that a cascade system consisting of a mixed channel of 0.25 cu.m. capacity and of two columns filled with porcelain Rasching rings of 0.25 cu.m. capacity was used as destabilizer. The feed bein unchanged, the dwelling time diminished by 1.5 hours whereas the efficiency of the purification remained unchanged. Prolonging the dwelling time to 9 hours by the reduction of the feed, the chemical oxygen demand reduced to 500 to 800 mg/1 and the fat content to 20 mg/1, meaning a further improvement by 3 to 4 per cent of the ef iciency of the purification. In case of disconnecting the destabilizer but otherwise under identical conditions, the achievable efficiency was not more than 35 to 40 per cent in chemical oxygen demand and 75 to 85 per cent in the fat removal. The precipitation was poor and the sludge was difficult to be dehydrated. As an example of the sludge utilization, the decanted sludge containing 25 per cent dry substance, obtained in the course of the effectuation of Example 1, being mixed in a quantity of 0.5 to 5 per cent to the fuel oil directly before the feeding to the burners, the efficiency of the firing improved and also the CO- and NO γ -emission of the flue gas reduced. In the course of firing experiments carried out by intermixing 3 per cent sludge, the utilizable heat quantity increased by 2 to 3 per cent. The GO-content of the flue gas reduced by 40 per cent, its NO-concentration, however, by 80 per cent. In case of an appropriate mixing, the fuel mixture can be pre-mixed also in a tank, moreover, in case of adding some surface-active substance, e.g. 0.2 to 0.4 per cent of petroleum sulphonate, the mixture can be stored for several hours in the above concentration without stirring. According to another possibility of utilization, the sludge containing 27 per cent dry substance, obtained from the purification process carried out according to Example 2 being dried by the hot flue gas of- the furnaces operated with natural gas, the carbon dioxide emission reduces, while nutritive component containing considerable quantity of protein and milkfat, as well as CaCO* and MgCO,, utilizable for forage is obtained. The dried sludge can be preserved and advantageously utilized. A favourable opportunity for utilization presents itself in the production of various food-preparations for hens. In the course of the examinations carried out together with private breeders, no numerical difference could be proved in the development of egg-output. It could be, however, observed that considerably less eggs were broken with the poultry stock fed with food preparation mixed with dried sludge and the hens showed a preference for the sludge residues of coarser grain. As a further possibility for utilization, it was stated and tried that the expediently decanted sludge obtained according to Example 1 could be advantageously utilized when arranged on coal storages, coal silos. Its quantity can be expediently 3 to pe3? cent of the coal, but exploiting well the surface drying, it can be added up to 10 per cent without the reduction of the utilizable heat quantity. The caloric value of the sludge in dried condition is identical with that of the o f-grade lignites. At the same time, its ash content improves the oxidation properties of the coal. A part of Mg(0H) 2 being replaced by more alkaline CaO (Example 2) the sludge provides for an advantageous effect slowing down the oxidation during the storage of the coal. The CO- and NO-emission of the flue gas is reduced by 15 per cent, and 60 per cent, respectively, during the burning of the composition. Finally, it was proved by experiments that the sludge obtained with the process according to Examples 1 to 3, end especially to Examples 1 to 2, is of-advantageous compos±jαr. in respect to the utilization for amelioration. The protein and at components of the sludge decompose in the soil in a very short time and increase the organic,nitrog n, phosphorus, Mg and Fe(III)salt content of the soil. The dispersion on the soil either continuously or with taking into consideration the cultivation cycle is possible also after the suitable storage, or compost-production. The more alkaline pH is explicitly advantageous in respect of the latter. The utilization of sludges is especially advisable for the treatment of acid soils as well as for the preliminary fertilization of magnesium-demanding cultures, such as sugar beet.

Claims: What we claim isj 1. An improved process for the purifying treatment before discharge of waste-waters from the dairy industry through the coagulation of the fat- and protein-content by chemical treatment and through the removal of the forming sludge, c h a r a c t e r i z e d in that the milk emulsion appearing as waste-water, being contacted with a biomass between the formation and the chemical treatment and being simultaneously aerated, is biologically destabilized through the surface transformation of the protein case of the emulsified particles. 2. The process according to Claim l c h a r a c - t e r i z e d in that as a biomass the active sludge containing bacterial flora suitably resistent to the usual detergents and disinfectants, taken from the sewerage of the dairy industry is used. 3. The process according to Claim 1 or 2 c h a r a c t e r i z e d in that during the de¬ stabilizing contacting of the milk emulsion with the biomass the aeration is varied preferably by stirring, in proportion to the current waste-water output. 4. The process according to any of Claims 1 to 3, c h a r a c t e r i z e d in that the contacting of the milk emulsion with the biomass is carried out for 0.5 to 48 hours, expediently for 1 to 24 hours. 5. The process according to any of Claims 1 to 4, c h a r a c t e i s e d in that the dwelling time of the used biomass is adjusted to 1 - 30 days, expediently to 5 - 15 days by the sludge retention. 6. The process according to any of Claims 1 to 5, c h a r a c t e r i z e d in that the sludge forming during the purifying treatment or only the solid content thereof is economically further utilized. - - 7. The process according to Claim 6, c h a r a c ¬ t e r i z e d in that the sludge or its concentrate containing 3 to 100 per cent dry substance is burnt in a furnace while being mixed with solid or liquid energy carriers. 8. The process according to Claim 6, c h a r a c¬ t e r i z e d in that the sludge or its concentrate containing 3 to 100 per cent dry substance is used as fodder by itself or mixed with the known feeding agents, and feeding substances, respectively. 9. The process according to Claim 6, c h a r a c¬ t e r i z e d in that the sludge or its concentrate containing 3 to 100 per cent dry substance is introduced by itself or mixed with known fertilizers and/or in form of compost manure into the soil. 10. The process according to any of Claims 1 to 9, ' c h a r a c t e r i z e d in that the pre-purified waste-water is subjected to an aero-biological after- purification with active sludge combined with air injection. 11. The process according to Claim 10, c h a r a c ¬ t e r i z e d in that as active sludge the communal sludge is used in a quantity of 0.1 to 0.4 kg organic matter to be destroyed for 1 kg sludge, in which optional bacterial flora is planted, and cultivated, respectively. 12. An equipment for carrying out the process according to any of Claims 1 to 5, c h a r a c t e r i z e d in that it contains at least one active-sludge destabilizer inserted between the waste-water drain(s) of the dairy plant and the precipitator operating with chemical inter- mixer is suitable for the intermixing of chemical coagulating agents, provided also with sludge retaining and aerating structural elements, and, resp. units. 13• The equipment according to Claim 12, c h a r c¬ t e r i z e d in that the total volume of the de¬ stabilizer(s) makes out the 2 to 0.01- old preferably 1 to 0,05-fold of the daily waste-water output.

Inventors: BENCZE LAJOS, KARPATI ARPAD, BENCZE, LAJOS, KARPATI, ARPAD
Applicants: VESZPREMI VEGYIPARI EGYETEM
Application year: 1987
Main classification: C02F3
IPC codes: A23K1, C02F1, C02F3, C02F9, C05F1, C05F7