Method for concentrating an effluent

Abstract: The invention provides a method for concentrating an effluent such as more or less liquid manure, in particular slurry, comprising the steps of: 1) providing the effluent (1); 2) sieving the effluent (3); 2a) removing the retained fractions; 3) subjecting to microfiltration (10) the fractions allowed through in step 2; 3a) removing the retained fractions; 4) subjecting to reverse osmosis (20) the fractions allowed through in step 3; 4a) removing the retained fractions; and 5) discharging the water obtained in step 4. The method according to the invention comprises a pre-separation using for instance a rotating sieve press, a microfiltration step and finally a treatment based on reverse osmosis. A considerable concentration of effluents can be achieved with the invention.

Description: The invention relates to a method for concentrating an effluent. Coming to mind here are for instance contaminated water, in which substances are dissolved, in which substances are to be found in colloidally dissolved form, and/or a mixture of water with substances. Envisaged for instance is the concentrating of more or less liquid manure and particularly manure slurry. The object of the invention in this latter respect is for instance to enable manure treatment on the farm, by contractors and by manure processing cooperatives. The invention provides a method for concentrating an effluent such as more or less liquid manure, in particular slurry, comprising the steps of: 1) providing the effluent; 2) sieving the effluent; 2a) removing the retained fractions; 3) subjecting to microfiltration the fractions allowed through in step 2; 3a) removing the retained fractions; 4) subjecting to reverse osmosis the fractions allowed through in step 3; 4a) removing the retained fractions; and 5) discharging the water obtained in step 4. The method according to the invention comprises a pre-separation using for instance a rotating sieve press, a microfiltration step and finally a treatment based on reverse osmosis. A considerable concentration of effluents can be achieved with the invention. It has for instance been found that 50 to 70% clean water can be obtained from slurry with a corresponding increase in the concentration of the manure. The clean water is for instance suitable for cleaning stalls or for overhead irrigation. In addition the obtained water is clean such that it can be discharged onto surface water without conflicting with legal requirements. The concentrated manure, which may or may not be mixed with the concentrate from the reverse osmosis, can be treated in factories or be distributed. Some of the advantages of the system according to the invention are: a smaller storage capacity is required. transport capacity can be considerably reduced. the manure is of better quality and can be spread over the land or be injected into the ground at considerably smaller cost. To further increase the effectiveness of the various treatments the diverse steps could be performed more frequently. The outlet side of a treatment station is connected for this purpose to the infeed side. In order to prevent as far as possible emission of ammonia, there can be added to the effluent, prior to the microfiltration, a quantity of liquid with a pH such that the resulting pH lies between 6 and 7. The concentrated fractions can for instance be collected in a storage tank and be transported away for use in agriculture. The liquid fraction obtained after sieving is pumped to the microfiltration station, where among other things the suspended solid substance particles are filtered out of the liquid. By regularly reversing the flow direction for a short time the collected solid material can be removed from the microfilters. The particles of solid material are carried away for instance to a storage tank. The water allowed through the microfilters, in which very finely distributed contaminants are still to be found, is carried to the final station where a treatment based on reverse osmosis takes place. Sieving can advantageously take place using a rotating sieve. The sieving operation can take place for example with a sieve having a mesh width of 50-300 µm. Microfiltration can preferably take place using membranes having pores smaller than 0.3 µm. The invention will now be elucidated with reference to the annexed schematic diagram of a device designed to perform the method according to the invention. Slurry present in a container 1 is added by means of a pump 2 to a rotating sieve installation 3. The thick fraction is partially fed back to the container 1 by means of a pump 4 and carried partially to a container 5 by means of a pump 6. The thin, watery fraction is fed via a pump 7 to an intermediate storage tank 8. The now partly cleaned effluent is carried from this storage tank 8 to a microfiltration station 10 by means of a pump 9. Such a station is per se known and comprises a number of microfiltration tubes with an axial passage and discharge to the sides. Use is made of a number of adjacently disposed tubular membranes enclosed by a jacket. circulation takes place in this case by means of a circulation pump 11 which provides a continuous flow from the bottom to the top through the microfiltration units 12. The liquid allowed through the units at the top is fed back to the intake of the circulation pump 11 and there fed once again to the units 12. The watery fraction is carried through the said filter tubes to the sides through the jacket of the units 12 to a pump 14. Such units are per se known and are supplied by the Dutch company X-Flow B.V. and others. The pump 14 pumps the permeate to a storage tank 15. The thick fraction is carried via a pump 13 to the storage tank 5. A connection 26 can serve to supply diluted acetic acid in a quantity such that the remaining pH lies in the order of 6 to 7. This can counter ammonia emission during the treatment of manure. By means of a pump 16 the liquid can be pumped up out of the tank 15 and be carried by means of a metering pump 17 via a so-called candle filter 18 and a high pressure pump 19 under a high pressure, for instance in the order of 70 bar, to a station 20 which performs a final cleaning based on reverse osmosis. The in this case three reverse osmosis units 21 connected in cascade are of per se known type and are supplied by the American company Dow Chemical and others. The concentrate at the outlet of the reverse osmosis station is carried by means of a pump 22 to the tank 5. The water obtained after the reverse osmosis is carried via a pump 33 to a storage tank 24, from which it can be pumped by means of a pump 25 for further use or transport. The metering pump 17 serves to keep the units 21 clean. The contents of storage tank 5 which consist of concentrated manure, can be transported regularly to a business that uses manure, for example an arable farm or a cattle farm, while the clean water from storage tank 24 is very suitable for cleaning stalls, overhead irrigation or like applications. If desired, this water can be discharged without problem onto surface water because the installation according to the invention is also capable of complying with the strictest environmental requirements. The permeate obtained after sieving and/or microfiltration can, after it has been brought with an acid, for instance diluted acetic acid, to a pH in the order of 6 to 6.5, be used as flushing liquid for flushing out the manure in stalls. The freshly produced manure in the stall falls via openings in the floor, for example in the form of gratings, into the weakly acidic liquid. The formation of ammonia gas is hereby prevented, which is of benefit to the atmosphere in the stall and to the environment. it is noted that, depending on the desired quality of the water, a further cleaning is possible by once again applying the reverse osmosis. The appended table gives by way of example the effectiveness of the system according to the invention in concentrating pig slurry. It can be seen clearly from the table that the system according to the invention is capable of realizing a concentration of the manure such that the obtained water is clean in the legal sense of the word and can therefore be discharged without problem. In order to perform the reverse osmosis use can be made of a thin-film composition membrane.

Claims: Method for concentrating an effluent such as more or less liquid manure, in particular slurry, comprising the steps of: 1) providing the effluent; 2) sieving the effluent; 2a) removing the retained fractions; 3) subjecting to microfiltration the fractions allowed through in step (2); 3a) removing the retained fractions; 4) subjecting to reverse osmosis the fractions allowed through in step (3); 4a) removing the retained fractions; and 5) discharging the water obtained in step (4). Method as claimed in claim 1, characterized by : 6) treating the fractions again according to step (2a) in step (2). Method as claimed in claim 1, characterized by: 7) treating the fractions again according to step (3a) in step (3). Method as claimed in claim 1, characterized by : 8) adding prior to step (3) a dosed quantity of liquid with a pH such that the resulting pH lies approximately between 6 and 7. Method as claimed in claim 1, characterized by : 9) performing step (2) using a rotating sieve. Method as claimed in claim 1, characterized by: 10) performing step (2) using a sieve with a mesh width of 50-300 µm. Method as claimed in claim 1, characterized by: 11) performing step (3) with a membrane having pores smaller than 1 µm. Method as claimed in claim 7, characterized in that step (3) is performed with a membrane having pores smaller than 0.6 µm. Method as claimed in claim 8, characterized in that step (3) is performed with a membrane having pores smaller than 0.3 µm. Method as claimed in claim 1, characterized by: 12) performing step (3) by regularly reversing the flow direction for a short time. Method as claimed in claim 1, characterized in that for performing step (3) use is made of a filter on a basis of polyethersulphone.

Inventors: LOOHUIS BERNARDUS JOHANNES, LOOHUIS, BERNARDUS JOHANNES
Applicants: HAFLO MILIEUTECHNIEK BV, HAFLO MILIEUTECHNIEK B.V.
Application year: 1992
Main classification: C02F1
IPC codes: A01C3, B01D61, C02F1