CA1182227A

CA1182227A - Effluent waste water treatment

Info

Publication number: CA1182227A
Application number: CA000390086A
Authority: CA
Inventors: Frank C. Hume
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-13
Filing date: 1981-11-13
Publication date: 1985-02-05

Abstract

ABSTRACT OF THE DISCLOSURE

A treatment of refinery waste water is disclosed.
The treatment avoids the formation of sludge, thus avoiding the problems of disposing of the sludge. The process com-prises the steps of vigorously mixing and aerating the effluent to maintain waste material present in the effluent in suspension such that minimum flocculation of waste material occurs, continuing the mixing and aerating step for a sufficient period of time such that oxygen reduction of a substantial portion of the waste material in the effluent occurs, and passing the mixed and aerated effluent to at least one settling basin for a sufficient retention time for oxygen reduction or oxidation of substantially all the remaining portion of the waste material to occur.

Description

2;~

rhe prcsent invention relates to trcatment of r~finery waste water. More specifically, the present invention rcl~tcs to an aeration process which treats effluent waste wa~er so there îs minimum build up of slud~e deposits.
ConYenti-onal waste water treatment systems for industrial waste, particularly oil refineries include many diflerent methods such as, chemical treatment, dissolved ~ir flotation units, bio-reactors, clarifiers, ~ilters and the like.
Recently7 aeration has been added to the list of water trcatment systems but in most aeration systems effluent waste water is fed into an aeration basin where it is agitated with aeration devices for about a day. The aeration assists in reducing and oxidizing the waste material causing flocculation to occur which eventually forms into sludge. In these aeration systems the effluent from the aeration basin contains a very low waste material concentra-tion, but a very high sludge concentration and this sludge must be treated in various ways. It can be exposed to a new environ-ment in settling basins where it is further reduced or oxidized, small amounts can be mixed with effluent and discharged or it can be wasted separately by land farming or incineration. The removal of this sludge, however, is an additional step involving additional expense.
The present invention provides an aeration system for treating effluent ~aste water which substantially avoids the formation o~ flocs, or clumps of micro-organisms into ~hich oxygen diffusion is slow, and consequently reduces the sludge formation, thus avoiding the necessity of having to dispose of the sludge. In the present process the effluent is vigol-ously mixed and aerated to ensure an adequate oxygen concentration, to maintain the ~aste material present in the effluent ln sus-pension and suppress the formation of filamentous forms, thus reducing flocculation of the ~aste material. The vigorous mixin~

and ~erating ~ction takes place for a sufficient period of time such that an oxygen reduction of a substantial portion of the waste material occurs, the oxygen transfer bein~ lligher because there are no flocs or clumps of micro-organis~ns into which oxygen diffusion might be slowed up.
The present invention provides in a process for effluent waste water treatment, the improvement of treating effluent such that substantially no sludge is formed comprising the steps of, vigorously mixing and aerating the effluent to maintain waste material present in -the effluent in suspension such that minimum flocculation of waste material occurs, con-tinuing the mixing and aerating step for a sufficient period of time such that oxygen reduction of a substantial portion of the waste material in the effluent occurs, and passing the mixed and aerated effluent to at leas$ one settling basin for a sufficient retention time for oxygen reduction or oxidation o~ substantially all the remaining portion of the waste material to occur.
The period of time for the mixing and aerating is sufficient such that oxygen reduction of at least about 80~ of the waste material in the ef~luent occurs, and in a preferred embodiment at least about 90%. This period of time is prefer-ably for at least about 3 days, and the retention time of the mixed and aerated effluent in at least one settling basin is preferably ~or at least about 4 days. In one embodiment the effluent is skimmed directly after the mixing and aerating step, and in another embodiment an additional skimming step occurs after the effluent has been retained in the settling basin.
Recycling o~ at least a portion of the mixed and aerated effluent at the end of the aeration basin may occur, either continuously or from time to time Furthermore, seeding of the effluent with a biologically active water prior to the mixing and aernting step may also take place.

The mixing and aerating step preferably occurs ln an aeration basin containing a plurality of static mixers in the form of vertical tubes having alternating right and le~t hand helical vanes therein, and including supplying air underneath each of the static mixers, The temperature of the effluent in the aeration basin is preferably maintained so that it does not fall below about 13C, In order to control this temperature, steam injection may be provided to the effluent, In drawings which illustrate the embodiments of the invention, Fig, 1 is a flow sheet showing one embodiment of the process for effluent water waste treatment of the present invention, Fig, 2 is a flow sheet showing another embodiment of the process for effluent water treatment, Fig, 3 is a plan view of one embodiment of an aeration basin suitable for the process of the present invention.
Fig, 4 is a detailed side view taken at line 4-4 of Fig. 3 showing one type of aeration device suitable for the process of the present invention.
The general principle of biological treatment of waste water is the reduction and oxidation of the waste material by a growing microbial population, By exposing this new microbial population to additional reduction and oxidization, it ls i`urther broken down so that it does not form sludge or solid waste m~tter.
Effluent waste water is generally measured by the biochemical oxygen demand (BOD) level, which is a measurement o~ the required oxygen reduction of the waste material in the effluent.
Referring now to Fig, 1, the effluent waste water ls shown entering a skimmer 9 which removes free oil. The ef~luent waste water then passes to an aeration basin 10, which contains a plurality of static aerators 11, Each aeratGr is in the form 32;~

~f a vertical tube with alternating right and le~t hand helices, generally a IL~P~ O

plastic extrusion, and each aerator 11 has a header pipe 12 passing u~derneathl with an air orifice such that air from a header pipe 12 passes up through each static aerator 11. An air supply 13, such as a compressor or blower is provided to s-lpply air to the static aerators 11, The aerators 11 are arranged in rows across the aeration chamber 10. It is preferIed to have a higher concen-tration of aerators 11 in the first half of the aerator basin 10, and then slightly fewer aerators for the last few rows, leaving a space at the end of the basin 10 where no aerators exist, The e~fluent entering the aeration basin 10 is subjected to vigorous mixing and aerating to maintain the waste material present in the effluent in suspension, and suppress the formation of fila-mentous forms which would promote the formation of clumps of micro-organisms into which oxygen diffusion might be slow. Thus, minimum flocculation occurs due to this vigorous mixing, and at the same ti~e adequate o~ygen concentration is present such that oxygen reduction of a substantial portion of the waste material occurs in the effluent, Generally7 80% of the oxygen reduction occurs in the aeration basin and in a preferred embodiment 90%
of the waste material is subjected to oxygen reduction in the aeration basin 10.
The effluent remains in the aeration basin 10 for at least 3 days, and a percentage of the effluent may be recycled from the end of the basin back to the beginning again, depending partially on the flow of effluent through the aeration basin 10, the BOD content of the effluent, and the capacity of the basin.
The treated effluent leaYing the aeration basin 10 is fed to a first settling basin 14, followed by a second settling b~sin 15.
The total retention time in these two basins, 14 and 15, is at least about 4 days, Little or no sludge is present in the effluent leaving the aeration basin 10 and the waste material Z~

present in the treated effluent is subjected to further oxygen reduction and oxidation in the se-ttling bnsins 14,15, so that substantially all the remaining portion of the waste materlal is reduced or o~idized, It is found that little or no sludge is deposited in either settling basins 14,15. The effluent leaving the settling basin 15 comes within most specifications for waste water and can be discharged into a river or other body of water.
A skimming basin 16 is shown in Fig.l for the effluent leaving the settling basin 15, Any sludge present in the effluent is removed by allowing the sludge to rise to the surface of the skimming basin where it can be removed by skimming from time to time if a build up occurs.
The retention time of the waste water in the settling basins 14,15 is generally at least four days and in some cases more basins may be used depending on the quantity and quality of effluent leaving the treatment system.
Another embodiment of the process is illustrated in Fig. 2 wherein the effluent waste water enters a skimmer 20 which removes free oil. From the skimmer 20 effluent flows to an aeration basin 21 which has a recirculating line 22 with a pump 23 to allow a portion of the effluent together with any sludge formed in the aeration basin 21 to be recirculated to the beginning of the aeration basin. Whether or not the recirculation system is used is dependent on the results of oxygen reduction occurring in the effluent as it is vigorously mixed and aerated passing through the aeration basin 21, This partly depends on the BOD content of the effluent entering the aeration basin 21, also on the effluent flow through the basin, A compressed air supply 24 supplies air through an air header 25 under the stntic mixers 26. The number of static mixers and the airflow to the mixers are .selec-ted to provide the necessary oxygen reduction in the effluent. After a retention time of generally at lenst 82;~27

3 days in the aeration basin 21, the effluent passes to a skim-ming basin 27 for removing any solid matter such - 5A _ ``" 1~82~7 as ~locculents or free oil present in the e~fluent, The effluent then passes to a settling basin 28 where it is retained preferably for 4 days so that the overall retention time in the system is at least 7 days, The effluent then passes through a second skimming basin 29 to remove any remaining free oil, at which time the effluent is fully treated and the BOD content reduced to acceptable limits.
It is preferred that the aerating process occurs with the effluent at a temperature not below about 13C. In order to maintain this temperature, steam 30 is injected into the effluent prior to entering aeration basin 21, and a thermometer 31 checks the temperature of the effluent before entering the aeration basin 21. In certain instances it is preferred to seed the effluent as it enters the aeration basin 21 with biologically active water to commence the microbial activity.
An aeration basin 10 is shown in Fig. 3 having nineteen lateral rows 32 of aerators 11 in the front portion of the basin 10 forming a main aerator section. Each row 32 containlng ten aerators, evenly spaced, and lateral headers 33 extending under each row 32 of aerators 11 connected to a central header 34 from an air supply. At the end of the main aerator section is a secondary aerator section with four lateral rows 35 each con-taining eight aerators 11 spaced apart evenly so that less aeration occurs in the secondary aerator section compared to the main aerator section. Lateral headers 36 from the four rows 35 in the secondary aerator section join to the main hQader 34, so that the air supplied to each aerator has substantinlly the same flow. Effluent entry 37 into the front portion of the aeration basin 10 ensures that the effluent has to pass throuDh the vigorous agitation in the main aerator section followed by the slightly reduced agitation in the secondary aerator section before reaching the end of the basin 10 where little or no aeration occurs, but reduction or oxidation of thz waste material '7 still takes place, finally exiting through exit plpe 38 and passing to a settling basin.
Fig. 4 illus$rates an aerator 11 suitable for the present invention preferably formed of a polyethylene tube, having alternating right and le~t hand helices 40 one on -top of the other~ The alternating helices 40 agitate the water as it passes up through the tube, and also contributes to the mixing.
Arms 41 extend from the base of the mixer 11 to a weight 42 sitting on the bottom 43 of the aeration basin. A lateral header 33 is shown passing directly underneath the static mixer 11 connected to the main header 34. The lateral header 33 has an aperture 44 at the side thereof which allows air to pass out of the lateral header 33 and up through the helical portions 4~
and continuing up to the water level 45 A number of commercial aerators of this type are available. Some of them have different mixing elements, however, the type of mixer illustrated has been found successful because little or no clogging occurs either in the helices 40 or the air aperture 440 It is preferred that the turnover time in the aeration section is calculated to be approximately 7 minutes. However, this turnover time is dependent on the number of aerators and the depth of water in the aeration basin Aerator efficiency is higher ~or greater depths, but the turnover time increases.
However, the deeper the aeration basin, the more heat it retains and space considerations can become a factor if the basins are shallow In one embodiment the basin was 18 ft. deep and an aeration turnover time was calculated as 8 minutes. In another embodiment the basin was 11 ft. deep and the turnover time was less than 7 minutes Example:
An aeration basin was prepared 160 ft. x 60 :~t. with an average effluent waste water depth of 11 ft. An uir blower 22?7 discharged 1,460 scfm of air at 5 lbs. per square inch ~auge, into a 10~' header which ran the length of the basin, 16 lateral headers extended from $he main header into the basin, the first 10 lateral headers had six aerators each and the last six lateral headers had five aerators each. The flow rate through the aeration basin can vary from 200,000 gallons per day to 800,000 gallons per day. E~fluent waste water quality remains uneffected. The results of tests run on the system are illustrated in Table I.

TABLE I
Effluent entering aeration basin BOD5 350 mg/l Phenol 2 Oil and Grease115 T.S.S. 75 ppm Effluent after 3 days in aeration basin and 5 days in settling basins BOD5 24 mg/l Phenol 0.008 Oil and Grease 6 T~S~So 25 ppm As illustrated in Table I there is an improvement in BOD content o* over 90% and a reduction in phenol, oil and grease and T.S.S, content.
Other tests carried out included the addition of phosphate as a nutrient at a concentration of about 0.1 ppm but this had no apparent e~fect on the process. It has been found that the process can be adapted for existing aer~tion systems having a number of settling basins hy the additlon of an aeration basin before or between the settling basinsO If many set-tling basins are included, then the more basins available the better ~2~ ~?

the end product tends to be, Various changes may be made to the proces~ without departing from the scope of the present invention, which is limited only by the following claims.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for effluent waste water treatment, the improvement of treating effluent such that substantially no sludge is formed, comprising the sequential steps of:
skimming the effluent to remove free oil, vigorously mixing and aerating the effluent to maintain waste material present in the effluent in suspension such that minimum flocculation of waste material occurs, continuing the mixing and aerating step for at least three days such that oxygen reduction of a substantial portion of the waste material in the effluent occurs, and passing the mixed and aerated effluent to at least one settling basin for at least four days such that oxygen reduction or oxidation of substantially all the remaining portion of the waste material occurs.

2. Process according to claim 1 wherein the period of time for the mixing and aerating is sufficient such that oxygen reduction of at least about 80% of the waste material in the effluent occurs.

3. Process according to claim 1 wherein the period of time for the mixing and aerating is sufficient such that oxygen reduction of at least about 90% of the waste material in the effluent occurs.

4. The process according to claim 1 including the step of skimming the effluent directly after mixing and aerating.

5. The process according to claim 1 or claim 4 including the additional step of skimming the effluent after retention in the settling basin.

6. The process according to claim 1 wherein the mixing and aerating occurs in an aeration basin, and a portion of the mixed and aerated effluent at the end of the basin is recycled back into the basin.

7. The process according to claim 1 including the step of from time to time seeding the effluent with biologically active water prior to the mixing and aerating.

8. The process according to claim 1 wherein the mixing and aerating occurs in an aeration basin containing a plurality of static mixers in the form of vertical tubes having alternating right and left hand helical vanes therein, and inclusing supplying air underneath each of the static mixers.

9. The process according to claim 8 wherein the temperature of the effluent in the aeration basin is maintained such that it does not fall below about 13°C.

10. The process according to claim 9 wherein steam injection is provided to ensure temperature of the effluent in the aeration basin does not fall below about 13°C.