CA1040760A - Water treatment with nitrogen dioxide - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Water is treated to reduce or eliminate the tendency of waste waters to pollute the waterways into which they are discharged, to purify drinking water supplies, to control taste and odor, and to disinfect it, by dissolving therein a small but effective amount of NO2 based on the weight of solids suspended in the water.

Description

The present invention relates to the treatment Or waste waters 80 as to reduce or eliminate the tendency of the waste waters to pollute the waterway~
into which the waste waters are discharged, and the treatment of water to pur-ify drinking water supplies, to control taste and odor, and to disinfect it.
Such pollution of waterways has been detrimental to public health, fish life and other aquatic life and to the use of these waterways for recreation and as sources of industrial and drinking water supplies. Pollution and its potential hazards are not necessarily caused by the discharge of toxic wastes per se but are primarily due to the discharge of organic wastes in amounts such that there is not enough oxygen in the waterway to support the oxidizing res-plratory neede of the aerobic purifying mlcroorganiems that multiply very rapid-ly ae long as the food and oxygen supply lasts. Theee organisms use the pol-lut~nts a~ a source of food and energy. The end product of the aerobic micro-organiems used in the treatment o~ pollutants is carbon dioxide and water.
When the oxygen in the waterway and the re-oxygenation capacity of the waterway is inadequate, the aerobic organisme die, decay and putrify. Contrary to public opinion, theee wa~tee continue to be biodegradab}e but the proces~ o$
purificatlon ie taken orer by anaerobic microorganism~, biota that secure food, energy and oxygen by putreraction o~ the organic material in the waste waters.
The by-products of the anaerobic organieme are foul-smelling, odoriferoue chem-ical compounds and, unlike aerobic organisms, produce an environment that i8 ~ conducive to pathogenlc organism~ and dangerous to public health. When the 1- ~ oxygen supply ln the waterway again becomes adequate, the anaerobic organiems die and the aerobic organigm~ take over and use the remaining organic material in the waste water and that i'rom the dead anaerobic ~d aerobic organisms for food and energy. When the food supply is adequate, the microorganisms multiply very rapidly. As the food supply is exhausted, the rate of growth of the micro-organisms gradually declines until the death rate is greater than the growth rate and the waters thus bec e purified of organic wa~tes and living and dead bacteria. The purified wsters become clear and of a quality that will support fish and other aquatic life and they can be used for recreational purposes snd as a source of water supply for industrial and public use. The technology described briefly sbove is known as the growth curve Or cellular microorganisms.

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' ' ' , lV4~760 The organic material in waete waters i8 currently removed by the use of - aerobic-type bacteriological sy~tems. The degree Or re~oval can be over 95~
but generslly a removal oi~ between 85 - 90~ i8 satisractory. The systems are Or the trickling filter type or some modification Or the activated sludge proc-ees. On the trickling filter, the bacteria grow on etones. They remove the organic pollutantg as the wa~te waters trickle downward through the stones.
The living and dead bacteria are removed by a gravity-type clarifier before the liquid is di~charged into the waterway.
In the activated eludge process and its modification~, the organisms are grown euspended ln the liquid and air is supplied to the bacteria in the form of compreesed atmospheric air difruged therein. The living and dead bacteria are also removed by a gravity-type claririer berore the liquld is discharged into tho waterway. In the activated sludge procesees, the settled organiems are continuouely returned to the inlet end of the aeration tank as seed organisms.
The excess organiems as in the trickling filter are discharged into a se F ate container for digeetion by aerobic or anaerobic organiem~ or for dispoeal by inclneration. The final product is dieposed Or generally on land as a humus for agrlcultural purposee or land rill.
Devlcee for promoting biological processes for the treatment of the eolu-ble liguid waete fraction as well ae the insoluble fraction are costly to con-etruct and coetly to maintain and operate and they are eub~ect to frequent up-sets based on the use Or currently known technology, psrticularly lf the waste waters contain pollutants that are toxic such as phenols and heavy metale and waete waters that reach the biological treatment plant in a eeptic condition due to anaerobic digeetion Or the waetee in the sewers enroute to the plant.
Pretreatment to remove or minimize the efrects of these inhibitory chemical compounds and septic sewages hae been helpful but not entirely eatieractory, psrticularly ae to the septicity produced enroute due to the length of the interceptor eewer eyetem conveying the waste waters to the treatment plant.
In order to reduce the cost of waete water treatment plante, phyeical-chemical methode are now being investigated. In theee proceeses, the waete watere are treated with lime to impart to them a high pH as a meane to hydrolyze the ineoluble organic pollutante. The clarified wastee are then paesed through

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1~4~760 a sand filter for further clarification and then on to and generally through rilters containing carbon media for absorption Or the soluble organic pol-lutants. The carbon filters do a good ~ob of removal but the systems do not appear to be economically feagible. The carbon filters clog readily and the cost of regenerating and replacing lost and spent carbon based on current knowledge i~ too high. Ozonation is now being studied in lieu of the carbon rilters .
The physical-chemical procesees and the biological processes with the aid Or chemicals do a good ~ob of removing the nutrient phosphates but the removal Or the nutrient nitrogen as ammonia still is a problem. Air stripping at high pH has been tried as well ae such oxidants as chlorine, oxy acids, potassium permanganate and ozone. Each seems to have its drawbacks. Ozone appears to be the most promising.
It ie known in the art that in aerobic biological proceeees, the bacteria oxidize and eyntheeize the organic pollutante to C02 ~ H20~cellular material.
In the proceee, the bacterla oxidize the alcohole through aldehydee and ketonee to organic acide and by further oxidation and decarbolyzation into C02 and H20.
For example~ it 18 well known that when a hydroxy acid euch ae pyruvic acid ie ~ormed, upon $urther oxidatlon it is eaeily oxidized to an aldehyde I C02 ~
H20, ~hich method ie used to degrade an acid etep-by-etep by elimination of a carbon ae C02. It ie aleo known that organic chemical compounds in general can be oxidized through alcohols into dlbasic organlc acids such as oxalic acld which ror example on further oxidation are easily oxidized to C02 and H20.
The bacteria apparently $ollow the sQme mechanisms in the oxidation and syn-theeie o$ organic pollutante which they u~e as a source of $ood and energy andthue purii~ the waete waters o$ the organic pollutants. Aerobic organiems also exist in the biota that oxidize ammonia to nitrates and aerobic-anaerobic organisms that denitrify nitratee to molecular nitrogen.
In some waste water treatment processes, nitrates in the $orm o$ ammon-ium nltrate and sodium nltrate have been added to the waste waters being treated,as a source o$ oxygen and/or nitrogen. It has been $ound by experience that the aerobic organisms can use the oxygen in nitrites and nitrates if the supply of dissolved oxygen in the waste water~ is not sufficient. The aerobic bacteria

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lV4()760 do not seem to be able to use for respiration the oxygen in other chemical compounds containing oxygen. The denitrifying organisms apparently release molecular oxygen when the nitrates are denitrified to molecular nitrogen.
This invention relates to a method of treating domestic sewage waste water, comprising dissolving an effective amount of NO2 in domestic sewage waste water containing as organic materials: bacteria, other micro-organisms, fats, alcohols, aldehydes, ketones, carbohydrates with aldehyde ends, organic acids, ammonia, ammonium compounds, cellulose, primary amines, amino acids and urea, said effective amount being from one milligram to 50 grams of nitrogen dioxide per gram of organic material, and then discharging the treated domestic sewage waste water into a waterway, said amount being effective to serve as a source of oxygen for microorganisms present in the waste water, and as an oxidizing agent for aerobic-anaerobic bacterial processes in the waste water, and as a hydrogen acceptor for biochemical ! reactions in the waste water, and as a chemical reagent that bacteria in ! the waste water can use as a source of nutrient nitrogen, and as an oxidiz-ing agent that will oxidize fats, alcohols, aldehydes, ketones, carbohydrates ;~, with aldehyde ends and organic acids present in the waste water to molecular nitrogen, and as a chemical reagent to convert cellulose and fats present in the waste water to more biodegradable compounds, and as a chemical re-agent that will react with primary amines and amino acids which contain an amino group present in the waste water to yield nitrogen and alcohol as degradation products, and as a chemical reagent that will react with urea present in the waste water to yield carbon dioxide and nitrogen as degrad-ation products, and as a chemical reagent for lysis or disintegration of the cell walls of microorganisms present in the waste water so that the material of which the organisms are made can be destroyed by serving as a source of food and energy for other living organisms present in the waste water.
It has been found by experiments that the microorganisms can and do use nitrogen dioxide as a source of oxygen if adequate residual dissolved oxygen is not available in the waste waters being treated. Accordingly, the present invention uses nitrogen dioxde as ~I) a source of oxygen in part 1~
_4_ ~r ..' 1040~60 or in its entirety for the microorganisms, (2) as an oxidizing agent alone or as an aid to the aerobic-anaerobic bacterial processes, (3) as a hydro-gen acceptor for biochemical reactions, (4) as a chemical reagent that the bacteria can use as a source of nutrient nitrogen as well as a source of life-sustaining oxygen and at the same time as an oxidizing agent to work with and supplement the oxidation being done by the bacteria, (S) as a powerful oxidizing agent that will oxidize organic compounds such as fats, alcohols, aldehydes, ketones, carbohydrates with aldehyde ends and organic aclds into C02 and H20, ~6) as an oxidizing reagent to oxidize ammonia and ammonium compounds to molecular nitrogen, (7) as an oxidizing agent that will oxidize toxic inorganic chemical compounds such as cyanides and phenol-creosotes and the like compounds to harmless biodegradable and taste- and odor-free compounds, (8) as a chemical reagent that will convert such organic compounds as cellulose and fats to a more biodegradable compound, ~9) as a chemical reagent that will react with primary amines and amino acids which contain an amino group and will yield nitrogen and an alcohol as a de-gradation protuct, (10) as a chemical reagent that will react with urea and will yield C02 + N2 as the complete degradation product, and tll) as a chemical reagent for lysis or disintegration of the microorganism cell walls ; 20 so that the material of which the organisms are made can be destroyed by serving as a source of food and energy for the other living organisms and thus eliminate or reduce the problem of sludge disposal.
By nitrogen dioxide is meant N02 and its precursors, e.g. N20 and N0, which form N02 in situ in the presence of oxygen.
Accordingly, it is an object of the invention to use nitrogen dioxide alone, in series or in parallel with biological waste water treat-ment processes as an enhancement to biological treatment of waste waters, for destruction of -4a-;', ~ .
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,,: ' 1040~760 taste and odor compounds in drinking water, and for destruction of toxic ~; microorganisms and organic and inorganic chemical compounds in waste water and the like.
Municipal waste water treatment plants handle more than domestic wastes from homes and apartments. On a nationwide average, about 55~ Or the waste water comeg from homes and commercial e~tablishments and 45~ rrom industry.
Increasingly complex manu$acturing processes, coupled with rising in-dustralization, create greater amounts Or exotic wastes potentially toxic to humans and aquatic life not only in the discharges from industry into waterways and m~nicipal sewer systems but also in the form Or household products. These wastes per se might be biodegradable but when tbey are dis-charged into a 6anitary sewer system~ these harmless waste waters mix with ..
other chemicals and domestic wastes and orten become nonbiodegradable or toxic or otherwise resistant to biologlcal treatment processes.
Domestic sewages that are rresh are more amenable to aerobic biological ¦ treatment than domestic wastes that have become septic in storage or enroute I to the treatment works due to the length of time in transmlssion. In long tranemission mslns, due to lack of a source of oxygen, anaerobic organisms take over and decompose by putrefaction the organic material in the waste waters. Such waste waters being decomposed to a different degree on reaching the waste water treatment plant are anaerobic and resistant to biodegradability and are saturated with hydrogen sulphide which is toxic to bacteria as well as man and contain inorganic and organic compounds that are at reduced oxida-tion levels and must be raised to higher oxidation levels to prevent pollu-tion Or waterways. In order to make these wastes amenable to aerobic bio-logical treatment, the toxic products must be neutralized and the conditions in the sewers enhancing anaerobic conditions must be changed 80 as to provide in effect an aerobic atmosphere.
By applying nitrogen dioxide in the sewer system some distance ahead of the plant, at the plant, and in the seed sludge being recirculated in the plant singly or in any c fbination, the toxic and septic waste waters can be readily converted to conditions very amenable to aerobic biological treatment, thereby to provide an aerobic atmosphere in the waste waters and oxidize the inorganic ,, , . . ' 104~760 and organic wa~tes from a lower level to a higher oxidation level. Such treat-ment with oxides of nitrogen will prevent the production of obnoxious odors in the vicinity of the plant and will cut down on the capital co~t of construction ; and operating costs.
The lower oxidation product~ of sulphate through sulphur are a ~ource of trouble in aerobic treatment. Under anaerobic condition~ the ~ulphur bacteria reduce sulphates to hydrogen ~ulphide, and under aerobic conditions the sulphur-oxidizing bacteria use a large amount of di~olved oxygen and carbon dioxide oxidizing reduced forms oi~ sulphur to sulphates. Unfortunately, the sulphur-oxidizing organisms are predaminstely autotrophic. That i8~ they require neither organic carbon nor organic nitrogen for growth but are able to build up carbohydrates, rats and proteins out Or carbon dioxide and inorganic salts thus producing a higher organic losd on the treatment plant and in the process a larger amount of oxygen is required for respiration and metabolism. The oxidation of sulphites by molecular dissolved oxygen in water is slow but by nitrogen dioxide they are rapidly oxidized to sulphates, the final oxidation state Or sulphur. By using the nitrogen dioxlde for oxidation Or reduced $orms Or sulpbate~ the sulphur-oxidizing bacteria can be eliminated at a great sa~ing in operating cost. In sddition, clarification will be improved because the predominant sulphur-oxidizing bacteria are rilamentous and do not settle well in gravity claririers. A great source of sulphur bacteria is supernatant liguors from anserobic digesters and septic sew~ges enroute to the treatment works.
Since waste waters contain many lower and complex oxidation products that are oxidized to higher levels~ the advantages of the use Or the nibrogen dl-oxlde for direct oxidation singly, in series or in parallel with aerobic bio-i logical treatment Or reduced organic and inorganic products to hlgher oxida-~i tion levels becomes very e~ident.
Nltrogen dioxide can be applied and U8~ at the source Or the pollutant discharges ~rom industry witb or without pretreatment ~acllities and ahead ;~ Or or after pretreatment raclllties.
, :, ` In municipal or regional systems, nitrogen dloxlde can be applled and used - ln the system some dl~tance above and ahead of the treatment raclllties; in tbe , : , 104~)760 wet well and in the pump dlscharge main Or pump station3; at the head end of treatment ~ystems or at the head end o~ any Or the treatment unit~ including supernatant liquid from anaerobic digesters; in anaerobic or aerobic digesters;
in the compressed air or surrace aeration systems Or aeration tanks~ in return seed eludges, in recirculated n OWB and in the final treated er n uent and at other locations.
Nitrogen dioxide and its precursors are very eoluble in water. They can bo applied as a solutlon in water ueing a rotometer or by some other similar de~ice to messure the gas dossge being spplied to the 301ution water or they can be applied as a eas through similar metering and control devices directly to the waters being treated, or directly as a liquid. It is preferred to use nltrogen dioxlde as a gas arter passing the gas through a rotometer or some otber measurlng and control devlces and to apply the gas dlrectly to the waste water belng treated. At locatlons where the depth and flow are not adequate to dlssolve all the gas being applled~ lt will be necessary to apply nltrogen dioxide in solutlon. The gas dissolves very rapidly and can be applied into cold waters or into hot waters without any apparent dirriculty. The pipeline fceding the gae~ however, should be insulated or kept wsrm because at tempera-tures below 70.1 F. and atmospheric pressure nltrogen dioxlde changes from a gas to a llquld.
WhRn nitrogen dioxide is lntroduced into waste water which is at a tempera-ture above the boiling polnt Or nitrogen dioxide at atmospheric preseure, it le desirable that the point Or introductlon be surrlclently below the surrace Or the waote water that substantially complete dissolution Or the N02 will occur without 10B8 to the atmosphere. It has been found ror exsmple that at sn in-troduction rate Or about 10 cubic reet Or N02 per hour~ the point Or lntro-ductlon should be submerged at least about two feet 80 as to prevent bubbles Or N02 reachlng the surrace. At about 30 cubic feet per hour, the N02 should be introduced at a depth of at least about three feet; while at a depth o~
about ~our ~eetor more, the introductlon rate of N02 can be as great as deslred without 1088 to the atmosphere.
Temperatures for the reactions are not crltlcal. Room temperature or the ~ outside temperature~ Or the atmosphere or Or the water~ likely to be treated :.`
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1()4~11760 are not crltical except that the pipe conveying the gas to the point Or treat-ment should be insulated or heated by a thermal cable or other means, for the ~ea~on pointed out above. Nitrous oxide, nitric oxide and nitrogen trioxide remain as a gas at temperatures below -21C. and thus need no protection against ~reezlng.
Pressure is not critical. The reaction proceeds at atmospheric pressure as ~ell as at higher and lower pressures, particularly at pressures normally encountered in water treatment and waste water treatment plant~.
During the reaction~ the pollutant is oxidized by the nitrogen dioxide.
Por example, nitrous oxide is generally not as powerrul as nitric oxide as an oxidlzing agent. Therefore, less nitric oxide will be required to oxidize the eame pollutant. ~o treat the same pollutant, lese nitrogen dioxide (N02) is needed to treat the same pollutant than ir nitric oxide (N0) were used.
In the art of waste water treatment, the biochemical oxygen demand of the untreated waste waters ~BCD5) over a period oi~ 5 days is general~y used as a design parameter i~or biological waste water treatment plants. For example, the average B0D5 of domestic waste waters is around 200 mg./l. or they contaln approximately 1668 pounds o~ BoD5 per million gallons o~ waste water. ~o completely deetroy this organic lo~ding by biological treatment~ approximately 1 to 1.25 pounds Or oxygen are required per pound Or B0D5 removed. 0f the total amount Or oxygen required, approximately 0.5 pound is consumed by the bacteria ror oxidation and conversion Or approximately 3 ~ of the organic ma-terial into C02 and H20 and 63% of the organic material is synthesized into cell material. An addition~l 0.75 pound must be provlded then to completely ~ 25 oxidize the cell material produced which in turn produces an ash content Or ;~ 0.12 pound per pound Or B0D5. Approximately 1.0 pound Or the oxygen is re-~ quired per 200 pounds Or active bacteria for respiration, and for stronger . .
~;~ waste waters two to three times as much is required.
. , It can readily be ~een ~rom the above rigures that i~ chemical oxidizers 3 are used for direct oxidation, the amount of oxygen required to oxidize pol-lutants may be as low or lower than 0.5 pound Or oxygen per pound Or biode-` gradable organic material and in other waste waters it may be much higher, perhaps twice as much or more, than that required by biological treatment due 104~760 to the oxidation of pollutants that are resi~tant to biological treatment but are readily oxidized by chemical oxidizlng reagents. For example~ lienin~
which i6 almost nonbiodegradable~ can be completely oxidized by nitrogen di-oxide.
When industrial waste waters are treated, for example, industrial wa~te waters containing phenols, cyanides, etc., the amount o~ nitrogen dioxide re-quired for complete destruction may be as much as five times Breater than that requlred ~or oxidizing pollutants in dcmestic sewage. The term "phenols" is used herein in its ordinary sense in the art of waste water treatment, to deslgnate the mixed aromatlc hydroxy compounds produced by anaerobic deccmpo-sit10n of the protelns in sewage and by metabolism in the human body. ~hese are ordinarily present in trace amounts to a maximum Or about 15 milligrams per liter; but when $ndustrial waste is added to the sewer system, the content of phenol6 as for example rrom steel mill operations can be as much as 1000 milligrams per liter or more.
On river and lake waters used as sources of water supply~ the amount of nitrogen dioxide requlred should be very small because the amount oi~ pollu-tants in such waters is generally very small. ~hese pollutants, however, are generaIly a source o$ taste and odors in such waters and mu~t be destroyed.
Chlorine and potassium permanganate are generally used to destroy these taste-and odor-producing compounds. In the present invention, it is proposed to use nitrogen dioxide for this purpose because nitrogen dioxide provides com-plete destruction without forming additional products and it d oe 8 not increasethe dissolved solids content Or the water.
~; 25 The rollowing examples are given, not to limit the invention, but rather to enable persons ~killed in the art to practice the invention.
,, EUWP~E 1 Waste water at a temperature Or 20 C. and containing 10 milligrams per :: `
~ liter Or phenols is treated at the source bei~ore the untreated waste waters . :., are discharged into the waterway or sewage collection system, by applying ni-trogen dioxide in vapor phase at a submergence oi' ~our feet through a control ~; valve followed by a rotometer at a flow rate that can vary ~rom 1 to 7 milli-grams Or N02 per milligram Or phenols and in the present example is 2 mllli-. . ~

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1(~4(~760 grams of N02 per milligram of phenol~. Ireatment is batchwise with a deten-tion time of at least 15 minuteg, specifically~ 30 minutes in the pre6ent example. The phenols and cyanides are readily oxidized, largely to carbon dioxlde and water.

Example 1 is repeated except that the nitrogen dioxide is applied to the waste waters at the head end of a treatment plant constructed to treat combined industrial and domestic waste waters. The quan$ity of pollutants (BOD5) is 600 milligrams per liter of waste water and the nitrogen dioxide is applied at a rate of l to 32 milligrams per milligram of BODs, or 3 mg./mg. in thls example.

Example l is repeated except that the N02 is applied upstream in the sewer system from the treatment works in a pipeline conveying the waste waters.
The BOD5 is 400 milligrams per liter and the rate of N02 application is as in Example 2. Treatment at this location prevents the waste waters ~rom becom-lng septlc and odorii~erous and provldes chemical oxidation as a pretreatment of the waste water to a deslrable degree.

Example l 18 repeated, except that the N02 is applied to the effluent waete waters Or the primary clarlfier tank between the primary tank and the blological treatment unlt 80 as to reduce the organic load on tbe biological ~, treatment unit and to destroy toxic compounds that may be in tbe untreated wagte waters. Treatment at this location conserves nitrogen dioxide, because tbe primary claririer tank normally removes by gravity settling about 20-35 the organic pollutants in the untreated waste waters. The BCD5 18 350 mg./liter and the N02 appllcation rate is the same as in Examples 2 and 3.
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~., Example l 18 repeated, except that the nitrogen dloxide i8 applied ahead of the blological treatment unlt as a source of nutrient nitrogen as well as a source of oxygen for biological metabolism and at a rate of about 1 pound o~
nitrogen dloxide per 200 pounds of biologlcal life determined as volatile sus-pended solids in the system. The consumption rate can be about 1 milligram of `, -10-~- '' ~ ' ' ~ ' ' ' ' " " ' ~ ' 1~4~760 nitrogen dioxide per milligram o~ BOD5 when the nitrogen dioxide serve~ as a nutrient.

Example 5 is repeated, except that nitrogen dioxide is applied to the flow which i8 returned, from the clarlfier tank that rollows the biological treatment unit, to the head end of the treatment plant. The quantity of ni-trogen dioxide applied i8 about 1 to 25 milligrams of N02 per gram of mixed liquor suspended solids, in this example 3 milligrams N02 per gram of solids, as the return flow is from a trlckling filter type of plant. For trickling 1~ filters, the average suspended solids in the return flow is gener~l1y less than 1000 milllgrams per liter and the BOD5 thereor is usunlly about 500 milligrams per liter. In activated sludge-type plants~ the average suspended solids in the return n ow is about 10,000 milligrams per liter and the BODs thereof is approximately 5000 mllligrams per liter. This oxygen demand in both csses is cau~ed by respiration reguirement~ of the organisms and is generally expressed as 5 milligrams Or oxygen per hour per gram Or volatile suspended solids. In thls ex~mple, nltrogen dloxlde is u~ed primarily as an addltion 1 source of nutrient nitrogen and oxygen and to oxldize some Or the by-products Or aerobic oxldation. It is desirable to limit the guantity Or nitrogen dioxide in this example~ as gubstantially more tends to kill the biological life, and this is not desirable at this point Or the biological treatment. It may be that, when ~ such low concentratione Or N02 are used, the N02 neutralizes the toxic by-t products Or metabolism leached i~rom the organisme into the water in which the organisms are suspended. It may also be that N02 kills rilamentous organisms which are undeeirable and which do not settle well, but d oe e not kil1 the desir-~ :!
~ ~ able biota at such low concentrations Or N02.
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8XlULrL 7 Example 1 is repeated, except that nitrogen dioxide is applied to the super_ natant erflue~t from an anaerobic digestion tank berore the supernatant is dis-~` 30 charged back into the liquid phase of the treatnent plant. Anaerobic digester supernatant effluents are very toxic to biological treatment and have a high :' -` oxygen demand. The BOD5 i~ 400 milligrams per liter and the N02 naw rate is ( as in Example 2.

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EXA~LE
Example 1 ie repeated, except tbat nitrogen dioxide is applied to the re-circulated stream of a ~econdary aerobic digester 80 ae to destroy the cell wall ; of the microorganisms and to make them available in tbe destroyed iorm as a sou-rce oi food and energy in a eubseguent biological treat~ent unit and to reduce or s~bstantially eliminate the problem of sludge diepoeal. The BCDs is 300 milli-grame per liter and the rate of N02 application is 1 to 6 milligrams per milli-gram oi BCD5, or 2 milligrame N02 per miIligram BaD5 in the pre~ent example.
A~LE 9 Example 8 is repeated, except that the N02 is applied to the content~ Or an anaerobic digester.

Example 1 is repeated, except that nitrogen dioxide ie applied to the iinal plant erfluent before it is discharged into the waterway to oxidize any unoxidlzed ammonia which m~y be in the plant einuent to a higher oxidation level euch a~ gaeeoue nltrogen and water. Ammonia le thus eliminated as a nutrient for algae and other aquatic growth in the recelving waterway. The ammonia nitrogen content oi the eifluent is 7 milligrame per liter and the rate oi N02 appllcatlon ie 1-14 milligrams, ln thle case 3 mllligrams, Or N02 'I
! 20 per mllligram of ammonia nltrogen.
EXAMP$E 11 i ~ Example 1 is repeated, except that nitrogen dioxide is applied to the " ~
` ilnal efiluent of the treatment plant berore it is diecharged into the water-: :i way, this time as a disinrectant or sterilizing agent to klll the microorgan-isms and deetroy the vira in the plant efrluent. The content Or microorganism and virue cell material prior to treatment ie 15 milligrame per liter and the rate Or N02 application ie 1-6 milligrame per miIligra~ Or microorganiem and : ,.,.~
~i virue cell material, in this case 2 milligrams per milligram.
EXAMEkE 12 ~, 30 Example 1 is repeated, except that the nitrogen dioxide ie added to the waste waters for oxidation o~ lower oxidation state sulphur compounds to the inal oxidlzed state sulphate. Thls is to prevent the putreiactlon enroute to the treatment works due to the breakdown oi sulphur compounds by anaerobic :: . .

' 1~4~3760 microorganisms into hydrogen sulphide and other odoriferous reduced sulphur compound~. The waste waters contain 5 milligrams per liter of lower oxidation state sulphur compounds and the N02 is used at a flow rate of 1-3 milligrams per milligram of reduced sulphur compounds, in this example 1 milligram N02 per milligram reduced sulphur compounds.

Example 1 is repeated, except that nitrogen dioxide i~ applied at the in-let end of the water ~iltration treatment plant a~ a disinfectant and as a chemi-cal reagent to neutralize and oxidize toxic material and/or taste- and odor-produclng material in the source of water supply i~or drinking water. The ni-trogen dioxide is supplied at the rate of 1-24 milligrams per liter, in this example 10 milligrams per liter, to oxidize and destroy the taste- and odor-producing compounds before the water is pumped into the system for public dis-tribution.

ELg~E 14 Example 1 is repeated, except that nitrogen dioxide is applied to the e~luent oi~ a treatment plant before the effluent is dlscharged into the water-way to destroy and/or render less potent vitamins such as B12 and biotin and plant growth ~rmones such as indol and enzymes that are produced in the plant efnuent by the biota in the waste waters being treated as a by-product oi' metabollsm. These substances i~eed algae and other aquatic plants and are known to be produced in biological treatment plants. The B12 content is about 76 micrograms per 100 grams o~ suspended solids and the N02 is applied at a rate o~ about 2 milligrams per milligram o~ plant growth ~actor.
From a consideration of the foregoing disclosure, there~ore, it will be evident that the invention comprises the application to waste water o~ a small .!
;~. but e~rectiw amount o~ N02, the amount being erfective to reduce the pollutant tendency of the waste water prior to discharge into a waterway. Depending on the particular function o$ the N02 and the system considered, the small but 30 efi'ective amount will be at least about 1 milligram oi~ N02 per gram o~ 8U8-, ~:
pended solids in the waste water. Por most purposes, there is no upper limit o~ N02, the use o~ excess N02 being merely wasteful. In general, however, it i~ not use~ul to apply N02 at a rate greater than 50 grams per gram o~ a sus-pended solld. 104~760 From a consideration of the foregbing disclo~ure, therefore, it will be evident that the initially recited obJects o$ the present invention have been achieved.
Although the present invention has been descrlbed and illustrated in con-nectlon with pre$erred embodiments, it is to be understood that modi$ications and variations may be resorted to without departing $ram the spirit of the in-vention, as those skilled in this art w$11 readily understand. Such modi~ica-tions and variations are considered to be within the purview and scope o$ the present invention as defined by the appended claims.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of treating domestic sewage waste water, comprising dissolving an effective amount of NO2 in domestic sewage waste water containing as organic materials: bacteria, other microorganisms, fats, alcohols, aldehydes, ketones, carbohydrates with aldehyde ends, organic acids, ammonia, ammonium compounds, cellulose, primary amines, amino acids and urea, said effective amount being from one milligram to 50 grams of nitrogen dioxide per gram of organic material, and then discharging the treated domestic sewage waste water into a waterway, said amount being effective to serve as a source of oxygen for microorganisms present in the waste water, and as an oxidizing agent for aerobic-anaerobic bacterial processes in the waste water, and as a hydrogen acceptor for bio-chemical reactions in the waste water, and as a chemical reagent that bacteria in the waste water can use as a source of nutrient nitrogen, and as an oxidiz-ing agent that will oxidize fats, alcohols, aldehydes, ketones, carbohydrates with aldehyde ends and organic acids present in the waste water to molecular nitrogen, and as a chemical reagent to convert cellulose and fats present in the waste water to more biodegradable compounds, and as a chemical reagent that will react with primary amines and amino acids which contain an amino group present in the waste water to yield nitrogen and alcohol as degradation prod-ucts , and as a chemical reagent that will react with urea present in the waste water to yield carbon dioxide and nitrogen as degradation products, and as a chemical reagent for lysis or disintegration of the cell walls of microorgan-isms present in the waste water so that the material of which the organisms are made can be destroyed by serving as a source of food and energy for other living organisms present in the waste water.

2. A method as claimed in claim 1, said amount being 1 to 32 milligrams of nitrogen dioxide per milligram of organic material.

3. A method as claimed in claim 1, and introducing said nitrogen dioxide into said domestic sewage waste water in vapor phase beneath the surface of the domestic sewage waste water.

4. A method as claimed in claim 3, in which the point of introduction of said nitrogen dioxide is at least about two feet below the surface of the domes-tic sewage waste water.