Waste water process

A method is provided for the treatment of a waste water stream characterized by having toxic and corrosive properties due to the presence of a cyanides formates and a halide of a metal or ammonia comprising adding a ferrous ion to said waste water to convert the cyanides to iron cyanides, adding a base to said waste water until the pH of said waste water is adjusted to the range from about 9 to 11 to precipitate a sludge containing said iron cyanides, feeding said waste water to a biological reactor to convert said formates to carbon dioxide and a biological residue and recovering an environmentally upgraded waste water stream from said biological reactor.

BACKGROUND OF THE INVENTION 
The partial oxidation of distillate hydrocarbons to produce a gaseous 
mixture of hydrogen and carbon monoxide in the synthesis gas process is 
well known. According to this process, a carbonaceous gas or a distillate 
fuel, such as fuel oil, naphtha, methane, propane and refinery off-gases, 
and an oxygen-rich gas are introduced into a free-flow, non-catalytic 
synthesis gas generator at a temperature in the range from about 
1500.degree. to 3000.degree. F. and a pressure in the range of about 1 to 
250 atmospheres to effect the partial oxidation of the carbonaceous fuel 
to a synthesis gas stream comprising a mixture of hydrogen, carbon 
monoxide, carbon dioxide and water together with relatively minor amount 
of hydrogen sulfide, carbonyl sulfide, argon, nitrogen, cyanide, ammonia 
and methane. Water is used as a quench medium to cool the synthesis gas 
produced in the generator. After the separation of the synthesis gas and a 
major proportion of the volatile by-products gases, such as CO.sub.2 and 
H.sub.2 S, from the quench water, a waste water stream remains containing 
small amounts of cyanides, formates and other by-products of the reaction. 
While this waste water stream contains toxic by-products of the synthesis 
gas process, it is, nevertheless, suitable as a recycle stream for the 
process either in admixture with the feed to the synthesis gas generator 
or as the quench medium to cool the hot synthesis gas mixture issuing from 
the gas generator. No waste water disposal problem occurs when the waste 
water stream can be continuously recycled in the synthesis gas process. 
The reduced availability of natural gas and of petroleum gases and 
distillates as feedstocks materials has led to intensive efforts to 
develop other carbonaceous materials as fuels in the synthesis gas 
process. Among the carbonaceous materials under intensive investigation 
are petroleum residuum, petroleum coke, subbituminous, bituminous and 
anthracite coal, lignite, shale, organic waste material, sewage sludge, 
crude oil residues, coke and liquified coal and coal fractions. 
When the fuel employed in a synthesis gas process contains significant 
amount of water-soluble salts, such as a halide of a metal or ammonia, 
these salts are transferred to the waste water together with the cyanides 
and the formates produced in the process. While the concentration levels 
of these impurities in the waste water remains low, the waste water or at 
least a portion thereof can be recycled to the synthesis gas process 
either to be mixed with the fuel feed to the generator or introduced into 
the quench zone of the generator to cool the hot gaseous product being 
produced. However, when the concentration levels of the impurities in the 
waste water are high or become high as a result of recycling, then a waste 
water stream must be withdrawn and disposed of. Since this waste water 
contain environmentally significant amounts of cyanides and formates, and 
at least one halide salt of a metal or ammonia, it is characterized as 
having both toxic and corrosive properties. The toxicity of the cyanides 
and the BOD of the formates are well established. The term "corrosive" as 
employed herein refers to the corrosive effect of the halide-containing 
waste water on process equipment. It is important to substantially reduce 
or to remove the noted components of this waste water stream before it can 
be disposed of. 
A variety of materials or a carbonaceous nature may be employed as the feed 
material or fuel to a synthesis gas process as indicated above. The 
compositions of these materials as well as the by-products produced and 
the waste water stream from the process vary greatly. In certain 
instances, the waste water will contain metals including such metals as 
nickel and the transition metals chromium and vanadium, ammonia and 
sulfides in combination with the previously noted environmentally 
significant components of the waste water stream. The process of the 
invention is also effective for substantially reducing or removing these 
components of the waste water stream. 
THE PRIOR ART 
U.S. Pat. No. 3,725,270 discloses a pollution abatement process for waste 
water which involves mixing the waste water with a hydrocarbonaceous fuel 
and feeding this mixture to a synthesis gas generator. 
U.S. Pat. No. 4,003,833 discloses a process for treating an aqueous stream 
containing cyanide which comprises contacting the stream with formaldehyde 
and a compound capable of generating HSO.sub.3.sup.- ion at specified 
conditions of pH, temperature and reactant-cyanide ratios. 
U.S. Pat. No. 3,904,518 discloses a method for treating waste water 
employing biologically active solids. The disclosure of this reference is 
incorporated in the disclosure of this invention. 
SUMMARY OF THE INVENTION 
In accordance with this process, a toxic and corrosive waste water stream, 
which contains environmentally significant amounts of cyanides and 
formates, and a halide of a metal or ammonia, is treated with ferrous 
ions, employing an amount of ferrous ions in moles that is in excess of 
the total moles of cyanides present in the waste water, while maintaining 
the pH of the waste water in a range from about 7 to 9 until a substantial 
portion of the cyanides are converted to iron cyanides. A base is added to 
the waste water to adjust the pH of the waste water to a range from 9 to 
11 and to effect the separation of precipitation of a sludge containing 
the iron cyanides. The waste water is separated from the sludge and is 
then fed to a biological reactor which is effective to convert organic 
materials, such as formates, to carbon dioxide and a biological residue. 
The treated waste water from the biological reactor is environmentally 
upgraded and suitable for disposal. By pH is meant the negative logarithm 
of the molar hydrogen ion concentration. 
SPECIFIC EMBODIMENT OF THE INVENTION 
The waste water stream that can be upgraded by the novel process of the 
invention is characterized as a toxic and corrosive waste water stream due 
to the presence therein of environmentally significant amounts of cyanides 
and formates, and a halide of a metal or ammonia. Such as waste water 
stream is generated, for example, in a synthesis gas process in which the 
fuel feed to the gas generator is a petroleum residuum, petroleum coke, 
subbituminous, bituminous, or anthracite coal or liquified coal fractions, 
lignite, shale, organic waste material, sewer sludge, crude oil residues, 
coke and liquified coke or similar crude or impure carbonaceous material. 
While a synthesis gas process can generally be conducted at a temperature 
ranging from about 1500.degree. to 3000.degree. F., it has been found 
advantageous with certain of the foregoing fuels to employ a temperature 
in the generator ranging from about 2200.degree. to 3000.degree. F. 
It will be understood that gaseous carbonaceous feedstocks, such as natural 
gas, methane, ethane or propane, or distillate carbonaceous feedstocks, 
such as naphtha, and butane, when employed as a fuel in the noted 
synthesis gas process, do not produce a waste water stream having both 
toxic and corrosive properties and therefore such a waste water stream 
does not require treatment by the special process that is described 
herein. 
The waste water stream for which the present process is particularly 
intended can be described as a toxic and corrosive waste water stream 
containing significant amounts of cyanides, formates, and a halide of a 
metal or ammonia. The metal halide may be an alkali metal, alkaline earth 
metal or a heavy metal halide or chloride. The cyanides is such as waste 
water will exist in both the free and combined forms. The term "free" is 
used to mean the CN-ion or molecular HCN. The term "combined" is used to 
mean stable complex cyanide containing ions of which Fe(CN).sub.6.sup.-4 
is an example. The waste water intended for treatment in the prescribed 
process of the invention will contain total cyanides (i.e., free and 
combined cyanides) in a concentration ranging from about 5 ppm (parts per 
million) on a weight basis up to 1000 ppm or more. More commonly, the 
concentration range of the cyanides in the waste water will be from about 
10 to 100 ppm. An environmentally significant amount of cyanides is herein 
defined as 5 ppm or above. In general, environmental regulations prohibit 
the disposal in sewers and streams of a waste water containing significant 
amounts of cyanides. 
Another major component of the waste water to be treated by the process of 
the invention is the formates. These compounds, which are inherently 
produced in a process such as the synthesis gas process, give the waste 
water a high biochemical oxygen demand (BOD) rendering it unsuitable or 
unacceptable for discharge. The waste water stream intended for treatment 
in the prescribed process will contain formates in a concentration ranging 
from about 100 to 20,000 ppm with the more common range being from about 
500 to 10,000 ppm. An environmentally significant amount of formates is 
defined herein as 100 ppm or above. 
The presence of halides in the waste water stream is responsible for the 
corrosive characteristics of the stream toward process equipment and 
limits or prevents the recycling of the stream containing cyanides and 
formates in order to effect the destruction of these substances in the 
manner disclosed in U.S. Pat. No. 3,725,270. The halides generally consist 
of one or more of the salts of a metal or ammonia. The predominant halide 
present is the chloride ion. The metal may be from a metal from Groups 1A, 
2A, 5B, 6B or 8 of the Periodic Table. The bulk of the halide component of 
the waste water will comprise sodium, calcium, iron, nickel and ammonium 
halides and, more particularly, the sodium, calcium, iron, nickel and 
ammonium chlorides although other heavy metal halides can be present. 
The waste water effluent intended for treatment by the process of this 
invention will generally contain from about 25 to 20,000 ppm of halides 
with the more common concentration range being from about 50 to 5000 ppm 
of halides. Still more particularly, the waste water effluent will contain 
from about 100 to 1000 ppm of halides, measured as sodium chloride. An 
amount of metal halide of 25 ppm or above is defined as corrosive to 
process equipment. 
Certain carbonaceous materials, which are suitable for use as fuels in a 
partial oxidation or a synthesis gas process, will contain heavier metals 
which can appear in the waste water in a toxic or environmentally 
significant concentration. Included in this class are nickel and the 
transition metals vanadium and chromium. Any one or more of these metals 
can appear in the waste water in a concentration ranging from about 5 to 
1000 ppm although more commonly at a concentration from about 10 to 250 
ppm. Five ppm of any of these metals constitutes an environmentally 
unacceptable amount. 
The waste water effluent produced when a petroleum or a coal derived fuel 
is employed in a partial oxidation process can also contain significant 
amounts of sulfides, thiocyanates (as distinct from free and combined 
cyanides) and carbon. These by-products of a partial oxidation reaction 
may each constitute from 5 to 1000 ppm or more of the waste water 
effluent. More commonly, the concentration of the sulfides and 
thiocyanates will fall in the range from about 10 to 250 ppm. Thiocyanates 
in this concentration is not considered environmentally significant. 5 ppm 
of sulfide or more constitutes an environmentally unacceptable amount. 
Ammonia is inevitably produced in a partial oxidation process and a 
substantial portion of the ammonia will be dissolved in the waste water. 
The concentration of the ammonia in the waste water effluent of a 
synthesis gas process can range from about 100 to 10,000 ppm with the more 
common ammonia concentration range being from about 500 to 5000 ppm. 
The ammonia may be retained in the waste water and carried into the 
biological reactor where it can be incorporated into a biological residue 
to a limited extent or metabolized by means of a suitable bacterial agent. 
Optionally, the ammonia can be stripped from the waste water stream after 
it has been separated from the sludge formed following the second chemical 
treatment operation. If it is desired to partially or completely strip the 
ammonia from the waste water, a stripping step can be employed under 
controlled conditions. Ammonia in an amount of 50 ppm or more is 
considered environmentally significant. 
The conversion of formates and other organic carbonaceous material in the 
waste water to carbon dioxide and a biological residue is conducted in a 
reactor containing biologically active solids or biota according to 
conventional procedures. The waste water at a pH from 9 to 11 is 
introduced into the biological reactor and contacted with the biologically 
active solids at a temperature ranging from about 5.degree. to 40.degree. 
C. The waste-water in this reactor is preferably maintained under constant 
agitation in order to optimize the reaction. It is also desirable to 
monitor the composition of the waste water stream entering the biological 
reactor in order to insure the presence of sufficient nitrogen and 
phosphorus nutrients in the reactor for optimum performance. In the event 
of any nutrient deficiency in this reactor, nutrients can be supplied 
according to conventional procedures. 
The waste water which issues from the biological reactor will be a 
substantially upgraded waste water stream due to the removal of a major 
amount of the toxic cyanides and of the BOD-contributing organic carbon 
components, such as the formates. In general, with the removal of the 
toxic cyanides and of the oxygen-demanding organic carbon components, the 
resulting waste water system is environmentally suitable for disposal in a 
conventional manner. 
While the novel process of the invention is particularly well suited to 
upgrade a waste water stream which contains environmentally significant 
amounts of cyanides and formates, and at least one halide of a metal 
selected from Group 1A or 2A of the Periodic Table, the prescribed process 
is also effective for treating a waste water stream containing the noted 
contaminants in combination with one or more of the metals nickel, 
vanadium and chromium and/or sulfides and ammonia present in the waste 
water stream. 
In the practice of the process of the invention, the prescribed waste water 
stream is first treated with ferrous ions. This treatment can be effected 
at any temperature ranging from about room temperature up to a temperature 
below the boiling point of the waste water, i.e., from about 60.degree. to 
210.degree. F. while the pH of the waste water is maintained in the range 
from about 7.0 to 9.0. A portion of the ammonia stripped out as described 
above, can be recycled to adjust the pH acidic waste water (pH&lt;7.0) to the 
necessary range. If necessary, the pH of the waste water may be adjusted 
to the necessary range in a conventional manner. It is preferred to effect 
the ferrous ion addition to the waste water at an elevated temperature 
ranging from about 125.degree. to 200.degree. F. and, more particularly, 
from 160.degree. to 200.degree. F. 
The ferrous ions are supplied in the form of a ferrous salt, such as 
ferrous sulfate, ferrous chloride or similar ferrous compound. The amount 
of ferrous ions to be added, measured in moles, is an amount in excess of 
the total moles of cyanides present, namely the total moles of free and 
combined cyanides (excluding thiocyanates). Broadly, the range in moles of 
ferrous ions added should be from about 1.2 to 10 times the moles of 
cyanides. The preferred amount of ferrous ions to be added is an amount 
from about 2 to 6 times the moles of total cyanides. If the waste water 
contains other by-products which tend to compete for the ferrous ions, 
such as sulfides, the amount of ferrous ions added should be increased to 
compensate for this and thus maintain the ferrous ion to cyanides ratios 
described above. 
The ferrous ions are added under conditions which insure that they remain 
as ferrous ions until they have reacted in the waste water to convert the 
cyanides, or a substantial portion thereof to iron cyanides. If desired, 
an inert atmosphere can be employed to insure maintaining the ferrous ions 
in the necessary reactive state. The reaction between the ferrous ions and 
the cyanides is quite rapid particularly if the waste water is maintained 
at a temperature from 180.degree. to 200.degree. F. which is a 
particularly preferred temperature range. 
The waste water which has been treated with the ferrous ions is next 
treated with a base or a basic reacting material to adjust the pH of the 
treated waste water to the range from 9.0 to 11.0 and to effect the 
precipitation of a sludge containing the ion cyanides from the treated 
waste water. A variety of bases or basic reacting materials can be 
employed for this purpose including the oxides, hydroxides and carbonates 
of alkali metals and alkaline earth metals and ammonium hydroxide. The 
preferred bases are lime, sodium hydroxide, magnesium hydroxide and sodium 
carbonate. Lime or calcium oxide, which in solution becomes calcium 
hydroxide, is particularly preferred for this step of the process. 
The lime cooperates with the ferrous ions to weigh down the sludge 
precipitate and is most effective for removing suspended solids. The use 
of lime has a surprising effect in the biological reactor. For reasons not 
understood, the lime enhances biological activity in the biological 
reactor of the present process as compared to other bases, such as sodium 
hydroxide. 
After the sludge has formed and settled or precipitated following the 
addition of the base, the waste water is separated from the sludge. This 
waste water, which is characterized by a substantially reduced level of 
cyanides but containing a high level of formates and a salt or salts of a 
metal or metals selected from Groups 1A or 2A of the Periodic Table is 
suitable as a feed to a biological reactor. Thus, this waste water is 
introduced into a biological reactor which is effective for converting the 
formates in the waste water to carbon dioxide and a biological residue. 
While the waste water following its separation from the sludge can be 
directly passed into the biological reactor, it is a preferred practice to 
adjust the pH of the waste water to optimize biological activity in the 
biological reactor. The preferred pH range for the biological reactor is 
from about 6 to 8 with a pH of about 7 being particularly preferred. The 
pH adjustment can be made according to conventional known methods. The pH 
employed in the biological reactor is vital or critical to this process. 
At low pH values below a pH of 6, the biological activity in the reactor 
is markedly reduced. On the other hand, at high pH values above a pH of 8, 
calcium carbonate will precipitate from the waste water solution and lead 
to plugging of the equipment. The pH adjustment, is required, can be made 
according to conventional known methods. In the even that an alkali metal 
hydroxide is used for neutralization instead of lime, there is no danger 
of forming a calcium carbonate precipitate and the upper pH limit is about 
9. 
The following example illustrates the process of the invention for a 
particular waste water stream.

EXAMPLE I 
A waste water stream was continuously removed from the quench zone of a 
partial oxidation synthesis gas reaction in which a petroleum residuum was 
employed as the feed to a synthesis gas generator operated at a 
temperature of about 2400.degree. F. and a pressure of 950 psig. The waste 
water withdrawn from the quench zone was characterized by having the 
following approximate analysis: 
______________________________________ 
pH 8.5 
Sulfide 20 ppm.sup.(1) 
CN total 20 ppm 
CN free 10 ppm 
Formates 4000 ppm 
Total Suspended Solids 
200 ppm 
Ammonia 2500 ppm 
Cl 50 ppm 
SCN 20 ppm 
Metals.sup.(2) 100 ppm 
______________________________________ 
.sup.(1) ppm = parts per million on a weight basis. 
.sup.(2) Approximately equal aounts of nickel, vanadium and iron. 
The waste water was introduced into a first reaction vessel under a 
nitrogen atmosphere at a temperature of 180.degree. F. with the pH of the 
waste water being about 8.5. A solution of ferrous sulfate and 
concentrated sulfuric acid was added to the waste water in the first 
reactor at a rate of about 0.01 pounds of ferrous sulfate 
(FeSO.sub.4.7H.sub.2 O) per gallon of feed water and 0.0007 pounds of 
concentrated sulfuric acid per gallon of feed water. This reaction mixture 
was maintained at 175.degree. F. with constant agitation and an average 
residence time of about 0.1 hrs. in this reaction vessel. 
The treated waste water from the first reactor was directed into a second 
reactor while being maintained at a temperature of 175.degree. F. Calcium 
hydroxide was added to the waste water at a rate of about 0.04 pounds 
Ca(OH).sub.2 per gallon of feed water while the reaction mixture was 
maintained at about 170.degree. F. with constant agitation over a 
residence time of approximately 4 minutes. The treated waste water from 
the second reactor was passed into a clarifier to remove suspended solids 
from the stream in the form of a sludge. 
The waste water from the clarifier now substantially free of suspended 
solids was passed into a stripping tower wherein a major fraction of the 
ammonia was removed by counter-current with steam. The water issuing from 
the stripper was passed into a biological reactor wherein organic matter, 
such as formates, was consumed or converted to carbon dioxide and a 
biological residue suitable for disposal. The waste water issuing from the 
biological reactor was substantially upgraded, being characterized by the 
following approximate analysis: 
______________________________________ 
pH 7.5 
Sulfide &lt;1.0 ppm 
CN total &lt;3.0 ppm 
CN Free &lt;1.0 ppm 
Formates &lt;50 ppm 
Total suspended 
solids &lt;40 ppm 
Ammonia &lt;20 ppm 
BODs, filtered &lt;10 ppm 
BODs, unfiltered &lt;40 ppm 
SCN.sup.- &lt;1.0 ppm 
Metals.sup.1 &lt;1.0 ppm 
______________________________________ 
.sup.1 Includes nickel, vanadium, and iron. 
No detectable amounts of phenol were found in the waste water from the 
biological reactor. 
The treated waste water was substantially upgraded by the removal of major 
proportions of the environmentally significant contaminants found or 
present in the untreated waste water. The particularly objectionable free 
cyanides was reduced to essentially a trace amount and the high BOD level 
of the formates were reduced by about 99 percent. The heavy metal 
contaminants and the sulfides were also removed leaving only trace levels 
of these components in the waste water.