EPA-660/2-74-035
May 1974
Environmental Protection Technology Series
^•^•^
mprovement of Treatment
of Food Industry Waste
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring,, Environmental Protection Aqency^ have
been grouped into five series. These five bread
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer c>nd a sr.aivirr.uin interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
U. Environmental Monitoring
5. Socioeconomic Environmental studies
This report has baen assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY ^series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
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EPA-660/2-74-035
May 1974
IMPROVEMENT OF TREATMENT OF FOOD INDUSTRY WASTE
By
Sidney B. Tuwiner
Project 12060 ESY
Program Element 1BB037
Project Officer
Allyn Richardson
Environmental Protection Agency
John F. Kennedy Federal Bldg.
Boston, Massachusetts 02203
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.25
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EPA Review Notice
This report has been reviewed by the EPA,
and approved for publication. Approval
does not signify that the contents
necessarily reflect the views and policies
of the Environmental Protection Agency, nor
does mention of trade names or commercial
products constitute endorsement or recommen-
dation for use.
11
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ABSTRACT
Laboratory studies were conducted to determine the feasibility
of reducing the COD demand of cheese whey waste generated
from dairy processing plants Three primary processing variables
were studied; these were agitation, temperature and current
density Results indicate electrolytic oxidation efficiency
was best at 70°C, agitation at 9 6 feet per second and a
current density of 9.5 amperes per square foot (equivalent
to 6 amperes in the test cell investigated)
Concentration of 60 percent of the whey protein was also
possible by collection of the froth produced during elec-
trolysis. This mechanism of COD reduction could afford
recoverable protein from the whey
Carbon absorption of the electrolyzed whey was also shown
to be extremely effective in reducing the COD The carbo-
hydrates after oxidation to carboxylic acids are very readily
absorbed, the carbon loading being in excess of that expected
for secondary effluents.
The feasibility of combining the electrolytic oxidation with
froth collection and carbon absorption is proposed as a
possible attractive procedure for recovery of values from
the whey
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CONTENTS
Section
Page
II
III
IV
V
VI
VII
CONCLUSIONS
RECOMMENDATIONS
INTRODUCTION
MATERIALS AND METHODS
ELECTROCHEMICAL REACTIONS
RESULTS
DISCUSSION
VIII ACKNOWLEDGMENTS
IX
REFERENCES
5
9
15
21
63
69
71
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FIGURES
Page
1 Electrolysis Reactor
2 Electrodes and Spacer Details 11
3 Electrolysis of Acid Whey - Voltage, COD 23
and pH vs Time (Run #9)
4 Electrolysis of Acid Whey - Voltage, COD 24
and pH vs Time (Run #11)
5 Electrolysis of Acid Whey - Voltage, COD 25
and pH vs Time (Run #12)
6 Electrolysis of Acid Whey - Voltage, COD 26
and pH vs Time (Run #13)
7 Electrolysis of Acid Whey - Voltage, COD 27
and pH vs Time (Run #14)
8 Electrolysis of Acid Whey - Voltage, COD 28
and pH vs Time (Run #15)
9 Electrolysis of Acid Whey - Voltage, COD 29
and pH vs Time (Run #16)
10 Electrolysis of Acid Whey - Voltage, COD 30
and pH vs Time (Run #17)
11 Electrolysis of Acid Whey - Voltage, COD 31
and pH vs Time (Run #18)
12 Electrolysis of Acid Whey - Voltage, COD 32
and pH vs Time (Run #19)
13 Electrolysis of Acid Whey - Voltage, COD 33
and pH vs Time (Run #20)
14 Electrolysis of Acid Whey - Voltage, COD 34
and pH vs Time (Run #21)
vi
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FIGURES (Continued)
Page
15 Electrolysis of Acid Whey - Voltage, COD 35
and pH vs Time (Run #23)
16 Electrolysis of Acid Whey - Voltage, COD 36
and pH vs Time (Run #24)
17 Electrolysis of Acid Whey - Voltage, COD 37
and pH vs Time (Run #27)
\
18 Electrolysis of Acid Whey - Voltage, COD 38
and pH vs Time (Run #28)
19 Electrolysis of Acid Whey - Voltage, COD 39
and pH vs Time (Run #29)
20 Electrolysis of Acid Whey - Voltage, COD 40
and pH vs Time (Run #30)
21 Electrolysis of Acid Whey - Voltage, COD 41
and pH vs Time (Run #31)
22 Electrolysis of Acid Whey - Voltage, COD 42
and pH vs Time (Run #32)
23 Electrolysis of Acid Whey - Voltage, COD 43
and pH vs Time (Run #33)
24 Electrolysis of Acid Whey - Voltage, COD 44
and pH vs Time (Run #34)
25 Electrolysis of Acid Whey - Voltage, COD 45
and pH vs Time (Run #35)
26 Electrolysis of Acid Whey - Voltage, COD 46
and pH vs Time (Run #37)
27 Electrolysis of Acid Whey - Voltage, COD 47
and pH vs Time (Run #38)
vii
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FIGURES (Continued)
Page
28 Electrolysis of Acid Whey - Solution pH vs 50
COD at 3 Amps
29 Electrolysis of Acid Whey -Solution pH vs 51
COD at 6 Amps
30 Electrolysis of Acid Whey - Solution pH vs 52
COD at 9 Amps
31 Electrolysis of Acid Whey - Solution pH vs 53
COD at 12 Amps
viii
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TABLES
Page
Composition of Cheddar Cheese Whey 6
2 Current Efficiency and Power Requirements 54
at 3, 6, 9 and 12 Amps
Froth Separation of Whey 56
Adsorption of COD by Activated Carbon 58
IX
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SECTION I
CONCLUSIONS
1. The electrochemical oxidation of the organic components
of sour whey may be technically feasible
2. Preliminary estimates indicate the capital cost of an
electrochemical system for oxidation may compare favorably
with that of a biological system of the same capacity. This
is based on a cost of $78 per daily pound of COD removed.
3. The indicated power requirement for electrochemical
oxidation is, within the ranges of temperature and agitation
which were studied, approximately 8 kwh per pound COD
removed.
4. Electrochemical partial oxidation of sour whey permits
recovery of at least half of the protein in a froth concen-
trate, based on the results of two runs The solution
remaining after froth separation may be treated for final
disposal by further electrochemical oxidation and/or by
activated carbon adsorption.
5. In the electrochemical partial oxidation of sour whey
the primary reaction is that of conversion of lactose to
lactonic acid. Secondary reactions result in formation of
gluconic and galactonic acids. These are refractory to
further oxidation of primary and secondary hydroxyl and the
breaking of carbon-carbon bonds
6. Investigation of very limited scope indicates that for
an activated carbon the adsorption of products of partial
electrochemical oxidation may be represented by a Freundlich
equation within a substantial range of carbon loading.
7 The further oxidation of the acidic products of partial
oxidation of whey is highly dependent on temperature for the
electrode system and conditions of this study A practical
method of electrochemical oxidation to remove COD requires a
temperature of at least 35 , and preferably 50 C.
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8 The electrode system of this investigation was designed
with alternate layers of expanded-metal anode and cathode
separated by inert plastic net spacers. This permitted liquid
circulation through to the electrode layers. The circulation
was provided by propeller and turbine stirrers and the rate
of exidation is dependent on the intensity of circulation as
measured by the fps of linear velocity of the agitator.
9. Under the conditions employed in this study, with
temperature from 35° - 70°C, agitation intensity from 7.0 -
26.1 fps, and anode current density from 4 75 - 19.0 asf,
the electrochemical efficiency of oxidation is not greatly
dependent on the pH between about 2.3 - 5.0.
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SECTION II
RECOMMENDSTIONS
Based on the results and conclusions of this study, and in
consideration of the need to alleviate pollution from whey
while recovering the valuable components of this material,
the following recommendations are made for further study
and development:
1. It was shown that 60 percent of the protein of whey can
be collected as a 25 percent concentrate in the initial froth
generated during electrochemical oxidation of whey A program
should be initiated to investigate this technique of froth
collection as a mechanism for recovering whey values and for
decreasing the COD of the resulting whey This would improve
the economic feasibility of electrochemical oxidation of the
remaining COD.
2. Based on 5 experiments on a bench top scale, electro-
chemically treated whey produced acids which are adsorbed on
Darco G-60 (Atlas Chemical Industries) activated carbon.
Further study is needed on this aspect
3. If the results and conclusions of the present study are
confirmed in further bench scale studies, initiate a pilot
study of the method of electrochemical total oxidation of whey,
using data generated from this study and those proposed above,
to establish the economics of the process This is provided
that cost projections and technical feasibility estimated
from further bench scale tests compare favorably with alternative
methods of whey treatment.
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SECTION III
INTRODUCTION
Whey from dairy processing plants constitutes a significant
source of water pollution in many areas of the United States.
The wastes generated by these plants may be characterized
either as concentrated wastes with high solids concentration
and BOD, or as dilute wastes which are obtained in rinsing
of curds and cleaning of equipment The problems of handling
these two general types of waste are quite different.
Whey remains as the liquid fraction when milk is curdled
and the curds are separated by screening. These curds
contain most of the casein and fat while the whey contains
the lactose, salts, albumin and globulin as well as acid
substances, such as lactic acid, which assist the curdling
process. Characteristics of the cheese depend on the
conditions of curd formation. These conditions ,do not
greatly affect the chemical composition of the whey except
with regard to the concentrations of these acids and that
of calcium and phosphate.
Sweet whey is obtained when the curdling is primarily with
rennet, an enzyme obtained from the stomachs of cattle.
Some lactic acid is present, however, to assist in the
process. Acid whey is obtained when curdling is produced
primarily by lactic acid developed by fermentation of the
milk with lactobacillus or by addition of mineral acid. The
sour milk is heated and the rate of curdling is a function
of both pH and temperature
It is believed that the applicability of the results of this
study is not limited to the specific acid whey which was used
inasmuch as acid substances are produced from the lactose
regardless of the initial acidity.
Table 1 indicates the percent
typical whey. Other types of
of various components of a
whey may vary from this analysis
somewhat. Probably the most variable component is the protein
content which depends considerably on the conditions of
curdling.
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TABLE 1
Composition of Cheddar Cheese Whey
Components Percent^
Total solids 6 57 - 7.13
Protein 0.82 - 0 95
Fat 0 12 - 0 36
Lactose 4.62 - 5.05
Acid as Lactic 0 144 - 0 236
Ash 0.366 - 0 649
This study is intended to develop a method of treatment of
the concentrated waste and, specifically, the whey which is
produced in cheese-making. In the non-dairy food processing
industry, there are similar wastes such 'as blood from
slaughter houses and liquor from the blanching of vegetables,
which may be amenable to similar methods of treatment
It is desirable, whenever economic circumstances permit, to
recover the value in these wastes For example, products
for human or animal nutrition are often produced by concen-
trating and drying. To a considerable extent, the recovery
of whey solids as dried whole whey and as specialty food
products is being practiced. One such specialty is partly
desalted whey solids for infant feeding.
The capital cost of equipment for evaporation and drying is
extremely high per unit capacity in small sizes, resulting
in high unit operating cost in small plants attempting
recovery of whey solids. Under existing circumstances, the
value of the whey solids recovered is far less than the cost
of evaporation and drying unless the scale of operation is
quite large. As a consequence, a large amount of whey is
discharged to waste.
Discarded whey is sometimes digested anaerobically in septic
tanks This results in a relatively minor reduction of
BOD. Aerobic treatment is possible also but the whey must
be diluted by some fiftyfold to permit the organisms to
proliferate. Here again the cost of treatment is exceedingly
high, particularly in the smaller size plants, both in capital
and operating costs
6
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This investigation was conducted to develop an electro-
chemical method of oxidation of the organic components of
whey. In the proposed system, the electrolytic process
is designed to convert these organics into carbon dioxide,
water and nitrogen. The process may be either batch or
continuous, and there is no need for use of chemicals or
the separation of solids or for solid-waste disposal
Power, which is the principal item of operating expense in
this system, is available in most rural areas The system
may be used under constant load or with off-peak power,
depending on the relative economy The power is used to
reduce the BOD and COD.
During the treatment process, the organic components of the
whey are converted in stages, and there is a wide variety
of substances present at any time In the conversion of
any substance by oxidation, the oxidized product or products
constitute a smaller oxygen demand than the parent substance
It is possible to follow the course of the conversion by
monitoring the COD. It is possible also to estimate the
current efficiency by noting that the faraday equivalence
of oxygen is approximately 1,520 ampere-hour per pound of
oxygen. (3.35 amp-hr/gram) Ideally, this amount of current
should reduce the oxygen demand of the whey by exactly one
pound.
The power requirement depends on the cell voltage. It is
to be expected that this will always exceed the decomposition
potential for water, which is 1.229 volts. With these
assumptions, the minimum power usage must be 1.867 kwh/lb
oxygen demand reduction (4.12 watt-hr/gram) In practice,
the power requirement is several times this minimum as is
shown in Table 2, which is a summary of results of the
present study.
This study examined the effects of various parameters such
as temperature, agitation and current density on current
and power efficiency. With this information, the power
requirement can be optimized. The capital cost for the
cell and electrodes decreases as current density increases;
however, the power cost increases. The system is optimized
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when the incremental power cost resulting from increased
current density equals the incremental saving in cost of
financing the capital investment
8
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SECTION IV
MATERIALS AND METHODS
The system is based on the principle of anodic oxidation of
various components of the solution, while hydrogen gas is
liberated by reduction at the cathode. Power efficiency
requires prevention of concentration polarization at the
electrodes by stirring and by a design configuration permitting
maximum mixing flow The present anode design, fabricated
from expanded titanium sheet platinized for minimum over-
voltage, permits good circulation
To minimize the path of the electrolytic current and thereby
minimize the cell voltage, the cathodes which are 14 mesh
woven bronze screens, are placed in close proximity to the
anode, one cathode on either side Polyethylene mesh screen
is placed between each cathode and the anode to provide
uniform spacing while precluding contact of the electrodes
and consequent shorting.
Figure 1 represents the configuration of the electrode system
and agitator in the glass vessel, which is 12 inches high
with an internal diameter of 4 75 inches Figure 2 represents
an enlarged sectional view of this electrode system showing
the separation of the cathode screening from the platinized
anode.
The electrode system was made from an anode, 6 x 24 inches,
of platinized expanded titanium sheet with a facing cathode
of 14 mesh woven copper wire screen on each side of the anode
The copper screening was cut to the same size as the anode
and each cathode was separated by a layer of polyethylene mesh
from the opposing anode face
This multilayered composite, consisting of two cathodes,
two layers of polyethylene mesh and an anode, was coiled
into a spiral to fit within the 4-75 inch diameter at one
of the vessels. Electrical contact was provided by one inch
wide tabs, one to each electrode The anode tab was of
platinized titanium sheet welded to the anode, and the cathode
-------
tabs were an integral part of the woven screening of the
cathodes The three tabs rose upward from the upper edges
of the coiled electrode layers and were provided with
copper lugs for connection with the current source.
Each assembly included an overhead stirrer mounted to
provide an agitator within the spirally coiled electrode
system. This was designed to provide circulation of the
whey radially outward from the agitator and through the
multiple layers of the electrode system.
The details of the electrode system are shown in Figure 2
which is a sectional representation, showing the electrodes
and separators in their spatial relationship, and indicating
the direction of flow of in process whey through the
electrode layers and over the active electrode area. This
configuration is one which permits the gases which are
generated (hydrogen, nitrogen and carbon dioxide) to rise
within the electrode system and supernatant whey
This configuration of the electrode system, involving
a layered assembly of foraminous electrodes and spacers, and
combining the features of freedom of circulation, and of
gas release, with close electrode spacing, is novel.
The working volume in all experimental runs was 3 liters.
A constant liquid level was maintained by automatic additions
of makeup water equal to the evaporation. The temperature
was controlled thermostatically and the cell current was
controlled by a power supply.
Inasmuch as the lactose is the principal component resisting
oxidation and constitutes the major fraction of the whey
solids, minor variations in whey composition do not greatly
affect the treatment requirements The process requirements
are thus approximately the same for most types of whey.
The method of preparing whey used during this investigation
consists of the addition of concentrated HCl to raw milk
and subsequently holding the milk at 49°+0,25 C for 16 hours.
At the end of this time the curdled milk is filtered and the
curd is discarded. The COD of the whey produced in this way
is approximately 62,000 mg/1.
10
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JPIGURE 1
ELECTROLYTIC OXIDATION CELL
FIGURE 2 - SECTION AA
ELECTRODE AND SPACER DETAIL
ENLARGED
Platinized
titanium anode
Polyethylene
spacer
Bronze screen
cathode
11
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Process Parameters
In all 25 experimental runs conducted in this study, the
volume of whey was 3 liters, the anode area 244 square ,
inches and the cathode area 241 square inches; these areas
were computed on the basis of the total wetted surface.
The overall dimensions of the anode and each of the 2 cathodes
were 6 inches by 24.25 inches.
The parameters explored for electrolytic oxidation were
temperature, time and agitation. During the period of
treatment, the decrease in COD was measured as a function
of time to determine efficiency. Each ,3-35 ampere-hour of
current is theoretically capable of oxidizing one gram of.
COD. One ampere-day is similarly equivalent to 7 16 grams
of COD. Therefore, for a 3 liter batch, theoretically,, each
ampere-day is equivalent to 2,900 mg/1 of COD. In practice,
the reduction of COD is always less than the theoretical.
The ratio of the actual, to the theoretical, COD reduction
is the current efficiency Some inefficiency arises due to
use of the, anode current in producing oxygen rather than in
eliminating COD and by the reduction at the cathode of products
previously oxidized at the anode.
The anode current efficiency is affected by temperature,
agitation and current density These parameters govern
both the anode and cathode reaction kinetics The current
efficiency and the rate at which the COD falls are, therefore,
complex functions of these operating vehicles
These evaluations of current efficiency and energy are based
on the COD, or chemical oxygen demand. This is obtained in
accordance with a standardized analytical method which is
based on a determination of the quantity of chromic acid
consumed in oxidation of a sample in a solution at the boiling
point under prescribed conditions This quantity is then
converted to equivalents of oxygen. Current efficiency is
calculated as a percentage of a gram-equivalent of COD
reduction per faraday Energy efficiency is expressed as
kwh per pound COD reduction.
A few isolated tests were performed to determine the feasi-
bility of protein recovery from acid whey by collecting the
12
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froth generated by the gas evolved from the electrolytic
cell. This froth was recovered by skimming with a spatula
until the froth appeared to be barren. The protein-depleted
whey, partially oxidized elect roc heroically, was then tested
for its treatability using Darco G-60 activated carbon as
an adsorbent An adsorption isotherm at 25°C was obtained
by determination of the COD of a diluted solution in tests
with varying amounts of the adsorbent. This adsorbent, a
product of Atlas Chemical Industries, was selected in this
program because it is a fairly typical example of an
industrial product which has been used in wastewater treat-
ment and in development programs
As indicated on page 58, the adsorption, A, in rag/gm carbon
of COD, is represented as a function of the COD concentration,
C, in mg/1, by a Freundlich equation:
A - 0.132 C1'13 + 20%
within the concentration limits from 31 - 670 mg/1. The
Freundlich equation is used, not because it represents the
experimental data better than any other equation but because
it is the equation which has been widely adopted in reporting
the results of carbon adsorption of wastewater components
13
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SECTION V
ELECTROCHEMICAL REACTIONS
The electrochemical reactions leading to the elimination of
COD from whey are numerous because of the complexity of a
system which contains products of oxidation and degradation
of carbohydrates as well as those of protein components. We
have additionally the oxidation of chlorine to hypochlorite,
which reacts in turn with organic components whereupon it
completes a cycle, returning to chloride
Hypochlorite is produced when chlorine, generated at the
anode, combines with alkali which is produced, together with
hydrogen, at the cathode These reactions may be represented
by
2C1~ - Cl£ + 2e~ V-l anode reaction, oxidation
H20 + 2e- - 20H" + H2 V-2 cathode reaction, reductior
i
Cl£ + OH~ ** HC10 + Cl" V-3 secondary reaction, electrc
reaction products
'•i
The hypochlorous acid, or hypochlorite, is capable of
oxidizing various organic components of the system. These
components are also capable of being directly oxidized at
the anode There is no simple method of distinguishing
experimentally between the two. Some of the chlorine or
hypochlorite reacts producing chloramides and chloramines
with nitrogenous components. These compounds are capable of
serving as oxidants, in turn, for other organic substances.
The principal organic component of whey is lactose, which is
very reactive to oxidation, being converted readily to
lactonic acid as follows:
15
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0
CH-
CHOH
CHOH
CHOH
CH
CHOH
CHOH
0 CHOH
CH
CH2OH
beta-lactose
CH-
CH2OH
0
[0]
oxidation
V-3
'• - V.
c
D C
C
r
iii
:HOH
:HOH c
'H
COOH
CHOH
CHOH
CH V-4
CHOH
CH2OH CH2OH
beta-lactonic acid
The reactant, beta-lactose, is here represented as a
disaccharide of galactose and glucose, shown as pyrosan
rings connected by an ether linkage Oxidation opens the
right hand, or glucose, pyrosan with hydrolysis of ether
linkage, producing galactonic and gluconic acids. Treatment
of lactose with bromine and of glucose with chlorine is
described and is said to result in production of these
acids 3,4 various other sugars have been oxidized similarly,-'
with acid yields of 50-70 per cent The formation of the
free acids tends to promote degradation. Investigators who
have sought to obtain high yields of aldonic acids were led
16
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therefore to buffer the sytem with barium carbonate or
barium benzoate to obtain, for example, yields of 96
per cent for gluconic acid, or 90 per cent for xyIonic
acids 6,7,8,9
More severe treatment produces oxidation of primary and
secondary alcohol groups to aldehydes and ketones Rhamnose,
for example, yields 5-ketorhamnic lactone *-® With yet more
severe treatment the ketones are oxidized to carboxyls with
accompanying degradation. Ultimately the organic matter is
converted to carbon dioxide and water.
Electrochemical oxidation is the subject of patents,H
claiming the oxidation of sugars in the presence of soluble
bromides Bromine, produced electrochemically, oxidizes the
aldose to the aldonic acid and is reduced to bromide In
some cases the yields are almost theoretical.12 if the
reaction is not controlled, di-basic saccharic acids, 2-keto,
5-keto and 5-keto aldonic acids may also be produced.13,14
With platinum electrodes it is possible to obtain a yield of
55 per cent gluconic acid from glucose.15 The yield, using
alternating current with electrodes, is low The electrolytic
oxidation of lactose in bromide solutions is a function of
current density, anode material and bromide concentration.
According to investigators, oxidation of aldehydes is easily
effected in the presence of bromide and iodide ions, but not
chloride or fluoride ions
The system for oxidation of proteins is at least as complex
as that for lactose and carbohydrates. Proteins are polyamide
polymers composed of amino-acid monomers Hypochlorite or
chlorine, produced electrochemically as described above, react
at the amide linkages between amino-acid units They produce
K-chloramides, as follows:
RX-CO-NH-R2 + C12 = Ri-CONCl-R2 + HCl y-5
The chlorination reduces the stability of the amide linkages
so that the protein dissociates into smaller fractions, and
ultimately into N-chloramino acids Further reaction with
17
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chlorine or hypochlorite produces N,Nf - dichloramino acids.
NHC1-R2 + Cl2 = NC12-R2 + HCl V-6
These compounds, especially the simpler ones, are unstable,
especially when the solutions are heated. Among the products
are nitrogen, carbon dioxide and acids of lower molecular
weight.29 one possible explanation of this result may be
indicated by a comparable reaction which occurs when amino-
acids are oxidized anodically In this case, amines are
found in the product solution. It is hypothecated that the
primary reaction is one of oxidation to ammonia and an
aldehyde For example, aminoacetic acid produces ammonia,
formaldehyde and carbon dioxide, as follows:
NH2CH2COOH + 0 = NH3 + HCHO + C02 V-7
2NH3 + HCHO = CH2(NH2) + H20 V-8
When chlorine or hypochlorite are present, both the aldehyde
and ammonia react, the one to form acid and the other to form
chloramine and ultimately nitrogen 30 ^n a stepwise reaction
as follows:
HCHO + HOCl = HCOOH + HCl V-9
NH3 + Cl2 = NH2C1 + HCl V-10
NH2C1 + Cl2 - NHCl + HCl V-ll
NHCl + Cl2 - NCl3 -I- HCl V-12
2NCls = N2 + 2C12 V-13
2NHC1 - N2 + 2HC1 V-14
Products of anodic oxidation may be reduced at the cathode
in a system in which the anode and cathode compartments are
not separated. This reduction may result in a loss of
current efficiency since the products of cathodic reduction
reverse the desired anodic oxidations.
Thus, carbon dioxide is reduced to formic acid. «»•*•' Keto
18
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•I o
groups are reduced to methylene ° and oxalic acid is
reduced to glyoxalic, glycolic and tartaric acid.19,20
The composition of the cathode surface may also influence
the reduction kinetics Ketones are reduced to pinacols
when the cathode is lead or mercury, whereas with copper
only hydrogen is produced. Antimony and silver manifest
an intermediate behavior.21»22 jn ^Q present program, we
have chosen to employ a copper alloy as cathode to avoid
side-products such as pinacols or ketonic substances The
difference in cathodic behavior is owing, at least in part.
to the higher hydrogen overvoltage over lead and mercury. *»
19
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SECTION VI
RESULTS
Figures 3-27 are plots of the COD, cell voltage and pH as
functions of electrolysis time. It is evident from these that
initially there is a decrease in pH during oxidation of the
whey This probably reflects formation of carboxylic acids
by oxidation of lactose. These acids are subsequently con-
verted to carbon dioxide and water. Between the initial
formation of acids and the final state of oxidation, there
is formation of polycarboxylic compounds together with a
degradation to compounds with fewer carbon atoms. Simul-
taneously, there may be reduction of some of these substances
at the cathode with subsequent re-oxidation by the anode.
Although the graphs of pH vs time reflect the influence of
the parameters of temperature, current density and agitation,
they all indicate in successive stages, an initial pH
reduction reaching a minimum or lower limit, a second stage
of more or less constant pH, and a third stage in which the
pH rises. In the interpretation of these stages it is
reasonable to assume that during the first stage acids are
produced and that during the third stage acids are destroyed
or removed. The chemical, or electrochemical, reactions
which are responsible for these changes are outlined in
Section V From these equations it is evident that the
formation of acid substances is dependent on the presence of
lactose and its derivatives As these become depleted the
acids become subject to a more severe oxidation, producing,
ultimately carbon dioxide and water.
The intermediate stage in which there is a more or less
constant level of pH may be ascribed to a situation in which
the two types of reaction occur simultaneously and in which
there may be a significant cathodic reduction of acids as
well as degradation from oxidation at the anode or from
hypochlorite The result is the exhibition of a "steady
state" in which there are compensating pH effects.
In the graphs which illustrate the reduction of COD with
time it is also possible to discern three stages In the
initial stage the rate of reduction is relatively high.
Following this there is a more prolonged stage in which the
rate of COD reduction is more or less constant and somewhat
21
-------
less than in the initial stage In a final stage there is a
progressive falling off of the rate of COD reduction.
The rate of COD reduction reflects the rate of electrochemical
oxidation, less the rate of cathodic reduction. As indicated
in Section V, the initial oxidation of lactose proceeds very
readily and, we may assume, with high current efficiency.
This accounts for the first stage. Subsequent reduction in
stage two occurs with somewhat greater difficulty Nevertheless
the rate-limiting reaction is not necessarily diffusion
controlled owing to the fact that there is, presumably, an
ample concentration of oxidizable matter in the solution. The
third stage is one in which the rate of COD reduction is
influenced by the depletion of oxidizable matter in the
solution. One would normally suppose under the circumstances,
that this rate would be controlled by mass transfer limitations
and therefore that the rate of COD reduction would increase
with agitation intensity and that this increase would occur
especially at high current density.
When reference is made to the graphs of Figures 3-27 it is
apparent that there is no simple relationship of current
density or of agitation intensity to the current efficiency
Of course, the rate of COD reduction invariably is increased
by an increase of current density However, the current
efficiency, which measures the efficiency of current
utilization, first increases at low current density and
decreases at higher density beyond the point of maximum
efficiency. As a further indication of the complexity of
the system all of these are affected by agitation intensity
and, more especially, by temperature.
The configuration of the electrodes and the materials of their
construction are also undoubtedly very important parameters
However, the scope of this investigation did not permit the
study of their effects One electrode system, as described
in Section V, was used in all of the runs.
22
-------
FIGURE 3 RUN: 9 '
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
N>
Co
53
(X
CURRENT (AMPS) : 3
TEMPERATURE (°C) : 35/50
AGITATION (ft./sec ): 8.0
STIRRER TYPE: 2 Bladed Propeller
'TIME (days)
j I I
0
10
15
20
25
30
35
40
_ 2
- 3
45
50
55
-------
FIGURE 4 RUN: 11
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
NS
3
_ 2
CURRENT (AMPS) : 3
TEMPERATURE ( °G ): 35/5(
AGITATION (ft./sec ): 8.0
TYPE: 2 Bladed
Propeller
Temp. 50°C
VOLTS
perature increased
TIME (days)
>_ i:
0
-------
FIGURE 5 RUN: 12
Electrolysis of: Acid Whey - Voltage, COD and pH vs Time
to
increased to 50°C
CURRENT
TEMPERATUR
AGITATION
STIRRER TY
(UC): 35/50
ft./sec.):
E: 4 B laded Tu:
j TIME (days)
-------
FIGURE 6 RUN: 13
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT AMPS:
TEMPERATURES: 35"C
AGITATION (ft./sec.): 17.5
STIRRER TYPE: 3 Bladed
Propeller
TIME (days)
- 3
- 2
26
-------
FIGURE 7 RUN: 14
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT
TEMPERATURE
AGITATION (i
STIRRER TYPE
(°C): 60
t /sec.) :
: 4 Bladed
TIME (days)
0
-------
FIGURE 8 RUN: 15
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
00
- 3
Increased to 35°
. Increased to 50
CURRENT (AMPS): 3
2 TEMPERATURE (°C): 35/50/60
AGITATION (ft./sec.): 14.8
STIRRER TYPE: 3 Bladed
Propeller
0
15
,20
-------
FIGURE 9 RUN: 16
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
S3
vo
CURRENT (AMPS) :
TEMPERATURE (°G):
AGITATION (ft/sec) :
STIRRER TYPE: "4
TIME (days)
I ' '
-------
FIGURE 10 RUN: 17
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
sed to 6 amps
Current Increa
M CURRENT (AMPS)
TEMPERATUR
g AGITATION (ft /sec ): 7.0
r •* L— ** _ - t «
STIRRER TY^E: 3 Bladed
Propeller
TIME (.days)
15
20
-------
FIGURE 11 RUN: 18
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
Cu
CU11RENT (AMPS) : i
TElflPERATURE (UC) :
TATION (ft./se<
RRER TYPE: 4 B
70
): 9.2
aded Turbine
31
-------
FIGURE 12 RUN: 19
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
CURRENT (AMPS) : 6
TEMPERATURE (°C) : 70
AGITATION (ft /sec ): 14.
STIRRIR TYPE: 3 Bladed Prc
re
o.
8
peller
o
o
o
o
TIME (days)
I (_
0
10
32
-------
FIGURE 13. RUN: 20,
Electrolysis of Acid whey - Voltage, COD and PH vs Time
CURRENT (AMPS): 6
TEMPERATURE (°C): 60
AGITATION (ft/sec):
STIRRER TYPE: 4 Bladeti
9.6
Turbine
TIME (days)
0
-------
FIGURE 14 RUN: 21
Electrolysis of Acid whey - Voltage, COD and pH vs Time
tc
ex
g CURRENT (AMPS)
•o TEMPERATURE ( C
AGITATION (ft.
STIRRER TYPE:
0
I I I I
6
): 60
sec ): 14.8
3 Bladed
Propeller
TIME (days; .
I I I
TO
33
34
-------
FIGURE 15 RUN: 23
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
CURRENT (AMP
TEMPERATURE
ff
: 4 Bladed
Turbine
- 3
- 2
- 1
35
-------
FIGURE 16 RUN: 24
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT (AMPS^: 6
TEMPERATURE ( C):70
AGITATION (ft./sec ) : 14.8
STIRRER TYPE: 3 Biased
Propeller
TIME (days)
36
-------
FIGURE 17 RUN: 27
Electrolysis of Acid whey - Voltage, COD and pH vs Time
8
A... ' '
^CURRENT (AMPS^t 6
TEMPERATURE ( C): 70 j
oAGITATION (ft./sec ); 14.8
STIRKER TYPE: 3 Bladed
Propeller
TIME (days)
- 3
- 2
37
-------
FIGURE 18 RUN: 28
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT (AMPS) :
TEMPERATURE (°C)
AGITATION (ft Is
STIRRER TYPE: 4
70 ~~
): 9.6
Sladed Turbine
8
TIME (days)
I I I
COD
J I I
0
38
-------
FIGURE 19 WAS MISSING FROM ORIGINAL
MANUSCRIPT
39
-------
FIGURE 20 RUN: 30
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
2 U_
CURRENT (AMPS):
TEMPERATURE (°C
AGITATION (ft
STIRRER TYPE:
L
12
): 70
sec ): 9.6
Bladed
Turbine
40
-------
FIGURE 21 RUN: 31
Electrolysis of Acid whey - Voltage, COD and pH vs Time
H-
VOLTS
CURRENT
TEMPERATURE ( C);
AGITATION (ft/sec|): 9.6
STIRRER TYPE: 4 Bladed Turbine
70/60
8 , Tpffi(days)
0
41
-------
FIGURE 22 RUN: 32
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT (AMPS): 12
TEMPERATURE (5C):
AGITATION (ft./sec.
STIRRER TYPE: 3
60
): 14.8
Propeller
TIME (days)
- 5
- 4
- 2
42
-------
FIGURE 23 RUN: 33
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
§
pH
CURRENT (AMPS): 12
TEMPERATURE (°C): 50
AGITATION (ft./sec.):
STIRRER TYPE: 4 Blade
Tur
TIME (
-------
FIGURE 24 RUN: 34
Electrolysis of Acid whey - Voltage, COD and pH vs Time
TEMPERATURE (°C): 70
AGITATION (ft./sec.):
26.1/14.8
_ 6
_ 5
- 4
- 3
- 2
- 1
44
-------
FIGURE 25 RUN: 35
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
CURRENT (AMPS): 12.9
TEMPERATURE (°C): 70
AGITATION (ft./sec.
STIRRER TYPE: 3 Blade
§ TIME (days)
- 5
- 1
45
-------
FIGURE 26 RUN: 37
Electrolysis of Acid Whey - Voltage, COD and pH vs Time
CURRENT (AMPS): 9
TEMPERATURE (°C): 70
AGITATION (ft./sec.): 26.1
STIRRER TYPE: 3 Bladed
Pr oe Her
TIME (days)
v J '
- 5
- 3
- 2
46
-------
FIGURE 27 RUN: 38
Electrolysis of Acid whey - Voltage, COD and pH vs Time
CURRENT (AMPS):
TEMPERATURE (°C)
AGITATION (ft./sec.):
STIRRER TYPE: 4 Bladed
Turbine
. TIME (days)
47
-------
The reason for the complex effect of agitation intensity on
the current efficiency is probably related to the increase of
mass transfer at the cathode, as well as at the anode, when
the intensity is increased. One effect may be beneficial while
the other is deleterious to efficient current utilization.
Moreover both effects are related to all of the system
parameters.
Even for the cell voltage, which would be expected to be
reduced by increased agitation intensity, the situation
observed experimentally is quite complex and the relationship
to agitation intensity is not wholly unambiguous This cell
voltage is a sum of the voltages at each electrode, that
which is because of concentration polarization effects in
the barrier layers near the electrodes and the voltage which
is because of the resistivity in the intervening solution.
It is not possible to estimate the relative contribution of
each individual component of the cell voltage from the
experimental results of this study Ohmic resistance of the
current path within the electrolyte is small relative to the
electrical impedence at the electrodes. Observe, for example,
that in Run 17 summarized in Figure 10, an increase from
3 to 6 amperes of cell current results in an increase of only
0.15 volt in the cell voltage This indicates that the major
impedence of the circuit is non-ohmic, and therefore not
within the solution.
The effect of agitation intensity on cell voltage is most
evident at higher current density. Comparing Figures 26 and
27 representing the results of Runs 37 and 38, it is seen
that with other conditions being comparable, the cell voltage
at 8.8 fps agitation speed is very significantly higher than
26 1 fps. These results are obtained with a cell current of
9 amperes In these runs which were at 12 amperes the cell
voltages are relatively high and difficult to reproduce
There was also some evidence of cathode scale formation and
anode corrosion in some of the runs at this, the highest cell
current in these experiments.
Temperature is an extremely important parameter, as is
evident from the summary of data in Table 2 and from the
48
-------
graphs of individual runs in Figures 3-27, there is, under
comparable conditions throughout the range of conditions
studied, an increase of current efficiency and a reduction
of power required as the temperature is increased The
highest temperature in these studies was 70°C. At higher
temperatures the evaporation of solution with the gases
which are produced in electrolysis becomes extremely high.
It is reasonable to anticipate that results at temperatures
above 70°C would be still more favorable. This requires a
cell system designed to operate under pressure so that the
vaporization of water is held within reasonable limits.
The most favorable conditions, based on the energy require-
ments, were at 9.5 asf (equivalent to 6 amperes of cell
current) at a temperature of 70°C and with agitation equiva-
lent to 9.6 feet per second (fps) The mean ampere efficiency
under these conditions is 54 9 per cent to reduce the COD
by 90 per cent. The DC power requirement is 7.76 kwh per
pound of COD removed, or 0.48 kwh per pound of whey, at full
strength.
Reference has been made above to three stages of electro-
chemical oxidation based on pH changes and also based on the
rates of COD reduction. Inasmuch as the pH changes are a
result of acids formed during the earlier stage and later
consumed, it is of interest to relate these changes of COD
with pH. This is done in Figures 28-30 for the data obtained
in this investigation for the various runs
Recovery of Protein from Whey
The method of electrochemical oxidation developed in this
investigation appears to offer a means for recovery of a
considerable part of the protein content of the whey This
protein, which is rich in albumins and globulins, would be of
considerable value to the food industry for baked goods or
49
-------
FIGURE 28
Electrolysis of Acid Whey - Solution pH vs COD at 3 Amps
6 _
4 _
COD (mg/ IxlO"3)
o zfo30
COD (mg/ lxlO'3)
80 60
40
20
J
0
50
-------
FIGURE 29
Electrolysis of Acid Whey - Solution pH vs COD at 6 Amps
20
COD (mg/ IxlO"3)
I
40
20
COD (mg/ IxlO"3)
I I
0
60
40
20
0
COD (mg/ IxlO"3)
60
40
#27
20
'Run #28
0
51
-------
FIGURE 30
Electrolysis of Acid Whey - Solution pH vs COD at 9 Amps
Run # 35
.un
# 38
GOD (mg/ 1x10"3)
i
Run # 37
60
40
20
0
52
-------
FIGURE 31
Electrolysis of Acid Whey - Solution pH vs COD at 12 Amps
5 i-
• COD (mg/ IxlO"3)
Run #29
60
40
20
0
I COD (mg/ 1x10 ) I
60 40
20
0
53
-------
Cn
TABLE 2
Current Efficiency and Power Requirements at 3, 6, 9 and 12 Amps
Current Efficiency
Agitation
(ft/sec)
8.0
7 0
14.8
17 5
9 2
7 0
14.8
9 2
9 6
26 1
8.8
14.8
26.1
8 2
9 6
Current
(amp)
3
3
3
3
3
6
6
6
6
9
9
12
12
12
12
Power Requirement
(%) (kw-hr/lb oxygen)
Blade Type 35°C
2 propeller 19
19
3
3 " 19
3 " 29
4 turbine 33
3 propeller
3
4 turbine
4
3 propeller
4 turbine
3 propeller
3 "
4 turbine
4
50°C 60°C
39
35
35 43
43 47*
29
35
32
37
22
32
70°C
59
45
52*
50
55
53
50
35
51
47
50
29
31
35*
35UC 50°C 60°C
20 9
25
10
21 10 8
14
14 10 9*
13
11
14
17
29
31
70UC
7
8
8*
10
8
9
10
15
8
14
12*
43
40
18*
* Volume control unsatisfactory
-------
as an additive to the casein of cheese In contrast, the
lactose, though a major component of whey and though useful
as an infant food supplement and for tableting, would never
find markets for more than a fraction of that which could be
produced.
In addition to investigating the areas relating to oxidation
of whey as originally proposed, we have also determined the
feasibility of collecting the whey protein as a concentrate
in the froth generated during the electrolysis This was
done in Runs No. 5 and 6 in which the whey was oxidized at
ambient temperature Here the froth was collected during the
run and analyzed. The remaining whey solution was also
collected and analyzed.
These results summarized in Table 3, are indicative of the
possibility of recovering a substantial portion of the
protein from the whey by collecting the froth. Thus, in
Run 6 almost 60 per cent of the whey protein is recovered
in the froth which, on drying, produces a solid containing
25 per cent protein and a minor amount of ash.
It is clear from a study of the composite content of protein
in the samples from Runs 5 and 6 that the former contained
17 53 grams of protein, or 0 75 per cent whereas the latter
contained 26 62 grams, or 1.25 per cent of the whey The
difference reflects a variation in the conditions of curdling
in these experiments which is reflected in the protein
distribution between the curd and the whey Not unexpectedly
the froth recovery of the protein was higher from the higher
protein-containing sample
Carbon Adsorption
Activated carbons have been used to remove color bodies from
sugar solutions since they do not have a marked adsorption
affinity for either sucrose (a disaccharide) or for the
invert sugars (monosaccharides) Adsorption of lactose
(disaccharide) is also comparably weak.
Although activated carbon has been proposed and is used in
55
-------
TABLE 3
Froth Separation of Whey
Composition
Percent Distribution
Remainder
Froth
Composite
Remainder
Froth
Compos ite
Volume
Run No. (ml)
5 1,900
11 450
11 2,350
6 1,700
11 420
11 2,120
Solids
(gm)
160.5
45.8
115.4
62.8
Protein
(gm)
9 33
8 20
10.78
15 84
Ash
(gm)
20.32
3.00
23.32
Volume
(ml)
70.85
19-15
100.00
80.2
19 8
-
Solids
77.8
22.2
100.0
64.75
35.25
-
Protein
(gin)
53.2
46 8
100.0
40.4
59.6
-
Ash
87 14
12.86
100.00
-------
tertiary treatment of waste waters, the treatment is
relatively ineffective for the removal of COD generated
from carbohydrates. Cheese whey waste, therefore, responds
to treatment with activated carbon only to the extent that
the nitrogenous substances are removed, and the lactose
tends to pass on through the carbon adsorbent.
It appears, however, from the limited data of this investiga-
tion, that the electrolytic oxidation products of lactose
are readily and strongly absorbed by carbon as shown in
Table 4 These oxidation products consist largely of
carboxylic acids which are easily produced by the electrolytic
oxidation of whey If carbon is added to the oxidized whey
solution and allowed to equilibrate, the COD loading absorbed
by the carbon is related to the concentration in mg/1 of COD
in the filtered solution. This relation can be expressed, at
least over a portion of the concentration range, by a
Freundlich-type isotherm which is given by
A - BC1/k
where A is the adsorption in grams COD/gm carbon, B and k are
constants and C is the solution's concentration in mb/1 of
COD.
As stated above, in Run 6 nearly 60 per cent of the protein
was recovered in a froth. The whey remaining after froth
separation of this protein was 80.2 per cent of the original
volume of whey This solution was then treated with powdered
activated carbon in *a series of test determinations to establish
the adsorption isotherm of the carbon with respect to COD.
The carbon, Darco G-60, was selected as representative of an
adsorbent which has been tested and used in waste water
treatment.30
This study included only 5 test determinations on a single
treated whey solution. It is possible therefore only to draw
some very tentative conclusions from the results which are
summarized in Table 4. The carbon loading is estimated for
each test from the difference in COD of the solution before
and after treatment with the carbon. In the test which is
57
-------
summarized in the last row of the Table the quantity absorbed
is only 2 57 mg of COD out of 70 mg in the solution; This
adsorption is subject to considerable uncertainty because it
is derived from the small difference between two relatively
large quantities, each of which is subject to analytical
error Thus a small percentage error in eachr of the two
analyses may result in a relatively large error in the carbon
loading. It is for this reason that the data summarized in
the last column of Table 4 is not considered very reliable.
TABLE 4
Adsorption of COD by Activated Carbon
Carbon Added COD in Filtrate COD Adsorbed COD Loading
gm/100 ml mg/1 mg mg/gm Carbon
25 31 66 9 2.7
5 27 67 3 13.4
0.5 360 340 68
05 640 60 120
005 670 30 600
Each determination was performed by dilution of 1 ml of the
oxidized whey with water to 100 ml and subsequent addition of
the quantity of carbon indicated in the first column of Table
4. A determination of the COD concentration before and after
treatment was then made. The difference represents the change
which is the result of adsorption. When this quantity is
converted to milligrams per gram of carbon added to the
solution, it represents the loading of the adsorbent.
From a log-log plot of the experimental data, the best linear
representation corresponds to the Freundlich isotherm
A - 0.132 C1*13 + 20%
where A is the mg/gm adsorption of COD and C is the solution
concentration, mg/1.
58
-------
In a commercial process, the spent carbon, loaded with the
oxidation products from the electrolytic oxidation of whey
would be regenerated by thermal treatment. This has been
accomplished in other projects for advanced waste treatment
From the loading of the carbon which has been found, there
is the possibility of approaching 1,000 mg of COD adsorption
per gram of carbon. This is many times the loading in
conventional waste treatment with adsorbent carbon.
There is a possibility that, in view of this high loading,
the calcined carbon will exceed in quantity the amount which
is used for treatment. If this is in fact the case, there is
a net output of carbon. The extra carbon is derived from the
calcination of the carbohydrate-derived adsorbate.
It needs to be determined whether the regenerated carbon may
be processed to develop adsorption characteristics which are
comparable with those of the carbon used in these tests As
a matter of fact, it is necessary to demonstrate that these
characteristics are maintained even after many cycles of
treatment and regeneration. The present study is not intended
to establish the commercial feasibility but merely to explore
the potential for development.
Electrolytic Oxidation
At a current efficiency of 100 percent and with a cell voltage
equal to the decomposition potential of water, the electrical
energy to remove a pound of COD is 1.867 kwh. The best result
obtained, based on energy requirement, is 6 68 kwh. This was
obtained using the following conditions: 70°C, 9 2 ft/sec
agitation rate and a low current density (3 amps or 4.75 asf)
as shown in Table 2. It is probable that still higher
temperatures, requiring pressurized cell construction, would
yield still better energy efficiency.
Substantially, the same efficiency is obtained at higher
current density using higher stirrer speeds This is indicative
of the importance of mass transfer at the electrode surfaces
in enhancing electrochemical oxidation. At comparable agita-
tion and current density, the efficiency is improved as the
59
-------
temperature is increased. The maximum operating temperature
was 70°C which, in an open vessel, was the practical upper
level in order to avoid excessive vaporization. Improvements
may be expected if a closed system is used. *«>
.*•'<-...
During the electrolytic oxidation, as the COD is reduced,
there is a point at which further reduction is more difficult
and less efficient Under suitable conditions, a reduction
of at least 90 percent is possible while, with some sacrifice
of efficiency, virtually complete removal of COD is feasible
To reduce one pound of COD per day requires 8.68 square feet
of electrode area, assuming 14.25 amp/sq ft and 51.2 percent
current efficiency
By way of comparison a plant treating one million gallons per
day (MGD) of waste containing about 1,000 mg/1 of COD was
estimated to cost $650,000, or about $78 per daily pound of
COD. To be competitive, a plant based on electrochemical
oxi ation (of whey) would have to cost no more than $78 for
8 68 square feet of electrode area, or about $9 per square
foot including all accessory equipment and other costs. This
is not outside the design capability. The cost comparison
with conventional treatment becomes much more favorable with
smaller plants, typically those producing whey in which the
unit capital investment for conventional biological treatment
is much higher than the $78 per daily pound of COD-
The cost allowance per square foot of anode surface in the
methods of this study must include provision for rectifiers
and process equipment such as tanks, pumps, piping and
instrumentation. All of these costs vary with the design
capacity, which requires engineering studies beyond the
scope of the present study
A most important economic consideration is that of power cost
for approximately 7 5 kwh per pound of oxygen demand. This
is considerably more than for biological oxidation but there
are benefits in process simplicity, equipment size and material
handling which may compensate for this increased power require-
ment. This will depend on power rates and on the design
capacity
60
-------
The electrochemical system which was developed in this study
transforms the organic waste, ultimately, to carbon dioxide,
water and nitrogen. There is no attendant problem of
clarification, sludge handling or sludge disposal. Whey
flows into the system and water containing dissolved salts
flows out. Supervisory costs other than for power should be
nominal
With design of a compact electrode assembly, the system
should be small in size and the effluents clear and sterile
having only a mild vinegar odor which disappears on dilution,
or on continuing the electrochemical oxidation (at reduced
efficiency) to near completion.
61
-------
SECTION VII
DISCUSSION
During the course of this investigation two methods for de-
creasing the COD level became evident. These are, based on
two bench scale runs and a limited number of adsorption test
determinations,
1. separation of whey proteins in the froth prior
to electrochemical oxidation decreases the COD
of the resulting whey, giving a solution
containing 60 percent of the total whey protein
as a 25 percent concentrate, and/or
2. removal of the oxidation products from the whey
electrolysis by carbon adsorption. This is
feasible since the intermediate oxidation
products of the whey are carboxylic acids which
are readily absorbed by the carbon.
These methods could be used in conjunction with the electro-
lytic oxidation to decrease the COD of whey and are discussed
below
Froth Separation
The procedure to form a froth and, subsequently, to collect
the froth has certain advantages when used in conjunction
with the electrolytic oxidation of whey Of significance,
froth separation in a small or moderate capacity plant is
much more attractive economically than is evaporation and
drying. Furthermore, the economic value of whey is princi-
pally in the protein. Froth separation enhances this value
by separating the protein from both the lactose and the salts
which are in the whey
With limited experimentation of this process it has been
found that 60 percent of the total protein of the whey could
be recovered in the froth. The protein was present as a
63
-------
25 percent concentrate Optimization of this process would
1. decrease the electrical requirement for
oxidation of the whey, and
2. yield a concentrate amenable to subsequent
electrodialysis or ultrafiltration for
purification and concentration of the
protein values
The recovery of a considerable portion of the protein of the
whey by froth separation prior to further treatment to
eliminate lactose is also potentially very attractive since
it would lower electrochemical energy requirements
Adsorption of Oxidation Products by Carbon
The use of activated carbon in conjunction with partial
electrochemical oxidation of the lactose of whey results in
a high loading of the carbon. This presents an alternative
method of COD removal which requires a much smaller electrode
installation. The method of carbon adsorption is applicable
to treatment of daily plant washings as well as to the more
concentrated whey The problems of regeneration of the
carbon are yet to be explored.
Activated carbon has found application in the tertiary treat-
ment of waste water, that is, on a feed consisting of clari-
fied effluent of biological treatment In a comparison of
prior applications of activated carbon with that of the
present study, the following generalizations are to be
considered:
1. In well treated, clarified secondary effluent,^ very
little organic material escapes from a column containing
unspent carbon.
2 If the secondary treatment is poor, as with raw whey,
there usually is breakthrough of soluble organics even when
the carbon is new This result should be expected since
certain groups of materials in poorly treated waste water
and in raw whey are known to resist adsorttion on carbon. To
demonstrate the poor adsorbability of some examples from some
64
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of these groups, batch adsorption tests were conducted by
Bishop et al" using one gram of powdered carbon per liter
of solutions of various pure substances
3. Electrochemically, partially oxidized whey contains
substances which, because of their concentration and tendency
to adsorption, permit much higher carbon loadings than are
possible in tertiary treatment of waste water
Inasmuch as the cost of physical loss of carbon in regeneration
is the major item of cost in carbon treatment of waste water,
the possibility of a self-sustaining carbon regeneration
appears to warrant further study The possible combination
of froth recovery of protein combined with activated carbon
removal of electrochemically oxidized lactose is an economi-
cally attractive possibility
It is of interest to compare the data (represented in Figure 2),
which was obtained in this study, with that of Allen et al24
in which secondary effluent was treated with activated carbon,
both virgin and reactivated. Both of these are more highly
loaded for equivalent COD in the effluent solution than in
the case of electrochemically oxidized whey The whey, being
much more concentrated than any secondary sewage effluent,
should permit a higher loading of COD/lb of carbon. This
might ultimately reach as high as 50 pounds COD/100 Ib of
carbon for whey compared to about 35 pounds COD/100 Ib for
secondary effluent, assuming a system of whey-carbon contacting.
This is, however, based on somewhat questionable extrapolation
from present data.
In practice, the actual design capacity for a carbon
adsorption system with secondary effluent is from 50-100
percent higher than the isotherm capacity This apparent
increase in loading is probably a result of biological
activity ^
It is evident, therefore, that additional effort aimed at
combining the pre-elimination of COD in whey by froth collec-
tion, followed by electrolytic oxidation and the removal of^
COD by carbon adsorption may yield an economically, attractive
65
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process, particularly if the carbon is regenerated and, if
in fact, extra carbon can be derived from the calcination
of carbohydrate derived adsorbate
Alternate Methods
There are a number of alternative methods which are under
development to utilize the components of cheese whey. It
is possible to recover protein by acidifying the whey and
then centrifuging. Another method is ultrafiltration to
retain the protein and allow passage of the lactose and salts
Still another method is to demineralize whey by electrodialysis
and then concentrate and cool to crystallize the lactose.
There are also various possible combinations of these means
When utilizing ultrafiltration, the pressure required is 60
psi at 49°C to recover a 25 per cent protein concentrate. The
cost of a plant to treat 250,000 Ibs/day of whey has been
estimated at $610,000 and the annual operating cost, $196,000.25
This operating cost is about 5$ per pound of contained oxygen
demand and it includes the cost of reverse osmosis treatment
for lactose recovery The limited scope of the present study
does not permit a firm estimate of the cost of foam recovery
of the protein. We did, however, achieve a 60 per cent
recovery of the total protein as a 25 per cent concentrate,
and this does not necessarily represent the optimum performance
of this system.
The greatest drawback of any membrane system for a product
which must be sold to the food industry is that of the
difficulty of sterilization Equipment for foam separation
may be designed of polished stainless steel which may be
sterilized by steam and cleaned with alkaline compounds
Membrane systems are not usually capable of being designed
for comparable sterilization, cleaning and inspection.
Following the recovery of the protein as a concentrate, the
economic value of the solution containing lactose is marginal.
Although there are markets for lactose as a specialty, it
is doubtful whether there is the market potential to absorb
66
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large amounts except at a very low price in competition with
beet or cane sugar molasses In most locations, the problem
will, therefore, be one of determination or development of
the most economical method of disposal while avoiding pollution,
If the treatment is biological, it must be, in part at least,
aerobic as stated above. Even raw whey contains insufficient
nitrogen to sustain full elimination of oxygen demand
Combination with domestic sewage is the ideal method if it
is possible It provides both dilution and the provision of
nitrogen. When this method is not possible because of loca-
tion, the alternatives are evaporation, reverse osmosis,
electrochemical oxidation or a combination including carbon
adsorption. All of these, except evaporation, require
extensive development before their advantages and limitations
may be fully evaluated
67
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SECTION VIII
ACDNOWLEDGMENTS
The author wishes to thank Messrs Allen Cywin, William Lacy,
Allyn Richardson, H. George Keeler and Dr. Gilbert S. Jackson
of the Environmental Protection Agency for their comments and
suggestions
69
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SECTION IX
REFERENCES
1. Babbitt, H.E and Bauman, E.R., "Sewage and Sewage
Treatment", 8th ed., p. 648, John Wiley, New York
(1962)
2. Webb, B.H. and Johnston, A.M., "Fundamentals of Dairy
Chemistry", Avi Publishing Co., Westport, Conn., (1961)
3. Hlasiwetz, H., Ann. 119, 281 (1861)
4. Hlashvetz, H. and Haberman, J., Ibid 155 (1870).
5 Kibani, H. and Kleeman, Ber. 17_, 1296 (1884)
6 Bunzell, H.H. and Mathews, A.P , J Am. Chem. Soc ,
31,, 464 (1909)
7 Clows, H.A. and Tollens, B., Ann. 310, 164 (1899)
8. Hudson, C.S. and Isbell, H.S., J. Am. Chem. Soc ,
51,, 2225 (1929)
9 Bur Stand. J Res 3_, 57 (1929)
10. Votocek, E. and Malacheta, S., Anales Soc espan. fis
6 quim. 27_, 494 (1929).
11. Isbell, U.S. Pat. 1,976,731; Helwig, E.I., U.S. Pat.
1,895,41A (Jan. 24, 1933)
12. Isbell, H.S. and Frush, H.S., Bur Stand. J Res 6_,
1145 (1931)
13. Pasternack, R. and Regna, P P , U,S. Pat 2,222,155
(Nov. 19, 1940).
14. Cook, FW and Major, R. I., J Am. Chem. Soc 57_,
773 (1935)
15- Kappanna, A. and Joshi, K.M., J Sud. Chem. Soc. 29_,
69 (1952)
71
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16. Teeter, T E. and Van Rysselbergh, P., Proc. 6th
Meeting Comm. Electrochem. Thermodyriam. & Kinetics,
(1955), 38-42
17 Fisher, F and Prziza, 0. Ber 4£, 256 (1914)
18 Swan, S. Jr , Bull. Cent Elektrochem. Res. Inst.
Karaikud (India) 2_, No. 1, 6-11 (1955)
19. Listopador, V V and Antropov, L.I., Nauch. Trudy
Novocherkassk Politekh. Inst. 34., 87-98 (1956)
20. Izgaryshev, N.A. and Aramova, L.I., Zhur. Obsche
Khim. (J Gen. Chem.) 18, 337 (1948)
21, Juday, R.E. and Sullivan, W J., J Org. Chem. 20,
617 (1955)
22. Miller, E.Z., Elektrochem. 33^ 253 (1927)
23. Bishop, D.E., et al, "Studies on Activated Carbon
Treatment", Journal - WPCF, Vol. 39, 188-203 (1967),
24 Allen, J B., Clapham, T.M., Joyce, R.S. and Sukenik
V.A. Unpublished Report from Pittsburgh Activated
Carbon Company to USPHS, Oct. 1, 1964 as cited in
FWPCA Report No TWRC-11, May, 1969
25 "Membrane Processing Upgrades Food Wastes", Envir
Science Tech., May, 1971.
26 "Standard Methods for Examination of Water and
Wastewater", Am. Pub Health Ass'n, New York (1965),
pp. 510-14.
27 Allen, M.J , "Organic Electrode Processes, Reinhold Pub,
Co., New York (1958), Fitcher and Schmid, Helv. Chem.
Acta, 3, 704 (1920)
28. Smith, P.A.S., "The Chemistry of Open-Chain Organic
Nitrogen Compounds", W.A. Benjamin, Inc , New York
(1965), pp 27, 51.
72
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29 Ibid., p. 193.
30. "Study of Powdered Carbons for Waste Water Treatment and
Methods for Their Application", West Virginia Pulp and
Paper Company, FWPCA Contract No. 14-12-75, Sept 1969,
p. 4
73
tHJ.S. GOVERNMENT PRINTING OFFICE: 1974 546-319/396 1-3
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Report Hi-
w
4, Title
Improvement of Treatment of Food Industry Waste
7, Author! s}
Sidney B. Tuwiner
9. Organization
"•5
•«?
15, Supplementary
RAI Research Corporation
225 Marcus Boulevard
Hauppage, L.I., N.Y 11787
£, Repor; Uare
6,
8. Per»'otr••;'•(•-« O
Res-."' Mu
12060 ESY
/.,-.- of <*-pr-r> six!
., 'erioj Covered
Environmental Protection Agency Report No. EPA-660/2-74-035, May 1974.
. Abstract
Laboratory studies were conducted to determine the feasibility of reducing the COD
demand of cheese whey waste generated from dairy processing plants. Three primary
processing variables were studied; these were agitation, temperature and current
density. Results indicate electrolytic oxidation efficiency was best at 70°C,
agitation at 9.6 feet per second and a current density of 9.5 amperes per square
foot (equivalent to 6 amperes in the test cell investigated). Concentration of
60 percent of the whey protein was also possible by collection of the froth pro-
duced during electrolysis. This mechanism of COD reduction could afford recover-
able protein from the whey- Carbon adsorption of the electrolyzed whey was also
shown to be extremely effective in reducing the COD. The carbohydrates after oxi-
dation to carboxylic acids are very readily adsorbed, the carbon loading being in
excess of that expected for secondary effluents. The feasibility of combining the
electrolytic oxidation with froth collection and carbon adsorption is proposed as
a possible attractive procedure for recovery of values from the whey.
17a. Descriptor
Dairy Industry*, By-products*, Electrolysis, Oxidation, Froth Flotation,
Activated Carbon, Adsorption
17b. Identifiers
Cheese Whey*, Protein recovery*, Electrolytic Oxidation, Agitation, Chemical
Oxygen Demand Reduction
17c. COWRR FieSd & Group
J 8. Availability 1 13. Secoriiy Class.
* ,'J<«j>ort>
Tib.' Secaiiiy Cia-K.
(Psga)
Abstractor j.R. Boydston
; 21. NO of.
Pases
n. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D.C. 2024O
,T... .,ix PNERL, EPA, Corvallis, Oregon
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