Journal of Environmental Protection, 2010, 1, 53-58
doi: 10.4236/jep.2010.11007 Published Online March 2010 (http://www.SciRP.org/journal/jep)
53
Impacts of Chromium from Tannery Effluent and Evaluation
of Alternative Treatment Options
Alebel Abebe Belay
School of Environmental health, Jimma University, Jimma, Ethiopia.
Received December 25th, 2009; revised February 2nd, 2010; accepted February 3rd, 2010.
ABSTRACT
The paper has focused on the challenges/impacts of tannery effluent and evaluates the alternative treatment options
used to treat, recover or recycle chromium from the waste water. The paper was done entirely on secondary data by
consulting literature sources including scientific journals, chapters of books, conference report papers and websites.
The results of this review paper indicated that chromium is highly toxic and carcinogenic to human beings, animals,
plants and the general environment (soil and water sediment). It is found out that chrome is the primary threat when
ever tanning industry comes in to practice. Though many treatment options were evaluated to prevent its consequence
on the environment, neither of them could achieve to treat or recover chrome 100%. Treatment options are either; inef-
ficient, complicated, en ergy demanding, costly o r applicable to a certa in parts of the world due to techno logy or skilled
man power demand. Therefore, to tackle this serious challenge stringent environmental regulation with law enforce-
ment has to be exercised to use better treatment system which is widely applicable. Polluters must also know the envi-
ronmental cost of their industry and treated according to polluter pay or precautionary prin ciples. Moreover, the gen-
eral public has to be aware of it and all concerned organizations and governments has to work hand in hand to reach
zero discharge level or at least to attain the EPA chrome discharge limit.
Keywords: Chromium Toxicity, Environmental Impact, Chromium Recovery and Recycling, Chromium Treatment
Option, Tannery Effluen t
1. Introduction
All sectors of our society generate waste: industry, agri-
culture, mining, energy, transportation, construction and
consumers. Waste contains pollutants which are dis-
carded materials, process materials or chemicals. Pollu-
tion could be caused by these pollutants when they are
released beyond the assimilation capacity of the envi-
ronment. Industrial wastes are generated from different
processes and the amount and toxicity of waste released
varies with its own specific industrial processes [1]. Tan-
nery effluents are ranked as the highest pollutants among
all industrial wastes. They are especially large contribu-
tors of chromium pollution. For instance, in India alone
about 2000–3000 tone of chromium escapes into the en-
vironment annually from tannery industries, with chro-
mium concentrations ranging between 2000 and 5000
mg/l in the aqueous effluent compared to the recom-
mended permissible discharge limits of 2 mg/l [2].
There are two types of tanning systems which are
vegetable tanning, which does not contain chromium,
and chrome tanning. However, due to the high pollution
load and low treatability, conventional vegetable tanning
can’t be considered more environmentally friendly than
chrome tanning. Moreover, vegetable tanned leathers
have different physical properties and specific applica-
tions, but is biodegradable [3]. Currently more than 90%
of global leather production of 18 billion sq. ft is through
chrome-tanning process [4]. Chromium salts (particularly
chromium sulphate) are the most widely used tanning
substances today. Hides tanned with chromium salts have
a good mechanical resistance, an extraordinary dyeing
suitability and a better hydrothermic resistance in com-
parison with hides treated with vegetable substances.
Unfortunately only a fraction of the chromium salts used
in the tanning process react with the skins. The rest of the
salts remain in the tanning exhaust bath and are subse-
quently sent to a depuration plant where the chromium
salts end up in the sludge [5]. One of the major emerging
environmental problems in the tanning industry is the
disposal of chromium contaminated sludge produced as a
by-product of wastewater treatment. Tannery effluents
severely affect the mitotic process and reduce seed ger-
mination in extensively cultivated pulse crops [2].
At high concentrations chromium is toxic, mutagenic,
carcinogenic, and teratogenic. Chromium exists in oxida-

54 Impacts of Chromium from Tannery Effluent and Evaluation of Alternative Treatment Options
tion states of +2, +3, and +6. The trivalent oxidation state
is the most stable form of chromium and is essential to
mammals in trace concentration and relatively immobile
in the aquatic system due to its low water solubility. The
hexavalent chromium is much more toxic to many plants,
animals, and bacteria inhabiting aquatic environments.
Most micro-organisms are sensitive to Cr (VI) toxicity
but some groups possess resistance mechanisms to toler-
ate high levels. A relationship was found between the
total chromium content of soil and the presence of metal
tolerant/resistant bacteria [2]. In natural waters two stable
oxidation states of Cr persist (III and VI), which have
contrasting toxicities, motilities, and bioavailability. Cr
(VI) is motile and highly toxic and soluble in water and it
is a strong oxidizing agent that causes severe damage to
cell membranes [6].
Worldwide chromium contamination of soils has
arisen predominantly from the common practice of
land-based disposal of tannery wastes under the assump-
tion that the dominant species in the tannery waste would
be the thermodynamically stable Cr (III) species. How-
ever, recent detection of significant levels of toxic Cr (VI)
in surface water and groundwater in different part of the
world raise critical questions relating to current disposal
of Cr-containing wastes. Despite the thermodynamic
stability of Cr (III), the presence of certain naturally oc-
curring minerals, especially MnO2 oxides, can enhance
oxidation of Cr (III) to Cr (VI) in the soil environment.
This factor is of public concern because at high pH, Cr
(VI) is bio available, and it is this form that is highly
mobile and therefore poses the greatest risk of ground-
water contamination [7].
Cleaner technologies used to reduce chromium in
waste water such as high exhaustion process, direct or
indirect chromium recycling cannot eliminate completely
from effluent coming from post tanning section. In re-
sponse to this challenge, replacement of chromium with
combinations of metallic cat ions, for example titanium,
magnesium, aluminium and zirconium, was tried but the
results obtained at the moment are not completely satis-
fying for all types of leather. Synthetic organic tanning
agents, alone or in combination with a metallic cat ion
can be considered as a substitute for chromium in some
types of leather, provided that environmental and work-
ers health regulations are complied with [3].
Although Cr III is an essential nutrient for human be-
ings, there is no doubt that Cr (VI) compounds are both
acutely and chronically toxic. The dose threshold effect
for this element has not yet been determined accurately
enough to allow regulations to be defined. However
some risk assessment analysis is currently being under-
taken. Cr III is less toxic than some other elements (Hg,
Cd, Pb, Ni and Zn) to mammalian and aquatic organism,
probably due to the low solubility of this element in its
trivalent form. Cr III compounds also have a very low
mobility in soils and are thus relatively unavailable to
plants [ibid]. The direct discharge of effluents from tan-
neries in to water bodies has become a growing envi-
ronmental problem in these days. Most of these waste
waters are extremely complex mixtures containing inor-
ganic and organic compounds that make the tanning in-
dustry potentially a pollution-intensive sector [8].
In general chrome waste from leather processing poses
a significant disposal problem to human health and the
environment. Today, all tanneries must thoroughly check
their waste streams. Chrome discharge into those streams
is one of the components that have to be strictly con-
trolled. The environmental impact of chrome waste from
tanneries has been a subject of extensive scientific and
technical dispute. Statutory limits have since been set for
chrome discharge and disposal, and relevant guidelines
have been drawn up throughout the world. Due to high
correlation between chrome tanning and its environ-
mental impact, checking of the efficiency of processing
operations and treatment plant takes on prime importance.
Therefore, the objective of this paper is to describe po-
tential impact of tannery waste, evaluate the different
chrome treatment methods and to discuss the challenges
faced to chrome removal technologies.
2. Chromium Toxicity and its Accumulation
Industrial activities like electro plating, metal cleaning
and dyeing processing, cement, and leather tanning are
the major sectors that play role in releasing chromium
into the environment. Chrome in the hexa-valent form is
very toxic. It is quite intriguing that contaminated field
by industrial effluent show a mobilization ration of less
than 5 (potentially toxic) for selected plant specious.
Surprisingly, the mobilization ratios for weeds become
greater than 5, which have healthy morphology in the
early flowering stage [9].
A study done by Marchese et al, 2008 about the rate of
accumulation of chromium in four fresh water plant spe-
cies, clams, crabs, and fishes showed that, all the four
fresh water species and animals were found with high
concentration of chromium which is an indication of its
high accumulation potential. This clearly indicates that
this problem become more serious and toxic to human
beings which are found at the top of the food web due to
its toxicity and bio accumulation effect.
In the tanning industry leather processing involves
conversion of put rescible hide or skin into leather. Tan-
ning agents could help permanent stabilization of the
skin matrix against biodegradation. This industry has
gained a negative image in society with respect to its
pollution potential and therefore is facing a severe chal-
lenge. The unit processes that cause tanneries the most
difficult with regard to perceived environmental impact
are unharing and chrome tanning. Basic chromium sul-
fate (BCS) is a tanning agent, which is employed by 90%

Impacts of Chromium from Tannery Effluent and Evaluation of Alternative Treatment Options 55
of the tanning industry. Conventional chrome tanning
results in wastewater containing as high as 1500−3000
ppm (parts per million) of chromium; however, the pre-
sent day high-exhaust chrome tanning methods lead to a
wastewater containing 500−1000 ppm of chromium [10].
But, the discharge limits for trivalent chromium vary
broadly ranging from 1 to 5 mg/l in the case of direct
discharge into water bodies and 1 to 20 mg/l in the case
of discharge into the public sewer system. Therefore, the
treatment plant used by the tanning industry needs to
treat the influent by 200 fold to send to water bodies,
which is not practical in most of the cases [11].
3. Chrome Recovery and Recycling
Conventional chrome tanning in leather production pro-
duces spent liquors containing significant amounts of
chromium and other polluting substances, both organic
and inorganic. From the total chromium used for tanning
only 60% to 70% is utilized, while the rest 30 to 40%
remains in the spent tanning liquor, which is normally
sent to a wastewater treatment plant. This inefficient use
of chromium and its release to the environment has to be
compensated by designing a good recovery and recycling
scheme. The recovery of chromium from spent tanning
and re-tanning baths provides a significant economic
advantage in terms of both its reuse and the simplifica-
tion of the processing of global wastewaters [12].
Several recovery techniques such as chemical pre-
cipitation, membrane processes, adsorption, redox ad-
sorption, and ion exchange have been proposed for this
purpose. Among these membrane process offer very
interesting opportunities for the recovery and recycling
of primary resources from spent liquors of unit opera-
tions such as soaking, unhairing, degreasing, pickling,
dyeing, and chromium tannage. Studies showed that the
application of nanofiltration (NF) and reverse osmosis
(RO) in combination can provide better recovery of
unreacted chromium from high concentrated spent tan-
ning effluent. However, this technique is being chal-
lenged by the presence of considerable biological oxy-
gen demand (BOD) and proteins, which can cause
fouling and subsequent system failure, either temporar-
ily or permanently [12].
In practice, there are two ways of chrome recycling
methods which are widely practiced: these are direct and
indirect recycling. The direct form entails spent float
being recycled direct to the chrome tanning processing
for re-use. While, the indirect form entails precipitating
and separating the chrome from the float containing re-
sidual chrome, and then re-dissolving it in acid for re-use.
The efficiency of both methods can be very high (more
than 90%); it depends on the effectiveness of the float
collection process and the recycling/reusing technique.
Of the two approaches, chrome recovery is more widely
used than chrome precipitation. However, it is mandatory
to adopt and practice the new technologies which are
more efficient in recovering this chemical, which is a big
challenge to tanning industry [13].
Use of chemical compounds for chrome treatment is
not a new phenomenon. A study conducted by M. ali
awan et al., 2003 identified three aqueous oxidants,
namely; Hydrogen peroxide, Sodium Hypochlorite and
Calcium Hypochlorite independently in oxidizing Chro-
mium (III) containing tannery wastewaters to soluble
chromate (CrO4
2-) under alkaline conditions. Among
those, Hydrogen peroxide was potentially a suitable oxi-
dant as it could recover chromate (CrO4
2-) up to 98%
(from synthetic Cr3+ solution) and 88% (from effluent I).
Despite the different experimental conditions (tempera-
tures and oxidation time) for all the three oxidants com-
plete (100%) recovery could not be achieved. The recov-
ery of chromium could help in reducing the possibility of
oxidizing Cr III to Cr VI (carcinogenic) compound and
helps to rescue the financial and environmental cost oc-
curred as a result of its discharge [14]. Other kinds of
methods like combined system have to be also tested
since it might improve the efficiency of recovering
chromium from tanning process. In fact experimental
conditions like, temperature, PH, time, need to be con-
trolled to have more efficient recovery.
4. Treatment Medias Used for Chromium
Removal
A wide range of physical and chemical processes are
available for the removal of Cr (VI) from effluents. A
major drawback with those treatment systems is sludge
production, and, high operational cost and some of them
are complicated for management. This actually makes
the application of these technologies to be limited only in
developed countries. In response to this challenge a dif-
ferent attempt were undertaken to produce a media which
was feasible and cost effective to use by the majority. A
research was done S. M. Nomanbhay and K. Palanisamy,
2005 by preparing a new composite bio sorbent which
has been done by coating chitosan onto acid treated oil
palm shell charcoal (CCAB). It is an attractive option
because of its cost effective treatment system. Among
other low cost absorbent identified chitosan has the
highest sorption capacity for several metal ions including
Chrome. Chromium adsorption was influenced by initial
PH, agitation, dose of adsorbent and contact time. For
instance at a PH of 5 the media managed to treat 92 % of
chromium, which is significant. Further control of these
environmental conditions in the laboratory may improve
its treatment capacity [15].
A comparison study also conducted by leaching raw
tannery effluent through mono and mixed columns (dif-
ferent grades) of vermiculite to evaluate their removal
efficiency of chromium. The mixed column of vermicu-
lite has the highest chromium removal (74.6%) while the

56 Impacts of Chromium from Tannery Effluent and Evaluation of Alternative Treatment Options
mono vermiculite achieved 63.6%. This improvement in
chrome removal efficiency is brought by the use of com-
bined medias which increase its adsorption capacity. It
was also found out that, it could remove cat ions like Ca,
Na, Mg and K. of course high cat ion exchange helps to
make the system more efficient [16].
Recently different studies are concentrating use of
combined medias under the control of laboratory envi-
ronment and the results seem promising. A research has
been done in Ethiopia by Tadesse et al, 2005 to check
the removal efficiency of chromium from tannery efflu-
ent in a horizontal settling tanks and subsequent Ad-
vanced Integrated Wastewater Pond System (AIWPS)
reactors. The raw combined effluent from the tannery
had a different PH and its removal efficiency was meas-
ured in detention time and PH to come up with the best
chrome removal efficacy. After a one day detention time
58-95% of trivalent chromium has been removed in the
primary settling tank when the PH is approached to 8,
which is the optimum precipitation PH for trivalent
chromium.
A significant amount of chromium has also removed
in the secondary facultative pond and maturation pond.
The presence of sulphide plays a role in the overall re-
moval of chromium. It has some coagulating effect be-
sides maintaining a conducive pH for the formation of Cr
(OH)3 precipitate. However, since chromium doesn’t
make any stable precipitate with sulphide, it has no any
effect in the chromium removal chemically. With Cr (III)
concentration of 0.2–0.8 mg/l in the final treated effluent,
the AIWPS preceded by horizontal settling tanks pro-
duced effluent that could easily meet most of the current
Cr (III) discharge limits. This study is prominent in find-
ing ways to achieve the maximum removal of chromium
and producing an effluent that meet the standard criteria
to discharge to water bodies. This technique needs get
attention to be considered and applied in the conven-
tional tannery treatment system to improve its efficiency
and prevent the alleged environmental consequence due
to the toxic effluent discharge [11].
The ever increasing concern about the deterioration of
the environmental condition could be a driving force to
assess and remediate pollutant from the ecosystem. On
this regard the use of plant species especially algae be-
come acknowledged in indicating and managing metal
pollution. Despite the fact that a large scale study and
experience has been developed in different countries to
use algal ponds as effective means of sewage treatment
system the accumulation potential of algal species and
seasonal variation of tolerance is not exhaustively ad-
dressed. Rai et al., 2005 did a study on seasonal variation
of algal growth in tannery effluent and metal accumula-
tion potential for chromium removal scheme. It has been
noticed that different algal species found with accumu-
lated chromium in their tissue, which could be used in
developing bioremediation strategy for pollution abate-
ment. Of course, factors like population density, volume
of effluent, the nature of mixing with effluent and opti-
mum algal biomass should be considered and well ex-
amined before promoting for wide application [17].
Wastewater characterization is an important step in
designing effective treatment facilities for industrial
wastewaters. This is especially true for tanneries which
exhibit significant differences in their production proc-
esses that generate effluents of unique and complex na-
ture. Characterization is also needed for assessing the
performance of individual unit operations and processes.
Most pollutants in wastewaters appear to exist either in
particulate form or are associated with particulates. This
understanding led to the wastewater treatment strategy of
removing particulate and colloidal matter in the primary
step using suitable coagulants. A study investigated
about chemically enhanced primary treatment (CEPT)
technology that uses different coagulants for enhanced
pollutants removal at the primary stage of the wastewater
treatment. Among those coagulants used, alum has been
found to be the suitable coagulant for tannery wastewater
in a dose range of 200–240 mg/L as Al2(SO4)3 and it has
removed 98.7–99.8% of chromium. The final effluent
also met the national effluent quality standards for chro-
mium and total suspended solids. However other COD
content needs secondary treatment for the tannery efflu-
ent. Therefore, CEPT technique offers almost complete
removal of chromium and produces an effluent that will
no more affect the receiving water bodies [18].
5. Process Modification
Commercial conventional chrome tanning has poor
chromium uptake, only about 55–60% (average). So,
constant innovative process modifications for cleaner
technology have been of the utmost importance in the
leather-processing sector to safeguard our environment.
The method employed in the leather processing industry
subjects the hides and skins to treatment with a wide va-
riety of chemicals and passage through various unit op-
erations. All this involves an enormous amount of time
and they contribute to an increase in chromium, COD,
chlorides, sulfates and other mineral salts, which end up
as effluent. But, perhaps more alarmingly, the process
uses profuse quantities of water in areas where there is
rapid depletion of ground water. Very provoking re-
search paper was presented by Mukherjee, 2006 in the
international union of leather technologies and chemist
societies (IULTCS) Congress to overcome this great
challenge. This study explored a process to reduce water
usage, vis-a-vis deliming, pickle and basification-free
chrome tanning [19].
This leads to a substantial decrease in chemical con-
sumption by 20% for chrome tanning alone. Consump-
tion of water can be cut by 37–40%. It is also an energy

Impacts of Chromium from Tannery Effluent and Evaluation of Alternative Treatment Options 57
efficient technology. This exceptional approach is very
appealing to tanning companies, environmentalist and
also invites other researchers to do some job for possible
improvement or it guides somehow to a new direction.
There are some key words frequently used by scientists
like pollution prevention, waste minimization, product
empowerment and process innovation. However, these
approaches are very much confined within recycling of
wastewater to a maximum number of cycles followed by
discharging or use of environmentally-friendly chemicals.
In principle discharge of minimum pollution loads or a
zero-discharge concept should be the topic of the day to
prevent pollution completely [19].
From this intensive review of literature it is evident
that chromium is very toxic to human health, animals and
the environments (soil, water, sediments plants and etc).
There are many options of treating chromium from tan-
nery effluent and some treatment techniques managed
nearly 99% of removal of chromium from the spent liq-
uor. Usually, these kind of technologies are complicated,
expensive, energy intensive, can be applied on a specific
region, others need skilled personnel and some technolo-
gies not yet commercialised. However, technology like
electro coagulation could give very high removal of
chromium (98%) and reproducibility to developing
countries due to its low cost. Despite all these scientific
attempts tanning industry is still one of the major polluter
of the environment worldwide. Therefore, to prevent the
public health and environmental impact of tannery waste
in general and chromium in particular the environmental
regulation like effluent discharge limit has to be stringent
and organization should be powerful to the extent to take
measure by applying polluter principle or precautionary
principle to avoid the effect of toxicity and bioaccumula-
tion.
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