Tannery Wastewater Treatment Using Activated Sludge Process System (Lab Scale Modeling)

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International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869, Volume-2, Issue-5, May 2014
21 www.erpublication.org
Abstract A study was conducted to evaluate the feasibility
of activated sludge process for the treatment of tannery
wastewater in a l ab scale model under local conditions.
Wastewater was collected from chromium st age, Elmontazah
tannery, Ein Elsira tanneries, Cairo, Egypt. The reactor was
operated with the activated sludge process under batch mode
using a tannery wastewater as feed. A lab scale model
comprised of primary sedimentation tank (5 L), aeration tank
(5 L) and final clarifier (5 L). The model was operated
continuously for 120 hours of contact. The pH of wastewater
was firstly adjusted till pH 6.5 to enhance biosorption capacity.
The wastewater samples of the effluent were analyzed after
time interval 2h, 6h, 12h, 24h, 48h, 72h, 96h and finally 120 h to
find process efficiency. Results of the study demonstrated that
the removal
efficiency of about 98.3% and 98.4% for BOD5
(Biological Oxygen Demand) and COD (Chemical Oxygen
Demand) respectively, could be obtained under a HRT of 120 h.
Results were also showed decrease in chromium ion, ammonia
nitrogen, phosphorous and oil & grease concentrations up to
99.3%, 98.8%, 98.6% and 99.1%, respectively. Results were
also showed decrease in the color absorbance. Activated sludge
was characterized using SEM examination with EDAX analysis
and FT-IR technique.
The kinetic coefficients k (maximum substrate utilization
rate), Ks (half velocity constant), Y( cell yield coefficient) and
Kd (decay coefficient) were found to be 1.2 day-1, 209 mg/L,
0.18 and 0.039 day-1, respectively. These coefficients may be
utilized for the design of activated sludge process facilities for
tannery wastewater.
Index Terms Chromium, Municipal Activated Sludge,
Organic loads, Tannery wastewater
I. INTRODUCTION
Although the leather t anning in dustry is known to be
one of th e leading economic sectors in many countries,
there has been an increasing environmental concern
regarding the r elease of various recalcitrant pollutants in
tannery wastewater. Leather tanning is a wide common
industry all over the world. It is considered one of the m ost
important industries in Mediterranean countri es. Because of
their complex wastewater characteristics leather tanneries
are generally located in so called organized in dustrial
districts [1].
Tanneries are typically cha racterized as pollution intensive
Manuscript received April 25, 2014.
Ahmed M. Abou Elmagd, Department of Civil Engineering, Benha
University / Shoubra Faculty of Engineering / Shoubra, Cairo, Egypt,
Phone/ Mobile No. 002-01006243247, 002-01143460405,
M.S. Mahmoud, Sanitary and Environmental institute (SEI), Housing and
Building National Research Center (HBRC), Giza, Egypt, Phone/ Mobile No.
002-01157927521,
industrial complexes which generate widely varying and
high-strength wastewater. Major problems are due to
wastewater containing heavy metals, toxic chemicals,
chloride, lime with h igh dissolved and suspended salts and
other pollutants. A typical process flow sheet in an integrated
leather tannery industry is showed in Fig. 1.
Chromium salts used during the tanning process
generate two forms of chrome; h exavalent chromium and
trivalent chromium. Hexavalent chromium is highly toxic
to living organi sms even at low concentration causing
carcinogenic effect [2]. Trivalent chromium may be p resent
in the waste or can be produced from the h exavalent
chromium by chemical tr eatment. Soluble tr ivalent
chromium causes toxicity in anaerobic digestion due to the
accumulation of the metal in the i ntracellular fraction of
biomass [3]. Several components in the effluent contain
nitrogen as part of t heir chemical structure, which can lead
to development of anaerobic conditions harmful to the
aquatic life. The environmental protection regulations
stipulate that industr ies are not allowed to emit sulfide an d
chromium in the wastewater [4]-[5].
In Egypt, the tannery wastewater is discharged directly
to the main domestic sewage pipeline without proper
treatment which adds difficulties to the sewer system and to
the wastewater treatment plants [6]. The high
concentrations of pollutant s with low biodegradability in
tannery wastewater represent a serious and actual
technological and environmental challenge.
Treatment of tannery wastewater is carried out by
physical or chemical or biological or combination of these
methods [7]-[8]-[9]-[10].
Fig. 1 A typical process flow sheet in an integrated
leather tannery industry
Tannery Wastewater Treatment Using Activated
Sludge Process System (Lab Scale Modeling)
Ahmed M. Abou Elmagd and M.S. Mahmoud
Tannery Wastewater Treatment Using Activated Sludge Process System (Lab Scale Modeling)
22 www.erpublication.org
Treatment methods in which the removal of
contaminants is brought about by biological activity are
known as biological unit processes. Biological treatment is
used primarily to remove the biodegradable organic
substances (colloidal or dissolved) from wastewater.
Basically, these substances are converted into gases that can
escape to the atmosphere and into biological cell tissue that
can be removed by settling. Biological treatment is also
used to remove n utrients (nitrogen & phosphorus) from
wastewater. With proper environmental control, wastewater
can be treated biologically in most cases.
Biological treatment methods use microorga nisms,
mostly bacteria, in the biochemical decomposition of
wastewater to stable end products. More m icroorganisms,
or sludge’s, are formed and a portion of the waste is
converted to carbon dioxide, water and other end products.
Generally, biological treatment methods can be divided into
aerobic an d anaerobic methods, based on availability of
dissolved oxygen [11].
Biological methods, like activated sludge process, are
invariably employed for the secondary treatment of a large
number of industrial wastewaters. Knowledge of the
microbial kinetics and determina tion of the kinetic
coefficients for a particular wastewater ar e, th erefore,
imperative for the rational design of treatment facilities
[12]-[13].
Biological processes are usually prescribed for treating
industrial effluents to reduce organic content as they have
economic advantages over chemical oxidation [14].
However, high concentration of tan nins and oth er poorly
biodegradable compounds as well as metals can inhibit
biological treatment [15]-[16].
The natural affinity of biological compounds for
metallic elements could contribute to economically
purifying heavily metal-loaded wastewater. Activated
sludge MLSS (mixed liquor suspended solids) contain
microbial cells and spores. Th ese cells have been reported
to be capable of trapping metals by cell wall components,
altering metal uptake, a bsorbing into the cells by forming
metal complex, producing metabolites extracellularly to
chelate and precipitate these metals, or storing metals in th e
cytosol in association with various metal -binding pr oteins
[17]. It also offers th e advantage of having cell wall
material which shows excellent metal-binding properties.
The microbial cell wall of consists chiefly of neutral
carbohydrate and hexosamine, with smaller amounts of
lipid and protein [18].
The activated sludge process (ASP) is the most common
and versatile biological process used worldwide for the
secondary treatment of domestic, municipal and industrial
wastewater. With the course of time, several modifications of
the ASP have been made to improve the degree of treatment
in accordance with stringent effluent standards.
Optimization was also brought into account to reduce the
establishment and operating costs of wastewater treatment
plant [19].
In view of the above, the present study was undertaken
with the objective to determine the ability of Activated sludge
process to remove toxic constituents from tannery
wastewater and to determine different kinetic coefficients for
tannery wastewater so that these may be utilized for the
design of treatment facilities in tannery sector
II. MATERIALS AND METHODS
A. Analytical methods and equipment used in the study:-
T70+ UV/VIS Spectrophotometer PG instr uments Ltd
was used for colorimetric spectrophotometer
measurements according to (20).
Cole Parmer Turbid meter 0200 NTU, Chicago, USA.
A Scanning Electron Microscope SEM with EDAX
analysis (Inspect S. FEI Company, Holland) was used to
characterize the surface of municipal activated sludge.
Functional gr oups in activated sludge process were
determined by the Fourier transform infrared (FTIR)
spectroscopy (Shimadzu S 201 PC spectrophotometer
Japan) in the transmittance % mode in the range 4000
400 cm-1.
Flame at omic absorption spectrophotometer AAS (ICE
3000 series, AAS Thermo Scientific) was used for the
analysis of chromium ions using air acetylene - nitrous
oxide flame technique.
EUTECH pH-700 instrument Singapore meter was used
for measuring pH value, with a range of 0.00 to 14.00 and
an accuracy of ±0.02.
B. Experimental Set-up:-
The activated sludge reactor, used for the present study,
was developed in the laboratory. The lab scale model
comprised of primary sedimentation tank having volume of
about 5.0 L, aeration tan k having volume of about 5.0 L
and final clarifier having volume of about 5.0 L was used
for th e tr eatment study. The aeration tank was operated
continuously for 120 hours of contacts. Primary and
secondary clarifiers were operated for 45 minutes. The
secondary clarifier was equipped with a trough to collect
the effluent. The schematic di agram of the lab scale
activated sludge reactor used in the study is shown in Fig.
2.
Fig.2 Schematic diagram of the experimental set-up
C. Samples collection site:-
Samples of wastewater from contaminated sites with
tannery wastewater - chromium stage Elmontazah
Air
pump
Primary
sedimentation tank
Aeration
tank
Final
sedimentation
tank
Air
diffuser
Influent
Sample
Sample
International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869, Volume-2, Issue-5, May 2014
23 www.erpublication.org
tannery, Ain El Sira, Cairo, Egypt, were collected, analyzed
within 8h and stored in a refrigerator at 4ºC.
D. Acclimation of Biomass and Reactor Start-up:-
Activated sludge was collected from a nearby dr ain
from Zenin wastewater treatment plant. T he pH of tann ery
wastewater was firstly adjusted using 0.1 M HCL and 0.1 M
NaOH. Th e reactor was fed with tannery wastewater in
primary sedimentation tank for 45 min then transferred to
the aeration tank for 120 hour, th en transferred to th e final
clarifier for 45 min. The whole reactor content was kept
under aerobic condition by supplying adequate air from
aqua pumps, air flow capacity of 1.33 L.mi n-1. Various
parameters like pH, MLSS, Total suspended solids (TSS),
sludge volume index (SVI), COD, BOD, chromium,
ammonia n itrogen, ph osphorous, oil & grease, Turbidity,
dissolved oxygen concentration (DO) and temperature of
the reactor were monitored regularly under different
hydraulic retention time (HRT). The DO concentration in
the reactor always maintained more than 2 mg.L-1 during
the continuous operation to ensure requirement of DO for
carbon oxidation.
The removal percent was measured as:-
Removal % = (C0 Ce)/ C0 * 100
Where, (C0) and (Ce) are the in itial and final
concentrations (mg.L-1), respectively.
E. Analytical Methods:-
All the parameters were analyzed according to the
procedures described in the Standard Methods [20]. The
analysis of each parameter was done in triplicate.
III. RESULTS AND DISCUSSION
Tannery wastewater is one of the most important sources
of environment pollutan ts. The detailed composition of
tannery wastewater sample before and after sedimentation
tank is presented in Table 1. The pH value is around the
acidity (around 4.0 pH unit). Scan spectrum curve of tannery
wastewater sample showed the color absorbance along with
different wavelengths from 400 nm to 600 nm was presented
in Fig. 3.
Laboratory scale reactors are normally used to determine
kinetic coefficients and usually employed for its easy
operational contr ol. Th e procedure is to operate the unit
continuously for two hours to five days. COD, BOD,
Turbidity, TDS, TSS, Ammonia, Phosphorous and Oil &
Grease data for influent and effluent are determined at steady
state conditions [21].
During the course of study, the reactor temperature
fluctuated between 29 to 31°C, which falls within the suitable
temperature ran ge for heterotrophs treating wastewater
under aerobic conditions [22]. The pH of the reactor
remained between 6.5 and 7.0 which is a suit able range for
biological treatment [23]. DO of the reactor remained
between 3 and 4.5 mg/L which was above the desirable range
of 2 mg/L for biological treatment [24]. The major pollution
parameters for tannery wastewater are (BOD), (COD),
suspended solids (TSS), nitrogen and chromium.
Aerobic microorganisms use organic carbon in the
influent and convert it to biomass and carbon dioxide. A
large amount of sludge is generated along with high energy
consumption in the process. It is evident from our results
that the adopted HRTs exerted significant effect on the
reactor performance in terms of COD, BOD, Tur bidity,
TDS, TSS, Ammonia, Phosphorous and Oil & Grease. At
HRT of 2h, the r emoval efficiency was 53.3 % and 37.5 %
for COD and BOD, respectively. At HRT of 72h, the
removal efficiency was 83.8 % and 82.7 % for COD and
BOD, respectively. At HRT of 120 h, the removal efficiency
was 98.4 % and 98.3 % for COD and BOD, respectively as
shown in Fig. 4 and 5. Th e r eactor performance is also
expressed in terms of design parameters like COD removal
efficiency and food-to microorganism (F/M) r atio (COD
basis). Th erefore, th e COD removal efficiency is plotted
against COD loading rate and F/M ratio as shown in Fig. 6.
Table (1) Physicochemical analysis for tannery
wastewater sample
Constituents
Before
Sedimentation
tank
After
Sedimentation
tank
Units
Color
Dark Green
Green
Abs.
580n
m
0.296
0.294
Abs.
418n
m
0.396
0.372
pH
4.01
4.06
Turbidity
540
465
NTU
TSS
2250
1800
mg/L
TDS
6600
6570
mg/L
COD
4100
3250
mg/L
BOD
2040
1690
mg/L
ammonia
nitrogen
52
48
mg/L
Phosphorous
63
58
mg/L
Oil and
Grease
34.2
29.1
mg/L
Chromium
840
815
mg/L
Fig. 3 UV Scan Spectrum Curve for tannery wastewater
sample