We evaluate the applicability of a reverse osmosis (RO) system that combines powdered activated carbon (PAC) and ultrafiltration (UF) to treat the effluent discharged from tannery wastewater treatment plants. Conventional treatment processes such as neutralization, clariflocculation, and biological processes are used to clean the effluent before feeding to the PAC and UF combined RO system. The efficiency of the combined system was evaluated using the chemical oxygen demand Mn (CODMn), color, pH, turbidity, total nitrogen, total phosphate, and conductivity. The PAC was effective in greatly reducing the CODMn and color. The turbidity and silt density index of the UF permeate satisfied the water quality indices required for the RO feed. The RO system was constantly maintained at approximately 75% RO recovery, and the RO permeate satisfied the water quality requirements for reusing the processed water. Therefore, the PAC-UF combined RO system can be used to process effluent discharged from tannery wastewater treatment plants for reuse.

INTRODUCTION

Tanning is one of the oldest industries and requires huge amounts of water (approximately 15 to 20 m3 per ton of hide processed) in several stages, generating enormous quantities of liquid effluents. Tannery wastewater typically contains high levels of salts, organic and inorganic matter, colored matter, dissolved and suspended solids, ammonia, organic nitrogen, and pollutants such as sulfides, chromium and other toxic metal salts (Aboulhassan et al. 2008). The characteristics of raw wastewater are listed in Table 1 (Fababuj-Roger et al. 2007). Tannery wastewater, which generates many complex and high effluent loads, is difficult to treat and requires extensive treatment prior to reuse. Conventional processes such as oxidation, chemical, and biological processes are used to treat the tannery wastewater (Durai & Rajasimman 2011).

Table 1

Characteristics of tannery wastewater

Parameter Feed tannery wastewater 
COD (mg/L) 5,000–5,500 
BOD5 (mg/L) 3,000–3,500 
Suspended solids (mg/L) 2,500–3,000 
Cr3+ (mg/L) 80–100 
SO42– (mg/L) 1,800–2,000 
Cl (mg/L) 5,000–6,000 
pH 8–9 
Conductivity (μs/cm) 10–12 
Parameter Feed tannery wastewater 
COD (mg/L) 5,000–5,500 
BOD5 (mg/L) 3,000–3,500 
Suspended solids (mg/L) 2,500–3,000 
Cr3+ (mg/L) 80–100 
SO42– (mg/L) 1,800–2,000 
Cl (mg/L) 5,000–6,000 
pH 8–9 
Conductivity (μs/cm) 10–12 

COD, chemical oxygen demand; BOD, biological oxygen demand.

The final effluent discharged from tannery wastewater treatment plants cannot be reused because of its high load of organic matter, color, and high concentration of total dissolved solids (TDS).

To minimize pollution from tannery wastewater, several authors proposed the adoption of integrated clean technologies (Rao et al. 2003) and treatment of the waste streams, mainly by using membranes. This approach removes the pollutants and allows reuse of the processed water. Reverse osmosis (RO) membranes can solve the problem of TDS in the effluent and are necessary if reusing the effluent is the goal. Moreover, the high organic matter content in the effluent requires exhaustive pretreatment to minimize membrane fouling before RO (Phuntsho et al. 2011). The effectiveness of the powdered activated carbon (PAC) pretreatment and the consequent improvement of the membrane performance has been reported in studies concerned with membrane fouling in the PAC–ultrafiltration (UF) process used in water containing natural organic matter and (or) particles. Thus, further investigations into the effect of PAC and UF pretreatment on an RO system are needed (Gai & Kim 2008; Huang et al. 2009; Matsui et al. 2009).

The main objective of this study was to investigate the performance of PAC and UF pretreatment in an RO system, and to evaluate the subsequent reuse of the effluent discharged from tannery wastewater treatment plants.

METHODS

Commercial PAC was purchased from Shin Ki Chemical Ind. Co. Ltd and was used without further purification. The PAC was analyzed by the KSM 1802 method: it had a dry weight of 9.8 wt %, iodine number of 915 mg/g, methylene blue value of 175 mg/g, and pH of 7.7. A hollow fiber UF membrane made of polyacrylonitrile (Mann + Hummel Ltd, Germany) was used in the experiments. The outside-in UF membrane possesses a nominal cutoff of 100 kDa. The total active membrane area is 45 m2. A spiral-wound polyamide RO membrane with effective membrane area of 7.6 m2 was purchased from Toray Chemical Corporation (RE8040-FL).

This work comprises three stages: (1) PAC adsorption, (2) pretreatment (UF system), and (3) the RO system. Figure 1 shows a schematic of the PAC and UF combined RO system. PAC adsorption tests were performed to characterize the adsorption of chemical oxygen demand Mn (CODMn) and color, using PAC in a 1 m3 reaction tank at concentrations of 0.8, 0.9, 1.0, and 1.2 g/L. The tests were conducted at an agitation speed of 60 rpm and contact time of 30 min. The filtration conditions of the UF system were set to a feed pump frequency of 20 Hz, a filtration time of 5 min, a backwashing time of 30 s, and an air-scouring time of 30 s. The system efficiency was evaluated by observing the turbidity, silt density index (SDI), and the permeate flow rate.
Figure 1

A schematic illustration of the PAC and UF combined RO reuse system.

Figure 1

A schematic illustration of the PAC and UF combined RO reuse system.

The UF permeate was collected, stored in the 1 m3 tank, and periodically fed using a high pressure pump to a pilot-scale RO system. The RO system operated in single-pass two-stage mode with a permeate flow rate of 12.3 L/min and feed flow rate of 16.5 L/min. A concentrate flow rate of 4.2 L/min was used in the transfer to the raw water tank, and the system recovery was about 75%.

RESULTS AND DISCUSSION

Figure 2 shows the physicochemical and biological characteristics of the treated wastewater effluent. The raw wastewater is mainly characterized by using the COD, color, total nitrogen (TN), total phosphorus (TP), pH, turbidity, and conductivity. The average values of COD, color, TN, turbidity, and conductivity are approximately 90.5 mg/L, 383.4 PtCo, 45.4 mg/L, 29.2 NTU, and 9255.2 μs/cm, respectively.
Figure 2

Variation of treated tannery wastewater quality over time.

Figure 2

Variation of treated tannery wastewater quality over time.

The adsorption efficiencies of COD, color, and TN at PAC dosages of 0.8, 0.9, 1.0, and 1.2 g/L are shown in Figure 3. The PAC adsorption efficiency for COD and color are considerably higher than that for TN. In addition, the PAC adsorption efficiency for COD increased with increasing PAC dosage from 0.8 g/L to 1.2 g/L, at about 43.4 mg/L and 69.1 mg/L, respectively (approximately 1.6 times higher than for a PAC dosage of 0.8 g/L). The average COD adsorption capacity of different PAC dosages is about 55 mg COD/g PAC. For a PAC dosage of 1.2 g/L, the adsorption efficiencies for color and TN are about 95.1% and 35.8%, respectively.
Figure 3

Effect of PAC dosage on the removal of COD, color, and TN.

Figure 3

Effect of PAC dosage on the removal of COD, color, and TN.

Figures 4 and 5 show the performance and treatment efficiency of the UF system for PAC dosages of 0.8, 0.9, 1.0, and 1.2 g/L. As shown in Figure 4, increasing the PAC dosage decreases the permeate flow rate and backwashing flow rate, whereas the backwashing pressure increases because higher PAC dosages have higher osmotic pressures. Subsequently, increasing the PAC dosage decreases the permeate flux owing to the membrane fouling by PAC adsorption. Figure 5 shows the SDI and turbidity of the UF permeate. The turbidity and SDI of the UF permeate were always lower than 0.8 NTU and 2.6, irrespective of the PAC dosage, which satisfies the RO requirements of less than 1 NTU and 5, respectively.
Figure 4

Effect of PAC dosage on flow rate and pressure of the UF system.

Figure 4

Effect of PAC dosage on flow rate and pressure of the UF system.

Figure 5

Effect of PAC dosage on the SDI and turbidity of the UF system.

Figure 5

Effect of PAC dosage on the SDI and turbidity of the UF system.

The RO system was operated at a feed flow rate of 16.5 L/min and an operational pressure of 9.7 kg/cm2. The performance of the RO system was evaluated in terms of the permeate pollutant concentrations and the membrane rejection in terms of conductivity. Figure 5 and Table 2 show data regarding the feed and the streams of permeate and concentrate in the RO experiments. Figure 6 shows the flow rate and pressure of the feed. The permeate and concentrate streams were constant over the 30-day test period, and a 75% membrane rejection was maintained. As expected, the conductivity rejection was higher than 95%, and COD, TN, and TP removal was higher than 80%. The RO permeate thus satisfies the water quality indices for reuse.
Table 2

Feed, permeate and concentrate characteristics in RO experiments

Items COD (mg/L) TN (mg/L) TP (mg/L) pH Conductivity (μs/cm) 
Feed 15.9–25.1 30.1–42.6 0.06–0.5 7.4–7.6 8,360–9,812 
Permeate 0.5–4 5–7.7 0.03–0.1 7.6–8 353–487 
Concentrate 59.8–96.5 70.3–97 0.11–0.9 7.35–7.43 19,456–22,990 
Reuse <10 <10 <0.2 7–8 <500 
Items COD (mg/L) TN (mg/L) TP (mg/L) pH Conductivity (μs/cm) 
Feed 15.9–25.1 30.1–42.6 0.06–0.5 7.4–7.6 8,360–9,812 
Permeate 0.5–4 5–7.7 0.03–0.1 7.6–8 353–487 
Concentrate 59.8–96.5 70.3–97 0.11–0.9 7.35–7.43 19,456–22,990 
Reuse <10 <10 <0.2 7–8 <500 
Figure 6

Variation of flow rate and pressure in the RO system.

Figure 6

Variation of flow rate and pressure in the RO system.

CONCLUSIONS

The high organic matter content, color, and salts in tannery wastewater require exhaustive pretreatment prior to using RO systems. The combination of a PAC and UF system greatly reduced the COD and color of tannery wastewater. In addition, the turbidity and SDI of the UF permeate satisfied the feed water requirement of the RO system. The RO system was constantly maintained at approximately 75% RO recovery, and the RO permeate satisfied the reused water level for processing. Therefore, a PAC and UF combined RO system can effectively process the effluent discharged from tannery wastewater treatment plants.

ACKNOWLEDGEMENTS

This research was supported by a grant (code 15IFIP-C088924-02) from Industrial Facilities & Infrastructure Research Program funded by the Ministry of Land, Infrastructure and Transport (MOLIT) of the Korean government.

REFERENCES

REFERENCES
Aboulhassan
M.
Souabi
S.
Yaacoubi
A.
2008
Pollution reduction and biodegradability index improvement of tannery effluents
.
Int. J. Env. Sci. Technol.
5
,
11
16
.
Durai
G.
Rajasimman
M.
2011
Biological treatment of tannery wastewater–a review
.
J. Environ. Sci. Technol.
4
,
1
17
.
Fababuj-Roger
M.
Mendoza-Roca
J.
Galiana-Aleixandre
M.
Bes-Pia
A.
Cuartas-Uribe
B.
Iborra-Clar
A.
2007
Reuse of tannery wastewaters by combination of ultrafiltration and reverse osmosis after a conventional physical-chemical treatment
.
Desalination
204
,
219
226
.
Huang
H.
Schwab
K.
Jacangelo
J. G.
2009
Pretreatment for low pressure membranes in water treatment: a review
.
Environ. Sci. Technol.
43
,
3011
3019
.
Phuntsho
S.
Listowski
A.
Shon
H.
Le-Clech
P.
Vigneswaran
S.
2011
Membrane autopsy of a 10-year-old hollow fibre membrane from Sydney Olympic Park water reclamation plant
.
Desalination
271
,
241
247
.
Rao
J. R.
Chandrababu
N.
Muralidharan
C.
Nair
B. U.
Rao
P.
Ramasami
T.
2003
Recouping the wastewater: a way forward for cleaner leather processing
.
J. Cleaner Product.
11
,
591
599
.
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