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Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt TECHNO-ECONOMIC STUDY OF THE TWO-STAGE / TWO PASS RO
MEMBRANE SYSTEM FOR CHROMIUM RECOVERY - PART-4
Azza I. Hafez
Prof. Dr., Ch. Eng., National Research Center, El-Tahrir Street, Dokki, Cairo, Egypt Tel. + 20 (2) 3370933, Fax + 20 (2) 3370931,
ABSTRACT

In Egypt more than 85% of tanneries adopt chromium tanning process because of its
processing speed, low cost, light color of leather and greater stability of resulting
leather. In chromium tanning process 20 – 40% of applied chromium is usually
remain un-reacted and discharged directly into sewerage system without treatment.
Two local medium size tannery shops in Egypt were investigated. The chemical
analysis of the spent chromium effluents indicated that chromium content ranged from
1300 – 2500 mg cr6+ /L, while NaCl concentration varies from 40000 to 50000 mg/L.
Physical and chemical pretreatment of spent chromium Liquor was investigated on
bench scale and published earlier in Part-1. RO membrane separation of chromium
from pretreated solution on pilot plant scale experiments were investigated in another
work and published as Part-2. Based on results of pilot plant and in order to achieve
the local limits (<5 mgCr6/l) the “Two-Stage/Two-Pass RO System” was selected for
this purpose, where the chemically pretreated chromium effluent will be directed to the
RO membrane separation unit(s), and the resulted concentrate will be further
concentrated via an additional RO membrane unit(s). The proposed design of the
Two–Stage/Two–Pass RO membrane system and its performance was investigated as
Part-3.
The aim of the present work is to evaluate economically a full scale treatment and membrane recovery plant of 360m3/day capacity that capable to handle the chromium rich wastewater based on the experimental results of the bench scale pretreatment and the low pressure RO recovery pilot plant. The Financial analyses of the treatment and Cr-recovery plant was investigated. The total fixed capital cost was estimated as US$ 1.821 million, while the annual operating cost amounts US$ 71 thousand. The cash flow analyses and the net present value of the project were carried out. Keywords: Economic study, Chromium Recovery, RO Membrane Separation,
Financial Analyses, Fixed Capital Cost, Present Value Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt INTRODUCTION
Tanneries are among those industrial activities mostly responsible for their negative
environmental impact [1]. Environmental pollution problems caused by the discharge
of un-reacted effluent from tanneries with high chromium content and other pollutants
have become of increasing concern in Egypt. There are more than 300 tanneries in
Egypt, 75% of these tanneries are small and medium workshop [2]. More than 85% of
tanneries adopt the chromium tanning process, where 60-80% of the chromium applied
in the form of chromium sulphate is taken by the leather, and the balance is discharged
as a waste in the sewerage system causing a serious of environmental impact [3,4].
A research project was financed by the US-AID grant #ENV2-004-044 in cooperation
with the National Research Center (NRC), had carried out on two local medium-size
workshops using the classical chromium tanning method. Their spent chromium
liquors are characterized by high chromium concentration (1300–2500 mg Cr 6+/l) and
high sodium chloride concentration (40000 – 50000 mg/l). The wide literature survey
indicated that most of the previous work focused on removal of chromium through pH
adjustment and chemical deposition [5]. The use of RO membrane technique in
removal and recovery of chromium from the tanning effluent is quite limited [6,7].
Because the membrane separation is highly sensitive to organic and inorganic
suspended solids and colloid, the research project was classified to three phases. Phase
one was concerned with the physiochemical pretreatment methods of the spent
chromium effluents collected from the two local medium-size workshops. The detailed
field work, bench-scale investigation and the laboratory results had published earlier in
Part-1 by Hafez et al. [8]. The compiled results of the physicochemical treatment,
which included; coarse filtration, pH adjustment, chemical coagulation and
precipitation by using organic and inorganic polymers, proved the removal of nearly
98% of S.S, 75% of COD and 71% of Cr6+. However, the remaining chromium still
very high and beyond the local standard limits (< 5 mg/l) for discharging into
sewerage systems.
So, the second phase was concerned with the experiments of the chromium removal
efficiency from the pretreated spent liquor by using a pilot-scale set up of the low-
pressure RO membranes (LPRO) (7 and 16 bar), this in order to make the cost suitable
and can be afforded by the end-user. Different working pressures under variable salt
concentration were carried out to remove the hazardous chromium from the spent
tanning effluent and recover it for further reuse. The study proved that the RO
membrane technique is able to separate chromium efficiently from the pretreated
chromium tanning wastewater. It was found that the high concentration of NaCl
largely affected adversely chromium separation. Reducing of NaCl concentration to
5000 mg/l helps in recommending of using low pressure membrane units for
separation and recovery of chromium from waste water of the tanning shops. The
results of phase-2 had been published separately as Part-2 by Hafez et al. [9].
Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Phase-3 is under press as part-3 which focused on the design of a full-scale low
pressure RO membrane treatment plant that is capable to handle bigger amounts of
chromium-rich wastewater collected from a complex of several small to medium
tannery workshops. Several simulated design models were used based on the earlier
bench scale and pilot plant results to choose the RO system to be technically
evaluated.
The Objective of the present work is to analyze and evaluate the economics of the
treatment and the chromium recovery plant of the Two-stage/Two-pass LPRO system
that proposed in phase-3.

TECHNICAL STUDY

The proposed design will be applied at El-Robeiky area in Badr City, where the Old
Cairo tanneries including Cairo–Tan and EL-Radio tanneries will be relocate,
depending on the industrial planning concept of the Government with future
development plans for various sectors in Egypt.
The proposed design is concerned only with the treatment and recovery of chromium
wastewater effluent, where the other streams will be treated in the central treatment
plant which will be constructed by the Government at El-Robeiky area in Badr-City.
In order to achieve the local limits (<5 mg Cr6+/l) the “Two-Stage/Two-Pass RO
System” was selected for this purpose, where the chemically pretreated chromium
effluent will be directed to the RO membrane sepation unit(s), and the resulted
concentrate will be further concentrated via an additional RO membrane unit(s). The
recovered permeate will be further treated through an polishing RO membrane unit.
The resulted permeate from the two-pass will be within the limits of the National
Egyptian laws for discharging to sewerage system, or could be reused in tanning
processes or irrigation purpose.
1. The Major Design Considerations

The major design considerations can be summarized as:
a- Separation between the different streams and chromium effluent stream.
b- Pretreatment, chemical treatment and chromium recovery, with max capacity of
360 m3/ day, considering that the working time (run-off period) is 20 hours, and 4 hrs kept for chemical cleaning of membranes, filters washing and maintenance. c- The compiled results of the physicochemical treatment which proved the removal of nearly 98% of S.S, 75% of COD and 71% of Cr6+. d- The estimated maximum concentrations of chromium effluent (3000 mg/L), which expected to be raised with about 125% (4000 mg/L) after the completion of the water conservation program. Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt e- The removal efficiency of chromium by membrane separation is estimated as 99.5%, regarding that the obtained removal in bench scale experiments was 99.8%.
2. The Scheme of Treatment and Chromium Recovery

The scheme of treatment and chromium recovery can be concluded as follows:
a- Isolation of the chromium waste water effluent from the final waste water streams
b- Collecting of the isolated chromium wastewater effluents at holding tank in the c- The isolated chromium effluent should be pretreated to remove oil and grease and neutralized to adjust pH, chemical treated by coagulation technique and chrome recovery by using membrane separation technique. Preatreatment is necessary to prevent membrane damage. d- The treated chromium effluent is passed to Two Stage / two psss RO system.
3. The Components of The Treatment and Recovery Plant

The components of the treatment and recovery plant are consist of:
1- The pretreatment units which consist of: the holding tank, the oil separator, the
neutralization unit and the coarse Filtration Unit. 2- The chemical treatment units which consists of : the flocculation unit (flash mixer unit and flocculator), and the clarifying Unit. 3- The RO treatment units which consist of: chlorination dosing unit, pH adjustment unit, antiscalant dosing unit, dechlorination dosing unit, low pressure pumps and pipe-works, media filters, fine filters, micron filters, high pressure pump and pipe-works, reverse osmosis membranes and vessels, concentrate and permeate networks, automatic pressure & temperature gages, automatic chemical monitors (Cl2, pH, Temp.), automatic electrical control, and main control panel and starters. 4- The two-stage/two pass RO Cr recovery plant which consists of: RO Membrane- Separation Unit (MSU) of Cr-Recovery Level = 60%, RO Membrane-Concentration Unit (MCU) of Cr-Recovery Level = 55% and RO Membrane-Polishing Unit (MPU) of Cr-Recovery Level = 70%. Schematic block diagrame of the proposed combined treatment and recovery of chromium wastewater effluents is shown in figure (1). The flow diagram, as well as the materials balance of the “Two-Stage/Two-Pass RO System” is shown in figure (2). Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Equipment sizes were estimated based on plant capacity, material balance and the
proposed design.
ECONOMIC STUDY

Economic indicators of treatment and chromium recovery units of chromium
wastewater effluent is estimated based on the previous technical study. Technical
parameters are considered to determine the capital investment costs, which includes
fixed capital costs, operating costs and labor salaries.
All prices are of year 2003 where 1US$ = 6.5L.E.
The economic study includes the following:
1. Fixed Capital Cost
The fixed capital costs comprise the following items:
a- The delivered equipment costs which is encompassed: the cost of concrete
structured and metallic equipment, dredging, filling, painting and supports. b- Equipment installation, it costs 15% of the purchased equipment cost. c- Measurements and control instrumentation are estimated as 10% of the purchased d- Piping system, it costs 30% of the purchased equipment cost. e- Land cost, it was ignored because there are available area for plant implementation f- Site development, it costs 10% of equipment cost. g- Engineering and Supervision amounts to 30% of fixed capital cost. h- Contingency, it is estimated as 10% of the equipment cost. All costs based on the local market prices.
Table (1) presents list of purchased equipment.
Table (2) presents the total fixed capital cost.
2. Operating Costs
It comprises of the following items
Raw materials which include sulphuric acid and polymer. Chlorine, antiscalant agents. Utilities which comprise process water cost (L.E. 1.25) and electricity cost (1 kW.h costs L.E. 0.50) Maintenance which is nearly 1% of purchased equipment costs. Services and analysis: they cover daily, weekly and monthly analyses. Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Administration costs: which is about 11% of total operating costs. Insurance: it amounts to 1% of total fixed costs. Depreciation which is 10% for steel equipment costs, 2.5% for constructed equipment and building, and 20% for contingencies.
3. Labors
It includes salaries and wages of staff and labors.
Table (3) presents the annual operating cost.
Table (4) presents the total operating cost for three months.
FINANCIAL ANALYSES

The proposed treatment and chromium recovery plant is of 360 m3/day. The treatment plant based on the separation between the different streams and chromium effluent stream, pretreatment chemical treatment, then chromium recovery by using the Two Stage / Two Pass RO system. The initial capital expenditure of this project was calculated for the proposed system (including the Two–Stage/Two–Pass RO membrane system) which amounts to L.E. 11.838 million (US$ 1.821 million). The annual operating expenses were estimated as L.E. 460 thousand (US$ 71 thousand). The annual gains are consist of two main sources the recovered chromium (the
concentrate) and the reuse of treated water (the permeate).
From material balance figure (2) the chromium recoverd from the 120 m3/day MSU is
3209 mg/l., the chromium recoverd from the 45 m3/day MCU is 7096 mg/l. and the
chromium recoverd from the 120 m3/day MPU is 51 mg/l. so, the annual chromium
recovered will be 255 ton which costs L.E. 1.148 million. Also from material balance
figure (2) the recovered water which will be reused is 172.2 m3/day and will give
annual revenue of L.E 65 thousand. So the total annual gains are L.E. 1.1213.
The feasibility of the treatment and recovery plant using the Net Present Value (NPV)
method are shown in table (5). The results of the analysis yeilded a possitive NPVof
approximately L.E 12.813 million over 15 years projected cash flow. This is because
the annual operating expenses are lesser than the annual gains, so by carrying the cash
flow annalyses the investment costs and the annual operating costs can be recovered
after 15 years.
CONCLUSION

a- There are two main economic benefits arising from the implementation of the
chromium recovery plant. First, the project revealed the most efficient clean Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt process for chromium recovery and water reuse and their annual gains will amounts L.E. 1.213 million and so reduce import and subsequent foreign currency. Secondly, the new plant will generate a new job opportunities for labor of different skill levels and accordingly help in decreasing the unemployment problem in the economy The economics of the treatment and Cr-recovery plant was analyzed and estimated, which included: the fixed capital costs, operating costs and labor salaries. The total fixed capital cost was estimated as L.E. 11.838 million (US$ 1.821 million), while the annual operating cost amounts L.E. 460 thousand (US$ 71 thousand). The Net Present Value analysis was positive of approximately L.E. 12.813 million.The investment costs and the annual operating costs can be recovered after 15 years. The proposed chromium treatment and recovery plant is planed to construct soon at El-Robeiky area in the new industrial Badr City.
ACKNOWLEDGMENT
The author is indebted to U.S. Egypt Science and Technology Program for financial
support of this work. The author is grateful to Engineer Taha Eid and Engineer Ali
Hassan, chairpersons of Radio Tan and Cairo Tanneries for their help during the
project period.

REFERENCES
[1] Assomac Servizi SRL and EGLTALEC Report entitled: Preparation of a Master
Plan and Conceptual Protection for the new leather tanning area, Badr City, Cairo, Egypt (1998). [2] A.R. Khwaja, Studies on pollution abatement of wastes from leather industries. Ph.D. Thesis. University of Roorkee, India. (1998). [3] A.I. Hafez, Development of a Management System to Treat Wastewater Effluent and Use Clean Technology for Chromium Recovery from El-Radio and Cairo–Tan Tanneries, U.S. and Egypt Cooperation Project Report No.: Env2- 004-044, (2000). [4] S. Siegel and D. Clifford, Removal of Chromium from Ion Exchange Reagent Solution, EPA Report No. 600/2-83-007 (1988). [5] Z. Kowalski, Treatment of Chromic Tannery Wastes. J. of Hazardous Materials, 37 [6] A. Cassano, E. Drioli, R. Molinar, C. Botolutti: Quality improvement of recycled chromium in the tanning operation by membrane process, 2nd Annual Meeting of the European Desalination Society, Gienoa, Italy, 1996, pp. 193-203. [7] M. Mulder, "Basic Principles of membrane technology", Kluwer Academic Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt [8] A.I. Hafez, M.S. El-Manharawy, M.A. Kehdre, Treatment of chromium tannery wastewater effluent- A case Study, Part-1. Bulletin of the National Research Centre, Egypt, Vol.28, No.2, pp. 171-184 (2003). [9] A.I. Hafez, M.S. El-Manharawy, M.A. Kehdre, RO membrane removal of unreacted chromium fro spent tanning effluent - A Pilot-Scale Study, Part–2. International Congress on Membranes and Membrane Processes, Toulouse, France 7-12 July 2002. Journal of Desalination, Vol. 144, pp. 237-242, Elsevier Science Publications. Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Table-1: Purchased equipment costs
(Price of 2005, 1US$= 6.5L.E.)
Equipment
Price/Unit,
Total Cost ,
Total Cost ,
1000 L.E.
L.E. 1000
Total Pretreatment cost
Total Treatment Cost
Total Advanced Recovery Cost
TOTAL COST
Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Table-2: Total fixed capital cost
Cost, L.E. 1000
Cost, US$ 1000
Total Fixed Capital cost
Table-3: Annual operating cost
Cost, 1000 L.E.
Cost, 1000 US$
TOTAL ANNUAL OPERATING COST
Table-4: Operating cost (For 3 months)
Cost, 1000 L.E.
Cost, 1000 US$
TOTAL OPERATING COST FOR
(THREE MONTHS)
Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Table-5: Projected cash flow and financial return L.E 000'S for the chromium recovery plant
DESCRIPTION
Pre.comm.
EXPENDITURE
1- Const and purchased
O&M expenses
Total O&M expenses
Annual Gain
Total Annual Gains
Annual Cash Flow
Assumptions: The capital expenditures are represented by the estimated cost for chromium treatment and recovery plant. Life time of the project is 15 year. O&M expenses are inflated by 55 annually. Annual gaining consists of the quantity of chromium recovered and recycled permeate. Cost of chromium increase by 5% while selling water price will be increased by 5% in the last five years. Tenth International Water Technology Conference, IWTC10 2006, Alexandria, Egypt Fig. 1: Schematic Block Diagrame of the Proposed Combined Treatment and Recovery of Chromium Wastewater Effluents.
Cr = 10.75 mg/l Cr = 29.2 mg / l Cr = 15.6 mg/l MPU
MCU
MSU
Fig. 2: Two Stage/Two Pass RO System For Chromium Removal & Recovery.
. MCU: Membrane Concentration Un i t . MPU: Membrane Polishing Unit.

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