COMPARATIVE PRELIMINARY EVALUATION OF TWO IN-STREAM WATER TREATMENT TECHNOLOGIES FOR THE AGRICULTURAL REUSE OF
DRAINAGE WATER IN THE NILE DELTA
SUPPLEMENTAL DATA
Table S1. Details relative to the Edfina drainage canal.
Edfina village and drainage canal (DC) are located in West of the Nile River Delta (31° 17’
45.14’’ N and 30° 30’ 18.9’’2 E), 60 km south east of Alexandria. The drain is serving 2106 m2 (200 hectares) of croplands, and dumps its water in the Shamasma drain that carries good quality water and could be used for irrigation after mixing with canal fresh water if not receiving sewage contamination load from Edfina drain. About 3000 people live in scattered houses along a main avenue. Their untreated sanitary waters are collected in a small pipe network that, due to the lack of municipal wastewater treatment system, discharges directly into the Edfina drainage canal. Daily about 300 m3 of raw sewage are dumped in the drain causing a serious environmental pollution. The drainage canal has a trapezoidal section about constant along the canal, a length of 2200 m, a mean bottom width of 1 m and a top width of 2.3-2.7 m. The canal bottom slope is about 0.05 m in 100 m (0.05%) and the depth of flow (water level) is about 0.8 m at the beginning of the DC and 1.0 m just before the outlet. The actual flow area increases along the canal in occasion of the irrigation events (2-4 a month) which cause an increase in the volumetric flow rate and the water depth. Nevertheless, also on occasion of the irrigation events the flow regime is still subcritical and uniform in all the canal and surface water has nearly the same slope of the bottom of the canal. The outlet of the drainage canal is a pipe with 0.8 m diameter which determines a stable water level in the drain path.
Table S2. Experimental procedure applied for the growth of the aerobic and facultative fractions of the bacterial community sampled from the Edfina drainage canal.
An average sample of the DCW was taken and used to produce an enriched microbial consortium to be used in the aerobic/anaerobic nitrification/denitrification test aimed at simulating a canalised facultative lagoon. The aerobic and facultative fractions of the indigenous bacterial community were initially grown under shaking (150 rpm) at 30°C in 1 L baffled flask equipped with screw cap filled with 250 mL of DCW. The mixture of organic substrates reported in Table S3, mimicking the composition and COD of municipal wastewaters, was used to grow and enrich the consortium. Similarly, (NH4)2SO4 and KNO3
were used to supply periodically additional inorganic N to the medium, in order to replenish the consumed NH4-N and NO3-N. The indigenous microbial community was incubated in the medium at room temperature in the dark under alternate aerobic/anoxic conditions obtained by flushing, at the end of each growth phase, the flask head space with either nitrogen or air and closing tightly the cap. Further sub-culturing steps were performed by transferring the enriched bacterial community in fresh DCW at 20% (v/v) and the culture volume was scaled-up to 1.5 L in a 5 L bottle under magnetic stirring (450 rpm).
COD, Total N, NH4-N and NO3-N concentrations were monitored during incubation and the carbon and N sources were added whenever COD and total N were partially or completely depleted.
Table S3. Composition of the COD source periodically supplied in the laboratory-scale tests conducted in the 2-STR plant simulating a canalized facultative lagoon (from Seib et al.
2016).
Constituent % mass content
Non-fat dry milk 27%
Soluble potato
starch 27%
Yeast extract 14%
Casein peptone 14%
CH3COONa·3H2O 15%
L-Cysteine 2%
Table S4. Layout and operational conditions of the laboratory-scale pilot plant aimed at simulating the aerobic and anoxic layers of a canalized facultative lagoon.
In order to gain insight on the performances in COD reduction and nitrification/denitrification attainable in a CFL using the microbial consortium enriched from drainage canal water, a laboratory-scale pilot plant comprising 2 hydraulically- connected bioreactors, one mimicking the aerobic and one the anoxic layer of an actual CFL, was designed and assembled. Two jacketed glass stirred tank reactors (STR) with a working volume range of 0.5-2.0 L were used (Sartorius, Germany). The STRs were equipped with temperature, dissolved oxygen, redox potential and pH probes, two Rushton impellers and a ring-shaped gas sparger located below the lower impeller. In the plant, schematically represented in Fig. 1, the two STRs were hydraulically connected to each other and water recirculated with a controlled exchange flow rate f by means of a peristaltic pump. The same flow rate was applied from the aerobic vessel to the anaerobic one and from the anaerobic vessel to the aerobic one, to assure a constant working volume in the two bioreactors. The control of pump’s volumetric flow rate allows to control the COD, oxygen and nitrate exchange rate between the aerobic and anaerobic STR, thus simulating the mass transfer rate between the aerobic and anaerobic layer of the actual CFL. This configuration is designed to work in fed-batch conditions with constant volume, with a periodic supplementation of organic substrates (Table S1), ammonium and nitrates, so as to periodically re-establish the initial conditions. The first STR was stirred at 400 rpm and purged with an air flow of 0.75 L/min (0.375 vvm) to maintain fully aerobic conditions.
The second STR was stirred at 400 rpm and no O2 was sparged. Fully anoxic conditions were obtained in the second STR under all the experimental conditions tested in this work, as a result of the balance between O2 advection through the exchange volumetric flow rate f and biological oxygen consumption. The liquid volumes in the two STRs were changed during the experiments in the 1-2 L range. The exchange flow rate f was varied between 0.13 and 0.50 L/h. Preliminary fixed volume fed-batch tests were carried out with the aerobic and anoxic STRs not hydraulically connected to each other, after inoculation at 50% v/v with the previously enriched bacterial community, in order to start up the system (disconnected STR tests). Then, a second set of experiments was carried out with the two STRs hydraulically connected and with a variable volumetric flow rate f (two-STR tests).
COD, total N, NO3-N and NH4-N concentrations were monitored over time in both bioreactors. During the system start up (disconnected STRs), the mixture of organic substrates was periodically added to each STR whenever a partial or complete COD depletion occurred. Similarly, ammonium sulphate was periodically added to the aerobic STR to replenish the consumed NH4-N, while potassium nitrate was fed to the anaerobic STR to replenish the consumed NO3-N. In the two-STR tests, only the mixture of organic substrates was periodically added, in particular only to the aerobic STR in order to simulate a surface discharge of untreated municipal wastewater.
Table S5. Procedure and assumptions applied in the cost benefit analysis of the upgrade of an existing canal to an ICW or CFL.
The cost benefit analysis (CBA) of the upgrade of an existing drainage canal to an ICW or to a CFL was performed according to the European Union guidelines for the appraisal of investment products (European Commission 2014).The starting assumption of the CBA was that a successful implementation of the proposed technologies for drainage water treatment requires a positive financial perspective for the farmer. The goal of the CBA was thus to assess the financial sustainability of the DC modification by comparing the Financial Rate of Return of the investment (FRR) relative to the upgrade of an existing canal to an ICW or CFL with a reasonable value of the Weighted-Average Cost of Capital (WACC) for the Egyptian context. The Financial Net Present Value (FNPV) for both options was calculated as well.
The WACC was selected as the key threshold in order to determine a positive investment decision (Miles and Ezzell 1980; Gitman and Mercurio 1982). Indeed, the farmer or a farmer association, which can be the actual promoter of the investment, has to obtain capital in order to finance the upgrade of the drainage canal into an effective in-stream water treatment system. This means that the cost of capital in addition to the potential financial sustainability of the project will determine the willingness of the farmer to invest. The cost of capital depends on the regional context. On the basis of previous experiences relative to the Egyptian context in this work the minimum WACC required to generate a positive business case for the farmers was set to 10%.
The benchmark condition selected for the CBA was the use of the low-quality water available at the exit of a typical drainage canal to irrigate a non-food crop. In particular the cultivation of cotton was considered, as it is a widespread crop in the Nile delta region. The following data were assumed for cotton: water consumption = 15500 m3/ha/y, cotton yield = 2240 kg/ha/y, production cost = 0.097 $/kg (MALR 2016; Seada et al. 2016). It was assumed that, thanks to the upgrade of the DC to an ICW or CFL, the farmer could use the resulting higher- quality water after dilution 1:1 with fresh Nile water to irrigate a food-crop that can be consumed after thermal treatment (cooking). In this case a higher revenue is expected. In particular, rice was selected as a representative crop for the Egyptian context, and the following data were assumed for rice: water consumption = 11900 m3/ha/y, rice yield = 9400 kg/ha/y, production cost = 0.133 $/kg (MALR 2016; Seada et al. 2016). A final datum to be assumed is crop price. For rice, an average price of 0.28 $/kg was assumed, corresponding to the mean rice price in Egypt. In addition, in order to assess the effect of possible variations of the rice market price on the financial rate of return of the investment, the analysis was repeated with a 25% increase and a 25% decrease of the rice price. The case of cotton is more complex, as its price in Egypt decreased during the past 5 years down to a price very close to the production cost, due to competition exerted by low-cost cotton produced abroad. On the other hand, the market price of Egyptian cotton could significantly increase in the next years if the government will decide to curb cotton importation. For this reason, a range of possible market prices of cotton was considered in the CBA, starting from a minimum value equal to the current production cost.
The CBA was referred to a 30-year period and was carried out following a differential approach: all the investment costs relative to drainage canal transformation were considered, whereas only incremental or decremental differences between the operative and maintenance costs between the starting condition (benchmark, drainage canal) and the final condition (ICW or CFL) were considered. All the costs that are not affected by the DC transformation were not computed as they apply in the same way to the existing drainage canal and to the ICW or CFL. In the CBA, decreases in cost and avoided costs (namely sludge dredging and cotton
production cost) were treated as revenues, and the lack of the revenues from cotton (substituted by rice) was considered as a cost.
Table S6. Rationale for the selection of the input flow rate in the ICW and CFL design.
As first step in the ICW design, a 350 m3/d volumetric flow rate was selected, 14% higher than the actual one, to cope with expected future population growth. An additional issue to address was the influence of the irrigation events on the water volumetric flow rate along the drainage canal. The actual drain outfall discharge of the formed DC ranges from 330 to 4000 m3/d, the two values corresponding to the no-irrigation and full-irrigation events respectively. Indeed, the increase in flow rate due to drainage water has two opposite effects on the ICW performance: i) a dilution effect, with a decrease in concentrations that makes easier the attainment of the legal concentration limits, ii) a reduction in the hydraulic retention time (HRT), which reduces pollutant conversion. The development of a reliable model of the occasional variations in volumetric flow rate due to the water drained from the fields along the DC during the irrigation events is very demanding. On the other hand, as these events are relatively rare (2-4 events/month), they have a moderate effect on the mean performance of the ICW. For these reasons, the irrigation events were neglected in the ICW and CFL design.
Table S7. Main dimensions and retention times of the drainage canal (DC) and of the designed ICW and CFL.
Technology Section Lengt
h
Maximum depth
Surface HRT
m m m2 d
DC - 2200 1.15 5573 8.70
ICW: upgraded design
Sedimentation Pond 200 1.80 400 1.70
Constructed wetland 1400 1.00 3150 4.50
Disinfection canal 600 0.75 1350 1.30
CFL: design Sedimentation Pond 200 1.80 400 1.70
Canalized lagoon 1023 2.00 4090 13.3
Disinfection canal 977 0.75 2296 2.63
Table S8. Inventory relative to the upgrade of a 350 m3/d drainage canal to an in-stream constructed wetland or to a canalized facultative lagoon.
Components considered Unit
Upgrade to in-stream constructed wetland
(ICW)
Upgrade to canalized facultative lagoon
(CFL)
1. Infrastructure per unit process per unit process
1.1 Excavation volume
Sedimentation pond (ICW & CFL) m3 137 137
Facultative lagoon (CFL) m3 2823
1.2 Cement
Sedimentation pond (ICW & CFL) m3 15 15
Constructed Wetland (ICW) m3 8.4 -
Facultative lagoon (CFL) m3 - 116
1.3 Sand
Sedimentation pond (ICW & CFL) m3 120 120
Constructed Wetland of 4 plots (ICW) m3 700 -
Facultative lagoon (CFL) m3 - 924
1.4 Other components
Metals kg 875 -
Limestones - sedimentation pond
(ICW & CFL) kg 1000000 1000000
Limestone - Facultative lagoon (CFL) kg 7700000
Plants (ICW) kg 7875
2. Operation. Waste and plants to be disposed: variation in comparison to the drainage canal
per unit process per unit process
Sludge kg -96 t/y -
Waste plants (ICW) kg 1750 -
3. Emissions to water: variation in
comparison to the drainage canal per m3 water treated per m3 water treated
Total Suspended Solids g/m3 -124 -106
BOD g/m3 -62 -90
COD g/m3 -119 -150
Total Nitrogen g/m3 -17 -5
Table S9. Main results and performance obtained in the two-STR pilot tests simulating a canalized facultative lagoon. The specific depletion rates were calculated as (total mass in the 2 STRs) / (total volume of the 2 STRs) / (time). A negative value of the nitrate specific rate indicates a net production of nitrate, as a result of the balance between nitrification and denitrification.
Volume ratio
Exchange flow rate
Aerobic STR
Anaerobic STR
Specific depletion rates
Vaerobic/Vanaerobic f residence
time
residence time
COD NH4-N NO3-N total-N
L L/h h h d-1 d-1 d-1 d-1
0.5 0.13 7.9 15.9 0.405 0.028 0.027 0.034
0.17 6.0 11.9 0.993 0.021 -0.004 0.074
0.33 3.0 6.1 0.600 0.034 0.021 0.041
0.50 2.0 4.0 0.947 0.024 0.009 0.024
2.0 0.13 15.9 7.9 2.733 0.055 -0.028 0.054
0.33 6.1 3.0 0.475 0.025 -0.004 0.039
0.50 4.0 2.0 0.450 0.032 -0.010 0.015
Table S10. Assumptions and procedure relative to the kinetic analysis aimed at designing the canalized facultative lagoon.
The second section of the CFL was dedicated to the actual canalized lagoon, the heart of the CFL technology. The first step in the design of the canalized lagoon was to assess the mean residence time required for the removal of COD, nitrogen and pathogens. The starting point was the kinetic analysis of the COD/BOD depletion by natural depuration occurring in the DC. The data of concentrations vs residence time obtained from the experimental data reported in Table 1 (section “DC”) were processed using the same assumptions used for the existing ICW data: the data were interpolated with a first order model and first-order constants were assessed for BOD (kBOD,DC = 0.38 d-1), COD (kCOD,DC = 0.41 d-1) and FC (kFC,DC = 1.38 d-1). These constants are empirical lumped parameters that include the mean biomass concentration in the DC. The same kinetic analysis was performed on the two-STR pilot experimental data relative to both the first and second set of tests. Namely, the concentration trends over time were interpolated using the same first-order approach. Two mean first-order constants were determined for COD (kCOD,lab STR = 2.5 d-1) and total N (kTN,lab STR = 0.43 d-1). The COD constant resulted 6 times higher than the total N constant, in agreement with the general observation that N removal represents the limiting process in the sizing of the canalized lagoon. These constants are lumped parameters that include the average biomass concentration in the lab-scale tests.
For the assessment of the first-order constants to be used in the CFL design, it was assumed that the ratio between kCOD and kTN should be the same in the DC, in the two-STR system and in the designed CFL, as it depends on the composition of the microbial consortium but not on the biomass concentration, which changes significantly from one condition to the other:
kCOD, CFLdesign
kTN ,CFL design
=kCOD, DC
kTN , DC =kCOD ,lab STR
kTN ,lab STR
In the CFL design, the BOD and COD first-order constants were assumed equal to those calculated for the DC. This conservative assumption is based on the observation that, as the CFL is ultimately a canal characterized by a higher depth than the existing DC, it will lead to BOD and COD degradation performances at least equal to those of the DC. Conversely, the N first-order constant kN,CFL design, which could not be obtained from the DC data, was calculated as follows, coherently with the above-reported assumption:
kTN ,CFL design=kTN ,lab STR∙
(
kCOD ,CFL designkCOD, labSTR
)
The final assessed values used for the CFL design were: kBOD,CFL design = 0.38 d-1, kCOD,CFL design = 0.41 d-1, kTN,CFL design = 0.072 d-1, kTC,CFL design = kFC,CFL design = 1.38 d-1. As in the case of ICW design, the values measured after the sedimentation pond were used as inlet concentrations.
The Art.51 limits were used as target values and the required mean residence times were calculated for BOD (6.1 d), COD (5.6 d) and TN (13.3 d). As expected, the longest residence time is required by total N depletion. In conclusion, a residence time of 13.3 d was assumed for the design of the canalized lagoon section.
Table S11 Elements for the assessment of the coliform removal performances of the disinfection canal placed after the canalized lagoon.
Considering that the total canal length is fixed and equal to 2200 m, and that the initial 200- m section was dedicated to the sedimentation pond, the residual 977 m portion was dedicated to the disinfection treatment. The key parameters to have the same disinfection potential observed experimentally in the ICW are residence time and depth of flow. As the remaining available length for the disinfection canal in the CFL treatment train is 223 m shorter than that of the existing ICW, in order to maintain the same residence time without changing the water depth, a 10-cm increase in width was necessary. Under this design condition, the same disinfection yield measured in the existing disinfection canal (following the existing ICW) can be assumed. The data in Table 1 (section “ DC”) were used to calculate such yield, which resulted equal to 86%. As the final target value for TC is 5000 MPN/100mL (art. 51 of Law 92/2013), a TC concentration of about 36000 MPN/100mL must be guaranteed at the disinfection canal inlet. Using the first constant for TC calculated from the DC data, the required HRT to reach that concentration at the end of the canalized lagoon would be 3.0 d, a value largely below the actual 13.3 d value used for the canalized lagoon design. Nevertheless, the disinfection capability of the canalized lagoon is supposed to be lower than that of the DC as the water depth is considerably higher. For this reason, the kTC of the canalized lagoon is expected to be lower than that of the DC. The kTC value required to guarantee at the end of the disinfection canal the TC threshold reported by Art.
51 (5000 MPN/mL) resulted equal to 0.31 d-1, 4.5 times lower than that in the DC (1.38 d-
1).
Table S12. Cost benefit analysis of the upgrade of a drainage canal to either an in-stream constructed wetland (ICW) or a canalized facultative lagoon (CFL): CAPEX, OPEX, revenues, financial net present value and financial rate of return. The lack of revenues from cotton production were calculated assuming a cotton market price in Egypt equal to 0.137
$/kg. The revenues from rice sales are based on an average rice market price of 0.28 $/kg.
ICW CFL
Total value (k$)
% contributio
n
Total value (k$)
% contribution
CAPEX
Excavation 0.274 0% 5.92
1 2%
Materials 27.2 11% 153 44%
Plants for ICW 2.36 1% 0 0%
Total investment cost 29.8 12% 159 46%
OPEX
Plants manual cutting and disposal 24.6 10% 0 0%
Rice production cost 126 52% 126 36%
Lack of revenues from cotton production 62 26% 62 18%
Total O&M costs 212 88% 188 54%
Total cost (CAPEX+OPEX) 242 346
Revenues
Revenues from rice sales 266 266
Avoided cost of cotton production 16 16
Decreased cost of sludge dredging &
disposal 4 0
Total revenues 287 283
Financial Net Present Value (FNPV) 45.1 -63.8
Financial Rate of Return of the investment (FRR) 26.8% 4.7%
Figure S1. Schematic representation of the ICW treatment train implemented in the Edfina drainage canal.
0 100 200 300 400 500 600 700 800 900 1000
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Initial COD concentration (mg/L)
Denitrifcation rate (mgTN/h/L)
Figure S2. Laboratory-scale tests conducted in the 2-STR plant simulating a canalized facultative lagoon: denitrification rates obtained in the anaerobic bioreactor at different initial COD concentrations, during the initial tests in which the 2 STRs were disconnected from each other.
0 2 4 6 8 10 12 14 0
10 20 30 40 50 60 70 80 90 100
NH4-N aerobic STR NH4-N anaerobic STR
NO3-N aerobic STR NO3-N anaerobic STR
Time (h)
NH4-N and NO3-N (mg/L)
0 2 4 6 8 10 12 14
0 50 100 150 200 250 300 350
0 200 400 600 800 1000 1200 Total N aerobic STR
Toral N anaerobic STR
COD aerobic STR Power (COD aer- obic STR)
COD anaerobic STR
Time (h)
Total N (mg/L) COD (mgO2/L)
Figure S3. Laboratory-scale tests conducted in the 2-STR plant simulating a canalized facultative lagoon: concentrations of NH4-N, NO3-N (upper plot), total N and COD (lower plot) in the aerobic (full lines) and anaerobic (dashed lines) STRs (Vaerobic/Vanaerobic = 0.5, f = 0.17 L/h).
0 1 2 3 4 5 6 7 8 9 10 0
50 100 150 200 250 300 350 400 450
0 200 400 600 800 1000 1200 1400 NH4-N
NO3-N Total N COD
Time (h)
N total mass (mg) COD total mass (mg O2)
Figure S4. Laboratory-scale tests conducted in the 2-STR plant simulating a canalized facultative lagoon: total masses of NH4-N, NO3-N, total N and COD in the entire 2-STR system (Vaerobic/Vanaerobic = 0.5, f = 0.17 L/h).
Figure S5. Laboratory-scale tests conducted in the 2-STR plant simulating a canalized facultative lagoon. Effect of hydraulic residence time in the anaerobic bioreactor on the specific rate of total nitrogen removal in the system. Results obtained in the two sets of tests characterized by different values of the Vaerobic/Vanaerobic ratio.
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