- Email: [email protected]
Phytoremediation of Phosphorus and Nitrogen with Canna x generalis Reeds in Domestic Wastewater through NMAMIT Constructed Wetland
Available online at www.sciencedirect.com
ScienceDirect Aquatic Procedia 4 (2015) 349 – 356
INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015)
Phytoremediation of Phosphorus and nitrogen with Canna x generalis Reeds in Domestic Wastewater through NMAMIT Constructed Wetland Samson O. Ojoawoa*, Gaddale Udayakumarb and Pushparaj Naikb Department of Civil Engineering, Ladoke Akintola University of Technology, PMB 4000, Ogbomoso, Nigeria b Department of Civil Engineering, NMAM Institute of Technology, Nitte-574110, Udupi District, India *Corresponding Author, e-mail: [email protected]
a
Abstract A proven method of removing contaminants from secondary wastewater being more recently embraced is bioremediation. This paper focuses on phytoremediation of excessive phosphorus and nitrogen using Canna x generalis reeds through a constructed wetland in the domestic wastewater of NMAM Institute of Technology (NMAMIT), Nitte, Udupi District, India. The 30.0m x 6.0m x 1.0m wetland was constructed as an adjoining facility to the Wastewater Treatment Plant (WTP) of the Institute, for postsecondary treatment. The reeds were transplanted over3 the gravel bed after being grown for 2 months in the Institution’s nursery. Reeds with rhizomes measuring approximately 15cm were planted over the gravel just touching the roots to the effluent, at a density of 4 to 5 clumps per square meter, approximately 30-40cm apart. The compartmentalized wetland is being fed by a 4 inch pipe leading effluent from the Secondary Sedimentation tank at a Hydraulic Loading Rate (HLR) of 0.02m 3s-1 and with a Retention Time (R.T) of 3hrs. Replicate Samples were obtained weekly for a period of one month from the raw wastewater inlet, constructed wetland inlet and outlet sewers, and the final effluent from the Wastewater Treatment Plant (W.T.P). Tap water from the Institute was also sampled over same period as the control. These were all subjected to Laboratory analysis for pH, Turbidity, Nitrate, Phosphate and the Phenolic compounds using APHA’s Standard Method. Findings revealed that treatment with the Cannas made the Sample slightly more alkaline (pH ranged from 6.73 to 6.76); reduced the turbidity from 30NTU to 20NTU; mean concentration values of Nitrate, Phosphate and Phenolic compounds at the end of treatment were respectively reduced by 51.9, 8.9, and 1.0 % respectively. The study concludes that Canna plant is very efficient in remediating Nitrogen contaminants, fairly effective on Phosphorus and incapable of removing Phenolic compound pollution. Canna x generalis is therefore recommended for Nitrogen bioremediation in domestic wastewater. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015. Peer-review under responsibility of organizing committee of ICWRCOE 2015
Keywords: Phytoremediation; Canna x generalis; Wastewater; Wetland
2214-241X © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi:10.1016/j.aqpro.2015.02.047
350
Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 * Corresponding author. E-mail address: [email protected]
1. Introduction Phyto-remediation is the utilization of plant to remove and accumulate contaminants from environment. It includes the use of plants to mitigate, transfer, stabilize or degrade pollutants in soil, sediments and water. Recent studies on biomass of some selected plants, particularly macrophytes and rhizomes, provide leading clues on means of improving the quality of wastewater (Misbahuddin and Farduddin, 2002; Mohan et al., 2006; Dana, 2014; Alade and Ojoawo, 2009; Aremu et al., 2012). A wetland is a land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem (DEP, 2011). For most or all times of the year, wetlands have wet areas. While natural wetlands are capable of reducing the pollution load of the adjacent water bodies, the artificial or constructed wetlands are constructed either to reintroduce a wetland in an area or to treat wastewater, in which case they are also referred to as treatment wetlands. (Baskar et al., 2014; Jay, 2014). Wetland construction is usually done in shallow pits that are installed with a drain pipe in a bed of pebbles or gravels and sand layers, upon which the native vegetation is planted. The vegetation may be emergent macrophyte, floating plant or submerged plant species. To prevent pollution of the underground water beneath the wetland, an impermeable membrane is provided at the bottom. According to (Baskar et al., 2014), the basic types of treatment wetlands are free water surface (FWS) wetland and subsurface flow (SSF) wetland. The SSF constructed wetland is further classified into horizontal subsurface flow (HSSF) and vertical subsurface flow (VSSF). When the wastewater is channeled to flow through the constructed wetland, it is treated by the various processes of sedimentation, filtration, oxidation, reduction, adsorption, precipitation, bacterial metabolism, nitrification, de-nitrification, and plant uptake (Jay, 2014). Constructed wetlands have the potential to treat a variety of wastewaters by removing organics, suspended solids, pathogens, nutrients and heavy metals (Antoniasdis et al., 2007). Evapotranspiration may significantly reduce the amount of discharged flow and may influence the removal rate of nutrients from constructed wetlands (Gikas et al., 2013). Phosphorous is one of the major nutrients contributing in the increased eutrophication of lakes and natural waters. Its presence causes many water quality problems including increased purification costs, decreased recreational and conservation value of an impoundments, loss of livestock and the possible lethal effect of algal toxins on drinking water. (Metcalf and Eddy, 1991; Gray, 2005). Controlling phosphorous discharged from municipal and industrial wastewater treatment plants is a key factor in preventing eutrophication of surface waters. Usually, the removal of phosphorous from wastewater involves the incorporation of phosphate into total suspended solids and the subsequent removal from these solids. Phosphorous can be incorporated into either biological solids (e.g. micro organisms) or chemical precipitates. Large input of nitrogen, to ground and surface waters may result in excessive growth of algae and other aquatic weeds. Moreover, a build-up of nitrate in drinking water supplies poses a health hazard to humans particularly infants, as well as livestock (Kotaiah and Swamy, 1994). Nitrates cause “Methemoglobinemia” or “Blue baby disease” among infants. Nitrate determination is essential to ascertain the state of decomposition of organic matters present in wastewater. It is used to assess the self-purification properties of water bodies and nutrient balance in surface water and soil. Nitrate is highly mobile anion formed by microbial conversion of nitrite, and drinking water Standards has recommended a permissible nitrate value of 10 mg/l (Kotaiah and Swamy, 1994). Kim et al., (2012) employed a constructed wetland composed of a pond- and a marsh-type wetland to remove nitrogen (N) and phosphorus (P) from effluent of a secondary wastewater treatment plant. Nutrient concentrations in inflow water and outflow water were closely monitored. In the field monitoring, ammonium (NH 4 +) decreased from 4.6 to 1.7 mg L−1, nitrate (NO3−) decreased from 6.8 to 5.3 mg L−1, total N (TN) decreased from 14.6 to 10.1 mg L−1, and total P (TP) decreased from 1.6 to 1.1 mg L−1. Average removal efficiencies (loading basis) for NO3−, NH4+, TN, and TP were over 70%. Phosphorus was significantly removed similarly in the system and it was concluded that a constructed wetland composed of a pond- and a marsh-type wetland is highly effective for the removal of N and P from effluents of a secondary wastewater treatment plant. This paper examines the phytoremediation potentials of Canna x. generalis in reducing nitrogen and phosphorus pollutants of domestic wastewater through a constructed wetland
2. Materials and method
Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356
2.1 Sewage treatment in the study area NMAM Institute of Technology has the vision of controlling water pollution by internally treating the all wastewater from the campus before finally discharging the effluents. In line with this, by June 2006 a Sewage Treatment Plant was established behind the Boy’s Hostel in order to treat the large amount of sewage and kitchen/bath waste emerging from the hostel. The design capacity of the plant was 125,000 liters/day for the hostel population strength of 400 students. After the commencement of Plant’s operation, 3 more hostel blocks have been constructed and the student strength rose to 1,083 (NMAMIT Resident Engineer’s Records, 2014). The key Unit Operations of the plant include Screening, Equalization, Aeration, Sedimentation, Disinfection, and Reed Bed Phytoremediation. The flowchart of the Plant’s Layout is given in Figure 1.
Fig. 1. Flow chart of Sewage Treatment Plant at NMAMIT Campus Source: NMAMIT Resident Engineer’s Records, 2014 At the initial stages, in non monsoon period, the treated sewage effluent was effectively used for gardening and lawn watering purposes and in monsoon sewage was disposed outside of the campus after treatment. Recently due to the development of massive gardens, increased student strength and stressed water sources, the treated effluent is being utilized for flushing the urinals and water closets along with gardening applications.
2.2 The experimental Reed-Bed Unit The NMAMIT reed bed is a treatment HSSF wetland of dimensions 30.0m x 6.0m x1.0m and of two (2) equal-sized shallow masonry watertight tanks constructed in parallel along the length (Figure 2).
Fig.2. Construction process of the Reed bed It is partitioned into ten (10) cells and each of the cells is separated by alternating baffle walls to increase the Hydraulic Retention Time (H.R.T) as the secondary effluent travels through the system. The effluent from sewage treatment plant is fed from one end just below the gravel line and it flows along the length of the pond, takes U turn enters into another pond and flows in reverse direction from where effluent is finally taken to
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Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 the polished water storage tank. The pond is given a bed slope of 0.5 in 100, filled with 20mm and downsizes granite metal for a depth of 0.6 m from the bottom. The outlet to the tank is at about 50 mm lower than gravel line. The reeds (Cannas spp), which resemble banana plant but with a thin stem are locally available in limited numbers in campus garden, so they were planted in separately prepared nursery yard for 2 months and grown into about a foot near the treatment plant before transplanting them over 3
the gravel bed (Figure 3). Reeds with rhizomes measuring approximately 15cm were planted over the gravel just touching the roots to the effluent, at a density of 4 to 5 clumps per square meter, approximately 30-40cm apart. The compartmentalized wetland is constantly being fed by a 4 inch pipe leading effluent from the Secondary Sedimentation tank at a HLR of 0.02m3s-1 and a RT of 3hrs.
(a)
A transplanted seedling
(b) Growing plants after 3 weeks of transplant
(c) Matured reed bed after 2 months of transplant Fig. 3. Transplanted and grown reed bed of Canna x generalis
2.3 Sampling and Laboratory analysis Replicate Samples were obtained weekly for a period of one month from the raw wastewater inlet (RWI), constructed wetland inlet (PrePhyto) and outlet (PostPhyto) sewers, and the WTP’s final effluent (WTPFE). Tap water (TW) from the Institute was sampled over same period as the control. On each occasion they were collected in stoppered 2-litre plastic containers and were immediately subjected to Laboratory analysis for pH, Turbidity, Nitrate, Phosphate and the Phenolic compounds at the Environmental Engineering and Biotechnology Laboratories of NMAM Institute of Technology. Digital pH meter; Systronics μpH System361 was employed the pH measurement; Turbidity measurement was also electrometrical, with the use of Systronics Digital Nephelo-turbidimeter 132; Determination of Nitrates in the samples was by spectrophotometry, conducted with the aid of Systronics Spectrophotometer169 (λ = 410nm). Phosphate concentrations were monitored by Fiske
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Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 & Subbarow’s 1,2,4-aminonaphthosulphonic acid (ANSA) method using Photochem 0-18 Colorimeter (λ = 660nm), while Phenolic compounds were estimated by Amino-Antipyrene method with the use of same Colorimeter but at λ = 530nm, all in line with APHA, 2005 Standards.
3. Results and discussion 3.1 The laboratory analysis results The mean values of results from the measured parameters in the samples over the 4 weeks period are as presented in Table I. The last row of the Table indicates the maximum limits specified by the Effluent Standard (EPA, 2010). The recorded temperature ranged between 31.2 and 32.5 in the phytoremediation process. It is observed that on the average, the turbidity value in the PostPhyto sample is about two-third the initial inlet one into the wetland. Similarly, reduction is noted in the post-treatment values of nitrate, pH, phosphate and phenolic compounds. The pH slightly became more alkaline during the treatment, it was observed to have marginally increased from 6.73 in the inlet to 6.76 at the wetland outlet. Nitrate removal is however at a higher magnitude with a drastic reduction of about 52% in its value after the treatment. The mean phosphate reduction in the treatment is 8.9% while the wetland shows insignificant removal of 1% phenolic compound after 4 weeks.
Table 1. Mean values of measured parameters over 4 weeks, minimum and maximum values are indicated in italicized brackets. Average results (min – max) Phenolic Sample/Standards
Tempe-
Turbidity
rapture
(NTU)
pH
Nitrate (mg/l)
Phosphate (mg/l)
Compounds (mg/l)
o
( C) RWI
32.1 (31.4 – 32.3)
40 (37 – 42)
6.71 (6.36 6.99)
130.0 (121.3 – 139.4)
1.92 (1.73 – 2.12)
45.20 (42.1 – 47.2)
PrePhyto
32.0 (31.5
30 (23 – 42)
6.73 (6.44 –
108.0 (93.4 –
1.78 (1.74 –
38.00 (35.4 –
7.19)
123.5)
1.82)
40.0)
6.76 (6.71 –
52.0 (32.9 –
1.62 (1.56 –
37.62 (34.7 –
6.84)
67.8)
1.69)
39.5)
6.30 (5.98 –
20.0 (14.4 –
1.56 (1.43 –
10.00 (9.5 – 10.5)
6.50)
23.5)
1.66)
2.2 (2.1 – 2.3)
6.60 (6.64 –
22.0 (18.5 –
N.D
N.D
7.0)
26.4)
1.9
33.3
-0.4
51.9
8.9
1.0
Below 35
N/A
6.00 – 9.00
50.0
4.00
1.00
– 32.5) PostPhyto
31.4 (31.2
20 (18 – 21)
– 32.0) WTPFE
30.7 (30.5
20 (18 – 21)
– 30.9) TW
28.7 (28.5 – 28.9)
% reduction in PrePhyto and PostPhyto values
EPA Effluent Standard limits
Note: N/A = Not Accessed; N/D = Not Detected
3.2 Discussion of results Comparison of trends in the measured inlet and outlet parameters of the wetland is shown from Figures 4 to 8. As illustrated, the treatment generally led to reduction in values of all the measured parameters apart from the pH. Turbidity appears to have reached the treatment peak with the plant when compared with its value in the final effluent, both having 20NTU values. There is however a marginal difference in the phenol contents of both the inlet and outlet samples of the wetland culture.
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50 40 30 20 10 0
PrePhyto PostPhyto 1
2
3
4
Fig. 4. Comparison of Turbidity in PrePhyto and PostPhyto Samples
7.4 7.2 7 6.8 6.6 6.4 6.2 6
PrePhyto PostPhyto 1
2
3
4
Fig. 5. Comparison of pH in PrePhyto and PostPhyto Samples
150 100 PrePhyto 50
PostPhyto
0 1
2
3
4
Fig. 6. Comparison of Nitrate in PrePhyto and PostPhyto Samples
1.9 1.8 1.7 1.6 1.5 1.4
PrePhyto
PostPhyto 1
2
3
4
Fig. 7: Comparison of Phosphate in PrePhyto and PostPhyto Samples
Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356
42 40
38 PrePhyto
36
PostPhyto
34 32 1
2
3
4
Fig. 8. Comparison of Phenolic compounds in PrePhyto and PostPhyto Samples The nutrient removal by Cannas generally occurred to lower extents, but was discovered to be within the range reported by some earlier researchers on horizontal flow constructed wetlands (Mantovi, et al., 2003; Garcia et al., 2005; Calheiros et al., 2007). The outlet samples were observed to be clearer as the turbidity has been reduced by about one-third of the inlet values into the wetland. The phytoremediation is also noted to have slightly improved the colour and odour of the wastewater over the treatment period. According to Brix, 1994, 1997 wetland plants generally take up nutrients in insignificant amount compared to the inflow loading of wastewater. In this study, the result shows that 52% removal of nitrate when compared to other measured parameters is very significant. It is about five times the uptake of phosphorus and fifty times the phenolic compounds removal. The order of Cannas remediation efficiency has been found as Nitrate > Phosphorus > Phenolic compounds. These findings corroborate the report of Vymazal (2005) that the removal of nutrients (nitrogen and phosphorus) is usually low in constructed wetlands and does not exceed 50% when dealing municipal sewage. The present study is also in agreement with the discovery of Aremu et al., 2012 that water hyacinth (Eichhornia crassipes) absorbed more nitrate (45.5%) than phosphorus (37.8%) in a wastewater treatment study. In addition, Tanner (2001) concluded that the net accumulation of phosphorus in plant tissues in mature wetlands is comparatively lower. It is also in agreement with the report of Brix (1994) that the phosphorus uptake capacity of macrophytes is lower than the nitrogen uptake capacity. Comparing the values of parameters in the PostPhyto with the EPA effluent Standard on Table I, it is found that the initial heavy nitrate pollution load (108 mg/L) in the wastewater prior to treatment has been remediated to nearly an acceptable level of 52 mg/L. Phosphate has been within the permissible limit but it’s concentration level was further reduced by about 10% through phytoremediation. However, the treatment has shown an insignificant reduction in the phenolic compound pollutant level of the wastewater, which were assumed to have been introduced by storm water eroded into the drains. The treated effluent from the system has characteristics that are relatively far from that of the tap water as the control, but has met the wastewater effluent Standards, making it acceptable for recycling in flushing the urinals and water closets, then for gardening and other related purposes.
4. Conclusion Canna x. generalis constructed wetland system at NMAM Institute of Technology has been found as very efficient in remediating Nitrogen contaminants, fairly effective on Phosphorus and incapable of removing Phenolic compound pollution. The treatment also improved the physical characteristics of the wastewater such as colour, turbidity and odour. The treated effluent from the system has met the wastewater effluent Standards, making it acceptable for recycling in flushing the urinals and water closets, then for gardening and other related purposes. Canna x generalis is therefore recommended for Nitrogen bioremediation in domestic wastewater.
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5. Acknowledgements The authors are grateful to the Authorities of Ladoke Akintola University of Technology, Ogbomoso, Nigeria and NMAM Institute of Technology, Nitte, India for full supports leading to the success of this study.
6. References Alade G.A and Ojoawo, S.O. 2009. Purification of domestic sewage by water hyacinth (Eichhornia crassipes). Int. J. Environ. Technol. & Management. 10 (3&4), 286-294. Aremu, A.S., Ojoawo, S.O and Alade, G.A. 2012. Water hyacinth (Eichhornia crassipes) culture in sewage: Nutrient removal and potential applications of bye-products. Transnational J. Sc. & Tech. 2 (7), 104-111. Antoniasdis.A., Takavakoglou.V., Zalidis.G., Poulios.I. 2007. Development and evaluation of an alternative method for municipal wastewater treatment using homogeneous photocatalysis and constructed wetlands. Catalysis Today, 124. 260-265. APHA. 2005. Standard Methods for the Examination of Water and Wastewater, APHA, AWWA and WEF, 21 st Edition. Baskar, G., Deeptha, V.T., Annadurai, R. 2014. Comparison of Treatment Performance between Constructed Wetlands with different Plants, International Journal of Research in Engineering and Technology, 3 (4): 210 – 214. Brix, H. 1994. Functions of macrophytes in constructed wetlands. Water Sci. Technol. 29 (4), 71-78. Brix, H. 1997. Do macrophytes play a role in constructed wetlands? Water Sci. Technol. 35 (5), 11-16. Calheiros, C.S.C, Rangel A. O.S.S., Castro, P.M.L. 2007. Constructed wetland systems vegetated with different plants applied to the treatment of tannery wastewater. Water Resear. 41, 1790-1798. Dana, A.M. 2014. Phytoremediation as an Alternative Method to Remove Lead and Cadmium from Wastewater Using Some Aquatic Plants, European Int. Jour. of Sc. and Tech., 3 (4), 4. Day.J.W. et al., 2004. The use of wetlands in the Mississippi Delta for wastewater assimilation : a review”, Journal of Ocean and Coastal Management, 47, 671-691. DEP. 2011. Department of Environmental Protection State of Florida Glossary. State of Florida. Retrieved 2011-09-25. EPA. 2010. Effluent standards, retrieved @ www.epa.gov on 13th August, 2013. Garcia, J., Aguirre, P., Barragan, J., Mujeriego, R., Matamoros, V., Bayona, J.M. 2005. Effect of key design parameters on the efficiency of horizontal subsurface flow constructed wetlands. Ecol. Eng. 25, 405-418. Gikas, P., Ranieri, E. and Tchobanoglous, G. 2013. Removal of iron, chromium and lead from waste water by horizontal subsurface flow constructed wetlands. Kim, D.G., Park J., Lee D., and Kang, H. 2012. Removal of nitrogen and phosphorus from effluent of a secondary wastewater treatment plant using a pond-marsh wetland system. Water Air, Soil, Poll. 214 (37): 2012. Kotaiah, B and Swamy, K.N. 1994. Environmental Engineering Laboratory Manual, Charotar Publishing House, Gujarat, India, 25 – 26. Mantovi, P., Marmiroli, M., Maestri, E., Tagliavini, S., Piccinini, S., Marmiroli, N., 2003. Application of a horizontal subsurface flow constructed wetland on treatment of dairy parlor wastewater. Bioresour. Techn. 88, 85-94. Metcalf and Eddy, Inc., 1991. In: Tchobanoglous, G., Burton, F.L (revisors), Wastewater Engineering: Treatment, Disposal and Reuse, third edition. McGraw-Hill Publishing, NY, USA. Misbahuddin, M., Farduddin, A. 2002. Water hyacinth removes arsenic from arsenic-contaminated drinking water, Arch. Environ. Health, 57 (6), 516-518. Mohan, D., Pittman Jr., C.U., Steele, P.H. 2006. Pyrolysis of wood/biomass for bio-oil; a critical review, Energy Fuels, 20 (3), 848-849. Tanner, C.C. 2001. Plants as ecosystem engineers in subsurface-flow treatment wetlands. Water Sci. Technol. 44 (11-12), 9-17. Vymazal, J (2005) Horizontal sub-surface flow and hybrid constructed wetlands systems for wastewater treatment. Ecol. Eng. 25, 478-490.
ScienceDirect Aquatic Procedia 4 (2015) 349 – 356
INTERNATIONAL CONFERENCE ON WATER RESOURCES, COASTAL AND OCEAN ENGINEERING (ICWRCOE 2015)
Phytoremediation of Phosphorus and nitrogen with Canna x generalis Reeds in Domestic Wastewater through NMAMIT Constructed Wetland Samson O. Ojoawoa*, Gaddale Udayakumarb and Pushparaj Naikb Department of Civil Engineering, Ladoke Akintola University of Technology, PMB 4000, Ogbomoso, Nigeria b Department of Civil Engineering, NMAM Institute of Technology, Nitte-574110, Udupi District, India *Corresponding Author, e-mail: [email protected]
a
Abstract A proven method of removing contaminants from secondary wastewater being more recently embraced is bioremediation. This paper focuses on phytoremediation of excessive phosphorus and nitrogen using Canna x generalis reeds through a constructed wetland in the domestic wastewater of NMAM Institute of Technology (NMAMIT), Nitte, Udupi District, India. The 30.0m x 6.0m x 1.0m wetland was constructed as an adjoining facility to the Wastewater Treatment Plant (WTP) of the Institute, for postsecondary treatment. The reeds were transplanted over3 the gravel bed after being grown for 2 months in the Institution’s nursery. Reeds with rhizomes measuring approximately 15cm were planted over the gravel just touching the roots to the effluent, at a density of 4 to 5 clumps per square meter, approximately 30-40cm apart. The compartmentalized wetland is being fed by a 4 inch pipe leading effluent from the Secondary Sedimentation tank at a Hydraulic Loading Rate (HLR) of 0.02m 3s-1 and with a Retention Time (R.T) of 3hrs. Replicate Samples were obtained weekly for a period of one month from the raw wastewater inlet, constructed wetland inlet and outlet sewers, and the final effluent from the Wastewater Treatment Plant (W.T.P). Tap water from the Institute was also sampled over same period as the control. These were all subjected to Laboratory analysis for pH, Turbidity, Nitrate, Phosphate and the Phenolic compounds using APHA’s Standard Method. Findings revealed that treatment with the Cannas made the Sample slightly more alkaline (pH ranged from 6.73 to 6.76); reduced the turbidity from 30NTU to 20NTU; mean concentration values of Nitrate, Phosphate and Phenolic compounds at the end of treatment were respectively reduced by 51.9, 8.9, and 1.0 % respectively. The study concludes that Canna plant is very efficient in remediating Nitrogen contaminants, fairly effective on Phosphorus and incapable of removing Phenolic compound pollution. Canna x generalis is therefore recommended for Nitrogen bioremediation in domestic wastewater. © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015. Peer-review under responsibility of organizing committee of ICWRCOE 2015
Keywords: Phytoremediation; Canna x generalis; Wastewater; Wetland
2214-241X © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of ICWRCOE 2015 doi:10.1016/j.aqpro.2015.02.047
350
Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 * Corresponding author. E-mail address: [email protected]
1. Introduction Phyto-remediation is the utilization of plant to remove and accumulate contaminants from environment. It includes the use of plants to mitigate, transfer, stabilize or degrade pollutants in soil, sediments and water. Recent studies on biomass of some selected plants, particularly macrophytes and rhizomes, provide leading clues on means of improving the quality of wastewater (Misbahuddin and Farduddin, 2002; Mohan et al., 2006; Dana, 2014; Alade and Ojoawo, 2009; Aremu et al., 2012). A wetland is a land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem (DEP, 2011). For most or all times of the year, wetlands have wet areas. While natural wetlands are capable of reducing the pollution load of the adjacent water bodies, the artificial or constructed wetlands are constructed either to reintroduce a wetland in an area or to treat wastewater, in which case they are also referred to as treatment wetlands. (Baskar et al., 2014; Jay, 2014). Wetland construction is usually done in shallow pits that are installed with a drain pipe in a bed of pebbles or gravels and sand layers, upon which the native vegetation is planted. The vegetation may be emergent macrophyte, floating plant or submerged plant species. To prevent pollution of the underground water beneath the wetland, an impermeable membrane is provided at the bottom. According to (Baskar et al., 2014), the basic types of treatment wetlands are free water surface (FWS) wetland and subsurface flow (SSF) wetland. The SSF constructed wetland is further classified into horizontal subsurface flow (HSSF) and vertical subsurface flow (VSSF). When the wastewater is channeled to flow through the constructed wetland, it is treated by the various processes of sedimentation, filtration, oxidation, reduction, adsorption, precipitation, bacterial metabolism, nitrification, de-nitrification, and plant uptake (Jay, 2014). Constructed wetlands have the potential to treat a variety of wastewaters by removing organics, suspended solids, pathogens, nutrients and heavy metals (Antoniasdis et al., 2007). Evapotranspiration may significantly reduce the amount of discharged flow and may influence the removal rate of nutrients from constructed wetlands (Gikas et al., 2013). Phosphorous is one of the major nutrients contributing in the increased eutrophication of lakes and natural waters. Its presence causes many water quality problems including increased purification costs, decreased recreational and conservation value of an impoundments, loss of livestock and the possible lethal effect of algal toxins on drinking water. (Metcalf and Eddy, 1991; Gray, 2005). Controlling phosphorous discharged from municipal and industrial wastewater treatment plants is a key factor in preventing eutrophication of surface waters. Usually, the removal of phosphorous from wastewater involves the incorporation of phosphate into total suspended solids and the subsequent removal from these solids. Phosphorous can be incorporated into either biological solids (e.g. micro organisms) or chemical precipitates. Large input of nitrogen, to ground and surface waters may result in excessive growth of algae and other aquatic weeds. Moreover, a build-up of nitrate in drinking water supplies poses a health hazard to humans particularly infants, as well as livestock (Kotaiah and Swamy, 1994). Nitrates cause “Methemoglobinemia” or “Blue baby disease” among infants. Nitrate determination is essential to ascertain the state of decomposition of organic matters present in wastewater. It is used to assess the self-purification properties of water bodies and nutrient balance in surface water and soil. Nitrate is highly mobile anion formed by microbial conversion of nitrite, and drinking water Standards has recommended a permissible nitrate value of 10 mg/l (Kotaiah and Swamy, 1994). Kim et al., (2012) employed a constructed wetland composed of a pond- and a marsh-type wetland to remove nitrogen (N) and phosphorus (P) from effluent of a secondary wastewater treatment plant. Nutrient concentrations in inflow water and outflow water were closely monitored. In the field monitoring, ammonium (NH 4 +) decreased from 4.6 to 1.7 mg L−1, nitrate (NO3−) decreased from 6.8 to 5.3 mg L−1, total N (TN) decreased from 14.6 to 10.1 mg L−1, and total P (TP) decreased from 1.6 to 1.1 mg L−1. Average removal efficiencies (loading basis) for NO3−, NH4+, TN, and TP were over 70%. Phosphorus was significantly removed similarly in the system and it was concluded that a constructed wetland composed of a pond- and a marsh-type wetland is highly effective for the removal of N and P from effluents of a secondary wastewater treatment plant. This paper examines the phytoremediation potentials of Canna x. generalis in reducing nitrogen and phosphorus pollutants of domestic wastewater through a constructed wetland
2. Materials and method
Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356
2.1 Sewage treatment in the study area NMAM Institute of Technology has the vision of controlling water pollution by internally treating the all wastewater from the campus before finally discharging the effluents. In line with this, by June 2006 a Sewage Treatment Plant was established behind the Boy’s Hostel in order to treat the large amount of sewage and kitchen/bath waste emerging from the hostel. The design capacity of the plant was 125,000 liters/day for the hostel population strength of 400 students. After the commencement of Plant’s operation, 3 more hostel blocks have been constructed and the student strength rose to 1,083 (NMAMIT Resident Engineer’s Records, 2014). The key Unit Operations of the plant include Screening, Equalization, Aeration, Sedimentation, Disinfection, and Reed Bed Phytoremediation. The flowchart of the Plant’s Layout is given in Figure 1.
Fig. 1. Flow chart of Sewage Treatment Plant at NMAMIT Campus Source: NMAMIT Resident Engineer’s Records, 2014 At the initial stages, in non monsoon period, the treated sewage effluent was effectively used for gardening and lawn watering purposes and in monsoon sewage was disposed outside of the campus after treatment. Recently due to the development of massive gardens, increased student strength and stressed water sources, the treated effluent is being utilized for flushing the urinals and water closets along with gardening applications.
2.2 The experimental Reed-Bed Unit The NMAMIT reed bed is a treatment HSSF wetland of dimensions 30.0m x 6.0m x1.0m and of two (2) equal-sized shallow masonry watertight tanks constructed in parallel along the length (Figure 2).
Fig.2. Construction process of the Reed bed It is partitioned into ten (10) cells and each of the cells is separated by alternating baffle walls to increase the Hydraulic Retention Time (H.R.T) as the secondary effluent travels through the system. The effluent from sewage treatment plant is fed from one end just below the gravel line and it flows along the length of the pond, takes U turn enters into another pond and flows in reverse direction from where effluent is finally taken to
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Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 the polished water storage tank. The pond is given a bed slope of 0.5 in 100, filled with 20mm and downsizes granite metal for a depth of 0.6 m from the bottom. The outlet to the tank is at about 50 mm lower than gravel line. The reeds (Cannas spp), which resemble banana plant but with a thin stem are locally available in limited numbers in campus garden, so they were planted in separately prepared nursery yard for 2 months and grown into about a foot near the treatment plant before transplanting them over 3
the gravel bed (Figure 3). Reeds with rhizomes measuring approximately 15cm were planted over the gravel just touching the roots to the effluent, at a density of 4 to 5 clumps per square meter, approximately 30-40cm apart. The compartmentalized wetland is constantly being fed by a 4 inch pipe leading effluent from the Secondary Sedimentation tank at a HLR of 0.02m3s-1 and a RT of 3hrs.
(a)
A transplanted seedling
(b) Growing plants after 3 weeks of transplant
(c) Matured reed bed after 2 months of transplant Fig. 3. Transplanted and grown reed bed of Canna x generalis
2.3 Sampling and Laboratory analysis Replicate Samples were obtained weekly for a period of one month from the raw wastewater inlet (RWI), constructed wetland inlet (PrePhyto) and outlet (PostPhyto) sewers, and the WTP’s final effluent (WTPFE). Tap water (TW) from the Institute was sampled over same period as the control. On each occasion they were collected in stoppered 2-litre plastic containers and were immediately subjected to Laboratory analysis for pH, Turbidity, Nitrate, Phosphate and the Phenolic compounds at the Environmental Engineering and Biotechnology Laboratories of NMAM Institute of Technology. Digital pH meter; Systronics μpH System361 was employed the pH measurement; Turbidity measurement was also electrometrical, with the use of Systronics Digital Nephelo-turbidimeter 132; Determination of Nitrates in the samples was by spectrophotometry, conducted with the aid of Systronics Spectrophotometer169 (λ = 410nm). Phosphate concentrations were monitored by Fiske
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Samson O. Ojoawo et al. / Aquatic Procedia 4 (2015) 349 – 356 & Subbarow’s 1,2,4-aminonaphthosulphonic acid (ANSA) method using Photochem 0-18 Colorimeter (λ = 660nm), while Phenolic compounds were estimated by Amino-Antipyrene method with the use of same Colorimeter but at λ = 530nm, all in line with APHA, 2005 Standards.
3. Results and discussion 3.1 The laboratory analysis results The mean values of results from the measured parameters in the samples over the 4 weeks period are as presented in Table I. The last row of the Table indicates the maximum limits specified by the Effluent Standard (EPA, 2010). The recorded temperature ranged between 31.2 and 32.5 in the phytoremediation process. It is observed that on the average, the turbidity value in the PostPhyto sample is about two-third the initial inlet one into the wetland. Similarly, reduction is noted in the post-treatment values of nitrate, pH, phosphate and phenolic compounds. The pH slightly became more alkaline during the treatment, it was observed to have marginally increased from 6.73 in the inlet to 6.76 at the wetland outlet. Nitrate removal is however at a higher magnitude with a drastic reduction of about 52% in its value after the treatment. The mean phosphate reduction in the treatment is 8.9% while the wetland shows insignificant removal of 1% phenolic compound after 4 weeks.
Table 1. Mean values of measured parameters over 4 weeks, minimum and maximum values are indicated in italicized brackets. Average results (min – max) Phenolic Sample/Standards
Tempe-
Turbidity
rapture
(NTU)
pH
Nitrate (mg/l)
Phosphate (mg/l)
Compounds (mg/l)
o
( C) RWI
32.1 (31.4 – 32.3)
40 (37 – 42)
6.71 (6.36 6.99)
130.0 (121.3 – 139.4)
1.92 (1.73 – 2.12)
45.20 (42.1 – 47.2)
PrePhyto
32.0 (31.5
30 (23 – 42)
6.73 (6.44 –
108.0 (93.4 –
1.78 (1.74 –
38.00 (35.4 –
7.19)
123.5)
1.82)
40.0)
6.76 (6.71 –
52.0 (32.9 –
1.62 (1.56 –
37.62 (34.7 –
6.84)
67.8)
1.69)
39.5)
6.30 (5.98 –
20.0 (14.4 –
1.56 (1.43 –
10.00 (9.5 – 10.5)
6.50)
23.5)
1.66)
2.2 (2.1 – 2.3)
6.60 (6.64 –
22.0 (18.5 –
N.D
N.D
7.0)
26.4)
1.9
33.3
-0.4
51.9
8.9
1.0
Below 35
N/A
6.00 – 9.00
50.0
4.00
1.00
– 32.5) PostPhyto
31.4 (31.2
20 (18 – 21)
– 32.0) WTPFE
30.7 (30.5
20 (18 – 21)
– 30.9) TW
28.7 (28.5 – 28.9)
% reduction in PrePhyto and PostPhyto values
EPA Effluent Standard limits
Note: N/A = Not Accessed; N/D = Not Detected
3.2 Discussion of results Comparison of trends in the measured inlet and outlet parameters of the wetland is shown from Figures 4 to 8. As illustrated, the treatment generally led to reduction in values of all the measured parameters apart from the pH. Turbidity appears to have reached the treatment peak with the plant when compared with its value in the final effluent, both having 20NTU values. There is however a marginal difference in the phenol contents of both the inlet and outlet samples of the wetland culture.
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50 40 30 20 10 0
PrePhyto PostPhyto 1
2
3
4
Fig. 4. Comparison of Turbidity in PrePhyto and PostPhyto Samples
7.4 7.2 7 6.8 6.6 6.4 6.2 6
PrePhyto PostPhyto 1
2
3
4
Fig. 5. Comparison of pH in PrePhyto and PostPhyto Samples
150 100 PrePhyto 50
PostPhyto
0 1
2
3
4
Fig. 6. Comparison of Nitrate in PrePhyto and PostPhyto Samples
1.9 1.8 1.7 1.6 1.5 1.4
PrePhyto
PostPhyto 1
2
3
4
Fig. 7: Comparison of Phosphate in PrePhyto and PostPhyto Samples
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42 40
38 PrePhyto
36
PostPhyto
34 32 1
2
3
4
Fig. 8. Comparison of Phenolic compounds in PrePhyto and PostPhyto Samples The nutrient removal by Cannas generally occurred to lower extents, but was discovered to be within the range reported by some earlier researchers on horizontal flow constructed wetlands (Mantovi, et al., 2003; Garcia et al., 2005; Calheiros et al., 2007). The outlet samples were observed to be clearer as the turbidity has been reduced by about one-third of the inlet values into the wetland. The phytoremediation is also noted to have slightly improved the colour and odour of the wastewater over the treatment period. According to Brix, 1994, 1997 wetland plants generally take up nutrients in insignificant amount compared to the inflow loading of wastewater. In this study, the result shows that 52% removal of nitrate when compared to other measured parameters is very significant. It is about five times the uptake of phosphorus and fifty times the phenolic compounds removal. The order of Cannas remediation efficiency has been found as Nitrate > Phosphorus > Phenolic compounds. These findings corroborate the report of Vymazal (2005) that the removal of nutrients (nitrogen and phosphorus) is usually low in constructed wetlands and does not exceed 50% when dealing municipal sewage. The present study is also in agreement with the discovery of Aremu et al., 2012 that water hyacinth (Eichhornia crassipes) absorbed more nitrate (45.5%) than phosphorus (37.8%) in a wastewater treatment study. In addition, Tanner (2001) concluded that the net accumulation of phosphorus in plant tissues in mature wetlands is comparatively lower. It is also in agreement with the report of Brix (1994) that the phosphorus uptake capacity of macrophytes is lower than the nitrogen uptake capacity. Comparing the values of parameters in the PostPhyto with the EPA effluent Standard on Table I, it is found that the initial heavy nitrate pollution load (108 mg/L) in the wastewater prior to treatment has been remediated to nearly an acceptable level of 52 mg/L. Phosphate has been within the permissible limit but it’s concentration level was further reduced by about 10% through phytoremediation. However, the treatment has shown an insignificant reduction in the phenolic compound pollutant level of the wastewater, which were assumed to have been introduced by storm water eroded into the drains. The treated effluent from the system has characteristics that are relatively far from that of the tap water as the control, but has met the wastewater effluent Standards, making it acceptable for recycling in flushing the urinals and water closets, then for gardening and other related purposes.
4. Conclusion Canna x. generalis constructed wetland system at NMAM Institute of Technology has been found as very efficient in remediating Nitrogen contaminants, fairly effective on Phosphorus and incapable of removing Phenolic compound pollution. The treatment also improved the physical characteristics of the wastewater such as colour, turbidity and odour. The treated effluent from the system has met the wastewater effluent Standards, making it acceptable for recycling in flushing the urinals and water closets, then for gardening and other related purposes. Canna x generalis is therefore recommended for Nitrogen bioremediation in domestic wastewater.
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5. Acknowledgements The authors are grateful to the Authorities of Ladoke Akintola University of Technology, Ogbomoso, Nigeria and NMAM Institute of Technology, Nitte, India for full supports leading to the success of this study.
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