Removal of Ammonia from Hatirjheel Water through Phytoremediation. Mehnaz Shams, Iftaykhairul Alam, Md. Atauzzaman and Muhammad Ashraf Ali 1

Transcription

1 Paper ID: EE- 17 International Conference on Recent Innovation in Civil Engineering for Sustainable Development (IICSD-1) Department of Civil Engineering DUET - Gazipur, Bangladesh Removal of Ammonia from Hatirjheel Water through Phytoremediation Mehnaz Shams, Iftaykhairul Alam, Md. Atauzzaman and Muhammad Ashraf Ali 1 Department of Civil Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka 1, Bangladesh Abstract In Bangladesh, most surface water bodies are susceptible to contamination from disposal of untreated domestic and industrial wastewater. Surface water bodies receiving wastewater are characterized by low levels of DO and high concentrations of BOD, COD, Ammonia and other nutrients. Year-long monitoring of Hatirjheel water quality showed sustained high concentrations of Ammonia, with concentrations approaching mg/l in at some locations; such high concentration of Ammonia is adversely affecting the entire ecosystem of Hatirjheel. In this study, pilot-scale experiments have been carried out to assess possible removal of Ammonia from Hatirjheel water through phytoremediation utilizing three plant species: (a) Water lettuce, (b) Duckweed, and (c) Water hyacinth. Among these, water hyacinth was found to be efficient in removing Ammonia from water; Ammonia concentration was reduced from 1. mg/l to about 1 mg/l within a week. Nitrification and incorporation of ammonia/nitrate into algal mass, with concomitant rise in ph, have been found to be important mechanisms for transformation of ammonia in the experimental systems. The sediment of Hatirjheel has been found to contribute significant amount of ammonia to the water column; estimated ammonia flux varied from. to 13. mg ammonia per kg of sediment. While phytoremediation holds promise for removal of Ammonia from water, ammonia flux from the bottom sediments of Hatirjheel could make it difficult to remove Ammonia from Hatirjheel water. Keywords: Flux of ammonia, phytoremediation, water column 1. Introduction Ammonia occurs naturally in water bodies arising from microbiological decomposition of nitrogenous compounds in organic matter; ammonia is also introduced into surface water bodies through discharge of wastewater. At particularly high concentrations it can harm aquatic lives [1]. Hatirjheel serves very important hydrologic functions of draining and detaining storm water from a large area of Dhaka city. Although designed to retain storm water, the storm sewers discharging into Hatirjheel carry both storm water and sewage, causing pollution of the water body. One of the major pollutants in Hatirjheel water is ammonia, which is adversely affecting the entire ecosystem of Hatirjheel. Organic sludge accumulating at the bottom sediment of Hatirjheel undergoes decomposition and releases the decomposition products, including ammonia, in the water column. This study assesses removal of ammonia from water through phytoremediation [, 3,, ] utilizing three commonly available plant species.. Material And Methods.1. Collection of plant samples and water The Khude (Local name) or Duckweed (Azolla pinnata) and Topa (Local name) or Water lettuce (Pistia stratiotes) plant samples were collected from ponds in Gazipur, while the Kochuripana 1 Corresponding Author, Professor of Civil Engineering, BUET, Dhaka; mashrafali@gmail.com; Tel.: IICSD-1

2 NH 3 -N(mg/L) 17 (Local name) or Water hyacinth (Echhornia erassipes) plants were collected from Dasherkandi area (close to Aftabnagar). Water samples were collected in large drums (1 L capacity) from Hatirjheel... Phytoremediation experiments Two glass aquariums (thickness of glass having 1 cm) with dimensions of 3 x3 x. (91cm x 91cm x 7cm) were used for carrying out the phytoremediation experiments and placed on the rooftop of Civil Engineering Building, BUET. In the first phase, phytoremediation experiments were carried out using Water lettuce and Duckweed; while during the second phase, phytoremediation experiments were carried out using Water hyacinth. For comparison, blank experimental set up with only Hatirjheel water (and no plants) was used in both phases..3. Estimation of ammonia flux from sediment Two 7 liter plastic buckets were used in the experimental set up; liter sediment sample collected from Hatirjheel was placed in one bucket. Then 3 liters of Hatirjheel water was added to both the buckets. Initially both buckets were placed in a shaded area (away from sunlight); subsequently, the buckets were kept under sunlight to see the possible effect of sunlight on ammonia removal/transformation. 3. Result And Discussion 3.1. Phytoremediation experiments with Water lettuce and Duckweed Figure 1 shows variation of ammonia concentration in water samples from the first phase of experiments with Water lettuce and Duckweed. While ammonia removal from the water samples was very efficient within a week, the plants do not appear to have any effect on ammonia removal, since ammonia removal from water samples with plants were almost identical to that of the blank. Possible mechanisms of ammonia removal from water are: (1) Conversion of ammonia to nitrate (nitrification); () Escape of ammonia to air; (3) Uptake of ammonia by plants; and () Incorporation of ammonia into algal mass Figure 1. Variation of ammonia concentration in water Vs Time with Topa with Khude If the increase in nitrate concentration comes from conversion of ammonia to nitrate, then the estimated maximum conversion of ammonia to nitrate for the three samples is as follows (see Figure ): : (11. 3.) =. mg/l (7.% of initial ammonia conc.) ; : (.1 3.) =. mg/l (3.% of initial ammonia conc.); : ( ) =. mg/l (.% of initial ammonia conc.). Hence, at the peak level of nitrate concentration, conversion of ammonia to nitrate could account for significant removal/ transformation of ammonia in the water samples (see Figure ). IICSD-1

3 ph NO 3 -N (mg/l) Figure. Variation of nitrate concentration in water Vs Time with Topa sample with Khude This conversion (from ammonia to nitrate) should be accompanied by lowering of ph (due to release of H + ); however, ph of all water samples increased during the first week of experiment (see Figure 3). So a process was active that increased the ph of water samples significantly. The chemical reaction for formation of algae is often written as follows: 1 CO + 1 NO 3 + HPO H O + 1 H + = C 1 H 3 O 11 N 1 P + 13 O (1) So, algal bloom, accompanied by consumption of H +, could be responsible for the observed rise in ph of water (see Eq. 1). High algae (specifically Chlorophyll a) concentrations (see Table 1) and elevated levels of DO in the water samples support this phenomenon. So it appears that incorporation of ammonia/nitrate in algal mass may be responsible for removal/ transformation of ammonia in the experimental water samples Figure 3. Variation of ph in water Vs Time Table 1: Chlorophyll a concentration in water samples from the first phase of experiment Sample ID Date of testing s after commencement of experiment Chlorophyll a (μg/l) 1 // // // //1 1. with Topa with Khude IICSD-1

4 NO 3 -N (mg/l) NH 3 -N (mg/l) 17 At ph above 9., ammonia escapes to air from water. But as discussed earlier, the rise in ph was mainly due to formation of algal mass. So escape to air was probably not the dominant mechanism for ammonia removal. Also due to the identical removal rate of ammonia from all samples including blanks, uptake of ammonia by plants do not appear to be the dominant ammonia removal mechanism. 3.. Phytoremediation experiments with Water hyacinth Figure shows variation of ammonia concentration in water samples from the second phase of experiments with Water hyacinth. Concentration of ammonia decreased with time in both samples in identical rate and it comes close to a stable level after about to 7 days. 1 1 with Kochuripana sample Figure. Variation of ammonia concentration in water Vs Time For these experiments, conversion of ammonia to nitrate does not appear to be significant, as peak of nitrate concentration was only about mg/l, and eventually nitrate concentration goes down, indicating other mechanisms for removal of nitrate (see Figure ). With Kochuripana sample Figure : Variation of nitrate concentration in water Vs Time The ph value of the water sample with Water hyacinth decreased during the course of the experiment, as shown in Figure. Thus, for the sample with Water hyacinth, formation of algal mass does not appear to be an important mechanism for removal/transformation of ammonia/nitrate. Also, the ph value of the water sample with Water hyacinth did not reach 9.; hence, escape of ammonia into air is not an important mechanism for ammonia removal/transformation from the water sample with Water hyacinth. On the other hand, the ph of the blank increased significantly (see Figure ). So reduction of ammonia for the blank sample appears to be due to incorporation of ammonia/nitrate in algal mass. As the three possible mechanisms (i.e., incorporation into algal mass, nitrification, escape to air) do not appear to be important mechanisms for ammonia removal for the water sample with Water hyacinth, the only logical way for removal of ammonia from the water sample with Water hyacinth is uptake of ammonia by the Water hyacinth plants. IICSD-1

5 NH 3 -N (mg/l) ph Figure : Variation of ph in water Vs Time With Kochuripana sample 3.3. Estimation of ammonia flux from sediment to water column Figure 7 shows Ammonia concentration of water samples in contact and without contact with Hatirjheel sediment. Ammonia concentration in in contact with Hatirjheel sediment is always higher than that without the sediment. It shows that ammonia is contributed to the water column from the sediment. Figure 7 also shows that Ammonia removal from both the water samples was relatively slow in the absence of direct sunlight and became very fast in direct sunlight, signifying the role of sunlight in formation of algal mass and removal of ammonia from water. The estimated ammonia flux from sediment to water column (in mg Ammonia per kg of sediment) varies from. to 13. (Table ). Thus, contribution of ammonia from sediment to the water column could be significant Sample with sludge (without sunlight) Sample without sludge (without sunlight) Sample with sludge (with sunlight) Sample without sludge (with sunlight) Figure 7: Variation of ammonia concentration in water Vs Time Table : Estimation of ammonia flux from sediment Date Estimated Ammonia Flux from Sediment (mg Ammonia/kg of Sediment) 13//1. 1// // // // //1* 1. 19//1* -- //1*.7 1//1*. *Samples were kept without direct exposure to direct sunlight up to 17 th June 1; from 1th June, 1 the samples were kept in sunlight. IICSD-1

6 1. Conclusions Uptake of ammonia by Water lettuce and Duckweed has not been found to be significant. But, Water hyacinth appears to be efficient in removing ammonia from water. Sediment of Hatirjheel contributes significant amount of ammonia to the water column. More detailed study should be carried out to better understand the removal of ammonia from water by Water hyacinth, including factors affecting removal and removal rates along with the feasibility of this process. Also a study should be carried out for detailed assessment of contribution of sludge in ammonia concentration in Hatirjheel.. References [1] Francis-Floyd, R., Watson, C., Petty, D., and Pouder, D. B. (1), Ammonia in Aquatic Systems, University of Florida Fisheries and Aquatic Sciences Department, Document TA1. [] Anandha V. R., Kalpana S. (1), Performance Analysis of Nutrient Removal in Pond Water Using Water Hyacinth and Azolla with Papaya Stem, International Research Journal of Engineering and Technology (IRJET), Vol. (1). [3] Headley, T.R., Tanner, C. C. (11), Innovations in constructed wetland treatment of storm waters utilizing floating emergent macrophytes. Critical Reviews in Environmental Science and Technology. [] Hettiarachchi, G. M., Nelson N. O., Agudelo-Arbelaez S. C., Mulisa Y. A., and Lemunyon J. L. (1), Phytoremediation: protecting the environment with plants. Kansas State University. [] Williams, J. B. (), Phytoremediation in wetlands ecosystems: Progress, Problems and Potential. Critical Rev. Plant Sci. 1(): 7-3 IICSD-1