Browsing by Author "Jayaweera, MW"

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item: Article-Abstract
Biogas production from water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nitrogen concentrations
Jayaweera, MW; Dilhani, JAT; Kularatne, RKA; Wijeykoon, SLJ
This paper reports the biogas production from water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nitrogen concentrations of 1-fold [28 mg/L of total nitrogen (TN)], 2-fold, 1/2-fold, 1/4-fold and 1/8-fold and plants harvested from a polluted water body. This studywas carried out for a period of 4 months at ambient mesophilic temperatures of 30.3–31.3◦Cusing six 3-barreled batch-fed reactors with the innermost barrel (45 L) being used as the digester. There was no marked variation in the C/N ratios of the plants cultured under different nitrogen concentrations. The addition of fresh cow dung having a low C/N of 8 resulted in a significant reduction in the C/N ratios of the water hyacinth substrates. However, gas production commenced 3 days after charging the reactors and gas production rates peaked in 4–7 days. The volatile solids (VS) degradation and gas production patterns manifested that in conventional single-stage batch digesters acidogenesis and methanogenesis ofwater hyacinth requires a retention time of around 27–30 days and 27–51 days, respectively. Substrates in the f-1 digester (i.e., the digester containing plants grown under 28 TN mg/L) having the lowest VS content of 45.3 g/L with a highest C/N ratio of 16 showed fairly higher gas production rates consistently (10–27 days) with higher gas yields containing around 50–65% of CH4 (27–51 days). Moreover the highest overall VS (81.7%) removal efficiencies were reported from the f-1 digester. Fairly higher gas production rates and gas yields with fairly higher CH4 contents were also noticed from the f-2 digester containing substrates having a C/N of 14 and f-out digester (containing the plants harvested from the polluted water body) having the lowest C/N ratio of 9.7 with a fairly high VS content of 56 g/L. CH4 production was comparatively low in the f-1/8, f-1/4 and f-1/2 digesters having VS rich substrates with varying C/N ratios.We conclude that water hyacinth could be utilized for biogas production irrespective of the fact that the plants are grown under higher or lower nitrogen concentrations and that there is no necessity for the C/N ratio to be within the optimum range of 20–32 required for anaerobic digestion. Further it is concluded that several biochemical characteristics of the substrates significantly influences biogas production besides the C/N ratio.
item: Article-Abstract
Contribution of water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutrient conditions to Fe-removal mechanisms in constructed wetlands
Jayaweera, MW; Kasturiarachchi, JC; Wijeykoon, SLJ; Kularatne, RKA
Severe contamination of water resources including groundwater with iron (Fe) due to various anthropogenic activities has been a major environmental problem in industrial areas of Sri Lanka. Hence, the use of the obnoxious weed, water hyacinth (Eichhornia crassipes (Mart.) Solms) in constructed wetlands (floating aquatic macrophyte-based plant treatment systems) to phytoremediate Fe-rich wastewaters seems to be an appealing option. Although several studies have documented that hyacinths are good metal-accumulating plants none of these studies have documented the ability of this plant grown under different nutrient conditions to remove heavy metals from wastewaters. This paper, therefore, reports the phytoremediation efficiencies of water hyacinth grown under different nutrient conditions for Fe-rich wastewaters in batch-type constructed wetlands. This study was conducted for 15 weeks after 1-week acclimatization by culturing young water hyacinth plants (average height of 2072 cm) in 590 L capacity fiberglass tanks under different nutrient concentrations of 1-fold [28 and 7.7 mg/L of total nitrogen (TN) and total phosphorous (TP), respectively], 2-fold, 1/2-fold, 1/4-fold and 1/8-fold with synthetic wastewaters containing 9.27 Fe mg/L. Another set-up of hyacinths containing only Fe as a heavy metal but without any nutrients (i.e., 0-fold) was also studied. A mass balance was carried out to investigate the phytoremediation efficiencies and to determine the different mechanisms governing Fe removal from the wastewaters. Fe removal was largely due to phytoremediation mainly through the process of rhizofiltration and chemical precipitation of Fe2O3 and Fe(OH)3 followed by flocculation and sedimentation. However, chemical precipitation was more significant especially during the first 3 weeks of the study. Plants grown in the 0-fold set-up showed the highest phytoremediation efficiency of 47% during optimum growth at the 6th week with a highest accumulation of 6707 Fe mg/kg dry weight. Active effluxing of Fe back to the wastewater at intermittent periods and with time was a key mechanism of avoiding Fe phytotoxicity in water hyacinth cultured in all set-ups. Our study elucidated that water hyacinth grown under nutrient-poor conditions are ideal to remove Fe from wastewaters with a hydraulic retention time of approximately 6 weeks.
item: SRC-Report
Effective process conditions and reactor design parameters for oil separation by electrocoagulation
Wijeykoon, SLJ; Abeysinghe, RAKP; Karunaratne, U; Jayaweera, MW
Thermal power generating plants, service stations and oil refineries generate oily wastewaters which are recognized to be a severe threat to aquatic environments. Electrocoagulation has received considerable attention lately as a clean technology option yet absence of reactor design criteria and scientific understanding of the complex phenomena involved remain as a drawback to its widespread application. Laboratory experiments were conducted to determine the optimum operating parameters such as electrode type, influent pH, initial oil concentration, electrode polarity change, electrode surface area: reactor volume, current density and electrode spacing on COD removal efficiency. The effective pH for oil removal is dependent on the anode material used. A pH of 4 is suitable when A1 is used where as the effect of pH is negligible for iron electrodes. High removal efficiencies are obtained for moderate oil concentrations of 400-500mg/l as COD. The optimum current density and electrode surface area to volume ratio were 46.9 A/m2 and 8.5 m2/m3 respectively. The electrode polarity switch leads to rapid dissolution of the electrodes and improved COD removal efficiency. The developed design parameters enable the design of low cost compact treatment units that could be powered by DC sources for effective oil separation from wastewaters.
item: Thesis-Abstract
Effects of operating conditions on electrodialytic concentration of silver from photo-processing effluents
Botheju, PDC; Jayaweera, MW
Electrodialysis is now recognized as a cleaner technology for reclaiming waste chemical solutions including industrial effluents contaminated with heavy metals. Compared with the conventional separation methods (chemical precipitation, filtration, evaporation, electrolysis, etc.), electrodialysis offers remarkable advantages such as less area requirement, ability to incorporate into the production process itself, avoidance of the generation of hazardous chemical sludge and many more. In this study, Electrodialytic recovery of Silver (Ag) from photo-processing effluents was investigated with the aim of understanding the possible effects of various operating conditions on the process. In this study a laboratory fabricated four-membrane, five-compartment, Electrodialysis cell was used with the cationic and anionic selective ion exchange membranes Asahi Kasei K501SB and A501SB, respectively, which are originally used for seawater desalination. The removal efficiency of Ag+ at different current densities was studied, using synthetically prepared metal ion solutions and actual industrial effluents containing Silver (photo processing effluents). Time dependent sampling was done and analyzed with a flame atomic absorption spectrophotometer (GBC 932). According to the experimental results, very significant removal efficiencies were observed in the range of current densities studied. At low current densities of 2 and 4 mNcm2, removal percentages observed were 36 and 53.5, respectively. However at high current densities of 8 and 10 ma/cm", removal percentages increased up to 85 and 96 respectively (for an initial feed concentration of 1000 mg/L). However at those high current densities, ion exchange membranes were found to be damaged due to high heat dissipation. It was also noticed that at low concentrations of feed solution (i.e. 300 and 100 mg/L), the removal efficiencies were reduced remarkably. Considering these results Electrodialysis with the aid of desalination ion exchange membranes could be recognized as an efficient and locally made sustainable technology for treating silver containing effluents having a sufficiently high contamination level, while reclaiming the metal silver for reuse. However the necessity of a final smoothing treatment stage such as metal replacement, ion exchange or adsorption is stressed to obtain higher quality water. Few experimental trials on Electrowinning were also conducted at a single electrical potential (5V), in order to compare the power consumption of the two processes. Results revealed that the power consumption for electrodialysis is comparatively lower than electrowinning (i.e. by only considering the power consumption of the reactor, without accessories). Necessity of the construction of pilot scale reactors is recognized for a full economical review of the two process schemes. On the other hand experiments must be carried out on the synthesis of ion exchange membranes having good permselectivity towards multivalent cations, so that the Electrodialysis process could be applicable on treating other industrial effluents contaminated with multivalent metal cations.
item: Conference-Extended-Abstract
Growth characteristics of water hyacinth: an application to bolgoda lake
(2002) Fernando, PUD; Gamage, NPD; Jayaweera, MW
Water hyacinth (Eichhornia crassipes (Mart). Solms) is considered as a serious pest in many lakes, irrigation canals, stagnant ponds, waterways and semi-wet areas in Sri Lanka. Bolgoda Lake has been severely affected by excessive growth of water hyacinth, which resulted in clogging of major waterways, adversely affecting navigation. This study was carried out to determine the growth characteristics of water hyacinth under influence of the physical and chemical factors in Bolgoda Lake. The parameters such as biomass, biomass production per day, phosphorus and nitrogen content in plant tissues and pH, temperature, salinity, phosphorus and nitrogen content in the water body were measured.
item: Conference-Extended-Abstract
Heavy metal levels of groundwater in Ratmalana-Moratuwa industrial area: a comprehensive survey carried out in 2002
(2002) Gunawardhana, WDDH; Jayaweera, MW; Kasturiarachchi, JC
Ratmalana-Moratuwa industrial area has been subject to heavy pollution from various industries for more than a decade. This area is believed to have been polluted with heavy metals that have some drastic adverse impacts on human beings. Since there has not been a comprehensive study done to get an insight into the degree of contamination so far, an attempt was made to understand the existing scenario in terms of predominant heavy metals.
item: Thesis-Abstract
Iron and manganese removal from textile effluents in anaerobic attached growth bioreactors
(11/30/2011) Gomes, PIA; Jayaweera, MW; Wijekoon, S
At present several primary and secondary treatment techniques have been used to remove iron (Fe) and manganese (Mn) from low polluting textile wastewaters. However past surveys and studies carried out in the industrial areas of Sri Lanka have revealed that contamination of waterways and groundwater with Fe and Mn has been still high indicating that proper methods are neither in existence nor efficient to remove them from low polluting wastewaters. Therefore in this article we discuss the performance of an upflow anaerobic bioreactor, which is used to remove Fe and Mn from textile wastewaters. A laboratory scale study on Fe and Mn removal in upflow anaerobic bioreactor of a working volume of 20 litres with coir fibre as the filter medium was investigated for a period of 312 days using a synthetic wastewater with similar physical and chemical characteristics of a typical textile effluent. The usage of coir fibre can be justified considering its high surface area per unit volume, hence providing more area for the biofilm formation. The maximum Fe and Mn levels considered were 10 mg/l and 5 mg/l respectively, which are the typical average values of textile effluents subsequent to the primary and secondary treatments in Sri Lanka. Ten sub experimental runs (R0-R9) were conducted with varying HRTs (5 days to 1 day), ratios of COD:SO42- (20 to 3.5), Fe levels (0.005 to 10 mg/l) and Mn levels (0 to 5 mg/l). During initial stages good gas production, high COD removal and relatively low sulphate reduction were observed, indicating major proliferation of methane producing bacteria (MPBs). COD:SO42- of 3.5 was identified as the optimum point at which sulphate reducing bacteria (SRBs) out competed MPBs and further reduction of this ratio caused total and/or significant inhibition of MPBs, thus making conditions favourable for bacterial immobilisation of Fe and Mn. After this point the gas production ceased while the system started giving rotten egg smell, as a result of H2S production taking place due to the metabolism of SRBs. The results indicated highly satisfactory percentage of Fe and Mn removal, in which the effluent contained Fe and Mn below the permissible levels ( 1.6 mg/l and 1.1 mg/l for Fe and Mn respectively) stipulated by US National Pollution Discharge Elimination System (NPDES) for inland surface waters at HRTs higher than 3 days. Results of the mass balance showed more Fe accumulation (65%) in sediments whereas 27% in the filter media. On the other hand out of the accumulated Mn, sediments contained only 26%, where as 65% were found to be attached to the filter media. Both metals in sediments mainly consist in the form of sulphides, indicating a sulphate reduction being the major mechanism of removal. Most of metal ions attached on the filter media too seem to be a direct consequence of sulphate reduction. The high removal efficiencies suggested that the bioreactors consisting coirfibres are a very good low-cost method of removal of Fe and Mn from the textile effluents. Keywords: Bioreactor; Fe; methane producing bacteria; Mn; sulphate reducing bacteria; Textile effluents
item: Article-Abstract
Letter to the Editor: Response to “Comments on ‘Removal of aluminium by constructed wetlands with water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions’ ”
Jayaweera, MW
item: Conference-Extended-Abstract
Optimization of biogas production using water hyacinth (eichhornia crassipes)
(2003) Jayaweera, MW; Gamage, NPD; Wijekoon, SLK; Dilhanil, JAT
The water hyacinth (Eichhornia crassipes) has been classified as an obnoxious freshwater weed in the tropical and subtropical regions of the world due to its rapid growth rate and asexual reproduction. In Sri Lanka widespread infestations occurred since its introduction to the Botanical Gardens in 1904. However it is reported that the aerial tissues (i.c. stems and leaves) of water hyacinth could be effectively utilized for biogas production under anaerobic conditions.
item: Thesis-Abstract
Optimization of biogas production with water hyacinth
Dilhani, JAT; Jayaweera, MW; Gamage, NPD; Wijeyakoon, SLJ
The water hyacinth (Eichhornia crassipes [Mart.] Solms) due to its high growth rate and vegetative reproduction has been classified as an obnoxious freshwater weed especially in the tropics and subtropics. It has been reported that the presence of water hyacinths in waterways results in the displacement of native freshwater plants due to intense competition for light, space and essential resources such as nutrients, restricts navigation, fishing activities, cultural and social usage by affecting water quality, harbors diseasing causing vectors, etc. However the use of water hyacinth in the production of biogas has been an appealing solution to control the ever expanding infestation of this nuisance plant. This study therefore aimed at optimizing the biogas production from water hyacinth by enhancing the hydrolysis process. This study also attempted to investigate the optimum nutritional state (i.e. C/N and C/P ratios) required for effective biomethanation and to evaluate the kinetics of anaerobic digestion. This study was conducted using six numbers of batch bed barreled digesters each having a capacity of 451. For this study aerial parts (stems and leaves) of water hyacinth were used as the substrate with fresh cow dung mixed in the ratio of 2:3 by wet weight (w/w). Several parameters such as TS and VS were measured once a week while TOC, TN and TP were measured every 2 weeks. Biogas production rate, p H and temperature were measured on a daily basis. The study was conducted at ambient mesophillic temperature for a period of 4 months. Both C/N and C/P ratios decreased after mixing with cow dung having a very low C /N and C/P ratio o f 8 and 165, respectively. The C /N ratios did not approach to the optimum range of 20-30. Nevertheless the C/P ratios exceeded the optimum ratio of 167 required to enhance biogas production. However gas production commenced from all digesters within 3 days of the study (i.e. a production rate of 0.73-1.35 1/kg/day was recorded). This study showed that substrates having TS and VS contents in the range of 63-77 g/1 and 45-50 g/1, respectively produced biogas more efficiently. Higher gas production rates were obtained from the substrates in the f-1 digester (i.e. digester containing the hyacinths grown in a nutrient solution containing 28 TN mg/1 and 7.7 TP mg/1) particularly during the period of 14th - 27th day. f-1 digester had the highest C/N ratio of 16, with an optimum initial pH of 7.28 and temperature of 30.3°C to account for optimum biogas production. This study concluded that cow dung and water hyacinth mixtures produced biogas even though the C/N ratios were not with in the optimum range of 20-30. Nevertheless higher biogas productions were reported from substrates having higher C/N ratios of 16. Chen and Hashimoto model fitted well with the experimental data except for a few initial values since the correction for the temperature, pH and mass transfer were not accounted. Kinetic constants pm and K for the substrates were in the range of 0.0074-0.0332 day"1 and 0.0360-0.0386 day"1 , respectively.
item: Thesis-Full-text
Phthalic acid esters in urban watercourses of Colombo and their treatment
(2019) Danushika, UAAG; Jayaweera, MW; Bandara, NJGJ; Manatunge, JMA
Urbanization of many cities with industrial, commercial, and residential areas in the world takes place at an unprecedented scale. Di-2 Ethylhexyl Phthalate (DEHP) is commonly used as a plasticizer in a number of industries which has become a precursor to cause DEHP contamination of watercourses through untreated or partially treated industrial wastewater effluents. Such contamination may result in bioaccumulation and bio-concentration in biota, so that it will adversely affect humans through the food chains. The presence of six PAEs (dimethyl phthalate (DMP), diethyl phthalate (DEP), di (n-butyl) phthalate (DBP), benzyl butyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di(n-octyl) phthalate (DnOP)) in 22 shallow urban watercourses in Colombo and suburbs of Sri Lanka was investigated and the effect on fish community was analyzed. EPA 8061A method was used in analyzing PAE concentrations in samples and Gas Chromatography / Mass Spectrometer was used. Titanium dioxide (TiCb) and Modified Coal-derived Fly Ash (MCFA) were successfully synthesized and characterized using Fourier-Transform Infrared Spectroscopy, Environmental Scanning Electron Microscopy, and X-ray diffraction. Effectiveness and efficiency of TiC>2 and MCFA in the removal of DEHP from wastewaters was identified. According to the results obtained, the average concentrations of DEP, DBP, BBP, and DEHP in all watercourses varied between 2.5-265.0, 1.0-32.0, 61-108, and 12— 165 pg/L, respectively. DMP and DnOP values were below the limits of quantification (DMP-0.5 pg/L, DnOP-l.O pg/L) for all watercourses. DEHP was the most abundant PAE in many watercourses. The significant factors affecting the ubiquitous presence of PAEs in watercourses are the inherent properties of each PAEs, the presence of industrial and household products with great potential for the migration of PAEs in the sub-catchments, and the quality of receiving water. The contamination levels of PAEs in most of the watercourses are alarmingly high, as evidenced by higher concentrations of DEHP and DBP than those of Canadian permissible levels for the protection of aquatic life (16 and 19 pg/L). iii Isolated lakes which are not adjoining to urban industries, showed depleted adverse effects, most of the urban lakes were observed a significant potential for adverse effects on fish. Thus, the ecological risk of PAEs in urban watercourses in Sri Lankan environments should be considered. TiC>2 nanoparticles were used to remove DEHP through photocatalysis. The photocatalysis with TiC>2 for the destruction of DEHP was found to be a promising technique in removing DEHP from industrial wastewaters. The most economical dosage of TiC>2 would be one gram and it needs to be photocatalysed for a period greater than 44 minutes for complying with the permissible level stipulated for DEHP (16 pg/L) for the protection of aquatic life. The cost of the photocatalysis with Ti02 was around Rs.120 and the cost could be further reduced when the material (TiC>2) is reused for subsequent usage. Even TiC>2 was reused for five times, inherent properties for photocatalysis were not changed. An initial level of 171 pg/L of DEHP was successfully removed with 98% efficiency by three grams of MCFA dosage and consequently, regenerated with NaOH twice for the effective use. The maximum monolayer adsorption capacity of MCFA was 63.6 pg/g of DEHP. MCFA is a potential candidate for the effective removal of DEHP from industrial wastewaters as its raw materials are readily available.
item: Conference-Full-text
Prediction of dissolved oxygen in harbours using artificial neural networks: an application to the port of Colombo
(2001) Dayanthi, WKCN; Jayaweera, MW
Maintenance of high dissolved oxygen (DO) level in harbours is highly important as it could give rise to catastrophic effects if it is depleted affecting day- to- day port functions such as dredging activities and other maintenance work. The depletion of DO results not only in toxic gases such as methane and hydrogen sulphide but also in accumulation of wastes. Frequent monitoring of DO is therefore imperative, but creates practical difficulties due to ship movements and other activities. Hence, prediction of DO with an empirical model using Artificial Neural Networks (ANNs) was done with success with an application to the Port of Colombo (PoC). This model aims to reduce the frequency of monitoring DO and to foresee the responses of the system due to environmental changes. The performances of ANNs were compared with Multiple Linear Regression (MLR). Monthly values of 14 water quality parameters at several depths for a particular period were collected. The values of weather parameters of rainfall and wind velocity for the corresponding period were also collected. The inputs of the best model were temperature, depth and five rainfall intensities (including rainfall values on four immediate previous days). A sensitivity analysis was carried out to assess the potentials of small changes in each input on the neural network output. MLR model with the same number of input variables indicated a low value for R after several transformations. The rainfall intensity of the 3rd previous day was the most influential variable among the ANN inputs affecting the output. In conclusion, it could be inferred that the ANN model is capable of predicting DO in PoC considerably well compared with MLR.
item: Article-Abstract
Removal of aluminium by constructed wetlands with water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions
Jayaweera, MW; Kasturiarachchi, JC; Kularatne, RKA; Wijeykoon, SLJ
This article reports the phytoremediation efficiencies of water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions for Al rich wastewaters in batch type constructed wetlands (floating aquatic macrophyte-based plant treatment systems). This study was conducted for 15 weeks after 1 week acclimatization by culturing young water hyacinth (average height of 20 ± 2 cm) in 590 L capacity fiberglass tanks under different nutrient concentrations of 2-fold [56 and 15.4 mg/L of total nitrogen (TN) and total phosphorous (TP), respectively], 1-fold, 1/2-fold, 1/4-fold and 1/8-fold with synthetic wastewaters containing 5.62 Al mg/L. A control set-up of hyacinths comprising only Al with no nutrients was also studied. A mass balance was carried out to investigate the phytoremediation efficiencies and to identify the different Al removal mechanisms from the wastewaters. Chemical precipitation of Al(OH)3 was a dominant contribution to Al removal at the beginning of the study, whereas adsorption of Al3+ to sediments was observed to be a predominant Al removal mechanism as the study progressed. Phytoremediation mainly due to rhizofiltration was also an important mechanism of Al removal especially during the first 4 weeks of the study in almost all the set-ups. However, chemical precipitation and sediment adsorption of Al3+ was a dominant contribution to Al removal in comparison with phytoremediation. Plants cultured in the control set-up showed the highest phytoremediation efficiency of 63% during the period of the 4th week. A similar scenario was evident in the 1/8-fold set-up. Hence we conclude that water hyacinth grown under lower nutritional conditions are more ideal to commence a batch type constructed wetland treating Al rich wastewaters with a hydraulic retention time of approximately 4 weeks, after which a complete harvesting is recommended.
item: Conference-Full-text
Removal of iron (fe) from industrial wastewaters by constructed wetlands: an application of water Hyacinth (EICHHORNIA CRASSIPES (mart.) solms) stands
(2005) Jayaweera, MW; Kasturiarachchi, JC; Kularatne, RKA
Severe contamination of water resources including groundwater with iron (Fe) due to various anthropogenic activities has been a major environmental problem in the industrial areas of Sri Lanka. At present Fe rich industrial' wastewaters are mostly treated with chemical precipitation. Moreover this technique is generally costly, depends on many intrinsic environmental parameters and requires intensive management and long-term maintenance. Hence the use of the obnoxious weed water hyacinth (Eichhornia crassipes (Mart.) Solms) in constructed wetlands to phytoremediate Fe rich wastewaters seems to be an appealing option. Although several studies have documented that hyacinths are good metal accumulating plants none of these studies have documented the effects of the nutritional status of the plants on the phytoremediation of metal rich industrial wastewaters. Hence in this paper we report the possible Fe removal efficiencies under different nutritional conditions of water hyacinth in batch type constructed wetlands. This study was conducted for 15 weeks by culturing water hyacinth in 590 I capacity fiberglass tanks under different nutrient concentrations of 2-fold (56 TN mg/l and 15.4 TP mg/l), l-fold, 112-fold, 114-fold and lI8-fold with Fe rich industrial wastewaters containing 9.27 Fe mg/l. A control set-up of hyacinths containing only Fe as a heavy metal but without any nutrients was also studied. A mass balance was conducted to investigate the phytoremediation efficiencies and to determine the different mechanisms governing Fe removal from the wastewaters
item: Conference-Extended-Abstract
Removal of nitrogen and phosphorus from wastewaters by phytoremediation using water hyacinth ieichhornia crassipiesy
(2003) Wijeyekoorr, SLT; Jayaweera, MW; Hirimburegama, K; Kasturiarachchi, JC; Fernando, PUD
Water hyacinth (Eichhomia crassipes [Mart.] Solms.) is one of the most prominent freefloating aquatic weeds found throughout the tropical and subtropical areas of the world. In Sri Lanka the water hyacinth was first introduced in 1904 to the Botanical Gardens. Since then it has been recognized as one of the most troublesome aquatic weeds in many freshwater bodies. However it has been documented that water hyacinth has a unique ability to remove nutrients and heavy metals from polluted waters.
item: Thesis-Abstract
Removal of nutrients (N and P) and heavy metals (Fe, Al, Mn and Ni) from industrial wastewaters by phytoremediation using water hyacinth (Eichhornia crassipes) under different nutritional conditions
(2014-07-07) Kasturiarachchi, JC; Jayaweera, MW; Wijeyekoon, SLJ; Hirimburegama, K
This study was investigated the utilization of phytoremediation strategies to remove nitrogen, phosphorus and heavy metals (Fe, Al, M n and Ni) from wastewaters by water hyacinth {Eichhornia crassipes [Mart.] Solms). Batch studies were conducted for 15 weeks using fiberglass tanks in which healthy young plants were grown for a period of 15 weeks under different nutrient concentrations o f 2-fold (56 T N mg/1 a nd 15.4 T P mg/1), 1-fold (28 T N mg/1 a n d 7.7 T P mg/1), 1/2-fold (14 T N mg/1 a n d 3.85 TP mg/1), 1/4-fold (7 T N mg/1 a n d 1.93 T P mg/1), 1/8-fold (3.5 T N mg/1 a n d 0.96 TP mg/1) and control (without nutrients). In each week plants, water and sediments were analysed for TN and TP. The phytoremediation potential of heavy metal removal was determined at above nutrient concentrations with the addition of the constant heavy metal concentrations (Fe-9.27mg/1, Al-5.62mg/1, Mn- 0.92 mg/1and Ni-0.21mg/1) in fiberglass tanks. Plant, water and sediment were analyzed for heavy metals during the 15 weeks of culture period. A mass balance was conducted to investigate the phytoremediation efficiencies and to determine the different mechanisms governing nutrient and heavy metal removal from the wastewaters. Our results manifested that hyacinth could be effectively utilized in constructed wetlands to phytoremediate N rich wastewaters than P. Plant uptake was the major TN and TP removal mechanism during the initial periods. Accumulation of a high content of nitrogen in plant tissues due to plant uptake and denitrification was found to be the key mechanisms involved in the efficient removal of nitrogen at the latter part of the study period. Plant uptake of phosphorus and chemical precipitation together with adsorption on to the detritus are the key mechanisms of phosphorus removal. However the phosphorus removal seems to be not high with that of nitrogen indicating that hyacinth systems are not ideal for phosphorus removal from wastewaters. In conclusion, very young plants having seems to be ideal to commence a constructed wetland after a period of acclimatization and approximately 56-63 days of hydraulic retention time is recommended for optimum phytoremediation of nitrogen as well as phosphorus. Phytoremediation of Fe largely due to the process of rhizofiltration and the chemical precipitation followed by flocculation and sedimentation were the key Fe removal mechanisms during the first few weeks of the study. Plants grown in the control set-up showed a highest phytoremediation efficiency of 47% during optimum growth at the 6th week with a highest accumulation of 6707 Fe mg/kg dry weight. Root effluxing of Fe to the waste waters at intermittent periods and with time was a key mechanism of avoiding Fe phytotoxicity in water hyacinth. It can be concluded from this study that water hyacinth is an ideal plant for a batch removal of low polluting Fe rich industrial wastewaters under completely nutrient poor conditions. Very young plants are ideal to commence a constructed wet land after a period of acclimatization and approximately 42 days hydraulic retention time is recommended for optimum phytoremediation. Phytoextraction was the key Mn removal mechanism and root effluxing of Mn was observed intermittently possibly to avoid any phytotoxicity caused by an excessive accumulation of Mn in hyacinths. Hyacinths cultured in the 1/8-fold set-up showed a highest accumulation of 1133 Mn mg/kg dry weight with an optimum removal of 79% at the 9th week. Hence very young plants inhabiting waterbodies containing approximately 3.5 TN mg/1 a n d 0.96 TP mg/1 seems to be more ideal for a batch removal of low polluting Mn rich wastewaters in constructed wetlands. Acclimatization of the plants is necessary for at least 1 week prior to the removal of Mn and then approximately 63 days hydraulic retention time is recommended to optimize phytoremediation. Chemical precipitation followed by flocculation and sedimentation with phytoremediation mainly due to rhizofiltration were the key Al removal mechanisms Control and 1/8-fold set-ups showed higher phytoremediation efficiencies of 63% and 54%, respectively with maximum accumulations of 4278 Al mg/kg dry weight and 4224 Al mg/kg dry weight, respectively. Therefore young plants of completely nutrient starved adult hyacinths seems to be more ideal for a batch removal of low polluting Al rich industrial wastewaters in pilot scale constructed wetlands. A hydraulic retention time of approximately 28 days is recommended for optimum removal after a period of acclimatization of the young plants. The results manifested that hyacinths are essentially Ni excluders since higher levels of Ni were detected in water throughout the study.
item: Conference-Extended-Abstract
The role of the mottled water hyacinth weevil (neochetina eichhorniaes on biological control of water hyacinth in Sri Lanka
(2003) Gamage, NPD; Jayaweera, MW; De Silva, SD; Kasige, AP
Water hyacinth (Eichhornia crassipesi has become one of the most obnoxious freshwater weeds \~ith numerous widespread infestations occurring in the North Western. Central and Southern provinces in Sri Lanka. Water hyacinth competes with native plants and phytoplankton in aquatic system for essential nutrients and space due to its rapid grow tho Further it clogs waterways thereby restricting recreational activities including fishing and navigation. lowers dissolved oxygen in water and limits light penetration due to the formation of an extensive network of mats.
item: Thesis-Abstract
Treatment of industrial wastewater containing heavy metals by electrodialysis
Gunawardhana, WDDH; Jayaweera, MW
Ratmalana-Moratuwa industrial area has been subject to heavy pollution from various industries for more than a decade. This area is believed to have been polluted with heavy metals that have some drastic adverse impacts on human beings and surrounding ecosystems. Since there has not been a comprehensive study done to get an insight into the degree of contamination so far, an attempt was made in understanding the existing scenario in terms of predominant heavy metals. In Ratmalana-Moratuwa industrial area, 79 groundwater wells were selected with biased sampling for heavy metal analysis. All wells were sampled for Fe, Mn, Ag, Ni, AI, Cr, Cu, Pb, Cd, Zn and Co. The analysis was carried out with the technique of Atomic Absorption Spectrophotometry and the results from well waters revealed that Fe, Mn, Ag, Ni, and Al levels were greater than those stipulated for drinking water by WorId Health Organization. Hence all most all wells were found to be abandoned merely due to the taste and colour problems. Most of the industries tend to discharge untreated or partially treated effluent into the nearby drains and hence there is a likelihood of groundwater being affected. 36 industrial effluents were sampled for heavy metal analysis and the results from industrial effluents revealed that Pb, Cr, Cu concentrations were high compared to Sri Lankan Standards for discharge of effluents into inland surface waters. Similarly the concentrations of Fe, AI, Mn, Ag and Co were found to be comparatively high but no enforceable standard levels are available in Sri Lanka. There is a greater need for cleaner technologies for the treatment of heavy metal contaminated wastewaters. Electrodialysis is one such technique that has many advantages such as avoidance of hazardous sludge production, less area requirement, application of low voltage and operation under ambient pressure. Although few studies have been conducted for heavy metal concentration by electrodialysis, in this study a laboratory fabricated four-membrane, five-compartment, electrodialysis cell was used with commercially available cationic and anionic selective membranes to investigate the effect of current density and permselectivity on selected heavy metal concentration. Initially a NaCl solution was desalinized to confirm the permselectivity and separation efficiency for Na ion. Subsequently experiments were carried out to concentrate heavy metals, from selected ionic solutions containing Al and Ni ions. Although there was no optimization of conditions for desalination, the initial concentration of the feed water decreased by 69% with an applied current density of 10 m/vcm". For stable operation and a higher current efficiency, a lower current density of 10 mAlcm2 should be employed for the reactor configuration used to minimize effects such as co-ion transport, anode dissolution and heat loss. The permselectivity of the membrane contribute strongly to the degree of separation of heavy metals. The use of different permselective membranes together with complexation techniques need to be further investigated to improve separation efficiencies for heavy metals.
item: Conference-Extended-Abstract
Treatment of silver (Ag) containing effluents using electrodialysis
(2004) Botheju, PDC; Wijeyekoon, SLJ; Jayaweera, MW; Dissanayaka, DMDOk
Electrodialytic recovery of Ag+ ions from industrial effluents (basically photographic effluent.s~ was.",) investigated with the aim of reclaiming and recycling of the metal Ag, mainly considering the fact that Ag being a very valuable metal and also a toxic heavy metal. Eco-toxicity of this kind of metal elements is well recognized and supposed to be due to their bio concentration and bioaccumulation nature associated with various food chains. On the other hand, in a highly competitive market and environmental conscious society, it is very important to recover these metals in more economically and environmentally sound means, than the conventional approach of disposing these effluents into common sewage lines with or without metal recovery using old electrolysis techniques. A recent study carried out in the Rathmalana- Moratuwa area, revealed that, a significant amount of ground water wells situated in this area are polluted with Ag and other heavy metals, beyond the normal acceptable levels. (Heavy metal levels of groundwater in Ratmalana-Moratuwa industrial area, A comprehensive survey carried out in 2002 by Dayani Gunawardana ). Thus the necessity of a cleaner, greener and economically viable local technology for the treatment of metal contaminated wastewaters is crucial at the moment, when comparing with conventional, inefficient and less economical treatment options
item: Conference-Abstract
Use of Ultra-Violet assisted Titanium Dioxide photocatalysis for the removal of di (2-ethylhexyl) phthalate from industrial wastewaters
Danushika, UAAG; Jayaweera, MW; Bandara, NJGJ; Manathunge, JMA; Gunawardena, WB
Urbanization of many cities with industrial, commercial, and residential areas in the world takes place at an unprecedented scale. Di (2-ethylhexyl) Phthalate (DEHP) is a commonly used plasticizer in number of industries and becomes a precursor to cause DEHP contamination of watercourses through untreated or partially treated industrial wastewater effluents. Such contamination by DEHP may result in bioaccumulation and bio-concentration in biota so that it will adversely affect humans through food chain. Titanium dioxide (TiO2) nanoparticles were experimented to remove DEHP through photocatalysis. The photocatalysis with TiO2 for the destruction of DEHP was found to be a promising technique in removing DEHP from industrial wastewaters. The most economical dosage of TiO2 would be one gram and it needs to be photocatalysed for a period of approximately 45 minutes for complying with the permissible level stipulated for DEHP (16 μg/L) for the protection of aquatic life. The cost of the photocatalysis with TiO2 was around Rs. 120 and the cost could be further reduced when the material (TiO2) is regenerated for subsequent usage. TiO2 was regenerated for three times with inherent properties for photocatalysis being not changed. This technique could be successfully applied to lessen the DEHP levels in the urban watercourses of Sri Lanka.