Browsing by Author "Wijeykoon, SLJ"

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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: Article-Abstract
Mechanisms of Manganese Removal from Wastewaters in Constructed Wetlands Comprising Water Hyacinth (Eichhomnia crassipes (Mart.) Solms) Grown under Different Nutrient Conditions
Kularatne, RKA; Kasturiarachchi, JC; Manatunge, JMA; Wijeykoon, SLJ
This article discusses key mechanisms involved in removing 1 mg/L Mn from synthetic wastewaters in constructed wetlands comprising water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutrient levels of 1-fold (28 mg/L and 7.7 mg/L of total nitrogen and total phosphorus, respectively), 2-fold, 1/4-fold, and 1/8-fold. A mass balance was carried out to evaluate the key removal mechanisms. Phytoremediation mainly due to phytoextraction substantially contributed to manganese removal. However, chemical precipitation was absent, suggesting that manganese has a higher solubility in the given average pH (6.2 to 7.1) conditions in constructed wetlands. Bacterial mediated immobilization mechanisms also did not contribute to manganese removal. Sediments constituted a minor sink to manganese, implying that manganese has a poor adsorption potential. Constructed wetlands comprising water hyacinth are effective at removing manganese from wastewaters despite the fact that the plants are grown under higher or lower nutrient conditions. Water Environ. Res., 81, 165 (2009).
item: Thesis-Abstract
Oil and grease removal from thermal power plant effluent using electrocoagulation
Karunarathne, KAPU; Wijeykoon, SLJ
The fuel oil used in thermal power plants mainly falls into the category of low grade fuel such as Heavy Fuel Oil (HFO). They cannot be readily burnt in engines of thermal power generation and need to be further refined. They are refined at the power plant itself. The outcome of this refining process is wastewater rich in heavy oil particles. This has an enormous impact on the country's environment, thus cannot be readily discharged into the environment. Therefore, this study was mainly focused to investigate a scientifically based and an economically viable solution to removal of the oily wastewater. In this case, application of the novel and emerging technique "Electrocoagulation (EC)" for the treatment of oily wastewater generated in thermal power plants was tried out. This technique has been tested successfully for several wastewater treatment solutions in the world (Appendix). However, it has to be noted that EC method has been applied for only a few applications of oily wastewater treatments. In this study, a laboratory scale EC reactor was made using a glass beaker as shown in Fig: 3.1) and results so obtained would help to design an industrial scale EC reactor. Different operation parameters such as influent pH, current density, initial oil concentration and electrode material were examined. During this examination, effect of one parameter for electrocoagulation was studied keeping the other parameters constant. For example, effect of pH on the electrocoagulation was studied keeping the other parameters such as current density, type of electrode material, and initial concentration of the oily wastewater constant. Further, effect of pH on electrocoagulation was examined by using range of.pl-l from 2 to 12, effect of current density was evaluated by varying 2.33 mA/cm2 to 46.8 mA/cm2, effect of initial concentration of oily wastewater was varied from 66 mg/L to 419 mg/L and effect of type of electrodes material was investigated using C and Al electrodes. In addition, performance of the method was mainly tested in terms of COD removal efficiency. The effect of pH on the performance of the method-was not significant in the range of pH - 4 and pH - 10. However, a sharp decrease of COD removal efficiency was not observed when pH was less than 4 and greater than 10. Optimal current density was found as 4.6mA/cm2 , and it was found that there was a little effect of initial oil concentration. Further, Aluminum was found as the most appropriate electrode for anode and there was no effect of cathode material on the efficiency of the EC method. According to the results, it appears that the Electrocoagulation method could be applied for oily wastewater treatment solution to obtain sustainable result
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.