Mahesh Jayaweera

Biogas production from water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nitrogen concentrations

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 study was carried out for a period of 4 months at ambient mesophilic temperatures of 30.3–31.3°C using 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 of water 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.

Removal of aluminium by constructed wetlands with water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different nutritional conditions

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.

Rapid degradation of FOG discharged from food industry wastewater by lipolytic fungi as a bioaugmentation application

ABSTRACT Fats, oils and grease (FOG) congregate in grease traps and are a slowly biodegradable particulate organic matter, which may require enzymatic or hydrolytic conversion to form readily biodegradable soluble organic matter. The existing treatment methods employ water-based hydrolysis of FOG to form long-chain fatty acids (LCFAs). The LCFAs discharged into wastewater treatment system create functional difficulties, especially the inhibitory effect caused by accumulation of LCFAs. This study aims to find an effective treatment method for this persistent problem encountered in conventional wastewater treatment system. Solid-state degradation by lipolytic fungi was performed in a tray-type reactor as a novel approach of bioaugmentation. Grease trap waste samples were dried to have moisture content of 25–35% and mixed with coir fiber (1% w/v) for proper aeration. Each 10 mg/g dry weight of substrate was inoculated with 1 mL of spore suspension (1 × 10⁷ spores/mL) of lipolytic fungi. Thereafter, moisture content in the reactor was increased to 65%, and incubated at 30°C. Within 72 h of post incubation, degradation efficiency of about 50% was recorded by fungal isolates. The feasibility of using developed protocol for FOG degradation was tested with a laboratory-scale prototype reactor.

Glyphosate and AMPA of agricultural soil, surface water, groundwater and sediments in areas prevalent with chronic kidney disease of unknown etiology, Sri Lanka

Abstract Glyphosate, which is commercially available as Roundup®, was the widely used herbicide in Sri Lanka until 2015 and is suspected to be one of the causal factors for Chronic Kidney Disease of unknown etiology (CKDu). This research, therefore, aims at studying the presence of glyphosate and Aminomethylphosphonic acid (AMPA) in different environmental matrices in CKDu prevalent areas. Topsoil samples from agricultural fields, water samples from nearby shallow wells and lakes, and sediment samples from lakes were collected and analyzed for glyphosate and AMPA using the LC/MS. Glyphosate (270–690 µg/kg) and AMPA (2–8 µg/kg) were detected in all soil samples. Amorphous iron oxides and organic matter content of topsoil showed a strong and a moderate positive linear relationship with glyphosate. The glyphosate and inorganic phosphate levels in topsoil had a strong negative significant linear relationship. Presence of high valence cations such as Fe3+ and Al3+ in topsoil resulted in the formation of glyphosate-metal complexes, thus strong retention of glyphosate in soil. Lower levels of AMPA than the corresponding glyphosate levels in topsoil could be attributed to factors such as the strong adsorption capacity of glyphosate to soil and higher LOQ in the quantification of AMPA. The glyphosate levels of lakes were between 28 to 45 µg/L; no AMPA was detected. While trace levels of glyphosate (1–4 µg/L) were detected in all groundwater samples, AMPA (2–11µg/L) was detected only in four out of nine samples. Glyphosate was detected in all sediment samples (85–1000 µg/kg), and a strong linear relationship with the organic matter content was observed. AMPA was detected (1–15 µg/kg) in seven out of nine sediment samples. It could be inferred that the impact on CKDu by the levels of glyphosate and AMPA detected in the study area is marginal when compared with the MCL of the USEPA (700 µg/L).