E. V. Ramasamy

Potential of two epigeic and two anecic earthworm species in vermicomposting of water hyacinth

The potential of two epigeic species (Eudrilus eugeniae Kinberg, and Perionyx excavatus Perrier) and two anecic species (Lampito mauritii Kinberg and Drawida willsi Michaelson) of earthworms was assessed in terms of efficiency and sustainability of vermicomposting water hyacinth (Eichhornia crassipes, Mart. Solm.). In different vermireactors, each run in duplicate with one of the four species of earthworms, and 75 g of 6:1 water hyacinth:cowdung as feed, vermicasts were produced with steadily increasing output in all the reactors. E. eugeniae was by far the most efficient producer of vermicasts, followed by the other epigeic P. excavatus. The two anecics came next, with D. willsi being the least effective which could generate only about half the quantity of vermicasts achieved in a corresponding time by E. eugeniae. In all the reactors, the earthworms grew well, increasing their weights by more than 250%. The maximum net gain of weight (average 30.7 g) was by E. eugeniae, followed by P. excavatus, L. mauritii and D. willsi. This trend, which followed the efficiency of vermicast production, was also shown in terms of reproductive ability as measured by the number of offspring produced by the four species.

Screening of four species of detritivorous (humus - former) earthworms for sustainable vermicomposting of paper waste

Four species of detritivorous (humus – former) earthworms were tested for their ability to vermicompost paper waste blended with cowdung in 6:1 (w/w) ratio. The anecic Lampito mauritii, Kinberg and the epigeic Eudrilus eugeniae, Kinberg were the most effective of the four species employed; 20 animals of each of these species generated castings amounting to about 52% of the feed mass (75 g) per fortnight. The performance of these two species was followed by the anecic Drawida willsi, Michaelsen and the epigeic Perionyx excavatus, Perrier; they achieved approximately 46% vermiconversion in comparable settings. The vermireactors were sustainable as the animals have remained consistently healthy and reproductive over a period of six months, and are continuing to remain so, turning in a steadily rising vermicast output. During this period E.eugeniae have grown to 2.3 times their original weight while the other three species have more than trebled their weights. The studies establish the feasibility of vermicomposting as a viable process for the gainful utilization of paper waste in an environmentally clean manner. They also indicate that all the four species of the worms screened by us are suitable for the process, with L.mauritii and E.eugeniae a shade more efficient than the other two species.

High - Solids Anaerobic Digestion for the Recovery of Energy from Municipal Solid Waste (MSW)

Anaerobic digestion of municipal solid waste (MSW) was studied in ‘high solids digesters’ (HSDs) for generating energy (as methane). Three kinds of HSDs were employed in which the waste along with inoculum (consisting of pre-digested cow dung slurry) were subjected to anaerobic digestion. The first type (HSD-I) was provided with two chambers; the upper chamber served as a solid phase in which only the solid portions of vegetable waste were subjected to digestion, while the lower chamber served as liquid phase where the leachates were allowed to ferment. The second type (HSD-II) was similar to HSD-I but had no partition. The third type (HSD-III) had two distinct units, one for solid phase and the other for the liquid phase; the units were connected by a tap with a flow regulator valve. The reactor performance was assessed in terms of biogas yield. The results of the study indicate that the performance efficiency (in terms of biogas yield) of the HSDs increased with the increase in the degree of phase separation. The performance of the digesters was further enhanced by providing additional props to facilitate biodegradation, such as biofilm support systems (BSS) in the liquid phase unit/chamber of the HSDs.

Mercury in the sediments of Vembanad Lake, western coast of India

Mercury, a global pollutant, is popping up in places where it was never expected before and it burdens in sediments and other non-biological materials. It is estimated to have increased up to five times the pre-human level due to anthropogenic activities. Vembanad backwaters, one of the largest Ramsar site in India, which have extraordinary importance for its hydrological function, are now considered as one of the mercury hot spots in India. In this study, surface sediment samples of Vembanad Lake and nearshore areas have been seasonally analysed for total mercury and methyl mercury concentrations while the core sediment samples were analysed for total mercury. The results showed that the northern part of the lake was more contaminated with mercury than the southern part. The mercury concentration was relatively high in the subsurface sediment samples, indicating the possibility of historic industrial mercury deposition. A decreasing trend in the mercury level towards the surface in the core sediment was also observed. The geochemical parameters were also analysed to understand the sediment mercury chemistry. Anoxic conditions, pH and organic carbon, sulphur and Fe determined the presence of various species of mercury in the sediments of Vembanad Lake. The prevailing physical and geochemical conditions in Vembanad Lake have indicated the chances of chemical transformation of mercury and the potential hazard if the deposited mercury fractions are remobilised.

Enhancement in the treatment efficiency and conversion to energy of dairy wastewaters by augmenting CST reactors with simple biofilm support systems

Dairy wastewaters are rich in organic carbon and nutrients. When disposed without proper treatment they cause severe pollution of water and land. But if treated by anaerobic fermentation such wastewaters can yield useful clean energy in the form of methane. The systems commonly used for such fermentation throughout the world are Continuously Stirred Tank Reactors (CSTRs). We describe attempts to upgrade CSTR performance by incorporating biofilm support systems (BSSs) within the existing reactors. The focus of the work has been to find inexpensive and easy-to-install BSS which could significantly enhance the rate of waste treatment as well as quantum of energy recovery (as methane). Our experiments with various BSS options have revealed that rolls of nylon mesh (∼1mm openings), of 5 cm height and 2 cm dia, when incorporated in CSTRs at the biofilm-surface : digester-volume ratio of 0.3 cm2 cm−3, enabled the CSTRs to perform better with up to 25% improvement in methane yield. The studies, thus, reveal that simple devices of the type used by us as BSS can significantly improve the performance of CST anaerobic digesters treating dairy wastes. The enhancement is evidently due to the development of active biofilms on the BSS which not only enhance the contact of the water with micro-organisms but also reduce microbial washout. Further, such devices are inexpensive and very easy to incorporate - the gains are thus achieved with very little cost and effort. BSSs were also found by us to enhance conversion of volatile fatty acids – derived earlier by us from aquatic weed water hyacinth – into methane-rich biogas.

Leachate pollution index as an effective tool in determining the phytotoxicity of municipal solid waste leachate

Phytoremediation is a promising option for the treatment of municipal solid waste leachate. Combining the leachate pollution index with the phytotoxicity data will be useful in predicting the suitable concentration of leachate for the phytoremediation applications. Understanding the tolerant mechanisms of plants to leachate stress will further help to select the appropriate dose. The aim of the study was to investigate the effect of different concentrations of leachate on germination, growth, chlorophyll content and antioxidant enzyme activities in the plant Vigna unguiculata. The crude leachate has an LPI value of 31.99 with high concentration of organic matter, ammonia and dissolved solids. The results of the phytotoxicity study suggest that at lower concentrations the leachate enhanced the germination and promoted plant growth. Up to 5% concentration (v/v) of the leachate which had a LPI value of 11.84 the growth promotion was observed in V. unguiculata. This was made possible by the controlled modulation of reactive oxygen species through the enhanced antioxidant enzyme activities. However at higher concentration, the pollutants in leachate disrupt the enzyme activities and leads to the peroxidation of membrane lipids and significantly affected the plant growth. The study suggest that phytotoxic effects in plants are directly related to the LPI value and leachate with LPI values less than 10 are likely to promote plant growth and LPI values greater than 10 are likely to exert detrimental effect on the plant.

Distribution of priority pollutants in the sediment of Vembanad Estuary, Peninsular India

The existence of Organochlorine pesticides (OCPs) and trace metals in tropical aquatic environments may cause a severe threat on account of their ubiquitous nature and long persistence. Monitoring of such contaminants has assumed immense significance in recent times. The present study assessed the OCPs and trace metal contamination in the surface sediments of the Vembanad wetland system in India. Various pollution indices were calculated to determine the sediment quality of the system and were also compared with uncontaminated sediments. Geo-accumulation index for Mercury varied from moderately to extremely polluted. The mean concentration of pesticide residues and trace metals in the sediments of Vembanad is found to be higher than in other aquatic systems in India. The situation demands further studies which focus on the potential bioaccumulation of OCPs and metals in the benthic food chain, succeeding biota and their impact on human consumption as the system supports a huge population for their livelihood. The Present study provides a baseline information on the spatial distribution of priority pollutants along with ecological risk status of Vembanad estuarine system (VES).