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Waste is a misplaced resource. The municipal solid waste (MSW) or garbage being discarded in millions of tones in the country is undoubtedly a resource; similar is the case with millions of liters of wastewater of domestic origin as plenty of nutrients are being wasted by discharging the sewage without any treatment. Such kind of discharges leads to soil and water pollution which in turn necessitates the need suitable treatment processes which are generally energy and cost intensive. The urban sewage contain wastewater originating from all residential, commercial, market areas and also includes the surface run‐off and storm water. Biological removal of contaminants from the contaminated site is known as bioremediation. When plants are used to remove metals / contaminants from the soil or water the term 'Phytoremediation' is used, while algae are used for the same purpose in water medium then it is termed as 'Phycoremediation'.This report deals with the decontamination of wastewater with phytoremediation.

The bioconversion potential of two epigeic species (Eisenia foetida Sav. and Eudrilus eugeniae Kinberg) of earthworms was assessed in terms of efficiency and sustainability of vermicomposting of Taro (Colocasia esculenta (Linn) Schott in Schott and Endl). In different vermireactors, each run in triplicates with one of the two species of earthworms, and 60 g of 6:1 Colocasia:cowdung as feed, vermicasts were produced with steadily increasing output in all the reactors. E. eugeniae was found to be more efficient producer of vermicasts than E. foetida. In all reactors, the earthworms grew well, increasing their weights and number.

The feasibility of using upflow anaerobic sludge blanket (UASB) reactors for the treatment of dairy wastewaters was explored. Two types of UASBs were used––one operating on anaerobic sludge granules developed by us from digested cowdung slurry (DCDS) and the other on the granules obtained from the reactors of M/s EID Parry treating sugar industry wastewaters. The reactors were operated at HRT of 3 and 12 h and on COD loading rates ranging from 2.4 kg per m 3 of digester volume, per day to 13.5 kg m −3 d −1 . At the 3 h HRT, the maximum COD reduction in the DCDS-seeded and the industrial sludge-seeded reactors was 95.6% and 96.3%, respectively, better than at 12 h HRT (90% and 92%, respectively). In both the reactors, the maximum, the second best, and the third best COD reduction occurred at the loading rates of 10.8, 8.6 and 7.2 kg m 3 d −1 , respectively. At loading rates higher than 10.8 kg, the reactor performance dropped precipitously. Whereas in the first few months the reactors operating on sludge from EID Parry achieved better biodegradation of the waste, compared to the reactors operated on DCDS, the performance of the latter gradually improved and matched with the performance of the former.

In an attempt to develop a system with which the aquatic weed water hyacinth (Eichhornia crassipes, Mart. Solms) can be economically processed to generate vermicompost in large quantities, the weed was first composted by a 'high-rate' method and then subjected to vermicomposting in reactors operating at much larger densities of earthworm than recommended hitherto: 50, 62.5, 75, 87.5, 100, 112.5, 125, 137.5, and 150 adults of Eudrilus eugeniae Kinberg per litre of digester volume. The composting step was accomplished in 20 days and the composted weed was found to be vermicomposted three times as rapidly as uncomposted water hyacinth [Bioresource Technology 76 (2001) 177]. The studies substantiated the feasibility of high-rate composting-vermicomposting systems, as all reactors yielded consistent vermicast output during seven months of operation. There was no earthworm mortality during the first four months in spite of the high animal densities in the reactors. In the subsequent three months a total of 79 worms died out of 1650, representing less than 1.6% mortality per month. The results also indicated that an increase in the surface-to-volume ratio of the reactors might further improve their efficiency.

Six-month long trials were conducted on different vermireactors fed with one of the following forms of water hyacinth: (a) fresh whole plants, (b) dried whole plants, (c) chopped pieces of fresh plants, (d) 'spent' weed taken from reactors after extracting volatile fatty acids (VFAs), (e) precomposted fresh weed and (f) precomposted spent weed. The first four forms were studied with and without cowdung. The experiments revealed three clear trends (i) of the various forms of the weed assessed, the precomposted forms were the most favoured as feed by Eudrilus eugeniae, Kinberg, while the fresh whole form was the least favoured, (ii) the different forms of spent weed were favoured over the corresponding forms of fresh weed, and (iii) blending of cowdung (approximately 14% of the feed mass) with different forms of water hyacinth had a significant positive impact on vermicast output, growth in worm zoomass, and production of offspring relative to the corresponding unblended feed. In all reactors, the 'parent' earthworms steadily grew in size over the six-month span, and produced offspring. There was no mortality. The experiments thus confirm that water hyacinth can be sustainably vermicomposted in any of the forms with E. eugeniae.

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 (-1 mm 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.

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.

Litter of the mango ( Mangifera indica ) tree leaves was composted and then converted into vermicast by the action of the earthworm Eudrilus eugeniae Kinberg. After over nine months of continuous operation the vermireactors with 62.5 animals l −1 generated ∼13.6 g vermicast per litre of reactor volume (l) per day (d) whereas the reactors with 75 animals l −1 produced ∼14.9 g vermicast l −1 d −1 . This difference in performance of the reactors operating in duplicate at the two different earthworm densities was statistically significant (⩾90% confidence level) for most of the nine-month span. The animals grew well in all reactors, increasing their zoomass by ∼103% and producing ∼157 offspring. Not a single of the 1100 animals died during the first four months. In the subsequent five months a total of 122 worms died, representing a loss of ∼2% per month. We attribute this to the normal process of ageing. The ability of the earthworms to survive, grow and breed in the vermireactors fed with composted mango tree leaves, and a rising trend in vermicast output inspite of the death of a few worms after four months of reactor operation, indicate the sustainability of this type of vermireactors. The studies also indicate that even better vermireactor efficiency may be possible by modifying the reactor geometry. Studies on changes in C:N ratio during composting and vermicomposting revealed that whereas composting helped in lowering the ratio due to loss of carbon in bacterial metabolism, vermicomposting had no such effect on the ratio.