Economic evaluation of sewage treatment processes in India

This paper evaluates the total annual cost including capital and operation and maintenance (O&M) costs for the up-flow anaerobic sludge blanket (UASB) and waste stabilization pond (WSP) systems operated in India. It also compares UASB and WSP systems with the activated sludge process (ASP) and biological aerated filter (BAF) systems in terms of total annual cost and chemical oxygen demand (COD) removal cost by assuming various annual interest rates and land prices. It was found that the relationship between capital and O&M costs per unit size of a UASB or WSP system and its treatment capacity can be established by a first-order equation. The relation between the cost of organic removal and capital or O&M cost for various sewage treatment systems at various annual interest rates revealed that, for the Indian context, UASB could be the most suitable option in terms of expenses and treatment efficiency.     

Ecotoxicological characterization of tannery wastewater in Dhaka, Bangladesh

Tanning industries are one of the main economic activities in Bangladesh. It has been well documented that wastewater discharged from tanneries without appropriate treatment results in detrimental effects on the ecosystem. No ecotoxicity evaluation of any aquatic environment in Bangladesh has been conducted so far. In this study a battery of toxicity bioassays and chemical analysis were carried out from water samples obtained from three sampling points: upstream from discharging site on River Buriganga (S1), raw wastewater effluent (S2), and downstream the discharging sluice gate (S3), in the Hazaribagh tannery area of Dhaka City, Bangladesh. While S1 and S3 water samples did not show significant toxicity in the bioassays tested, S2 exhibited high acute toxicity to the bacterium Vibrio fischeri (15-min Microtox test, EC50 = 9.8%), the higher plant Lactuca sativa (5-day root elongation inhibition test, EC50 = 14.2%), and the microcrustacean Daphnia magna (24-hour mobility test, EC50 = 31.5%). The results suggested that the raw wastewater effluent had detrimental effects on broad spectrum of organisms in the aquatic ecosystem and bacterium was the most sensitive. The chemical analysis revealed that sample S2 contained an extremely high concentration of chromium (47 g l(-1)). Additionally microbiological analysis indicated that the sampling area is impacted by fecal pollution, increasing the environmental health risk for its inhabitants.     

When fragmented coral spawn? Effect of size and timing on survivorship and fecundity of fragmentation in <Emphasis Type="Italic">Acropora formosa</Emphasis>

In order to determine competency of sexual reproduction and survival rate after fragmentation, the branching coral Acropora formosa was fragmented and fragments in three different sizes (ca. 5, 10 and 20 cm long) and three different stages of gametogenesis were transplanted on coral pavement. Their oocyte development and fecundity, as well as spawning were monitored for a 3-year period. The oocyte development was affected by both fragment size and by the developmental stage of oocytes when fragmented. In small fragments, the oocytes were resorbed while in large fragments they continued development. Oocytes in the early vitellogenic stage at the time of fragmentation were resorbed, whereas those in the late stage continued developing. Smaller fragments showed a lower survival rate and histological observations of their gonads revealed resorption of oocytes, suggesting that there was a trade-off of energy between reproduction and survival. Transplanted fragments often spawned one month earlier than the donor colonies in the first year, but spawning occurred in the same month as the donors or did not occur at all in the second year and none spawned in the third year. The risk of colony death may cause the fragments to re-allocate energy for sexual reproduction.     

Oceanic diffusion and the pelagic insects Halobates spp. (Gerridae: Hemiptera)

Five pelagic Halobates species occupy a vast area from 40^∘ north to 40^∘ south in the three major oceans. Oceanic diffusion, constantly acting to disperse these insects, must be an important factor in determining their life history and distribution. We investigated the effects of oceanic diffusion on the following aspects of these insects. (1) The estimated radius of a patch of Halobates could be expanded by oceanic diffusion alone from an initial point of origin to 1250 km in 60 d. This distance is about 1/12 of the maximum distributional range of H. micans in the Pacific Ocean. Mutual encounter rates due to oceanic turbulence could be as high as 11 d⁻¹ even at low population densities (100 ind km⁻²). This suggests that individuals from their original habitat could find mates even when they had been carried a long distance. Thus, extensive gene mixing may occur over the whole range of a species' distribution. (2)␣Estimated growth rates are rather low (0.0026 to 0.0079 d⁻¹) compared with those of other insects. However, they are offset by a long life span (over 90 d) and an extended oviposition period (perhaps over 2␣months). Thus, pelagic Halobates spp. appear to have adopted a strategy of slow growth and prolonged longevity to cope with living in an unstable physical environment that is constantly disturbed by storms and winds. Received: 5 February 1995 / Accepted: 30 October 1997     

Restoring mechanism of mechanical properties of recycled polyethylene pellet moldings by a repelletizing treatment using a twin-screw extruder

Journal of Material Cycles and Waste Management - To develop material-recycling processes for used plastic products, it is necessary to design new material-recycling techniques to optimize the...