Biological denitrification of high strength nitrate waste using preadapted denitrifying sludge

Denitrification of synthetic high nitrate waste containing 9032 ppm NO(3)-N (40,000 ppm NO(3)) in a time period of only 6h has been achieved in our previous study using activated sludge. The activated sludge culture was acclimatized by a stepwise increase in the nitrate concentration of synthetic waste. In the present work, studies were carried out on the changing microbial population of the sludge and the physiology of nitrate metabolism during the various stages of adaptation process to high strength synthetic nitrate waste. During the course of adaptation, with an increase in the nitrate concentration, a sharp increase in the number of denitrifiers was found with an equally rapid decrease in the nitrifying community. Two key enzymes involved in the first two steps of the denitrification process were also studied during this period. The results of the study suggest that specific enzyme levels increase as the activated sludge adapts itself to higher nitrate concentrations. Biological denitrification of high nitrate waste is a slow process and to increase the rate of denitrification, parameters such as pH, temperature, C:N and biomass concentration of the process were optimized using orthogonal array method. Optimized conditions increased the specific nitrate reduction rate by 54% and specific nitrite reduction rate by 45%.     

Cadmium accumulation and its influence on lipid peroxidation and antioxidative system in an aquatic plant, Bacopa monnieri L

Bacopa monnieri L. plants exposed to 10, 50, 100 and 200 microM cadmium (Cd) for 48, 96 and 144 h were analysed with reference to the accumulation of metal and its influence on various enzymatic and non-enzymatic antioxidants, thiobarbituric acid reactive substances (TBARS), photosynthetic pigments and protein content. The accumulation of Cd was found to be increased in a concentration and duration dependent manner with more Cd being accumulated in the root. TBARS content of the treated roots and leaves increased with increase in Cd concentration and exposure periods, indicating the occurrence of oxidative stress. Induction in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) was recorded in metal treated roots and leaves of B. monnieri. In contrast, a significant reduction in catalase activity in Cd treated B. monnieri was observed. An increase was also noted in the levels of cysteine and non-protein thiol contents of the roots of B. monnieri followed by a decline. However, in leaves, cysteine and non-protein thiol contents were found to be enhanced at all the Cd concentrations and exposure periods. A significant reduction in the level of ascorbic acid was observed in a concentration and duration dependent manner. The total chlorophyll and protein content of B. monnieri decreased with increase in Cd concentration at all the exposure periods. Results suggest that toxic concentrations of Cd caused oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, B. monnieri is able to combat metal induced oxidative injury involving a mechanism of activation of various enzymatic and non-enzymatic antioxidants.     

Effects of monospecific and mixed-algae diets on survival, development and fatty acid composition of penaeid prawn (Penaeus spp.) larvae

Four species of microalgae (Chaetoceros muelleri, Tetraselmis suecica, Tahitian Isochrysis sp. (T-iso) and Dunaliella tertiolecta) with distinctly different fatty acid profiles were grown in continuous culture and fed to prawn larvae (Penaeus japonicus, P. semisulcatus and P. monodon) as monospecific diets. The best two diets (C. muelleri and T. suecica) were also fed as a mixed diet. Experiments were run until the larvae fed the control diet of C. muelleri metamorphosed to Mysis 1. The survival and development (i.e. performance) of the larvae were affected by algal diet, and the diets were ranked in the order of decreasing nutritional value: C. muelleri ≥ T. suecica > T-iso > D. tertiolecta. Larvae fed a mixed diet of C. muelleri and T. suecica (2:3 by dry weight) performed as well or better than those fed C. muelleri, and the performance of both these groups of larvae was better than those fed T. suecica. The lipid and carbohydrate compositions of the algae had little or no effect on the lipid and carbohydrate compositions of the larvae or their performance. However, the larvae that performed best (i.e. those fed C. muelleri) had significantly more lipid and carbohydrate than those that performed worst (i.e. those fed D. tertiolecta). Larvae fed C. muelleri or the mixed-algae diet had higher proportions of the essential fatty acids eicosapentaenoic acid [EPA, 20:5(n-3)] and arachidonic acid [ARA, 20:4(n-6)] than the larvae fed on other diets. Furthermore, the larvae fed T. suecica, which showed intermediate performance between larvae fed C. muelleri and T-iso or D. tertiolecta, also had higher proportions of EPA and ARA. Both C. muelleri and T. suecica contained EPA and ARA, but T-iso and D. tertiolecta did not, except for trace amounts of EPA in T-iso. The fatty acid ARA appears to be much more important in the diet of larval prawns than has so far been considered. The level of the essential fatty acid docosahexaenoic acid [DHA, 22:6(n-3)] in the algal diet and the larvae was not related to the performance of the larvae; only C. muelleri and T-iso contained DHA. However, the nauplii contained large proportions of DHA, suggesting that these were sufficient to meet the larval requirements for DHA during their development to Mysis 1. Mixed-algae diets could improve the performance of larvae by providing a more comprehensive range of fatty acids. Received: 22 April 1998 / Accepted: 3 December 1998     

Ethnicity,housing and personal factors as determinants of VOC exposures

Previous studies investigating effects of personal, demographic, housing and other factors on exposures to volatile organic compounds (VOC) have focused on mean or median exposures, and generally not the high exposures that are of great interest. This paper identifies determinants of personal VOC exposures on a quantile-specific basis using a nationally representative sample. The NHANES 1999–2000 VOC dataset was merged with personal, demographic, housing, smoking and occupation variables. Bivariate analyses tested for differences in geometric means and quantiles across levels of potential exposure determinants. Multivariate sample-weighted ordinary least-squares (OLS) and quantile regression (QR) models were then used to adjust for covariates. We identify a number of exposure determinants, most of which varied by exposure quantile. The most striking finding was the much higher exposures experienced by Hispanics and Blacks for aromatic VOCs (BTEX: benzene, toluene, ethylbenzene and xylenes), methyl tert-butyl ether (MTBE), and 1,4-dichlorobenzene (DCB). Exposure to gasoline, paints or glues, and having a machine-related occupation also were associated with extremely high BTEX and MTBE exposures. Additional determinants included the presence of attached garages and open windows, which affected exposures of BTEX (especially at lower quantiles) and MTBE (especially at higher quantiles). Smoking also increased BTEX exposures. DCB was associated with air freshener use, and PERC with dry-cleaned clothing. After adjusting for demographic, personal and housing factors, age and gender were not significant predictors of exposure. The use of QR in conjunction with OLS yields a more complete picture of exposure determinants, and identifies subpopulations and heterogeneous exposure groups in which some individuals experience very elevated exposures and which are not well represented by changes in the mean. The high exposures of Hispanics and Blacks are perplexing and disturbing, and they warrant further investigation.     

Distributions of personal VOC exposures: a population-based analysis

Information regarding the distribution of volatile organic compound (VOC) concentrations and exposures is scarce, and there have been few, if any, studies using population-based samples from which representative estimates can be derived. This study characterizes distributions of personal exposures to ten different VOCs in the U.S. measured in the 1999-2000 National Health and Nutrition Examination Survey (NHANES). Personal VOC exposures were collected for 669 individuals over 2-3 days, and measurements were weighted to derive national-level statistics. Four common exposure sources were identified using factor analyses: gasoline vapor and vehicle exhaust, methyl tert-butyl ether (MBTE) as a gasoline additive, tap water disinfection products, and household cleaning products. Benzene, toluene, ethyl benzene, xylenes chloroform, and tetrachloroethene were fit to log-normal distributions with reasonably good agreement to observations. 1,4-Dichlorobenzene and trichloroethene were fit to Pareto distributions, and MTBE to Weibull distribution, but agreement was poor. However, distributions that attempt to match all of the VOC exposure data can lead to incorrect conclusions regarding the level and frequency of the higher exposures. Maximum Gumbel distributions gave generally good fits to extrema, however, they could not fully represent the highest exposures of the NHANES measurements. The analysis suggests that complete models for the distribution of VOC exposures require an approach that combines standard and extreme value distributions, and that carefully identifies outliers. This is the first study to provide national-level and representative statistics regarding the VOC exposures, and its results have important implications for risk assessment and probabilistic analyses.     

Phytoremediation of radiostrontium ((90)Sr) and radiocesium ((137)Cs) using giant milky weed (Calotropis gigantea R.Br.) plants

Potential of plants to remove radionuclides/toxic elements from soils and solutions can be successfully applied for removal of important radionuclides such as strontium-90 (⁹⁰Sr) and cesium-137 (¹³⁷Cs). When uptake of ¹³⁷Cs and ⁹⁰Sr by Calotropis gigantea plants incubated in distilled water spiked with the radionuclides either alone or in combination was studied, it was found to have a high efficiency for the removal of ⁹⁰Sr, with 90% being removed from solutions (5 × 10³ kBq l⁻¹) within 24 h of incubation. However, in case of ¹³⁷Cs, about 44% could be removed from solutions (5 × 10³ kBq l⁻¹) at the end of 168 h of incubation. Accumulation of ⁹⁰Sr and ¹³⁷Cs was higher in roots compared to shoots. The plants could remediate both ⁹⁰Sr and ¹³⁷Cs when they were added together to the solution. When two months old plants were incubated in low level nuclear waste, 99% of activity disappeared at the end of 15 days. The present study suggests that C. gigantea could be used as a potential candidate plant for phytoremediation of ⁹⁰Sr and ¹³⁷Cs.     

Environmentally adjusted productivity measurement: an Australian case study

This paper critically examines various methods for estimating productivity incorporating environmental effects for the Australian agricultural sector. The agricultural sector has been selected because of its strategic position in the economy of Australia. The findings of this study indicate that the application of environmentally adjusted productivity methods is a credible approach to measure productivity, in the context of sustainable development. Although the empirical findings of this research are case study specific, the results provide evidence supporting the adoption of these techniques to other sectors of the economy when measuring productivity and needing to be cognisant of sustainable development. The findings suggest that adjusting for the environmental impacts of soil erosion can result in higher or lower agricultural productivity depending on the assumptions we make regarding damage costs of erosion. It is argued in this paper that, for soil erosion in Australia, assumptions yielding higher productivity (i.e., upwardly adjusted) are justified. Finally, the findings of this study and the use of the methods presented point to important gaps in data availability. This gap needs to be addressed by policy makers if sustainable development objectives are to be credibly assessed using these techniques.     

Heavy metal pollution abatement using rock phosphate mineral

The low-grade rock phosphate of Jhabua, Madhya Pradesh (India), was investigated for its possible application in the removal of lead, copper, zinc and cobalt ions from aqueous solutions. Effects of contact time, amount of adsorbent and initial concentration of metal ions were studied. Adsorption of heavy metal ions was found to follow the order: Pb2+ > Cu2+ > Zn2+ > Co2+. The probable mechanism of metal ions removal by rock phosphate was found to be by its dissolutions followed by subsequent precipitation.