Papers by T. Sreekrishnan
Chemical Engineering & Technology, 2016
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the final Version of Record (VOR). This work is currently citable by using the Digital Object Identifier (DOI) given below. The final VoR will be published online in Early View as soon as possible and may be different to this Accepted Article as a result of editing. Readers should obtain the final VoR from the journal website shown below when it is published to ensure accuracy of information. The authors are responsible for the content of this Accepted Article.
Process Biochemistry, 2003
ABSTRACT Production of hydrogen sulphide by sulphate reducing bacteria (SRB) is a serious problem... more ABSTRACT Production of hydrogen sulphide by sulphate reducing bacteria (SRB) is a serious problem in anaerobic wastewater treatment, because it causes corrosion and reduces the value of methane in the biogas produced. The surface and adhesion characteristics of SRB as measured through the zeta potential are different from those of methanogens. We therefore tested the hypothesis that by choosing a carrier material with the proper surface characteristics (zeta potential) it should be possible to selectively immobilize methanogens while excluding SRB. In a series of batch tests with different support materials complete elimination of SRB was obtained on supports made of nylon, a result in line with our original hypothesis. Maximum preferential immobilization of methanogens was obtained at a temperature of 37oC with media containing volatile fatty acids (VFA) as the carbon source. Preferential immobilization of methanogens was achieved in an anaerobic fluidized bed reactor (AFBR) with nylon granules as support and in an anaerobic rotating biological contactor (ARBC) with acrylic disc as support. H2S-free biogas containing 63 % and 38 % methane were obtained from the AFBR and ARBC, respectively.
Advanced Science Letters, 2014
ABSTRACT As a clean and renewable source of energy, hydrogen is a promising alternative to fossil... more ABSTRACT As a clean and renewable source of energy, hydrogen is a promising alternative to fossils fuel. The ultrasonic probe pretreatment was done on the mixed microflora present in Cow dung. Ultrasonic probe pretreatment was carried out for different time periods i.e., 10, 20, 30, 40, 45 minutes in separate reactors. Power of the probe was 1000 Watts and 25 KHz frequency. A normal (Control) reactor was also set up without any pretreatment. Maximum hydrogen production was produced in the reactor (UT40) which was exposed to ultrasonication probe for 40 minutes. The maximum hydrogen production percentage in the total biogas was 81.23% and cumulative biohydrogen production was 97.95 ml L−1 on 25th day in the UT40 reactor while in normal reactor biohydrogen production percentage was only 23.5% and cumulative biohydrogen production was 40.56 ml L−1. Results from this batch study indicates that as the time of pretreatment increases, biohydrogen production was also increases upto 40 minutes but beyond this time i.e., when pretreatment was done for 45 minutes, a decrease in biohydrogen production was observed. Volatile fatty acid (VFA) accumulation was also observed in all the reactors. Total VFA in UT40 reactor was found to be 6647 mg L−1 which contained 41% acetic acid; 13% propionic acid and 45% butyric acid.
Journal of Hazardous, Toxic, and Radioactive Waste, 2014
ABSTRACT Lactic acid accumulation is a common phenomenon in animal bodies during anaerobic respir... more ABSTRACT Lactic acid accumulation is a common phenomenon in animal bodies during anaerobic respiration, but it is rarely found in natural systems like cattle manure digestion plants or anaerobic municipal sewage sludge bioreactors. The objective of this study was to demonstrate lactic acid production and accumulation during anaerobic digestion of municipal solid waste (MSW) leachate. Three reactors were set up containing cow dung, cow dung plus leachate, and only leachate to carry out anaerobic digestions. The amount of lactic acid accumulated in the reactor containing cow dung only was much less in comparison to the reactor containing cow dung plus leachate. This may be because of the suppression of sulphate reducing bacteria (SRB) and other groups of bacteria which utilize lactic acid, by some component in MSW leachate. The accumulated lactic acid might have come from various bacterial sources. For the identification of responsible organisms, the authors performed polymerase chain reaction (PCR), cloning, and denaturing gradient gel electrophoresis (DGGE)-based experiments. Surprisingly, lactic acid bacteria were also present in MSW leachate. A Lactobacillus identification ladder (LIL) was constructed for identification of prevalent Lactobacillus species (LAB) in MSW leachate by amplifying 16S rDNA of seven pure cultures of LAB bacteria using LAB group specific primer and mixing them in a single tube. By comparing the relative migration of amplicons from MSW leachate with respect to LAB species identification ladder in denaturing gradient electrophoresis gel (DGGE), it was found that Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus fermentum species were present in the MSW leachate.
Journal of Environmental Sciences, 2010
A two-stage process has been developed for stabilization of sludge and removal of heavy metals fr... more A two-stage process has been developed for stabilization of sludge and removal of heavy metals from the secondary activated sludge with high rate of energy and time conservation. The first stage of the process involves autoheated thermophilic aerobic digestion at 55-60°C inoculated with less-acidophilic thermophilic sulfur-oxidizing microorganisms (ATAD). The results show that it is possible to maintain the autoheated conditions (55-60°C) in the ATAD reactor up to 24 hr, leading to reduction of 21% total solids (TS), 27% volatile solids (VS), 27% suspended solids (SS) and 33% volatile suspended solids (VSS) from the sludge. The sludge pH also decreased from 7 to 4.6 due to the activity of less-acidophilic thermophilic microorganisms. In the second stage operation, the digested sludge (pH 4.6, TS 31.6 g/L) from stage one was subjected to bioleaching in a continuous stirred tank reactor, operated at mean hydraulic retention times (HRTs) of 12, 24 and 36 hr at 30°C. An HRT of 24 hr was found to be sufficient for removal of 70% Cu, 70% Mn, 75% Ni, and 80% Zn from the sludge. In all, 39% VSS, 76% Cu, 78.2% Mn, 79.5% Ni and 84.2% Zn were removed from the sludge in both the stages.
Journal of Biotechnology, 2013
Industrial effluents differ in their organic composition thereby providing different carbon sourc... more Industrial effluents differ in their organic composition thereby providing different carbon sources to the microbial communities involved in its treatment. This study aimed to investigate the correlation of microbial community structure with wastewater composition and reactor's performance. Self-immobilized granules were developed in simulated wastewater based on different carbon sources (glucose, sugarcane molasses, and milk) in three hybrid anaerobic reactors operated at 37 • C. To study archaeal community structure, a polyphasic approach was used with both qualitative and quantitative analysis. While PCR-denaturing gradient gel electrophoresis of 16S rRNA gene did not reveal major shifts in diversity of archaea with change in substrate, quantification of different groups of methanogens and total bacteria by real-time PCR showed variations in relative abundances with the dominance of Methanosaetaceae and Methanobacteriales. These data were supported by differences in the ratio of total counts of archaea and bacteria analyzed by catalyzed reporter deposition-fluorescence in situ hybridization. During hydraulic and organic shocks, the molasses-based reactor showed the best performance followed by the milkand the glucose-based reactor. The study indicates that carbon source shapes the microbial community structure more in terms of relative abundance with distinct metabolic capacities rather than its diversity itself.
Environmental Technology, 2007
Development of aerobic granules in the aeration tank of an activated sludge system has been studi... more Development of aerobic granules in the aeration tank of an activated sludge system has been studied. The introduction of activated carbon particles into the aeration tank resulted in the formation of biogranules containing activated carbon as core nuclei. The presence of activated carbon also induced the formation of self-immobilized granules, which did not have any carrier particle at their core. The presence of aerobic granules enhanced the treatment efficiency of the reactor. At an organic loading rate of 32.8 kg COD m(-3)d(-1) and 0.78 h hydraulic retention time (HRT), the reactor showed 96% COD removal efficiency. At an HRT of 0.272 h and organic loading rate of 46.7 kg COD m(-3)d(-1), the reactor outlet COD remained below 100 mg l(-1). Settling velocity studies carried out on the biogranules showed that the drag coefficient of biogranules is greater than that of the rigid particle at the same Reynolds number.
Bioresource Technology, 2004
Biogas, a clean and renewable form of energy could very well substitute (especially in the rural ... more Biogas, a clean and renewable form of energy could very well substitute (especially in the rural sector) for conventional sources of energy (fossil fuels, oil, etc.) which are causing ecological-environmental problems and at the same time depleting at a faster rate. Despite its numerous advantages, the potential of biogas technology could not be fully harnessed or tapped as certain constraints are also associated with it. Most common among these are: the large hydraulic retention time of 30-50 days, low gas production in winter, etc. Therefore, efforts are needed to remove its various limitations so as to popularize this technology in the rural areas. Researchers have tried different techniques to enhance gas production. This paper reviews the various techniques, which could be used to enhance the gas production rate from solid substrates.
Bioresource Technology, 2006
Determination of chemical oxygen demand (COD) of samples having high suspended solids concentrati... more Determination of chemical oxygen demand (COD) of samples having high suspended solids concentration such as cattle dung slurry with open reflux method of APHA-AWWA-WPCF did not give consistent results. This study presents a modification of the open reflux method (APHA-AWWA-WPCF) to make it suitable for samples with high percentage of suspended solids. The new method is based on a different technique of sample preparation, modified quantities of reagents and higher reflux time as compared to the existing open reflux method. For samples having solids contents of 14.0 g/l or higher, the modified method was found to give higher value of COD with much higher consistency and accuracy as compared to the existing open reflux method.
Journal of Bioscience and Bioengineering, 2002
The solid-state bioconversion of wheat straw by Phanerochaete chrysosporium for the production of... more The solid-state bioconversion of wheat straw by Phanerochaete chrysosporium for the production of animal feed was studied. This study was performed based on a central composite experimental design. The conditions of the seed culture most suitable for rapid induction of the ligninolytic activity of the fungus, when the seed culture is subsequently used for solid-state bioconversion of wheat straw, were determined. When the seed culture with an initial pH of 5.8 was grown under agitated conditions at 130 rpm in baffled flasks at 38 degrees C, it was predicted to give lignin degradation of 19.5% and cellulose degradation of 17.8%. A time profile study of the solid-state bioconversion of wheat straw indicated that the highest lignin and lowest cellulose degradation levels occurred on the sixth day of cultivation. The desirability coefficient for this process also passed through a maximum of 0.705 on the sixth day.
Research Article- ASCE, 2015
The effectiveness of anaerobic wastewater treatment is limited by pollutants in industrial wastew... more The effectiveness of anaerobic wastewater treatment is limited by pollutants in industrial wastewaters inhibiting microorganisms, leading to digester failure. Acclimatization enables the microorganisms to develop the capacity to degrade them faster, preventing reactor failure. The present study focuses on the acclimatization of anaerobic sludge to treat two pollutants, chromium (VI) and 4-chlorophenol (4-CP), in two separate batch reactors. Microbial community profiles were obtained to find their effects on microbial populations. Both chemical and microbial data indicated inhibition of biogas production. A 50% reduction in methane concentration was observed at 150 ppm of Cr (VI), whereas for 4-CP, it was observed at 200 ppm. Sulfate-reducing bacteria present in the anaerobic sludge helps to remove heavy metals by facilitating the formation of insoluble metal sulfides. The effect of their presence in an anaerobic system containing 150 ppm Cr (VI) was studied by adding 30-mM sodium molybdate, which inhibited the sulfate reducing bacteria.
Journal of Hazardous, Toxic, and Radioactive Waste
Sustainable Water Resources Management
Environment international, Jan 6, 2018
Antimicrobial resistance (AMR) is a major global concern, especially in India where the burden of... more Antimicrobial resistance (AMR) is a major global concern, especially in India where the burden of infectious diseases is high and health care spending is low. Here we quantified total coliform, faecal coliforms (FC), carbapenem-resistant enteric bacteria (CRE), bla, and three integron genes in samples collected from wastewater effluent of 12 hospitals, 12 sewage treatment plants (STPs), 20 sewer drains, and five locations along the Yamuna River in New Delhi over two seasons. Significant correlations were found between FC levels, CRE (r = 0.903, p = 0.004, n = 49) and bla (r = 0.787, p = 0.003, n = 49) concentrations across all samples. Concentrations of coliforms, CRE, bla, int1, and int3 were highest in hospital effluents compared to other locations in both seasons. Although absolute concentration data indicate greater abundances of CRE and bla in the winter, normalised data indicates greater carriage of bla per cell in summer samples. In general, observed CRE levels were highest i...
Environmental Monitoring and Assessment
Journal of Hazardous, Toxic, and Radioactive Waste
Environmental Technology, 2017
Journal of environmental science & engineering, 2014
The studies were carried out to find out transport parameters to predict leachate transport and c... more The studies were carried out to find out transport parameters to predict leachate transport and contaminant plume profile underneath a municipal solid waste(MSW) dump. For this, both theoretical and practical avenues were explored. Batch experiments with disturbed soil were carried out with a tracer dye Brilliant Blue FCF to obtain the adsorption isotherm of the tracer. Column experiments with undisturbed realistic soil column were carried out to determine physico-chemical transport parameters using the tracer dye. MSW leachate transport were simulated and sensitivity analysis for MSW leachate transport was carried out for different Darcy velocity for pulse input.For determination of mass-transfer coefficient between the immobilized and mobilized water phase, we usedthe concept of number of transfer units (NTUs) and height of transfer units (HTUs) frequently used by Chemical Engineers. The obtained value of mass transfer coefficient calculated by this method was in excellent agreeme...
Uploads
Papers by T. Sreekrishnan