Biomedical subjects
Publications and source records attributed to T Viraraghavan.
Non-viable fungal biomass of Aspergillus niger, coated with iron oxide was investigated for its potential to remove arsenic from an aqueous solution. A. niger biomass coated with iron oxide showed maximum removal (approximately 95% of As(V) and 75% of As(III)) at a pH of 6. No strong relationship was observed between the surface charge of the biomass and arsenic removal.
Oil production generates a significant amount of water byproduct known as produced water. Following primary gravity separation, produced water is normally disposed of by injection into the formation from which it came. However, high amounts of suspended solids or oil in the produced water may cause clogging of the injection formation. This study evaluated the effectiveness of coalescence/filtration in treating two produced water samples obtained from Saskatchewan heavy oil production sites. In the coalescence/filtration experiments, percentage removals of oil and suspended solids were observed to be as high as 97 and 91 percent, respectively. Mechanisms of filtration and coalescence were identified and observed through experimental data and mathematical models. The maximum coalescence efficiency observed was three percent at the lowest flow rate. Coalescence efficiencies decreased with increasing flow rate. Experimental data for single and two-phase flow were shown to fit the Carmen-Kozeny filtration equation. Coalescence/filtration satisfied a first order rate equation using the Crickmore model.
Thallium (Tl) is a rare but widely dispersed element. All forms of thallium are soluble enough to be toxic to living organisms. Thallium is more toxic to humans than mercury, cadmium, lead, copper or zinc and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1861. Its chemical behavior resembles the heavy metals (lead, gold and silver) on the one hand and the alkali metals (K, Rb, Cs) on the other. It occurs almost exclusively in natural waters as monovalent thallous cation. The solubility of thallous compounds is relatively high so that monovalent thallium is readily transported through aqueous routes into the environment. Tl can be transferred from soils to crops readily and accrues in food crops. The fascinating chemistry and high toxicity potential make thallium and its compounds of particular scientific interest and environmental concern. Thallium was detected in base-metal mining effluents. The conventional removal of heavy metals from wastewater has little effect on thallium. In this review, various treatment options and removal technologies are enumerated in order to protect the environment from thallium toxicity.
Solid waste management in Kathmandu valley of Nepal, especially concerning the siting of landfills, has been a challenge for over a decade. The current practice of the illegal dumping of solid waste on the river banks has created a serious environmental and public health problem. The focus of this study was to carry out an evaluation of solid waste management in Nepal based on published information. The data showed that > or =70% of the solid wastes generated in Nepal are of organic origin. As such, composting of the solid waste and using it on the land is the best way of solid waste disposal. This will reduce the waste volume transported to the landfill and will increase its life.
A 2(5-1) fractional factorial design was conducted for the biosorption of pentachlorophenol (PCP) using Aspergillus niger biomass. Effects of several factors on the percentage removal of PCP from aqueous solutions were evaluated. These factors were as follows: type of biomass (autoclaved- chemically modified); pH (3-11); concentration (1-10 mgl(-1)); temperature (6-32 degrees C); and dissolved oxygen (2.5-20 mgl(-1)). Time of shaking (equilibrium time), volume of the solution and mass of biomass were kept constant. The results showed that type of biomass and pH had a larger impact on the removal of PCP. Concentration of PCP in the aqueous solution, temperature, and dissolved oxygen only marginally affected the removal efficiency of PCP.
Pulp and paper mills generate varieties of pollutants depending upon the type of the pulping process. This paper is the state of the art review of treatability of the pulp and paper mill wastewater and performance of available treatment processes. A comparison of all treatment processes is presented. Combinations of anaerobic and aerobic treatment processes are found to be efficient in the removal of soluble biodegradable organic pollutants. Color can be removed effectively by fungal treatment, coagulation, chemical oxidation, and ozonation. Chlorinated phenolic compounds and adsorable organic halides (AOX) can be efficiently reduced by adsorption, ozonation and membrane filtration techniques.
From the performance analysis of the anaerobic digestion system at the Regina Wastewater Treatment Plant, it was found that the anaerobic digestion system at the Regina plant was generally operated in a stable condition as indicated by pH, volatile acids and alkalinity levels. The operation of the anaerobic digestion system was not optimal because of the low volatile solids concentration and low volatile solids loading rate, especially because of high HRT. Two options, thickening the primary sludge and increasing the volatile solids loading rate, were recommended for the optimal operation of the digestion system. After examining a number of kinetic models, it was found that the Chen-Hashimoto model could be used to predict the volumetric methane production rate and the first-order model could be used to predict the efficiency of volatile solids reduction. The study showed that utilization of digester gas for power production was the best alternative for the excess digester gas. 13.3% of the electrical demand and 35.5% of the plant's total energy could be met based on digester gas wasted, assuming 25% as the conversion efficiency.
Laboratory-scale UASB reactors were started-up successfully at 20 degrees C and operated at temperatures of 32, 20, 15, 11, and 6 degrees C applying several hydraulic retention times (HRTs) ranging from 48 to 3 h during an operational period of approximately 900 days. Changes in temperature and HRTs impacted the reactor performance. However, overall reactor performance (70 to 90% COD removal) was found to be stable up to an HRT of 6 h and temperature of 11 degrees C. The performance of UASB reactor was not very stable during 6 degrees C operation, even though 30 to 50% of COD removal could be achieved. Biomass aggregation in the form of granules/bio-pellets (mean size ranged from 1.8 mm to 3.0 mm) could be achieved during 20 degrees C operation. The impact of temperature on morphology, surface structure, and shape of bio-pellets was explored. Morphological and elemental composition analyses showed the possible mechanism of biomass aggregation in UASB reactors. This study demonstrated that the UASB process could be applied successfully with some minor adjustment for the treatment of municipal wastewater in temperate and cold regions (average summer temperature 11-25 degrees C).
Due to the extensive application of artificial nitrogen-based fertilizers and animal manure on land, many water agencies face problems of increasing concentrations of nitrate in groundwater. The contamination of groundwater by nitrate may pose a significant public health problem. The threat of methemoglobinemia is well documented and reflected in the US drinking water standard of 10 mg/L as nitrate-nitrogen. Approximately 45% of Saskatchewan's population use groundwater for drinking purposes, out of which, approximately 23% (230,000) are rural residents. The water used is made available from over 48,000 privately owned wells in regions where there is an extensive application of chemical fertilizers. Biological denitrification, ion exchange, and reverse osmosis (RO) processes were selected for a field study. Field studies were conducted on these processes. The sulfur/limestone autotrophic denitrification (SLAD) process was selected to achieve biological removal of nitrate from groundwater. The feasibility of the system was evaluated under anaerobic conditions. An ion exchange study was conducted using Ionac A554 which is a strong anion exchange resin. In the case of groundwater containing low sulfate concentrations, A554 offered high nitrate removal. However, the disposal of regenerant brine can be a problem. A reverse osmosis unit with Filmtec membrane elements (FT30-Element Family) was used in the study on nitrate removal. The unit effluent average nitrate concentration was less than the maximum allowable concentration.
The present study examined the feasibility of treating municipal wastewater by a UASB system under low-temperature conditions. Two reactors were started-up at 20 degrees C and subsequently operated at temperatures of 32, 20, 15, 11, and 6 degrees C applying several hydraulic retention times (HRTs) ranging from 48 to 3 h during an operational period of approximately 900 days. Chemical oxygen demand (COD) removal efficiency ranged from 70 to 90% up to an HRT of 6 h and 11 degrees C. The performance of the reactor was not very satisfactory during 6 degrees C operation (average COD removal 40%). Sulfate reduction played an important role in COD reduction. Digital image analysis and scanning electron microscopic observations of sludge samples revealed aggregation of biomass in the form of irregular shaped granules (mean size ranged from 1.5 to 3.0 mm). The hydraulic regime in the reactor was impacted by the change in operating temperature. This study demonstrated that the UASB system could be applied successfully for pre-treatment/treatment of municipal wastewater under low-temperature conditions.
The present study examined the use of perlite for the removal of cadmium from aqueous solutions. The effects of pH and contact time on the adsorption process were examined. The optimum pH for adsorption was found to be 6.0. Residual cadmium concentration reached equilibrium in 6h and the rate of cadmium adsorption by perlite was rapid in the first hour of the reaction time. Ho's pseudo-second-order model best described the kinetics of the reaction. Batch adsorption experiments conducted at room temperature (22+/-1 degrees C) showed that the adsorption pattern followed the Freundlich isotherm model. The maximum removal of cadmium obtained from batch studies was 55%. Thomas model was used to describe the adsorption data from column studies. The results generally showed that perlite could be considered as a potential adsorbent for cadmium removal from aqueous solutions.
An investigation was conducted to examine aerobic digestion of the phosphorus-laden sludge produced at the Regina Wastewater Treatment Plant and feasibility of land use of this sludge combined with the dewatered anaerobically digested primary sludge from this plant. Experimental studies showed that aerobic digestion can be employed for the stabilization of the chemical sludge. Results of the feasibility analysis showed that mixing the two digested sludges met the heavy metal criteria set by various guidelines for agricultural use, presented the advantage of an increased concentration of nutrients and a decreased concentration of heavy metals, and a longer useful life of the agricultural site compared to using dewatered anaerobically digested primary sludge alone. Land application of the mixed digested sludges would be a more appropriate method of sludge disposal compared to the present practice of landfilling the dewatered sludge and lagooning the chemical sludge.
Aspergillus niger is capable of removing dyes from an aqueous solution. In the study, the roles played by three major functional groups: carboxyl, amino and phosphate, and the lipid fraction in the biomass of A. niger in biosorption of four dyes, Basic Blue 9, Acid Blue 29, Congo Red and Disperse Red 1, were investigated. These functional groups in A. niger were chemically modified individually to determine their contribution to the biosorption of dyes. It was found that biosorption of dyes was influenced by the functional groups in the fungal biomass and the chemical structure of the dyes.
Phenols in trace quantities are usually present in the treated effluent of many wastewater-treatment plants. Phenol contamination of drinking water even at 1 microg/l concentration can cause significant taste and odor problems. This study investigates the use of non-viable pretreated cells of Aspergillus niger to remove phenol from an aqueous solution. Five types of non-viable pretreated A. niger biomass powders were used as a biosorbent to remove phenol present in an aqueous solution at a concentration of 1,000 microg/l. Sulfuric acid-treated non-viable biomass powder, which was the most effective, was used as a biosorbent in a further study. The maximum removal of phenol was observed at an initial pH of 5.1 for the sulfuric acid-treated biomass. The adsorption of phenol by pretreated A. niger biomass was best described by the Brunauer Emmet Teller model. Desorption of phenol using distilled deionized water was found to be approximately 5% suggesting a strong biosorption by the biomass. Sulfuric acid-treated biomass beads developed through immobilization in polysulphone were used in a column study. Approximately 66% of phenol was removed in the column operated at an initial pH of 5.1 and an initial concentration of 1,000 microg/l of phenol.
Mucor rouxii biomass was immobilized in a polysulfone matrix. The spherical immobilized biomass beads were packed in a column. The biosorption column was able to remove metal ions such as Pb, Cd, Ni and Zn not only from single-component metal solutions but also from multi-component metal solutions. Column kinetics for metal removal were described by the Thomas model. For single-component metal solutions, the metal removal capacities of the beads for Pb, Cd, Ni and Zn were 4.06, 3.76, 0.36 and 1.36 mg/g, respectively. For a multi-component metal solution containing Cd, Ni and Zn, the capacities were 0.36, 0.31 and 0.40 mg/g for Cd, Ni and Zn, respectively. The adsorbed metal ions were easily desorbed from the beads with 0.05N HNO3 solution. After acid desorption and regeneration with deionized water, the beads could be reused to adsorb metal ions at a comparable capacity.
In recent years, there has been an intensive research on fungal decolorization of dye wastewater. It is becoming a promising alternative to replace or supplement present treatment processes. This paper examines various fungi, living or dead cells, which are capable of decolorizing dye wastewaters; discusses various mechanisms involved; reports some elution and regeneration methods for fungal biomass; summarizes the present pretreatment methods for increasing the biosorption capacity of fungal biomass; discusses the effect of various factors on decolorization.
The 'Modified Sturm Test' uses carbon dioxide production as the primary end point in assessing the biodegradation potential of organic chemicals. This test was conducted by a commercial laboratory to assess the potential biodegradability of an oil stabilizer sample from an oil company in Canada. There was a high percentage conversion of total organic carbon present in the sample but carbon dioxide measured was low. Many possibilities were analyzed in this paper in order to understand the situation. The analysis showed that the test was subject to criticism from the point of view of CO2 measurement, 10-day window period, and aeration/mixing conditions.
Batch kinetic and isotherm studies were carried out to determine the adsorptive characteristics of peat and bentonite mixtures for pentachlorophenol, and to examine the hydraulic conductivity of peat-bentonite mixtures to determine if they are applicable for use as cutoff barriers. Batch kinetic studies showed that over 90% of PCP was removed from water spiked with approximately 1 mg/l of PCP using a peat-bentonite (5%) mixture. The equilibrium time was 8 hours. The optimum pH range for adsorption of PCP by the peat-bentonite mixture was found to be 3-3.5. Batch isotherm studies showed that the adsorption of PCP by the peat-bentonite mixture from aqueous solution was best described by the Freundlich isotherm equation. Batch adsorption studies using various ratios of bentonite in the mixture showed that the adsorption of PCP decreased linearly with increased amount of bentonite in the mixture, indicating that adsorption of PCP by the peat moss portion of the mixture was the dominant process. The inverse of the hydraulic conductivity was found to increase exponentially with an increase in the bentonite content of the mixture over the range studied. The minimum hydraulic conductivity observed was 3.3 x 10(-7) cm/s for a 50% peat-50% bentonite mixture. Peat-bentonite mixtures can be used to successfully remove PCP from aqueous media and can be used effectively as a barrier to attenuate the migration of PCP through soil and groundwater systems.