Biomedical subjects

R D Tyagi

Publications and source records attributed to R D Tyagi.

At least 37 records · Page 2Linked to original sources

PubMed2002

Studies on the production of B. thuringiensis based biopesticides using wastewater sludge as a raw material.

Growth and delta-endotoxin yield of Bacillus thuringiensis (Bt) subsp kurstaki in tryptic soy yeast extract (TSY) medium, soybean meal based commercial medium and wastewater sludge medium were studied. The viable spores (VS) count in sludge medium was comparable to that obtained in laboratory and commercial media. The entomotoxicity of the fermentation liquid (Bt grown sludge) against Choristoneura fumiferana was comparable to the concentrated commercial Bt formulation available in the market (Foray 48B). A higher entomotoxicity was observed in a sludge medium than in the TSY or soybean meal media. The secondary and mixed (mixture of primary and secondary) sludges from various wastewater treatment plants were also evaluated for spore formation and entomotoxicity yield. The VS count was higher in a mixed sludge compared to the secondary sludge at a similar sludge solids concentration. Both VS count and entomotoxicity yield was found to be a function of sludge solids concentration in the medium. The optimum value of solids concentration for Bt production was found to be 25 g (-1) (dry weight basis). Beyond this concentration, a drop in VS count and entomotoxicity yield was observed. A low C:N ratio in the secondary sludge and a high C:N ratio in the mixed sludge resulted in a higher entomotoxicity. The optimum value of C:N ratio in combined sludge for Bt production was found to be 7.9-9.9. Relationships between entomotoxicity and maximum specific growth as well as with specific sporulation rate were developed.

Animals↗

PubMed2002

Wastewater sludge as a substrate for growth and carrier for rhizobia: the effect of storage conditions on survival of Sinorhizobium meliloti.

The inoculation of legumes with rhizobia is used to maximise nitrogen fixation and enhance the plant yield without using N fertilisers. For this reason many inoculant types were developed and optimised. In our study, the effects of the growth medium, the carrier, the temperature and the storage period were determined on the survival of Sinorhizobium meloliti. Secondary sludge from Communauté Urbaine de Quebec wastewater treatment plant and standard medium (YMB) were used for rhizobial growth. Dehydrated sludge from Jonquière wastewater treatment plant, peat and a mixture of peat and sludge were used as carrier materials. Results showed that the wastewater sludge offered better protection for rhizobia survival during freezing and thawing at -20 degrees C than the standard medium. In general, results also showed the suitability of using sludge as a carrier because it had the same or a higher potential than peat to support survival of S. meliloti. In the case of YMB-grown rhizobia, peat- and sludge-based carriers appeared to be similar in terms of survival rate during the storage at 4 and 25 degrees C. For secondary sludge-grown rhizobia, the survival was better in sludge than in peat based carrier. Generally, the cell count remained higher than 10(8) cells/g for up to 80 days at 4 and 25 degrees C in both carriers (sludge and peat). However, for the secondary sludge-grown cells stored in peat-based carrier at 4 degrees C, the viable cells decreased under 10(8) cells/g at the 81st day of storage but remained acceptable compared to the standard (10(7) cells/g of carrier).

Biotechnology↗

PubMed2002

Production of S. meliloti using wastewater sludge as a raw material: effect of nutrient addition and pH control.

The utilization of wastewater sludge as a raw material for the production of legume inoculant is considered as a new viable alternative for recycling. The effect of addition of nutrient sources (yeast extract and glycerol) and the pH control on S. meliloti was investigated in a shake flask and at controlled pH in a 15 l fermentor. Different concentrations of yeast extract (0.5, 1, 2 and 4 g l(-1)) and glycerol (2.5, 5, 7.5 and 10 g l(-1)) were added to the secondary sludge. The cell yield as well as the generation time were affected by the addition of these nutrient sources. The maximum cell yield (8.85x10(9) cfu ml(-1)) was achieved in 32 hours of incubation with the addition of 4 g l(-1) of yeast extract. This value was 3.2 times higher than from the non-supplemented sludge. Moreover, at this yeast extract concentration, the cell concentration in the stationary phase did not decrease. The addition of glycerol to sludge samples containing 4 g l(-1) of yeast extract further improved the rhizobial growth but not significantly compared with the control. The highest yield (16.5x10(9) cfu ml(-1)) was obtained with 7.5 g l(-1) of glycerol and 4 g l(-1) of yeast extract. In fermentor experiments, pH did not seem to be a limiting factor and the increase of pH up to 8.85 in uncontrolled fermentor seems to have no effect on rhizobial growth and cell yield.

Conservation of Natural Resources↗

PubMed2002

Different options for metal recovery after sludge decontamination at the Montreal Urban Community wastewater treatment plant.

The MUG (Montreal Urban Community) treatment plant produces approximately 270 tons of dry sludge daily (270 tds/day) during the physico-chemical treatment of wastewater. Recently, this treatment plant endowed a system of drying and granulation of sludge for valorization as an agricultural fertilizer having a capacity of 70 tds/day (25% of the daily sludge production). However, the metal content (mainly Cu and Cd) of the sludge surpasses the norms for biosolids valorization. In order to solve this problem, a demonstration project, from the lab scale to the industrial pilot plant, was carried out to test the Metix-AC technology for the removal of metals. A strongly metal-loaded filtrate was generated during the sludge decontamination. Tests concerned the study of the metal recovery by total precipitation and selective precipitation, as well as the use of alternative products for the metal precipitation. Other works consisted to simulate the acid filtrate recirculation from the decontaminated sludge (25% of the total volume) in the untreated sludge (75% of the total volume) intended for the incineration. The total precipitation with hydrated limeappearedeffectivefortherecoveryof metals (87% Cd, 96% Cr, 97% Cu, 98% Fe, 71% Ni, 100% Pb, 98% Zn). However, this option entails the production of an important quantity of metallic residue, which should be disposed of expensively as dangerous material. The selective iron precipitation does not appear to bean interesting option because the iron in solution within the leached sludge was principally present in the form of ferrous iron, which cannot be precipitated at pH lower than five. On the other hand, the use of commercial precipitating agents (TMT-15, CP-33Z, CP-NB and CPX) without pH adjustment of filtrate gave good results for the recovery of Cu and, to a lesser degree for the recovery of Pb. However, the efficiency for the other metals' (Cd, Cr, Fe, Ni and Zn) recovery was weaker (< 25%). Finally, the acid filtrate recirculation containing solubilised metals in untreated sludge destined for incineration appears to be the most interesting option. Metals in solution in the acid filtrate, precipitate or adsorb effectively (97% Cd, 97% Cr, 99% Cu, 82% Ni, 100% Pb and 87% Zn) on the solids of the untreated sludge. Moreover, TCLP tests were done on ashes produced during the incineration of sludge mixed with the acid filtrate produced during sludge decontamination. These tests showed that there were no significant differences, as regards the extractability of metals, between such ashes and those produced during the untreated sludge incineration without addition of filtrate. Therefore, it was predictable that this method can respect the current environmental standards required by the different governmental authorities.

Chemical Precipitation↗

PubMed2002

Simultaneous production of biopesticide and alkaline proteases by Bacillus thuringiensis using sewage sludge as a raw material.

The simultaneous production of Bacillus thuringiensis (Bt) based biopesticide and proteases was studied using synthetic medium and wastewater sludge as a raw material. The studies were conducted in shake flask and computer controlled 15-L capacity fermentors. Measuring viable cell and spore counts, entomotoxicity and protease activity monitored the progress of the biopesticide production process. A higher viable cell count and spore count was observed in synthetic Soya medium, however, higher entomotoxicity and protease activity were observed in wastewater sludge medium. Thus, the wastewater sludge is a better raw material than commercial Soya medium for the biopesticides and enzyme production. The maximum entomotoxicity and protease activity observed in the fermentor was 9,332 IU/microL and 4.58 IU/mL, respectively. The proteases produced by Bt were also characterised. Two types of proteases were detected; neutral proteases with pH optimum 7.0 and alkaline proteases with pH optimum 10-11. Further, two types of alkaline proteases were detected; one having a pH and temperature optimum at 10 and 50 degrees C while the other at 11 and 70 degrees C. The protease thermal stability was found to increase in the presence of CaCl2, indicating the proteases were metalloproteases.

Animals↗

PubMed2001

Assessment of toxicity reduction after metal removal in bioleached sewage sludge.

Sewage sludge can be applied to land to supply and recycle organic matter and nutrients. Trace elements in sludge, however, may accumulate in the soil with repeated sludge applications. Reducing metal content may therefore reduce the adverse effects of sludge application. The objective of this study was to evaluate the efficiency of bioleaching technology in reducing metal content and toxicity as measured by a battery of terrestrial and liquid-phase bioassays. Sludge-soil mixtures simulating the application of sludge to land were tested by means of terrestrial bioassays, barley (Hordeum vulgare L.) seed germination (5 d) and sprout growth (14 d), lettuce (Lactuca sativa) seed germination (5 d), and worm (Eisenia andrei) mortality (14 d). Liquid-phase bioassays, Microtox (Vibrio fischeri, 15 min), lettuce root elongation (L. sativa, 5 d), cladoceran mortality (Daphnia magna, 48 h), and SOS Chromotest (Escherichia coli) were used after elutriation of the sludge. Comparison of the bioassay results (except for D. magna) before and after treatment demonstrated that this bioleaching process reduced both sludge toxicity and metal content. In addition, lower Cu and Zn concentrations found in barley sprouts following treatment supported the assumption that the bioleaching process, by decreasing metal content and bioavailability, reduced sewage sludge toxicity. This study also emphasized the interest of using ecotoxicological bioassays for testing biosolids. In particular, the terrestrial bioassays after simulation of land application and the Microtox test after sludge elutriation proved to be the most appropriate procedures.

Animals↗

PubMed2001

Wastewater treatment sludge as a raw material for the production of Bacillus thuringiensis based biopesticides.

Seven wastewater sludges of different origins and types were used as an alternate culture medium for producing Bacillus thuringiensis variety kurstaki HD-1. The sludge samples were used under three different preparations: without pre-treatment, with acid treatment (hydrolysed sludge) and the supernatant obtained after centrifugation of the hydrolysed sludge. The sludge composition varied widely with origin and the type of sludge. Growth and sporulation were evaluated by the total viable cell count and spore count of the preparations. Growth, sporulation and endotoxin production were affected by the sludge origin. Hydrolysed sludge gave the highest viable cell and spore counts while the liquid phase (supernatant) gave the lowest. Non-hydrolysed primary sludge from Valcartier was unable to sustain bacterial growth because of its low pH. Bioassays were conducted against larvae of spruce budworm to evaluate entomotoxic potential of the preparations obtained. In general, sludge hydrolysis increased the entomotoxicity yields. Similar entomotoxicity was observed in Black Lake secondary sludge (4100 IU/microL) as that obtained in the reference soya medium (3800 IU/microL). The use of the sludge supernatant (liquid phase) was not recommended due to the low entomotoxic potential obtained.

Bacillus thuringiensis↗

PubMed2001

Extraction of Cr(III) and other metals from tannery sludge by mineral acids.

A comprehensive investigation on the extraction conditions of Cr(III) and other metals from tannery sludge using mineral acids was performed. The effect of various factors (the extraction time, the type of mineral acid, the consumption of acid, pH, sludge solids concentration, temperature, and the type of sludge) on the leaching yield of metals was studied. The results indicate that the metal extraction time for most of the metals was 2h at 25 degrees C. The most suitable acid for Cr(III) extraction was sulphuric acid. A relationship for the acid requirement to adjust different sludge pH at varying sludge solids concentration was established. The leaching yield of chromium varied with sludge pH and the suitable pH for Cr(III) extraction was between 2.0 to 3.0. The optimum sludge solids concentration for Cr(III) extraction was 78.5 g x l(-1). The leaching yield of Cr(III) decreased with the increased temperature. The type of sludge (wet or dry) has no effect on the leaching yield of Cr(III) The metal adsorption and bonding on the insoluble organic colloid matter as well as the formation of metal precipitates may be two possible reasons for the decreased extraction yield of metals with increased solids concentration.

Acids↗

PubMed2001

Prediction of metal precipitates in tannery sludge leachate based on thermodynamic calculations.

Thermodynamic calculations were performed in order to predict the formation of metal precipitates during the tannery sludge leaching. Gibbs free energy deltaG=RTln(Qc/Kc) of precipitation reaction was used to examine the formation of precipitates during the leaching process. The values of activity equilibrium constant (Ka) of various precipitation reactions were adopted from the literature. The Ka values were corrected to obtain the corresponding values of concentration product (Qc) and concentration equilibrium constant (Kc) using the activity coefficients (gamma) of the ions. The activity coefficients (gamma) of the ions was calculated using Davies equation Lngammai=-1.172Zi2((I0.5/(1+I0.5))-0.3I) (aqueous solution, 25 degrees C, 1 atm, I>0.3 mol x l(-1)). The values of ionic strength (I) at different sludge solids concentration and leaching pH were obtained by measuring the concentration of all ionic species in the leachate. The thermodynamic calculations indicated that the possible metal precipitates formed during the leaching process were (am)Cr(OH)3, (am)CrPO4, (am)Fe(OH)3, alpha-FeOOH(goethite), FePO4.2H2O, (am)AIPO4-2H2O, CaSO4.2H2O(gypsum). The solubility of these precipitates was found to decrease with the increase in the ionic strength (or sludge solids concentration). The results of computations were supported by the experimental observations.

Chemical Precipitation↗

PubMed2001

Acid and alkaline treatments for enhancing the growth of rhizobia in sludge.

Wastewater sludges have been proposed as an effective media for the production of rhizobia. The effect of total suspended solid (TSS) concentrations and pretreatments of sludge on the growth of Sinorhizobium meliloti were investigated. Acid (pH 2.0-6.0 obtained with H2SO4) and alkaline (50-200 mequiv.wt./L of NaOH) treatments were applied to enhance the biodegradability of primary (0.325%-3.2% TSS obtained by dilution of original sample) and secondary (0.2%-0.4% TSS obtained by concentration of original sample) sludges. In primary sludge without pretreatment, the highest cell count (11.10 x 10(9) cfu/mL) was obtained with 1.3% TSS. However, a maximum cell count of 13.00 x 10(9) cfu/mL was reached using an acid treatment of pH 2.0 and a 0.325% TSS concentration. Moreover, the alkaline treatment with 100 mequiv.wt./L of NaOH and 0.65% TSS increased the cell yield to 21.00 x 10(9) cfu/mL. For secondary sludge without pretreatment, no enhancement of growth was observed while increasing TSS concentration. This may be due to the increase of inhibitory substances, such as heavy metals, and of the Ca and Mg concentrations. As in primary sludge, some acid and alkaline treatments of secondary sludge tend to improve the cell count of S. meliloti. However, the highest value of 9.80 x 10(9) cfu/mL obtained with 0.4% TSS at pH 2.0 was lower than that obtained with primary sludge. It was also observed that S. meliloti grown in treated sludges maintained its capacity to nodulate alfalfa.

Colony Count, Microbial↗

PubMed2001

Effect of surface active agents on the production of biopesticides using wastewater sludge as a raw material.

Effect of surface active agents on the production of Bacillus thuringiensis based biopesticides using secondary wastewater sludge as a raw material was studied. The experiments were conducted in a shake flask and nine different commercial surface active agents were used at a concentration of 0.2% (v/v). The sludge samples after addition of surface active agents were sterilised at 121 degrees C for 30 min. The progress of biopesticide production was monitored by measuring viable cells and viable spores counts. The entomotoxicity was determined through bioassay against 3rd instar larvae of spruce budworm. ATPLUS 522, Tween 80 and Tween 85 increased the entomotoxicity potential in comparison to the control. The highest increase of 24% in entomotoxicity was observed when sludge was fortified with Tween 80.

Animals↗

PubMed1996

Isolation, phenotypic characterization, and phylogenetic position of a novel, facultatively autotrophic, moderately thermophilic bacterium, Thiobacillus thermosulfatus sp. nov.

Thiobacillus thermosulfatus ATCC 51520T (T = type strain) was isolated from sewage sludge samples enriched with elemental sulfur. The cells of this organism were gram negative, rod shaped, motile, facultatively autotrophic, and strictly aerobic and contained polyphosphate inclusions and polyhedral bodies. During growth on thiosulfate, the following intermediates were produced: tetrathionate, trithionate, and sulfate, and the pH was lowered from neutrality to around 2.5. Autotrophic growth was observed at pH values between 4.3 and 7.8 and at temperatures of 34 to 65 degrees C; optimum growth occurred at pH 5.2 to 5.6 and 50 to 52.5 degrees C. Ubiquinone Q8 was present in the respiratory chain. The DNA contained 61 +/- 1 mol% G+C. No denitrification was observed under autotrophic and heterotrophic conditions. The cells produced a glycocalyx during growth in the presence of S0. As determined by a 16S rRNA gene sequence analysis, T. thermosulfatus is a distinct species that belongs to the beta subdivision of the Proteobacteria and is closely related phylogenetically to Thiobacillus perometabolis. The GenBank accession number for the complete 16S rRNA gene sequence of T. thermosulfatus is U27839.

Bacteriological Techniques↗

PubMed1995

Microbial ecology of simultaneous thermophilic microbial leaching and digestion of sewage sludge.

The microbial population encountered during a simultaneous thermophilic microbial leaching and digestion process at 50 degrees C, based on microbial sulfur oxidation, was investigated. The cell count of the sulfuric acid producer Thiobacillus thermosulfatus increased, followed by a decrease. In the absence of sulfur (control: conventional thermophilic digestion), Thiobacillus thermosulfatus population decreased under the detection limit. Acidophilic and neutrophilic heterotrophic populations increased during the leaching process, and the final acidophilic population count was higher than the neutrophilic population. During the thermophilic digestion (control), the final neutrophilic population count was higher than the acidophilic. Six heterotrophic bacterial strains were isolated and partially characterized. Bacillus was the most predominant genus. The type of bacterial populations in thermophilic microbial leaching and digestion, as well as the thermophilic digestion process (control), were the same, while only the relative concentrations changed. In both processes, the bacterial indicators decreased under the detection limit after 12 h. Mesophilic heterotrophic population was more affected by the thermophilic microbial leaching process than by thermophilic digestion. Sludge mineralization was probably more influenced by the final cell concentration rather than the presence of an individual species or mixed population.

Bacteria↗

PubMed1993

Bacterial leaching of metals from sewage sludge by indigenous iron-oxidizing bacteria.

Bioleaching of metals can be achieved in sewage sludge using Thiobacillus ferrooxidans, which obtains its energy requirements from the oxidation of added ferrous iron. The purpose of this study was to verify the presence of indigenous T. ferroxidans and to evaluate their adaptive capacity and leaching potential. Nineteen sludges (primary, secondary, aerobically and anaerobically digested, oxidation pond) were tested and all of them contained indigenous iron-oxidizing bacteria. The acclimation of these organisms by successive transfers allowed a rise of sludge redox potential over 450 mV and a decrease of sludge pH between 3.8 and 2.2 over a 10-day incubation period. The metal solubilization efficiencies were Cd: 55-98%, Cr: 0-32%, Cu: 39-94%, Mn: 71-98%, Ni: 37-98%, Pb: 0-31% and Zn: 66-98%, were reached with these indigenous strains. The results obtained show that the metal bioleaching may be easily realized by direct acclimation of sludge microflora.

Journal Article↗

PubMed1992

Performance of RBC coupled to a polyurethane foam to biodegrade petroleum refinery wastewater.

Biological treatment of petroleum refinery wastewater was studied in a rotating biological contactor (RBC) coupled to a polyurethane foam (PUF) as a porous biomass support. The PUF was attached on both sides of biodisks. The biodegradation studies were carried out at varying hydraulic and organic loadings. COD removal efficiency of up to 87% was achieved. The results obtained in terms of biodegradation of COD, NH3-N, phenol, hydrocarbons and suspended solids in this study were compared with those in the literature. The RBC-PUF bioreactor was found to have a better performance than a conventional RBC for the biodegradation of the above mentioned parameters. A higher concentration of active biomass (77 g TVS/m2) was observed in the RBC-PUF as compared to other treatment systems. A linear relationship between COD applied and COD removed was observed for the combined four stage system as well as for the individual stages.

Journal Article↗

PubMed1992

Cooperation between two Thiobacillus strains for heavy-metal removal from municipal sludge.

A mixed culture of two fast-growing bacterial strains for heavy-metal solubilization of municipal sewage sludge has been developed. Strain VA-7 decreases the initial sludge pH (7-8.5) to a value between 4.0 and 4.5. Then, strain VA-4 begins growing and further reduces the pH to values below 2.0. The rapid decrease of sludge pH by a mixed culture through sulfur oxidation into sulfuric acid solubilizes the toxic metals (Cd 83-96%, Cr 16-54%, Cu 85-87%, Mn 91-94%, Ni 78-79%, Pb 28-46%, Zn 82-96%) to levels recommended for intensive use of residual sludge in agriculture. A study of the physiological and metabolic characteristics of these strains revealed that isolate VA-7 is a strain of Thiobacillus thioparus (ATCC 55127), while isolate VA-4 corresponds to a Thiobacillus thiooxidans (ATCC 55128). These bacterial strains possess distinctive physiological characteristics that allow them to easily grow and solubilize heavy metals in municipal sludge.

Hydrogen-Ion Concentration↗

PubMed1991

Effects of medium composition on the bacterial leaching of metals from digested sludge.

The effects of parameters (soluble iron, K(2)HPO(4), MgSO(4), Ca(NO(3))(2), KCl and (NH(4))(2)SO(4)) on bacterial leaching of heavy metals from anaerobically digested sludge have been studied in a batch process using a strain of Thiobacillus ferrooxidans. The sludge was found to be a deficient iron source. Metal leaching rate was increased proportionally with the ferrous iron. Amendment of the sludge with a nitrogen source increased the metal solubilization efficiency to a very small extent. Addition of phosphate and other nutrients did not show any effect on the microbial leaching rate.

Journal Article↗

PubMed1988

Heavy metals removal from anaerobically digested sludge by chemical and microbiological methods.

The metal removal from anaerobically digested sludge was studied by chemical treatment and microbial leaching processes in laboratory reactors. The removal of metals increased with decreased sludge solid concentration and pH. In the acid treatment process, a pH of 1.5 was required to reduce the copper concentration in the sludge to an acceptable level. In the microbial processes mixed culture gave 10% better solubilisation of metals than in single culture. The acid requirement was lower for the microbial process. The cost of sludge treatment in terms of chemicals was found to be decreased by 80% in microbial leaching.

Journal Article↗