A potential new commercial method for processing leather to reduce environmental impact

INTRODUCTION

Current leather processing method involves dehairing and fibre opening employing lime and sulphide, which results in higher negative impact on the environment due to its uncleanness. This method of dehairing and fibre-opening process accounts for nearly 70-80% biochemical oxygen demand and chemical oxygen demand (COD) in tannery wastewater and also the generation of H(2)S gas.

MATERIALS AND METHODS

Hence, an attempt has been made to reduce the environmental impact of the leather processing through a biochemical approach, employing proteolytic enzyme and sodium metasilicate for performing the above process more cleanly.

RESULTS AND DISCUSSION

The developed process exhibits significant reduction in environmental parametres such as COD and total solid loads by 55% and 25%, respectively. This method completely avoids the formation of lime sludge.

CONCLUSION

The functional properties of the leathers are also on par with conventionally processed leathers. Further, the process seems to be commercially viable.

Electrochemical treatment of tannery wastewater using DSA electrodes

In this work we studied the electrochemical treatment of a tannery wastewater using dimensionally stable anodes (DSA) containing tin, iridium, ruthenium, and titanium. The electrodes were prepared by thermal decomposition of the polymeric precursors. The electrolyses were performed under galvanostatic conditions, at room temperature. Effects of the oxide composition, current density, and effluent conductivity were investigated, and the current efficiency was calculated as a function of the time for the performed electrolyses. Results showed that all the studied electrodes led to a decrease in the content of both total phenolic compounds and total organic carbon (TOC), as well as lower absorbance in the UV-vis region. Toxicity tests using Daphnia similis demonstrated that the electrochemical treatment reduced the wastewater toxicity. The use of DSA type electrodes in the electrochemical treatment of tannery wastewater proved to be useful since it can promote a decrease in total phenolic compounds, TOC, absorbance, and toxicity.

DNA damage induced by industrial solid waste leachates in Drosophila melanogaster: a mechanistic approach

Genomic stability requires that error-free genetic information be transmitted from generation to generation, a process that is dependent upon efficient DNA repair. Industrial leachates which contain mixtures of diverse chemicals are a major environmental concern. The interaction between these chemicals may have synergistic, antagonistic, or simply additive effects on biological systems. In the present study, the Comet assay was used to measure the DNA damage produced by leachates of solid wastes from flashlight battery, pigment, and tanning factories in the midgut cells and brain ganglia of Drosophila melanogaster mutants deficient in DNA repair proteins. Larvae were allowed to feed for 48 or 72 hr on diets containing 0.1, 0.5, and 2.0% (v/v) of the leachates. Physicochemical analysis run on the solid wastes, leachates, and treated larvae detected elevated levels of heavy metals. Leachates produced significantly greater levels of DNA damage in mutant strains mei41 (deficient in cell cycle check point protein), mus201 (deficient in excision repair protein), mus308 (deficient in postreplication repair protein), and rad54 (deficient in double strand break repair protein) than in the OregonR(+) wild-type strain. Larvae of the ligaseIV mutant (deficient in double strand break repair protein) were hypersensitive only to the pigment plant waste leachate. Conversely, the dnase2 mutant (deficient in protein responsible for degrading fragmented DNA) was more sensitive to DNA damage induction from the flashlight battery and tannery waste leachates. Our data demonstrate that repair of DNA damage in organisms exposed to leachates is dependent upon several DNA repair proteins, indicative of the involvement of multiple overlapping repair pathways. The study further suggests the usefulness of the Comet assay for studying the mechanisms of DNA repair in Drosophila.

Sodium metasilicate based fiber opening for greener leather processing

Growing environmental regulations propound the need for a transformation in the current practice of leather making. The conventional dehairing and fiber opening process results in high negative impact on the environment because of its uncleanliness. This process accounts for most of the biochemical oxygen demand and chemical oxygen demand in tannery wastewater and generation of H2S gas. Hence, this study explores the use of a biological material and a nontoxic chemical for performing the above process more cleanly. In this study, the dehairing and fiber opening processes has been designed using enzyme and sodium metasilicate. The amount of sodium metasilicate required for fiber opening is standardized through the removal of proteoglycan, increase in weight, and bulk properties of leathers. It has been found that the extent of opening up of fiber bundles is comparable to that of conventionally processed leathers using a 2% sodium metasilicate solution. This has been substantiated through scanning electron microscopic analysis and softness measurements. The presence of silica in the crust leather enhances the bulk properties of the leather. This has been confirmed from the energy dispersive X-ray analysis. Performance of the leathers is shown to be on par with conventionally processed leathers through physical and hand evaluation. The process also exhibits significant reduction in chemical oxygen demand and total solid loads by 55 and 24%, respectively. Further, this newly developed process seems to be economically beneficial.

Statistical source identification of metals in groundwater exposed to industrial contamination

Levels of selected metals Na, Ca, Mg, K, Fe, Mn, Cr, Co, Ni, Cd, Pb and Mn were estimated by flame atomic absorption spectrophotometry in groundwater samples from Kasur, a significant industrial city of Pakistan. Salient mean concentration levels were recorded for: Na (211 mg/l), Ca (187 mg/l), Mg (122 mg/l), K (87.7 mg/l), Fe (2.57 mg/l) and Cr (2.12 mg/l). Overall, the decreasing metal concentration order was: Na>Ca>Mg>K>Fe>Cr>Zn>Co>Pb>Mn>Ni>Cd. Significantly positive correlations were found between Na-Cr (r=0.553), Na-Mn (r=0.543), Mg-Fe (r=0.519), Mg-Cr (r=0.535), Pb-K (r=0.506) and Pb-Ni (r=0.611). Principal Component Analysis and Cluster Analysis identified tannery effluents as the main source of metal contamination of the groundwater. The present metal data showed that Cr, Pb and Fe levels were several times higher than those recommended for water quality by WHO, US-EPA, EU and Japan. The elevated levels of Cr, recorded as 21-42 fold higher compared with the recommended quality values, were believed to originate from the tanning industry of Kasur.

Suppression of IL-6 level in human peripheral blood mononuclear cells stimulated with PHA/LPS after occupational exposure to chromium

The toxic metals alter the immune response of animals as well as humans. In addition to the well documented and numerous toxic effect of chromium on various target organs, number of studies shown that acute and chronic exposure to inorganic chromium may result in impairment of immune functions in the experimental systems. Immunosuppression appears to be more subtle effect of exposure to heavy metals. Therefore, we have taken two different groups of chromium exposed individuals. These were leather tanning workers and chromeplaters. These groups of individuals were regularly exposed to chromium. All the leather tanning workers were highly exposed to chromium having a mean of 96.60+/-113.95 mg/dl (range 12.4-417.21 mg/dl). A suspension of exposed and unexposed human PBMC (0.5x10(6) cells/ml) prepared and cultured in RPMI-1640 supplemented with 10% FCS for 18 h in the presence or absence of PHA (5 microg/ml) and LPS (10 ng/ml) which used for stimulation of IL-2, IL-4, TNF-alpha, IL-10 and IL-6, respectively. The levels of Th1/Th2 cytokine: IL-2, IL-4, TNF-alpha, IL-10 and IL-6 were evaluated in the sera and PHA/LPS stimulated culture supernatant of human PBMCs of chromium exposed workers. In these workers the level of IL-6 was 543.95+/-123.75 pg/ml and 388.40+/-61.24 pg/ml in PHA/LPS stimulated culture supernatant of normal individuals and highly chromium exposed workers, which was significant (P<0.05). This observation suggests that IL-6 levels were suppressed in chromium exposed groups as compared to unexposed healthy volunteers. Although the level of IL-2 in PHA stimulated culture supernatant of PBMCs was suppressed in chromium exposed individuals but it was not significant, IL-4 and IL-10 could not be detected. However, there was no difference in TNF-alpha levels in sera samples as well as unstimulated culture supernatant of h-PBMCs of chromium exposed individuals as compared to control.

Safe disposal of toxic chrome buffing dust generated from leather industries

The high concentration of trivalent chromium along with organic/inorganic compounds in chrome buffing dust (CBD), the solid waste discharged from leather industries, causes severe groundwater contamination on land co-disposal and chronic air pollution during thermal incineration. In the present investigation, CBD was subjected to starved air incineration (SAI) at 800 degrees C in a thermal incinerator under different flow rates of oxygen to optimize the oxygen required to incinerate the organic compounds and simultaneously preventing the conversion of Cr(3+) to Cr(6+). The energy audit of SAI of buffing dust under the external supply of oxygen was carried out under different incineration conditions. The bottom ash from SAI was effectively solidified/stabilized using Portland cement and fine aggregate. The solidified blocks were tested for unconfined compressive strength and heavy metal leaching. Unconfined compressive strength of the blocks was in the range of 120-180 kg/cm(2). The stabilization of chromium(III) in the cement gel matrix was confirmed using Scanning Electron Microscopy SEM, Electron Paramagnetic Resonance spectroscopy (EPR) and X-ray diffraction spectroscopy (XRD). Leachability studies through TCLP on solidified blocks were carried out to determine the degree of leaching of chromium and organic compounds (expressed as COD) under standard conditions.

Technological transfer to demonstrative scale of sequencing batch biofilter granular reactor (SBBGR) technology for municipal and industrial wastewater treatment

The paper reports the results of an experimental investigation aimed at transferring to demonstrative scale an innovative technology (SBBGR-Sequencing Batch Biofilter Granular Reactor) for the treatment of municipal and industrial wastewater by financial support of the EU Life programme. When this technology was applied for treating municipal wastewater, the results showed that the system was able to remove 80-90% of COD, total suspended solids and ammonia independently of the hydraulic residence time investigated (i.e., from 12 to 4 h). In the case of tannery wastewater, chosen as representative of concentrated industrial wastewater, SBBGR technology was suitable for removing 80-90% of the COD, suspended solids and ammonia content up to organic loading values of 3.5 kg COD/m3.d. During both periods, the process was characterised by a very high sludge age value (theta(c) approximately 150 d) that led to a biomass concentration as high as 35 gTSS/L(bed) and a sludge production much lower (5-6 times lower) that than commonly reported for conventional treatment plants.

Development of the Sulphidogenesis Cum Ammonia Removal Process for treatment of tannery effluent

The present paper describes the development of Sulphidogenesis Cum Ammonia Removal Process (SCARP) with a simple sulphide inhibition control. The process was developed using synthetic effluent and its application for treatment of primary treated tannery effluent was demonstrated. This paper also discusses the effects of HRT and loading rates. The developed SCARP could treat efficiently the primary treated tannery effluent with influent concentrations of COD, SO4(2-) and NH4+ equal to 3,900 mg/L, 3,000 mg/L and 300 mg/L, respectively. An HRT of 10.5 hours was found to be adequate for COD, NH4-N and SO4(2-) loading rates of 8.9 kg COD/m3/d, 0.68 kg NH4+/m3/d, 6.84 kg SO4(2-)/m3/d, respectively. The overall removal efficiencies of COD, NH4-N and SO4(2-) for the above loading rates were in the ranges of 90.8-91.8%, 84-88.3% and 64.2-70.2%, respectively. The system performance was satisfactory for different loading rates and low COD/SO4(2-) ratios. The developed SCARP has good potential as a cost effective alternative treatment process to existing extended aeration process with nitrification-denitrification for the secondary treatment of tannery effluent.

Use of chitosan for chromium removal from exhausted tanning baths

A novel approach, based on chitosan heavy-metal sequestrating ability, is proposed for chromium(III) removal from spent tanning liquor. Experimental results, obtained at lab-scale using real wastewater, are presented and discussed. Resulting efficiencies are extremely high, and strongly dependent on chitosan dose and pH value. Comparative analyses with other polysaccharides is also carried out showing that amine groups are more efficient than carboxyl and sulphate ones. Chromium recovery from sorption complexes and chitosan regeneration is finally proposed to optimize the whole process.

Thermal behaviors and heavy metal vaporization of phosphatized tannery sludge in incineration process

The high concentration of heavy metal (Cu, Cr, Zn, Pb) in tannery sludge causes severe heavy metal emissions in the process of incineration. In the present investigation, the tannery sludge was treated with 85% phosphoric acid before the incineration process in the tube furnace to control the heavy metal emissions. The thermal behavior and heavy metal vaporization of pre-treated tannery sludge were investigated, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were also implemented to elucidate the chemical mechanisms responsible for the thermal behavior and weakening of heavy metal vaporization of pre-treated tannery sludge. The results obtained show that the differences in thermal behaviors between untreated and pre-treated tannery sludge are caused by the reaction of phosphoric acid and calcium carbonate. The vaporization percentage of heavy metal decreased efficiently with the increasing volumes of H3PO4, which indicated the important thermal stability of the water-insoluble metallic phosphates (Ca18Cu3(PO4)14, Ca9Cr(PO4)7, Ca19Zn2(PO4)14, PbMgP2O7) formed during tannery sludge phosphatation.

Substrate storage concepts in modeling activated sludge systems for tannery wastewaters

In spite of a variety of model structures proposed for activated sludge systems, calibration of these models for industrial wastewaters still stands untouched. In the scope of this study, a conceptual framework for the application of ASM1, ASM3 and 3 models, involving simultaneous growth and storage under dynamic conditions is presented and these models have been used for simulating biodegradation/tannery wastewaters. A comparative representation of the modeling results obtained with 5 different models is provided. The comparison of the simulation results showed that the possibility of describing the real case increases as the model gets more detailed. Although structured models are supposed to provide a better description of the dynamic behavior observed for tannery effluents, the insufficiency experienced in the experimental determination of all the storage products when complex substrate compositions are concerned, hindered the accurate determination of model coefficients. Furthermore, modeling results for different F/M ratios clearly emphasized the challenge in the definition of readily biodegradable COD. Process stoichiometry and wastewater fractionation should be defined cautiously with additional data in order to provide substantial basis for the evaluation of the respirometric response in batch tests for model calibration.

Seasonal variation of some heavy metal pollution with environmental and microbiological parameters in sub-basin of Kocabas Stream (Biga, Canakkale, Turkey) by ICP-AES

Waste water pollution in industrial areas is one of the most important environmental problems. Heavy metal pollution, especially chromium species in waste water sources from tannery affects our lives. Kocabas Stream is located in south-west Marmara region and Biga town is positioned in the sub basin on the stream. This water source functions as the water for irrigation in agriculture, drinking water for animals and for human use. Thus, this study is of great importance. Waste water pollution can affect all ecosystems and human health by directly or indirectly as in food chain. The concentration of heavy metals (Pb, Cd, Cu, Zn and Cr) were pre-analysed by ICP-AES method in water samples taken from sub-basin of Kocabas stream. In the results of these analyses, concentrations of the metals except chromium were founded at the limit value. But the total concentration of the Cr was found at high levels of between 0.0082 +/- 0.0001 and 5.7231 +/- 0.0921 mg l(-1) over the limit value (0.05 mg l(-1); WHO, EPA, TSE 266 and inland water quality classification) at sampling points very close to tannery factories. Also physicochemical and microbiological parameters of Kocabas Stream were determined. The effects of the experimental results on environment were investigated.

Multivariate analysis of selected metals in agricultural soil receiving UASB treated tannery effluent at Jajmau, Kanpur (India)

Tannery effluent and soils samples were collected from 12 different sites of an agricultural area receiving treated tannery wastewater near Kanpur city (India). The samples were analyzed for heavy metals (Fe, Cr, Zn, Mn, Cu, Ni and Pb) content with a view to assess the impact of industrial wastewater on agricultural soils. The results revealed elevated levels of Fe and Cr in agricultural soils irrigated with treated tannery effluents. Cluster analysis of tannery effluent and soil datasets yielded two groups of the metals and demonstrated their relationship in each media. Principal component analysis performed on two datasets yielded two significant factors each for the effluents and soils, suggested tanneries as the probable sources of metals in the soils.

Immune response in the tilapia, Oreochromis mossambicus on exposure to tannery effluent

The objective of the study was to investigate the effect of chronic exposure to sublethal concentrations of tannery effluent (TE) on the specific immune response and nonspecific immunity in tilapia, Oreochromis mossambicus. The effluent from the tannery was collected directly from a chrome-tanning factory situated in Dindigul district, Tamil Nadu, India. Apart from chromium (88.2 ppm), the effluent contained appreciable amount of calcium carbonate and sodium sulphate. Groups of fish (45-50 g) were exposed to 0.0053, 0.053 or 0.53% [0.1%, 1% or 10% LC50] of TE for 28 days. The specific immune response of fish was assessed by antibody response to heat-killed Aeromonas hydrophila by ELISA and bacterial agglutination assay. Nonspecific immune mechanisms were assessed in terms of serum lysozyme activity, production of intracellular reactive oxygen species (ROS) and reactive nitrogen intermediates (RNI) by peripheral blood leucocytes (PBL). The results indicate that chronic exposure of fish to 0.53% of TE, significantly suppressed antibody response, nonspecific serum lysozyme activity, and ROS and RNI production. Exposure to 0.053% (1% LC50) of TE also caused a similar suppressive effect though at a lesser degree. In conclusion, the study shows, that exposure to sublethal concentrations of TE, can lead to adverse effects on selected immune reactions in tilapia. Further, these findings may be important in terms of monitoring fish health and risk assessment during periods of fluctuating levels of pollutants in the natural and farm environments.

Natural and anthropogenic contamination of the Fratta-Gorzone river (Veneto, Italy)

Stream-bed sediment samples were collected in 2001 and 2004 along the Fratta-Gorzone River (Italy) to assess the level of heavy metal contamination. The river stretch most affected by discharges of tannery effluent showed total and pseudo-total Cr levels (up to 2,860 mg/kg) that greatly exceed national and international chemical sediment quality standards. The most contaminated section of the river bed is located downstream of the main industrial discharge. However, a large fraction of the Cr present in the sediment appears to be of lithogenic origin. At most sites, more than 50% of Cr is not soluble in aqua-regia and thus unlikely to be very mobile or easily bio-available. A negligible risk to the benthic community can be inferred for Pb, Zn, Cd, Cu and Ni. This work highlights the limitation of using existing chemical sediment quality standards alone for risk assessment. The collection and analysis of suspended solids, the determination of river discharge and of dissolved Cr at 10 field stations allowed to estimate the particulate and dissolved Cr load and to locate the river stretch that was the likely source of contaminated sediment. The pumping of dilution water from the Adige River into the Fratta-Gorzone River did not produce the expected contaminant dilution effect due to re-suspension of contaminated solid particles and the release of Cr in solution.

Study of the evaporation process of saline waste from the tanning industry

The second and third steps of wastewater treatment in the tanning industry generate sludges that are rich in salts, organic matter and suspended solids. Since these are formally catalogued as industrial wastes by environmental legislation, they cannot be disposed of directly but need a final treatment. One of the problems with these wastes is their high water content, which has to be reduced. In the particular case of the concentrated streams from the secondary and tertiary treatment steps, the sludges are first concentrated by evaporation, and the evaporated water is used in other parts of the plant. This study, which preceded evaporator design, analysed the evaporation process (laboratory scale) of a saline residue produced in the reverse osmosis step of the treatment of tanning wastewaters by the company Aquagest Levante, S.A. in Lorca (Murcia, Spain), to ascertain its behaviour in the evaporation process and the evolution of its physical properties. The study served to determine the exact mineralogy and ionic composition as well as the characteristics of the waste in question. This information was used in the last step of the design of the evaporation equipment.

Assessment of single extraction methods for the prediction of bioavailability of metals to Brassica juncea L. Czern. (var. Vaibhav) grown on tannery waste contaminated soil

Various single extractant (DTPA, EDTA, NH(4)NO(3), CaCl(2), and NaNO(3)) was used to evaluate the bioavailability of heavy metals from tannery wastewater contaminated soil and translocation of metals to the plant of Brassica juncea L. Czern. (var. Vaibhav). The extraction capacity of the metals was found in the order: EDTA>DTPA>NH(4)NO(3)>CaCl(2)>NaNO(3). Cluster analysis between different extractants showed close relationship between DTPA, CaCl(2), NH(4)NO(3) except EDTA and NaNO(3), which showed dispersed relationship. Principal components analysis (PCA) applied to metals extracted with EDTA showed different grouping of metals (i) Na, Co, Pb, Ni and (ii) K, Mn, Zn, Cr, in the loading plot which showed similar availability from contaminated soil. PCA applied on metals accumulation data in the plants also exhibited different grouping of variables (i) Cu, Co, Ni, Cd and (ii) Mn, Zn, Pb, Fe showed almost similar accumulation pattern in the plants. The data displayed positive loading for Mn and negative loading for Cr with PC(2). Cd and Zn have shown high loadings in PC(1) and PC(2), respectively. The translocation of most of the tested metals (Pb, Mn, Cd, Ni, Fe) in the shoot of the plant was found better except Cr, Cu, Co and K. The correlation analysis between different extractable metals and metal accumulation in the shoot of the plant showed significant positive correlation with Pb and Cr. Overall, extraction capacity and cluster analysis augmented that EDTA was found suitable extractant for tannery wastewater contaminated soil to B. juncea.

Wastewater toxicity of tannin- versus chromium-based leather tanneries in Marrakesh, Morocco

The toxicity of leather tanning wastewater from a traditional tannery (TT), which is based on vegetable tannin (VT), was compared with wastewater from a tannery combining the use of chromium-based tanning (CT) with VT-based tanning operations. Wastewater samples from a TT and a CT plant as well as from five sewer sampling points were collected in Marrakesh, Morocco, and the concentrations of VT and some selected inorganics were measured. A set of bioassays were used to test wastewater toxicity in sea urchin (Paracentrotus lividus) embryos and sperm, in Daphnia magna, and in marine microalgae (Dunaliella tertiolecta). Toxicity end points included: (1) developmental defects, embryonic mortality, sperm fertilization success, and offspring damage in sea urchins; (2) D. magna immobilization; and (3) algal growth rate inhibition. Toxicity tests on TT and CT effluents (TTE and CTE) were run at dilutions ranging from 0.1% to 2% (sea urchins and algae) or up to 12% in D. magna. Parallel bioassays were run on VT extract (VTE) at nominal tannin concentrations ranging from 0.1 to 10 mg l(-1). The results showed higher toxicity of CTE compared with TTE. CTE toxicity in sea urchins and algae showed concentration-related trends, whereas TTE exerted hormetic effects at levels of 0.1% to 0.2% and toxic effects at levels >or=1%. The same trends were observed for VTE, suggesting a prevailing role of tannin in TTE-associated effects. The moderate wastewater toxicity of VT-based tanneries might prompt interest in the VT tanning process.

Anaerobic ammonia removal in presence of organic matter: a novel route

This study describes the feasibility of anaerobic ammonia removal process in presence of organic matter. Different sources of biomass collected from diverse eco-systems containing ammonia and organic matter (OM) were screened for potential anaerobic ammonia removal. Sequential batch studies confirmed the possibility of anaerobic ammonia removal in presence of OM, but ammonia was oxidized anoxically to nitrate (at oxidation reduction potential; ORP=-248+/-25 mV) by an unknown mechanism unlike in the reported anammox process. The oxygen required for oxidation of ammonia might have been generated through catalase enzymatic activity of facultative anaerobes in mixed culture. The oxygen generation possibility by catalase enzyme route was demonstrated. Among the inorganic electron acceptors (NO(2)(-), NO(3)(-) and SO(4)(2-)) studied, NO(2)(-) was found to be most effective in total nitrogen removal. Denitrification by the developed culture was much effective and faster compared to ammonia oxidation. The results of this study show that anaerobic ammonia removal is feasible in presence of OM. The novel nitrogen removal route is hypothesized as enzymatic anoxic oxidation of NH(4)(+) to NO(3)(-), followed by denitrification via autotrophic and/or heterotrophic routes. The results of batch study were confirmed in continuous reactor operation.

Electrolytic recovery of chromium salts from tannery wastewater

Tannery wastewater collected from a local leather industry in Peshawar, Pakistan was subjected to DC electrolysis in a simple cell having two static sheet electrodes and stirring assembly after proper dilution and adjustment to desired conditions. One percent HNO(3) and 1% NaHCO(3) were used as electrolytes and pH adjusters. The latter salt also worked as sodium source for anodic deposition of Na(2)Cr(2)O(7). Various combinations of electrodes were tested and conditions optimized for best electrode couple with increased recovery and removal of chromium in the form of Cr(OH)(3) and/or Na(2)Cr(2)O(7) at cathode and anode, respectively. The recovery of 99% chromium was achieved after 2h electrolysis at a cell potential of 1.0 V, pH 5.0 and stirring rate of 500 rpm using Pb sheet as anode and Cu sheet as cathode. The most interesting and novel finding of this work was the recovery of the mentioned salt(s) alone at Cu cathode or Pb anode or collectively at both electrodes by proper control of pH. Such treatment not only minimizes the environmental water pollution, but results in the formation of useful products employed for recycling purpose in tannery or other related industry to make the process economical.

[Anthrax in the canton of Zurich between 1878 and 2005]

Historical records reporting cases of animal anthrax in the canton of Zurich between 1878 and 2005 were analysed on the level of political communities regarding occurrence and number of cases, animals affected, and number of communities affected. Data were correlated with industrial activities (tanning, wool and horse hair processing) in a community and to the prevailing meteorological conditions. A total of 830 cases of animal anthrax has been recorded in 140 of 171 communities. Occurrence correlated with industrial activities in a community such as companies handling potentially contaminated materials (hides, fur, wool, hair, meat, or bone meal). The influence of wool processing companies (P = 0. 004) and tanneries (P = 0. 032) was significant whereas horse hair processing had no effect. However, a statistical relationship between the number of cases reported and meteorological data (rainfall, mean temperature) was not found.

Enhanced Cr bioleaching efficiency from tannery sludge with coinoculation of Acidithiobacillus thiooxidans TS6 and Brettanomyces B65 in an air-lift reactor

Bioleaching process has been demonstrated to be an effective technology in removing Cr from tannery sludge, but a large quantity of dissolved organic matter (DOM) present in tannery sludge often exhibits a marked toxicity to chemolithoautotrophic bioleaching bacteria such as Acidithiobacillus thiooxidans. The purpose of the present study was therefore to enhance Cr bioleaching efficiencies through introducing sludge DOM-degrading heterotrophic microorganism into the sulfur-based sludge bioleaching system. An acid-tolerant DOM-degrading yeast strain Brettanomyces B65 was successfully isolated from a local Haining tannery sludge and it could metabolize sludge DOM as a source of energy and carbon for growth. A combined bioleaching experiment (coupling Brettanomyces B65 and A. thiooxidans TS6) performed in an air-lift reactor indicated that the rates of sludge pH reduction and ORP increase were greatly improved, resulting in enhanced Cr solubilization. Compared with the 5 days required for maximum solubilization of Cr for the control (single bioleaching process without inoculation of Brettanomyces B65), the bioleaching period was significantly shorten to 3 days for the combined bioleaching system. Moreover, little nitrogen and phosphorous were lost and the content of Cr was below the permitted levels for land application after 3 days of bioleaching treatment.

[Removal of Cr from tannery sludge by bioleaching in air-lift reactor: a pilot study]

A bioleaching process performed in 280 L air-lift reactor was developed for extracting Cr from tannery sludge. Cr removal efficiency under different aeration amount with a range from 1.0 m3/h to 3.0 m3/h was investigated. The results showed that the sludge could be homogeneous quickly for different aeration treatment even if aeration amount was as low as 1.0 m3/h. But the obvious effect of aeration amount on pH decrease and subsequent Cr dissolution in tannery sludge during bioleaching was observed. If the aeration amount was below 1.5 m3/h, it at least took 90 h to reach 80% Cr removal efficiency. In the light of Cr removal efficiency and energy consume, the aeration amount of 2.0 m3/h was considered as an optimum one for bioleaching in this trial. Cr removal efficiency could reach above 92.5% at 72 h. In the sludge bioleaching system dissolved oxygen increased obviously with the decrease of pH. Eventually, dissolved oxygen rised to 5 mg/L or more when aeration amount was maintained at 2.0 m3/h or more. Therefore, it was suggested that the aeration amount in ALR could be adjusted to a lower level in the late stage of tannery sludge bioleaching in order to save operation cost.

Chromium fractionation in semi-arid soils amended with chromium and tannery sludge

We studied Cr fractionation in three semi-arid soils (cultivated, under-the-canopy, and outside-the-canopy soils). The soils were amended with: Cr3+, Cr6+, tannery sludge, Cr3++tannery sludge, and Cr6++tannery sludge and all soils were incubated for 30 and 120 days at 25 degrees C. The Cr in three semi-arid soils was fractionated using sequential extraction (Tessier scheme). Data of Cr fractionation were used to find the correlations with microbial activities determined in previous work. The microbial activities: CO2-C evolved, dehydrogenase activity and nitrification were determined in the same soils amended with the same treatments. Tannery sludge was added at 0.0125 g g(-1) soil and Cr3+ or Cr6+ at 250 microg g(-1) soils. After 120 days of incubation, higher values of concentration of Cr were found in the residual fraction in the three soils amended with all the treatments, except cultivated and outside-the-canopy soils amended with Cr6++tannery. The non-residual fraction tended to decrease with time except in cultivated and outside-the-canopy soils amended with Cr6++tannery sludge. CO2-C evolved was significantly correlated (p<0.05 and p<0.001) with fractions bound to: Mn oxides, Fe oxides organic matter at 30 and 120 days of incubation (from r=0.827 to 0.979). Dehydrogenase activity was correlated with fractions bound to Fe oxides and bound to organic matter, and nitrification with fraction bound to organic matter at 30 days of incubation (r=0.874, 0.959, and 0.803, respectively). These results suggest that even in a sparingly available Cr fraction in semi-arid soils has effect on microbial activities.