Metal contamination in soil and vegetables around Savar tannery area, Dhaka, Bangladesh: A preliminary study for risk assessment.

Monitoring of heavy metal concentrations in soil and their accumulation in vegetables grown in the newly shifted tannery area of Savar, Bangladesh, is crucial for human health. Heavy metals (i.e., Cr, Pb, Cu, Zn, Ni, and Cd) concentrations in soil and vegetable samples were determined by atomic absorption spectrophotometer (AAS). In soil, 3220 mg/kg Cr was observed, which was 32-fold greater than the WHO/FAO recommended limit. Ecological risk indices such as the contamination factor, enrichment factor, pollution load index, and geoaccumulation index showed metal levels as moderately to very highly contaminated. The non-carcinogenic risk (NCR) was found to be higher, and the carcinogenic risk (CR) exceeded the acceptable value 1 × 10-6 and posed greater risks to children than adults, especially for Cr in soil. The main exposure pathway for soil metals was 97.8-99.9% due to oral ingestion. The concentration of heavy metals especially Cr, Pb, Zn, and Cd, in vegetables was alarming as they crossed the safety limit. The calculated mean hazard index (8.71) for vegetable samples showed elevated levels of potential NCR, while CR for Cr and Cd, exceeded the acceptable limit of 1 × 10-6, indicating the probability of cancer risk to humans through the consumption of vegetables. This study revealed a to-and-fro analysis of the present scenario of the tannery area, giving importance to human health and the environment.

Composting of limed fleshings generated in a tannery: sustainable waste management.

In tanneries, limed fleshing is an unavoidable waste generated in beamhouse operation. Proper management of limed fleshing with protein, fat, lime, and sulfide will help to protect the natural environment and at least reduce the pollution that ends up in it. In this study, excluding any pretreatment, limed fleshing is used for compost production. Chopped and mixed limed fleshing with chicken manure, cow dung, and sawdust was heaped onto a horizontal bamboo frame. Three composting heaps were fabricated weighing 720, 700, and 760 kg. The turning of composting materials in the heaps causes temperature changes in the thermophilic range. The thermophilic temperatures in these heaps were 69.07 °C (heap 1), 69.9 °C (heap 2), and 69.19 °C (heap 3) which ensured the death of the pathogenic organism. The quality of compost was assessed based on the nutrients-nitrogen (N), phosphorous (P), potassium (K), and sulfur (S) content. NPKS in the compost fulfils the requirements of the investigated materials as compost. The largest amounts of metals- zinc (Zn), copper (Cu), chromium (Cr), lead (Pb), and nickel (Ni) of the compost detected in the heaps were, respectively, 200.3, 37.4, 20.3, 12.0, and 3.9 mg/kg. Cadmium (Cd) in the compost was below the detection limit. Scanning electron microscope (SEM) photographs show the decomposing of composting materials. This study indicates that limed fleshing can be converted into nutrient-enriched compost without any pretreatment. Using an easy, simple, and adaptable technique could reduce the volume of solid waste generated in the tannery to reduce environmental pollution.

Sustainable use of tannery sludge in brick manufacturing in Bangladesh.

Chromium-rich tannery sludge generated from tanneries has the potential to become a serious environmental burden in Bangladesh and a promising avenue for disposal of this sludge is by stabilizing it in clay brick products. But for sustainable industrial application of such technique it needs to be ensured first that the engineering properties of bricks as a building material are not diminished by addition of sludge, the process becomes energy efficient compared to alternatives and the use of such bricks do not pose any harmful environmental effects in the long run. In this study, clay bricks were prepared with different proportions of sludge (10%, 20%, 30% and 40% by dry weight) in both laboratory-controlled and field conditions and their suitability as a construction material was assessed based on their strength, water absorption, shrinkage, weight-loss on ignition and bulk density. For the sludge incorporated bricks, the compressive strength ranged from 10.98MPa to 29.61MPa and water absorption ranged from 7.2% to 20.9%, which in most cases met both the Bangladesh and ASTM criteria for bricks as a construction material. Volumetric shrinkage, weight loss and efflorescence properties of sludge-amended bricks were found to be favorable and it was estimated that an energy saving of 15-47% could potentially be achieved during firing with 10-40% tannery sludge-amended bricks. The quality of sludge-amended bricks made in the brick kiln was relatively inferior compared to bricks produced in the laboratory due to operating in a less-controlled environment with respect to maintaining adequate compaction and optimum moisture content. The leaching behavior of several heavy metals (Cr, As, Cu, Ni, Cd, Pb and Zn) from sludge-amended bricks has been found to be insignificant and far below the Dutch regulations and USEPA regulatory limits. Results from this study indicate that tannery sludge can be sustainably stabilized in clay bricks and large-scale application of this technique can be envisaged in the context of Bangladesh where brick remains a dominant building material.