Laboratory scale studies on removal of chromium from industrial wastes

Chromium being one of the major toxic pollutants is discharged from electroplating and chrome tanning processes and is also found in the effluents of dyes, paint pigments, manufacturing units etc. Chromium exists in aqueous systems in both trivalent (Cr 3+) and hexavalent (Cr 6+) forms. The hexavalent form is carcinogenic and toxic to aquatic life, whereas Cr 3+ is however comparatively less toxic. This study was undertaken to investigate the total chromium removal from industrial effluents by chemical means in order to achieve the Pakistan NEQS level of 1 mg/L by the methods of reduction and precipitation. The study was conducted in four phases. In phase Ⅰ, the optimum pH and cost effective reducing agent among the four popular commercial chemicals was selected. As a result, pH of 2 was found to be most suitable and sodium meta bisulfate was found to be the most cost effective reducing agent respectively. Phase Ⅱ showed that lower dose of sodium meta bisulfate was sufficient to obtain 100 % efficiency in reducing Cr 6+ to Cr 3+, and it was noted that reaction time had no significance in the whole process. A design curve for reduction process was established which can act as a tool for treatment of industrial effluents. Phase Ⅲ studies indicated the best pH was 8.5 for precipitation of Cr 3+ to chromium hydroxide by using lime. An efficiency of 100 % was achievable and a settling time of 30 minutes produced clear effluent. Finally in Phase Ⅳ actual waste samples from chrome tanning and electroplating industries, when precipitated at pH of 12 gave 100 % efficiency at a settling time of 30 minutes and confirmed that chemical means of reduction and precipitation is a feasible and viable solution for treating chromium wastes from industries.

The influence of old leather tannery district on chromium contamination of soils,water and plants

The paper demonstrates the actual level of chromium contamination at the site of the old tannery waste lagoon in Serniki community (SE Poland). Despite the fact that since 1994 this area is not exploited, the chromium presence is still detected in soil, water and plants. The current study is the 4th phase (after 1989, 2001 and 2004) of checking and controlling the chromium concentration in this territory. The chromium content was assessed after soil and plant mineralization using FAAS method. Total chromium concentrations in soil samples reached values of 2.25 - 18.25 mg·kg-1 dry mass. Levels of chromium in water samples ranged between 0.008 and 0.017 mg·dm-3 for Wieprz River and the trough, situated in the tannery centre, respectively. Absorption of chromium by plants depended from the plant species. The highest Cr content in the stalks of Oenothera biennis, whilst the lowest in Phragmites australis were detected. Finally, it was assumed that soil chromium content noted in 2009 was by 42% - 83% lower in relation to the data from 2004. Consequently, nowadays the tannery waste lagoon site is not so threat to the health of local residents and to the surrounding ecosystem.

Research progress on resource utilization of leather solid waste

Leather making is the process of converting raw hides into leather.Amounts of solid waste containing hazardous and high value components are generated during this process.Therefore,the elimination of the potential pollution and resource utilization of leather solid waste are the primary research hotspots.Herein,we comprehensively review the recent advances in the resource utilization of leather solid waste generated from chrome tanning including the utilization of tannery hair waste,untanned solid waste,chrome-containing leather solid waste,tannery sludge and finished leather waste,emphasizing on the general and novel utilization approaches.Finally,the remaining challenges and perspectives were summarized,in order to accelerate the development of resource utilization of leather solid waste.