Tannery effluent, Chemical parameters, Chromium, Water hyacinth
The study area is comprised of tannery area in Hazaribagh Thana situated on the Southwestern part of Dhaka city, Bangladesh. It is located between 23°45′ to 23°44′ north latitudes and 90°21.85′ to 90°22.15′ east longitudes. Firstly, 2.5 L effluent sample was collected in plastic bottles from chrome tanning sector of tannery industry for analyzing initial characteristics. Then, 21 L effluent sample was collected again from the same source for treatment purpose by using water hyacinth (Eichhornia crassipes) and sedimentation. Water hyacinth samples were collected in polythene bags from nearby ponds of Mawlana Bhashani Science and Technology University (MBSTU) Campus, Tangail. For phytoremediation process, 2 separate buckets each with 7 L of effluent were taken and surface of the effluents in both buckets were covered by water hyacinth. Then, one was exposed in open air for 7 days and another was for 15 days. Again, another bucket with 7 L effluent was taken, and then exposed in open air for 15 days without water hyacinth. Treatment of effluent by using water hyacinth was conducted for two separate time duration: 7 and 15 days. On the other hand, treatment by sedimentation process (without water hyacinth) was conducted for 15 days only. Phytoremediation of tannery effluent was experimented by water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes). Water samples were collected from the same source at the time for both studies. The initial values of the chemical parameters and Cr were estimated also and already it has been published in Akter et al. (2014). These values were used as initial values here in the present study. Each of the effluent sample (100 mL) was filtered through filter paper (Whatman No. 41; 0.45 µm pore size). Filtrate and the collected effluent samples (100 mL each) were preserved with 2 mL concentrated nitric acid to prevent precipitation of Cr. Then, these effluent samples were diluted 20 times with distilled water and subjected to digestion with 5 mL di-acid mixtures. After digestion, samples were again filtered and diluted 10 times. Three samples of water hyacinth were collected from each bucket and were thoroughly washed to remove all adhered soil particles. Then, samples were cut into small pieces, air dried for 2 days and finally dried at 100OC in hot air oven for 4 hours. In warm condition, the samples were finely ground. Fine powder of water hyacinth samples were subjected to acid digestion (Lokeshwari and Chandrappa, 2006). Another 3 plant samples were taken before grown in the bucket for initial analysis. The pH of water samples was measured by using a pH meter (WTW pH 522, Germany), Total Dissolved Solids (TDS) was measured by TDS meter, and Electrical Conductivity (EC) was measured by EC meter (HM digital, Germany). Biochemical Oxygen Demand (BOD) was determined by using 5 days incubation method (APHA, 2012). The concentration of Cr in water and plant samples were analyzed by atomic absorption spectrophotometer (AA-7000, Shimadzu, Japan) (APHA, 2012).