Textile industries are one of the largest and vital industrial sectors of Bangladesh with regard to earn foreign exchange and labor employment, providing 4.5 million jobs of which 80% are women and contributes 13% to GDP [1]. This industry involves processing or converting raw material into finished cloth materials employing various processes, operations and consumes large quantities of water and produces extremely polluting waste effluents mostly by dyes and chemicals [2]. These dyes and chemicals, originating from the various steps of production in textile industry, in water often causes it AbstractThe work was conducted for improving textile effluent quality via turbidity removal by electrocoagulation (EC) using aluminum sacrificial electrode. Effluents were treated at 30 minutes and 30 volts (30min-30V) and 60 minutes and 40 volts (60min-40V) condition in a 1000 ml reactor cell with anode distance of 4 cm. Prior to EC experiment, physico-chemical parameters of effluent were measured and turbidity level was found eight times higher than the Department of Environment (DoE) standard. Turbidity removal ranged from 53 to 96.2% and 58 to 97.5% for condition one and two, respectively. Dissolved oxygen (DO) increased satisfactorily for both conditions. Total operational cost ranged from 62.50 to 70.41 taka/m 3 at 30min-30V and 159.57 to 187.7 taka/m 3 at 60min-40V. Moreover, sludge formation ranged from 6.73×10 -4 to 8.41×10 -4 kg in first condition and 1.21×10 -3 to 1.5431×10 -3 kg in second one. So, EC treatment was very effective and capable of elevating quality of the textile wastewater effluent in terms of turbidity to discharge into inland surface water. During EC operation it was also possible to lessen the total cost in maximum removal by changing the operating condition and 30min-30V was enough to get environmental friendly solution. Results will encourage the industry-owner to treat polluted effluents by EC.

Dissolved arsenic concentrations in the Ganges, Brahmaputra Rivers and confluence of these two rivers show important seasonal variations and maximum arsenic concentrations are observed during the monsoon season (July–October). These seasonal variations of dissolved arsenic concentrations were closely related to intense river-water discharge during the monsoon season with high arsenic-rich suspended particulate matter (SPM) loads. These arsenic-rich SPM mainly are primarily originated from erosion of agricultural land in upstream region irrigated with arsenic contaminated shallow groundwater and to some extent weathering of bed rocks. Considerable amount of iron and manganese enriched SPM adsorbs arsenic and increased water temperature in the summer accelerates microbially-mediated reduction of arsenic (V) to more soluble arsenic (III). Additionally, dissolution of solid arsenic-bearing mineral phases also attributes to high arsenic concentrations in water and causes seasonal variations. It is realized that the SPM of these two major rivers primarily controls the arsenic inputs into the Ganges-Brahmaputra-Meghna delta system. The cycling of arsenic in this delta is related to the monsoon seasonal dynamics, land use patterns and biogeochemical processes.Keywords: Arsenic; Ganges; Brahmaputra; Seasonal variation; Bangladesh.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i1.7820J. Sci. Res. 4 (1), 65-75 (2012)

Karnopara Canal water containing high COD values (1050 mg O2/L) was treated by electrocoagulation (EC) method covering a wide range of operating conditions such as, water pH, internal electrode distances, final pH, supplying 30V electricity for constant time period (30 minutes) through same electrode material (Al electrode). The effects of different operating parameters on the efficiency of the process were examined. Targeting to reduce the COD value within the recommended limit (200 mg O2/L), this research work was emphasized on EC treatment at the simplest and cheapest way. The batch experiment results showed that the high COD contained canal water can be effectively treated using electrocoagulation. The overall COD removal efficiencies have been obtained at 87.3%, under optimum operating conditions. Taking all the factors into account, it was found that polluted Karnopara canal water can be treated using EC consisting of Al electrodes without pre-adjustment of pH at laboratory. Therefore, EC technique to reduce high COD from canal surface water is found effective, cheaper and environmental friendly. DOI: http://dx.doi.org/10.3329/bjsir.v47i1.10728 Bangladesh J. Sci. Ind. Res. 47(1), 77-82, 2012

Abstract:Freshwater aquaculture is by far the most ancient aquatic living resource production system known in the world. An experiment was conducted to evaluate the growth performance of prawn and tilapia (male) under different sex (male and female) contribution of prawn in polyculture ponds for a period of four months from September 2010 to December 2010. The experiment was designed with 3 treatments like T 1 (All male Tilapia-4938/ha + All male Prawn 19,753/ha), T 2 (All male Tilapia -4938 / ha + All female Prawn 19,753/ha) and T 3 (All male Tilapia -4938/ decimal + all male Prawn 19876 + all female prawn 19876/ha), each with 2 replications. The mean stocking weight of prawn was 2.87 g and that of tilapia was 37.36 g. Total stocking density of prawn and tilapia (24,691/ha), basal fertilization (Cowdung 2470kg/ha, Urea 50kg/ha and TSP 50kg/ha), periodic fertilization (Cowdung 50kg/ha/day, urea 1.25kg/ha/day and TSP 1.25kg/ha/day) and feeding regime (diet containing 30% protein level at the rate of 2-5% of prawn and fish body weight twice daily) were same for all the treatments. Water quality parameters (water temperature, transparency, dissolved oxygen, pH, NH 3 -N and alkalinity) were monitored fortnightly and the growth parameters were monitored monthly. Mean values of water quality parameters were found within the suitable range. Treatment T 1 varied more significantly (P<0.05) than that of others for the mean values of growth parameters (final weight, weight gain, SGR, survival rate and yield) of prawn and tilapia.

The abundance of macro benthic organisms was observed from a migratory bird visiting lake in Jahangirnagar University, Savar for a period from July 2016 to June 2017. A total of 22 species belonging to three phyla (viz. Mollusca, Annelida and Arthropoda) and 14 families was recorded with maximum abundance in summer season and minimum in winter season. Molluscan population (37%) was dominant in benthos, followed by Annelida (31%) and Arthropoda (28%). Average values of water temperature, dissolved oxygen and water pH were within standard permissible ranges in the aquatic habitats of the country. Water and soil parameters were in suitable ranges for the growth and abundance of benthos. Correlation indicated that Mollusca and Annelida were closely dependent on water temperature, water pH, water depth, soil organic carbon and soil organic matters, whereas Arthropoda had less dependency on them. In the present study lower Shanon-Wiener diversity index (2.55-2.92) and low species richness (18-24) clearly demonstrated that the lake is moderately polluted.