J. Khatoon
Bangladesh University of Engineering and Technology, Bangladesh
M. D. Hossain
Professor
Civil Engineering Department, Bangladesh University of Engineering & Technology
Ammonia Removal, Anoxic Unit, Biodegradability, Sequential Batch Reactor.
Bangladesh University of Engineering and Technology, Bangladesh
Risk Management in Agriculture
Waste water, Leather/tannery
3.1 Collection of Wastewater Different wastewater streams are generated at different times and as a result, the effluent characteristics in the main drain vary significantly. Since no equalization tank is provided, the hourly samples collected over one production cycle are thoroughly mixed in a drum to make a representative tannery sample. Tannery wastes have a deficiency of nutrients for proper biological growth. For this, domestic sewage was added to the tannery sample at 1:4 (domestic: tannery) ratios. BOD5, COD, DO, pH, color, turbidity, total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), NH3-N, NO3-N, NO2-N, chromium, sulphate, sulphide were determined for identifying influent characteristics following standard methods (AWWA, 1998). Here influent wastewater has a biodegradation ratio equal to 0.58.
3.2 Acclimatization of Micro-organism Tannery wastewater is highly toxic and toxic impurities hinder the microbial activities, raw samples collected from tannery had to be seeded with acclimatized sludge. For acclimatization, textile sludge of 10 liters was kept at rest for 2 hours then sludge was separated from supernatant. Continuous aeration of textile sludge was started and 100 ml. of combined wastewater (tannery + domestic) was added every day. pH was adjusted between 6.0 and 7.0. COD and MLSS were measured from time to time. Continuous aeration was stopped where there was an indication of the increasing value of MLSS. This occurred after 30 days. For the first case (extended aeration activated sludge process), acclimatized sludge was mixed with the combined raw sample in the proportion of 200:800, 300:700 and 400:600 to make a 1L mixed sample. These proportions resulted in maintaining F/M ratios to 0.28, 0.22 and 0.18 respectively. Acclimatized sludge was added prior to aeration for all three cases. Both acclimatized sludge and combined raw sample were settled for two hours and settled sludge was mixed with the supernatant portion of the combined raw sample. But for the third case, settled sludge was mixed with the supernatant portion left after alum coagulation.
3.3 Experimental Set-up In order to examine the appropriate technology, ASP has been studied using two cases.
Two equal-volume Imhoff cones were used for two cases. The samples in the cone were continuously aerated with a diffuser. The rising velocity of air bubbles creates sufficient agitation in the waste. This agitation makes the contact between food and micro-organism, resulting in a higher rate of bacterial growth which has great importance in the biological treatment of tannery effluent. Due to the presence of a high quantity of ammonia in tannery wastewater, there is a necessity for the anoxic unit to remove ammonia in the form of nitrogen gas through denitrification. DO was 0.2 mg/l during the anoxic period. In case – 2, coagulation was conducted after secondary sedimentation. For coagulation, alum (Al2(SO4)3 .18 H2O) was used as coagulant because alum reduced COD and color. Used alum dose was 50 mg/l for the case of the oxicanoxic-oxic cycle. pH was kept between 6 & 7. DO (Dissolved Oxygen) of the reactor was maintained above 0.2 mg/l which is required for satisfactory biological treatment.
Journal of Engineering Science 06(1&2), 2015, 67-73
Journal