Tannery Wastewater Treatment using Alkaliphilic Sediment Inoculum in Anoxic-Oxic Bioprocess
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Date
2011-04
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Addis Ababa University
Abstract
Tanning is one of the oldest industries known by its voluminous wastewater and the use of hugetype and amount of chemicals. In Ethiopia there are over twenty tanning industries. Most ofwhich release their wastes without pretreatment. TWW is known particularly by its highorganic load, nitrogenous, sulfide and chromium contents and by its salinity and alkalinity. Inthe presence of these toxic substances and saline and alkaline conditions, TWW treatment bybiological methods using conventional neutrophilic organisms is hardly efficient. The objectiveof this study was to treat TWW by naturally alkaliphilic sludge obtained from Soda Lake Chituwater and sediment using lab-scale anoxic-oxic activated sludge treatment system and toevaluate the adaptability of the inoculated sludge to the toxic tannery wastes. The efficacy ofthe alkaline sludge and performance of the reactors was evaluated by analyzing COD, TN,NH4 +, S2-, SO4 2-, NO3 -, Crtot, MLVSS, MLSS and pH of the raw and treated TWW. The systemwas operated on continuous basis, but physicochemical data was obtained at specific OLR of1.92gCOD/L/d and 1.64gCOD/L/d at feed 1 and feed 2 respectively. The system was able toremove 99% S2-, 93%TN and 89% NO3 - at feed 1 and 96% NH4 +, 93% COD and 92% Crtot atfeed 2 from raw TWW. The result showed that at relatively high OLR there was slightly betterremoval of sulfides, TN and nitrate but higher removal of COD, ammonia and chromium wasobserved at comparatively lower OLR. In addition, the treatment process was effective inremoving the color and notorious odor of TWW. Among the key factors of the activated sludgein treating the nitrogenous TWW are denitrifying bacteria. Adaptability of inoculatedmicroorganisms to the TWW was evaluated by isolating denitrifying bacteria from theinoculant lake sediment and from the steady state treatment system. Comparative characterizations of these isolates showed that there was little difference in their pH optima(9.5-10.5) and range, chromium tolerance (250-2500mg/l) and preferences to energy sources.Also the differences in their cell wall chemistry (<3%), colony morphology, starch hydrolyzingability and catalase reaction were minimal. But remarkable difference was evident in nitratereducing ability and salt tolerance. Denitrifying isolates obtained from the treatment systemwere found to be complete nitrate reducers, incomplete nitrate reducers, exclusively nitritereducers and both nitrite and nitrate reducers, but isolates from the inoculum were onlycomplete and incomplete nitrate reducers. Presence of exclusively nitrite reducers, both nitriteand nitrate reducers and tolerance to high salinity by the denitrifying isolates obtained fromthe treatment system (DS) showed a shift in denitrification function by the inoculated microbialcommunity. The shift in denitrification function and tolerance to high salinity conditions by theDS isolates was supposed to be associated to the adverse nature of TWW and strict anoxiccondition to which the bacteria adapt the new environment than resisting it.
Key words: Tannery wastewater; Lake Chitu, alkaliphiles; denitrifying bacteria; lab scaleactivated sludge.
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Keywords
: Tannery wastewater; Lake Chitu, alkaliphiles; denitrifying bacteria; lab scale activated sludge