Abstract
A pilot scale anaerobic sequencing batch reactor (ASBR) was operated at different organic loading rate (1.03, 1.23, 1.52 and 2.21 kg.m-3.d-1) in order to determine the chemical oxygen demand (COD) removal and methane production kinetic models. The system was operated at mesophilic temperature. The wastewater was fed using submersible pump in every twenty four hours and agitated with hydraulic pump for fifteen minutes in every one hour. The COD removal efficiencies was found to be between 69-85% and the methane yield was also between 0.17±0.2 and 0.30±0.02 m3/kg COD removed. In the kinetic studies, modified Stover-Kincannon and second-order models were found to be the most appropriate model for ASBR treating tannery wastewater than first order model. The saturation value constant and maximum COD removal rate found in Stover-Kincannon model were 5.57 and 5.56 kg of COD m-3.d-1, respectively. The kinetic studies of volumetric methane production showed that Michaelis-Menten model was found to be capable of predicting the volumetric methane production in ASBR that treat tanney wastewater. Key words: Anaerobic sequencing batch reactor (ASBR), chemical oxygen demand (COD) removal, Michaelis-Menten, second order, Stover-Kincannon.
Highlights
Tanning is almost a wet process that uses about 30 to 40 L of water/kg of hides or skin processed and discharges about 90% of the consumed water as wastewater (IFC, 2007)
The influent had high total nitrogen (TN), NH4+-N and sulfate values ranges from 451±47.5 to 517±112 mg/l, 231±45 to 270±66 mg/l and 390±76.9 to 520±99.13 mg/l, respectively; likewise, sulfide and phosphate concentrations ranged from 92.9±23.27 to 127±43.3 mg/l and 18±4.5 to 23.5±6.5 mg/l, respectively
The results of this study indicate that chemical oxygen demand (COD) removal efficiency was highest in the first phase of operation and lowest in the final phase of operation
Summary
Tanning is almost a wet process that uses about 30 to 40 L of water/kg of hides or skin processed and discharges about 90% of the consumed water as wastewater (IFC, 2007). The wastewaters, which are discharged without proper treatment, would contaminate surface and ground water as well as soils. A tanning industry can cause groundwater pollution of about 7 to 8 km radius (Mondal et al, 2005). There are more than 30 tanneries under operation in Ethiopia. These tanning industries generate 11,312 m3 wastewater per day and disposed to the surrounding water bodies without proper treatments (LIDI, 2010). It is characterized by a high load of pollutants which require proper treatment before it would be discharged into the receiving water body.
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