Abstract
Most of the leather industries in Ethiopia discharge their effluent partially or without any treatment to the nearby water bodies. This creates a serious effect on aquatic biota and surrounding environment due to its high organic loading and chromium content. To minimize the effect, tannery wastewater should be treated before the effluent is discharged to the environment. Therefore, the main objective of the study was to use a two stage laboratory scale Anaerobic Sequence Batch Digester (Reactor) in order to investigate the potential of composite tannery wastewater to produce biogas. Two Stage Anaerobic Sequence Batch Digester was used because it has a conducive environment for micro-organisms at different temperature. The present study characterized composite tannery wastewater with respect to biogas production parameters. Four sets of conditions were investigated: Mesophilic to mesophilic; thermophilic to thermophilic; mesophilic to thermophilic and thermophilic to mesophilic in the hydrolysis/acidification and methanogenesis stages (reactors), respectively. The Organic Loading Rate (OLR) was ranged between 9.58 and 10.28 kg COD/m3 day throughout the study. The highest volume of biogas (7232 ml) and content of methane (69.75%) was in the thermophilic‑thermophilic phase. The removal efficiency of total solid (TS) and volatile solids (VS) of all digesters were in the range of 52 to 69 and 58 to 81%, respectively, treatment of composite tannery wastewater by a two stage Anaerobic Sequence Batch Digester (Reactor) (ASBR) produces high amount of methane at thermophilic - thermophilic phase and the lowest produced in mesophlic- mesophlic phase. Digesters in mesophilic-thermophilic (D3) produced higher biogas and biogas quality than digesters with thermophilic- mesophlic (D4) ones. Key words: Anaerobic sequential batch reactor, wastewater to energy, tannery wastewater management.
Highlights
IntroductionAccumulation of large volumes of dried-sludge in treatment compound has become common (Leta et al, 2004)
Using measuring cylinder based on the aformentioned ratio, the composite samples were prepared at Modjo Tannery, and for every seven days, 20 L composite sample was prepared and transported to the research lab at the Centre for Environmental Sciences, Addis Ababa University, and stored at 4°C in the refrigerator until it was added to the digester for treatment
The average total solid (TS) of the substrate was 8.06%, the appropriate amount of the feedstock as the most favorable percentage of TS for biogas production is in the range of 8 to 10% (Jurgen et al, 2009; Ituen et al, 2007)
Summary
Accumulation of large volumes of dried-sludge in treatment compound has become common (Leta et al, 2004). This has immediate public health implications, which are manifested as frequent outbreak of major epidemic diseases and contributes to climate change as it releases greenhouse gases; methane and carbon dioxide (Abera, 2010). The industrial strategic development plan of Ethiopia gives great emphasis to improve export-led products to join the international market in large-scale such as leather products.
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