Abstract
The tanning process generates a saline effluent with high residual organics, sulfate and sulfide concentrations. The transition from a linear to circular economy requires reimagining of waste streams as potential resources. The organics in tannery effluent have the potential to be converted to renewable energy in the form of biogas if inhibitors to anaerobic digestion are removed. Hybrid linear flow channel reactors inoculated with culture-enriched halophilic sulfate reducing bacteria from saline environments were evaluated as a novel pretreatment step prior to anaerobic digestion for the concurrent removal of sulfur species and resource recovery (elemental sulfur and biogas). During continuous operation of a 4-day hydraulic retention time, the reactors were capable of near-complete sulfide oxidation (>97%) and a sulfate reduction efficiency of 60–80% with the formation of a floating sulfur biofilm containing elemental sulfur. Batch anaerobic digestion tests showed no activity on untreated tannery effluent, while the pretreated effluent yielded 130 mL methane per gram COD consumed.
Highlights
Tanning is the chemical process of transforming animal hides and skin to leather
A thin floating sulfur biofilm (FSB) formed on the surface of the reactor within the first 24 h after start-up, and a week later, there was a noticeable reduction in the odor
The analysis showed that HLFCR1 utilized notably more soluble chemical oxygen demand (COD) than was required for Biological SO4 2− reduction (BSR) over each HRT, while the soluble COD utilization across the Hybrid Linear Flow Channel Reactors (HLFCR) in series was almost double what could be attributed to the sulfate reduction (SR)
Summary
Tanning is the chemical process of transforming animal hides and skin to leather. It is one of the oldest raw material processing techniques in the world and is an important economic activity in many developing countries [1].The tanning process is chemically intensive and generates large quantities of highly turbid, saline and foul-smelling effluent that is laden with toxic metal salts such as chromium (Cr3+ ) and suspended solids, as well as organic residues and high concentrations of inorganic ammonium (NH4 + ), sulfates (SO4 2− ) hydrogen sulfides (HS− ), sodium (Na+ ) and chlorides (Cl− ) [2,3,4]. Tanning is the chemical process of transforming animal hides and skin to leather. It is one of the oldest raw material processing techniques in the world and is an important economic activity in many developing countries [1]. To meet ever-increasing environmental standards, three or four stages of treatment are required to remediate TWW to comply with legislated discharge criteria worldwide. These include preliminary treatment to screen out coarse material; primary treatment to remove suspended solids, metals and sulfides and secondary treatment to reduce the organic and other macronutrient loads. Secondary processes are typically aerobic biological systems or advanced oxidation systems [3]
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