Abstract
Anaerobic digestion technology provides an alternative route for sustainable management of organic waste. In this study, the performance of the hybrid upflow anaerobic sludge blanket (HUASB) reactor consisting of synthetic grass media as attached growth surface was investigated for the treatment of cattle slaughterhouse wastewater under mesophilic (35 ± 1 °C) condition. After acclimatization with synthetic wastewater, the reactor was loaded up to OLR 10 g L−1d−1, corresponding to 20 g COD/L at a varying hydraulic retention time (HRT) of 24, 30, 36, 42, and 48 h. The system attained a maximum COD removal efficiency of 97% total suspended solids (TSS), volatile suspended solids (VSS), fats, oil, and grease (FOG), color removal, and turbidity were found as 97%, 284 mg/L, 79%, 78%, and 91% respectively. The biogas production after 48 h was found as 38 L/d, with about 85% methane and specific methane production of 0.24 LCH4/gCODadded. The ratio of alkalinity was 0.22, while ammonia nitrogen concentration reached a maximum of 839 mg/L at a steady state. Scanning electron microscopic (SEM) analysis revealed a predominance of Methanosarcina bacteria with the coccoidal shape at the end of the performance study. Therefore, the results of the experiment showed that increasing HRT significantly affects the performance of the system.
Highlights
Commercial cattle slaughterhouse wastewater is considered to be high-strength industrial wastewater due to high chemical oxygen demand (COD), biological oxygen demand (BOD), fats, oil, and grease (FOG), and total suspended solids (TSS)
organic loading rates (OLR) 0.5 and 1.5 g/L, reaching 96% at a steady-state OLR of 1.75 g/L. These results indicate that the acclimatization period of the seed sludge was over, and the reactor was ready to receive raw slaughterhouse wastewater exclusively
The results revealed that hydraulic retention time (HRT) of 48 h was sufficient enough to produce high biogas with high methane content
Summary
Commercial cattle slaughterhouse wastewater is considered to be high-strength industrial wastewater due to high chemical oxygen demand (COD), biological oxygen demand (BOD), fats, oil, and grease (FOG), and total suspended solids (TSS). Discharge of untreated and improperly treated slaughterhouse wastewater into a receiving water body affects the quality of water mainly by introducing macronutrients (nitrogen and phosphorus), resulting in excessive growth of algae in the receiving water surface and reduction of dissolved oxygen supply to the aquatic environment. The absence of dissolved oxygen supply to the aquatic environment could result in the death of the aquatic animals as a result of eutrophication. Eutrophication effect subjects the aquatic environment to anaerobic condition, leading to the release of a large amount of methane (CH4 ) and carbon dioxide (CO2 ) freely into the atmosphere. The release of these gases forms a large portion of greenhouse gases. The high concentration of color in the slaughterhouse wastewater (SWW) could impede light penetration to the aquatic environment
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