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Domestic wastewater treatment using upflow anaerobic sludge blanket (UASB) reactor with the addition of conductive materials

Mousoulea Aikaterini

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Summary

Urban wastewater management is currently one of the greatest challenges facing modern societies, as it is linked not only to the protection of public health and the natural environment, but also to the need to utilize energy and water resources. Conventional treatment technologies, although effective, often have limitations in terms of energy consumption and sludge management. In this context, anaerobic digestion has emerged as an alternative and particularly efficient process, capable of simultaneously offering high organic pollutant removal and biogas production. In particular, upflow anaerobic sludge blanket (UASB) reactors have found wide application internationally, thanks to their ability to operate with high organic loads, low energy consumption, and stable performance. This thesis focuses on investigating the effect of adding electrically conductive materials (ECM) to the operation of a laboratory UASB reactor that treats municipal wastewater. These materials, mainly represented by granular activated carbon, have emerged in recent years as a critical factor in enhancing the mechanism of direct interspecies electron transfer (DIET). This mechanism facilitates cooperation between bacteria that break down organic substrates and methanogenic microorganisms, ultimately resulting in increased methane production.The experimental setup included an anaerobic reactor with a capacity of approximately 8 liters, made of PVC and Plexiglas, with a height of 70 cm and an operating level of 65 cm. The reactor was fed with wastewater collected from the biological treatment plant of the Technical University of Crete and operated at temperatures of 25–30 °C, i.e., under psychrophilic conditions. The operation was divided into two phases: (a) operation without conductive materials and (b) operation with the addition of granular activated carbon (grain diameter 0.8–2.4 mm). During the experiments, systematic sampling and measurements of key parameters were carried out, such as chemical oxygen demand (COD), pH, production and composition of the biogas produced, and total solids (TS).The results of the first phase (without ECM) showed that the UASB reactor was operating satisfactorily, with COD removal ranging around 35%. Biogas production was continuous, with a production rate of 0.41 L/day. In addition, some fluctuations in pH were observed, which led to temporary deviations in system stability.In the second phase, after the addition of conductive materials, the picture changed significantly. The COD removal exceeded 50%. Biogas production increased by 85% compared to the first phase, at a rate equal to 0.76 L/day. At the same time, the system showed greater pH stability (6.8-7.9) and increased resistance to changes in organic load. In addition, Biochemical Methane Potential Tests (BMPs) of sewage sludge were carried out with the addition of different conductive materials, namely a) porous carbon generated from banana residues (BPC) and b) commercial granular activated carbon (GAC). The results showed that BPC had a slight negative effect on the process while the addition of GAC at high concentration had a slight positive effect. Overall, the study demonstrated that the addition of electrically conductive materials to UASB anaerobic reactors can lead to a significant improvement in their operation. The findings show that this technology contributes to both efficient removal and energy recovery, enhancing the sustainability of wastewater treatment plants. The combined improvement in organic pollutant removal, operational stability, and methane production highlights the importance of ECMs as an innovative tool in the field of environmental engineering.

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