Hybrid system up-flow constructed wetland integrated with microbial fuel cell for simultaneous wastewater treatment and bioelectricity generation

Environmental pollution, particularly water pollution and energy crisis, are two significant challenges that our world is facing nowadays. This phenomenon has driven the exploration of sustainable wastewater treatment technology to address both challenges hand in hand. This thesis aimed to develop a hybrid system, which is up flow constructed wetland integrated with microbial fuel cell (UFCW-MFC) for simultaneous wastewater treatment and bioelectricity generation. The main objectives of the study were to investigate the feasibility, performance in terms of wastewater treatment and bioelectricity generation, the role of wetland plant, working principle and mechanism in UFCW-MFC. Six hybrid reactors were developed for a series of systematic study. Redox gradient present along the wetland bed was suitable for oxidation and reduction processes, and at the same time, they are needed by MFC as anaerobic anode and aerobic cathode. The present study revealed that the closed circuit system enhanced the organic matter degradation, denitrification and decolourisation, which inferred that the integration of CW into MFC can achieve higher treatment efficiency than CW and MFC standalone system. Besides that, the presence of plant achieved more promising result in bioelectricity generation compared to plant-free system. Wetland plant significantly contributed oxygen to the cathodic region through photosynthesis process. The increased sodium chloride concentration increased the conductivity and subsequently improved power generation. Furthermore, the study showed that aeration influenced power performance more than the electrolyte conductivity. The intermittent aeration at the rate of 600 mL/min found to be optimum for COD, nutrient removal and energy recovery. The fate of electron transport in UFCW-MFC in the presence of multiple electron acceptors (anode, azo dye and nitrate) was investigated. The presence of various pollutants, which are electron acceptor in anodic region, competed for electron and the most favourable electron acceptor in the study was nitrate, followed by azo dye and anode. Moreover, the influence of azo dye molecular structure on decolourisation rate and bioelectricity generation was investigated by using Acid Red 18 (AR18), Acid Orange 7 (AO7) and Congo Red (CR). The highest decolourisation rate was obtained from AR18 (96%), followed by AO7 (67%) and CR (60%). The power output also followed such trend. The higher decolourisation rate in AR18 was due to tautomerism, lower number of azo bond, more electron withdrawing groups and the position of electron withdrawing group substituent at para position to azo bond. Moreover, the degradation pathways of azo dyes were proposed and elucidated based on the respective dye intermediate products identified through UV-Vis spectrophotometry, high-performance liquid chromatography and gas chromatograph–mass spectrometer analyses. The results indicated that the dyes were decolourised at the anaerobic anodic region, and dye intermediates were further mineralized at the aerobic cathodic region to less harmful or non-toxic products