Simultabeous removal of colour, organic compounds and nutriens from synthetic wastewater containing Azo dye using aerobic-anaerobic baffled constructed wetland reactor

This thesis presents an improved approach on the simultaneous removal of colour, organic compounds, and nutrients from wastewater containing azo dye by using multiple zoned aerobic and anaerobic baffled constructed wetland reactors. Conventional constructed wetlands lack the provision of sequential aerobic and anaerobic treatment which is essential in the treatment of azo dyes, nutrients and organic compounds. An aerobic and anaerobic constructed wetland reactor is operationally and economically advantageous to adopt in the treatment of wastewater containing azo dye since the combination of these processes has the capability to mineralize organic compounds, decolourize colour from dye, aerobically nitrify and anaerobically denitrify nutrients in the wastewater. Acid Red 27 (AR27) was chosen as the model pollutant due to the wide usage and harmful nature which may cause adverse effects in human and animals besides being classified as an endocrine disruptor. The first part of this study involves the investigation of the performance of this system for nitrogen and organic compounds removal. The second part comprises of the introduction of AR27 into the system and the effects of AR27 on the performance of the system. Final part of the study revolved around the detailed analysis of the complete decolourization and mineralization of AR27. Besides that, a degradation pathway was proposed based on that analysis. The Aerobic - Anaerobic Baffled Constructed Wetland Reactors (ABCW) comprises of 5 vertical baffles that ensures an upward and downward flow within the system, which provides a longer treatment pathway through the wetland media. The ABCW reactor were planted with P.australis, where the hydraulic retention time was set to 1 day and fed with synthetic wastewater containing AR27. Intermediate aeration was supplied to control the aerobic and anaerobic zones within the system to enable the pollutants to pass through a series of sequential aerobic and anaerobic treatment. Performance of the ABCW was evaluated in terms of COD, NH4 +, NO3 - removal, decolourization and mineralization. Aerobic and anaerobic conditions were monitored through the ORP profiles while mineralization of organic compounds and proposed degradation pathway was conducted by several detailed analyses. The ABCW reactors demonstrated good performance in the simultaneous removal of colour, organic compounds, and nutrients, as COD removal ranged from 88 to 98%; NH4+ removal ranged from 93 to 98%; achieved 100% colour removal and complete mineralization of AR27 metabolites. This performance of the ABCW could be attributed to the long pathway travelled by the wastewater hence increasing contact time of pollutants with microbes and rhizomes. The synergistic effect of the combination of rhizomes, microbes and supplementary aeration also played an important role in the high performance of the ABCW reactor.