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Includes references (111-140 p.)

'ABSTRACT Microalgae serves as tiny aerators in a natural system, thereby producing oxygen for other bacteria and acting in fixing carbon dioxide produced by bacteria in a symbiosis system. The present optimization study tends to investigate a method for microalgaebacteria consortia biomass determination in a symbiosis system grown in a microbiology nutrient broth. The proposed method explored the use of chlorophyll-a concentration to derive the dry cell weight of the microalgae and hence used to get the dry cell weight portion of the bacteria in the mixed culture medium. Dry cell weight and determined average biomass productivities of microalgae with bacteria mixture gave final concentration of 0.198 g/L 0.015 ± 0.002 g.L-1.day-1 respectively. The dry cell weight and determined average biomass productivities of bacteria with microalgae mixture gave final concentration of 3.36 g/L and 0.33 ± 0.004 g.L-1.day-1 respectively. From the result, the microalgae in symbiosis relationship with bacteria showed the maximum specific growth rate of 0.184 day-1 and doubling time of 3.76 days. Bacteria in symbiosis relationship with microalgae showed the best specific growth rate of 0.60 day-1 and doubling time of 1.17 days. The method explored in the study has shown great potential for determination of microalgae-bacteria biomass in symbiosis system. Biotreatment of leachate by microalgae-bacteria in a sequencing batch mode using a photobioreactor was investigated. The microalgae-bacteria biomass initial concentration was maintained at 1:3 ratio. The increase in the initial concentration of the biomass in the 2nd batch favoured biomass growth, doubling biomass productivity, compared to the 1st batch. In both batches, N-NH4 was completely removed from the leachate. In the 2nd batch, the nitrate, COD and phenol removal efficiencies were above 90%. The relative toxicity reduced from 57.32 to 1.12% at the end of 2nd batch. The fatty acids content (C16-18) varied from 85.47 to 87.65% for the 1st batch and 86.72 to 87.69% for the 2nd batch. The crude glycerol content varied from 34.54 to 42.36% for the 1st batch and 33.64 to 39.55% for the 2nd batch. The coexistence of microalgae and bacteria played an important role in leachate treatment and biomass production for biorefinery purposes. Keywords: Landfill leachate; Sequencing batch mode; Microalgae; Bacteria; Biomass productivity.'