Surface charge plays an important role in the mechanism of cell attraction. It was also supported by previous study that at neutral pH, microalgae reveal a slightly negative charge because of the presence of proton-active carboxylic, phosphoric, phosphor-diester, hydroxyl, and amine functional groups (Abdul Hamid et al., 2014, Hadjoudja et al., 2010 and Molina Grima et al., 2003). In this study, the zeta potential of surface charge microalgae was reported to be negative within the range from −10 mV to −35 mV while fungus was negative at <−10 mV, which is in agreement with what was reported by other researcher (Murugesan et al., 2014). Thus molecular repulsion of microalgae-fungus complex was likely to be contributed by their charges that force the aggregation of microalgae biomass within the matrix structure of fungus filamentous hyphae.
Fig. 4 shows the reduction of microalgae biomass with 10 different inoculations dosage of sewage fungus. The results showed that there was no observable reduction of microalgae biomass at the low concentration of fungal inoculation dosage (0–15 mg L−1). The water column was turbid and green in colour, indicating the presence of suspended microalgae biomass. Within the treatment period, inoculation dosage of 30 mg L−1was determined to be the optimum concentration for effective removal of suspended Chlorella sp. biomass with 99% removal percentage. This finding was supported by the studies of Gómez et al. (1988) andSitanggang et al. (2010) which stated that low concentration of fungus pellets could cause the decrease of the efficiency of microalgae removal.
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