Author : M. Ahsan Bin Habib

Summary : Three freshwater microalgae Chlorella vulgaris, Selenastrum gracile, and Ankistrodesmus convolutus showed high growth performances in terms of specific growth rate (SGR) of cell and chlorophyll a, total carotene, and observed yield when grown in inorganic media with sodium acetate. Total protein of S. gracile was higher than A. convolutus followed by C. vulgaris, whereas reverse trend was observed in the case of total lipid. Among the 11 essential amino acids (EAAs), phenylalanine, leucine, and lysine were found to be higher in C. vulgaris, S. gracile, and A. convolutus than other EAAs. All the evaluated polyunsaturated fatty acids (PUFAs) of C18, C20, and C22 were higher in C. vulgaris grown in Bold Basal Medium with sodium (Na) acetate (BBMAC) and Modified Medium with Na acetate (MMAC) than cultures in other media. In addition, S. gracile and A. convolutus grown in BBMAC and MMAC contained significantly (p < .05) higher amount of PUFAs except linolenic acid (18:3n-3) and eicosatrienoic acid (20:3n-6) than cultured in other media. All together, 26 essential minerals were detected and 22 essential minerals were quantified where total bioaccumulated minerals were below the optimum level and significantly (p < .01) correlated with these minerals available in media.

The growth performance of C. vulgaris, S. gracile, and A. convolutus cultures in 40 percent and 60 percent latex concentrate rubber effluent (LCRE), 60 percent standard Malaysian rubber effluent (SMRE), and 10 percent digested palm oil mill effluent (POMED) without and with NA acetate were significantly (p < .05) higher than other dilutions and the control (N:P:K). Total protein of C. vulgaris, S. gracile, and A. convolutus grown in these effluent media without Na acetate was significantly (p < .05) higher than those microalgae cultures in these media with Na acetate. Total lipid content followed almost a reversed trend of total protein. Among the EAAs, arginine, methionine, leucine, and lysine were synthesized in higher amounts in C. vulgaris and A. convolutes; and methionine, leucine, and lysine in reasonably higher amounts in S. gracile grown in these media without and with Na acetate. Among the PUFAs, C20 and C22 of the microalgae grown in this effluent with Na acetate were found in higher amounts than those cultured in the effluent without acetate. However, the PUFAs of C18 were found in higher amounts in microalgae grown in effluent media without Na acetate and the control.

The optimum growth and cumulative fecundity of rotifer was recorded in pH values ranging from 7 to 8, in ammonical nitrogen from 1 to 3 mg/L, in nitrate-nitrogen from 20 to 25 mg/L, in nitrite-nitrogen from 5 to 10 mg/L, and in orthophosphate below 20 mg/L.

The growth performances and total carotenoids of Brachionus calyciflorus fed on C. vulgaris cultured in 40 percent and 60 percent LCRE, 60 percent SMRE, and 10 percent POMED without and with Na acetate were significantly (p < .5) higher than B. calyciflorus fed on C. vulgaris grown in control. Due to poor growth performances of B. calyciflorus fed on S. gracile and A. convolutus, the nutritional values were not analyzed. However, higher protein was biosynthesized in B. calyciflorus fed on C. vulgaris grown in effluent media than that of B. calyciflorus fed on C. vulgaris grown in the media with Na acetate. Total lipid showed a reversed trend of total protein. B. calyciflorus fed on C. vulgaris grown in effluent media with Na acetate synthesized higher amounts of phenylalanine, methionine, leucine, and lysine than that fed on C. vulgaris grown in effluent media without Na acetate. B. calyciflorus fed on C. vulgaris grown in these media with Na acetate contained higher long chain PUFAs like C22 than C20 followed by C18 than B. calyciflorus fed on C. vulgaris grown in the effluent media without Na acetate. A total of 26 essential minerals were bioaccumulated in B. calyciflorus fed on C. vulgaris where concentrations of 23 essential ones were below the optimum level.

From the study, it was observed that B. calyciflorus contained relatively high essential micronutrients like methionine, leucine, lysine, PUFAs, and essential minerals when fed on C. vulgaris cultured in 40 percent and 60 percent LCRE, 60 percent SMRE, and 10 percent POMED with and without Na acetate.