This study was aimed to investigate the growth characteristics of living diet Platymonas subcordiformis for aquaculture animals and its harmful organism Oxyrrhis marina in co-culture systems to provide experimental evidences for discussing their succession processes. The colour changes of culture media of P. subcordiformis and growth characteristics of O. marina and P. subcordiformis in co-culture were analysed by the combined methods of macro-observation, microscopic examination and microscopic counting. The results showed that with the decrease of the initial density of O. marina cell (0.65×104 cells mL-1, 0.37×104 cells mL-1 and 0.11×104 cells mL-1 in P. subcordiformis culture media), the time that the population of O. marina reached the stationary phase required longer, were 4d, 5d and 7d after inoculated by O. marina, respectively, and the death time of all cells of P. subcordiformis became longer, were 9d, 10d and 12d after inoculated by O. marina, respectively. After inoculation 9d, pale pink appeared in upper layer of culture media of P. subcordiformis in flasks and the density of O. marina was 2.10×105 cells mL-1. The results also indicated that the variation tendency of cell densities of O. marina and P. subcordiformis cultured in aquariums were consistent with that in flasks basically, pink flocs appeared in upper layer of culture media of P. subcordiformis after inoculation 12d and the density of O. marina was 2.10×106 cells mL-1. The experimental results showed that the feeding of O. marina on P. subcordiformis was affected by the initial concentration of O. marina, and P. subcordiformis populations were evolved to O. marina populations during the 15 days culture period, the colour of culture media appeared pale pink to pink depends on density of O. marina was confirmed, too. Also, the colour changes of P. subcordiformis culture media are indications of pollution by O. marina, which will be important for culture process of P. subcordiformis.

Aquatic weed Myriophyllum spicatum L. is one of the most invasive water plants known. In many countries, it is usually harvested and landfilled, where aerobic and anaerobic decomposition takes place. In this research, the kinetic, equilibrium, and desorption studies of biosorption of Pb(II), Cu(II), Cd(II), Ni(II), and Zn(II) ions onto compost of M. spicatum were investigated in batch experiments. Biosorbent was characterized by scaning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). SEM analysis showed that ion exchange between divalent cations Ca(II) and selected metals takes place. The results of FTIR exposed that carbonyl, carboxyl, hydroxyl, and phenyl groups are main binding sites for those heavy metal ions. The rate of adsorption of the five heavy metals was fast, which achieved equilibrium in 40 min, and followed the pseudo-second-order model well. Langmuir, Freundlich, and Sips equilibrium adsorption models were studied, and Sips isotherm gave the best fit for experimental data. Desorption by 0.1 M HNO₃did not fully recover the metals sorbed onto the compost, indicating that reusing this material as biosorbent is not possible. Furthermore, the use of spent biosorbent as a soil fertilizer is proposed.

Arsenic (As) contamination of the environment has emerged as a concerning issue recently for which phytoremediation has been suggested as a viable solution. Hydrilla verticillata (L.f.) Royle is a widely distributed rapidly growing aquatic weed possessing significant potential to accumulate As and is thus a potential candidate for the purpose of As phytoremediation. In the present study, an investigation of thiol metabolism was conducted in H. verticillata, which revealed differential effects upon exposure to arsenite [As(III)] and arsenate [As(V)]. The accumulation of arsenic was found to be higher upon exposure to As(III) than to As(V). Besides, As(III) was found to induce the activities of enzymes, such as cysteine synthase and γ-glutamylcysteine synthetase and the amounts of cysteine and glutathione (GSH) to higher levels than that observed with As(V). The activity of glutathione-S-transferase was, however, stimulated to a higher level upon exposure to As(V) than As(III). The activity of arsenate reductase was found to increase upon As(V) exposure at all concentrations and durations. In addition, a significant stimulation in the activity of phytochelatin synthase was noticed in vitro with an increase in As/GSH concentration and time of incubation. Arsenic detoxification in H. verticillata thus appeared to involve an induction of thiol synthesis and consumption in a coordinated manner, though differentially upon exposure to As(III) and As(V). The information gained through this study would help in better designing of the pilot experiment at the field level depending on the chemical composition of the contaminated water.