Optimization of simultaneous biomass production and nutrient removal by mixotrophic Chlorella sp. using response surface methodology.

The bioprospecting of potentially mixotrophic microalgae in a constructed wetland was conducted. A locally isolated microalga, Chlorella sp., was grown to determine the effect of temperature, aeration rate, and cultivation time on simultaneous biomass production and nutrient removal from piggery wastewater using central composite design (CCD). The most important variable for the biomass productivity of Chlorella sp. was aeration rate, while that for lipid content and nutrient removal efficiency was cultivation time. Total nitrogen (TN) and total phosphorus (TP) removal efficiencies were higher than that of chemical oxygen demand (COD) from piggery wastewater. The CCD results indicate that the highest biomass productivity (79.2 mg L(-1) d(-1)) and simultaneous nutrient removal efficiency (TN 80.9%, TP 99.2%, COD 74.5%) were obtained with a cultivation temperature of 25 °C, a cultivation time of 5 days, and an air aeration rate of 1.6 L L(-1) min(-1). Palmitic acid (C16:0) and linoleic acid (C18:2) were both abundant in Chlorella sp. cells under mixotrophic cultivation with piggery wastewater.

Integrated estuary management for diffused sediment pollution in Dapeng Bay and neighboring rivers (Taiwan).

This work investigated sediment samples collected from Dapeng Bay and three neighboring rivers (Kaoping River, Tungkang River, and Lingbeng River) in southwestern Taiwan, Republic of China. Multivariate statistical analysis techniques, i.e., factor analysis, cluster analysis, and canonical discriminant analysis were used for the evaluation of spatial variations to determine the types of pollution and to identify pollutant sources from neighboring rivers. Factor analysis results showed that the most important latent factors in Dapeng Bay are soil texture, heavy metals, organic matter, and nutrients factors. Contour maps incorporating the factor scores showed heavy metals accumulate along the lakesides, especially on the southeastern banks of the lakes. A cluster analysis was performed using factor scores computed from these latent factors. We then classified these areas into five distinct classes using sampling stations, and we illustrate that in the three river classes, the sediment properties are influenced by industrial and domestic wastewater and agricultural activities (including livestock rearing and farm activities). However, in Dapeng Bay, the rivers were influenced more by complicated biogeochemical processes; these could be identified as a type of pollution. Canonical discriminant analysis illustrated that two constructed discriminant functions made a marked contribution to most of the discriminant variables, and the significant parameters of porosity and Cd, Cr, Al, and Pb content were combined as the "heavy metal factor". The recognition capacities of the two discriminant functions were 82.6% and 17.4%, respectively. It is also likely that the annual mean of the water exchange rate is insufficient (taking about 7 days to eliminate pollutants) and therefore has significantly influenced the carbon and nutrient biogeochemical processes and budgets in the semi-enclosed ecosystem. Thus, the sediment properties are not similar between the lagoon and the neighboring rivers. Our results yield useful information concerning estuary recovery and water resources management and may be applicable to other basins with similar characteristics that are experiencing similar coastal environmental issues.

Effect of ozone and permanganate on algae coagulation removal--pilot and bench scale tests.

Both pilot and laboratory scale experiments are conducted to compare the effect of ozone and permanganate preoxidation on algae removal by alum coagulation. Both appropriately dosed preoxidants are shown to be beneficial to algae coagulation removal. This may be attributed to a decrease in cell stability; however, overdosing may cause cell lysis and the release of organics, which could interfere with algae cell coagulation. The presence of calcium further enhances the beneficial effect of preoxidation on algae coagulation; however, this phenomenon is more significant for using permanganate than ozone. It is speculated that this is due to the fact that the positively charged calcium ions can serve as bridges to hold the negatively charged MnO(2) and algal cells together. Further, this behavior also explains the superior performance of permanganate preoxidation compared to that obtained using ozone for algae coagulation removal in pilot testing, as the source water contains high calcium content.

Identification of pollution of Tapeng Lagoon from neighbouring rivers using multivariate statistical method.

This work investigated water samples collected from Tapeng Lagoon and three neighbouring rivers (the Kaoping River, Tungkang River and Lingbeng River) in Taiwan, Republic of China. Canonical discriminant analysis was applied to identify the source of pollution in neighbouring rivers outside Tapeng Lagoon. The two constructed discriminant functions showed a marked contribution to all discriminant variables, and the total nitrogen, algae, dissolved oxygen and total phosphate were combined as the nutrient effect factor. The recognition capacities of the two discriminant functions were 95.6% and 4.4%, respectively. The water quality in the Kaoping River most strongly controlled the water quality in Tapeng Lagoon. Disassembling the oyster frames and fishery boxes had improved the water quality markedly. The methodology and results provide useful information concerning watershed management and may be applicable to other basins with similar properties that are experiencing similar coastal environmental issues.

Water quality during development and apportionment of pollution from rivers in Tapeng Lagoon, Taiwan.

This work investigated water samples collected from Tapeng Lagoon, Taiwan. Factor analysis was conducted to explain the characteristics and the variation in the quality of water during the disassembly of oyster frames and fishery boxes. The result shows that the most important latent factors in Tapeng Lagoon are the ocean factor, primary productivity factor, and the fishery pollution factor. Canonical discriminant analysis is applied to identify the source of pollution in neighboring rivers outside Tapeng Lagoon. The two constructed discriminant functions (CDFs) showed markedly contribution to all discriminant variables, and that total nitrogen, algae, dissolved oxygen and total phosphate, combined in the nutrient effect factor. The recognition capacities in these two CDFs were 95.6%, 4.4%, respectively. The water quality in the Kaoping river most strongly determined that in the Tapeng Lagoon the best is. And disassembling the oyster frames and fishery boxes improves the water quality markedly. However, environmental topographic conditions indicate that strengthening stream pollution prevention and to constructing another entrance to the ocean are the best approaches for improving the quality of water in Tapeng Lagoon, especially by reducing eutrophication. These approaches and results yield useful information concerning habitat recovery and water resource management.

The mechanisms of potassium permanganate on algae removal.

The effect of potassium permanganate as preoxidant for algae-laden source water and the mechanism that it causes algae cells aggregation was investigated. Synthetic algae suspensions, prepared from lab-cultured Chodatella sp., were used for batch preoxidation and settling tests. In order to study the effect of water hardness on the function of permanganate, some algae suspensions were spiked with CaCl2 solution. Experiments with preformed MnO2 to look into its effect on algae cell aggregation were also conducted. The results show that preoxidation with potassium permanganate would promote the aggregation of algae cells, and this phenomenon was even more significant with the existence of hardness causing ion, calcium. In addition to incorporating its reducing product, MnO2, into algae floc, and increased its specific gravity, and therefore its settling velocity, permanganate may also induce the release of extracellular organic matters (EOM) from algae cell. Based on SEM observation, EOM probably enhanced the incorporation of MnO2 into algae floc. The role played by calcium ion in promoting the function of permanganate can be explained by charge neutralization and also bridging between negatively charged surfaces.