Kwong-Yu Chan

The effects of diesel oil and oil dispersants on growth, photosynthesis, and respiration ofChlorella salina

Low concentrations of BP light diesel (0.05%) and the oil dispersant BP1100X (0.005%), either alone or in mixture, stimulated the growth rate, biomass yield, chlorophyll a level and photosynthesis of the estuarine green algaChlorella salina CU-1, while the same concentrations slightly inhibited algal respiration. The increase in the level of chlorophyll a may be one of the factors leading to elevated photosynthesis. BP light diesel and BP1100X at higher concentrations, as well as the oil dispersants BP1100WD and Shell Oil Herder at all the tested concentrations, reduced growth, chlorophyll a level, photosynthesis, and respiration of the algal cells. The inhibitory action of BP light diesel and the oil dispersants was concentration-dependent. Although both algal photosynthesis and respiration were reduced by BP light diesel and the oil dispersants, the effect on respiration was less severe when compared with that on photosynthesis. Shell Oil Herder, either alone or in combination with BP light diesel, were most toxic among the three oil dispersants tested. In general, mixtures of BP light diesel and any one of the three oil dispersants were more toxic than the diesel oil or the oil dispersants alone. However, the stimulatory effect exerted by the mixture of 0.05% BP light diesel and 0.005% BP1100X was greater than those by the same concentrations of BP light diesel and BP1100X alone.

Metal contents of the two marine algae found on iron ore tailings

Abstract The two marine algae, Chaetomorpha brychagona and Enteromorpha crinita are found abundantly on the iron ore tailings of Tolo Harbour, Hong Kong, with a rather high level of various metals. Tissue analysis of the algae revealed that the contents of heavy metals (Fe, Mn, Pb and Zn) were higher than in the population collected from the two uncontaminated sites far away from the tailings. It was suggested that the algae were able to adapt to such a harsh environment with a comparatively high level of trace elements and the lack of basic nutrients. However, further studies are needed before any conclusion can be drawn. The delicate situation of the land-locked sea, Tolo Harbour, where the tailings and future heavy industrial site are situated, should not be overlooked.

Studies on cellulase production by a Bacillus subtilis

Bacillus subtilis AU-1 was found to produce carboxymethylcellulase (CMCase) and Avicelase activities in the culture supernatant when grown on a variety of carbohydrates as major carbon source. Maximum CMCase production was obtained in a liquid medium containing 0.2% D (+) raffinose as inducer, 0.5% each of yeast extract, casamino acids and proteose peptone at 50 °C and at an initial pH of 6.0. CMCase activity was detected at early log phase of growth, and reached the maximum level at early stationary phase of growth which occurred at the 10th hour of cultivation. The optimal temperature for CMCase activity was 65 °C, and the enzyme was highly stable up to 60 °C. CMCase synthesis was subjected to catabolite repression by glucose and cellobiose.

Effects of bottom sediments on the survival of Enterobacter aerogenes in seawater

Abstract The survival of the coliform bacterium Enterobacter aerogenes in seawater was greatly affected by the underlying bottom sediments. The presence of sediments which contained higher concentrations of organic nutrients than the overlaying seawater prolonged the survival and even enabled growth of the bacterial cells. Results obtained from chemical analysis indicated that sediments of fine-grained, silt-clay type contained highest amounts of organic nutrients as compared with sediments with larger particle sizes such as silt and sand grains. Thus, nutrient contents of the sediments were found to be inversely proportional to sediment particle size. The degree of prolonged survival of E. aerogenes was also found to be inversely proportional to the size of the sediment particles presented. Release of the bound nutrients which became available to cells of E. aerogenes from sediments by action of waves and human activities can explain, at least in part, why high counts of coliform bacteria are obtained in coastal and beach waters.

Nitrogen and phosphorus removal from sewage effluent with high salinity by Chlorella salina

Abstract Cells of Chlorella salina CU1 are able to grow well in domestic sewage effluent having salinities as high as 16 ppt. By using controlled C. salina CU1 cultures, it is possible to remove the nitrogen and phosphorus from the sewage effluent before it is discharged into marine coastal water. With a retention time of 8 days, 86% to 100% NH3-N, 98% NO3−-N and 98% PO43−-P are removed from the sewage effluent under laboratory conditions. It is also found that cells of C. salina CU1 prefer ammonia to nitrates as nitrogen source. Uptake of nitrates by the cells occurs only after the ammonia in the sewage effluent has been reduced to levels below 0·5 ppm. Ammonia at higher concentrations completely inhibits the nitrate uptake by the algal cells. Since cells of C. salina CU1 have a high protein content (44%), it is proposed that this unicellular green alga can be used to serve the dual function of wastewater purification and waste recycling through the production of algal protein from sewage effluent having high salinities.

Aerobic decomposition of Chlorella salina in freshwater and saline conditions

Aerobic decomposition of the estuarine unicellular green alga Chlorella salina CU-1 was studied in freshwater and saline cultures. Data obtained on suspended solids, COD, chlorophyll a and population growth of the bacteria as well as the regeneration of inorganic phosphorus and nitrogen from these decomposing cultures indicated that the rate and extent of decomposition were much greater in freshwater than in saline condition. It took 20 days and 50 days for decomposition to become evident in the freshwater culture and in the saline culture, respectively. The extent of decomposition as expressed in percent reduction of particulate COD was 77% in the freshwater culture and 48% in the saline culture. Regenerated inorganic phosphate accounted for 85% and 46% of the total original cellular phosphorus in the freshwater culture and in the saline culture, respectively. Nitrogen regeneration was a direct function of the amount of cellular decomposition. In the freshwater culture 88% and in the saline culture 63% of the original particulate organic nitrogen were converted to inorganic nitrogen. It was evident that the ability of C. salina CU-1 to exhibit facultative heterotrophy in saline condition, the mode of algae-bacteria interaction, and the density of the bacterial population in the decomposing algal culture were the factors leading to the observed differences in the pattern and duration of decomposition, as well as the extent and rate of inorganic nutrient regeneration in freshwater and saline environment.