P.S. Lau

Effect of algal density on nutrient removal from primary settled wastewater

Laboratory scale batch experiments were employed to examine the effect of initial inoculum sizes of algae on their activities and reduction of nutrients form the primary settled municipal sewage. The microalgae, Chlorella vulgaris, with four initial inoculum sizes, namely ‘superconcentrated’ (1 × 107 cells ml−1) ‘concentrated’ (5 × 106 cells ml−1), ‘medium’ (1 × 106 cells ml−1) and ‘low’ (5 × 105 cells ml−1), were applied to primarily treated sewage. The cell number and chlorophyll content of all algal cultures increased gradually in the first week and the rates of increase were similar in all cultures. During the experimental period, even in the ‘superconcentrated’ cultures, the self-shading problem was not found probably due to good mixing. At the end of the 10 days study, over 90% NH4+ —N and 80% PO43—P were removed from wastewater in all cultures except the ‘low’ one. The residual concentrations of NH4+—N, PO43—P, TKN and total P in wastewater were negatively correlated with the cell numbers and chlorophyll content of the cultures. These results indicated that the efficiency of reducing wastewater-borne nutrients by an algal system was directly related to the physiological activity and growth of the Chlorella cells which in turn were affected by the initial inoculum size. The super-concentrated culture with an initial algal density of 1 × 107 cells ml1 seemed to be more beneficial as this treatment achieved satisfactory nutrient removal within 7 days instead of 10. The sharp initial reduction of COD (>50%) and total organic-N (>60%) was not related to the algal number or chlorophyll content, the performance in the control (without algal cells) was similar to that of the algal cultures. This suggests that the removal of COD and TON was mainly due to the metabolism of the indigenous bacteria. Under the open system, the interaction between algal and bacterial cells was significant which could enhance the simultaneous removal of N, P and organic matter from primary settled sewage.

Wastewater Nutrients (N and P) Removal by Carrageenan and Alginate Immobilized Chlorella Vulgaris

Excess nutrients (N and P) discharged from sewage treatment plants has been identified as one of the major pollution point sources leading to eutrophication in the coastal water. Microalgae have been demonstrated as excellent nutrients stripper from the sewage. However, its application is limited by its harvesting problem at the end of the treatment process. In this study, the unicellular green alga Chlorella vulgaris was immobilized in two polysaccharide matrices, namely carrageenan and alginate, in form of spherical beads and was used to treat primary settled domestic wastewater in order to eliminate the harvesting limitation. Growth of the algal cells in the matrices was not inhibited and the exponential growth rates were 0.420, 0.441 and 0.417 day−1 for the free, carrageenan and alginate immobilized cells, respectively. Although algal cells in the carrageenan and alginate matrix exhibited a longer lag period (2 and 3 days, respectively) than the free cells (1 day), the immobilized cells were more meta...

The isolation and characterization of Type 1 metallothionein (MT) cDNA from a heavy-metal-tolerant plant, Festuca rubra cv. Merlin

Abstract Festuca rubra cv. Merlin originated from lead and zinc mining areas in the UK has shown multi-metal tolerance ability in laboratory studies. A Type 1 metallothionein (MT) gene mcMT1 was cloned from the copper induced cDNA library of F. rubra cv. Merlin. The mcMT1 cDNA was 492 bp in full length, including a 50 bp 5′ noncoding domain, 213 bp open reading frame and a 211 bp 3′ termination. The coding region of mcMT1 represented a putative 70-amino acid protein with a molecular weight of 7.1 kDa. At each of the N- and C- terminal of the putative protein, six cysteine residues were arranged in a CXCXXXCXCXXXCXC and CXCXXXCXCXXCXC structure, respectively, indicating that it was a Type 1 MT. Southern blot hybridization suggested that there were at least two loci for the mcMT1 gene in the genome. Northern blot analysis showed an enhanced and persistent expression of mcMT1 in the F. rubra, Merlin within 24 h upon copper and cadmium exposure. Functional complementation studies using the Saccharomyces cerevisiae cup1Δ mutant ABDE-1 (metal sensitive) confirmed the functional nature of this mcMT1 gene in sequestering both essential (Cu, Zn) and non-essential metals (Cd, Pb, Cr).

Biodegradation capacity of tributyltin by two Chlorella species

Two microalgal species, Chlorella vulgaris and Chlorella sp., which showed high tributyltin (TBT) tolerant ability were investigated for their capabilities in degrading TBT at sublethal concentration. The distribution of TBT and its degraded products dibutyltin (DBT) and monobutyltin (MBT) in the incubation medium, extracellular surface and intracellular fraction were monitored during an exposure period of 14 days. Results showed that biosorption of TBT by the algal cell wall was the major mechanism in reducing 40% of the initial TBT from the medium in the first 2 days. The half-life of TBT incubated with C. vulgaris was 60 h while that of Chlorella sp. was 80 h. The occurrence of DBT at Day 1 in the culture medium provided direct evidence to the biodegradation of TBT by both Chlorella species. At the end of the experimental period, 27 and 41% of the original TBT were recovered as DBT and MBT in cultures of C. vulgaris, respectively. In contrast, DBT appeared to be the only degradation product of Chlorella sp. and only 26% of the original TBT was transformed to DBT. Despite the same genus, TBT was debutylated to a greater extent to MBT by C. vulgaris, while DBT was the end degradation product by Chlorella sp. The capability of such debutylating process therefore accounted for the higher tolerant ability of C. vulgaris than Chlorella sp.

Effect of carrageenan immobilization on the physiological activities of Chlorella vulgaris

The microalga, Chlorella vulgaris, was immobilized in carrageenan gel. The growth of C. vulgaris in the carrageenan matrix exhibited a one day longer lag period when compared with the free cells. However, growth of the immobilized cells in the log phase was not hindered, as shown from the specific growth constant (k) which was virtually the same as that of the free cells (0.397 vs 0.362 d−1). The rate of chlorophyll synthesis in the immobilized cells was double that of the free cells, compensating for the self-shading or gel-screening effect. The depletion of the nutrient ions, nitrate and phosphate, from the medium showed no significant difference between the immobilized and free cells. For the activity of nitrate reductase, though the immobilized cells had assimilated a similar amount of nitrate as the free cells, their kinetic profiles were different. The nitrate reductase activity increased more slowly than that of the free cells and had a maximal level about half that of the free cells (300 vs 700 × 106 μmol NO2 μg protein−1 h−1). The decline in the nitrate reductase activity in the immobilized cells was also less drastic than that in the free cells upon the depletion of nitrate ions in the medium. This study provided evidence that carrageenan gel had no adverse effect on the growth and physiology of the immobilized microalga. The enzyme activity was also conserved in the immobilized cells. Carrageenan could thus be an alternative gel matrix for immobilizing microalgae.

The toxicity of marine sediments in Victoria Harbour, Hong Kong

Abstract When the toxicity of marine sediment in Hong Kong was evaluated, it was found that the seven sediments collected within Victoria Harbour were severely contaminated with heavy metals, at concentrations many times higher than those in sediments collected from outside the harbour. The highest metal content was recorded in site VS14 (located near the airport runway and the industrialized area), with copper, zinc, lead and chromium values of 3789, 610, 138 and 601 mg kg −1 dry wt, respectively. This site also had the greatest alkaline phosphatase activities (15 fluorescent intensity unit g −1 wet wt), the largest number of total coliforms (910 CFU g −1 wet wt) and sulphate-reducing bacteria (8.5 × 10 4 cells g −1 wet wt), implying that site VS14 was also contaminated with organic matter and nutrients. Sediment bioassays, Microtox and algal tests, demonstrated that sediment elutriates obtained from site VS14 were of greatest toxicity. The EC 10 value in Microtox tests was 17% elutriate, and the 96-h IC 50 values using Skeletonema costatum and Dunaliella tertiolecta were 40 and 79% elutriate, respectively. No toxic effects were found in sediment samples collected from the control site outside Victoria Harbour. Significant correlations were found between the results of the algal toxicity test (using S. costatum ) and the coliform count and metal content of the sediments. The Microtox test was less sensitive than the algal bioassay, and no sediment elutriate, even from the site mostly contaminated by heavy metals, caused more than 50% inhibition of the light-emitting activity of the bacteria. In this study, S. costatum (the diatom) provided a more sensitive and reliable test species than D. tertiolecta (the flagellate) in differentiating the toxicity of marine sediments.

Effect of size, tissue parts and location on six biochemical markers in the green-lipped mussel, Perna viridis

The effect of size and tissue parts as well as site locations on a suite of six anti-oxidative biochemical markers, viz. the enzyme degrading neural transmitters acetylcholinesterase (AChE), the Phase II transforming enzyme glutathione-S-transferase (GST), the anti-oxidative enzymes superoxide dismutase (SOD) and catalase (CAT), the lipid metabolite malondialdehyde (MDA) and the ratio of CAT/MDA, in the bivalve mollusc, Perna viridis, was studied. Field mussels were collected from the piers of University of Science and Technology (UST), Pak Sha Wan or Hebe Haven (PS) and Sai Kung (SK) in Port Shelter, Hong Kong. Statistically, ANOVA showed that the activity of all six biochemical markers were generally tissue dependent, size independent and location dependent. Tukey multi comparison test indicated that the biochemical activities fell into two groups, with SK the highest activity group in most cases. The significance of these findings in relation to long-term coastal water biomonitoring is discussed.

Effect of metal interference, pH and temperature on Cu and Ni biosorption by Chlorella vulgaris and Chlorella miniata

Chlorella vulgaris, an unicellular green alga which had extensively been used for wastewater nutrient removal studies, and a locally isolated Chlorella miniata were assessed for their Cu and Ni biosorption from single and mixed metal solutions. The locally isolated C. miniata had a higher maximal binding (qmax) of 23.26 mg Cu g−1 d.w. and 20.37 mg Ni g−1 d.w. than the 18.72 Cu g−1 d.w. and 12.06 mg Ni g−1 d.w. of C. vulgaris when unit biomass was concerned. However, when normalized to surface area of the cells, C. miniata showed a higher Ni but lower Cu biosorption than C. vulgaris. Both Chlorella species had a preferential Cu to Ni biosorption from mixed metal solutions. The Cu biosorption by both algal biomass was not significantly affected in the presence of 30 mg l−1 Ni. When Ni increased to 300 mg l−1, the qmax of Cu was reduced by 13% in C. vulgaris and 7.7% in C. miniata. On the contrary, presence of 30 mg l−1 Cu already lowered the qmax of Ni by 12% and 17% in C. vulgaris and C. miniata, respectiv...

Wastewater nutrients removal by Chlorella vulgaris : Optimization through acclimation

The unicellular green alga, Chlorella vulgaris, was acclimated in wastewater for a period of 14 days before employed in treating primary settled wastewater. The acclimated cells had significantly h...

Influence of organic-N sources on an algal wastewater treatment system

Synthetic wastewater enriched with either peptone or urea as organic-N source was used to grow Chlorella pyrenoidosa under axenic and open conditions. Commercial Bristol medium was used for comparison. The growth rate constant in the peptone-rich wastewater was comparable to that in Bristol medium (k=0.30 d−1 vs. 0.31 d−1) and much higher than its open counterpart (k=0.16 d−1). Both axenic and open peptone cultures exhibited a N-limiting condition for growth as revealed from the inorganic N/P ratios of 0.40 and 1.63 on day 5, which correlated with the rapid removal of 99% and 80% of NH4-N, respectively. Better growth in axenic culture was supported by the simple amino acids of the nutritive peptone which was depleted due to bacterial consumption in the open culture. The growth rate constant in the urea set under open condition was slightly higher than that of the axenic culture (k=0.20 d−1 vs. 0.15 d−1), while both were significantly lower than that in Bristol cultures. Growth in the urea set was P-limited as reflected from the high inorganic N/P ratios in open and axenic cultures, with values of 30.6 and 44.9 on day 5, respectively. This appeared to correlate to the rapid removal of 99% and 88% of PO4-P under axenic and open conditions, respectively. Bacterial interaction through hydrolysing urea to NH4-N sustained a more neutral pH in open culture and accounted for a better growth, while the acidic pH (<4) in the axenic set definitely retarded growth. The results suggest that the degree of N and P uptake and their reduction from wastewater by Chlorella pyrenoidosa depend on the types of organic-N sources in wastewater. The presence of bacteria in the culture would also affect the microalgal growth and nutrient removal, and the bacterial effect seems to relate to the types of organic N available in the wastewater.