The effects of wavelength and wavelength mixing ratios on microalgae growth and nitrogen, phosphorus removal using Scenedesmus sp. for wastewater treatment

In wastewater treatment using microalgae, the effects of wavelength and wavelength mixing ratio on microalgae growth and removal of nitrogen and phosphorus were evaluated using LEDs (white light, 670nm, 450nm, and 525nm). Microalgae production rates were enhanced by a maximum of 45% with 400-700nm white light compared to that of a single wavelength. The phosphorus removal rate was as high as 90% with blue light. When red light and blue light were mixed and supplied, the microalgae production rate was about 50% higher than the rate of the culture with white light. Nitrogen and phosphorus removal rates were as high as approximately 15mg/L/day at a wavelength mixing ratio of 7 (red light):3 (blue light) and 2.1mg/L/day at a wavelength mixing ratio of 5 (red light):5 (blue light).

Carbon dioxide fixation and lipid storage by Scenedesmus obtusiusculus

An indigenous microalga was isolated from the springs in Cuatro Ciénegas, México. It was morphologically identified as Scenedesmus obtusiusculus and cultivated in bubble-column photobioreactors in batch operation mode. This microalga grows at 10% of carbon dioxide (CO(2)) showing a maximum CO(2) fixation rate of 970gm(-3)d(-1). The microalga, without any nutrient limitation, contained 20% of nonpolar lipids with a biomass productivity of 500gm(-3)d(-1) and a maximum biomass concentration of around 6,000gm(-3) at 5% CO(2) and irradiance of 134μmolm(-2)s(-1). Furthermore, it was observed that the microalga stored 55.7% of nonpolar lipids when 5% CO(2) was fed at 0.8vvm and 54.7μmolm(-2)s(-1) under nitrogen starvation. The lipid profile included C16:0, C18:0, C18:1n9t, C18:1n9c, C18:3n6 with a productivity of 200g lipid m(-3)d(-1). Therefore, the microalga may have biotechnological potential producing lipids for biodiesel.

Potential biomass yield per phosphorus and lipid accumulation property of seven microalgal species

The potential biomass yield per phosphorus and lipid/triglyceride (TAG) accumulation properties of seven microalgal species: Scenedesmus sp. LX1, Chlorella ellipsoidea YJ1, Chlorella vuglaris, Chlorella sorokiniana, Chlorella pyrenoidosa, Dunaliella primolecta and Haematococcus pluvialis were investigated. Among the tested species, Scenedesmus sp. LX1 obtained the smallest minimal phosphorus content in cell (Q(0)) and the highest potential biomass yield of 6100kg-biomass/kg-P. After 12-day growth with intracellular phosphorus, Scenedesmus sp. LX1 accumulated about 30% lipid in biomass. Furthermore, the TAGs content per lipid of this strain (58.5%) as well as the lipid and TAGs yield per phosphorus (1800kg-lipid/kg-P and 680kg-TAGs/kg-P, respectively) were all significantly higher than that of any other species investigated in this study. Therefore, the phosphorus consumption to produce 1kg biodiesel using Scenedesmus sp. LX1 as feedstock was lowest among the tested species.

Attached cultivation technology of microalgae for efficient biomass feedstock production

The potential of microalgae biofuel has not been realized because of low productivity and high costs associated with the current cultivation systems. In this paper, an attached cultivation method was introduced, in which microalgae cells grew on the surface of vertical artificial supporting material to form algal film. Multiple of the algal films were assembled in an array fashion to dilute solar irradiation to facilitate high photosynthetic efficiency. Results showed that a broad range of microalgae species can grow with this attached method. A biomass productivity of 50-80 g m(-2) d(-1) was obtained outdoors for Scenedesmus obliquus, corresponding to the photosynthetic efficiency of 5.2-8.3% (total solar radiation). This attached method also offers lots of possible advantages over traditional open ponds, such as on water saving, harvesting, contamination controlling and scale-up. The attached cultivation represents a promising technology for economically viable production of microalgae biofuels.

Performance of a flat panel reactor in the continuous culture of microalgae in urban wastewater: prediction from a batch experiment

A laboratory-scale flat panel photobioreactor was operated for the continuous growth of Scenedesmus obliquus and consequent removal of nutrients in wastewater. This study develops a simple model by which biomass values in continuous operation can be predicted from kinetic growth parameters obtained from a shorter batch experiment. Based on this study, biomass concentrations and productivities in continuous operation can be successfully predicted as a function of the specific hydraulic retention time (HRT) assumed. Considerable biomass production and nutrient uptake from wastewater were achieved in the experiment. Optimum operating conditions for the reactor depend on the particular objective: the maximization of biomass production and carbon dioxide biofixation involves a HRT of 2 μ(-1) (specific growth rate), whereas efficient nutrient removal involves a HRT as close as possible to μ(-1) (as long as discharges comply fully with the parameters set); alternatively biomass intended for biodiesel or biogas production would involve a HRT > 2 μ(-1).

Photobiotreatment: influence of nitrogen and phosphorus ratio in wastewater on growth kinetics of Scenedesmus obliquus

Nitrogen and phosphorus concentration in the effluent of a wastewater treatment plant can vary significantly, which could affect the growth kinetic and chemical composition of microalgae when cultivated in this medium. The aim of this work was to study the rate of growth, nutrient removal and carbon dioxide biofixation as well as biomass composition of Scenedesmus obliquus (S. obliquus) when it is cultivated in wastewater at different nitrogen and phosphorus ratio, from 1:1 to 35:1. A more homogeneous method for calculating productivities in batch reactors was proposed. The proper N:P ratio for achieving optimum batch biomass productivity ranged between 9 and 13 (263 and 322 mg L(-1) d(-1) respectively). This was also the ratio range for achieving a total N and P removal. Above and below this range (9-13) the maximum biomass concentration changed, instead of the specific growth rate.The maximum carbon dioxide biofixation rate was achieved at N:P ratio between 13 and 22 (553 and 557 mg CO2 L(-1) d(-1) respectively). Lipid and crude protein content, both depend on the aging culture, reaching the maximum lipid content (34%) at the lowest N:P (1:1) and the maximum crude protein content (34.2%) at the highest N:P (35:1).

Dynamic model of microalgal production in tubular photobioreactors

A dynamic model for microalgal culture is presented. The model takes into account the fluid-dynamic and mass transfer, in addition to biological phenomena, it being based on fundamental principles. The model has been calibrated and validated using data from a pilot-scale tubular photobioreactor but it can be extended to other designs. It can be used to determine, from experimental measurements, the values of characteristic parameters. The model also allows a simulation of the system's dynamic behaviour in response to solar radiation, making it a useful tool for design and operation optimization of photobioreactors. Moreover, the model permits the identification of local pH gradients, dissolved oxygen and dissolved carbon dioxide; that can damage microalgae growth. In addition, the developed model can map the different characteristic time scales of phenomena inside microalgae cultures within tubular photobioreactors, meaning it is a valuable tool in the development of advanced control strategies for microalgae cultures.

Influence of the CO2 absorbent monoethanolamine on growth and carbon fixation by the green alga Scenedesmus sp

The influence of monoethanolamine (MEA) as a CO(2) absorbent on photoautotrophic culture of CO(2)-fixing microalgae was investigated. When 300 ppm MEA (4.92 mM) was added to blank culture medium, the dissolved inorganic carbon and the molar absorption ratio increased to 51.0mg/L and 0.34 mol CO2 = mol MEA, respectively, which was an almost 6-fold increase in CO(2) solubility. When free MEA up to 300 mg/L was added to a green alga Scenedesmus sp. culture that was supplied 5% (v/v) CO(2) at 0.1 vvm, both cell growth rate and final cell density were enhanced compared to when no MEA was added. The cell growth rate reached 288.6 mg/L/d, which was equivalent to 539.6 mg-CO(2)/L/d as a CO(2)-fixation rate and enhancement of about 63.0% compared to not adding MEA. Chlorophyll-a content and nitrate consumption rate increased correspondingly. MEA doses higher than 400mg/L inhibited cell growth, probably due to toxicity of the carbamate intermediate.

Nutrient removal from membrane bioreactor permeate using microalgae and in a microalgae membrane photoreactor

This paper explores the use of a novel microalgae membrane photoreactor (mMR) to polish the effluent from an aerobic membrane bioreactor (MBR) fed with domestic wastewater. Four microalgae species Chlorella (Chlorella sp.), Chlorella vulgaris (C. vulgaris), Scenedesmus quadricauda (S. quadricauda) and Scenedesmus dimorphus (S. dimorphus) were isolated from the environment and tested in batch reactors fed with permeate from the aerobic MBR to evaluate the nutrient removal rates for each species. All four microalgae species were able to completely remove NH4 in the reactor within 3 days. The removal rates of NO3, NO2 and PO4 were between 43-54%, 83-95% and 70-92%, respectively after 3 days in the batch reactor. Subsequently, an MBR-mMR system was operated for 23 days. The mMR was able to remove on average 50% of NH4, 75% of NO2, 35% of NO3 and 60% of PO4 consistently from the MBR effluent under the conditions tested.

Coupled nutrient removal and biomass production with mixed algal culture: impact of biotic and abiotic factors

The influence of biotic (algal inoculum concentration) and abiotic factors (illumination cycle, mixing velocity and nutrient strength) on the treatment efficiency, biomass generation and settleability were investigated with selected mixed algal culture. Dark condition led to poor nutrient removal efficiency. No significant difference in the N, P removal and biomass settleability between continuous and alternating illumination was observed, but a higher biomass generation capability for the continuous illumination was obtained. Different mixing velocity led to similar phosphorus removal efficiencies (above 98%) with different retention times. The reactor with 300 rpm mixing velocity had the best N removal capability. For the low strength wastewater, the N rates were 5.4±0.2, 9.1±0.3 and 10.8±0.3 mg/l/d and P removal rates were 0.57±0.03, 0.56±0.03 and 0.72±0.05 mg/l/d for reactors with the algal inoculum concentration of 0.2, 0.5 and 0.8 g/l, respectively. Low nutrient removal efficiency and poor biomass settleability were obtained for high strength wastewater.

[Growth, removal of nitrogen and phosphorus, and lipid accumulation property of Scenedesmus sp. LX1 in aquaculture wastewater]

Treating wastewater by high-lipid-content microalgae, which can couple with wastewater treatment and biodiesel production, has become a new research direction in the wastewater treatment field. A high-lipid-content freshwater microalgae, Scenedesmus sp. LX1 was studied concerning its growth, removal efficiencies of nitrogen and phosphorus, and lipid accumulation property while growing in aquaculture wastewater. Results showed that the specific growth rate, maximum population density and maximum population growth rate of Scenedesmus sp. LX1 were 0.44 d(-1), 7.46 x 10(6) cells x mL(-1) and 0.82 x 10(6) cells x (mL x d)(-1), respectively. At stationary phase of training, removal efficiencies of ammonia, nitrite, nitrate and phosphorus by Scenedesmus sp. LX1 were 95.5%, 96.3%, 85.8% and 98.8%, respectively. It's biomass [dry weight] was 0.38 g x L(-1), algae lipid content was up to 31.6%. In general, Scenedesmus sp. LX1 has larger advantage in aquaculture wastewater depuration and resource utilization respect, and it can be used as the preferred algae species for coupling process.

Acute toxicity of butachlor and atrazine to freshwater green alga Scenedesmus obliquus and cladoceran Daphnia carinata

Both single and joint toxicity of atrazine and butachlor to freshwater green alga Scenedesmus obliquus and cladoceran Daphnia carinata isolated from South China were investigated in the present study. The 96 h-EC(50) values of atrazine and butachlor to S. obliquus were 0.0147 and 2.31 mg L(-1), while the 48 h-LC(50) values to D. carinata were 60.6 and 3.40 mg L(-1), respectively. These results suggest that atrazine could be highly toxic to S. obliquus and slightly toxic to D. carinata, while butachlor exhibits moderate toxicity to both organisms. The additive indexes of atrazine and butachlor mixtures were -2.68 (-3.02 to -2.32) to S. obliquus and 0.054 (-0.025 to 0.238) to D. carinata, respectively. Therefore, the joint action of two herbicides was significant antagonism to S. obliquus, while significant synergism was not shown to D. carinata. Moreover, significant linear correlation between the natural logarithm of herbicide concentrations and growth rates of alga S. obliquus was observed. Taken together, it is the first study reporting the toxicity endpoints for mixture of atrazine and butachlor against S. obliquus and D. carinata isolated from south China. The present results would be helpful to provide data to assess the ecological risk of both herbicides to aquatic organisms.

Biomass production of a Scenedesmus sp. under phosphorous-starvation cultivation condition

Microalgae-based bioenergy has gained extensive attention, but the consumption of non-renewable resource such as phosphorous is inevitable in the production of its feedstock. In this work, the minimal phosphorous consumption for algal biomass production of Scenedesmus sp. LX1 was investigated by monitoring the growth and nutrient uptake under two different cultivation modes: phosphorous-starvation and luxury-nutrient. The results showed that continuous nitrogen and phosphorous feeding in luxury-nutrient mode had no stimulating effect on biomass productivity at the nutrient level in this study, TN: 245 mg L(-1), TP: 5.4 mg L(-1). However, the sustained growth of biomass after the exhaust of phosphate in phosphorous-starvation mode led to significant increase in the biomass yield of phosphorous up to 160 g biomass/g -P, which was nearly six times more than that with nutrient feeding. To minimize phosphorous resource consumption in production of algal biomass, a phosphorous-starvation cultivation mode is proposed.

[Experimental assessment of combined effect of nitrates and acute gamma-irradiation on green algae Scenedesmus quadricauda growth]

The combined effect of acute gamma-irradiation at doses of 0, 50, 100, 150 and 200 Gy and nitrates in concentrations of 0.04 g/dm3 (that corresponds to maximum permissible concentrations for fishery waters), 0.1, 0.25, 0.5, 1.0, 2.5 g/dm3 (that is close to NO3(-) level in water of a reservoir R-17 used as radioactive waste storage of the "Mayak" Production Association) and 5.0 g/dm3 (that is close to NO3(-) level in the water of radioactive waste storage reservoir R-9) on the unicellular green algae Scenedesmus quadricauda growth has been studied in laboratory conditions. It was shown that the joint effects of nitrates and y-radiation had an antagonistic character. Thus, it may be concluded that chemical pollution is the factor limiting the development of green algae in reservoir R-17; probably, both factors, chemical and radiating, are essential to the algocenosis degradation in reservoir R-9.

Accumulation characteristics of soluble algal products (SAP) by a freshwater microalga Scenedesmus sp. LX1 during batch cultivation for biofuel production

Algae cultivation is the essential basis for microalgal biofuel production. Soluble algal products (SAP) are significant obstacle to large-scale, high-cell-density cultivation processes. SAP accumulation during batch cultivation of Scenedesmus sp. LX1 (a unique strain accumulating lipid substantially while growing fast under low-nutrient conditions) with different initial nitrogen concentrations (7.4-34.0mgNL(-1)) was investigated. The SAP content varied in the range of 3.4-17.4mgDOCL(-1) at stationary phase, with average yield per cell of 0.5-2.5pgDOCcell(-1). High SAP accumulation up to 15.2-17.4mgDOCL(-1) were observed with initial nitrogen above 20.2mgNL(-1). The maximum SAP production rate per unit culture volume (r(SAP)) was 2.6mgDOC(Ld)(-1) and that per cell (ν(SAP)) was 1.5pgDOC(celld)(-1). The r(SAP) increased with cell growth rate and decreased with cell density linearly. The SAP accumulation was majorly due to the release of growth-associated products.

Access the toxic effect of the antibiotic cefradine and its UV light degradation products on two freshwater algae

Two common freshwater algae Microcystis aeruginosa and Scenedesmus obliquus were employed as test organism to evaluate the toxic effects of the widely used antibiotic, cefradine. In general, cefradine had significantly toxic effect on population growth and chlorophyll-a accumulation of two algae and the cyanophyceae was more sensitive than the chlorophyceae. In addition, cefradine UV light degraded products had adverse effect on M. aeruginosa's growth and chlorophyll-a accumulation. In comparison, even if S. obliquus had growth ability when exposed to cefradine UV light-degradation products, the algal photosynthesis function was also disrupted.

Eco-toxicological effect of carbamazepine on Scenedesmus obliquus and Chlorella pyrenoidosa

The acute and chronic toxicological effects of carbamazepine (CBZ) on Scenedesmus obliquus and Chlorella pyrenoidosa were explored for the first time in this study. The results showed that CBZ could significantly inhibit the growth of the two algae in almost all treatment groups. EC(50) values indicated that, CBZ had a relatively limited acute toxic effect (0-144 h) on S. obliquus and C. pyrenoidosa, while, chronic tests (5-30 d) displayed higher toxicity. Chlorophyll a syntheses were nearly all inhibited by CBZ exposure. However, superoxide dismutase (SOD) and catalase (CAT) activities in acute tests of both algae were markedly promoted. According to the results, Chlorophyll a content and CAT activity of S. obliquus were more sensitive to CBZ than that of C. pyrenoidosa. While for SOD, quite to the contrary, C. pyrenoidosa was more vulnerable. We obtained a similar result in chronic tests. This research furthers our understanding of CBZ toxicity to aquatic organisms.

Enantioselective toxic effects and biodegradation of benalaxyl in Scenedesmus obliquus

Enantioselectivity in ecotoxicity and biodegradation of chiral pesticide benalaxyl to freshwater algae Scenedesmus obliquus was studied. The 96 h-EC(50) values of rac-, R-(-)-, S-(+)-benalaxyl were 2.893, 3.867, and 8.441 mg L(-1), respectively. Therefore, the acute toxicities of benalaxyl enantiomers were enantioselective. In addition, the pigments chlorophyll a and chlorophyll b, antioxidant enzyme activities catalase (CAT) and superoxide dismutase (SOD) as well as lipid peroxide malondialdehyde (MDA) were determined to evaluate the different toxic effects. Chlorophyll a was induced by S-(+)-benalaxyl but inhibited by R-(-)-benalaxyl at 1 mg L(-1). Chlorophyll b were both induced at 1 mg L(-1), but S-(+)-form was fourfold higher than R-(-)-form. S-(+)-benalaxyl inhibited more CAT activities at 3 mg L(-1) and 5 mg L(-1), induced less SOD activity and MDA content at 5 mg L(-1) than R-(-)-benalaxyl. Based on these data, enantioselectivity occurred in anti-oxidative stress when S. obliquus response to benalaxyl. In the biodegradation experiment, the half-lives of S-(+)-benalaxyl and R-(-)-benalaxyl were 4.07 d and 5.04 d, respectively, resulting in relative enrichment of the R-(-)-form. These results showed that toxic effects and biodegradation of benalaxyl in S. obliquus were enantioselective, and such enantiomeric differences must be taken into consideration in pesticide risk.

Feasibility of microalgal cultivation in a pilot-scale airlift-driven raceway reactor

A Scenedesmus sp. was cultivated in a 23-L airlift-driven raceway reactor under artificial lighting and laboratory conditions, in batch and continuous modes. In batch mode, a maximum volumetric biomass productivity of 0.085 dry g L(-1) day(-1) was achieved under sparging at a CO(2)-to-air ratio of 1%, and a maximum CO(2) utilization efficiency of 33% was achieved at a CO(2)-to-air ratio of 0.25%. In continuous mode, the maximum volumetric biomass productivity was 0.19 dry g L(-1) day(-1). Biomass productivities per unit power input achieved in this reactor configuration (0.60-0.69 dry g W(-1) day(-1)) were comparable to or better than those reported in the literature for different photobioreactor designs (0.10-0.51 dry g W(-1) day(-1)). Based on the energy-efficient productivity and the high CO(2) utilization efficiency demonstrated in this study, the proposed airlift-driven raceway design holds promise for cost-effective algal cultivation.

Multimodal action and selective toxicity of zerovalent iron nanoparticles against cyanobacteria

Cyanobacteria pose a serious threat to water resources around the world. This is compounded by the fact that they are extremely resilient, having evolved numerous protective mechanisms to ensure their dominant position in their ecosystem. We show that treatment with nanoparticles of zerovalent iron (nZVI) is an effective and environmentally benign method for destroying and preventing the formation of cyanobacterial water blooms. The nanoparticles have multiple modes of action, including the removal of bioavailable phosphorus, the destruction of cyanobacterial cells, and the immobilization of microcystins, preventing their release into the water column. Ecotoxicological experiments showed that nZVI is a highly selective agent, having an EC(50) of 50 mg/L against cyanobacteria; this is 20-100 times lower than its EC(50) for algae, daphnids, water plants, and fishes. The primary product of nZVI treatment is nontoxic and highly aggregated Fe(OH)(3), which promotes flocculation and gradual settling of the decomposed cyanobacterial biomass.

Effects of an anionic surfactant (FFD-6) on the energy and information flow between a primary producer (Scenedesmus obliquus) and a consumer (Daphnia magna)

The effects of a commercially available anionic surfactant solution (FFD-6) on growth and morphology of a common green alga (Scenedesmus obliquus) and on survival and clearance rates of the water flea Daphnia magna were studied. The surfactant-solution elicited a morphological response (formation of colonies) in Scenedesmus at concentrations of 10-100 μl l(-1) that were far below the No Observed Effect Concentration (NOEC) value of 1,000 μl l(-1) for growth inhibition. The NOEC-value of FFD-6 for colony-induction was 3 μl l(-1). Daphnia survival was strongly affected by FFD-6, yielding LC(50-24h) and LC(50-48 h) of 148 and 26 μl l(-1), respectively. In addition, clearance rates of Daphnia feeding on unicellular Scenedesmus were inhibited by FFD-6, yielding a 50% inhibition (EC(50-1.5h)) at 5.2 μl l(-1) with a NOEC of 0.5 μl l(-1). When Daphnia were offered FFD-6-induced food in which eight-celled colonies (43 × 29 μm) were most abundant, clearance rates (~0.14 ml ind.(-1) h(-1)) were only 25% the rates of animals that were offered non-induced unicellular (15 × 5 μm) Scenedesmus (~0.56 ml ind.(-1) h(-1)). As FFD-6 concentrations in the treated food used in the experiments were far below the NOEC for clearance rate inhibition, it is concluded that the feeding rate depression was caused by the altered morphology of the Scenedesmus moving them out of the feeding window of the daphnids. The surfactant evoked a response in Scenedesmus that is similar to the natural chemically induced defensive reaction against grazers and could disrupt the natural information conveyance between these plankton organisms.

Biomass production and fatty acid profile of a Scenedesmus rubescens-like microalga

This investigation examined the effects of nitrogen-phosphate combined deficiency on the biomass yield, fatty acid methyl esters (FAME) production and composition from Scenedesmus rubescens-like microalga. A 15-day indoor culture was performed as a 3 × 3 factorial design (NaNO(3) levels: 3, 10 and 20mM; KH(2)PO(4) levels: 20, 50 and 150 μM). The algae grown under medium nitrogen concentration (10mM) and high phosphate concentration (150 μM) reached the highest biomass (1223.5 ± 152.5mg/L). Both nitrogen and phosphate had a significant influence on the FAME yield (P<0.05 and P<0.0001, respectively). The FAME yield from algae grown under low nitrogen (3mM) and phosphate concentration (20 μM) increased throughout the experiment and the highest FAME yield (42.2 ± 2.5% of AFDW) as well as C16 and C18 content (95.8 ± 1.6% of AFDW) was achieved under these conditions. Algae grown under medium nitrogen concentration (10mM) and low phosphate concentration (20 μM) had the highest FAME productivity (426.0mg/L ± 135.0mg/L). Thus, the lower nitrogen concentration (3mM-10mM) and low phosphate concentration (20 μM) would be an optimal combination tested to produce the most FAME from S. rubescens-like algae.

Degradation of polychlorinated biphenyls in aqueous solutions after UV-peroxide treatment: focus on toxicity of effluent to primary producers

The combination of UV irradiation and hydrogen peroxide (UV-H(2)O(2)) was shown to be effective in treating water spiked with 2,2',4,4',5,5'-hexachlorobipheny (PCB 153), reducing its concentration by as much as 98%. To test the toxicity of the effluent, bioassays involving three species of primary producers were performed. Results showed the effluent exerting an adverse effect on the algae Scenedesmus bijugatus and the duckweed Lemna paucicostata. On the other hand, exposure of the mungbean Vigna radiata to the effluent revealed mostly no statistically significant adverse effect or growth stimulation. This suggested that on an exposure period of 96 h, higher forms of chlorophyll-bearing species such as plants are relatively unaffected by trace concentrations of PCBs and degradation products, while less differentiated species like algae and duckweeds are vulnerable.

Growth and heavy metals accumulation potential of microalgae grown in sewage wastewater and petrochemical effluents

Microalgae exhibit a number of heavy metal uptake process by different metabolism. In this study, the ability of microalgae for removal of heavy metal from wastewater was studied. Growth and biochemical contents of microalgae were determined by spectrophotometer. Heavy metal analysis of wastewater effluents were performed by atomic absorption spectrophotometer before and after treatment at laboratory scale. The growth of Scenedesmus bijuga and Oscillatoria quadripunctulata in sewage wastewater was higher than those grown in synthetic medium. Whereas, the growth of S. bijuga and O. quadripunctulata in sterilized petrochemical effluents was slightly lower than that grown in the standard synthetic medium. The chlorophyll, carotenoid and protein content of S. bijuga and O. quadripunctulata grown in sterilized sewage wastewater were higher than those grown in the standard medium. Similarly S. bijuga and O. quadripunctulata grown in sterilized petrochemical effluents showed lower contents of pigments and protein than those grown in sewage and synthetic medium. Heavy metals copper, cobalt, lead and zinc were removed by 37-50, 20.3-33.3, 34.6-100 and 32.1-100%, respectively from sewage wastewater and petrochemical effluent using Ocillatoria culture. The metal absorption by S. bijuga were (Cu, Co, Pb, Zn) 60-50, 29.6-66, 15.4-25 and 42.9-50%, respectively from sewage and petrochemical effluents. Both species showed high level of heavy metal removal efficiency and metal sorption efficiency of both microalgae depended on the type of biosorbent, the physiological status of the cells, availability of heavy metal, concentration of heavy metal and chemical composition of wastewater.

[Effect of inorganic carbon supplement on the growth and lipid accumulation properties of Scenedesmus sp. LX1]

With secondary effluent as growth medium, the growth and lipid accumulation properties of Scenedesmus sp. LX1 in the control and carbon supplement (Na2CO3, NaHCO3 and CO2) groups were compared. After 14 days of cultivation, there was no significant difference in growth and lipid accumulation of Scenedesmus sp. LX1 among the 4 groups. The algal biomass, lipid and triacylglycerols production were 0.70-0.77 g x L(-1), 0.27-0.34 g x L(-1) and 0.029-0.033 g x L(-1), respectively, and the lipid content per algal biomass was 35% - 45%. The microalgal photosynthesis would increase the water's pH to about 9.2, which could induce CO2 transferring into secondary effluent. In control group, the amount of CO2 transferring from atmosphere into secondary effluent was 1.0 g x L(-1), occupying 97% of total fixed CO2 by microalga. Calculation shows that, the CO2 transferring from atmosphere into secondary effluent is enough to support microalgal growth and lipid accumulation. Therefore, to cultivate Scenedesmus sp. LX1 in secondary effluent, there is no need of carbon supplement.