Small scale photo bioreactor treatment of tannery wastewater, heavy metal biosorption and CO2 sequestration using microalga Chlorella sp.: a biodegradation approach

Recently, mass production of lipid along with heavy metal reduction is gaining momentum due to their cost-effective and greener approach towards waste water treatment. The purpose of this study is to investigate the small scale photo bioreactor treatment of tannery effluent using Chlorella sp. isolated form Yercaud lake, Tamil Nadu, India. The results showed a significant decrease in the heavy metals content in the tannery effluent after the treatment. Maximum reduction of the heavy metal Chromium (Cr) of 10.92 mg L−1 was recorded, followed by Cobalt (Co)-7.37 mg L−1, Nickel (Ni)-9.15 mg L−1, Cadmium (Cd)-8.48 mg L−1, Lead (Pb)-12.54 mg L−1, Zinc (Zn)-11.56 mg L−1 and Copper (Cu)-10.71 mg L−1 at the end of the 20th day of treatment. The microalgae, Chlorella sp. was analyzed for their biosorption ability and the maximum biosorption capacity (qmax) rate against heavy metals was 81.36, 70.53, 82.15, 63.29, 58.92, 83.43, 64.83 µg L−1 for Cr, Pb, Ni, Cd, Co, Zn, and Cu respectively. It matched with the Langmuir and Freundlich kinetics models. The maximum CO2 utilization was found to be 60.50% and maximum concentration of lipid, carbohydrate and protein was found to be 0.95 g L−1, 250 µg mL−1 and 160 µg mL−1, respectively. The presence of various groups such as hydroxyl, alkyl, carbonyl and carboxylic acids was confirmed using Fourier transform infrared analysis. Thus, the isolated microalgae showed good biosorption ability towards the various heavy metal pollutants from tannery waste water.

Evaluation of Cell-Viability, Intracellular Lipid-Component and Efficiency of Lipid-Extraction of Chlamydomonas reinhardtii Cells Treated by UV-C Irradiation Aiming to Use Cell Directly

Aim: We aimed finally to construct a system to utilize intracellular lipids of Chlamydomonas reinhardtii by direct cell-use. To realize the system, a system of simple cell-sterilization to avoid environmental contamination without degradation of intracellular lipids was required. Industrially, a simple collecting system of internal lipids was also required. Methods and results: C. reinhardtii cultured in a photo bioreactor under autotrophic condition was irradiated by UV-C. After the irradiation with different time to cells under different culturing conditions, those cells were evaluated for cell-viability by staining with neutral red, intracellular cell components and efficiency of lipid-extraction with GC/FID, respectively. By UV-C irradiation for 10 min, C. reinhardtii cells after N-depletion were sterilized. Additionally, although the cells were morphologically crumbled under an optical microscope, the contents and the components of intracellular lipids showed few differences. Conclusion: C. reinhardtii cells were efficiently sterilized by UV-C irradiation and few treated cells leaked the intracellular lipids, indicating that the lipids could not be simply collected by centrifuging direct cell collection. Significance and impact of study: In this study, the sterilized cells could gradually leak the intracellular contents, indicating the possibility of direct-use of the cells to utilize lipids produced by C. reinhardtii.

The Contribution Ratio of Autotrophic and Heterotrophic Metabolism during a Mixotrophic Culture of Chlorella sorokiniana

The contribution ratio of autotrophic and heterotrophic metabolism in the mixotrophic culture of Chlorella sorokiniana (C. sorokiniana) was investigated. At the early stage of mixotrophic growth (day 0–1), autotrophy contributed over 70% of the total metabolism; however, heterotrophy contributed more than autotrophy after day 1 due to the rapid increase in cell density, which had a shading effect in the photo-bioreactor. Heterotrophy continued to have a higher contribution until the available organic carbon was depleted at which point autotrophy became dominant again. Overall, the increase in algal biomass and light conditions in the photo-bioreactor are important factors in determining the contribution of autotrophy and heterotrophy during a mixotrophic culture.

Microalgae production using photo-bioreactor with intermittent aeration for municipal wastewater substrate and nutrient removal

Microalgae has emerged as a promising approach for removing substrate and nutrient from wastewater with the concomitant biofuel production. The substrate and nutrient removal are influenced by several factors such as C/N ratio, F/M ratio, pH, and DO. This study aims to determine the efficiency of substrate and nutrient removal with the growth rates of microalgae and biomass by varying the addition of aeration and substrate. Intermittently aerated reactors were used with the flow rate of 14 L/minute. The batch reactors were prepared by adding glucose substrate of 50 mg/L (Ra0A), 100 mg/L (Ra0B), and 150 mg/L (Ra0C) without aeration; 50 mg/L (Ra12A), 100 mg/L (Ra12B), and 150 mg/L (Ra12C) with 12-hour aeration, and 50 mg/L (Ra24A), 100 mg/L (Ra24B), and 150 mg/L (Ra24C) with 24-hour aeration. The substrate removal, expressed as chemical oxygen demand (COD) in the reactor with aeration, showed the efficiency of 73.88% ± 2.05 (12-hour aeration), 75.2% ± 3.97 (24hours aeration), and 69.86% ± 5.69(without aeration). Nutrient removal as ammonia-N (NH3-N) gave high removal value of 98.3% ± 0.11 and the removal of nutrient as phosphate (PO3-4) showed the efficiency of 54.3% ± 0.1. The growth rate of microalgae and biomass exhibited the highest value in Ra24C reactor with the values ??of 0.0229/day and 0.1295/day, respectively. The pH values ??indicated a shift from normal to alkaline while DO values ??increased by the addition of 12 and 24-hour aeration.

Carbon Fixation of a Microalgae scenedesmus sp. Pilot Culture under Different Nutritional Inputs

A culture of the microalgae Scenedesmus sp. in a pilot closed raceway photo bioreactor (CRPB), with flue gas injection from a diesel engine was implemented. Two different nutritional medium, Z-8 and EPA were used to feed the culture growth that was monitored in terms of total and partial biomass productivity, carbon fixation and oil production during nine days. The system was sequentially sampled measuring the gas flow and concentration of the injected CO2, the amount of biomass harvested and the concentration of CO2 in the degassing flow. In addition, the pH was measured in the culture to assess the amount of CO2 instantaneously dissolved. The results at the steady state, showed a carbon fixation efficiency ranging between 21.6 % and 44.9 %, and that the Z-8 medium was clearly better than the EPA in terms of CO2 capture and therefore biomass and oil production. A continuous increasing of oil content in microalgae biomass up to 6.6 % dry basis, with maximum oil production rate of 2.27 g m-3d-1 was observed, with a maximum rate of biomass production of 44.97 g m-3d-1 and a maximum carbon capture rate of 2.27 g m-3d-1 was achieved with the culture medium Z-8.