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Research Publications (Water and Wastewater Technology)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/841

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End date: 2019Subject: search.filters.subject.Microalgae

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Now showing 1 - 7 of 7
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    Uptake of inorganic and organic nutrient species during cultivation of a Chlorella Isolate in Anaerobically digested dairy waste
    (American Institute of Chemical Engineers, 2016-06-23) Wahal, Shantanu; Viamajala, Sridhar
    A natural assemblage of microalgae from a facultative lagoon system treating municipal wastewater was enriched for growth in the effluents of an anaerobic digester processing dairy waste. A green microalga with close resemblance to Chlorella sp. was found to be dominant after multiple cycles of sub-culturing. Subsequently, the strain (designated as LLAI) was isolated and cultivated in 203 diluted digester effluents under various incident light intensities (255–1,100 mmoles m22 s21) to systematically assess growth and nutrient utilization. Our results showed that LLAI production increased with increasing incident light and a maximum productivity of 0.34 g L21 d21 was attained when the incident irradiance was 1,100 mmoles m22 s21. Lack of growth in the absence of light indicated that the cul-tures did not grow heterotrophically on the organic compounds present in the medium. How-ever, the cultures were able to uptake organic N and P under phototrophic conditions and our calculations suggest that the carbon associated with these organic nutrients contributed significantly to the production of biomass. Overall, under high light conditions, LLAI cul-tures utilized half of the soluble organic nitrogen and >90% of the ammonium, orthophos-phate, and dissolved organic phosphorus present in the diluted waste. Strain LLAI was also found to accumulate triacylglycerides (TAG) even before the onset of nutrient limitation and a lipid productivity of 37 mg-TAG L21 d21 was measured in cultures incubated at an inci-dent irradiance of 1,100 mmoles m22 s21. The results of this study suggest that microalgae isolates from natural environments are well-suited for nutrient remediation and biomass pro-duction from wastewater containing diverse inorganic and organic nutrient species
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    An innovative electrochemical process to alleviate the challenges for harvesting of small size microalgae by using non-sacrificial carbon electrodes
    (Elsevier, 2015-09-04) Guldhe, Abhishek; Misra, Rohit; Singh, Poonam; Rawat, Ismail; Bux, Faizal
    Harvesting of microalgal biomass is still a bottleneck to its commercial scale application, due to small cell size, low culture densities, colloidal stability and thus unfavourable economics. Centrifugation is an efficient technique but the high energy consumption makes it unsuitable for low value microalgal products. Chemical flocculation and filtration are inefficient and time consuming methods for harvesting of small size microalgae. In this study, an electrochemical harvesting (ECH) process was assessed for the harvesting of a small size microalga Ankistrodesmus falcatus by using non-sacrificial carbon electrodes. Harvesting efficiency of ECH was compared to centrifugation and flocculation using alum and chitosan. The highest recovery efficiency was obtained by cen-trifugation (93% after 15 min) followed by ECH process (91% after 30 min), alum (86% after 60 min) and chitosan (55% after 60 min). However, the energy consumption of ECH process (1.76 kWh kg−1) was much lower than the centrifugation process (65.34 kWh kg−1). The biochemical composition of harvested biomass was also assessed, and it was found that the ECH process has no deteriorating effect on the quality of biomass. High recovery effi-ciency, low energy consumption and the use of non-sacrificial electrodes make ECH a sustainable harvesting technique for small size microalgae.
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    Cultivation of Chlorella pyrenoidosa in outdoor open raceway pond using domestic wastewater as medium in arid desert region
    (Elsevier, 2016) Dahmani, Siham; Zerrouki, Djamal; Ramanna, Luveshan; Rawat, Ismail; Bux, Faizal
    Chlorella pyrenoidosa was cultivated in secondary wastewater effluent to assess its nutrient removal capa-bilities. Wastewaters were obtained from a wastewater treatment plant located in Ouargla, Algeria. The experiments were conducted in winter under natural sunlight in an outdoor open raceway pond situated in the desert area. The highest biomass of the microalgae was found to be 1.71 ± 0.04 g/L. Temperatures ranged between 18 and 31 C. The average annual insolation was no less than 3500 h with an annual solar irradiance of more than 2000 kWh/m2. Analyses of different parameters including COD, NH4-N and TP were conducted throughout the cultivation period. Their average removal efficiencies were 78%, 95%and 81% respectively. The results demonstrated the potential of nutrient removal by microalgae grown on secondary wastewater in arid areas.
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    Synthesis of biodiesel from Scenedesmus sp. by microwave and ultrasound assisted in situ transesterification using tungstated zirconia as a solid acid catalyst
    (Elsevier, 2014-05-20) Guldhe, Abhishek; Singh, Bhaskar; Rawat, Ismail; Bux, Faizal
    Oleaginous Scenedesmus sp. was cultivated phototrophically in an open pond for biofuels production. The culture was harvested and subsequently dewatered and dried. The chemical properties of the Scenedesmus sp. lipids were determined as per standard ASTM methods. Biodiesel was synthesized by in situ transesterification from dried biomass using microwave and sonication techniques with tungstated zirconia (WO3/ZrO2) as a solid acid catalyst. In situ transesterification allowed minimizing the requirement of solvents by merging the two steps (i.e. extraction of lipid and conversion to biodiesel) to a single step. The use of a solid catalyst effectively reduces the purification cost of biodiesel due to ease of separation and potential for reuse. The conversion of Scenedesmus sp. lipids to biodiesel was determined by GC. Box–Behnken design was used for optimization of the variables to optimize the biodiesel yield and conversion. The efficiency of the two processes was compared.
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    Evaluation of operating conditions for sustainable harvesting of microalgal biomass applying electrochemical method using non sacrificial electrodes
    (Elsevier, 2015) Misra, Rohit; Guldhe, Abhishek; Singh, Poonam; Rawat, Ismail; Stenström, Thor-Axel; Bux, Faizal
    The efficient harvesting of microalgae is considered to be one of the challenging steps of algal biofuel production and a key factor limiting the commercial use of microalgae. To overcome the limitation of metallic electrodes depletion, the application of non-sacrificial electrode was investigated for the electrochemical harvesting (ECH) of microalgae. The effect of applied current, addition of electrolyte and initial pH were parameters investigated. The highest recovery efficiency of 83% was obtained for Scenedesmus obliquus at 1.5 A, initial pH 9 and 6 g L−1 NaCl with power consumption of 3.84 kWh kg−1. Recovery efficiency of ECH process was comparable to literature reported centrifugation, filtration and chemical flocculation techniques but with a much lower power consumption. The ECH process with addition of electrolyte enhanced the lipid extraction by 22% without any adverse effects. The ECH process with non sacrificial carbon electrodes could be a possible harvesting step at commercial scale microalgal biomass production.
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    Thermal behavior and pyrolytic characteristics of freshwater Scenedesmus sp. biomass
    (Taylor and Francis, 2015) Ranjith Kumar, R.; Ramesh, D.; Mutanda, Taurai; Rawat, Ismail; Bux, Faizal
    Thermal behavior and pyrolytic characteristics of Scenedesmus sp. biomass was investigated under five different heating rates of 5, 10, 20, 30, and 40°C/min by using thermogravimetric analysis. The calorific value and carbon content of the tested biomass sample was 17.65 kJ g−1 and 46.60%, respectively. The data generated for thermogravimetric analysis showed that three stages of thermal decompositions occurred for selected biomass materials for all of the tested heating rates. The maximum volatile matter was evolved in the second stage of thermal decomposition, with temperatures between 273 and 399°C. The maximum thermal decomposition temperature increased from 294 to 330°C as the heating rates increased from 5 to 40°C/min. The average apparent activation energy of selected biomass determined by Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods were found to be closer values 203 kJ mol−1.
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    The optimization of biomass and lipid yields of Chlorella sorokiniana when using wastewater supplemented with different nitrogen sources.
    (Pubmed, 2014-09) Ramanna, Luveshan; Guldhe, Abhishek; Rawat, Ismail; Bux, Faizal
    The potential of nitrogen sources supplementing domestic wastewater for the cultivation of microalgae was assessed. Urea, potassium nitrate, sodium nitrate and ammonium nitrate were evaluated for their effect on cultivation and lipid production of Chlorella sorokiniana. Urea showed the highest biomass yield of 0.220 g L−1 and was selected for further experimentation. Urea concentrations (0–10 g L−1) were assessed for their effect on growth and microalgal physiology using pulse amplitude modulated fluorometry. A concentration of 1.5 g L−1 urea produced 0.218 g L−1 biomass and 61.52% lipid by relative fluorescence. Physiological stress was evident by the decrease in relative Electron Transport Rate from 10.45 to 6.77 and quantum efficiency of photosystem II charge separation from 0.665 to 0.131. Gas chromatography analysis revealed that C16:0, C18:0, C18:1, C18:2 and C18:3 were the major fatty acids produced by C. sorokiniana. Urea proved to be an effective nitrogen supplement for cultivation of C. sorokiniana in wastewater.