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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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Author: search.filters.author.Guldhe, Abhishek

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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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    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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    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.