Browsing by Subject "Anaerobic digestion"

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    Anaerobic digestion of Spirulina sp. and Scenedesmus sp.: a comparison and investigation of the impact of mechanical pre-treatment
    (Springer, 2015) Inglesby, A E; Griffiths, M J; Harrison, S T L; van Hille, R P
    Anaerobic digestion (AD) is a unit process that integrates beneficially and sustainably into many bioprocesses. This study assesses and compares the production of methane from the biomass of the microalga Scenedesmus sp. and the cyanobacterium Spirulina sp. in batch anaerobic digesters. Anaerobic digestion of whole cell Spirulina resulted in a substantially higher methane productivity (0.18 L CH4 Lreactor−1 day−1) and methane yield (0.113 L CH4 g−1 volatile solids (VS)) compared to the digestion of whole cell Scenedesmus (0.12 L CH4 Lreactor−1 day−1 and 0.054 L CH4 g VS−1). Spirulina, possibly due to a combination of osmotic shock, the filamentous nature of the cells and lower mechanical strength of the non-cellulosic cell wall, was more readily degraded by hydrolytic and acidogenic microorganisms, resulting in the generation of a greater amount of acetic acid. This in turn provided greater substrate for methanogens and hence higher methane yields. In addition, Spirulina cells could be disrupted mechanically more quickly (1 h) than Scenedesmus cells (4 h) in a bead mill. Mechanical pre-treatment improved the final methane yields (L CH4 g VS−1) obtained from digestion of both substrates; however, the improvement was greater for Scenedesmus. Mechanical pre-treatment resulted in a 47 % increase in methane production for Spirulina compared to 76 % increase for Scenedesmus fed digesters. The more substantial increase observed for Scenedesmus was due to the relatively inefficient digestion of the whole, unruptured cells.
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    Anaerobic digestion of Spirulina sp. and Scenedesmus sp.: a comparison and investigation of the impact of mechanical pre-treatment
    (Springer, 2015-05) Inglesby, A E; Griffiths, M J; Harrison, S T L; Van Hille, R P
    AAnaerobic digestion (AD) is a unit process that integrates beneficially and sustainably into many bioprocesses. This study assesses and compares the production of methane from the biomass of the microalga Scenedesmus sp. and the cyanobacterium Spirulina sp. in batch anaerobic digesters. Anaerobic digestion of whole cell Spirulina resulted in a substantially higher methane productivity (0.18 L CH4 Lreactor −1 day−1) and methane yield (0.113 L CH4 g−1 volatile solids (VS)) compared to the digestion of whole cell Scenedesmus (0.12 L CH4 Lreactor −1 day−1 and 0.054 L CH4 g VS−1). Spirulina, possibly due to a combination of osmotic shock, the filamentous nature of the cells and lower mechanical strength of the non-cellulosic cell wall, was more readily degraded by hydrolytic and acidogenic microorganisms, resulting in the generation of a greater amount of acetic acid. This in turn provided greater substrate for methanogens and hence higher methane yields. In addition, Spirulina cells could be disrupted mechanically more quickly (1 h) than Scenedesmus cells (4 h) in a bead mill. Mechanical pre-treatment improved the final methane yields (L CH4 g VS−1) obtained from digestion of both substrates; however, the improvement was greater for Scenedesmus. Mechanical pre-treatment resulted in a 47 % increase in methane production for Spirulina compared to 76 % increase for Scenedesmus fed digesters. The more substantial increase observed for Scenedesmus was due to the relatively inefficient digestion of the whole, unruptured cells.
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    Biodegradability of wastewater and activated sludge organics in anaerobic digestion
    (2014) Ikumi, D S; Harding, T H; Ekama, G A
    The investigation provides experimental evidence that the unbiodegradable particulate organics fractions of primary sludge and waste activated sludge calculated from activated sludge models remain essentially unbiodegradable in anaerobic digestion. This was tested by feeding the waste activated sludge (WAS) from three different laboratory activated sludge (AS) systems to three separate anaerobic digesters (AD). Two of the AS systems were Modified Ludzack – Ettinger (MLE) nitrification-denitrification (ND) systems and the third was a membrane University of Cape Town (UCT) ND and enhanced biological P removal system. One of the MLE systems and the UCT system were fed the same real settled wastewater. The other MLE system was fed raw wastewater which was made by adding a measured constant flux (gCOD/d) of macerated primary sludge (PS) to the real settled wastewater. This PS was also fed to a fourth AD and a blend of PS and WAS from settled wastewater MLE system was fed to a fifth AD. The five ADs were each operated at five different sludge ages (10–60d). From the measured performance results of the AS systems, the unbiodegradable particulate organic (UPO) COD fractions of the raw and settled wastewaters, the PS and the WAS from the three AS systems were calculated with AS models. These AS model based UPO fractions of the PS and WAS were compared with the UPO fractions calculated from the performance results of the ADs fed these sludges. For the PS, the UPO fraction calculated from the AS and AD models matched closely, i.e. 0.30 and 0.31. Provided the UPO of heterotrophic (OHO, fE_OHO) and phosphorus accumulating (PAO, fE_PAO) biomass were accepted to be those associated with the death regeneration model of organism "decay", the UPO of the WAS calculated from the AS and AD models also matched well - if the steady state AS model fE_OHO = 0.20 and fE_PAO = 0.25 values were used, then the UPO fraction of the WAS calculated from the AS models deviated significantly from those calculated with the AD models. Therefore in plant wide wastewater treatment models the characterization of PS and WAS as defined by the AS models can be applied without modification in AD models. The observed rate limiting hydrolysis/acidogenesis rates of the sludges are listed.