6 research outputs found

    Modifying supersaturation rate with membrane area to volume ratio: scaling reduction and improved crystal growth control in membrane distillation crystallisation

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    This study provides detailed characterisation of nucleation kinetics, induction time and supersaturation to understand scaling and crystal growth in membrane distillation crystallisation. Membrane area was used to moderate supersaturation rate, as a method to transition across the metastable zone without modifying boundary layer conditions. Increasing membrane area sustained the same water vapour flux but increased supersaturation rate within the crystallising solution (sodium chloride). This reduced induction time and increased the supersaturation level at induction. Membrane scaling was minimised by increasing supersaturation rate despite an increase in nucleation rate. This conforms with classical nucleation theory but contradicts membrane distillation crystallisation literature, where elevated supersaturation is often linked to advanced scaling. The transition from heterogeneous to homogeneous nucleation was evidenced once greater supersaturation at induction was achieved. The probability for scaling within the low supersaturation domain was confirmed through diagnostic investigation of the scaling deposit formed, and the growth mechanism within the scaling layer related to the relevant supersaturation region. Crystal size and morphology were also related to the metastable region, where membrane-to-volume ratio can facilitate higher nucleation rates complemented by greater crystal growth. This study provides critical insight for the development of scaling mitigation strategies and creates a basis for the sustainable design of thermal membrane crystallisation systems

    Novel insight on the impact of enzymatic addition on organic loading rate in anaerobic digestion

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    Addition of enzymes to anaerobic digesters (ADs) has been reported as beneficial to the hydrolytic step of the process. Additional benefits have been described for bioadded reactors such as improved dewatering and lower energy requirements. This work aimed to assess the long-term and unaccounted effects of enzymatic addition on sludge digestion. Enzymesā€™ impacts were tested using different addition modes (bulk or gradual addition) and during operational changes on reactors operated for 295 days. Enzyme added in bulk, generated a 14% increase in biogas production (144 ml/gVSadded) compared to control (126 ml/gVSadded), whereas the same amount of enzyme added gradually produced a 10% increase (139 ml/gVSadded). These values however, where higher when the OLR was increase from 3 to 5.5 kg VS/(m3 day): 257, 212 and 149 ml/gVSadded for the enzyme added in bulk, the enzyme added gradually and the control respectively. Specific biogas yields (SBY), higher in bioadded reactors, were significantly different between control reactors and those reactors dosed in bulk. Furthermore, following OLR increase, the mode of enzyme addition resulted in different increases in gas production rate (GPR) when the enzyme was added in one dose compared to control and to a gradual addition, 121%, 32% and 93% respectively. These results offer a new hypothesis on the impact of bioadditions to AD during changing operational conditions, suggesting a potential stabilising effect of the enzymes in continuous systems

    Solid state anaerobic digestion of water poor feedstock for methane yield: an overview of process characteristics and challenges

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    Solid state anaerobic digestion (SSAD) of water poor feedstock may be a promising technology for energy recovery. Feedstocks having high solid concentration like lignocellulosic biomass, crop residues, forestry waste and organic fraction of municipal waste may be the appropriate feedstock for its biochemical conversion into energy carries like biomethane through SSAD. Compared to liquid state anaerobic digestion (LSAD), SSAD can handle higher organic loading rates (OLR), requires less water and smaller reactor volume and may have lower energy demand for heating or stirring and higher volumetric methane productivity. Besides these, pathogen inactivation may also be achieved in SSAD of biodegradable waste. Around 60% of recently built AD systems have adopted SSAD technology. However, the process stability of an SSAD system may have several constraints like limited mass transfer, process inhibitors and selection of digester type and should be addressed prior to the implementation of SSAD technology. In this article, a comprehensive overview of the key aspects influencing the performance of SSAD is discussed along with the need for mathematical modelling approaches. Further to this, reactor configuration for SSAD and digestate management requirement and practice for solid-state condition are reviewed for a better insight of SSAD technology

    Solid state anaerobic digestion of water poor feedstock for methane yield: An overview of process characteristics and challenges

    No full text
    Solid state anaerobic digestion (SSAD) of water poor feedstock may be a promising technology for energy recovery. Feedstocks having high solid concentration like lignocellulosic biomass, crop residues, forestry waste and organic fraction of municipal waste may be the appropriate feedstock for its biochemical conversion into energy carries like biomethane through SSAD. Compared to liquid state anaerobic digestion (LSAD), SSAD can handle higher organic loading rates (OLR), requires less water and smaller reactor volume and may have lower energy demand for heating or stirring and higher volumetric methane productivity. Besides these, pathogen inactivation may also be achieved in SSAD of biodegradable waste. Around 60% of recently built AD systems have adopted SSAD technology. However, the process stability of an SSAD system may have several constraints like limited mass transfer, process inhibitors and selection of digester type and should be addressed prior to the implementation of SSAD technology. In this article, a comprehensive overview of the key aspects influencing the performance of SSAD is discussed along with the need for mathematical modelling approaches. Further to this, reactor configuration for SSAD and digestate management requirement and practice for solid-state condition are reviewed for a better insight of SSAD technology
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