Browsing by Author "Arun, S"

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    Ammonium rich wastewater treatment and value addition using microalgae-bacterial consortia in photo-activated systems.
    (2021) Arun, S
    The conventional activated sludge process (ASP) for ammonium removal relies on mechanical aeration. In addition to very high operating cost due to mechanical aeration, ASP requires addition of external carbon source for nitrification and denitrification. On the other hand, microalgae-bacteria consortia are not only able to grow autotrophically on ammonium but also offer advantages, such as high N affinity, anoxic zone for denitrification, algal photosynthesis, shortcut nitrogen removal, biomass with good settling characteristics and energy production. Hence, this work was aimed at treatment and value addition to ammonium rich wastewater by using microalgae-bacterial consortia. The microalgae-bacterial biomass was initially studied for its ability to remove ammonium at a high concentration of 200 mg/L. Addition of organic carbon source in a photosequencing batch reactor (PSBR) during the dark period enhanced the activity of denitrifying bacteria (DNB) in the microalgae-bacterial consortium, which resulted in nitrogen as the main end product. Detailed bio-kinetics of ammonium removal by the microalgae-bacterial consortium revealed an active role played by microalgae, ammonium oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and DNB for achieving an efficient removal of ammonium. Both the ammonium and nitrogen gas production were best described by using the microalgae-AOB-methanol utilizing denitrifier (MUD) based bio-kinetic models. Also, the profiles of ammonium, nitrite, nitrate and DO in this study were accurately predicted by the microalgae-AOB-MUD bio-kinetic models. Estimated values of the bio-kinetic model parameters further supported the shortcut nitrogen removal without nitrate formation by microalgae, AOB and DNB in the consortium. Light intensity significantly affected the ammonium removal by microalgae-AOB-NOB consortium. Empirical model as mentioned earlier showed that light intensity below 40 μmol photons m−2 s−1 was ineffective towards nitrification due to oxygen limitation condition. Light intensity in the range 40-160 μmol photons m−2 s−1 was found suitable for complete nitrification, whereas a light intensity above 100 μmol photons m−2 s−1 caused inhibition of microalgal-AOB-NOB consortium, thereby resulting in a low nitrification efficiency. The effect of different nitrogen source competition using microalgae-bacterial consortia on ammonium removal was further studied and the NH4 + removal rate values were similar at 50 and 100 mg NH4+-N/L respectively, indicating enhancement in ammonium removal by both nitrification and microalgae uptake. By comparing the results from this work with a previous study, O2 supplied by microalgae through NH4 + uptake was found to strongly influence the overall NH4 + removal by consortium. Finally, ammonium removal by algae-AOB-DNB consortium was integrated in a microbial fuel cell (MFC) and the system was referred as an integrated shortcut nitrogen removal-microbial fuel cell. This study provided direct evidence of shortcut nitrogen removal in membrane photosynthetic microbial fuel cell (MPMFC) by integrating nitritation into the cathodic compartment, which demonstrated a very good ability to overcome issues related to high aeration cost and NOB activity.
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    Design, development and testing of user friendly, light weight and inexpensive artificial limb for trans-femoral amputees
    (2016) Arun, S
    The trans-femoral amputation is a surgical interference that severs the thigh segment between the hip and knee joint. Though many prosthetic devices are available in the market, each one of them has inherent limitations. Thus, an attempt was made to design and develop a light weight and user friendly artificial limb having improved functionality with affordability in addition to the development of new materials for the socket and knee joint. The knee joint was designed based on the Grashof's criterion, stance phase stability, and extension bias. Based on the static and dynamic analysis, the knee joint was fabricated using nylon and it was fixed for 9 trans-femoral amputees. It is confirmed from the rehabilitation studies that the performance of prosthesis and the health related quality of life of the patients were observed to be significantly improved. The poly (methyl methacrylate) PMMA/MWCNT was selected as a material for the knee joint and the epoxy based sandwich composites along with MWCNT reinforcement was proposed to be used as a material for the socket. Based on the mechanical characteristics, PMMA/0.25 wt.% MWCNT was suggested to make a knee joint, which was also found to be suitable to reduce the aging degradation, where the modified Halpin-Tsai model and Pukanszky model are used to predict the mechanical properties of PMMA/MWCNT composites. It was observed that the increase in mechanical and thermal properties of 0.3 wt. % MWCNT reinforced epoxy/glass fabric/stockinet layer sandwich composite, which is suggested to be make a socket, led to reduce the (i) weight of the socket; (ii) temperature gradient across the thickness of the socket; (iii) temperature raise inside the socket; (iv) metabolic cost of an amputee. It is also anticipated that the newly developed light weight, durable and user-friendly knee joint is expected to make huge impact in locomotive disabled people community due to its function, performance, affordability and near sound leg gait pattern and thus it is expected to increase the comfort level of trans-femoral amputees and decrease their metabolic cost.