Facile Synthesis of Activated Carbon from Cellulose in the Presence of Air for Ammonia Recovery in Resource-Constrained Settings

As efforts to provide sanitation services in low-resource rural settings of the world proliferate, nutrient recovery via source separation of urine becomes important for economic and environmental implications in these regions of challenging socio-economic constraints. Substantial N (in some cases > 50%) is lost from urine via off-gassed ammonia which can be captured and utilized more efficiently by the use of sorbents such as activated carbon synthesized locally in resource-constrained settings. My work is focused on developing a simple method to synthesize functionalized-activated carbon from locally available biomass at moderate temperatures (400-450)°C in the presence of air. Using cellulose as a model biomass and diammonium hydrogenphosphate (DAP) as the activating agent, the production of activated carbon is explored in a simple semi-batch Partial Oxidation (POX) reactor setup. DAP helps to facilitate low temperature pyrolysis of cellulose by the action of phosphoric acid which helps in depolymerization and the breakdown of glycosidic linkages present in lignocellulosic biomass. Further, the film of condensed phosphates prevents carbon oxidation at high temperature in the presence of air. This study provides insight into the interaction between DAP and biomass, as well as the char forming mechanism. Various characterization techniques such as N2 physisorption, XPS, DRIFTS, SEM, TEM, surface charge measurements and Raman spectroscopy are utilized to compare the properties between activated carbon formed under nitrogen and partial oxidative conditions. The interaction of DAP with cellulose is investigated and the nature of bonding of the heteroatoms to the carbonaceous matrix is elucidated. Our results indicate that the quality of activated carbon prepared under partial oxidation condition is comparable to carbon prepared under nitrogen, leading to the possibility of an activated biochar production scheme on a small scale. The prepared activated carbon is utilized to recover ammonia off-gassed from urine providing multiple benefits including odor removal and nutrient recovery since ammonia augmented biochar can serve as a soil amendment. The hygroscopic nature of the prepared activated biochar is useful for holding soil moisture during the dry season and is envisioned to provide better soil health for round the year crop production. The efficacy of the synthesized activated biochar as an ammonia adsorbent is evaluated from adsorption isotherms by studying equilibrium capacity and elucidating the nature of the interaction by Temperature Programmed Desorption (TPD) and DRIFTS measurements. Our results show promising capacities for ammonia adsorption from the gas phase. The total dry ammonia adsorption capacity of the synthesized activated carbons was found to be ~ (24-28) mg/g at 50°C, comparable in magnitude to zeolites. It was observed that > 90% of the adsorbed ammonia could be easily recovered by simple water washing at room temperature, facilitating facile regeneration.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146068/1/mnahata_1.pd

Rapid and Efficient Arsenic Removal by Iron Electrocoagulation Enabled with in Situ Generation of Hydrogen Peroxide.

Millions of people are exposed to toxic levels of dissolved arsenic in groundwater used for drinking. Iron electrocoagulation (FeEC) has been demonstrated as an effective technology to remove arsenic at an affordable price. However, FeEC requires long operating times (∼hours) to remove dissolved arsenic due to inherent kinetics limitations. Air cathode Assisted Iron Electrocoagulation (ACAIE) overcomes this limitation by cathodically generating H2O2 in situ. In ACAIE operation, rapid oxidation of Fe(II) and complete oxidation and removal of As(III) are achieved. We compare FeEC and ACAIE for removing As(III) from an initial concentration of 1464 μg/L, aiming for a final concentration of less than 4 μg/L. We demonstrate that at short electrolysis times (0.5 min), i.e., high charge dosage rates (1200 C/L/min), ACAIE consistently outperformed FeEC in bringing arsenic levels to less than WHO-MCL of 10 μg/L. Using XRD and XAS data, we conclusively show that poor arsenic removal in FeEC arises from incomplete As(III) oxidation, ineffective Fe(II) oxidation and the formation of Fe(II-III) (hydr)oxides at short electrolysis times (<20 min). Finally, we report successful ACAIE performance (retention time 19 s) in removing dissolved arsenic from contaminated groundwater in rural California

MODELLING AND SIMULATION OF A LAMINAR FLOW TUBULAR REACTOR (LFTR)

ABSTRACT: Residence Time Distribution (RTD) is a popular technique to determine the extent of non-ideality in reactors but can be used only after design and fabrication. There are no methods available to incorporate non-ideality at the design stage. However E curve is available for constant density laminar flow which can be used to predict conversion. The proposed model equation has analytical solutions only for some special cases such as elementary first-order and second order reactions and that too for special cases of reactants in stoichiometirc ratio. Therefore in the present work attempt has been made to formulate, test and validate a numerical model which will incorporate non-ideality in the reactor performance before the design is made. The results of this numerical model are compared with those of simulations carried out on commercial Computational Fluid Dynamics (CFD) package namely STAR CCM+ ver. 5.04.008. Numerical model results agree well with the simulation results. The small difference in the results of numerical method and simulation were analyzed and the reasons for the same were identified. The difference between the conversion obtained by the numerical model and simulation was found to increase, reach a maximum and then decrease as the Damkohler Number (N Da ) was increased. It was also found that for a reaction having kinetics , a maxima occurred at N Da = 1.63 irrespective of initial concentration of reactants. Further it was observed that the plot of conversions predicted by numerical model versus conversion in simulation was universal in the sense that all such curves overlapped for different values of rate constant and initial concentration of reactants for a given reaction type

Adapting a drinking water treatment technology for arsenic removal to the context of a small, low-income California community.

Small, low-income, and rural communities across the United States are disproportionately exposed to arsenic contaminated drinking water because existing treatment solutions are too expensive and difficult to operate. This paper describes efforts to overcome some barriers and limitations of conventional iron electrocoagulation (Fe-EC) to enable its use in the rural Californian (U.S.) context. Barriers and limitations of Fe-EC's application in rural California considered in this work include: 1) Frequent labor intensive electrode cleaning is required to overcome rust accumulation, 2) Electrolysis durations are long, reducing throughput for a given system size, and 3) Waste needs compliance with California standards. We report results from an investigation for overcoming these limitations via a field trial on a farm in Allensworth, a small, low-income, rural community in California. Our strategies to overcome each of the above barriers and limitations are respectively, 1) operating the Fe-EC reactor at high current density to result in sustained Fe production, 2) operating at high charge dosage rate with external H2O2, and 3) characterization of the arsenic-laden waste, and are discussed further in the paper. Main findings are: (1) Fe-EC removed arsenic consistently below the federal (and state) standard of 10 µg/L, (2) high current density failed to sustain Fe production whereas low current density did not, (3) electrolysis time decreased from > 1 hour to < 2 min with H2O2 dosing of 5 mg/L at higher charge dosage rates, (4) dilution of As-sludge is required to comply with State's non-hazardous waste status, and (5) discrepancies were observed between lab and field results in using current density to overcome labor-intensive electrode cleanings. Finally, implications of overcoming limitations to scale-up of Fe-EC in relevant California communities are discussed