M.S. - Biosystems Engineering

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    Simultaneous Removal of Carbon and Nitrogen by Using a Single Bioreactor for Land Limited Application
    (Water Resources Research Center, University of Hawaii at Manoa, 1998-05) Cao, Keping
    An Entrapped-Mixed-Microbial-Cell (EMMC) process was investigated for its simultaneous removal of carbon and nitrogen in a single bioreactor with the influent COD/N ratio varying from 4 to 15 and influent alkalinity of 140 mg CaCO3/L and 230 mg CaCO3/L. The reactor was operated with alternate schedules of intermittent aeration. Two different sizes of carriers (10 * 10 * 10 mm3 and 20 * 20 * 20 mm3) were studied. The medium carrier (10 * 10 * 10 mm3) system presents higher nitrogen removal and COD removal compared to the large carrier system. The nitrogen removal efficiency is related to the ratio of COD/N in the influent. With the increase of the COD/N ration in the influent, the nitrogen removal efficiency is increased. The average reductions of nitrogen were over 92% and the average reductions of SCOD and BOD5 are over 95% and 97%, respectively, in the medium carrier system. This is operated at the HRT of 12 hours and 0.5 hour aeration and 2 hours of non-aeration, and the COD/N ratio of 15 in the influent. Changing alkalinity from 140 to 230 mg CaCO3/L has no effect in both large and medium carriers for the nitrogen removal efficiency. The pH, oxidation – reduction potential (ORP) and dissolved oxygen (DO) were used to monitor the biological nitrogen removal. It was found that the ORP (range from -100 to 300 mV) can be used to provide better effluent quality measured as total-nitrogen of less than 10 mg/L. Also, the impact of influent COD/N ratio on the effluent quality (measured as Inorg.-nitrogen) for the EMMC process is very important. Compared to other two compact biological wastewater treatment processes, membrane bioreactor (MBR) and moving bed biofilm reactor (MBBR), the EMMC process with the intermittent aeration has higher removal efficiencies of carbon and nitrogen, easier operation, lower O&M cost, lower energy requirement, and more compact. The total cost requirement is less than $3.27 per 1000 gallons (3.785 m 3) of treated settled domestic sewage per day. It is apparent that the EMMC process is technically feasible for the simultaneous removal of carbon and nitrogen under the operation on a schedule of intermittent aeration and suitable to be used for replacement or upgrading of existing treatment plant at land limited area.
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    Integrating an Intermittent Aerator for a Swine Wastewater Treatment System
    (Water Resources Research Center, University of Hawaii at Manoa, 1997-05) Wang, Zhiyu
    Integrating an intermittent aeration for the treatment of combined dilute and anaerobic digested swine wastewater in a field swine wastewater treatment system was investigated. Four operations models in term of ratio of aeration to no-aeration of 60:36, 5:1, 4:2 and 3:3 hour were evaluated. At the HRT of 3.2 days and ration of aeration to non-aeration of 3:3, the removal efficiency of BOD5, Total-N, TSS and Total-P of 98.0%, 92.4%, 95.6% and 59.4% could be achieved, respectively. The effluent quality of BOD5, NO3ˉ–N, NH4+–N and TSS concentrations were 35±12mg/l, 2.6±0.8 mg/l, 36±28 mg/l and 78±13 mg/l, respectively. The operational criteria were developed for integrating the intermittent aeration in the swine wastewater treatment system (including anaerobic reactors and sedimentation unit). Economical evaluation of the swine wastewater treatment system integrating the intermittent aeration unit was conducted. It was found that break even point was the operation of 166 pigs if the biogas and stabilized sludge were utilized. If the byproducts were not utilized, the cost of the treatment system are $12.30, $7.92, $7.21, $7.06 and $6.09 for the operation of 300, 1000, 2000, 3000 and 5000 pigs per year, respectively. Integrating the intermittent aeration unit in the swine waste treatment system provides the effective odor control, reduction of energy cost and treated wastewater reuse without creating the deterioration of environmental quality.
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    Investigation Of A Biological Fuel Cell In Methane Hydrate Marine Sediment
    ( 2004-12) Kurasaki, Ryan
    A microbial fuel cell was tested in marine sediment samples collected from known methane hydrate sites to determine whether power levels of 0.1 - 1 W, typically supplied by batteries in seafloor instrumentation, can be achieved. This fuel cell oxidizes biologically produced sulfide in the sediment and reduces dissolved oxygen in the water column to produce electricity. The specific objectives of this study were to demonstrate feasibility of concept; identify the most probable oxidation reactions that will occur on an anode exposed to the microbial metabolites and identify the bacteria that produce these reactants; quantify important system parameters including exchange current density and charge transfer coefficient; and establish baseline fuel cell power output, potential, and current density. Sediment samples used in this study were taken from sites on Blake Ridge, Cascadia Margin, and the Gulf of Mexico. DNA extracted from Gulf of Mexico sediments closely matched the sulfate-reducing bacteria Desulfotomaculum. Cyclic voltammetry and sampled-current voltammetry techniques were applied to sulfide solutions produced by this bacterium in Bactosulfate API enrichment media. The most probable anode reaction was determined to be the oxidation of hydrogen sulfide to elemental sulfur. At higher potentials, iron sulfide may also be oxidized. Linear potential scans of a graphite electrode immersed in oxygenated synthetic seawater suggest that oxygen reduction to water dominates the cathode reactions. Fuel cells operated in sediment samples were able to generate up to 0.010 W/m2 of power during short discharges. This power density is similar to data reported for microbial fuel cells tested in situ in estuarine environments (Reimers et al., 2001). Higher currents were observed in a laboratory setup where fuel cell electrodes were immersed in separate compartments, filled with a liquid culture of sulfate-reducing bacteria and with synthetic seawater, that were separated by a tube of sediment. Power generated by this cell was 0.018 W/m2 .The mass transfer of sulfide to the sediment electrode was found to be the current limiting process. Tafel plots of the fuel cell current-voltage data were employed to estimate the values of the exchange current density and charge transfer coefficient. The charge transfer coefficient was 0.98 and the average value of the exchange current density was 5.75 mA/m2.
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    Design and comparative evaluation of a three-layer coffee dryer
    (University of Hawaii at Manoa, 2003-08) Correa-Piedrahita, Arturo ; Gautz, Loren ; Biosystems Engineering
    Drying is an important processing step that prevents coffee from being attacked by bacteria and fungus that deteriorate quality. After coffee has been dried correctly, that is, dried to at least of 12 % wet basis moisture content; it can be stored safely with minimum risk of spoilage and quality deterioration. This study evaluated the drying performance of coffee beans dried in a newly developed three-layer coffee dryer, against rotary driers and traditional sun-drying. All the dryers were evaluated by measuring the uniformity of final moisture content and mechanical performance. The conclusion of this study is that, compared to sun-drying and mechanical rotary dryers, the new three-layer coffee drier yields virtually identical uniformity in final moisture content, yet it is achieved through a lower cost. This study also concluded that fuel oil is the most economical fuel to be used in the operation of mechanical dryers. Also, this study concludes that the sun-drying technique is the most expensive system to dry coffee in Kona for two reasons: (1) sun-drying coffee is inherently a manual-labor intensive process; and (2) the cost of manual labor in Kona is high. Lastly, this study's focus on sun dryers also shows that higher uniformity of final moisture can be attained by the incorporation of a three-times-per-day "Cenicafe" raking technique.