Nitrous oxide (N2O) is known as one of the strong greenhouse gases and is emitted from aeration tanks of biological wastewater treatment plant. Strategy to control N2O emission from aeration tanks, however, has not been developed yet. We operated two identical pilot-scale anaerobic-anoxic-oxic (A2O) reactors to examine the effect of aeration intensity, especially to the first aerobic tank on N2O emission. The results indicate that the intensive aeration to the first aerobic tank increased N2O emission along with rapid ammonia oxidation and nitrite accumulation. On the contrary, moderate aeration provided gradual oxidation of ammonia, less nitrite accumulation and less N2O production. Batch tests with varied aeration intensities also demonstrated that intensive aeration enhances ammonium oxidation, resulting in the increased nitrite accumulation and the elevated N2O production, except in the case with high DO concentration (more than 2 mg/L). The conversion ratio of ammonia to N2O has good correlation to nitrite and nitrite/DO ratio. The effect of DO is complicated and still unclear. Mechanism of the elevated conversion to N2O is the effect of nitrite accumulation and might be the metabolic change of AOB.
A sequencing batch membrane biofilm reactor (SBMBfR) was developed towards simultaneous carbon, nitrogen and phosphorous removals from a low carbon/nitrogen (C/N) ratio wastewater. The SBMBfR is composed of two functional parts in a single-reactor vessel: (1) a fibrous-composite matrix of a gas-permeable hollow-fiber membrane on which a nitrifying biofilm grows and (2) activated sludge in which denitrifying polyphosphate-accumulating organisms (DNPAOs) are predominant. The reactor was operated in a batch manner with the turning on and off of the membrane aeration. Anaerobic period (without membrane aeration) allowed consumption of organic carbon by DNPAOs. They further took phosphate in the bulk with nitrite/nitrate produced via nitrification at the nitrifying biofilm during membrane aeration period. A higher nitrogen removal efficiency was obtained with the nitrifying biofilm formed on a gas-permeable membrane at various C/N ratios in synthetic wastewaters than without the biofilm, corroborating the significance of the biofilm as a region for ammonia oxidation. Continuous operation of the SBMBfR achieved average nitrogen and phosphorus removal efficiencies of 90% and 92%, respectively, at a C/N ratio of 2.0 indicating the effectiveness of the SBMBfR for nutrient removal from low C/N ratio wastewater.
This study investigated the potential application of pressurized CO2 for water disinfection. Under supporting high pressure, a high volume of CO2 microbubbles were produced in a liquid environment. Specifically, the inactivation effects of CO2 against Escherichia coli, bacteriophage MS2 and T4 were examined at equal pressures (0.3 - 0.9 MPa) and temperatures. The optimum conditions were found to be 0.7 MPa and an exposure time of 25 min. Under identical treatment conditions, a greater than 5.0 log reduction in E. coli was achieved, while over 3.0 log and nearly 4.0 log reductions were observed for phage MS2 and phage T4, respectively. Comparison of the inactivation effect of CO2, N2O, a common acid and buffer solution against phage MS2, revealed that the change in pH caused by CO2 plays an important role in its virucidal effects. Moreover, the pumping cycle and depressurization rate contributed to the inhibition of microorganisms. Overall, the results of this study indicate that CO2 has the potential for use as a disinfectant without the formation of by-products.
The present study investigates a newly developed method using propidium monoazide (PMA) to detect damage on the outer membrane of bacteria. In order to verify this method, Escherichia coli were disinfected by ultraviolet, chlorine and sawdust treatments assuming a composting toilet. The inactivation mechanisms were investigated by multiple detection methods focused on which parts and/or functions were damaged. The differences in detection principles among three kinds of growth media and the polymerase chain reaction (PCR) method were used as methods to investigate the damage caused by disinfection. In addition, damage to the outer membrane was distinguished using PMA as pretreatment following PCR or conventional cultivation media, Tryptic Soy Agar (TSA), called PMA-PCR and PMA-TSA, respectively. As a result, it was indicated that chlorination caused outer membrane damage, and that ultraviolet treatment did not. Sawdust treatment at high temperature damaged the outer membranes effectively. It was confirmed that PMA-TSA, a newly developed method, could detect damage on the outer membrane of Escherichia coli more sensitively and quantitatively than PMA-PCR.
High-concentration industrial molasses wastewater treatment was examined using biological reactors coupled with physicochemical filtration membranes. The biological processes combined two mesophilic upflow anaerobic sludge blanket (UASB) reactors, a multi-stage upflow anaerobic sludge blanket (MS)-UASB, and a regular UASB for primary anaerobic pre-organic removal, and a downflow hanging sponge (DHS) reactor, equipped with polyurethane sponge media for post-aerobic treatment. Concentrated blackstrap molasses was diluted [12,000 - 1,500 mg of chemical oxygen demand (COD)/L] with organic loading rate (OLR) of 4.5 - 57.7 kg-COD/m3/d (MS-UASB), 2.3 - 34.7 kg-COD/m3/d (UASB), and 0.2 - 6.0 kg-COD/m3/d (DHS). A 1:1.3 recirculation ratio within the MS-UASB was evaluated at different influent concentrations for COD, biogas (CH4) production, and nitrogen, phosphate, and color removal. The average total organic COD removal was over 92% with and without recirculation. A total of 150 NL/d of biogas with 64 - 75% methane content was collected at the maximum loading rate and influent concentration. Ammonia was reduced from 30 mg-N/L to 5 mg-N/L in the DHS reactor. The dark influent could not be reduced biologically; however, ultrafiltration and nanofiltration removed 98% of the color.
A model was developed to estimate the removal of pharmaceutical compounds in a sewage treatment plant. The model was based on the material balances of activated sludge and pharmaceuticals in liquid and solid phases in the aeration tank and the settler. Non-ideal mixing characteristics for the aeration tank were described using a tanks-in-series model. The model took into account the biological degradation of pharmaceuticals by microorganisms in the activated sludge in addition to sorption and desorption onto the microorganisms. The concentration profiles of activated sludge and pharmaceuticals in liquid and solid phases in the aeration tank could be predicted by the model using input data from laboratory tests, such as kinetic constants for degradation by the activated sludge, and adsorption-desorption onto the microorganisms. The model predictions were compared with the observed removal efficiencies for atenolol, carbamazepine, diclofenac, ibuprofen, sulfamethoxazole, and trimethoprim. The model could reasonably predict the removal trends for several pharmaceuticals.
The advantage of acidic operation below pH of 3 in membrane bioreactors (MBRs) for the treatment of molasses wastewater was examined. Stable operation of both an acidic reactor and a neutral pH reactor was observed for 91 days. Percent COD removal was 48.5% for the acidic reactor and 63.6% for the neutral pH reactor when biologically pretreated molasses wastewater was fed to the reactors. Higher percentage removals of COD (89.0% for the neutral pH reactor and 84.0% for the acidic reactor) were observed, when molasses wastewater (COD 650 mg/L) was directly fed to the reactor because of higher concentration of biologically degradable organic matter in the feed solution. In spite of lower percentage of COD removal in the acidic reactor, higher percentage of color removal was observed spectrophotometrically with the low pH operation. Higher percentage of color removal in the acidic reactor was probably due to the enhanced adsorption of colored substances in the acidic environment followed by gradual biological degradation.