Z. Yun

The effect of co-existing ions and surface characteristics of nanomembranes on the removal of nitrate and fluoride

Abstract The rejection rates of nitrate and fluoride were investigated by two nanomembranes which had different surface potentials. The surface potential of NTR 7250 and NTR 7450 were approximately −5mV and −10mV, around pH 7, respectively. The effects of calcium, magnesium and sulfate were also investigated since they usually co-existed in groundwater. The experiment indicated that sulfate would be rejected most among other ions in the groundwater. The chloride ions were rejected more than nitrate and fluoride ions. This experiment indicated that the electric repulsion between the nanomembrane and chloride ion was so high that it could even push some divalent sulfate ions through the membrane. The influence of chloride ions was complicated when magnesium and fluoride ions were in the solution. The experiment showed that when permeated divalent cations cause a strong demand for anion permeation to meet the electroneutrality, the least repulsive anions in the solution could pass a membrane with higher surface potential more than one with lower surface potential. The rejection rates of nitrate and fluoride ions were similar. However, the experimental results indicated that fluoride was less affected by the surface charge of the membrane than nitrate. The hydration effect of nitrate would be stronger at a membrane with lower surface potential. The reductions in rejection rates of monovalent ions were more significant at a membrane with a low surface potential. The 5mV difference in surface potential showed appreciably divergent behavior. However, the electrostatic repulsion between the divalent ion and the membranes seemed to be strong enough so that 5mV of surface charge difference between NTR 7250 and NTR 7450 did not cause any appreciable distinction. Most of the negatively charged groups on the membrane are shielded by cations at high salt concentration. The experiment indicated that calcium ions shielded membrane charges more effectively than magnesium ions. However, despite the charge shielding effect, the rejection rates against the divalent anion were high, and more ions were rejected by the membrane that has a high negative surface potential.

Transfer of antibiotic resistance plasmids in pure and activated sludge cultures in the presence of environmentally representative micro-contaminant concentrations

The presence of antibiotics in the natural environment has been a growing issue. This presence could also account for the influence that affects microorganisms in such a way that they develop resistance against these antibiotics. The aim of this study was to evaluate whether the antibiotic resistant gene (ARG) plasmid transfer can be facilitated by the impact of 1) environmentally representative micro-contaminant concentrations in ppb (part per billion) levels and 2) donor-recipient microbial complexity (pure vs. mixed). For this purpose, the multidrug resistant plasmid, pB10, and Escherichia coli DH5α were used as a model plasmid and a model donor, respectively. Based on conjugation experiments with pure (Pseudomonas aeruginosa PAKexoT) and mixed (activated sludge) cultures as recipients, increased relative plasmid transfer frequencies were observed at ppb (μg/L) levels of tetracycline and sulfamethoxazole micro-contaminant exposure. When sludge, a more complex community, was used as a recipient, the increases of the plasmid transfer rate were always statistically significant but not always in P. aeruginosa. The low concentration (10 ppb) of tetracycline exposure led to the pB10 transfer to enteric bacteria, which are clinically important pathogens.

Removal of Ammonium from Tannery Wastewater by Electrochemical Treatment

Abstract The removal of ammonium from coagulated tannery wastewaters was investigated by an electrochemical method using Ti/IrO2 as an anode. Operating variables including the current density, pH and chloride concentration were considered in order to determine their effect on the ammonium removal efficiency. A maximum ammonium removal rate of 78.9% was achieved after 30 min of electrochemical treatment with 4 A dm−2 of current density. During the electrolysis, it had been observed that the ammonium removal was accompanied with an elimination of the organics. Generation of hydroxyl radical was identified during the experiment with hydroxyl radical probe compound of pCBA. Chloride ion worked as the scavenger of hydroxyl radical. Role of free chlorine was the main oxidant for the elimination of ammonium and organic substances. As a result, the biodegradability of tannery wastewater increased after electrochemical treatment. The energy consumed per 1 kg of ammonium removal was 26.6 kWh for initial NH4-N concentration of 870 mg L−1.

Biological nitrogen and phosphorus removal in UCT-type MBR process.

A lab-scale UCT-type membrane bio-reactor (MBR) was operated for biological nitrogen (N) and phosphorus (P) removal simultaneously. In order to examine biological nutrient removal (BNR) characteristics of MBR, the lab unit was fed with a synthetic strong and weak wastewater. With strong wastewater, a simultaneous removal of N and P was achieved while application of weak wastewater resulted in a decrease of both N and P removal. Recycled nitrate due to the limited organic in weak wastewater operation probably caused a nitrate inhibition in anaerobic zone. In step feed modification with weak wastewater, both N and P removal capability recovered in the system, indicating that the allocation of COD for denitrification at anoxic zone was a key to increase the biological P removal. In addition, the analysis on the specific P uptake rate in anoxic zone demonstrated that denitrifying phosphorus accumulating organism (dPAO) played an important role to remove up to 40% of P along with N. The sludge production characteristics of UCT-type MBR were similar to ordinary activated sludge with BNR capability.

Effect of biologically mediated pH change on phosphorus removal in BNR system for piggery waste treatment

Since applicable amount of animal waste to farm land has been greatly reduced because of the nutrient overload, nitrogen and phosphorus removal from animal waste has received a great attention. This study was conducted to evaluate how phosphorus was removed during biological nutrient removal (BNR) from piggery waste using laboratory and full scale units operated at 25 to 40°C. The phosphorus removal was performed by chemical precipitation with struvite and hydroxyapatite (HAP), cellular formation, it is basically related with pH and organic and nitrogen loads resulting in influent COD/N ratios. The removal efficiencies increased from 50 to 90% as COD/N ratios increased to 6 to 7, but carbon was not limited beyond this ratio for denitrification resulting in a stable pH. Overall, about 70% of the phosphorus removal was due to the precipitates of struvite and/or HAP, and the remaining removal was due to the cellular P formation. Any significant temperature effect on phosphorus removal was not observed within the operating temperature. In order to maximize phosphorus removal in BNR system, additional anoxic stage must be furnished prior to discharge its final effluent after oxic stage.

Enhancement of reactor performance and pelletization by reactor modification in UASB system

Abstract Reactor performance and pelletization characteristics by reactor modification in a UASB system were investigated. The modified lab UASB reactor with a settler comprising 50% of the total reactor volume showed better performance in removing soluble organics, as well as producing lower TSS effluents at higher loading rates. The reason for the improved performance may be the formation of a deep sludge blanket in the modified settler. The advantages of the modified reactor system are observable in methane production and alkalinity requirements. Furthermore, the pellets from the UASB system with a modified settler showed better settleability and biomass holding capacity. The chemical composition of the biopellets was a little different from the common bacterial formula of C5H7O2N. Morphological characterization with SEM revealed many clusters, in terms of the physiological properties of hydrogen‐utilizing organisms, on the surface of pellets taken from the high hydrogen partial pressure zone in the modified reactor. This observation also suggests that the modified UASB system provides a better environment for the growth of hydrogen‐utilizing organisms.

Comparison of biochemical characteristics between PAO and DPAO sludges

A successful enhanced biological phosphorus removal (EBPR) was observed in both anaerobic-aerobic sequencing batch reactor (An-Ox SBR) to induce growth of phosphorus accumulating organism (PAO) and anaerobic-anoxic (An-Ax) SBR to induce growth of denitrifying PAO (DPAO). Although the EBPR performance of An-Ox SBR was higher by 11.3% than that of An-Ax SBR, specific phosphorus release rates in the An-Ax SBR (22.8 ± 3.5 mg P/(g VSS·hr)) and the An-Ox SBR (22.4 ± 4.8 mg P/(g VSS·hr)) were similar. Specific phosphorus uptake rates under anoxic and aerobic conditions were 26.3 ± 4.8 mg P/(g VSS·hr) (An-Ax SBR) and 25.6 ± 2.8 mg P/(g VSS·hr) (An-Ox SBR), respectively, which were also similar. In addition, an analysis of relationship of poly-β-hydroxyalkanoates (PHA) synthesized under anaerobic conditions with phosphorous release (Preleased/PHA synthesized) and of PHA utilized under anoxic and aerobic conditions with phosphorous uptake (Puptaked/PHAutilized) verified that biological activities of EBPR per unit biomass between DPAO and PAO were similar. An analysis of the specific denitrification rate of DPAO showed that NO(-)3-N can be denitrified at a rate that does not substantially differ from that of an ordinary denitrifier without additional consumption of organic carbon when the PHA stored inside the cell under anaerobic conditions is sufficiently secured.

The variation of volatile fatty acid compositions in sewer length, and its effect on the process design of biological nutrient removal

The potential of enhanced biological phosphorus removal (EBPR) in biological nutrient removal (BNR) systems critically depends on the availability and types of volatile fatty acids (VFAs) in sewage. Although the characteristics of VFAs in sewage are strongly related with the biochemical transformations in the sewer system, they have not been studied thoroughly in terms of BNR process design. We have investigated the characteristics of VFAs in influent of nine sewage treatment plants which represent typical small to very large sewer systems in Korea. We found that influent total VFACOD (VFA as chemical oxygen demand) concentrations ranged from 20.4 to 65.2 mg/L. Acetic acid was a predominant VFA in sewage, and the propionic acid (HPr) portion averaged 38.7% of total VFACOD. However the sewage from longer sewer systems showed more HPr content, indicating that type of VFA varied with the total sewer length. The finding is a particularly important consideration for BNR process design since availability of HPr positively behaved to suppress the unfavorable growth of glycogen-accumulating organisms. The implication of these findings for BNR process design is discussed in this paper.

Practical Aspects of Nitrogen and Phosphorous Removal with Floating Media SBBR

Abstract Practical aspect on the application of floating media for the sequencing batch biofilm reactor (SBBR) has not been studied in detail, especially focused on settling step, nutrient removal and temperature effects. Two types of floating media (sponge and plastic) had been examined for SBBR operation with sewage. Based on the observations with various experimental variables including temperature, media volume, operating methods, both SBBR units with sponge and plastic media generally produced a stable nitrified effluent, but depicted unstable phosphorus removal. The sponge media showed better nitrogen removal, while plastic media showed better phosphorus removal. Overall nutrient removal capability for SBBR was better than a typical SBR without media. In addition, SBBR with sponge media was capable to absorb shock loads, but could not effectively nitrify at a lower temperature even with an increased media volume. In order to produce lower SS effluent as well as minimize P release during the settling step, the floating media SBBR systems would require a dual settling stage.

Effect of the Organic and Nitrogen Removal and Electricity Production on Changing the External Resistor and the Inflow Loading in the Biocathode Microbial Fuel Cell

In order to remove the organic substances and the nitrate-nitrogen contained in wastewater, some researchers have studied the simultaneous removal of organics and nitrogen by using different biocathode microbial fuel cells (MFCs). The operating conditions for removing the contaminants in the MFCs are the external resistances, HRTs, the concentration of the influent wastewater, and other factors. This study aimed to determine the effect of the external resistors and organic loading rates, from the changing HRT, on the removal of the organics and nitrogen and on the production of electric power using the Denitrification Biocathode - Microbial Fuel Cell (DNB-MFC). As regards the results of the study, the removal efficiencies of did not show any difference, but the nitrate-nitrogen removal efficiencies were increased by decreasing the external resistance. The maximum denitrification rate achieved was in the external resistance , and the maximum power density was in . When the DNB-MFC was operated with increasing influent organic and nitrate loading by reducing the HRTs, the removal efficiencies were increased linearly, and the maximum nitrate removal rate was at HRT 0.6 h.