Effect of phosphorylated polyvinyl alcohol matrix size of cell entrapment on partial nitrification of ammonia in wastewater.

Partial nitrification is known as first and critical step for autotrophic nitrogen removal in high strength nitrogenous wastewater. Phosphorylated polyvinyl alcohol gel entrapment was used for suppressing oxygen to nitrite-oxidizing bacteria (NOB) in the gel matrix. The study investigated the effect of the size of gel matrix on partial nitrification. Results show that ammonia-oxidizing bacteria (AOB) proportion in the inoculum rather than the size of gel matrix governed ammonia oxidation. Nitrite oxidation depended on the size of gel matrix not the relative proportions of NOB and AOB in the inoculum. Larger size of gel matrix lead to less in situ oxygen penetration and available for NOB resulting in higher nitrite accumulation. This finding gains a better understanding of using suitable inoculum to control partial nitrification that is beneficial for the preparation of anaerobic ammonium oxidation-suited effluent.

Substrate loading rates conducive to nitritation in entrapped cell reactors: performance and microbial community structure.

This study aimed to elucidate the boundaries of ammonia and organic loading rates that allow for nitritation in continuous flow phosphorylated-polyvinyl alcohol entrapped cell reactors and to clarify the community structure of microorganisms involving nitrogen transformation in the gel bead matrices. At operating bulk dissolved oxygen concentration of 2 mg/L, nitritation was accomplished when the total ammonia nitrogen (TAN) loading rate was ≥ 0.3 kgN/m3/d. At TAN loading rates of ≤ 0.2 kgN/m3 /d, complete oxidation of ammonia to nitrate took place. Nitritation performance dropped with increased chemical oxygen demand (COD) loading rates indicating limitation of nitritation reactor operation at some COD loading conditions. 16S rRNA gene amplicon sequencing revealed that the uncultured Cytophagaceae bacterium, Arenimonas, Truepera, Nitrosomonas, Comamonas, unclassified Soil Crenarchaeotic Group, and uncultured Chitinophagaceae bacterium were highly abundant taxa in the reactors' gel bead matrices. qPCR with specific primers targeting amoA genes demonstrated the coexistence of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea, and Comammox in the gel bead matrices. AOB was likely the main functioning ammonia-oxidizing microorganisms due to the amoA gene being of highest abundance in most of the studied conditions. Nitrite-oxidizing microorganisms presented in less relative abundance than ammonia-oxidizing microorganisms, with Nitrobacter rather than Nitrospira dominating in the group. Results obtained from this study are expected to further the application of nitritation entrapped cell reactors to real wastewater treatment processes.

Inhibitory effect of phenol on wastewater ammonification.

This study aimed to elucidate inhibitory effect of phenol on ammonification of dissolved organic nitrogen (DON) in wastewater. Laboratory incubation experiments were conducted using primary and secondary effluent samples spiked with phenol (100-1000 mg/L) and inoculated with mixed cultures, pure strains of phenol-degrading bacteria (Acinetobacter sp. and Pseudomonas putida F1), and/or an ammonia oxidizing bacterium (Nitrosomonas europaea). DON concentration was monitored with incubation time. Phenol suppressed the ammonification rate of DON up to 62.9%. No or minimal ammonification inhibition was observed at 100 mg/L of phenol while the inhibition increased with increasing phenol concentration from 250 to 1000 mg/L. The inhibition was curtailed by the presence of the phenol-degrading bacteria. DON was ammonified in the samples inoculated with only N. europaea and the ammonification was also inhibited by phenol. The findings suggest that high phenol in wastewater could result in low ammonification and high DON in the effluent.

Dissolved oxygen/free ammonia (DO/FA) ratio manipulation to gain distinct proportions of nitrogen species in effluent of entrapped-cell-based reactors.

Oxygen-limiting and/or free ammonia (FA)-accumulating conditions are two common operating strategies for partial nitrification in wastewater. Controlling either bulk dissolved oxygen (DO) or free ammonia (FA) concentration to maintain partial nitrification can be challenging due to the strong interdependency between these two parameters as substrates for ammonia oxidation. In this study, DO/FA ratio is proposed as a controlling parameter for partial nitrification by entrapped-cell-based reactors. At DO/FA >1.5, both ammonia and nitrite oxidation proceeded without inhibition leading to complete oxidation of ammonia to nitrate. An effluent containing nitrate as the main nitrogen species can be produced at these ratios. At a DO/FA ratio range of 0.2-1.5, ammonia oxidation proceeded without efficiency deterioration, while nitrite oxidation decreased with decreasing DO/FA ratio. At the ratios of 0.2-0.6, an effluent containing mainly nitrite can be generated. At DO/FA <0.2, both ammonia oxidation and nitrite oxidation were inhibited and the effluent with nearly equal molar of ammonia and nitrite was obtained. By controlling DO/FA ratio, effluents with different proportions of nitrogen species can be produced allowing the entrapped-cell-based system to be adaptable as an initial reactor for various nitrogen removal approaches.

Partial nitrification in entrapped-cell-based reactors with two different cell-to-matrix ratios: performance, microenvironment, and microbial community.

In this study, we investigated the effect of different cell-to-matrix ratios (1% and 4%) on the partial nitrification of phosphorylated polyvinyl alcohol-entrapped-cell-based reactors and evaluated the microenvironment, microbial community, and microbial localization within the gel matrices. The results indicated that the reactor with a 1% cell-to-matrix ratio required 184 days of operation to reach partial nitrification that produced anaerobic ammonium oxidation-suitable effluent. In contrast, partial nitrification was achieved from the beginning of the operation of the reactor with the 4% cell-to-matrix ratio. The oxygen-limiting zone (dissolved oxygen = 0.5-1.5 mg L-1), where nitrite-oxidizing activity has been suggested to be suppressed and ammonia-oxidizing activity was reported to be maintained, occurred at 10-230 µm from the gel matrices surface. In addition, the layer of ammonia-oxidizing bacteria observed in this zone is likely to have played a role in obstructing oxygen penetration into the inner region of the gel matrices. The next-generation sequencing results indicated that members of the family Nitrosomonadaceae accounted for 16.4-20.7% of the relative abundance of bacteria at the family level, while members of the family Bradyrhizobiaceae, to which the genus Nitrobacter belongs, accounted for approximately 10% of the relative abundance of bacteria at the genus level in the gel matrices.

Entrapped-cells-based anaerobic forward osmosis membrane bioreactor treating medium-strength domestic wastewater: Fouling characterization and performance evaluation.

A novel entrapped cells-based-anaerobic forward osmosis membrane bioreactor (E-FOMBR) was developed. Its performance and fouling were investigated in comparison with suspended cells-based-anaerobic forward osmosis membrane bioreactor (S-FOMBR). E-FOMBR and S-FOMBR were operated under the same conditions with two widely used draw solutions (NaCl and (NH4)2SO4). The membrane fouling especially irreversible fouling in S-FOMBR was more severe than that in E-FOMBR regardless of the type of draw solution. The permeate flux of E-FOMBR were 1.79 and 1.85 LMH while those of S-FOMBR were 1.49 and 1.14 LMH with NaCl and (NH4)2SO4 as draw solutions, respectively. More deterioration of biological activity (suggested by lower organic removal) due to accumulation of salt was observed in S-FOMBR compared to E-FOMBR. Proteobacteria dominated in both FOMBRs but was more abundant in E-FOMBR than S-FOMBR. The superiority of E-FOMBR over S-FOMBR included higher and stable system performance, higher flux, and longer operation time.

Entrapped cells-based-anaerobic membrane bioreactor treating domestic wastewater: Performances, fouling, and bacterial community structure.

A laboratory scale study on treatment performances and fouling of entrapped cells-based-anaerobic membrane bioreactor (E-AnMBR) in comparison with suspended cells-based-bioreactor (S-AnMBR) treating domestic wastewater was conducted. The difference between E-AnMBR and S-AnMBR was the uses of cells entrapped in phosphorylated polyvinyl alcohol versus planktonic cells. Bulk organic removal efficiencies by the two AnMBRs were comparable. Lower concentrations of suspended biomass, bound extracellular polymeric substances and soluble microbial products in E-AnMBR resulted in less fouling compared to S-AnMBR. S-AnMBR provided 7 days of operation time versus 11 days for E-AnMBR before chemical cleaning was required. The less frequent chemical cleaning potentially leads to a longer membrane life-span for E-AnMBR compared to S-AnMBR. Phyla Proteobacteria, Chloroflexi, Bacteroidetes and Acidobacteria were dominant in cake sludge from both AnMBRs but their abundances were different between the two AnMBRs, suggesting influence of cell entrapment on the bacteria community.

Effects of inoculum type and bulk dissolved oxygen concentration on achieving partial nitrification by entrapped-cell-based reactors.

An entrapment of nitrifiers into gel matrix is employed as a tool to fulfill partial nitrification under non-limiting dissolved oxygen (DO) concentrations in bulk solutions. This study aims to clarify which of these two attributes, inoculum type and DO concentration in bulk solutions, is the decisive factor for partial nitrification in an entrapped-cell based system. Four polyvinyl alcohol entrapped inocula were prepared to have different proportions of nitrite-oxidizing bacteria (NOB) and nitrite-oxidizing activity. At a DO concentration of 3 mg l(-1), the number of active NOB cells in an inoculum was the decisive factor for partial nitrification enhancement. However, when the DO concentration was reduced to 2 mg l(-1), all entrapped cell inocula showed similar degrees of partial nitrification. The results suggested that with the lower bulk DO concentration, the preparation of entrapped cell inocula is not useful as the DO level becomes the decisive factor for achieving partial nitrification.

Archaeal amoA genes outnumber bacterial amoA genes in municipal wastewater treatment plants in Bangkok.

The contribution of ammonia-oxidizing archaea (AOA) to nitrogen removal in wastewater treatment plants (WWTPs) remains unknown. This study investigated the abundance of archaeal (AOA) and bacterial (ammonia-oxidizing bacteria (AOB)) amoA genes in eight of Bangkok's municipal WWTPs. AOA amoA genes (3.28 × 10(7) ± 1.74 × 10(7)-2.23 × 10(11) ± 1.92 × 10(11) copies l(-1) sludge) outnumbered AOB amoA genes in most of the WWTPs even though the plants' treatment processes, influent and effluent characteristics, removal efficiencies, and operation varied. An estimation of the ammonia-oxidizing activity of AOA and AOB suggests that AOA involved in autotrophic ammonia oxidation in the WWTPs. Statistical analysis shows that the numbers of AOA amoA genes correlated negatively to the ammonium levels in effluent wastewater, while no correlation was found between the AOA amoA gene numbers and the oxygen concentrations in aeration tanks. An analysis of the AOB sequences shows that AOB found in the WWTPs limited to only two AOB clusters which exhibit high or moderate affinity to ammonia. In contrast to AOB, AOA sequences of various clusters were retrieved, and they were previously recovered from a variety of environments, such as thermal and marine environments.

Abundance of amoA genes of ammonia-oxidizing archaea and bacteria in activated sludge of full-scale wastewater treatment plants.

In this study, the abundance and sequences of amoA genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were determined in seven wastewater treatment plants (WWTPs) whose ammonium concentrations in influent and effluent wastewaters varied considerably (5.6-422.3 mgN l(-1) and 0.2-29.2 mgN l(-1), respectively). Quantitative real-time PCR showed that the comparative abundance of AOA and AOB amoA genes differed among the WWTPs. In all three industrial WWTPs, where the influent and effluent contained the higher levels of ammonium (36.1-422.3 mgN l(-1) and 5.3-29.2 mgN l(-1), respectively), more than four orders of magnitude higher numbers of AOB amoA genes than AOA amoA genes arose (with less than the limit of detection of AOA amoA genes). In contrast, significant numbers of AOA amoA genes occurred in all municipal WWTPs (with ammonium levels in the influent and effluent of 5.6-11.0 mgN l(-1) and 0.2-3.0 mgN l(-1), respectively). Statistical analysis suggested that compared to other plants' parameters, the ammonium levels in the plants' effluent showed correlation with the highest p value to the abundance of AOA amoA genes.