High-rate partial nitritation using porous poly(vinyl alcohol) sponge.

Poly(vinyl alcohol) (PVA) has been utilized as a support material for the immobilization of nitrifying bacteria without the comprehensive survey of partial nitritation. In the present study, the activities of nitrifiers and the maximum nitrogen conversion rate of partial nitritation with PVA sponge-cubes were specified according to different conditions. The selective enrichment of ammonia-oxidizing bacteria (AOB) on PVA sponge-cubes was achieved by the competition between AOB and nitrite-oxidizing bacteria for dissolved oxygen. The efficiency of ammonia oxidation was proportional to the concentration of HCO3 (-) with the molar ratio of HCO3 (-)-C/NH4 (+)-N = 1.91 and a half of the ratio was applied to the further experiments to ensure stable partial nitritation. The maximum nitrogen conversion rate of partial nitritation was dependent on the volume, not the size of sponge-cubes. The partial nitritation showed the superior rate performance of 3.09 kg N/m(3) day with the packing ratio of 32 % of 5 × 5 × 5 mm(3) PVA sponge-cubes.

Effective seeding strategy using flat type poly (vinyl alcohol) cryogel for anammox enrichment.

In this study, anammox enrichment reactors were operated using flat type poly (vinyl alcohol) cryogel (cryoPVAG) with precultured anammox bacteria (PAB) and activated sludge (AS) from an anoxic tack of the A2O process to evaluate the effect of different seeding sources on anammox enrichment. In addition, cryoPVAGs with different thicknesses (1, 2, and 3 mm) were used to investigate the effects of the thickness on anammox enrichment. The regression analysis with a modified Gompertz model showed that the start-up period of the anammox enrichment using PAB inoculum was approximately 14 days earlier than that of AS inoculum at a nitrogen loading rate of approximately 1 kg-N m-3 day-1. Substrate diffusion was limited in 3-mm cryoPVAG with respect to trend in nitrogen removal rate. Quantitative PCR analysis indicated that in the initial phase, the 16S rRNA gene copy numbers of anammox microorganism in cryoPVAG were significantly different according to the seeding source, but finally converged to a similar level after anammox enrichment. The anammox reaction was initially promoted by cryoPVAG. Next, anammox biomass detached from cryoPVAG and enriched in the bulk phase to maximize NRR. Illumina MiSeq sequencing revealed that Candidatus Brocadia sinica led to the active anammox reaction, and its relative abundance decreased with increasing gel thickness.

Photocatalytic applications of paper-like poly(vinylidene fluoride)-titanium dioxide hybrids fabricated using a combination of electrospinning and electrospraying.

A paper-like photocatalyst was fabricated by electrospraying an N,N'-dimethylformamide (DMF) dispersion of titanium dioxide (TiO2) nanoparticles (NPs) on a poly(vinylidene fluoride) nanofiber (PVDF NF) mat prepared by electrospinning. Morphological studies revealed that the TiO2 NPs uniformly deposited as clusters on the surface of the PVDF NF mat. The immobilized amount of TiO2 was found to be 2.08, 2.44, 3.80, and 4.73 mg per 45 cm(2) of PVDF-TiO2 hybrids for the electrospraying of 10, 20, 40, and 60 ml of TiO2-DMF, respectively. The hybrid photocatalysts were effective in degrading bisphenol A (BPA), 4-chlorophenol (4-CP), and cimetidine (CMT), which dissolved in both deionized water and secondary wastewater effluents, with activity being proportional to the quantity of TiO2 NPs immobilized. For the highest loading amount of TiO2, BPA, 4-CP, and CMT degraded completely within 100, 100, and 40 min of UV irradiation, respectively. Stable photo-oxidation of CMT was maintained through 10 repeated cycles. During these cycles, it was confirmed that there was no loss of TiO2 NPs by inductively coupled plasma optical emission spectrometry. Our results suggest that effective and stable PVDF-TiO2 hybrid photocatalysts can be fabricated on a large scale by combining electrospinning and electrospraying techniques.

Study of nitrogen and organics removal in sequencing batch reactor (SBR) using hybrid media.

The removal of nitrogen and organics in a sequencing batch reactor (SBR) using hybrid media were investigated in this work. The hybrid media was made by the use of polyurethane foam (PU) cubes and powdered activated carbon (PAC). The function of activated carbon of hybrid media was to offer a suitable active site, which was able to absorb organic substances and ammonia, as well as that of PU was to provide an appropriated surface onto which biomass could be attached and grown. A laboratory-scale moving-bed sequencing batch reactor (SBR) was used for investigating the efficiency of hybrid media. The removal of nitrogen and organics for synthetic wastewater (COD; 490-1,627 mg/L, NH4(+)-N; 180-210 mg/L) were evaluated at different COD/N ratio and different anoxic phase conditions, respectively. The system was operated with the organic loading rate (OLR) of 0.1, 0.16, 0.24, and 0.28 kg COD/m3 day, respectively. Each mode based on OLR was divided as the periods of 45 days of operation time, except for third mode that was operated during 30 days. After acclimatization period, effluent total COD concentrations slightly decreased and the removal efficiency of organics increased to about 90% (COD; 70 mg/L) after 60 days and achieved 98% (COD; 30 mg/L) at the end of experiments. The organics reduction seemed to be less affected by shock loading since high organic loads did not affect the removal efficiency. The NIH4(+)-N concentrations in effluent showed almost lower than 1 mg/L and NO3(-)-N concentrations were high (150 mg/L) during a very low C/N ratio (C/N=2). Over 90% of T-N removal efficiency (T-N; 16 mg/L) was obtained during the last 20 days of the operation after controlling the COD/N ratio (C/N=7). The mixing condition and COD/N ratio at anoxic phase were determined as a main operating factors. In future, the optimal operating conditions of SBR system with hybrid media will be investigated from the view of maintaining a sufficient biomass to the hybrid media under the vigorous mixing conditions.