Effect of hydraulic retention time on performance of autotrophic, heterotrophic, and split-mixotrophic denitrification systems supported by polycaprolactone/pyrite: Difference and potential explanation.

Biological denitrification is still the most important pathway to purifying nitrate-containing wastewater. In this study, pyrite (FeS2 ) and polycaprolactone (PCL) were used as electron donors to construct sole or combined denitrification systems, that is, pyrite-based autotrophic denitrification (PAD) system, PCL-supported heterotrophic denitrification (PHD) system, and split-mixotrophic denitrification system (combined PAD + PHD), all of which were operated under five different hydraulic retention times (HRTs) for 150 days. The results showed that the removal rates (RE) of nitrate (NO3 - -N) and inorganic phosphorus (PO4 3- -P) by PAD were 91% and 94%, respectively, but the effluent sulfate (SO4 2- ) concentration was as high as 168.2 mg/L; the removal rate of NO3 - -N by PHD was higher than 99%, but the PO4 3- -P could not be removed ideally; the removal rates of NO3 - -N and PO4 3- -P by PAD + PHD were higher than 95% and 99%, respectively, and the effluent SO4 2- concentration was only 7.2 mg/L. Through the analysis of the surface scanning electron microscope (SEM) images of the two kinds of media before and after use, it was found that the coupled mode of PAD + PHD was more favorable for biofilm formation than the sole PAD or PHD process, and the microorganisms in the PAD + PHD mode made more full use of electron donors. Moreover, the biomass of the PAD + PHD mode was lower than that of the PAD or PHD process, but the denitrification efficiency of the coupled mode was more efficient, indicating that the functional microorganisms in the PAD + PHD mode might have a certain synergistic effect. PRACTITIONER POINTS: Removal rates of NO3 -, PO4 3 -, and SO4 2 - by PAD were 91%, 94%, and -233%, respectively. Removal rate of NO3 - by PHD exceeded 99%, but PO4 3 - could not be removed ideally. Removal rates of NO3 -, PO4 3 -, and SO4 2 - by PAD + PHD were 95%, 99%, and 86%, respectively. The coupled mode was more favorable for biofilm formation than the sole PAD or PHD. The coupled mode had lower biomass but got more excellent denitrification efficiency.

Removal of N,N-dimethylformamide by dielectric barrier discharge plasma combine with manganese activated carbon.

Manganese activated carbon (Mn-AC) was successfully prepared by the incipient wetness method and characterized by SEM, XRD, and FTIR. This study chose N,N-dimethylformamide (DMF) as the target pollutant, and the removal rate of DMF and removal mechanism were systematically studied by dielectric barrier discharge (DBD) plasma combined with Mn-AC. This study indicated that DBD plasma combined with Mn-AC could effectively remove DMF. With the addition of Mn-AC, the removal rate and mineralization rate of DMF within 40 min increased from 51.5% and 36.0% to 82.2% and 58.2%, respectively. The discharge power, initial concentration of DMF, initial pH of the solution, and dosage of Mn-AC affect the removal of DMF. The optimal discharge power is 16.19 W, and energy efficiency is 20.79 mg·kJ-1; low concentration DMF could be removed more effectively. Neutral and alkaline conditions showed better removal effect of DMF than acid conditions; Mn-AC optimal dosage is 1.0 g L-1. The concentration variations of O3, H2O2, and ·OH manifested that Mn-AC could effectively convert O3 and H2O2 to ·OH, thereby increasing the DMF removal rate. Quenching experiments showed that ·OH is the main active species in the reaction. Based on reaction products of DMF such as N-methylformamide, methanol, formaldehyde, and formic acid, possible degradation pathways were proposed. Prospect analysis demonstrated combining plasma systems with catalysts is promising.

The abundance and characteristics of microplastics in rainwater pipelines in Wuhan, China.

Urban rainwater runoff is considered to be an important way to transport microplastics into the freshwater. By analyzing the microplastics in rainwater pipelines in different land function areas in Hongshan District (Wuhan, China), the preliminary results of microplastics abundance and characteristics in rainwater pipelines and rainwater pipeline sediments were obtained. The microplastics abundance in water samples was 2.75 ± 0.76 to 19.04 ± 2.96 items/L, the abundance of microplastics in the sediment was 6.00 ± 1.63 to 27.33 ± 4.64 items/100 g. The highest abundance among the samples was in the business district and the lowest in the campus. The microplastics in water samples and sediment samples were mainly fragments, accounting for 44.7% and 57.1%, respectively. The proportion of particle size <1 mm was 75.0% and above. The color of microplastics was diversified, and colored particles occupied over 60.0%. The types of polymers detected were mainly polyethylene, polypropylene and polyester, which were related to the types of polymers widely used in life. This study shows that urban rainwater pipelines is one of the ways for land-based microplastics to migrate to freshwater, and the accumulation of microplastics in stormwater pipe sediments might be an important contributor to microplastics in freshwater area.

Na@La-modified zeolite particles for simultaneous removal of ammonia nitrogen and phosphate from rejected water: performance and mechanism.

Rejected water from sludge processing in wastewater treatment plants (WWTPs) is very harmful due to its high concentration of ammonia nitrogen and phosphorus. It is therefore necessary to find a low-cost and convenient technique to simultaneously remove ammonia nitrogen and phosphorus from rejected water. In this study, natural granular zeolite was modified by NaCl and La(OH)3 to obtain a new material (Na@La-MZP), with several advantages compared with powdered zeolite. Na@La-MZP could remove 92.61% ammonia nitrogen (50 mg/L) and 99.01% phosphate (60 mg/L) at the optimal conditions of dosage 12.5 g/L, initial pH 6.0 and reaction time 12 hours, which enabled the effluent to satisfy the discharge standard (GB 18918-2002) for municipal WWTPs in China. The maximum adsorption capacity of Na@La-MZP was determined as 17.92 mg NH4+-N/g and 9.53 mg P/g by the Langmuir isotherm. Pseudo-second-order kinetics could well illustrate the adsorption process and show that the ammonia nitrogen and phosphate can be degraded by chemical reaction. The characterizations of Na@La-MZP confirmed the removal mechanism of ammonia nitrogen and phosphate. The Na@La-MZP still maintained more than 75% removal efficiency after five reuses. Furthermore, the estimated cost of this treatment method was 0.22 $/m3 rejected water.

Achieving enhanced biological nitrogen removal via 2450 MHz electromagnetic wave loading on returned sludge in anaerobic-anoxic-oxic process.

To evaluate the enhancing of the biological nitrogen removal effectiveness by electromagnetic wave loading on returned sludge in the A/A/O reactor, some experiments were completed with the returned sludge loaded by 2,450 MHz electromagnetic wave. The excess sludge yield and pollutant removal effect of the system were evaluated. Results showed that stronger denitrification effect and less sludge yield were achieved. When 30% of the returned sludge was loaded by electromagnetic wave, the actual denitrification efficiency increased by 7% without dosage. The dissolution of carbon, nitrogen and phosphorus from loaded returned sludge was detected, thus providing the system with a supplemental carbon source of 4.6 g/d SCOD. The specific oxygen uptake rate of the oxic activated sludge increased by 14%, and the denitrification rate of the anoxic activated sludge increased by 29%. Illumina MiSeq analysis showed that the microbial richness increased obviously, and denitrifying bacteria (i.e. Dechloromonas, Zoogloea and Azospira, etc.) were accumulated.

Removal mechanisms of Cr(VI) and Cr(III) by biochar supported nanosized zero-valent iron: Synergy of adsorption, reduction and transformation.

In this study, sludge-derived biochar was prepared and utilized to support nano-zero-valent iron (NZVI-SDBC) for removing Cr(VI) and Cr(III) from aqueous solution with the aim of investigating their removal and transformation. Under the conditions of initial pH of 4, dosage of 1 g/L, temperature of 25 °C, and rotational speed of 160 rpm, 64.13% Cr species could be removed by NZVI-SDBC from Cr(VI) solution and 28.89% from Cr(III) solution. Coexisting ions experiments showed that Cu(II) and humic acids dramatically affected the removal of Cr(VI) and Cr(III), while the effect of Na(I) and Ca(II) was almost negligible. Based on this, through the coexistence and pre-loaded Cr(III) experiments, the conversion from Cr(VI) to Cr(III) was demonstrated to enhance the further attraction on Cr(VI) and promote the subsequent removal of Cr(VI). The SDBC of NZVI-SDBC could serve as electron shuttle mediator to facilitate the electron transfer between adsorbed Cr(VI) and NZVI for ortho-reduction. The transformation and removal mechanisms were further discussed by various characterizations. The kinetics of Cr(VI) removal suggested that the removal process of Cr(VI) could be divided into three phases dominated by different mechanisms (adsorption, direct/ortho reduction, electrostatic attraction), in which Cr(VI) and Cr(III) showed different behaviors of interaction. The removal of Cr(III) mainly depended on sufficient adsorption sites and the direct complexation with Fe(II). Finally, the reusability of NZVI-SDBC was assessed by adsorption/desorption recycling test. These results provided new insights into the removal and transformation mechanisms of Cr(VI) and Cr(III) by biochar-based nanocomposites.

Bioaugmentation of sequencing batch reactor for aniline treatment during start-up period: Investigation of microbial community structure of activated sludge.

The rapid start-up of sequencing batch reactor (SBR) was studied by adding efficient aniline-degrading bacteria strain AD4 (Delftia sp.), and the reactor start-up completion took only 15 days. The loading rate of aniline was 0.7 g aniline (g VSS*d)-1, which has been completely removed. The NH4+-N produced in the degradation process of aniline was also converted, which made the concentration of NH4+-N in the effluent of the reactor was always lower than that in the influent. Nitrification and denitrification played some roles in forming a dynamic equilibrium state of the whole system. The variation of microbial community during the start-up of the reactor was analyzed by high-throughput sequencing. At the phylum level, Proteobacteria, Bacteroidetes and Actinobacteria have always accounted for a large proportion. They also serve as functional bacteria for both aniline degradation and nitrogen removal. The biggest percentage jump was Flavobacterium and Acidovorax. The amount of high efficiency aniline degradation bacterium AD4 in the reactor increased at first, followed by decreasing and finally stabilized, which played an important role in the degradation of aniline.

Improvement of the sludge flocculation dewatering efficient by electromagnetic wave loading: research based on removal of bound water.

Excess sludge was loaded by 2450 MHz electromagnetic wave in this study. The mechanism of electromagnetic wave loading on the releasing of bound water before sludge flocculation dewatering was investigated through observing the changes of extracellular polymeric substances (EPS) composition, surface charge, and particle size distribution. The results showed that the 8.55 g/g total suspended solids (TSS) of bound water was reduced with 160 J/mL electromagnetic wave, and the moisture content of sludge decreased by 3.02%. The EPS structure in the sludge floc matrix was destroyed and the LB-EPS content reduced. Simultaneously, infrared spectrum analysis indicated that bound water content was correlated both to the changes of hydrophilic and hydrophobic functional groups. Moreover, protein secondary structure analysis found that looser protein structure facilitated the exposure of internal hydrophobic groups and further promoted the sludge hydrophobic properties. Additionally, electromagnetic wave disintegrated colloidal stability through dipole motion. The zeta potential increased from - 25.57 to - 14.32 mV; the medium particle size (d0.5) decreased from 119.99 to 80.41 µm. More small molecules created in the supernatant were helpful to release bound water, which could further improve flocculation dewaterability of sludge with electromagnetic wave loading.

Degradation of liquid phase N,N-dimethylformamide by dielectric barrier discharge plasma: Mechanism and degradation pathways.

The degradation of liquid phase N,N-dimethylformamide (DMF) using the dielectric barrier discharge (DBD) plasma was studied in the present study. The results showed that 1000 mg L-1 DMF could be degraded by DBD plasma under different input power, treatment time and initial pH values of aqueous solution. After 40 min with DBD plasma discharge, 52.2% degradation efficiency was achieved at DMF concentration of 1000 mg L-1 with an input power of 16.19 W under initial pH of 11.14 in aqueous solution, and the energy efficiency of the system was 13.2 mg kJ-1. The removal efficiency decreased with the presence of radical scavenger, manifesting that •OH plays a critical role in the degradation process. The value of TOC in DMF aqueous solution decreased from 790 mg L-1 to 507 mg L-1 in 40 min, which indicated that DBD plasma has the ability to mineralize a portion of DMF in liquid directly. Additionally, the analysis of FTIR, HPLC and the small molecular organic compounds before and after the DBD plasma degradation indicated that the intermediates of DMF in degradation process were N-methylformamide, methanol, formaldehyde and formic acid, which were finally mineralized into ammonia nitrogen, CO2 and H2O. Moreover, the possible degradation mechanism and pathways were proposed.

Degradation of aniline in aqueous solution by dielectric barrier discharge plasma: Mechanism and degradation pathways.

The degradation of aniline solution using the dielectric barrier discharge (DBD) plasma was studied in this paper. The results indicated that the initial concentration of aniline, applied voltage and initial pH value affected the removal efficiency of aniline significantly. After 12 min with DBD plasma treatment, 90.2% removal efficiency was achieved at aniline concentration of 100 mg L-1 with an applied voltage of 3.0 kV and pH 8.43. The removal efficiency decreased with the presence of radical scavengers, indicating that hydroxyl radical plays a key role in the degradation process. The removal efficiency increased obviously when Fe2+ was added. Additionally, the intermediate products generated in the degradation process of aniline were analyzed by some analytical techniques, including total organic carbon analysis, ultraviolet-visible spectroscopy, Fourier Transform Infrared spectroscopy, Gas Chromatography-Mass Spectrometer, etc. The results showed that the degradation of aniline was mainly due to the strong oxidizing capacity of hydroxyl radical produced by the DBD plasma system. Based on the intermediate products identified in the study, the possible degradation mechanism and pathways were proposed.

Start-up performance of anaerobic/aerobic/anoxic-sequencing batch reactor (SBR) augmented with denitrifying polyphosphate-accumulating organism (DPAO) and their gene analysis.

This paper was aimed at investigating the bio-augmentation performance of anaerobic/aerobic/anoxic-type sequencing batch reactor (SBR) during its start-up period by introducing a strain of denitrifying polyphosphate-accumulating organism (DPAO). Two SBR reactors were inoculated to study the start-up performance, with one for DPAO introduction and the other as the control specimen. A comparison, of microbial community diversity based on the reactor which obtained a better performance, was made between polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analyses encoded by 16S rRNA and functional genes (nirS, nirK). The results indicated that the introduction of DPAO had a positive effect on the biological system, including a reduction of the start-up period, the improvement of sludge characteristics and the removal efficiency of nutrients, especially for phosphorus. By comparing the phylogenetic relationship of 16S rRNA and functional genes (nirS, nirK) of the reactor augmented with DPAO, it could be found that the phylogenetic relationship of these genes were remarkably inconsistent with each other. Therefore, 16SrRNA should not be used to determine the microbial community diversity of functional bacteria which could accomplish denitrification, and gene nirK should not be neglected when determining functional bacteria.

Investigating the sorption behavior of cadmium from aqueous solution by potassium permanganate-modified biochar: quantify mechanism and evaluate the modification method.

In this work, a KMnO4-modified-biochar-based composite material with manganese oxide produced at 600 °C was fabricated to investigate the sorption mechanism of Cd(II) and to comprehensively evaluate the effect of the modification on biochar properties. Cd(II) adsorption mechanisms were mainly controlled by interaction with minerals, complexation with oxygen-containing functional groups, and cation-π interaction. The sorption capacity was significantly reduced after a deash treatment of biochar, almost shrunk by 3 and 3.5 times for pristine biochar (PBC) and modified biochar (MBC). For deashed PBC, oxygen-containing functional groups were the main contributor toward Cd(II) adsorption while interaction with minerals was significantly compromised and became negligible. The sorption capacity was also apparently decreased after the deash treatment of MBC; however, for deashed MBC, interaction with minerals still was the main contributor to the sorption ability, which could be attributed to the mechanism of interaction of Cd(II) with loaded MnOx on biochar. Cation-π interaction in MBC was notably enhanced compared to PBC due to the oxidation of KMnO4 on biomass. Also, sorption performance by oxygen-containing functional groups was also enhanced. Hence, the modification by KMnO4 has a significant effect on the Cd(II) sorption performance of biochar.

[Identification of a denitrifying polyphosphate-accumulating organism (DPAO) and study on its denitrifying functional genes].

A denitrifying polyphosphate-accumulating organism (DPAO) was isolated and identified, and the denitrifying functional genes were investigated. The strain ZQN2 was isolated using denitrifying medium. It was distinguished as DPAO by tests of aerobic phosphorus uptake, nitrate reduction, metachromatic granules and PHB (poly-beta-hydroxybutyrate) granules dyeing. Test of anaerobic phosphorus release/anoxic phosphorus uptake showed that strain ZQN2 released phosphorus and synthesized PHB at the anaerobic phase and used NO3- as acceptor to oxidize PHB during the anoxic phase with luxury phosphorus uptake, performing the function of simultaneous denitrifying phosphorus removal. The 16S rRNA gene sequence of strain ZQN2 was used for homology analysis and construction of phylogenetic trees. The results suggested that the 16S rRNA gene sequence of ZQN2 had up to 99% homology with those of many strains of Bacillus cereus strains in GenBank database. With physiological and biochemical reactions, the strain ZQN2 was identified as Bacillus cereus. The result of denitrifying functional gene study suggested that strain ZQN2 was the type of nirS+ and nirK-, which confirmed its denitrifying function from molecular biology point of view. Moreover, the phylogenetic analysis of nirS gene of ZQN2 showed that it was closely related to many strains of Pseadomonas aeruginosa, which was different from the analysis results of the 16S rRNA.