Treatment of nitrate containing wastewater by adsorption process using polypyrrole-modified plastic-carbon: Characteristic and mechanism.

Polypyrrole-modified plastic-carbon (PET-PPy) composite was prepared by using high porosity plastic-carbon materials and a special doping mechanism of polypyrrole to remove nitrate from water to achieve waste recycling. As a result, PET-PPy-500 showed remarkable nitrate adsorption in both acidic and alkaline wastewater. The pseudo-second-order kinetic and Langmuir isotherm models were fit for the nitrate adsorption by PET-PPy-500, and the maximum adsorption capacity predicted by the Langmuir model was 10.04 mg NO3-N/g (45.18 mg NO3-/g) at 30 °C. The ion exchange and electrostatic attraction were the main mechanisms of removing NO3- by PET-PPy-500, which was demonstrated by the interface characterization and theoretical calculation. The doped ions (Cl-) and/or other anions produced by charge transfer interaction were the main exchange ions in the process of NO3- adsorption. The main binding sites in the electrostatic adsorption process were nitrogen-containing functional groups, which can be confirmed by the results of XPS and density functional theory (DFT). Furthermore, DFT results also showed that the adsorption of nitrate by PET-PPy was a spontaneous exothermic process, and the adsorption energy at the nitrogen site was the lowest. The findings of this study provide a feasible strategy for the advanced treatment of nitrate containing wastewater.

Rice washing drainage (RWD) embedded in poly(vinyl alcohol)/sodium alginate as denitrification inoculum for high nitrate removal rate with low biodiversity.

Immobilization technology with low maintenance is a promising alternative to enhance nitrate removal from water. In this study, washing rice drainage (RWD) was immobilized by poly(vinyl alcohol)/sodium alginate (PVA/SA) to obtain RWD-PVA/SA gel beads as inoculum for denitrification. When initial nitrate concentration was 50 mg N/L, nitrate was effectively removed at rates of 50-600 mg/(L∙d) using acetate as carbon source (C/N = 1.25). Arrhenius activation energy (Ea) of nitrate oxidoreductase was 28.64 kJ/mol for the RWD-PVA/SA gel beads. Temporal and spatial variation in microbial community structures were revealed along with RWD storage and in the reactors by Illumina high-throughput sequencing technology. RWD-PVA/SA gel beads has a simple (operational taxonomic units (OTUs) ã€ˆ100). Dechloromonas, Pseudomonas, Flavobacterium and Acidovorax were the most four dominant genera in the denitrification reactors inoculated with RWD-PVA/SA gel beads. This study provides an inoculum for denitrification with high nitrate removal performance and simple microbial community structures.

Polypyrrole-grafted peanut shell biological carbon as a potential sorbent for fluoride removal: Sorption capability and mechanism.

In this study, an effective defluoridation adsorbent was developed by depositing polypyrrole (PPy) on granular peanut shell biological carbon (BC) via in situ chemical oxidative polymerization. The variables of defluoridation process (i.e., adsorbent dosage, fluoride solution pH, and anionic interference) were tested. The mechanism was determined by isotherm and kinetic studies, Brunauer-Emmett-Teller (BET) method, scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and automatic titration. The PPy-grafted BC (PPy/BC) composite performed commendably from pH 2.0 to 10.0, and exhibited high selectivity for fluoride in the presence of several co-existing anions. The experimental data were described well by a Langmuir isotherm curve, and the maximum adsorption capacity was 17.15 mg g(-1). Kinetic studies illustrated the adsorption process was accomplished via surface adsorption as well as by intraparticle diffusion. In addition, mesoporous diffusion was the rate-controlling step in intraparticle diffusion process. BET and SEM analysis revealed the sponge-like polymer adhered to the BC and plugged the pores. XPS, FTIR, and SEM confirmed that fluoride removal was accomplished via the replacement of doped ionizable chloride ions (Cl(-)) coupled with positively charged nitrogen (N(+)), computation of XPS data enabled the formulation of a three-layer-deep hypothesis for PPy.