A novel PSB-EDI system for high ammonia wastewater treatment, biomass production and nitrogen resource recovery: PSB system.

A novel process coupling photosynthetic bacteria (PSB) with electrodeionization (EDI) treatment was proposed to treat high ammonia wastewater and recover bio-resources and nitrogen. The first stage (PSB treatment) was used to degrade organic pollutants and accumulate biomass, while the second stage (EDI) was for nitrogen removal and recovery. The first stage was the focus in this study. The results showed that using PSB to transform organic pollutants in wastewater into biomass was practical. PSB could acclimatize to wastewater with a chemical oxygen demand (COD) of 2,300 mg/L and an ammonia nitrogen (NH4(+)-N) concentration of 288-4,600 mg/L. The suitable pH was 6.0-9.0, the average COD removal reached 80%, and the biomass increased by an average of 9.16 times. The wastewater COD removal was independent of the NH4(+)-N concentration. Moreover, the PSB functioned effectively when the inoculum size was only 10 mg/L. The PSB-treated wastewater was then further handled in an EDI system. More than 90% of the NH4(+)-N was removed from the wastewater and condensed in the concentrate, which could be used to produce nitrogen fertilizer. In the whole system, the average NH4(+)-N removal was 94%, and the average NH4(+)-N condensing ratio was 10.0.

Nature and role of surface carbonates and bicarbonates in CO oxidation over RuO(2).

Base metal oxides have long been of interest as catalysts for oxidation of small molecules such as CO or NO, but practical applications are limited by surface poisoning processes. With growing interest in the oxidation activity of metal oxides, it is important to understand and ultimately to learn to bypass surface poisoning. RuO(2), as a model metal oxide oxidation catalyst, is active for CO oxidation under UHV conditions but is deactivated by some surface poisoning processes at ambient pressures. In this work, we use plane-wave, supercell DFT calculations to characterize the structures of carbonate and bicarbonate on the RuO(2)(110) surface and determine their thermodynamic stability by constructing phase diagrams. We find that while a surface carbonate (CO) is stable at low O(2) pressures and high CO(2) pressures, it is not stable under practical catalytic conditions. A surface bicarbonate (HCO) is more stable and deactivates the RuO(2) surface over a wide range of CO(2) and oxygen pressures in the presence of trace amounts of water. Therefore, bicarbonate is likely the species responsible for experimentally observed surface poisons that deactivates RuO(2) during CO oxidation. OH* might also be a candidate responsible for surface poisoning when CO(2) pressure is very low. This study demonstrates that surface poisoning is sensitive to reaction environments such as water and CO(2) pressures.

Understanding mixing of Ni and Pt in the Ni/Pt(111) bimetallic catalyst via molecular simulation and experiments.

Molecular dynamics (MD) simulations employing embedded atom method potentials and ultrahigh vacuum (UHV) experiments were carried out to study the mixing process between the Ni and Pt atoms in the Ni/Pt(111) bimetallic system. The barrier for a Ni atom to diffuse from the top surface to the subsurface layer is rather high (around 1.7 eV) as calculated using the nudged elastic band (NEB) method. Analysis of the relaxation dynamics of the Ni atoms showed that they undergo diffusive motion through a mechanism of correlated hops. At 600 K, all Ni atoms remain trapped on the top surface due to large diffusion barriers. At 900 K, the majority of Ni atoms diffuse to the second layer and at 1200 K diffusion to the bulk is observed. We also find that smaller Ni coverages and the presence of Pt steps facilitate the Ni-Pt mixing. By simulated annealing simulations, we found that in the mixed state, the Ni fraction oscillates between layers, with the second layer being Ni-richer at equilibrium. The simulation results at multiple time scales are consistent with the experimental data.

Effect of NOM on arsenic adsorption by TiO(2) in simulated As(III)-contaminated raw waters.

The effect of natural organic matter (NOM) on arsenic adsorption by a commercial available TiO(2) (Degussa P25) in various simulated As(III)-contaminated raw waters was examined. Five types of NOM that represent different environmental origins were tested. Batch adsorption experiments were conducted under anaerobic conditions and in the absence of light. Either with or without the presence of NOM, the arsenic adsorption reached steady-state within 1h. The presence of 8 mg/L NOM as C in the simulated raw water, however, significantly reduced the amount of arsenic adsorbed at the steady-state. Without NOM, the arsenic adsorption increased with increasing solution pH within the pH range of 4.0-9.4. With four of the NOMs tested, the arsenic adsorption firstly increased with increasing pH and then decreased after the adsorption reached the maximum at pH 7.4-8.7. An appreciable amount of arsenate (As(V)) was detected in the filtrate after the TiO(2) adsorption in the simulated raw waters that contained NOM. The absolute amount of As(V) in the filtrate after TiO(2) adsorption was pH dependent: more As(V) was presented at pH>7 than that at pH<7. The arsenic adsorption in the simulated raw waters with and without NOM were modelled by both Langmuir and Frendlich adsorption equations, with Frendlich adsorption equation giving a better fit for the water without NOM and Langmuir adsorption equation giving a better fit for the waters with NOM. The modelling implies that NOM can occupy some available binding sites for arsenic adsorption on TiO(2) surface. This study suggests that in an As(III)-contaminated raw water, NOM can hinder the uptake of arsenic by TiO(2), but can facilitate the As(III) oxidation to As(V) at TiO(2) surface under alkaline conditions and in the absence of O(2) and light. TiO(2) thus can be used in situ to convert As(III) to the less toxic As(V) in NOM-rich groundwaters.

One-step treatment and resource recovery of high-concentration non-toxic organic wastewater by photosynthetic bacteria.

In order to achieve simple pollutant removal and simultaneous resource recovery in high-COD-non-toxic wastewater treatment, a one-step photosynthetic bacteria (PSB) method was established using batch study experiment. The effluent COD met the national discharge standard, and biomass with rich protein and high-value substances was efficiently produced. It eliminated the demand of post-treatment for conventional PSB treatment. Results showed that Rhodopseudomonas effectively treated brewery wastewater and achieved biomass proliferation. Yeast extract was the best additive for PSB growth and the effluent COD was below 80 mg/L with 400 mg/L yeast extract, meeting the national discharge standard. In addition, the PSB biomass increased by 2.6 times, and the cells were rich in protein, polysaccharide, carotenoids, bacteriochlorophyll and coenzyme Q10, reaching 420.9, 177.6, 2.53, 10.75 and 38.6 mg/g respectively. This work demonstrated the great potential of PSB for high-COD non-toxic wastewater treatment in one-step process.

Effects of dissolved oxygen concentration on photosynthetic bacteria wastewater treatment: Pollutants removal, cell growth and pigments production.

Dissolved oxygen (DO) is an important parameter in photosynthetic bacteria (PSB) wastewater treatment. This study set different DO levels and detected the pollutants removal, PSB growth and pigments production. Results showed that DO significantly influenced the performances of PSB wastewater treatment process. The highest COD (93%) and NH3-N removal (83%) was achieved under DO of 4-8mg/L, but DO of 2-4mg/L was recommended considering the aeration cost. PSB biomass reached 1645mg/L under DO of 4-8mg/L with satisfying co-enzyme Q10 content. The biomass yield was relatively stable at all DO levels. For bacteriochlorophyll and carotenoids, DO>1mg/L could satisfy their production. On the other hand, DO<0.5mg/L led to the highest dehydrogenase activity. According to the different purposes, the optimal treatment time was different. The most pigments production occurred at 24h; biomass reached peak at 48h; and the optimal time for pollutants removal was 72h.

Denitrification of aging biogas slurry from livestock farm by photosynthetic bacteria.

Huge amount of aging biogas slurry is in urgent need to be treated properly. However, due to high NH3-N concentration and low C/N ratio, this aging biogas slurry is refractory for traditional methods. Its denitrification has become a big challenge. In this paper, photosynthetic bacteria (PSB) were employed to handle this problem. The results showed denitrification of aging biogas slurry by PSB treatment was promising. The highest removal efficiency of NH3-N reached 99.75%, much higher than all other treatments. The removal of NH3-N followed pseudo zero order reaction under dark-aerobic condition. The better inoculation rate for NH3-N removal was 30%; and aerobic condition was more beneficial for NH3-N removal than anaerobic condition because of different metabolic pathways.

Effects of coverage on the structures, energetics, and electronics of oxygen adsorption on RuO2(110).

Plane-wave supercell DFT calculations within the PW91 generalized gradient approximation are used to examine the influence of oxygen coverage on the structure, energetics, and electronics of the RuO2(110) surface. Filling of O(br) and O(cus) sites is exothermic with respect to molecular O2 at all coverages and causes changes in local Ru electronic structure consistent with the changing metal coordination. By fitting the surface energies of a large number of surface configurations to a two-body interaction model, an O atom is calculated to be bound by 2.55 eV within a filled O(br) row and by 0.98 eV along an otherwise vacant O(cus) row. Lateral interactions modify these binding energies by up to 20%. O(cus)-O(cus) interactions are repulsive and diminish binding energy with increasing O(cus) filling. Due to the favorable relief of local strain, O(br)-O(br) interactions are attractive and favor filling of neighbor br sites. These interaction effects are relatively modest in absolute magnitude but are large enough to influence the ability of the RuO2(110) surface to promote oxidation of relatively weak reductants, such as NO and C2H4.