Xingzhang Luo

Trimethoprim: kinetic and mechanistic considerations in photochemical environmental fate and AOP treatment.

Trimethoprim (TMP), a bacteriostatic antibiotic, has recently been detected in wastewater and surface waters. In this study the sunlight mediated photochemical fate, and treatment using advanced oxidation and reduction (free radical) processes, have been investigated with respect to their effect on TMP. Photochemical fate, in the presence of humic acid, and advanced oxidation treatment both involve the hydroxyl radical (OH) as one of the reactive species of interest. Another reactive oxygen species, singlet oxygen (1O2), may also be important in the photochemical fate of TMP. The bimolecular reaction rate constants of TMP with 1O2 and OH were evaluated to be (3.2±0.2)×10(6) M(-1) s(-1) and 8.66×10(9) M(-1) s(-1), respectively. The reaction kinetics for the sub-structural moieties of TMP, 1,2,3-trimethoxybenzene (TMBz) and 2,4-diaminoprimidine (DAP), was evaluated to facilitate an understanding of the loss mechanisms. For TMBz and DAP the reaction rate constants with 1O2 were <1.0×10(4) and (3.0±0.1)×10(6) M(-1) s(-1), while with OH they were 8.12×10(9) and 1.64×10(9) M(-1) s(-1), respectively. The data suggests that the 1O2 attacks the DAP and the OH radical attacks the TMBz moiety. However, for TMP, 1O2 and OH reactions accounted for only ∼19% and ∼6%, of its total photodegradation, respectively. Therefore, the reaction of TMP with excited state natural organic matter is postulated as a significant degradation pathway for the loss of TMP in sunlit waters containing natural organic matter. There was no effect of pH on the direct or indirect photolysis of TMP. To complete the study for reductive treatment processes, the solvated electron reaction rates for the destruction of TMP, TMBz and DAP were also evaluated. The absolute bimolecular reaction rates obtained were, (13.6±0.01)×10(9), (6.36±0.11)×10(7) and (10.1±0.01)×10(9) M(-1) s(-1), respectively.

Enhancement of rural domestic sewage treatment performance, and assessment of microbial community diversity and structure using tower vermifiltration.

The performance of a novel three-stage vermifiltration (VF) system using the earthworm, Eisenia fetida, for rural domestic wastewater treatment was studied during a 131-day period. The average removal efficiencies of the tower VF planted with Penstemon campanulatus were as follows: chemical oxygen demand, 81.3%; ammonium, 98%; total nitrogen, 60.2%; total phosphorus, 98.4%; total nitrogen, mainly in the form of nitrate. Soils played an important role in removing the organic matter. The three-sectional design with increasing oxygen demand concentration in the effluents, and the distribution of certain oxides in the padding were likely beneficial for ammonium and phosphorus removal, respectively. The microbial community profiles revealed that band patterns varied more or less in various matrices of each stage at different sampling times, while the presence of earthworms intensified the bacterial diversity in soils. Retrieved sequences recovered from the media in VF primarily belonged to unknown bacterium and Bacilli of Firmicutes.

Performance and mechanisms of a microbial-earthworm ecofilter for removing organic matter and nitrogen from synthetic domestic wastewater.

The performance of a microbial-earthworm ecofilter for the treatment of synthetic domestic wastewater is evaluated, and the mechanisms of organic matter and nitrogen transformation investigated. Vermifiltration efficiently reduced chemical oxygen demand (COD) and ammonia nitrogen (NH(3)-N) from the influent. A combination of soil with sawdust possessed higher porosity and specific surface area than other media, and this microporous structure together with wormcast surface greatly facilitated COD reduction at depths from 5 to 35 cm. Nitrogen variations in wastewater were influenced by soil properties, earthworm activities, and wormcast characteristics. Their interaction with added nitrogen determined soil nitrogen distribution. In addition, denaturing gradient gel electrophoresis (DGGE) profiles revealed a highly diverse community of ammonia-oxidizing bacteria (AOB) and Nitrospira in soil layers. There was a positive correlation between the Shannon biodiversity index for AOB and decreasing NH(3)-N concentration, indicating that dominant soil microbes played a major role in removing NH(3)-N and nitrogen conversion. In contrast to previous reports, identification of retrieved sequences of AOB species showed that most belonged to an uncertain AOB genus. This biofiltration system is a low cost, efficient alternative for decontaminating local domestic wastewater.

Adsorption of p-nitroaniline from aqueous solutions onto activated carbon fiber prepared from cotton stalk.

Activated carbon fiber prepared from cotton stalk was used as an adsorbent for the removal of p-nitroaniline (PNA) from aqueous solutions. Liquid phase adsorption experiments were conducted and the maximum adsorptive capacity was determined. The effect of experimental parameters such as pH, salinity and temperature on the adsorption was studied. The obtained experimental data were then fitted with the Langmuir, Freundlich and Redlich-Peterson models to describe the equilibrium isotherms. The kinetics rates were modeled by using the pseudo-first-order and pseudo-second-order equations. The results indicated that cotton stalk activated carbon fiber (CS-ACF) is an effective adsorbent for the removal of PNA from aqueous solutions. The maximum adsorption capacity of 406 mg g(-1) was achieved at the initial PNA concentration of 200 mg L(-1). The optimum pH for the removal of PNA was found to be 7.6. The presence of ammonium chloride proved to be favorable for the process of adsorption. The adsorption amount decreased with increasing temperature. The Redlich-Peterson model was found to best represent the equilibrium data. The kinetic data followed closely the pseudo-second-order equation. Thermodynamic study showed the adsorption was a spontaneous exothermic physical process.

Degradation of diclofenac by ultrasonic irradiation: kinetic studies and degradation pathways.

Diclofenac (DCF) is a widely used anti-inflammatory drug found in various water bodies, posing threats to human health. In this research, the effects of ultrasonic irradiation at 585kHz on the degradation of DCF were studied under the air, oxygen, argon, and nitrogen saturated conditions. First, the dechlorination efficiencies under the air, oxygen, argon, and nitrogen saturated conditions were calculated to be 67%, 60%, 53% and 59%. Second, there was full mineralization of nitrogen during DCF degradation under the air, oxygen, and argon saturated conditions, but no mineralization of nitrogen under the nitrogen-saturated condition. Different from nitrogen, only partial mineralization of carbon occurred under the four gas-saturated conditions. Third, OH scavengers were added to derive the rate constants in the three reaction zones: cavitation bubble, supercritical interface, and bulk solution. Comparison of the constants indicated that DCF degradation was not limited to the bulk solution as conventionally assumed. Oxidation in the supercritical interface played a dominant role under the air and oxygen saturated conditions, while OH reactions in the cavitation bubble and/or bulk solution were dominant under the nitrogen and argon saturated conditions. After the addition of H2O2, reactions in the cavitation bubble and bulk solution kept their dominant roles under the nitrogen and argon saturated conditions, while reaction in the supercritical interface decreased under the air and oxygen saturated conditions. Finally, LC-MS analysis was used to derive the by-products and propose the main pathways of DCF degradation by ultrasonic irradiation.

Carbons prepared from Spartina alterniflora and its anaerobically digested residue by H3PO4 activation: Characterization and adsorption of cadmium from aqueous solutions

Two series of activated carbons were prepared from Spartina alterniflora and from its anaerobically digested residue by H(3)PO(4) activation at various process conditions, and used as adsorbents for the removal of cadmium (II) in aqueous solutions. The surface areas and pore volumes of carbons were derived from adsorption isotherms (N(2) at 77K). The surface chemistry of carbons was investigated by infrared spectroscopy. Comparison study indicated that physicochemical properties of the activated carbons were strongly dependent not only on activation conditions but also on biopolymer contents of precursors. Several isotherm models were investigated and the adsorption isotherm data were best represented by the Langmuir isotherm model, with a maximum monolayer adsorption capacity of 47.85 mg/g at 25 °C. The results showed that the activated carbon produced from S. alterniflora could be employed as a promising adsorbent for removing cadmium (II) from aqueous solutions.

Biostabilization enhancement of heavy metals during the vermiremediation of sewage sludge with passivant

The present study revealed the effects of fly ash (FA) and phosphoric rock (PR) on stabilization of sewage sludge (SS) after vermicomposting for 60 days. The earthworms in all vermibeds showed significant increases in tissue metal; however, the bioconcentration factors (BCFs) of all investigated metals (except Zn) differed among treatments. Additionally, significant differences were observed in the final system weight and SS+Passivant weight reduction among treatments, but not in the percentage reduction of total system weight and organic matter (OM). pH decreased from the initial levels, eventually reaching neutrality. Significantly greater earthworm heavy metals content, growth and reproduction rates and BCFs were observed, while a decreased percentage of total heavy metals concentration and a proportional decrease of extractable metals (except Cu and Zn) were observed in treatments mixed with FA and PR. Furthermore, significant linear correlations between BCFs and a reduction in percentage concentration of total metals (Cu, Pb, Cd and As) were shown, as well as BCF-Cu and relative proportional changes in extractable Cu. These results indicate that vermicomposting with proportions of FA and PR is better for stabilization and remediation of SS in a short period of time.

Effect of C/N ratios on the performance of earthworm eco-filter for treatment of synthetics domestic sewage

PurposeThe performances of filter systems that use earthworms and plants, combined with earthworm eco-filter (EE) systems in treating synthetic domestic sewage (SDS) with different C/N ratios, were investigated for a 9-month period.MethodsThe effects of the combination of filters, earthworms, plants, as well as the combination of earthworms and plants on SDS nutrient removal efficiency were separately investigated to select the optimum system for treating SDS. The results of the current study could be used to determine how treatment performance responds to different C/N ratios and to explain and predict the performance of an operating EE system.ResultsEE systems with earthworms and plants (EP groups) consistently performed better than the other types of systems (CK, E, and P; that is, without earthworms and without plants, with earthworms and without plants, and without earthworms and with plants, respectively) under all C/N ratios. The highest removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus, and total organic carbon were achieved under C/N ratios of 6:1, 6:1, 6:1, and 9:1, respectively. The optimum nutrient removal efficiency was achieved at C/N = 6, and the contribution order for nutrient removal was EP > P > E > CK.ConclusionsInfluent C/N ratios, the time of year, and the synergetic effects of earthworm behavior and microorganisms significantly affected nutrient removal efficiencies. Considering the removal of all nutrients, EE systems with plants and earthworms achieved optimum removal effects in July when the influent C/N ratio was controlled at 6. Appropriate control of carbon and nitrogen source concentrations permitted the achievement of optimal nutrient removal effects.

Effect of earthworm loads on organic matter and nutrient removal efficiencies in synthetic domestic wastewater, and on bacterial community structure and diversity in vermifiltration

In this paper, we studied the effect of earthworm loads on the removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen, and total phosphorus from synthetic domestic sewage and on the bacterial community structure and diversity of substrates in earthworm packing beds. The different vermifiltrations (VFs), including the control, are successful in removing both organic matter (OM) and nutrients. The removal rate of NH3-N at 12.5 g of earthworm/L of soil VF is higher compared with that at 0 and 4.5 earthworm load VFs. The highest Shannon index, in the earthworm packing bed, occurred at 16.5 earthworm load VF. Furthermore, the COD removal rate is significantly correlated with the Shannon index, which reveals that OM removal for synthetic domestic sewage treatment at VF might be more dependent on bacterial diversity at the earthworm packing bed. The band distributions and diversities of the bacterial community for samples from different earthworm loads in VFs suggest that the bacterial community structure was only affected within the earthworm packing bed when the earthworm load reached a certain level. The present study adds to the current understanding of OM and nutrient degradation processes in VF domestic wastewater treatment.

The current pollution status and control technology of the Taihu Lake Basin, Jiangsu Province, China.

Non‐point source pollution contributes greatly to lake eutrophication. This article explores a) the pollution status of rural southern Jiangsu and the Taihu Lake Basin; b) non‐point source pollution control; and c) vein river non‐point pollution control. Our work concerns an earthworm ecology filter, a capillary infiltration ditch, rural solid waste treatment and reuse technology. The tower earthworm eco‐filter and capillary infiltration ditch technology for effluent CODCr, NH3‐N, TN and TP meet the Environmental Quality Standards for Surface Water (China), Category IV.