Huijun He

Challenges and solutions for biofiltration of hydrophobic volatile organic compounds

Volatile organic compounds (VOCs) emitted to the environment highly probably result in ecological and health risks. Many biotechnologies for waste gases containing hydrophobic VOCs have been developed in recent years. However, these biological processes usually exhibit poor removal performances for hydrophobic VOCs due to the low bioavailability. This review presents an overview of enhanced removal of hydrophobic VOCs in biofilters. Mechanisms and problems relevant to the biological removal of hydrophobic VOCs are reviewed, and then solutions including the addition of surfactants, application of fungal biocatalysts, biofiltration with pretreatment, innovative bioreactors and utilization of hydrophilic compounds are discussed in detail. Future research needs are also proposed. This review provides new insights into hydrophobic VOC removal by biofiltration.

Nutrient removal and lipid production by Coelastrella sp. in anaerobically and aerobically treated swine wastewater

Coelastrella sp. QY01, a microalgae species isolated from a local pond, was identified and used for the treatment of anaerobically and aerobically treated swine wastewater (AnATSW). Microalgal growth characteristics, nutrient removal and lipid accumulation of QY01 cultivated in the initial concentration of AnATSW ranged from 63 to 319mg NH3-N/L were examined. The specific growth rate of QY01 cultivated in cultures ranged from 0.269 to 0.325day(-1) with a biomass productivity from 42.77 to 57.46mgL(-1)day(-1). Removal rates for NH3-N, TP and inorganic carbon in AnATSW at the various nutrient concentrations ranged from 90% to 100%, from 90% to 100% and from 74% to 78%, respectively. The lipid content of QY01 ranged from 22.4% to 24.8%. The lipid productivity was positive correlation with the biomass productivity. 40% AnATSW was optimal for QY01 cultivation, in which nutrient removal and productivity of biomass and lipid were maximized.

Removal of cadmium and lead from aqueous solutions using nitrilotriacetic acid anhydride modified ligno-cellulosic material

Cadmium (Cd2+) and lead (Pb2+) posed severe health risks worldwide. To remove these contaminants from aqueous solution, a nitrilotriacetic acid anhydride (NTAA) modified ligno-cellulosic material (NTAA-LCM) was prepared and characterized. Batch sorption experiments were performed to evaluate the influences of various factors such as contact time, pH, ionic strength, temperature and initial metal concentration on the sorption of metals. Results from elemental analysis and FTIR suggested that ester bonds and amine groups were successfully introduced into NTAA-LCM. Fast adsorption rates were observed, and the maximum sorption capacities of NTAA-LCM for Cd2+ and Pb2+ reached 143.4 and 303.5 mg g−1 at 298 K, respectively. Both the pseudo-second-order model and the Langmuir model described the adsorption extremely well. Thermodynamic analysis showed that the sorption was endothermic but spontaneous. The sorption was a chemical process involving surface chelation and ion exchange; this was reflected in the metal/NTA ratio. Additionally, NTAA-LCM retained high metal sorption capacity after seven cycles of regeneration by HNO3.

Biosorption of Pb(II) Ions from Aqueous Solutions by Waste Biomass from Biotrickling Filters: Kinetics, Isotherms, and Thermodynamics

AbstractA dried biomass wasted from biotrickling filters has been prepared for removing lead [Pb(II)] ions from aqueous solutions. The kinetics, isotherms, and thermodynamics of Pb(II) ion biosorption by the dried biomass were investigated. The results showed that the maximum Pb(II) ion biosorption capacity of a dried biomass was 160.0  mg/g at 25°C according to an evaluation using the Langmuir equation, which was fitted well to the adsorption data. The results of the kinetic studies revealed that the adsorption process followed the pseudo second-order model. The calculated thermodynamic parameters of ΔS°, ΔH°, and ΔG° suggested that the adsorption of Pb(II) ion was endothermic and spontaneous. Fourier transform infrared spectroscopy (FT-IR) analysis illustrated that the amide group and the hydroxide group affected Pb(II) ion removal significantly. This study demonstrated that a dried biomass wasted from biotrickling filters for the removal of n-hexane could be successfully used as adsorbent for the treat...

Role of biochar on composting of organic wastes and remediation of contaminated soils—a review

AbstractBiochar is produced by pyrolysis of biomass residues under limited oxygen conditions. In recent years, biochar as an amendment has received increasing attention on composting and soil remediation, due to its unique properties such as chemical recalcitrance, high porosity and sorption capacity, and large surface area. This paper provides an overview on the impact of biochar on the chemical characteristics (greenhouse gas emissions, nitrogen loss, decomposition and humification of organic matter) and microbial community structure during composting of organic wastes. This review also discusses the use of biochar for remediation of soils contaminated with organic pollutants and heavy metals as well as related mechanisms. Besides its aging, the effects of biochar on the environment fate and efficacy of pesticides deserve special attention. Moreover, the combined application of biochar and compost affects synergistically on soil remediation and plant growth. Future research needs are identified to ensure a wide application of biochar in composting and soil remediation. Graphical abstractᅟ

Treatment of anaerobically digested swine wastewater by Rhodobacter blasticus and Rhodobacter capsulatus

Two strains of photosynthetic bacteria, Rhodobacter blasticus and Rhodobacter capsulatus, were used in this work to investigate the feasibility of using photosynthetic bacteria for the treatment of anaerobically digested swine wastewater. The effects of crucial factors which influence the pollutants removal efficiency were also examined. Results showed that anaerobically digested swine wastewater could be treated effectively by photosynthetic bacteria. The treatment efficiency was significantly higher by the mixed photosynthetic bacteria than that by any unitary bacterium. The optimal treatment condition by mixed bacteria was inoculation of 10.0%(v/v) of the two bacteria by 1:1, initial pH of 7.0 and initial chemical oxygen demand of 4800mgL-1. Under these conditions, the removal rate of chemical oxygen demand was 83.3%, which was 19.3% higher than when using Rhodobacter blasticus or 10.6% higher than when using Rhodobacter capsulatus separately. This mixed photosynthetic bacteria achieved high chemical oxygen demand removal and cell yields.

Extractive desulfurization of dibenzothiophene by a mixed extractant of N,N-dimethylacetamide, N,N-dimethylformamide and tetramethylene sulfone: optimization by Box–Behnken design

In this paper, the performance of extractive desulfurization (EDS) from gasoline was studied using a mixed solvent, which consisted of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF) and tetramethylenesulfone (TMS). The effects of relevant parameters on EDS including volume ratio of DMAC/DMF/TMS, extraction temperature, extraction time, stirring speed, volume ratio of extractant and gasoline and initial concentration were investigated. The extraction removal of dibenzothiophene (DBT) and the residual sulfur content reached 99.1% and 9.5 ppm, respectively, at an optimal extractive condition of volume ratio of DMAC/DMF/TMS of 3 : 1 : 1 and volume ratio of extractant to gasoline of 1 : 5 at a stirring speed of 100 rpm over 10 min for extraction at 30 °C (ambient temperature) with five extraction stages. The DMAC/DMF/TMS extractant could be reused for several cycles maintaining high sulfur removal before being regenerated through adsorption. The impacts of three individual process variables such as, extraction time, extraction temperature and volume ratio of extractant to gasoline were investigated using Box–Behnken experimental design and their optimum values were found to be 15 min, 37 °C and 0.5, respectively. These results can be referred to for sulfur removal from gasoline in industrial applications.

Effects of surfactant and Zn (II) at various concentrations on microbial activity and ethylbenzene removal in biotricking filter

The effects of Tween-20, a non-ionic surfactant, and Zn (II) on microbial activity and removal performance for ethylbenzene in a biotrickling filter (BTF) were evaluated. Batch experiments were conducted to evaluate the surfactant and Zn (II) at various concentrations for their toxicity to microorganisms, and results indicated that Tween-20 was beneficial to microbial activity at all the tested concentration, while Zn (II) affected adversely when the concentration overpassed 5.0mgL(-1). Then effects of the two additives on removal efficiency of ethylbenzene were evaluated in a BTF at an empty-bed retention time of 30s and an ethylbenzene concentration of 1100mgm(-3). Results showed that the optimal concentrations of Tween-20 and Zn (II) were about 12 and 1.0mgL(-1), respectively. Compared to the results when neither of the two additives was added, Tween-20 improved ethylbenzene removal efficiency from 67% to 86% at the optimal condition, while on that basis, Zn (II) just increased the removal efficiency from 86% to 90%. The promoting effects of the two additives on recovering microbial activity and removing excessive biomass were also observed in this article.

Effect of salinity on removal performance and activated sludge characteristics in sequencing batch reactors

The removal performance, activated sludge characteristics and microbial community in sequencing batch reactors (SBRs) were studied at salinity ranging from 0 to 20 g/L. Results showed that salinity deteriorated the removal performance. Removal rate of ammonium (NH4+-N), total phosphorus (TP) and chemical oxygen demand (COD) were gradually dropped from 95.34%, 93.58% and 94.88% (0 g/L) to 62.98%, 55.64% and 55.78% (20 g/L), respectively. The removals of NH4+-N and TP were mainly influenced during aerobic phase. Besides, salinity increased the extracellular polymeric substances (EPS) content of activated sludge, decreased the content of protein (PN) and loosely bound extracellular polymeric substances (LB-EPS) which led to better settleability of activated sludge. Moreover, salinity inhibited the dehydrogenase activity (DHA) of activated sludge. Sequence analysis illustrated Zoogloea and Thioclava were predominant at 0 and 20 g/L salinity, respectively. The difference of microbial community under high salinity was likely caused by the variation of richness.

Influences of anion concentration and valence on dispersion and aggregation of titanium dioxide nanoparticles in aqueous solutions

Dispersion and aggregation of nanoparticles in aqueous solutions are important factors for safe application of nanoparticles. In this study, dispersion and aggregation of nano-TiO2 in aqueous solutions containing various anions were investigated. The influences of anion concentration and valence on the aggregation size, zeta potential and aggregation kinetics were individually investigated. Results showed that the zeta potential decreased from 19.8 to -41.4mV when PO43- concentration was increased from 0 to 50mg/L, while the corresponding average size of nano-TiO2 particles decreased from 613.2 to 540.3nm. Both SO42- and NO3- enhanced aggregation of nano-TiO2 in solution. As SO42- concentration was increased from 0 to 500mg/L, the zeta potential decreased from 19.8 to 1.4mV, and aggregate sizes increased from 613.2 to 961.3nm. The trend for NO3- fluctuation was similar to that for SO42- although the range of variation for NO3- was relatively narrow. SO42- and NO3- accelerated the aggregation rapidly, while PO43- did so slowly. These findings facilitate the understanding of aggregation and dispersion mechanisms of nano-TiO2 in aqueous solutions in the presence of anions of interest.