Hongchen Wang

Rapid on-site/in-situ detection of heavy metal ions in environmental water using a structure-switching DNA optical biosensor.

A structure-switching DNA optical biosensor for rapid on-site/in situ detection of heavy metal ions is reported. Mercury ions (Hg2+), highly toxic and ubiquitous pollutants, were selected as model target. In this system, fluorescence-labeled DNA containing T-T mismatch structure was introduced to bind with DNA probes immobilized onto the sensor surface. In the presence of Hg2+, some of the fluorescence-labeled DNAs bind with Hg2+ to form T-Hg2+-T complexes through the folding of themselves into a hairpin structure and dehybridization from the sensor surface, which leads to decrease in fluorescence signal. The total analysis time for a single sample was less than 10 min with detection limit of 1.2 nM. The rapid on-site/in situ determination of Hg2+ was readily performed in natural water. This sensing strategy can be extended in principle to other metal ions by substituting the T-Hg2+-T complexes with other specificity structures that selectively bind to other analytes.

Fluorescence resonance energy transfer based aptasensor for the sensitive and selective detection of 17β-estradiol using a quantum dot-bioconjugate as a nano-bioprobe

A unique fluorescence resonance energy transfer (FRET)-based aptasensor was constructed for the determination of 17β-estradiol using a quantum dot (QD) bioconjugate as a nano-bioprobe and a high-affinity, high-specificity fluorescence-labeled anti-17β-estradiol aptamer as a bio-recognition molecule. Based on the principles of QD-FRET and competitive bioassays, a number of samples containing various 17β-estradiol concentrations and a given concentration of the fluorescence-labeled DNA aptamer were incubated with a certain concentration of the QD nano-bioprobe solution. A higher 17β-estradiol concentration led to fewer fluorescence-labelled DNA aptamers bound to the QD nano-bioprobe surface and thus a lower fluorescence signal. The compound 17β-estradiol was quantified over a concentration range of 0.82 nM to 20.5 nM with a detection limit of 0.22 nM. The high specificity and selectivity of the sensor were demonstrated by evaluating the response of the sensor toward a number of potentially interfering endocrine-disrupting compounds or other chemicals. This sensor was also sufficiently stable for practical applications. The performance of the FRET-based aptasensor with spiked water samples demonstrated good recovery, precision and accuracy, indicating that it had a low susceptibility to water matrix effects.

Hapten-Grafted Graphene as a Transducer for Homogeneous Competitive Immunoassay of Small Molecules

A hapten-grafted graphene-based biosensor by integrating both the graphene nanosheets and immunoassay sensing technologies was developed for ultrasensitive homogeneous competitive immunoassay of small molecules. The structure of hapten-grafted graphene avoids the activity loss of biomolecules immobilized onto the graphene surface and is beneficial to preserve the binding affinity between small molecule and its specific antibody. The sandwich structure formed between hapten-grafted graphene nanosheets and fluorescence-labeled antibody increases the quenching efficiency of the organic dye, thereby resulting in high signal-to-background ratios and improved sensitivity for Bisphenol A (BPA) detection. On the basis of fluorescence resonance energy transfer (FRET) and homogeneous competitive immunoassay mechanism, high BPA concentrations in the sample reduce the amount of fluorescence-labeled anti-BPA antibody bound to graphene-BPA nanosheets, thus resulting in remarkable fluorescence signals. The linear quantification of BPA over concentration ranges from 0.5 to 50 nM with a detection limit determined as 0.12 nM. These findings show that the proposed method provides a powerful tool for the rapid and sensitive detection of small molecules in biological and environmental samples.

Highly sensitive and selective optofluidics-based immunosensor for rapid assessment of Bisphenol A leaching risk.

Bisphenol A (BPA), a xenoestrogenic endocrine-disrupting chemical, is used in many consumer products worldwide and is widely detected in the environment and in food. Combining the advantages of evanescent wave fiber optic sensor and microfluidic technology, an all-fiber optofluidics-based bioassay platform (AFOB) was developed for the rapid immunoassay and assessment of BPA. The captured molecular BPA-bovine serum albumin was covalently immobilized on the surface of the fiber optic sensor. A mixture of different concentrations of BPA and a certain concentration of fluorescence-labeled anti-BPA monoclonal antibodies after pre-reaction was introduced to the optofluidic cell. A higher concentration of BPA reduced the fluorescence-labeled antibodies bound to the sensor surface and thus reduced fluorescence signals. Under optimal conditions, the BPA quantified as 0.5-100 μg/L, with a detection limit of 0.06 μg/L. The high selectivity of the sensor was evaluated in terms of its response to several potentially interfering chemicals. The potential interference of an environmental sample matrix was assessed by spiked samples, and the recovery of BPA ranged from 90% to 120% with relative standard deviation values of <9.1%. The AFOB and high-performance liquid chromatography had a desired correlation (R(2)=0.9958). The sensing platform was successfully used to assess BPA leaching from polycarbonate bottles at 45 °C and 80 °C, indicating that more BPA was substantially leached at elevated temperature and extend time. Thus, the developed sensing strategy can be an alternative method to rapidly analyze and assess the migration mechanism and fate of BPA or other pollutants.

Optofluidics-based DNA structure-competitive aptasensor for rapid on-site detection of lead(II) in an aquatic environment

Lead ions (Pb(2+)), ubiquitous and one of the most toxic metallic pollutants, have attracted increasing attentions because of their various neurotoxic effects. Pb(2+) has been proven to induce a conformational change in G-quadruplex (G4) aptamers to form a stabilizing G4/Pb(2+) complex. Based on this principle, an innovative optofluidics-based DNA structure-competitive aptasensor was developed for Pb(2+) detection in an actual aquatic environment. The proposed sensing system has good characteristics, such as high sensitivity and selectivity, reusability, easy operation, rapidity, robustness, portability, use of a small sample volume, and cost effectiveness. A fluorescence-labeled G4 aptamer was utilized as a molecular probe. A DNA probe, a complementary strand of G4 aptamer, was immobilized onto the sensor surface. When the mixture of Pb(2+) solution and G4 aptamer was introduced into the optofluidic cell, Pb(2+) and the DNA probe bound competitively with the G4 aptamer. A high Pb(2+) concentration reduced the binding of the aptamer and the DNA probe; thus, a low-fluorescence signal was detected. A sensitive sensing response to Pb(2+) in the range of 1.0-300.0 nM with a low detection limit of 0.22 nM was exhibited under optimal conditions. The potential interference of the environmental sample matrix was assessed with spiked samples, and the recovery of Pb(2+) ranged from 80 to 105% with a relative standard deviation value of <8.5%. These observations clearly illustrate that with the use of different DNA or aptamer probes, the sensing strategy presented can be easily extended to the rapid on-site monitoring of other trace analytes.

Research advances in deriving renewable energy from biomass in wastewater treatment plants

Anaerobic digestion (AD) can be used to derive renewable energy from biomass in wastewater treatment plants, and the produced biogas represents a valuable end-product that can greatly offset operation costs. However, AD is a complex biological process involving many different kinds of microbial communities and biotransformation processes, and it is easily affected by start-up and operation conditions. In order to facilitate improvements in the AD process and enable predictions of biogas production quantities, this review discusses the microbial dynamics, scientific models, and reinforcement strategies of AD biogas production (i.e., sludge pre-treatment, bio-electrochemical and Fe/Fe3O4 technologies). During sludge pre-treatment, the focused-pulsed method can be introduced to promote cell lysis, and this requires specific treatment chamber designs. The bio-electrochemical method, especially in regard to the use of microbial electrolysis cells (MECs), can obviously improve biogas production while only consuming small amounts of energy. Mechanisms of AD-MEC systems and associated influencing factors are described in detail in this review. Engineered nanomaterials, which are increasingly being used in commercial products, may have detrimental or even beneficial effects on the sludge AD process. The use of low doses of Fe/Fe3O4 nanomaterials (≤0.5% (w/w)) as an economically viable and environmentally sustainable method for improving biogas production is discussed. In addition, removal methods for dissolved methane, which can have a negative environmental impact if not handled properly, in the anaerobic digester effluents are discussed in this review.

Online control of biofilm and reducing carbon dosage in denitrifying biofilter: pilot and full-scale application

Denitrifying biofilter (DNBF) is widely used for advanced nitrogen removal in the reclaimed wastewater treatment plants (RWWTPs). Manual control of DNBF easily led to unstable process performance and high cost. Consequently, there is a need to automatic control of two decisive operational processes, carbon dosage and backwash, in DNBF. In this study, online control of DNBF was investigated in the pilot-scale DNBF (600 m3·d–1), and then applied in the full-scale DNBF (10 × 104 m3·d–1). A novel simple online control strategy for carbon dosage with the effluent nitrate as the sole control parameter was designed and tested in the pilot-scale DNBF. Backwash operation was optimized based on the backwash control strategy using turbidity as control parameter. Using the integrated control strategy, in the pilot-scale DNBF, highly efficient nitrate removal with effluent TN lower than 3 mg·L–1 was achieved and DNBF was not clogged any more. The online control strategy for carbon dosage was successfully applied in a RWWTP. Using the online control strategy, the effluent nitrate concentration was controlled relatively stable and carbon dosage was saved for 18%.

Analysis of key microbial community during the start-up of anaerobic ammonium oxidation process with paddy soil as inoculated sludge

A sequencing batch reactor (SBR)-anaerobic ammonium oxidation (anammox) system was started up with the paddy soil as inoculated sludge. The key microbial community structure in the system along with the enrichment time was investigated by using molecular biology methods (e.g., high-throughput 16S rRNA gene sequencing and quantitative PCR). Meanwhile, the influent and effluent water quality was continuously monitored during the whole start-up stage. The results showed that the microbial diversity decreased as the operation time initially and increased afterwards, and the microbial niches in the system were redistributed. The anammox bacterial community structure in the SBR-anammox system shifted during the enrichment, the most dominant anammox bacteria were CandidatusJettenia. The maximum biomass of anammox bacteria achieved 1.68×109copies/g dry sludge during the enrichment period, and the highest removal rate of TN achieved around 75%.

Modification of natural zeolite and its application to advanced recovery of organic matter from an ultra-short-SRT activated sludge process effluent

Natural adsorbent was optimized from four natural adsorption materials (kaolin, bentonite, diatomite, and natural zeolite) through the comparison of their ability to recover organic matter from an ultra-short-sludge-retention-time (ultra-short-SRT) activated sludge process effluent. Natural zeolite was modified by the loading of three types of chemical coagulants (Fe2(SO4)3, Al2(SO4)3, and ZnSO4) and was used for the study of the advanced recovery of organic matter. The results of Brunauer-Emmett-Teller surface area (SBET) measurements, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses showed that natural zeolite was successfully modified, with decrease in the specific surface area of the modified zeolite (MZ), but some metal ions/metal oxides were loaded onto the surface of natural zeolite. Compared with chemical coagulant and natural zeolite, the organic recovery efficiency from the effluent of the MZs improved, and after the optimization process, the organic recovery efficiency of MZ4 (Zeolite:Fe2(SO4)3 = 4:1), MZ9 (Zeolite:Al2(SO4)3 = 4:1), and MZ13 (Zeolite:ZnSO4 = 2:1) reached 72.0%, 67.6%, and 61.2%, respectively. The MZs can allow a significant amount of recovery of soluble chemical oxygen demand (SCOD) from the effluent, with SCOD recovery efficiencies for MZ4, MZ9, and MZ13 of 44.8%, 44.3%, and 39.4%, respectively. The E4/E6, UV253/UV203, and SUVA analyses after the organic recovery experiments indicated that the generation potential of disinfecting byproducts or halogenated products was reduced in the treated effluent by the MZs. The mechanism can be considered in two ways: the coagulation effect of the loaded metal ions/metal oxides and the physical and chemical adsorption effect based on the hydrogen bond and ππ bond between the MZ and organic matter. This study facilitated the application of organic recovery from wastewater and the advanced treatment of effluent.

Effects of gibberellin on the activity of anammox bacteria

The enhancement of gibberellin (GA) on the activity of anaerobic ammonium oxidation(anammox) bacteria in short-term batch experiments(500 mL serum bottle) was studied in this paper. To make sure the accuracy of the data, each experiment group was conducted some statistical analysis. The results showed that GA played an important role in improving anammox activity when the GA dosage ranged from 0.1 to 1.5 mg L-1, and the total nitrogen removal rate (NRR) was increased by 34% when the GA dosage was 1 mg L-1. The monitoring results of extracellular polymeric substances (EPS) and biomass of anammox bacteria indicated that GA addition improved the secretion of EPS and the biomass increasing, whose amount achieved maximum under the GA dose of 1 mg L-1. Compared to the control test, the maximum improvement ratio of the EPS and biomass was 28.6% and 34%, respectively. In addition, the cloning results also indicated that the anammox bacterial community structure shifted in species level of Candidatus Brocadia genus during the experiment, and the most dominant anammox bacteria were Candidatus Brocadia fulgid.