Shi Hanchang

Microbial degradation of phthalic acid esters under anaerobic digestion of sludge

The microbial degradation by anaerobic sludge of three phthalates, priority pollutants, listed by both China National Environmental Monitoring Center and the U.S.EPA, namely, dimethyl (DMP), di-n-butyl (DBP) and di-n-octyl (DOP) phthalates was investigated. The experimental results indicated that the biodegradation rate and the biodegradability of three phthalates under anaerobic conditions appeared to be related to the length of the alkyl-side chains. More than 90% of DMP and DBP with the short alkyl-side chain phthalates can be degraded, whereas the DOP degradation appeared to be relatively slow under the same experimental conditions. The quantity of methane produced was measured and the results showed that both the ester groups and the phthalate ring were mineralized at a significant rate. The kinetics study demonstrated that the biodegradation of three phthalates conformed to the first-order model with respect to their concentrations.

Wastewater treatment in a hybrid biological reactor (HBR): effect of organic loading rates

Abstract A novel hybrid biological reactor which contained both suspended- and attached-growth biomass was developed by introducing porous materials into a regular activated sludge unit and used for the treatment of domestic wastewater. The development of suspended- and attached-growth biomass in this reactor and the effect of the organic loading rates (OLR) on the operational performance were investigated. SEM observation revealed three different patterns of biomass immobilization in carriers, micro-granules mechanically retaining in the polyurethane foam pores, small multi-cellular structures attaching to the inner polyurethane surface and individual microbial cells attaching on the polyurethane surface. The total biomass concentration in hybrid reactors increased to 4.30–5.75 g/l when the volumetric portion of the carrier was 15–30%. The concentration of attached-biomass increased with increase of OLR, moreover, the biomass fixed in the carriers predominated in the reactor at all OLR applied in this study, suggesting that the attached-biomass played a major role in COD removal.

Biodegradation of 2,4-dichlorophenol in an air-lift honeycomb-like ceramic reactor

Abstract A novel air-lift bioreactor, with a honeycomb-like ceramic column packed in the inner draft tube as the carrier for immobilization of microbial cells, was developed in this laboratory. A microorganism, identified as Achromobacter sp. and capable of degrading 2,4-dichlorophenol (2,4-DCP), was immobilized in the ceramic carrier and used for biodegradation of 2,4-DCP. Semi-continuous biodegradation of 2,4-DCP as a single substrate and in the presence of phenol as co-substrate was investigated. The results showed that when 2,4-DCP occurs alone, its biodegradation rate increased gradually from Run 1 to Run 6 and the degradation process could be described with zero-order kinetics model. When phenol was used as co-substrate, the existence of phenol could inhibit the biodegradation of 2,4-DCP and the biodegradation rate of 2,4-DCP decreased gradually. However, the biodegradation of phenol increased with the increase of run number of the batch experiments. In addition, continuous degradation of 2,4-DCP was also investigated. The results indicated that 2,4-DCP at the concentration ranged from 6.86 to 102.38 mg l −1 could be degraded at a dilution rate of 0.16 h −1 and the removal percentage ranged between 84 and 100%. The effect of interruption of 2,4-DCP supply to the bioreactor on the degradation ability of microbial cells was investigated by replacing 2,4-DCP with sodium acetate as the sole carbon source for 12 days. Intermission of 2,4-DCP supply did not cause the loss of chlorophenol-degrading ability.

Biodegradation of quinoline by gel immobilized Burkholderia sp.

Burkholderia sp, a gram-negative, rod-shaped, aerobe, capable of degrading quinoline was immobilized in calcium alginate gel beads and used for degradation of quinoline in aqueous solution in the reactor. The optimal conditions for immobilization of the microorganism, such as alginate concentration, calcium ion concentration, initial cell loading, hardening time and bead size, were determined with a view to improving the quinoline degradation rate. The characteristics of quinoline degradation by immobilized microbial cells were investigated. The repeated use of immobilized cells for quinoline degradation was performed and the results revealed that the bioactivity of immobilized cells was stable over 100 h in the repeated batch cultivation for quinoline degradation.

Biodegradation of phthalic acid ester in soil by indigenous and introduced microorganisms

The biodegradation of di-n-butyl phthalate (DBP) in soil microcosoms by indigenous microbial population and a DBP degrading inoculum as well as DBP adsorption by soil was investigated. The results demonstrated that the adsorption of DBP by soil conformed to Freundlich equation. The indigenous bacteria were capable of degrading phthalate in soil. The innoculation of the soil with DBP degrader enhanced the DBP degradation rate. The enumeration of microorganisms indicated a good correlation between phthalate degradation and microbial counts.

A reusable evanescent wave immunosensor for highly sensitive detection of bisphenol A in water samples

This paper proposed a compact and portable planar waveguide evanescent wave immunosensor (EWI) for highly sensitive detection of BPA. The incident light is coupled into the planar waveguide chip via a beveled angle through undergoing total internal reflection, where the evanescent wave field forms and excites the binding fluorophore-tagged antibodies on the chip surface. Typical calibration curves obtained for BPA has detection limits of 0.03 μg/L. Linear response for BPA ranged from 0.124 μg/L–9.60 μg/L with 50% inhibition concentration for BPA of 1.09 ± 0.25 μg/L. The regeneration of the planar optical waveguide chip allows the performance of more than 300 assay cycles within an analysis time of about 20 min for each assay cycle. By application of effective pretreatment procedure, the recoveries of BPA in real water samples gave values from 88.3% ± 8.5% to 103.7% ± 3.5%, confirming its application potential in the measurement of BPA in reality.

Temporal and spatial inhibitory effects of zinc and copper on wastewater biofilms from oxygen concentration profiles determined by microelectrodes.

To understand the temporal and spatial toxic effect of heavy metals on the microbial activities of biofilms, microelectrodes were used to measure the inhibitory oxygen (O(2)) concentration profiles resulted from the effects of zinc (Zn(2+)) and copper (Cu(2+)). Using the O(2) microprofiles as bases, the spatial distributions of net specific O(2) respiration were determined in biofilms with and without treatment of 5 mg/L Zn(2+) or 1 mg/L Cu(2+). Results show that microbial activities were inhibited only in the outer layer (∼400 μm) of the biofilms and bacteria present in the deeper sections of the biofilms became even more active. The inhibition caused by the heavy metals was evaluated by two methods. One was derived from the oxygen influx at the interface and the other was based on the integral of the oxygen consumption calculated from the entire O(2) profile. The two methods yielded significantly different results. We argue that the integral method results in more accurate assessment of toxicity than the surface flux determination.

A disposable cobalt-based phosphate sensor based on screen printing technology

Screen printing is a promising technology because of its simplicity, low-cost, high reproducibility, and efficiency in large-scale production. In this work, a cobalt-based phosphate sensor was successfully fabricated using the screen printing technology for the determination of phosphate concentration in the aqueous solution. The disposable sensor consists of a fully integrated cobalt (Co) electrode, which is a layer of carbon conductive ink (C) physically doped with Co powder, and Ag/AgCl reference electrode. The SEM images show that the morphology of the Co electrode changes after exposure to the phosphate solution, indicating that the expendable reaction exists during the measurement. At the Co/C ratio of 1:99, the cobalt-based phosphate sensor shows phosphate-selective potential response in the range of 10−4 to 10−1 mol/L, yielding a detection limit of 1×10−5 mol/L and a slope of over 30 mV/decade in acidic solution (pH 4.5) for H2PO4−. The proposed screen-printed sensor also exhibited significant reproducibility with a small repeated sensing deviation (i.e., relative standard deviation (R.S.D.) of 0.5%) on a single sensor and a small electrode-to-electrode deviation (i.e., R.S.D.<3.2%). The recovery study of H2PO4− in real wastewater samples gave values from 95.4% to 101.8%, confirming its application potential in the measurement of phosphate in real samples. Apart from its high selectivity, sensitivity, and stability comparable with a conventional bulk Co-wire electrode, the proposed phosphate sensor still yields many other advantages, such as low price, compactness, ease of use, and the possibility of integration with other analytical devices such as flow injection analysis.