Jiao Zhang

Enhanced dewatering of waste sludge with microbial flocculant TJ-F1 as a novel conditioner.

Microbial flocculant (MBF) TJ-F1 with high flocculating activity was investigated to be used as a novel conditioner for the enhanced dewaterability of the waste sludge from wastewater treatment plant (WWTP). The experimental results showed that TJ-F1 was better than poly(acrylamide [2-(Methacryloyloxy)ethyl]trimethylammonium chloride) (P(AM-DMC)), the most commonly used conditioner in China, in improving the dewaterability of the waste sludge in terms of both the specific resistance in filtration (SRF) and the time to filter (TTF). The key parameters influencing the dewaterability of the waste sludge conditioned by TJ-F1, including the system pH, CaCl(2) concentration and TJ-F1 concentration, were systematically investigated. The favorite pH for the conditioning process was around the neutral. CaCl(2) was found to be a good conditioning aid to TJ-F1. A right dosage of TJ-F1 was decisive for the conditioning process. The optimized conditioning process is that about 0.17% (w/w) TJ-F1 and 1.3% (w/w) CaCl(2) are added into the sludge, and then the system pH was adjusted to 7.5. The compound use of TJ-F1 and P(AM-DMC) was also testified to be feasible in improving the dewaterability of the waste sludge.

Characterization and flocculation mechanism of high efficiency microbial flocculant TJ-F1 from Proteus mirabilis

The characterization and the flocculation mechanism of microbial flocculant TJ-F1 with high flocculating activity, produced by Proteus mirabilis from a mixed activated sludge, was investigated. Mainly consisting of protein and acid polysaccharide, TJ-F1 owns a molecular weight of 1.2 x 10(5)Da, which brings strong van der Waals forces and ample binding-sites. It contains carboxyl, hydroxyl, amino groups and hydrogen bonds preferred for the flocculation process. The key parameters influencing the flocculation behavior were investigated by analyzing both the Zeta potentials of the flocculation systems and the flocculating efficiencies of TJ-F1. An alkaline condition promotes its flocculating efficiency. CaCl(2) aids TJ-F1 by effectively decreasing the absolute value of Zeta potential. Appropriate dose of TJ-F1 is crucial to the flocculating efficiency. During the precipitating process, the growing flocs sweep the small flocs and the suspended particles to form big flocs, which also contribute to the excellent flocculating efficiency of TJ-F1.

A novel nitrite biosensor based on conductometric electrode modified with cytochrome c nitrite reductase composite membrane

A conductometric biosensor for nitrite detection was developed using cytochrome c nitrite reductase (ccNiR) extracted from Desulfovibrio desulfuricans ATCC 27774 cells immobilized on a planar interdigitated electrode by cross-linking with saturated glutaraldehyde (GA) vapour in the presence of bovine serum albumin, methyl viologen (MV), Nafion, and glycerol. The configuration parameters for this biosensor, including the enzyme concentration, ccNiR/BSA ratio, MV concentration, and Nafion concentration, were optimized. Various experimental parameters, such as sodium dithionite added, working buffer solution, and temperature, were investigated with regard to their effect on the conductance response of the biosensor to nitrite. Under the optimum conditions at room temperature (about 25 degrees C), the conductometric biosensor showed a fast response to nitrite (about 10s) with a linear range of 0.2-120 microM, a sensitivity of 0.194 microS/microM [NO(2)(-)], and a detection limit of 0.05 microM. The biosensor also showed satisfactory reproducibility (relative standard deviation of 6%, n=5). The apparent Michaelis-Menten constant (K(M,app)) was 338 microM. When stored in potassium phosphate buffer (100mM, pH 7.6) at 4 degrees C, the biosensor showed good stability over 1 month. No obvious interference from other ionic species familiar in natural waters was detected. The application experiments show that the biosensor is suitable for use in real water samples.

New insight into adsorption characteristics and mechanisms of the biosorbent from waste activated sludge for heavy metals

The adsorption characteristics and mechanisms of the biosorbent from waste activated sludge were investigated by adsorbing Pb(2+) and Zn(2+) in aqueous single-metal solutions. A pH value of the metal solutions at 6.0 was beneficial to the high adsorption quantity of the biosorbent. The optimal mass ratio of the biosorbent to metal ions was found to be 2. A higher adsorption quantity of the biosorbent was achieved by keeping the reaction temperature below 55°C. Response surface methodology was applied to optimize the biosorption processes, and the developed mathematical equations showed high determination coefficients (above 0.99 for both metal ions) and insignificant lack of fit (p=0.0838 and 0.0782 for Pb(2+) and Zn(2+), respectively). Atomic force microscopy analyses suggested that the metal elements were adsorbed onto the biosorbent surface via electrostatic interaction. X-ray photoelectron spectroscopy analyses indicated the presence of complexation (between -NH2, -CN and metal ions) and ion-exchange (between -COOH and metal ions). The adsorption mechanisms could be the combined action of electrostatic interaction, complexation and ion-exchange between functional groups and metal ions.

High efficiency removal of 2-chlorophenol from drinking water by a hydrogen-based polyvinyl chloride membrane biofilm reactor

A continuously stirred hydrogen-based membrane biofilm reactor (MBfR) with polyvinyl chloride (PVC) hollow fiber membrane was investigated for removing 2-chlorophenol (2-CP) from contaminated drinking water. The bioreactor startup was achieved by acclimating the microorganisms from a denitrifying and sulfate-reducing MBfR to the drinking water contaminated by 2-CP. The effects of some major factors, including 2-CP loading, H(2) pressure, nitrate loading, and sulfate loading, on the removal of 2-CP by the MBfR were systematically investigated. Although the effluent 2-CP concentration increased with its increasing influent loading, the removing efficiency of 2-CP by the MBfR could be up to 94.7% under a high influent loading (25.71 mg/L d). The removing efficiency of 2-CP by the MBfR could be improved by higher H(2) pressure, and lower influent nitrate concentration and sulfate concentration. A high H(2) pressure can assure enough available H(2) as the electron donor for 2-CP degradation. The competition in the electron donor made nitrate and sulfate inhibit the degradation of 2-CP in the MBfR. The electron flux analyses indicated that the degradation of 2-CP only accounted for a small part of electron flux, and the autohydrogenotrophic bacteria in the MBfR were highly efficient for the 2-CP removal.

Associated Adsorption Characteristics of Pb(II) and Zn(II) by a Novel Biosorbent Extracted from Waste-Activated Sludge

AbstractThe associated adsorption of Pb2+ and Zn2+ by a novel biosorbent extracted from waste-activated sludge (WAS) after short-time aerobic digestion is systematically investigated by using aqueous binary metal solutions. Zn2+ slightly inhibited Pb2+ adsorption onto the biosorbent, while Pb2+ markedly inhibited Zn2+ adsorption onto the biosorbent. When the total mass concentrations of metal ions in the disposed solutions were the same, the total adsorption capacity of the biosorbent for Pb2+ and Zn2+ in the binary-metal solution was more than that for Pb2+ in a single-metal solution, but less than that for Zn2+ in a single-metal solution. Moreover, a rising proportion of Zn2+ concentration in the binary-metal solution was found to increase the total adsorption capacity of the biosorbent. Both the Langmuir model and Freundlich model commendably described the adsorption isotherms of Pb2+ and Zn2+ in the associated adsorption system. The maximal adsorption capacity for each metal ion in the binary-metal so...

Ultrasound-promoted extraction of cheap microbial flocculant from waste activated sludge

Ultrasound was uniquely applied to promote the extraction of cheap microbial flocculant (MBF) from waste activated sludge (WAS) of municipal wastewater treatment plants (WWTPs). Various influencing factors, including ultrasonic conditions (frequency, power density and treatment time) and WAS features (pH, concentration and source), were systematically investigated. The propitious ultrasonic conditions for MBF preparation from WAS were 20 kHz, 2.1 to 2.7 kW/L and 1 to 3 min. Natural sludge pH (about 7) was preferable to the MBF preparation. The major components of the extracted MBF contained polysaccharides, proteins and nucleic acids. The yield of the extracted MBF increased with rising sludge concentration. The wide application potential of the developed method was testified by the successful MBF extraction from the WAS samples of four full-scale municipal WWTPs with different typical processes. The ultrasonic method applied to extract MBF from WAS would not only provide a new way for WAS resource reuse, but also markedly cut down the cost of MBF preparation.

Interactions between metal ions and the biopolymer in activated sludge: quantification and effects of system pH value

The quantification and effects of system pH value on the interactions between Pb(II) and the biopolymer in activated sludge were investigated. The biopolymer had two protein-like fluorescence peaks (Ex/Em = 280 nm/326–338 nm for peak A; Ex/Em = 220–230 nm/324–338 nm for peak B). The fluorescence intensities of peak B were higher than those of peak A. The fluorophores of both peaks could be largely quenched by Pb(II), and the quencher dose for peak B was about half of that for peak A. The modified Stern-Volmer equation well depicted the fluorescence quenching titration. The quenching constant (Ka) values for both peaks decreased with rising system pH value, and then sharply decreased under alkaline conditions. It could be attributed to that the alkaline conditions caused the reduction of available Pb(II) due to the occurrence of Pb(OH)2 sediments. The Ka values of peak B were bigger than those for peak A at the same system pH values. Accordingly, the aromatic proteins (peak B) played a key role in the interactions between metal ions and the biopolymer.

pH dependent of the waste activated sludge reduction by short-time aerobic digestion (STAD) process

The short-time aerobic digestion (STAD) process has been found to be a unique and significant technique for the stabilization of waste activated sludge (WAS), but the influences of the system pH on the STAD process was unclear. This study systematically disclosed the influences of the system pH on the STAD process of WAS. Under neutral or weak alkaline conditions, although the biodegradation rates of VSS (~0.0085 h-1) were low, high biodegradation rates of TCOD (kTCOD) (~0.0096 h-1) were achieved. Less releases of the biopolymers from the WAS led to low concentrations of STOC, UV254, the low MW organic matters, NH4+ - N and PO43- - P in the supernatant. However, the appropriate pH for the microorganisms improved SOUR, indicating that the released substances were further reused or biodegraded by the microorganisms. Under acidic or alkaline conditions, the biodegradation rates of VSS (0.009-0.019 h-1) and TCOD (kTCOD) (0.005-0.009 h-1) were opposite with those under neutral or weak alkaline conditions. The releases of the biopolymers were increased, leading to high concentrations of STOC, UV254, the low MW organic matters, PO43- - P and NH4+ - N in the supernatant. However, the extreme pH inhibited the microbial activity. The SOURs were only 0.0097 h-1 and 0.0053 h-1 for system pH of 8.0 and 4.0, respectively. Accordingly, neutral and weak alkaline conditions should be more suitable for the STAD process of WAS. This work lays the foundation for optimizing system pH for the reduction of WAS in STAD system.

Simultaneously enhanced biopolymers production and sludge dewaterability of waste activated sludge by synergetic integration process of short-time aerobic digestion with cocoamidopropyl betaine and calcium oxide

Waste activated sludge (WAS) has seriously threatened the environment safety and the public health due to its rapid growth and complex components. Simultaneously enhanced the biopolymers production and the sludge dewaterability of WAS were investigated by synergetic integration process of the short-time aerobic digestion (STAD) with cocoamidopropyl betaine (CAPB) and calcium oxide (CaO). STAD could improve the biopolymers production by biosynthesis. CAPB could further significantly enhance the biopolymers production and optimized the constituents. CaO (0.1-0.2 g/g TSS) could dramatically enhance the sludge dewaterability by forming a multi-grid skeleton in WAS, while the biopolymers production could almost remain stable. Especially, the synergetic integration process of STAD with 0.1 g CAPB/g TSS for 8 h and 0.1 g CaO/g TSS could cost-effectively enhance both the biopolymers production and the sludge dewaterability. The produced biopolymers showed strong adsorbability for heavy metals (eg, 375 mg Cu2+/g biopolymers). Accordingly, the developed novel process is of big significance for resource utilization and volume reduction of WAS.