Heshan Zheng

Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment

This paper offers an effective pretreatment method that can simultaneously achieve excess sludge reduction and bio-hydrogen production from sludge self-fermentation. Batch tests demonstrated that the combinative use of ozone/ultrasound pretreatment had an advantage over the individual ozone and ultrasound pretreatments. The optimal condition (ozone dose of 0.158 g O(3)/g DS and ultrasound energy density of 1.423 W/mL) was recommended by response surface methodology. The maximum hydrogen yield was achieved at 9.28 mL H(2)/g DS under the optimal condition. According to the kinetic analysis, the highest hydrogen production rate (1.84 mL/h) was also obtained using combined pretreatment, which well fitted the predicted equation (the squared regression statistic was 0.9969). The disintegration degrees (DD) were limited to 19.57% and 46.10% in individual ozone and ultrasound pretreatments, while it reached up to 60.88% in combined pretreatment. The combined ozone/ultrasound pretreatment provides an ideal and environmental friendly solution to the problem of sludge disposal.

Ultrasonic-assisted ozone oxidation process of triphenylmethane dye degradation: evidence for the promotion effects of ultrasonic on malachite green decolorization and degradation mechanism.

This study aimed to prove the promotion effects of ultrasonic on malachite green (MG) decolorization in the ultrasonic-assisted ozone oxidation process (UAOOP), and propose the possible pathway of MG degradation. The decolorization of MG followed an apparent pseudo first-order kinetic law (initial MG concentration 100-1000 mg/L). When ultrasonic (US) was applied with ozone simultaneously, the apparent pseudo-first-order rate constant (K(app)) increased, and the time MG decolorized to the half of initial concentration (T(1/2)) shortened 185 s (1000 mg/L). Moreover, the stoichiometric ratio (Z(app)) between O(3) and MG was enhanced by US to 2.0 mol, saving 11% oxidant addition, comparing to individual ozone process. These results indicated that the application of US can reduce reaction time and dose of ozone addition. The possible pathway of MG degradation included three major approaches. And the result suggested that the reaction between MG and hydroxyl radical was substitution reaction rather than adduct reaction.

Characterizing the fluorescent products of waste activated sludge in dissolved organic matter following ultrasound assisted ozone pretreatments

This study investigated the effects of ozone and ultrasound (US) pretreatments, both individually and combined, on waste activated sludge reduction. Batch tests were conducted first to optimize the individual ozone and US pretreatments. Maximum sludge reduction ratios of 10.89% and 23% were obtained at 0.15g O3/g total solids ozone dose and 1.5W/mL US energy density, respectively. The combined ozone and US pretreatments were studied using response surface methodology. A maximum sludge reduction ratio of 40.14% was achieved by the combined ozone/US pretreatment with an ozone dose of 0.154g O3/g total solids and an US energy density of 1.445W/mL. The analysis of the dissolved organic matter by three-dimensional excitation-emission matrix fluorescence spectroscopy showed that the combined pretreatment was superior to the individual ozone and US pretreatments, and also demonstrated the synergetic effect of these two combined pretreatments.

Enhancement of volatile fatty acid production by co-fermentation of food waste and excess sludge without pH control: The mechanism and microbial community analyses.

The study provided a cost-effective and high-efficiency volatile fatty acid (VFA) production strategy by co-fermentation of food waste (FW) and excess sludge (ES) without artificial pH control. VFA production of 867.42mg COD/g-VS was obtained under the optimized condition: FW/ES 5, solid retention time 7d, organic loading rate 9g VS/L-d and temperature 40°C. Mechanism exploration revealed that the holistic biodegradability of substrate was greatly enhanced, and proper pH range (5.2-6.4) was formed by the high buffering capacity of the co-fermentation system itself, which effectively enhanced hydrolysis yield (63.04%) and acidification yield (83.46%) and inhibited methanogenesis. Moreover, microbial community analysis manifested that co-fermentation raised the relative abundances of hydrolytic and acidogenic bacteria including Clostridium, Sporanaerobacter, Tissierella and Bacillus, but suppressed the methanogen Anaerolineae, which also facilitated high VFA production. These results were of great guiding significance aiming for VFA recovery from FW and ES in large-scale.

Possible causes of excess sludge reduction adding metabolic uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide (TCS), in sequence batch reactors

Two parallel sequence batch reactors (SBRs) were operated, with and without TCS addition, to research the causes of sludge reduction by uncouplers. Three possible mechanisms of sludge reduction by TCS were studied: (1) occurrence of metabolic uncoupling, (2) consumption of more energy to resist the infection of TCS, (3) promotion of lysis-cryptic growth by TCS addition. Results showed the remarkable reduction of electronic transport system (ETS) activity and specific cellular ATP (SATP) in TCS reactor, which proved the occurrence of metabolic uncoupling. The increasing amounts of extracellular polymeric substances (EPS), as measured by chemical methods and excitation-emission matrix (EEM) fluorescence spectra, implied microorganisms consumed more energy to resist TCS. The similar DNA concentrations of the effluents in two reactors indicated sludge lysis was not intensified by TCS. Therefore, uncoupler might not only cause metabolic uncoupling but also induce more energy consumption in the production of some substances to resist uncoupler.

Adsorption of p-nitrophenols (PNP) on microalgal biochar: Analysis of high adsorption capacity and mechanism

Biochars derived from three microalgal strains (namely, Chlorella sp. Cha-01, Chlamydomonas sp. Tai-03 and Coelastrum sp. Pte-15) were evaluated for their capacity to adsorb p-nitrophenols (PNP) using raw microalgal biomass and powdered activated carbon (PAC) as the control. The results show that BC-Cha-01 (biochar from Chlorella sp. Cha-01) exhibited a high PNP adsorption capacity of 204.8mgg-1, which is 250% and 140% higher than that of its raw biomass and PAC, respectively. The adsorption kinetics and equilibrium are well described with pseudo-second-order equation and Freundlich model, respectively. BC-Cha-01 was found to contain higher polarity moieties with more O-containing functional groups than PAC and other microalgae-derived biochars. The strong polarity of binding sites on BC-Cha-01 may be responsible for its superior adsorption capacity. The biochars from Chlorella sp. Cha-01 seem to have the potential to serve as a highly efficient PNP adsorbent for wastewater treatment or emergency water pollution control.

Thermophilic hydrogen production from sludge pretreated by thermophilic bacteria: Analysis of the advantages of microbial community and metabolism

In this study, the effects of thermophilic bacteria pretreatment and elevated fermentation temperature on hydrogen production from sludge were examined. The highest hydrogen yield of 19.9mlH2g(-1) VSS was achieved at 55°C by using pretreated sludge, which was 48.6% higher than raw sludge without pretreatment, and 28.39% higher than when fermented at 35°C. To explore the internal factors of this superior hydrogen production performance, the microbial community and the metabolism analysis were performed by using high-throughput sequencing and excitation-emission matrix. The pretreated sludge showed better utilization of dissolved organic matter and less inhibition of metabolism, especially at thermophilic condition. The 454 sequencing data indicated that microbial abundance was distinctly reduced and extremely high proportion of hydrogen-producing bacteria was found in the thermophilic community (Thermoanaerobacterium accounted for 93.75%). Thus, the pretreated sludge and thermophilic condition showed significant advantages in the hydrogen production using waste sludge as substrate.

Application of low frequency ultrasound to stimulate the bio-activity of activated sludge for use as an inoculum in enhanced hydrogen production

In order to increase hydrogen yield and shorten the lag time, low frequency ultrasonic (LFU) pretreatment was applied to stimulate the bio-activity of the seed bacteria, using waste activated sludge as the inoculum. A pretreated, sterilized sludge sample was seeded as the substrate for bio-hydrogen production. A Unisense microsensor multimeter with a hydrogen microelectrode was employed to examine the hydrogenase activities at different ultrasonic densities and exposure times. The optimum conditions were achieved at an ultrasonic density of 125 W L−1 and a reaction time of 10 s. A maximum hydrogen yield of 13.03 mL H2/g TS was obtained by LFU pretreatment under these optimal conditions, which was 18% higher than that obtained when seeding the raw sludge sample. To gain a better understanding of the end product distribution, three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy was performed to characterize the dissolved organic matter (DOM) and extracellular polymeric substances (EPS) in the sludge samples during the anaerobic fermentation process. Hydrogen production from NADH/NAD+ conversion was also proved by EEM.

Enhanced sulfamethoxazole ozonation by noble metal-free catalysis based on magnetic Fe3O4 nanoparticles: catalytic performance and degradation mechanism

In this research, Fe3O4 nanoparticles were prepared by a low-cost route free of other agents, and applied in the catalysis of sulfamethoxazole (SMX) ozonation. It was proven that Fe3O4 nanoparticles significantly enhance SMX ozonation. Using a kinetics analysis, when Fe3O4 particles were added to the ozonation process, the reaction rate constant increased by 51% when the pH was 5. Moreover, we also identified that Fe3O4 enhanced the SMX ozonation removal rate by changing the degradation pathway. It was found that addition of Fe3O4 improved the production of Lewis acid active sites in SMX. These kinds of site in SMX are much easier to attack, which leads to a higher SMX removal rate and lower operational costs for the Fe3O4-based catalytic ozonation process compared to an O3 oxidation process. Finally, the SMX degradation pathways were classified for the first time, based on ozone oxidation types to give a guide for the quick and direct oxidation of SMX and other pollutants.

Simultaneous nutrient removal and reduction in sludge from sewage waste using an alternating anaerobic–anoxic–microaerobic–aerobic system combining ozone/ultrasound technology

A newly developed ozone/ultrasound technology combined with an alternating anaerobic–anoxic–microaerobic–aerobic (AAMA + O3/US) system achieved a 59.54% reduction in sludge production compared with a control system. Pyrosequencing showed that higher relative abundances of the microbial consortia responsible for nutrient removal were observed in the AAMA + O3/US system.