Keqiang Zhang

Influence of NaOH and thermal pretreatment on dewatered activated sludge solubilisation and subsequent anaerobic digestion: Focused on high-solid state

In this study, the influence of NaOH and thermal pretreatment of dewatered activated sludge (DAS) on the high-solid solubilisation and anaerobic digestion was separately investigated by monitoring common parameters. The results indicated that COD, proteins and carbohydrates were efficiently solubilised in both NaOH and thermal pretreated DAS samples. For NaOH pretreatment, the concentrations of volatile fatty acids (VFAs) and total ammonium nitrogen (TAN) firstly increased followed by decreasing with NaOH dose increasing. However, they decreased with the severity of thermal pretreatment. During the batch digestion experiments (at 37°C), for 80mg NaOHg(-1) total solid (TS) DAS pretreatment it resulted in a 6.99% decrease in cumulative methane yield (CMY) compared to untreated DAS. While for 80, 100, 120°C and 20mg NaOH pretreatment, CMY increased by 15%, 42%, 71% and 35%, respectively, in comparison to untreated DAS.

High prevalence and dissemination of β-lactamase genes in swine farms in northern China

β-Lactamase (extended-spectrum β-lactamase (ESBL)/AmpC/carbapenemase)-encoding genes, primarily discovered in clinical settings, are increasingly recovering from the environment, thus posing potential threats to public health. This paper addresses the occurrence of high-risk β-lactamase genes (bla genes) in Chinese swine farm and its surrounding farmland, and investigated their seasonal variation and fate in piggery wastewater treatment system (PWWTS) using real-time quantitative PCR. It is observed that blaTEM-1, blaGES-1,blaOXA-1 and blaAmpC were the dominant bla genes in swine farms, which were present in all pig feces, and prevailed through each treatment stage of PWWTSs. Furthermore, bla genes were more abundant in winter than that in summer, with 0.01-1.65 logs variation in swine wastewater. Troublesomely, significant bla gene levels were still discharged via the final effluents (up to 106 copies/mL) into farmland, resulting in the increase of bla gene abundance in soil (approximately 1-3 orders of magnitude). The discharge of bla genes in wastewater from swine farm highlights the need to mitigate the persistence and spreading of these elevated bla genes in agricultural systems.

Pressurized electro-dewatering of activated sludge: Analysis of electrode configurations (anode)

An electric field and mechanical pressure combined are considered an effective electro-dewatering (PED) technology for activated sludge. Here, the curved surface anodes were used for electro-dewatering to improve the effective anode area, and the PED characteristics were investigated for three anode types (flat plate, sawtooth plate and wave plate). First, evaluation methodology of the modified energy consumption ( [Formula: see text] ) and the modified processing capacity ( [Formula: see text] ) were established, with electro-dewatering factor (ξED), to evaluate the PED efficiency of different anode configurations under three raw sludge processing capacity modes. Second, the solid content distribution was analyzed by the layered method, and the electric field and current density distribution were analyzed by the finite element method. Finally, the gas emission mechanism of the curved surface anodes was discussed. When the raw sludge processing capacity and dewatering time (10 min) were the same, nearly the same extent of dewatering was achieved for the wave plate anode as for the flat plate anode. The total filtrate amount was 69.5 g and 59.0 g for the wave plate and flat plate anodes, respectively, and [Formula: see text] increased by 17.8% for the former. Under the same raw sludge thickness, the dewatering percentages in area A of the sawtooth plate and wave plate anodes were 10% and 11%, respectively, higher than that of the flat plate anode. However, according to numeric simulation results, the current density at the tips of the sawtooth plate anode can reach 740-770 A/m2, which can reduce its service life as compared to flat plate anode. In area D, gas was more easily emitted from the wave plate anode than from the flat plate anode, reducing the influence of the gas barrier layer on the electrical contact between the sludge cake and the anode.

A novel system of MnO 2 -mullite-cordierite composite particle with NaClO for Methylene blue decolorization

The MnO2-mullite-cordierite composite particle (MnO2-MCP) was prepared and firstly was applied as catalyst with sodium hypochlorite (NaOCl) as oxidant in heterogeneous Fenton-like system for methylene blue (MB) decolorization. The MnO2-MCP was characterized by XRD, SEM, EDS and BET analysis. The decolorization efficiencies of MB/MnO2-MCP, MB/NaClO, (MB after filtrating MnO2-MCP)/NaClO and MB/MnO2-MCP/NaClO were compared, which confirmed the interaction ability between MnO2-MCP and NaClO. After evaluating the role of adsorption of MB by MnO2-MCP, the catalytic oxidation effects of MnO2-MCP with NaClO on MB were exploited. The adsorption results showed that the new porous catalyst had certain adsorption capacity for MB and the adsorption fit best with Langmuir model. The central composite rotatable design (CCD) of response surface methodology (RSM) was used to design catalytic oxidation experiments of MB/MnO2-MCP/NaClO system, with influencing factors of catalyst dose, NaClO concentration, pH and initial MB concentration. The optimum conditions were 5.97 mM of NaClO, 37.9 g/L of catalyst dose, 5.74 of pH value and 100.71 mg/L of initial MB concentration, which could ensure nearly 100% MB decolorization. The effect of radical scavengers elucidated that superoxide anion (O2-) was the main species to decolorize MB. Then the possible degradation mechanism and pathway of MB were proposed in this MnO2-MCP/NaClO system.

Systematic analysis of occurrence and variation tendency about 58 typical veterinary antibiotics during animal wastewater disposal processes in Tianjin, China

Residue of veterinary antibiotics (VAs) in the animal breeding industry has become a problematic environmental issue. However, the residual levels of VAs as well as their variation tendency, degradation mechanisms and relationships with other parameters during animal wastewater disposal processes are still obscure. This study measured different samples during wastewater disposal processes from three farms, and systematically analyzed the residue, migration and removal of 58 kinds of typical VAs (6 classes) in Tianjin, China. The results showed that about 44 kinds of VAs were quantitatively detected. Tetracycline antibiotics (TCs) usually had higher residual concentrations than other classes of VAs in the raw wastewater; the highest residual concentration was 130.67 ± 5.90 μg/L which occurred for chlortetracycline (CTC). Pig farms generally had more VAs species and higher residual concentrations than dairy farms, and the proportion of different VAs was similar for dairy farms. The final removal rates of different VAs classes varied largely (negative to > 99.87%), and the highest removal rates usually occurred in biological processes for adsorption and biodegradation effects, and occasionally occurred in the final effluents. The correlation coefficients between VAs removal rates and chemical oxygen demand (COD) removal rates were much higher than those of total nitrogen (TN), total phosphorus (TP) and ammonia nitrogen (NH4-N) in pig farms, while opposite conclusion was obtained in dairy farms. Among different classes, TCs presented the highest daily mass loading of ND ~ 10,453.8 ± 471.7 mg/d in the influent and ND ~ 1141.6 ± 58.9 mg/d in the effluent in farm 1.

Ozone promoting organic nitrogen change to inorganic in anaerobic livestock wastewater

aInstitute of Agro-Environmental Protection, Ministry of Agriculture, P.R. China, Tianjin 300191, China, Tel. +86 22 23616653; email: wangfeng_530@163.com (F. Wang), Tel. +86 22 23616651; email: 29602655@qq.com (R. Lai), Tel. +86 22 23616653; email: 1548238072@qq.com (J. Liang), Tel. +86 22 23616689; email: 123720330@qq.com (K. Zhang), Tel. +86 22 23616673; email: 36849926@qq.com (J. Li), Tel. +86 22 23616651; email: zhangyue8805@163.com (Y. Zhang) bGraduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, China cScientific Observing and Experimental Station of Dali, Ministry of Agriculture, P.R. China, Yunnan 671005, China

Sewage sludge drying method combining pressurized electro-osmotic dewatering with subsequent bio-drying

In this study, pressurized electro-osmotic dewatering (PEOD) as a pretreatment process, instead of the conventional practice of adding bulking agents, for sewage sludge bio-drying was proposed. Initially, various parameters were optimized for obtaining dewatered sewage sludge (DSS), treated by an efficient, quick, and energy-saving PEOD process. The results show that the moisture content (MC) of sewage sludge could decrease from 83.41% to 60.0% within 7.5 min in the optimum conditions of the PEOD process. Subsequently, two DSS bio-drying tests were carried out to investigate the effects of inoculation. The highest temperature (68.1 °C) was obtained for T2 (inoculation), which was 3.6 °C higher than that for T1 (non- inoculation). The MC accumulative removal rate for T1 (41.49%) was slightly less than that for T2 (44.60%). Lastly, the volatile solid degradation dynamics model parameters were measured. The degradation rate constants (k) for T1 and T2 were 0.00501 and 0.00498, respectively.