Advanced Materials Research Vol. 878

Abstract: The emission characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were evaluated from a grate-type municipal solid waste incinerator (MSWI). The stack flue gas, fly ash and bottom ash samples were sampled and analyzed. Results indicated that the flue gas, fly ash and bottom ash presented their mean dioxin levels of 0.0723 ng I-TEQ/Nm³, 0.614 ng I-TEQ/g and 13.33 ng I-TEQ/kg respectively. The PCDD/Fs congener patterns, in flue gas, fly ash and bottom ash, showed large similarities in both concentration and I-TEQ profiles. The de novo synthesis plays a dominant role in the low-temperature post-combustion zone.

Abstract: Isotope tracer technique was used to separate released MSW moisture from rainfall in leachate to study leachate generation characteristics. Four cylindrical PVC landfill reactors (height: 0.2m, diameter: 0.16m) filled with different kind of man-made waste were compared to study the influence of MSW type on leachate quality and quantity. Rainfall infiltration releasing process was not seriously influenced by MSW type. More than a half of rainfall was released in the first 3 days (A1:57%, A2:68%, A3:77%, A4:53%). However, the proportion of released moisture in the first 5 days to total period time varied a lot in the four reactors (A1:46%, A1:35%,A3:12%,A4:9%). MSW with much kitchen waste was easy to degrade and the leachate releasing process concentrated in the first few days, while waste with much paper released water in a constant rate during the whole experimental period. Moreover, the moisture releasing process had an obviously relevance and regulation with degradation process. This study confirmed that initial moisture in solid could not be ignored especially in China where MSW was of high moisture content and biodegradable organics fraction.

Abstract: A common failure mode for landfills is clogging of the leachate collection system. Based on the studies of clogging about landfill leachate collection system, the influence factors about clog were comprehensively and systematically analyzed .The results show that calcium is the dominant mineral of the dry mass of clog material, and CaCO₃ is the main component of the clog. The growth of biomass, minerals precipitation and deposition of suspend inorganic particles are the three major mechanisms for the clogging of LCSs. However, the clogging rate and extend of LCSs is affected by particle size of the granular media, pipe spacing and pipe diameter, filter-separator layer, mass loading, saturated or unsaturated conditions and temperature. These conclusions have profound guiding significance for the design and operation of landfill leachate collection system.

Abstract: Plasma is ionized gas-like substance, comprised by the e-deprived atoms and electron-positron. Plasma possess the characteristics of high energy, high thermal capacity, fast response and electric conversion efficiency, which shows unique advantages and good prospects for the effective disposal of POPs wastes. This paper introduced the basic principle and mechanism of plasma arc technology as a non-combustion technology; reviewed the development of application of plasma technology in the processing of HFC23, organic fluoride industrial waste, phenyl chlorosilane residue, medical waste, printed circuit board, chemical weapons and other hazardous wastes; analyzed the major technical and economic advantages and disadvantages for the plasma technologies in the POPs waste treatment; And corresponding comments and suggestions were proposed to promote the application of plasma technology for POPs waste disposal in China.

Abstract: The application of sewage sludge on agricultural soils is a promising technical solution. Pot experiments were performed to study the effect of sewage sludge application on growth, physiology and accumulation of heavy metals in three kinds of wheat. The experimental results showed soil pH decreased significantly with the increase of the application of sewage sludge. The contents of Cu, Zn and Pb in the mixed soil did not exceed the Environmental quality standards for soils in China for Grade II (GB-1518-1995).Wheat obtained good growth activities after the application of sewage sludge, however, high land application of sewage sludge (the ratio of sludge in the mixed soil of dry weight was 20% and 25%) inhibited seed emergence and root length. The content of total chlorophyll in wheat increased with the increase of sewage sludge application first and reached a maximum, and then decreased with a further increase of sewage sludge. Compared with the control, the a/b value in chlorophyll showed trace change. The content of proline in wheat increased with the increase of sewage sludge in low doses of sewage sludge (5%, 10% and 15%), while there was no significant increase in the content in high land application of sewage sludge. The physiological metabolism of wheat will exhibit abnormality as the stress of pollutants from sludge exceeded the tolerance of wheat. The content of three kinds of heavy metals in wheat grain increased obviously with sludge application increasing, indicating an increasing trend, and had the phenomenon of exceeded the safety qualification of non-environmental pollution food in china at high doses of sewage sludge. Taking account of the effects of sewage sludge application on growth,physiology and accumulation of heavy metals in wheat, the doses of sludge in the mixed soil of dry weight should be lower than 15%.

Abstract: Sewage sludge proves to be difficult to dewater due to its composition and biological nature, and it is unsuitable for disposal with high moisture content. In the present work, sewage sludge is dewatered by the thermal compression, which shows unique separation advantages of various materials, and the effects of applied temperature and pressure on the dewatering performance are investigated. The filtrate SCOD reveals that higher temperature benefits the disruption of sludge flocs, resulting in the release of organic content. According to the accumulative filtrate volume, higher temperature and pressure facilitate the dewatering process, obtaining sludge cake with lower moisture content.

Abstract: Anaerobic microorganisms involved in VFAs fermentation have inherent requirements for trace metals. It is inferred that excess sludge contains inadequate amounts of bioavailable trace metals for high-rate VFAs fermentation. The unavailability of these trace metals is probably the primary reason of poor yield without any other obvious reason. However, trace metal requirements in VFAs fermentation are not often reported in literature. Therefore, minimum requirements for trace metals including Zn, Co, Cu, Fe and Mn in VFAs fermentation from excess sludge were investigated. Firstly, the effect of each trace metal element on the VFAs production was investigated, respectively. And then, response surface methology was employed to optimize the requirement conditions of these five trace elements. The results showed that these five metal elements had the potential to enhance the production of VFAs, and the improved influences were as follows: Fe > Co > Mn > Cu > Zn. However, the production of VFAs decreased obviously with a further increase of each trace element. The optimal mixed conditions of these five trace elements were found to be 0.0982% Fe, 0.0047% Co, 0.0053% Zn, 0.0038% Cu and 0.0936% Mn. Under the optimal conditions, the concentration of VFAs reached 8410 mg/L, and increased by 2.5 times compare with the control. Finally, the consistent results between the prediction and the experiment indicated that the established polynomial model was feasible, and VFAs production could be described well by this model.

Abstract: Compared to conventional mesophilic anaerobic digestion, thermophilic anaerobic digestion may offer attractive advantages such as higher volatile solid destruction efficiency, higher biogas generation, and higher disinfection effect and better dewater ability. In this study, two experiments of waste activated sludge were conducted to evaluate the influence of total solid and inoculums ratio on the biogas production and thermophilic (55±1°C) anaerobic process stability. In first experiment, the biogas production of 4 reactors with solid concentration of 6%, 8%, 10% and 12% respectively was observed. The biogas productions in 4 reactors were 4444 mL, 4891 mL, 5573 mL and 6327 mL respectively, the biogas productions per unit VS digested of each group were all above 360 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.5 and 8.4. In second experiment, the biogas production of 4 reactors with inoculums ratio of 20%, 30%, 40% and 50% respectively was observed. The biogas productions in 4 reactors were 4730 mL, 6630 mL, 6820 mL and 7175 mL respectively, the biogas productions per unit VS digested of each group were all above 340 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.4 and 8.6. Putting into consideration, the shortening of anaerobic digestion cycle, costs saving, and increasing economic benefits; choosing TS within the scope of 8-10%and inoculums ratio within the scope of 30-40% are more recommended. And the results showed that thermophilic anaerobic digestion process for waste activated sludge could be operated steadily.

Abstract: The effects of fly-ash on dewatering of sewage sludge were studied according to sludge specific resistance (SSR), dehydrated speed, and moisture content of sludge cake as investigation indexes through single-factor experiments by contrasting to cationic polyacrylamide (PAM). The results showed that SSR kept decreasing with the rising of fly-ash dosage. When the dosage of fly-ash was 0.02 g/(ml sludge), SSR reduced by 65.2%. When the dosage of fly-ash was over 0.03 g/(ml sludge) adding with PAM, the dehydrated speed will be increased by three fourths. Through the analyses of Zeta potential, scanning electron microscope (SEM) observation, combined with the dehydration experiments, it was thought that the mechanism of fly-ash on dewatering of sewage sludge was that their particles evenly dispersed in sludge floc skeleton structure and thus decreased the SSR and improved the permeability of the sludge cake. The disposal of dewatering sludge and recycling approaches after fly-ash condition were also discussed. They can be used as landfill or as raw materials in building fields.

Abstract: Great attention has been paid to the increasing amount of municipal sludge generated from wastewater treatment plants due to its potential risks to the surrounding environment. The municipal sludge, which mainly composed of polysaccharides, proteins as well as abundant groups of microorganisms, has been proved to be a promising biological material for hydrogen production by anaerobic fermentation. The tests systematically investigated the effects of initial pH on bio-hydrogen production from alkaline pretreated municipal sludge. The results showed that both hydrogenogen and methanogen were inhibited at the initial pH 2 to 4, which resulted in little hydrogen production. The methanogen inhibition was obvious by the rate of 94-98 % at the initial pH 5. The relatively high hydrogen production appeared at the initial pH 5 during the fermentation using the alkaline pretreated sludge at pH=12.0, and the corresponding pH at the end of fermentation was from 5.0 to 6.0, which was good for hydrogen production from saccharide. The hydrogenogen and methanogen could be promoted and the lag phase for hydrogen production could be shorten at the initial pH 6 to 10, however the corresponding hydrogen production was quite low. It also could be concluded that the alkaline pretreated sludge with initial pH 12.0 gave the highest hydrogen production, and the initial pH 12.0 for the alkaline pretreated sludge could inhibit methanogen growth and meanwhile maintain a high activity of the hydrogenogen.