Liangtong Zhan

Adsorption behavior and mechanism of Cd(II) on loess soil from China

Cadmium is a toxic heavy metal that has caused serious public health problems. It is necessary to find a cost effective method to deal with wastewater containing Cd(II). Loess soils in China have proven to be a potential adsorbent for Cd(II) removal from wastewater. The adsorption capacity of loess towards Cd(II) has been determined to be about 9.37 mg g(-1). Slurry concentration, initial solution pH, reaction time and temperature have also been found to significantly influence the efficiency of Cd(II) removal. The adsorption isotherms and kinetics of loess soil from China can be best-fit with the Langmuir model and pseudo-second order kinetics model, respectively. The thermodynamic analysis revealed that the adsorption process was spontaneous, endothermic and the system disorder increased with duration. The natural organic matter in loess soil is mainly responsible for Cd(II) removal at pH < 4.2, while clay minerals contribute to a further gradual adsorption process. Chemical precipitation dominates the adsorption stage at pH > 8.97. Further studies using X-ray diffraction, Fourier transform infrared spectra of Cd(II) laden loess soil and Cd(II) species distribution have confirmed the adsorption mechanism.

Secondary Compression of Municipal Solid Wastes and a Compression Model for Predicting Settlement of Municipal Solid Waste Landfills

The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.

An analytical solution to contaminant diffusion in semi-infinite clayey soils with piecewise linear adsorption

The adsorption of contaminants onto soil particles typically is nonlinear if the contaminant concentration is sufficiently high. A simplified piecewise linear adsorption isotherm consistent with experimental results is proposed as an approximation for nonlinear adsorption behavior. This approximation allows for the use of analytical solution to model solute diffusion of contaminants that exhibit nonlinear adsorption. A moving boundary is introduced to represent significant changes in the retardation factor of clay with an increase in solute concentration. The proposed analytical solutions were validated using experimental data presented in the literature. There is negligible difference between the results obtained by the proposed analytical solution and those obtained by the linear model when C(m)/C(0) reached 0.5. The results also show that the model based on linear adsorption using the initial secant of the Freundlich isotherm leads to significantly lower estimated breakthrough time for the contaminant of interest than that obtained using the proposed model. The earlier breakthrough is due to an under-estimation of the amount of adsorption. The proposed method is relatively simple to apply and can be used for evaluating experimental results and verifying more complex numerical models.

Biochemical, hydrological and mechanical behaviors of high food waste content MSW landfill: Preliminary findings from a large-scale experiment

A large-scale bioreactor experiment lasting for 2years was presented in this paper to investigate the biochemical, hydrological and mechanical behaviors of high food waste content (HFWC) MSW. The experimental cell was 5m in length, 5m in width and 7.5m in depth, filled with unprocessed HFWC-MSWs of 91.3 tons. In the experiment, a surcharge loading of 33.4kPa was applied on waste surface, mature leachate refilling and warm leachate recirculation were performed to improve the degradation process. In this paper, the measurements of leachate quantity, leachate level, leachate biochemistry, gas composition, waste temperature, earth pressure and waste settlement were presented, and the following observations were made: (1) 26.8m3 leachate collected from the 91.3 tons HFWC-MSW within the first two months, being 96% of the total amount collected in one year. (2) The leachate level was 88% of the waste thickness after waste filling in a close system, and reached to over 100% after a surcharge loading of 33.4kPa. (3) The self-weight effective stress of waste was observed to be close to zero under the condition of high leachate mound. Leachate drawdown led to a gain of self-weight effective stress. (4) A rapid development of waste settlement took place within the first two months, with compression strains of 0.38-0.47, being over 95% of the strain recorded in one year. The compression strain tended to increase linearly with an increase of leachate draining rate during that two months.

One-dimensional consolidation of saturated degradable porous media with degradation-dependent compressibility

For degradable porous media (DPM) experiencing solid particle or mass loss, the volume change process is complex. To investigate the pore water pressure response and associated deformation during the consolidation process of saturated DPM theoretically, the generalized governing equation for one-dimensional (1-D) consolidation of saturated DPM was proposed. Then, saturated municipal solid waste (MSW) was taken as an example. The generalized and simplified 1-D consolidation models were established for saturated MSW, respectively. Analytical solution to the simplified 1-D consolidation model considering degradation-dependent compressibility only was derived for saturated MSW. Based on this analytical solution, case studies were carried out. Excess pore water pressure (usw) being larger than the initial value was found in deeper waste during the early stage of consolidation under a constant surcharge load. This is because the loading effect resulted by the increase of compressibility is greater than the unloading effect resulted by the increase of void space. An increase of degradation rate coefficient c could result in greater loading effect, and hence causes increasing usw in waste. The numerical results are of wider interest, being applicable to other DPM.

The Effects of Temperature on Hydraulic Conductivity of Remolded Sewage Sludge

This paper examines the effect of temperature, with the range of 20 to 70 °C, on the hydraulic conductivities of remolded sewage sludge from different regions compared with the kaolin and clay. And the hydraulic conductivities of the heated sludge were measured with the confining stress of 60,100 and 200 kPa. The measured values of hydraulic conductivities for all the sludge increase with increasing temperature, and the hydraulic conductivities at 70 °C increase up to about 25–60 times those at 20 °C, while kaolin and clay are 2–4 times. When cooling from 70 °C to 20 °C, the hydraulic conductivities of sludge were about 7 times the initial values at 20 °C, revealing a hysteresis phenomenon. The changes in viscosity of water, the amount of bound water and organic matter contents with increasing temperature contribute greatly to the significant increase of hydraulic conductivity of sludge. The study also showed the hydraulic conductivities of sludge did not decrease with increasing confining stress.

Geotechnical Engineering Properties of Solidified Sludge in Qizishan Landfill Site, China

In order to have a better understanding of solidified sludge in a sewage sludge disposal pit, field and laboratory investigation were conducted on the geotechnical properties of the solidified sludge at the Qizishan Landfill in Suzhou, China. The field investigation included borehole sampling. The laboratory test involved the measurements of water content, organic matter content and shear strength for the borehole samples taken from Qizishan landfill sludge pit. The tests results demonstrated that the cohesive intercept (c) of the solidified sludge mostly range from 15 to 60 kPa; friction angle (φ) mostly range from 6° to 40°. The unconfined compressive strength for sludge normally about 180 kPa, but the unconfined compressive strength for some cement-like samples up to 250–300 kPa. Above analysis are useful for the in-situ sludge reinforcement methods, such as first in-situ vacuum preloading combined with subsequent solidification treatment. And it can provide the necessary geotechnical parameter and partly basis for sludge disposal design.

A Model for Aerobic Biochemical Degradation of Municipal Solid Waste

Based on the principles of electron currents conservation and mass conservation, this paper considers the two kinds biochemical reactions of organic aerobic oxidation and simultaneous nitrification-denitrification under the condition of aerobic degradation of municipal solid waste (MSW). Select rapid degradation cellulose (RDC), slow degradation cellulose (SDC), total sugar, fat, protein, and microorganisms as the limiting substrates, and write an aerobic biochemical reaction stoichiometric equation that can reflect the mass linkages among various substances. First-order kinetic equations were used to describe the kinetic behavior of biodegradable organics in the process of aerobic degradation, meanwhile the effects of temperature, water content, and oxygen concentration on the aerobic degradation rate of organic matter were also considered. The microorganism decay was described using a first-order kinetic equation. A model with a clear physical meaning and capable of simulating the time-varying process of aerobic degradation of MSW has been established. The robustness of the model still requires instance validation.

Methane hotspot localization and visualization at a large-scale Xi'an landfill in China: Effective tool for landfill gas management

The variation characteristics and influence factors of methane emission at Jiangchungou landfill, one of the largest landfill in China, has been investigated by a one-year field monitoring campaign during 2015-2016. The methane concentration above the landfill surface varied widely from negligible to 33,975 ppm. At least 75% of the methane concentration values of the sampling points are lower than the allowed limit (500 ppm). More than 95% of the high concentration zones (>500 ppm) were located in the temporary cover area (TA). Several environmental factors were found to be related to the variation of the concentration values. A clear correlation was observed between barometric pressure and exceeding-standard areas with a correlation coefficient of -0.743 (p < 0.1). The concentration values in the final cover area (FA) were about one order of magnitude lower than those observed in the TA due to the fact that rapid methane production rate happened in the first 180 days after the high kitchen content wastes were landfilled. The percentages of the measured concentration values exceeding 500 ppm near the gas collection wells in TA zone were 71.5% in November, 2015 and 55.7% in January, 2016 due to the leakage from the sides of gas collection wells. The average methane concentration values on the HDPE geomembrane was higher than those observed on the loess cover due to the fact that the geomembrane was relatively thin (0.5 mm) and can be easily damaged by the operation vehicles. Thicker geomembranes (>1.5 mm) with a good construction quality control are expected to provide better performance at this site.

Detection of Layered Diesel-Contaminated Sands

Underground contamination by nonaqueous phase liquids (NAPLs) is increasingly serious. Rapid and reliable detection of contaminated zone and degree is the first step to site remediation. In this paper, diesel and fine sand are used as experimental materials to investigate the applicability of using time-domain reflectometry (TDR) to detect layered diesel-contaminated sands. The major work includes (1) measurement of reflection waveform and dielectric constant for specimens with a diesel-contaminated layer sandwiched between saturated sand layers; (2) measurement of reflection waveform and dielectric constant for specimens with a diesel-contaminated layer sandwiched between dry sand layers; and (3) measurement of reflection waveform and dielectric constant for specimens with a diesel-contaminated layer sandwiched between a saturated sand layer and a dry sand layer. The experimental results show the following: (1) A significant decrease in dielectric constant is observed after a diesel-contaminated layer is sandwiched in saturated sand and (2) the interfaces between the diesel-contaminated layer and the saturated sand layer can be identified by analyzing the reflection waveform. The findings obtained in this paper provide guidance for the use of TDR for the field investigation of layered NAPLs contaminated site.