Zhifei Ma

Identification of nitrate sources in groundwater using a stable isotope and 3DEEM in a landfill in Northeast China

The groundwater was sampled in a typical landfill area of the Northeast China. Coupled stable isotope and three dimensional excitation-emission matrix (3DEEM) were applied to dentify diffused NO3(-) inputs in the groundwater in this area. The results indicated that combined with the feature of groundwater hydrochemistry and three-dimensional fluorescence technology can effectively identify the nitrate pollution sources. The nitrate was derived from manure and sewage by δ(15)N and δ(18)O-NO3(-) values of groundwater in the different periods. The excitation-emission matrix fluorescence spectroscopy was further evidence of groundwater DOM mainly which comes from the landfill. The protein-like was very significant at the sampling points near the landfill (SPNL), but only fulvic acid-like appeared at downstream of the landfill groundwater sampling points (DLGSP) in the study area. Partial denitrification processes helped to attenuate nitrate concentration in anaerobic environment.

Analysis for remedial alternatives of unregulated municipal solid waste landfills leachate-contaminated groundwater

A groundwater flow and solute transport model was developed using Visual Modflow for forecasting contaminant transport and assessing effects of remedial alternatives based on a case study of an unregulated landfill leachate-contaminated groundwater in eastern China. The results showed that arsenic plume was to reach the pumping well in the downstream farmland after eight years, and the longest lateral and longitudinal distance of arsenic plume was to reach 200 m and 260 m, respectively. But the area of high concentration region of arsenic plume was not to obviously increase from eight years to ten years and the plume was to spread to the downstream river and the farmland region after 20 years; while the landfill’s ground was hardened, the plume was not to reach the downstream farmland region after eight years; when the pumping well was installed in the plume downstream and discharge rate was 200m3/d, the plume was to be effectively restrained; for leakage-proof barriers, it might effectively protect the groundwater of sensitive objects within an extent time range. But for the continuous point source, the plume was still to circle the leakage-proof barrier; when discharge rate of drainage ditches was 170.26 m3/d, the plume was effectively controlled; the comprehensive method combining ground-harden with drainage ditches could get the best effect in controlling contaminant diffusion, and the discharge rate was to be reduced to 111.43 m3/d. Therefore, the comprehensive remedial alternative combining ground-harden with drainage ditch will be recommended for preventing groundwater contamination when leachate leakage has happened in unregulated landfills.

Effect of Arsenic on the Formation and Adsorption Property of Ferric Hydroxide Precipitates in ZVI Treatment

Treatment of arsenic by zerovalent iron (ZVI) has been studied extensively. However, the effect of arsenic on the formation of ferric hydroxide precipitates in the ZVI treatment has not been investigated. We discovered that the specific surface area (ca. 187 m2/g) and arsenic content (ca. 67 mg/g) of the suspended solids (As-containing solids) generated in the ZVI treatment of arsenic solutions were much higher than the specific surface area (ca. 37 m2/g) and adsorption capacity (ca.12 mg/g) of the suspended solids (As-free solids) generated in the arsenic-free solutions. Arsenic in the As-containing solids was much more stable than the adsorbed arsenic in As-free solids. XRD, SEM, TEM, and selected area electron diffraction (SAED) analyses showed that the As-containing solids consisted of amorphous nanoparticles, while the As-free solids were composed of micron particles with weak crystallinity. Extended X-ray absorption fine structure (EXAFS) analysis determined that As(V) was adsorbed on the As-containing suspended solids and magnetic solid surfaces through bidentate binuclear complexation; and As(V) formed a mononuclear complex on the As-free suspended solids. The formation of the surface As(V) complexes retarded the bonding of free FeO6 octahedra to the oxygen sites on FeO6 octahedral clusters and prevented the growth of the clusters and their development into 3-dimensional crystalline phases.

Identification of groundwater redox process induced by landfill leachate based on sensitive factor method

Landfill site is a significant source of groundwater pollution. To ensure that the groundwater contamination of landfills can be controlled and repaired scientifically, the identification of groundwater pollution process is needed. On the basis of biogeochemical process of leachate pollutants in the groundwater environment, a sensitive factor method for the identification of groundwater redox process from landfills was established in this research. The method encompasses four phases, including sensitive factors selection, redox zone characterization, weight calculation, and redox zone identification. In the sensitive factor index system employed here, five indicators involving dissolved oxygen (DO), nitrite, Fe2+, sulfide, and CO2 were selected. The boundary of each redox zones was determined by the quantitative method, and the weight of each indicator was calculated by combined weight method. This method was applied to a landfill site in the northeast of China. The result showed that there were five redox zones that appeared in pollution plume, including methanogenic zone (MGZ), sulfate reduction zone (SRZ), iron reduction zone (IRZ), nitrate reduction zone (NRZ), and oxygen reduction zone (ORZ). The results were consistent with the actual situation of the site. The sensitive factor method was scientific and effective to identify the groundwater redox process in landfill and can provide reference data related to investigation and remediation of groundwater pollution in landfill sites.

A nitrogen transformation model for multi-layer enhanced groundwater remediation technology

ABSTRACT The multi-layer enhanced groundwater remediation technology (MET) is an innovative platform that integrates physical chemistry, bioremediation, and phytoremediation technology to safely and effectively remediate ammonia nitrogen in groundwater. A nitrogen transformation model was established to study the mechanism of nitrogen transformation within ammonia nitrogen removal in the MET. The model considered organic nitrogen, ammonia nitrogen, and nitrate nitrogen as the variables, and ammonification, nitrification, denitrification, microbial assimilation, plant absorption, adsorption–desorption, and volatilization as the influencing factors. The unknown parameters of the model were obtained by fitting the data from a bench-scale experiment, and the results of the model validation and comparison showed that under the experimental initial conditions (the hydraulic load of the influent is 14.68 m3/(m2 d) and the concentration of the ammonia nitrogen is 25.0 mg/L) and after the device ran for 45d continuously, the simulated and measured average concentration values of ammonia nitrogen in the effluent were 1.701 mg/L and 1.775 m/L, respectively, and the relative deviation was 4.17%. The simulated and measured average concentration values of nitrate nitrogen in effluent were 11.474 mg/L and 11.244 m/L, respectively, and the relative deviation was 2.05%, and the total removal rate was 92.07%. Thus it can be seen that the predicted values of the nitrogen transformation model were in good agreement with the measured values, and the model could be applied to forecast the long-term remediation effects of nitrogen in groundwater by MET.