Ouping Deng

Heavy metal removal by GLDA washing: Optimization, redistribution, recycling, and changes in soil fertility

Soil washing, an emerging method for treating soils contaminated by heavy metals, requires an evaluation of its efficiency in simultaneously removing different metals, the quality of the soil following remediation, and the reusability of the recycled washing agent. In this study, we employed N,N-bis (carboxymethyl)-l-glutamic acid (GLDA), a novel and readily biodegradable chelator to remove Cd, Pb, and Zn from polluted soils. We investigated the influence of washing conditions, including GLDA concentration, pH, and contact time on their removal efficiencies. The single factor experiments showed that Cd, Pb, and Zn removal efficiencies reached 70.62, 74.45, and 34.43% in mine soil at a GLDA concentration of 75mM, a pH of 4.0, and a contact time of 60min, and in polluted farmland soil, removal efficiencies were 69.12, 78.30, and 39.50%, respectively. We then employed response surface methodology to optimize the washing parameters. The optimization process showed that the removal efficiencies were 69.50, 88.09, and 40.45% in mine soil and 71.34, 81.02, and 50.95% in polluted farmland soil for Cd, Pb, and Zn, respectively. Moreover, the overall highly effective removal of Cd and Pb was connected mainly to their highly effective removal from the water-soluble, exchangeable, and carbonate fractions. GLDA-washing eliminated the same amount of metals as EDTA-washing, while simultaneously retaining most of the soil nutrients. Removal efficiencies of recycled GLDA were no >5% lower than those of the fresh GLDA. Therefore, GLDA could potentially be used for the rehabilitation of soil contaminated by heavy metals.

Application of response surface methodology for the optimization of lead removal from contaminated soil using chelants

The remediation of Pb-contaminated soil has become an international concern in recent decades due to mines exploitation and fertilizer abuse. Batch chemical soil washing experiments were conducted to optimize Pb removal efficiency from contaminated soil by two biodegradable chelants, citric acid (CA) and [S,S]-ethylenediaminedisuccinic acid (EDDS). The influences of chelant concentration, pH and contact time were evaluated. In a single factor test, a maximum Pb removal efficiency of 77.84% was achieved with 100 mM CA solution and pH 2.0 for 60 min, while it reached 81.49% with 400 mM EDDS solution and pH 4.0 for 60 min. Response surface methodology (RSM) based on Box–Behnken design (BBD) was applied to optimize the experimental conditions. The interactions between selective factors were significant (P < 0.05). Polynomial models were developed for the experimental response and optimal conditions were obtained with high determination coefficients (R2 ≥ 0.90, P < 0.05). Furthermore, Pb removal efficiencies by CA and EDDS washing were 70.08 and 80.26%, respectively, under optimal conditions, and close to the predicted values (74.49 and 83.95%) from RSM. The results confirmed the accuracy and reliability of the optimization process using RSM. Therefore, response surface methodology is a suitable approach to determine the optimal parameters for chemical soil washing to remediate heavy metal polluted soil using biodegradable chelants.

Spatial variability of soil nitrogen in a hilly valley: Multiscale patterns and affecting factors.

Estimating the spatial distribution of soil nitrogen at different scales is crucial for improving soil nitrogen use efficiency and controlling nitrogen pollution. We evaluated the spatial variability of soil total nitrogen (TN) and available nitrogen (AN) in the Fujiang River Valley, a typical hilly region composed of low, medium and high hills in the central Sichuan Basin, China. We considered the two N forms at single hill, landscape and valley scales using a combined method of classical statistics, geostatistics and a geographic information system. The spatial patterns and grading areas of soil TN and AN were different among hill types and different scales. The percentages of higher grades of the two nitrogen forms decreased from low, medium to high hills. Hill type was a major factor determining the spatial variability of the two nitrogen forms across multiple scales in the valley. The main effects of general linear models indicated that the key affecting factors of soil TN and AN were hill type and fertilization at the single hill scale, hill type and soil type at the landscape scale, and hill type, slope position, parent material, soil type, land use and fertilization at the valley scale. Thus, the effects of these key factors on the two soil nitrogen forms became more significant with upscaling.

Enhancing the soil heavy metals removal efficiency by adding HPMA and PBTCA along with plant washing agents

Plant washing agents-water-extracted from Coriaria nepalensis (CN), Clematis brevicaudata (CB), Pistacia weinmannifolia (PW) and Ricinus communis (RC)-are feasible and eco-friendly for soil heavy metal removal, but their single application has limited removal efficiency. To improve their metal removal efficiencies, two biodegradable assistant agents, hydrolytic polymaleic anhydride (HPMA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), were investigated in combination with plant washing agents through batch soil washing experiments. Results showed that the addition of HPMA or PBTCA with plant agents greatly enhanced the removal efficiencies of soil heavy metals (p<0.05). Under acidic conditions, the maximum improvements in soil heavy metal removal reached 18.69% and 18.00% for soil Cd and Zn by PW+HPMA, respectively, and 12.89% for soil Pb by CN+HPMA. Under neutral or alkaline conditions, the largest improvements in soil Cd, Pb and Zn were 24.18%, 54.38% and 25.47% by PW+PBTCA, respectively. When compared with EDTA, the loss rates of soil nitrogen, phosphorus and potassium significantly decreased (p<0.05) and the soil organic carbon significantly increased (p<0.05) after washing with the combinations. Hence, the addition of HPMA or PBTCA with the plant agents could improve the removal of soil heavy metals.

Wet nitrogen deposition across the urban-intensive agricultural–rural transect of a small urban area in southwest China

Understanding of the spatial and temporal variation of the flux of atmospheric nitrogen (N) deposition is essential for assessment of its impact on ecosystems. However, little attention has been paid to the variability of N deposition across urban-intensive agricultural–rural transects. A continuous 2-year observational study (from January 2015 to December 2016) was conducted to determine wet N deposition across the urban-intensive agricultural–rural transect of a small urban area in southwest China. Significantly spatial and temporal variations were found in the research area. Along the urban-intensive agricultural–rural transect, the TN and NH4+-N deposition first increased and then decreased, and the NO3−-N and dissolved organic N (DON) deposition decreased continuously. Wet N deposition was mainly affected by the districts of agro-facilities, roads and build up lands. Wet NH4+-N deposition had non-seasonal emission sources including industrial emissions and urban excretory wastes in urban districts and seasonal emission sources such as fertilizer and manure volatilization in the other districts. However, wet NO3−-N deposition had seasonal emission sources such as industrial emissions and fireworks in urban district and non-seasonal emission sources such as transportation in the other districts. Deposition of DON was likely to have had similar sources to NO3−-N deposition in rural district, and high-temperature-dependent sources in urban and intensive agricultural districts. Considering the annual wet TN deposition in the intensive agricultural district was about 11.1% of the annual N fertilizer input, N fertilizer rates of crops should be reduced in this region to avoid the excessive application, and the risk of N emissions to the environment.

Sorption of tetracycline on H3PO4 modified biochar derived from rice straw and swine manure

Currently, the information about the sorption of tetracycline (TC) on animal manure derived biochar was rare although plant residue derived biochar showed high sorption of TC). Therefore, this study explored the sorption of TC on swine manure derived biochar, and compared with rice straw derived biochar simultaneously. Also, H3PO4 was adopted to modify both types of biochar. The sorption kinetic and isotherm data showed H3PO4 modification enhanced the sorption of TC on both types of biochar (especially swine-manure-biochar), and indicated the chemisorptions including H-bonding and π-π electron donor acceptor interaction might be the primary mechanism. Moreover, the strengthened electrostatic attraction between TC and biochars might largely explain the enhanced sorption capacity of TC along with pH increasing from 5.0 to 9.0. At the same conditions, swine manure derived biochar demonstrated lower sorption capacity of TC than rice straw biochar, but still could be good material for the sorption of TC.