Ecological Reconstruction and Safety Risk Assessment of Contaminated Sites

This study evaluated the environmental impact and overall benefits of incorporating humus composites in the anaerobic co-digestion of kitchen waste and residual sludge. The life cycle assessment method was used to quantitatively analyze the environmental impact of the entire anaerobic co-digestion treatment process of waste, including garbage collection, transportation, and final product utilization. Moreover, the comprehensive assessment of the environmental impact, energy-saving and emission-reduction abilities, and economic cost of using humus composites in the anaerobic co-digestion treatment process was conducted using a benefit analysis method. The results showed that the anaerobic co-digestion of kitchen waste and residual sludge significantly contributed to the mitigation of global warming potential (GWP), reaching −19.76 kgCO₂-eq, but had the least impact on the mitigation of acidification potential (AP), reaching −0.10 kgSO₂-eq. In addition, the addition of humus composites significantly increased the production of biogas. At a concentration of 5 g/L, the biogas yield of the anaerobic co-digestion process was 70.76 m³, which increased by 50.62% compared with the blank group. This amount of biogas replaces ~50.52 kg of standard coal, reducing CO₂ emissions by 13.74 kg compared with burning the same amount of standard coal. Therefore, the anaerobic co-digestion treatment of kitchen waste and residual sludge brings considerable environmental benefits. Full article

In this study, the contents of eight heavy metal(loid)s (As, Pb, Zn, Cd, Cr, Cu, Sb and Tl) in 50 sediment samples from a headwater of Beijiang River were studied to understand their pollution, ecological risk and potential sources. Evaluation indexes including sediment quality guidelines (SDGs), enrichment factor (EF), geo-accumulation index (I_geo), risk assessment code (RAC) and bioavailable metal index (BMI) were used to evaluate the heavy metal(loid)s pollution and ecological risk in the sediments. Pearson’s correlation analysis and principal component analysis were used to identify the sources of heavy metal(loid)s. The results showed that the average concentration of heavy metal(loid)s obviously exceeded the background values, except Cr. Metal(loid)s speciation analysis indicated that Cd, Pb, Cu and Zn were dominated by non-residual fractions, which presented higher bioavailability. The S content in sediments could significantly influence the geochemical fractions of heavy metal(loid)s. As was expected, it had the most adverse biological effect to local aquatic organism, followed by Pb. The EF results demonstrated that As was the most enriched, while Cr showed no enrichment in the sediments. The assessment of I_geo suggested that Cd and As were the most serious threats to the river system, while Cr showed almost no contamination in the sediments. Heavy metal(loid)s in sediments in the mining- and smelting-affected area showed higher bioavailability. According to the results of the above research, the mining activities caused heavier heavy metal(loid)s pollution in the river sediment. Three potential sources of heavy metal(loid)s in sediment were distinguished based on the Pearson’s correlation analysis and PCA, of which Cd, Pb, As, Zn, Sb and Cu were mainly derived from mining activities, Cr was mainly derived from natural sources, Tl was mainly derived from smelting activities. Full article

The surge in kitchen waste production is causing food-borne disease epidemics and is a public health threat worldwide. Additionally, the effectiveness of conventional treatment approaches may be hampered by KW’s high moisture, salt, and oil content. Hydrothermal carbonization (HTC) is a promising new technology to convert waste biomass into environmentally beneficial derivatives. This study used simulated KW to determine the efficacy of hydrothermal derivatives (hydrochar) with different salt and oil content, pH value, and solid-liquid ratio for the removal of cadmium (Cd) from water and identify their high heating value (HHV). The findings revealed that the kitchen waste hydrochar (KWHC) yield decreased with increasing oil content. When the water content in the hydrothermal system increased by 90%, the yield of KWHC decreased by 65.85%. The adsorption capacity of KWHC remained stable at different salinities. The KWHC produced in the acidic environment increases the removal efficiency of KWHC for Cd. The raw material was effectively transformed into a maximum HHV (30.01 MJ/kg). HTC is an effective and secure method for the resource utilization of KW based on the adsorption capacity and combustion characteristic indices of KWHC. Full article

Pyrolysis is an emerging and effective means for sludge disposal. Biochar derived from sludge has broad application prospects, however, is limited by heavy metals. In this study, the fate of heavy metals (HMs) in pyrolysis coupling with acid washing treatment for sewage sludge was comprehensively investigated for the first time. Most of the HMs redistributed in the pyrolyzed residues (biochar) after pyrolysis, and the enrichment order of the HMs was: Zn > Cu > Ni > Cr. Compared with various washing agents, phosphoric acid presented a superior washing effect on most heavy metals (Cu, Zn, and Cr) in biochars derived at low pyrolysis temperature and Ni in biochars derived at high pyrolysis temperature. The optimal washing conditions for heavy metals (including Cu, Zn, Cr, and Ni) removal by H₃PO₄ were obtained by batch washing experiments and the response surface methodology (RSM). The total maximum HM removal efficiency was 95.05% under the optimal washing specifications by H₃PO₄ (acid concentration of 2.47 mol/L, L/S of 9.85 mL/g, and a washing temperature of 71.18 °C). Kinetic results indicated that the washing process of heavy metals in sludge and biochars was controlled by a mixture of diffusion and surface chemical reactions. After phosphoric acid washing, the leaching concentrations of HMs in the solid residue were further reduced compared with that of biochar, which were below the USEPA limit value (5 mg/L). The solid residue after pyrolysis coupling with acid washing resulted in a low environmental risk for resource utilization (the values of the potential ecological risk index were lower than 20). This work provides an environmentally friendly alternative of pyrolysis coupling with acid washing treatment for sewage sludge from the viewpoint of the utilization of solid waste. Full article

This study examined the ability of the green microalgae Chlorella vulgaris to remove arsenic from aqueous solutions. A series of studies was conducted to determine the optimal conditions for biological arsenic elimination, including biomass amount, incubation time, initial arsenic level, and pH values. At 76 min, pH 6, 50 mgL⁻¹ metal concentration, and 1 gL⁻¹ bio-adsorbent dosage, the maximum removal of arsenic from an aqueous solution was 93%. The uptake of As (III) ions by C. vulgaris reached an equilibrium at 76 min of bio-adsorption. The maximum adsorptive rate of arsenic (III) by C. vulgaris was 55 mg/gm. The Langmuir, Freundlich, and Dubinin–Radushkevich equations were used to fit the experimental data. The best theoretical isotherm of Langmuir, Freundlich, or/and Dubinin–Radushkevich for arsenic bio-adsorption by Chlorella vulgaris was determined. To choose the best theoretical isotherm, the coefficient of correlation was used. The data on absorption appeared to be linearly consistent with the Langmuir (q_max = 45 mgg⁻¹; R² = 0.9894), Freundlich (k_f = 1.44; R² = 0.7227), and Dubinin–Radushkevich (q_D–R = 8.7 mg/g; R² = 0.951) isotherms. The Langmuir and Dubinin–Radushkevich isotherms were both good two-parameter isotherms. In general, Langmuir was demonstrated to be the most accurate model for As (III) bio-adsorption on the bio-adsorbent. Maximum bio-adsorption values and a good correlation coefficient were observed for the first-order kinetic model, indicating that it was the best fitting model and significant in describing the arsenic (III) adsorption process. SEM micrographs of treated and untreated algal cells revealed that ions adsorbed on the algal cell’s surface. A Fourier-transform infrared spectrophotometer (FTIR) was used to analyze the functional groups in algal cells, such as the carboxyl group, hydroxyl, amines, and amides, which aided in the bio-adsorption process. Thus, C. vulgaris has great potential and can be found in eco-friendly biomaterials capable of adsorbing arsenic contaminants from water sources. Full article

Cadmium (Cd) is one of the heavy metals that contaminate rice cultivation, and reducing Cd contamination in rice through agronomic measures is a hot research topic. In this study, foliar sprays of gibberellins (GA) and brassinolide (BR) were applied to rice under Cd stress in hydroponic and pot experiments. After foliar spraying of GR and BR, the biomass of rice plants grown in either hydroponics or soil culture was significantly higher or even exceeded that in the absence of Cd stress. In addition, photosynthetic parameters (maximum fluorescence values), root length and root surface area, and CAT, SOD and POD activities were significantly improved. The MDA content decreased in the shoots, suggesting that the application of GR and BA may have enhanced photosynthesis and antioxidant function to alleviate Cd stress. Furthermore, the BR and GA treatments decreased the Cd content of rice roots, shoots and grains as well as the Cd transfer coefficient. Cd chemical morphology analysis of rice roots and shoots showed that the proportion of soluble Cd (Ethanol-Cd and Water-Cd) decreased, whereas the proportion of NaCl-Cd increased. Analysis of the subcellular distribution of Cd in rice roots and above ground showed that the proportion of Cd in the cell wall increased after foliar spraying of GA and BR. The results indicate that after foliar application of GA and BR, more of the Cd in rice was transformed into immobile forms and was fixed in the cell wall, thus reducing the amount in the seeds. In summary, foliar sprays of GA and BR can reduce the toxic effects of Cd on rice plants and reduce the Cd content in rice grains, with GA being more effective. Full article