Effect of acidic erosion on properties of solidified sewage sludge.

Solidified sludge can be regarded as a new type of earth cover material for domestic waste landfill. But the acidic environment result from the leachate in landfill is a potential threat to cement-based material. In order to evaluate the deterioration risk of solidified sludge in acidic environment, the leaching process of solidified sludge components under different pH conditions was investigated by taking Ni and Cr as the indexes of semi-dynamic leaching test. Under strongly acid environment (pH = 2), the leaching rate of Cr is significantly higher than that in the weakly acid environment or nearly neutral environment, and the diffusion coefficient increased by an order of magnitudes. The leaching and diffusion coefficients of Ni undergo a small influence from the adding amount of cement and pH value. Both Ni and Cr have relatively low migration ratio.

Influence of wind and light on the floating and sinking process of Microcystis.

The vertical migration and accumulation of Microcystis colonies is a critical process in algal bloom formation. This work explored the effect of wind and light intensity on the vertical migration of Microcystis colonies. The wind-driven currents, light-driven changes in mass density of colonies, and the effect of colony size was coupled to simulate the vertical motion of colonies via Ansys Fluent and MATLAB. Results showed that light causes Microcystis to exhibit a 'day-sinking and night-floating' (d-n) phenomenon, however, wind weakens the phenomenon by forming a turbulent drag force that inhibits the vertical movement of Microcystis. This study proposed a kinetic ratio-based method, that there is a specific equilibrium turbulent kinetic energy and when turbulent kinetic energy of the water body is greater than the equilibrium turbulent kinetic energy, the d-n phenomenon does not occur. For Lake Taihu, the wind-driven turbulent kinetic energy is usually greater than the equilibrium turbulent kinetic energy. Therefore, Microcystis colonies may not exhibit the d-n phenomenon. Our findings provide a new theoretical basis for current process-based models in simulating algal blooms in large shallow lakes.

Char derived from sewage sludge of hydrothermal carbonization and supercritical water gasification: Comparison of the properties of two chars.

Supercritical water gasification (SCWG) is considered a promising technology for sewage sludge (SS) treatment and utilization; however, char produced by a side reaction has become a bottleneck in SCWG. In this study, SS and its model compound (10% humic acid) were treated in an autoclave by SCWG at 400 °C for 30 min and by hydrothermal carbonization (HTC) at 250 °C for 300 min. The char yield was 15.4% in SCWG and 41.3% in HTC. The chars were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller (BET) analysis, and elemental analysis. By comparing the properties the char produced by SCWG and the hydrochar produced by HTC, which has been considered a valuable product, the feasibility of using char as an additional product in SCWG was explored. Compared with the char produced by HTC, the char generated in SCWG exhibits a lower BET specific surface area (8.257 and 15.782 m2/g) and combustion activity, a higher proportion of small pores (with pore sizes of 1-2 nm), and greater thermal stability. The formation pathway of the two types of chars is related to both dehydration and aromatization; decarboxylation also occurs in char formation during SCWG. Humus was proved to be related to char formation during the SCWG of SS based on experimental results obtained with the model compound. This work provides insights needed to guide follow-up treatments or utilization of the char produced during the SCWG of SS.

Effect of competitive adsorption on the transport of multiple pollutants through a compacted clay liner.

Leachate transport through municipal solid waste (MSW) landfill liners can be slowed considerably by adsorption. MSW landfill leachate contains a large variety of pollutants at very different concentrations, and there will be competitive adsorption as these pollutants are transported through the landfill's compacted clay liner (CCL). In this study, we used batch adsorption tests and geotechnical centrifuge modelling to examine how the adsorption of pollutants commonly found in leachate changed under competitive adsorption conditions and how competitive adsorption affected the CCL breakthrough of multiple pollutants. The results showed that the adsorption of the target pollutant on clay decreased by approximately 30% when competing pollutants were added. The speed at which the pollutants were transported through a 2-m-thick CCL increased, and the breakthrough times reduced by up to 24.8%, when the competing pollutants were mixed. Competitive adsorption significantly promoted the CCL breakthrough of pollutants at low concentrations, but it had limited effect on pollutants at high concentrations.

Key factor on improving secondary advanced dewatering performance of municipal dewatered sludge: Selective oxidative decomposition of polysaccharides.

Advanced dewatering technologies with moisture content from nearly 80% to below 60% have attracted widespread attention in the field of municipal dewatered sludge disposal. The usage of the correct types of oxidants and the degradation of key component on the effect of secondary advanced dewatering performance is a rising focus. In this study, three types of typical oxidants (Fenton's reagent, H2O2, and KMnO4) were used to pre-treat dewatered sludge directly, then advanced dewatering performance, conversion rate of bio-bound water and decomposition trend of various organic biomass were analysed. Results showed that final moisture content of Fenton's reagent group reduced to below 50% with exposure to the compression of 1000 kPa for 30 min. Different oxidants that were characterized by selective oxidizability and, compared with other oxidants, mainly decomposed proteins, lipids and humic substances, the key component of polysaccharides, which may combine with the most water were primarily decomposed by Fenton's reagent. This promoted the conversion from bio-bound water to free water and advanced dewatering performance significantly. From a morphological perspective, the ratio of dissolved polysaccharides from three layers showed Pellets: tightly bound EPS (T-EPS): loosely bound EPS (L-EPS) = 52.28%-66.56%: 8.37%-12.75%: 23.15%-39.08%, and due to the cell-breaking capacity, Fenton's reagent could mainly promote the release of intracellular polysaccharides-bound water.

Mechanism of separation and removal of water from dewatered sludge using L-DME to dissolve hydrophilic organic matter.

Difficulties in advanced dewatering of dewatered sludge hinder sludge reduction and resource utilization. L-DME (liquified dimethyl ether) has been recently used for dewatering, but the effect of organic matter dissolution using L-DME during desorption and dehydration on water removal is not clear. In this study, dewatered sludge from urban sewage treatment plants was used to conduct experiments in sequencing dissolution-separation reactors. The changes in the dehydration rate, bound water and various organic matter levels at different times, L-DME additions, and the temperature were measured. The results show that L-DME can remove 90% of water, 100% of lipids, and 8-12% of organic matter in dewatered sludge. L-DME was mixed with the semi-like colloidal sludge, and high separation of water was achieved by mixing the L-DME with water and dissolving the hydrophilic organic matter to convert the solid-like into a two-phase (solid and liquid) substance, which can be easily separated. The dissolution of hydrophilic organic matter such as polysaccharides and proteins by L-DME promotes the conversion of bound water into free water, which is key to total water removal.

Char and tar formation during hydrothermal gasification of dewatered sewage sludge in subcritical and supercritical water: Influence of reaction parameters and lumped reaction kinetics.

The hydrothermal gasification of dewatered sewage sludge converts waste into syngas fuel (gas containing H2, CH4, CO, and CO2), but the formation of char and tar by a side reaction restricts practical applications. In this study, the formation of char/tar by the hydrothermal gasification of dewatered sewage sludge at 300-400 °C for 5-90 min with a heating rate of 8-50 °C/min is investigated. The results showed that the formation of tar/char reached equilibrium after 30 min, and an increase in the temperature and heating rate reduced the char yield. However, a higher tar yield was achieved at the highest temperature. Experiments on sludge with different moisture contents were also conducted, and the formation of char/tar was inhibited at a higher moisture content. The addition of NaOH and H2O2 can effectively reduce the char and tar yields, respectively. A lumped kinetic model for describing carbon conversion during the hydrothermal gasification of sewage sludge was developed to elucidate the char/tar formation mechanism. The experimental data were used to determine the model parameters, and the fitting results showed that solid-solid conversion from organic matter in sludge was the predominant char/tar formation pathway, with an activation energy of 7.1 kJ/mol. The experiments using the model compounds indicated that humus and protein are the main precursors of char and tar, respectively. This study provides insights for understanding the formation of char/tar from sewage sludge following hydrothermal gasification, which is vital for controlling the formation of char and tar to improve the gasification efficiency.

Ameliorative effect of acetylshikonin on ovalbumin (OVA)-induced allergic rhinitis in mice through the inhibition of Th2 cytokine production and mast cell histamine release.

Acetylshikonin has long been known as an anti-inflammatory and antioxidative reagent. However, the anti-allergic effect has not been studied. The aim of this study was to evaluate the effect of acetylshikonin on allergic rhinitis (AR) in mice. Mice were sensitized by intraperitoneal injection of OVA and aluminum hydroxide and challenged with intranasal instillation of OVA. Acetylshikonin was administered orally after nasal cavities challenge. Severity of allergic rhinitis was assessed according to nasal symptoms; serum OVA-specific immunoglobulin E (IgE), IgG1, and IgG2a level; and interleukin (IL)-4, IL-10, IL-5, IL-13, TNF-α, IL-12, and interferon (INF)-γ levels in nasal lavage fluid (NALF). Additionally, the histological change and the release of histamine in serum and nasal lavage fluid were evaluated by acid-Schiff stain and ELISA. Acetylshikonin attenuated manifestation of nasal symptoms in sensitized mice and inhibited production of Th2-related OVA-specific IgE, IgG1, and Th2 cell-produced IL-4, IL-5, IL-13, and mast cell produced histamine; however, it had no effect on Th1 cell-produced cytokines, like INF-γ. In addition, the degree of inflammatory cell infiltration and goblet cell hyperplasia was attenuated by acetylshikonin treatment. Our results suggest that acetylshikonin effectively reduces allergic inflammation in a mouse model of allergic rhinitis by its anti-allergic and anti-inflammatory properties.

A new method for determination of heavy metal adsorption parameters in compacted clay by batch tests.

Evaluation of adsorption properties of pollutants on artificial or natural clay strata is normally considered in investigations of soil and groundwater pollution. Batch adsorption tests can be used to obtain the adsorption parameters of clay particles; however, the results from these tests are usually very different from the adsorption of actual clay strata. If the adsorption parameters obtained by batch tests are used to directly evaluate the properties of adsorption of pollutants onto compacted clay, the predicted groundwater and soil pollution will be unsafe. Although the column diffusion tests are closer to the actual situation, they may require much more time, and diffusion and adsorption occur simultaneously in tests, making it difficult to accurately determine the adsorption parameters. To solve this problem, batch adsorption and column diffusion tests were conducted using three kinds of clay materials to investigate the mechanism of the differences in adsorption properties of heavy metal on clay particles and in compacted clay. The amount of adsorption per unit particle surface area of clay particles was found to be equal to that per unit pore surface area of compacted clay. A new simplified method was proposed to determine the adsorption parameters in compacted clay. It is easy to use and provide a reference for prediction and evaluation of soil and groundwater pollution.

Effect of the leachate head on the key pollutant indicator in a municipal solid waste landfill barrier system.

In previous studies of municipal solid waste (MSW) landfill barrier systems, chemical oxygen demand has been found to be the key pollutant indicator when estimating the breakthrough time for. However, the leachate head in a municipal solid waste landfill can be very high (>10 m in some Chinese landfills). The key pollutant indicator could be different at different leachate heads. The leachate head will continuously change during the use of a landfill. Different pollutants have different transport characteristics in the leachate, so it is necessary to determine whether changes in the leachate head change the key pollutant indicator for identifying breakthrough in a landfill barrier system. In this study, numerical models were used to investigate transport of common leachate pollutants through four typical landfill barrier systems with different leachate heads. Chemical oxygen demand reached the breakthrough threshold before the other pollutants, irrespective of (1) the leachate head and (2) changes in the leachate head. It was therefore clear that the leachate head did not affect the selection of the key pollutant indicator for identifying breakthrough in a landfill barrier system.

Studies on the chemical compatibility of soil-bentonite cut-off walls for landfills.

Leachate contains composite contaminants, and the chemical compatibility of soil-bentonite cut-off walls is unclear. To better understand the issue, Fujian standard sand is used to represent a sandy soil stratum. Two clays were used as additive to examine the chemical compatibility of the soil-bentonite model backfills under the condition of composite contaminants. The results indicate that there is a representative cation when the backfills are permeated with NaCl, CaCl2, and ZnCl2 solutions and an NaCl-CaCl2-ZnCl2 mixed solution of the same ionic strength. Ca2+ has the highest maximum ionic strength among all cations from leachates. Moreover, the change in hydraulic conductivity, bound water content and effective porosity of sand-bentonite with the Ca2+ concentration or chemical oxygen demand (COD) exhibit a concentration threshold; i.e., when the concentration is smaller than the threshold, the hydraulic conductivity and effective porosity significantly increase, whereas the bound water content rapidly decreases; when the concentration is higher than the threshold, the hydraulic conductivity, bound water content and effective porosity tend to stabilize. In addition, under the condition of composite contaminants, the threshold is observed, while the hydraulic conductivity, bound water content and effective porosity vary with the COD. Thus, both the type and concentration of chemicals can change the effective porosity and affect hydraulic conductivity. Furthermore, there is a power function relationship between permeability and the effective pore.

[Clinal analysis of 202 nasal bone fractures cases].

OBJECTIVE: To evaluate the age, sex, etiology, diagnosis and treatment time of nasal bone fractures. METHOD: Clinical data of 202 cases with nasal bone fractures treated in the hospital were retrospectively analysed. RESULT: A total of 202 cases,163 men (80. 7%) and 39 women (19. 3%). Fifty-two patients had a relationship with alcohol consumption, and all of them were males. The most frequent reasons of the injury were fight 46. 5% (94 cases) followed by falling-down 21. 3% (43 cases), traffic accidents 19. 3% (39 cases), works related 6. 5% (13 cases), sport injuries 5. 9% (12 cases) and others 0. 5% (1 cases). Patients distribution in seasons were: spring 54 cases (26.7%), summer 42 cases (20.8%), autumn 58 cases (28.7%), winter 48 cases (23. 8%). Diagnosis of nasal bone fractures were made positively by x-ray films in 79. 7% of cases, but 100% by CT. Positive predictive value of CT was superior to that of X-ray films in the diagnosis of nasal bone fracture. CONCLUSION: High morbidity of nasal bone fracture was seen in the age group of 20-29 years, and predominantly in male. Fight was found to be the main etiologic factor. We think that CT is necessary for diagnosing nasal bone fracture.