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•Enhanced-EK could enhance the cumulative EOF flow and electrical conductivity.•The combined biosurfactants and EK technique could improve toxic metal mobility.•Heavy metal flow ...direction and distribution were evaluated.•Heavy metal binding intensity increased after the electrokinetic treatments.
Heavy metal high content is strictly limited the land application of the sludge, which is considered as the best way for resource utilization. Hence, it is essential to explore a more effective way for reducing toxic metal. In this work, the combined biosurfactant and electrokinetic technique was used to promote toxic metals removal. Electroosmotic flow (EOF), sludge water content, electrolyte and sludge electrical conductivity variations, and removal efficiency, distribution, speciation and binding intensity of heavy metal variations were investigated during the electrokinetic process. The results demonstrated that the combined biosurfactant with electrokinetic technique could enhance toxic metals removal from sludge. In the enhanced electrokinetic treatment, the combined biosurfactant with electrokinetic technique can enhance cumulative electroosmotic flow, and the electrolyte electrical conductivity of anode and cathode, and the EK3 obtained a higher electrical conductivity (EC) than other EK treatments. Heavy metals obtained the highest removal efficiency during the EK3 treatment. Heavy metals distribution demonstrated that 58.63%, 71.34%, 63.04%, 52.95%, 61.74%, 56.24% of copper, zinc, chromium, lead, nickel and manganese migrated into the electrode solution, respectively, and 38.02%, 26.20%, 32.54%, 42.69%, 36.34%, 42.35% of copper, zinc, chromium, lead, nickel and manganese were still remained in the sludge. Heavy metal speciation indicated that the labile speciation percentage decreased. Whereas, the stable speciation percentage increased after the electrokinetic treatments. Heavy metal stability demonstrated that binding intensity increased, due to heavy metal have a higher stable speciation after the electrokinetic treatments.
In this work, the novel technology was used to remove heavy metal from sludge. The coupled with biodegradable ethylenediamine disuccinic acid (EDDS) and approaching anode electrokinetic (AA-EK) ...technique was used to enhance heavy metal removing from sludge. Electric current, sludge and electrolyte characteristics, heavy metal removal efficiency and residual content distribution, and heavy metal fractions percentage of variation were evaluated during the electrokinetic remediation process. Results demonstrated that the coupled with EDDS and AA-EK technique obtain a predominant heavy metal removal efficiency, and promote electric current increasing during the enhanced electrokinetic remediation process. The catholyte electrical conductivity was higher than the anolyte, and electrical conductivity of near the cathode sludge achieved a higher value than anode sludge during the coupled with EDDS and AA-EK remediation process. AA-EK technique can produce a great number of H+, which caused the sludge acidification and pH decrease. Cu, Zn, Cr, Pb, Ni and Mn obtain the highest extraction efficiency after the coupled with EDDS and AA-EK remediation, which were 52.2 ± 2.57%, 56.8 ± 3.62%, 60.4 ± 3.62%, 47.2 ± 2.35%, 53.0 ± 3.48%, 54.2 ± 3.43%, respectively. Also, heavy metal fractions analysis demonstrated that the oxidizable fraction percentage decreased slowly after the coupled with EDDS and AA-EK remediation.
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•Chelate and approaching anode electrokinetic promote electric current increasing.•Water content of near the anode sludge was higher than near the cathode.•Sludge electrical conductivity of near the cathode was higher than near the anode.•Approaching anode electrokinetic technique can promote heavy metal removal.
Stainless steel alloys, often used in circulating cooling systems of power plants using reclaimed water as coolant, can be affected by biocorrosion induced by biofilm formation. Extracellular ...polymeric substances (EPS) produced by bacteria play an important role in the different stages of biofilm formation, maturation and maintenance. The influence of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), isolated from Citrobacter freundii, on the adsorption properties and electrochemical behaviours of stainless steels 304, 316 L and 317 (SS304, SS316 L and SS317) in circulating cooling water, were investigated by evaluating the adhesion forces of SSs (AFM), surface analysis (SEM, XPS) and the effect of EPS on SSs (electrochemical measurements, ICP-MS). The results show that the LB-EPS and TB-EPS of the solutions influence the surface adsorption of stainless steels (SSs). The adhesion forces of SSs in TB-EPS are higher than those of LB-EPS. A statistical difference in the adhesion forces of SSs was detected, with higher adhesion force of SS317, followed by SS316L and finally by SS304. The adhesion forces to SSs are influenced by both the electrostatic force and metal surface hydrophobicity. LB-EPS and TB-EPS can inhibit the dissolution of metal elements on SS surfaces in circulating cooling water. The dissolution rate of each metal element on the surface of SS304, SS316 L and SS317 is different, and their dissolution trends are basically the same: Fe > Ni > Cr > Mn. In the presence of TB-EPS or LB-EPS, the dissolution rate of Fe on SS304, SS316L and SS317 decreases by 30.61%, 24.20% and 27.43% or 77.95%, 86.70% and 83.96%, respectively. Electrochemistry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicate that the formation of a protective film composed of organic complexes such as C-(Fe, Ni), C–O-(Fe, Ni), N-(Fe, Ni), N–O-(Ni, Fe) and FeOOH on the SS surfaces can slow down the corrosion rate of stainless steel to some extent. Moreover, EPS films formed on SS317 and SS316 L have higher resistance and lower conductivity than those formed on SS304.
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•The surface adsorption of SSs increases in the presence of LB-EPS/TB-EPS.•Metal dissolution rate on SS surfaces is basically the same: Fe > Ni > Cr > Mn.•The adhesion forces of SS317 and SS316L are greater than that of SS304.•LB-EPS had more significant inhibition on the dissolution of metal surface elements.•EPS films formed on SS317 and SS316L have higher resistance and lower conductivity.
It has been proved that the nitrogen can be removed from the sediment in a sediment microbial fuel cell system (SMFCs), but the competition between nitrate and oxygen for electrons would be a key ...factor that would affect the removal efficiency, and its mechanism is not clear. Based on organic sediment fuel, an SMFC was constructed, and the influence of dissolved oxygen (DO) on nitrogen transformation and cathodic microbial communities was investigated. The results showed that the best total nitrogen removal efficiency of 60.55% was achieved at DO level of 3 mg/L. High DO concentration affected the removal efficiency through the electrons' competition with nitrate, while low DO concentration suppressed the nitrification. Comamonas, Diaphorobacter and Brevundimonas were the three dominant genera responsible for denitrification at DO concentration of 3 mg/L in this study. The establishment of SMFCs for nitrogen removal by regulating DO level would offer a promising method for sediment treatment.
Heavy metal severely restricted the sludge agricultural use. Therefore, it is imperative to seek a novel and proficient method removal heavy metal from sludge. In this study, it proposed that a ...coupled with biodegradable chelating ligand iminodisuccinic acid and electrolyte circulation technology, which was used to enhance electrokinetic (EK) remediation removing heavy metal from the sludge. Electrical current, electrical conductivity and electrolyte pH, electrical conductivity and sludge pH, the toxic metal concentration with different time and remediation room section were evaluated in this work. Results demonstrated the combined iminodisuccinic acid and electrolyte circulation technology could enhance electrokinetic remediation removal toxic metal from sludge. Also, it can increase the cation and anion dissolution and electric current, and the cathode obtained a higher electrical conductivity of electrolyte and sludge than anode, and maintained a low pH of catholyte and sludge, the enhanced electrokinetic treatments obtained a higher removal efficiency than unenhanced electrokinetic remediation treatment, and the coupled with iminodisuccinic acid and electrolyte circulation enhanced electrokinetic treatment achieved the highest toxic metal extraction efficiency, Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 55.0 ± 3.78%, 66.8 ± 2.23%, 64.6 ± 3.87%, 49.3 ± 3.25%, 61.6 ± 4.22% and 57.2 ± 2.67%, respectively, which indicated that iminodisuccinic acid and electrolyte circulation technology can effectively enhance EK remediation removal heavy metals from sludge.
The cyclic activated sludge technology process was used to treat high-salinity mustard tuber waste-water and municipal wastewater. The effect of phosphorus removing agents on sludge activity and floc ...structure was investigated. Results indicated that polysilicate ferric, ferric chloride and aluminum sulfate improved the structure and density of sludge flocs. These three phosphorus removing agents had little effect on oxygen uptake rate (OUR) of heterotrophic bacteria and nitrifying bacteria and sludge dehydrogenase activity. The effect of aluminum sulfate on OUR of nitrite bacteria was significantly stronger than polysilicate ferric and ferric chloride. In the stable operation of the high-salt mustard wastewater and the urban sewage co-processing system of condition. The salinity was 5 g/L and the influent total phosphorus (TP) concentration was 7.3–8.7 mg/L, the effluent TP concentration was 2.1–3.6 mg/L in the biological phosphorus removal system. Results showed that the polysilicate ferric, ferric chloride and aluminum sulfate can enhance nitrogen removal from high-salinity mustard tuber wastewater. Biological and chemical phosphorus removal models were established, which used polysilicate ferric, ferric chloride and aluminum sulfate as the phosphorus removal agents, respectively. Phosphorus removal agents was conducive to further reduce the chemical oxygen demand and suspended solids values in the effluent from the treatment system, and the sequence of the enhanced effect was polysilicate ferric > ferric chloride > aluminum sulfate.
The level of heavy metals of the sludge in the landfills has attracted the environmental researchers due to their non‐biodegradability, persistence, toxicity and biomagnification. Heavy metals ...contamination and ecological risk assessment in the sludge landfills were assessed. In this work, the enrichment factor (EF) and geo‐accumulation index were used to analyze heavy metal pollution degree in the sludge landfills. Meanwhile, the potential ecological risk index was used to assess heavy metals potential ecological risk in the sludge landfills. Results indicated that heavy metal concentrations order was Cr > Cd > Ni > Zn > As>Cu = Pb > Hg. Cr, Cd and Ni coefficient variation were 57%, 53% and 38%, respectively, which indicated that Cr, Cd and Ni content have a large range variation. EF and geo‐accumulation index analyze heavy metal pollution degree in the sludge landfills. Results demonstrated that Hg, Cd, Cu and Zn obtained a high pollution degree. However, Cr, Ni, As and Pb have a low pollution in the sludge landfills. Potential ecological risk index indicated that Hg obtained the highest pollution degree, which demonstrated that the potential ecological risk level is the highest value (Eri ≥ 3500, RI ≥ 4163). Whereas, other heavy metals have a low pollution degree in the sludge landfills. Therefore, Hg, Cd and Cu content of sludge should be strictly restricted in agricultural use. Meanwhile, it should be strictly restricted Hg, Cd and Cu content of wastewater discharge, and reduced heavy metal content of sludge.
Heavy metal content and speciation of sludge, physicochemical properties of sludge, and the correlation between heavy metal content and speciations were investigated in this work. Results ...demonstrated that organic matter content of sludge ranged from 158.4 to 474.5 g kg
−1
, total nitrogen content from 9.95 to 27.45 g kg
−1
, total phosphorus content from 22.72 to 41.45 g kg
−1
, and total potassium content from 5.04 to 11.20 g kg
−1
. The sludge contains high content of organic matter, phosphorus and potassium and low content of nitrogen, it indicated that the sludge has a big prospect of agricultural use, and it could improve and increase soil fertility. Cu and Zn content exceed the agricultural use standard. Heavy metal speciations analysis indicated that Cu mainly exists in oxidizable speciation; Zn and Cd mainly exist in exchangeable and reducible speciation; Mn and Pb mainly exist in residual speciation; Cr, Ni, As and Hg mainly exist in oxidisable and residual speciations. These results indicated that Zn and Cd migration and bioavailability are strong in the environment, whereas Cu, Cr, Ni, As and Hg are weak. Mn and Pb are most stable in the sludge in these heavy metals. The correlation analysis indicated that heavy metal content and physicochemical properties obtained a positive correlation, such as with the heavy metal content, and total carbon, total nitrogen, ammonia nitrogen content obtained a positive correlation with heavy metal content, heavy metal had the same source and synergistic effect, and heavy metal content obtained a positive correlation with speciation in the sludge sample.
In this work, a new electrokinetic remediation technology was used to remove heavy metal and hydrocarbon from contaminated soil. The surfactant combined with PASP (Polyaspartic acid) was used to ...enhance heavy metal and hydrocarbon removing from contaminated soil. Electric current, soil pH, electroosmotic flow, water content variation, heavy metal removal efficiency and residual content distribution, heavy metal speciation, removal of TPH (total petroleum hydrocarbons), group composition of oil, mechanism of enhance electrokinetic remediation were investigated during the electrokinetic remediation process. Results indicated that Rhamnolipid, PASP, Tween 80 and SDS (sodium dodecyl sulphate) can reduce the heavy metal precipitation during the electrokinetic remediation process. Also, it can promote EOF (electroosmotic flow) and electrolyte evaporation during the EK remediation. The rhamnolipid (3.0 g.L
−1
) combined with PASP (3.0 g.L
−1
) can significantly improve Cu, Cr, Ni, Pb and hydrocarbon mobility and solubility during the EK remediations. Cu, Cr, Ni and Pb obtained the dominant removal efficiencies, which were 66.0 ± 3.45%, 61.2 ± 4.35%, 67.1 ± 3.21%, 61.8 ± 4.22%, respectively. Also, the TPH has attained a dominant removal efficiency of 80.2 ± 4.36% after the enhanced electrokinetic remediation. This research provides a novel in-situ remediation approach for reducing heavy metals and hydrocarbon from contaminated soil in an environmentally friendly way.
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