The accumulation of cadmium and lead in wheat grains is primarily determined by the soil-reducible cadmium level during wheat tillering.

The significant increase in cadmium (Cd) and lead (Pb) pollution in agricultural soil has greatly heightened environmental contamination issues and the risk of human diseases. However, the mechanisms underlying the transformation of Cd and Pb in soil as well as the influencing factors during their accumulation in crop grains remain unclear. Based on the analysis of the distribution trend of Cd and Pb in soil during the growth and development stages of wheat (tillering, filling, and maturity) in alkaline heavy metal-polluted farmland in northern China, this study investigated the response mechanism of soil heavy metal form transformation to soil physicochemical properties, and elucidated the main determining periods and influencing factors for Cd and Pb enrichment in wheat grains. The results showed that an increase in CEC and SOM levels, along with a decrease in pH level, contributed to enhancing the bioavailability of Cd in the soil. This effect was particularly evident during the tillering stage and grain filling stage of wheat. Nevertheless, the effects of soil physicochemical properties on bioavailable Pb was opposite to that on bioavailable Cd. The enrichment of Cd and Pb in grain was significantly influenced by soil pH (r = -0.786, p < 0.01), SOM (r = 0.807, p < 0.01), K (r = -0.730, p < 0.01), AK (r = 0.474, p = 0.019), and AP (r = -0.487, p = 0.016). The reducible form of Cd in soil during the wheat tillering stage was identified as the primary factor contributing to the accumulation of Cd and Pb in wheat grains, with a significant contribution rate of 84.5%. This study provides a greater scientific evidence for the management and risk control of heavy metal pollution in alkaline farmland.

Reducing nitrogen loss from farmland by layered double hydroxide-supported carbon dots-enhanced ammonium immobilization.

It remains a significant challenge to develop a kind of cost-effective and eco-friendly adsorbent with strong immobilization capabilities for ammonium in farmland. In this work, we employed Ca/Al layered double hydroxide-supported carbon dots (CDs@Ca/Al-LDHs) as a novel and efficient adsorbent for ammonium immobilization both in aqueous and soil environments. Such a composite could exhibit a high adsorption capacity towards ammonium in solution, which was four times higher than zeolite and three times higher than biochar under the same conditions. The mechanism investigations revealed that electrostatic interactions between the negatively charged CDs and the positively charged ammonium played a key role in the adsorption. In 30-day leaching experiments, the fabricated composite cumulatively reduced ammonium and nitrate by 6.3% and 9.7%, respectively at a dosage of 0.1% (w/w). Incubation experiments further confirmed that the developed composite could effectively inhibit ammonia volatilization and nitrification by immobilizing the ammonium within soil matrices. Our results demonstrated that CDs@Ca/Al-LDHs represented a promising candidate for cost-effective and eco-friendly immobilization of excess ammonium from over-fertilized farmland.

Comparison of methods for detecting protein extracted from excess activated sludge.

The protein contents of hydrolyzed sludge supernatant are commonly determined with the Kjeldahl method, but this method suffers from complicated operations, long process times, and large quantities of chemicals consumed. In this paper, the Lowry, bicinchoninic acid (BCA), and Bradford methods were used to test the precision and spiked recovery of proteins from sludge supernatants hydrolyzed by alkaline-thermal hydrolysis (ATH), enzymatic hydrolysis (EH), and ultrasound-assisted enzymatic hydrolysis (UEH), and the results were compared with those obtained with the Kjeldahl method. For all the hydrolytic processes, the sludge protein values determined with the three tested methods were within 0.05 of each other, which met the experimental requirement for accuracy. Both the Lowry and BCA methods had recovery rates of 95-105%, while the Bradford method showed large deviations and was not highly reliable. The three protein determination methods showed significant differences with the Kjeldahl method (P<0.05). However, the relative deviation between the Kjeldahl and BCA methods was the smallest (3-5%), followed by those between the Kjeldahl and the Lowry (11-21%) and Bradford methods (21-90%), and the causes of the deviations were analyzed based on the protein hydrolysate components and the mechanisms for the different detection methods. On the basis of these results, the BCA method was chosen as the most appropriate quantification method for use with sludge protein extraction, and it was used to analyze the protein contents extracted from residual sludge samples obtained from two sewage treatment plants. The reliability of the method was verified, and this lays a foundation for the extraction and reclamation of sludge proteins.

Optimization of protein recovery from sewage sludge via controlled and energy-saving ultrasonic-alkali hydrolysis.

The abundant protein in excess sludge can be recovered to prepare high value-added products. However, this sustainable treatment method still has large challenges, such as high energy consumption. In this work, the classical batch operation (BO) and semi-batch operation (SBO) modes were adopted and compared for ultrasonic-alkali hydrolysis. The results showed that the reaction time of SBO significantly decreased to half of that of BO with the same efficiency (ca. 70 %), indicating that SBO was much more energy-efficient. Moreover, analysis of the nitrogen solubility index and trichloroacetic acid-soluble nitrogen index demonstrated that the further proteolysis of protein under SBO was limited. Furthermore, the first-order reaction model fitted the hydrolysis data well (R2 ≥ 0.91) for both modes, in which the rate constant of SBO (k = 0.44 min-1) was 2.3 times that of BO. Finally, the properties of both products met the standards of foaming extinguishers.

Preparation of a sulfonated coal@ZVI@chitosan-acrylic acid composite and study of its removal of groundwater Cr(VI).

In this research, a new composite adsorbent (SC@ZVI@CS-AA) was designed and synthesized, and its application for the removal of Cr(VI) in groundwater was investigated. The interaction between SC@ZVI@CS-AA and Cr(VI) conformed to a pseudo-second-order model, and the adsorption process was dominated by chemisorption. The effects of material ratios, pH, temperature, SC@ZVI@CS-AA dosage, and coexisting ions on the removal of Cr(VI) were investigated. The removal efficiency of Cr(VI) by SC@ZVI@CS-AA reached 95%, and the reaction was significantly inhibited when SO42- was present. Thermodynamically, the adsorption of Cr(VI) proceeded spontaneously above 35 °C (ΔGθ < 0). According to scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, and synchronous thermal analysis, the removal mechanism of Cr(VI) by SC@ZVI@CS-AA was attributed to electrostatic attraction and reduction. In addition, SC@ZVI@CS-AA had good cyclic adsorption performance. Overall, the SC@ZVI@CS-AA composite showed great potential in the remediation of Cr(VI)-contaminated groundwater.

Intracellular and extracellular sources, transformation process and resource recovery value of proteins extracted from wastewater treatment sludge via alkaline thermal hydrolysis and enzymatic hydrolysis.

Excess sludge contains a large amount of protein and can be recycled to prepare industrial foaming agents, foliar fertilizers and other high value-added products. The optimization and effects of sludge protein extraction using the common processes of alkaline thermal hydrolysis (ATH) and enzymatic hydrolysis (EH) have been widely studied. This study focused on the protein extraction mechanisms of ATH and EH by comparing the ratio of intracellular to extracellular proteins extracted and the transformation of protein during the hydrolysis process. The extracellular protein content was 82.6 ± 5.07 mg/g VSS, and the content of intracellular protein extracted using ATH and EH was 376.9 mg/g VSS and 127.9 mg/g VSS, respectively. The ratio of intracellular to extracellular proteins extracted by ATH and EH was 4.5 and 1.5, respectively, indicating that ATH had a much better wall-breaking effect that allowed it to extract abundant intracellular proteins. The protein content obtained from ATH continuously increased over time, and approximately 38 % of proteins were further hydrolyzed to polypeptides. In contrast, the relatively low protein content extracted by EH possibly limited subsequent polypeptide hydrolysis, but subsequent hydrolysis to amino acids was not noticeably affected and was linearly correlated with the amount of protein extracted. An analysis of the recycling convenience and value of extracted proteins showed that the sludge dewatering performance increased by 86.7 % and 45.5 % after ATH and EH treatment, respectively, which was conducive to the subsequent separation of the protein solution. The protein extracted by ATH, with a large amount of peptides, would be beneficial to prepare industrial foaming agents, while the protein extracted by EH was rich in free amino acids and could be used to prepare foliar fertilizer.

Removal behavior and mechanism of amino/carboxylate-functionalized Fe@SiO2 for Cr(VI) and Cd(II) from aqueous solutions.

The novel iron-based reductive particles, functionalized with amino and carboxylic functional groups, were synthesized to remove Cr(VI) and Cd(II) ions from aqueous solutions. The morphological structure and surface functional groups of new composites were characterized with SEM, XRD, FTIR, BET, and other techniques. The influence of pH, initial concentration, adsorbent dosing, and temperature on removal efficiencies were explored by batch experiments. The adsorption capacity of Cr(VI) and Cd(II) increased by 159.95% and 76.60%, respectively, compared with Fe0, reaching 47.638 and 62.047 mg/g. EDS and XPS analysis showed most of Cr(VI) was reduced to Cr(III) and precipitated as ferrochrome oxide, and Cd(II) was mainly precipitated as hydroxide. Reduction-precipitation and complexation may predominate in the removal process of Cr(VI), which fitted well with Langmuir and Freundlich models and pseudo-second-order kinetics. While hydrolysis and complexation may prevail for Cd(II), which was suited with Langmuir model and pseudo-second-order kinetics. Having good magnetic properties, the A/C-Fe@SiO2 particles exhibited excellent reusable stability after four times regeneration experiments, promising a prospect for in-situ remediations of groundwater contaminated by Cr(VI) and Cd(II).

Enhancing enzyme activity via low-intensity ultrasound for protein extraction from excess sludge.

Rich protein within excess sludge could be recovered to prepare high value-added products such as liquid fertilizer and foaming agents. Low-intensity ultrasonication was adopted to help extract sludge protein by improving enzyme activity. Alkaline protease was added to the sludge for ultrasonic irradiation, and the maximum enzyme activity at 3500 kJ/kg TS was approximately 21% higher than that without ultrasonication. The protein extraction effect, specific resistance of sludge (SRS) and economics of low-intensity ultrasound-assisted enzymatic hydrolysis (LUEH) were compared with those of single enzymatic hydrolysis (EH) and HUEH under optimal conditions. The protein extraction rates of HUEH and LUEH were both higher than that of EH. Although the protein extraction rate of LUEH was 13.6% lower than that of HUEH, the amino acid content was similar because the low-intensity ultrasonic radiation promoted the enzyme activity and thereby enhanced the protein hydrolysis capacity. After hydrolysis, the SRS of LUEH was lower than that of HUEH, indicating that LUEH possessed a better dewatering performance, which was beneficial to the subsequent separation of the protein solution. The amount consumed by LUEH was approximately 20% lower than that consumed by HUEH and 17.3% lower than that consumed by EH. In addition, the enzyme dosage was reduced by approximately 38.5% with LUEH. Therefore, the total cost of LUEH was less than that of EH and HUEH, indicating that LUEH is more economically feasible for the extraction of protein from excess sludge.

Nitrogen removal performance and bacterial communities in zeolite trickling filter under different influent C/N ratios.

In this study, the degradation performance of nutrients in zeolite trickling filter (ZTF) with different influent C/N ratios and aeration conditions was investigated. Microaeration was beneficial for enhancing NH4+-N removal performance. Due to the sufficient carbon source supply under a C/N ratio of 8, a high removal efficiency of NH4+-N and TN was simultaneously observed in ZTF. In addition, TN removal mainly occurred at the bottom, which might be explained by the sufficient nutrients available for bacteria to multiply in this zone. The abundant genera were Acinetobacter, Gemmobacter, Flavobacterium, and Pseudomonas, all of which are heterotrophic nitrification-aerobic denitrification (HNAD) bacteria. In addition, biofilm only slowed down the adsorption rate but did not significantly reduce the adsorption capacity of zeolite. Bio-zeolite had NH4+-N well adsorption capacity and bio-desorption capacity. Biological nitrogen removal performance was superior to physicochemical absorption of zeolite. The results suggested that the physicochemical of zeolite and biochemical reactions of microorganism coupling actions may be the main nitrogen transformation pathway in ZTF. Our research provides a reference for further understanding the nitrogen removal mechanism of zeolite bioreactors.

Comparison of performance of two large-scale vertical-flow constructed wetlands treating wastewater treatment plant tail-water: Contaminants removal and associated microbial community.

The removal efficiency of contaminants in large-scale integrated vertical-flow constructed wetland (IVCW) and vertical-flow constructed wetland (VCW) for wastewater treatment plant (WWTP) tail-water was evaluated, and the microbial community was also investigated in this study. The results for 14 months study period indicated that 40.05% chemical oxygen demand (COD), 45.47% ammonia nitrogen (NH4+-N), 62.55% total phosphorus (TP), 55.53% total nitrogen (TN) and 57.20% total suspended solids (TSS) average removal efficiencies were achieved in the IVCW. There was a poor performance of TN removal in the VCW, with an average removal efficiency of 38.13%. There was no significant seasonal difference in TP removal, and a strong positive correlation between influent TP load and removed load. The high-throughput sequencing analysis revealed that Proteobacteria, Planctomycetes, Bacteroidetes and Acidobacteria were dominant in nature and wetland systems. The relative abundance of nitrifying bacteria, denitrifying bacteria and anammox bacteria confirmed that nitrification, denitrification and anammox may be the main processes for nitrogen removal in the IVCW.

Comparison of nitrogen and phosphorus removal efficiency between two types of baffled vertical flow constructed wetlands planted with Oenanthe Javanica.

The environmental problems related to rural domestic sewage treatment are becoming increasingly serious, and society is also concerned about them. A baffled vertical flow constructed wetland (BVFCW) is a good choice for cleaning wastewater. Herein, a drinking-water treatment sludge-BVFCW (D-BVFCW) parallel with ceramsite-BVFCW (C-BVFCW) planted with Oenanthe javanica (O. javanica) to treat rural domestic sewage was investigated, aiming to compare nitrogen and phosphorus removal efficiency in different BVFCWs. A removal of 23.9% NH4 +-N, 24.6% total nitrogen (TN) and 76.7% total phosphorus (TP) occurred simultaneously in the D-BVFCW; 56.4% NH4 +-N, 60.8% TN and 55.2% TP respectively in the C-BVFCW. The root and plant height increased by an average of 7.9 cm and 8.3 cm, respectively, in the D-BVFCW, and by 0.7 cm and 1.1 cm, respectively, in the C-BVFCW. These results demonstrate that the D-BVFCW and C-BVFCW have different effects on the removal of N and P. The D-BVFCW mainly removed P, while C-BVFCW mainly removed N.

Protein extraction and sludge dewatering performance of ultrasound-assisted enzymatic hydrolysis of excess sludge.

Excess sludge contains a high amount of protein, which can be recovered to prepare protein foaming agents and other products with high added value. Enzymatic hydrolysis (EH) is a promising technology for the recovery of protein from excess sludge, and ultrasound has been identified as a potential method to assist in sludge disintegration. Ultrasonic pretreatment was combined with alkaline protease hydrolysis to extract protein from excess sludge produced by A2/O treatment (S1) and an oxidation ditch treatment (S2), and the extraction effects and changes in sludge dewatering performance were studied. The effects of the six factors ultrasonic power density, ultrasonication time, enzyme dose, pH, hydrolysis temperature and hydrolysis time were analyzed. The results showed that the ultrasound-enhanced enzymatic method could effectively extract sludge protein. Although the extraction efficiencies for the different municipal sludges were different, their extraction conditions were relatively similar. Considering the protein extraction rate and sludge dewatering performance, the selected extraction conditions were as follows: ultrasonic power density, 1 W/mL; ultrasonication time, 20 min; enzyme dose, 3500 U/g; pH 11; hydrolysis temperature, 60 °C; and hydrolysis time, 3 h. Under these conditions, the protein extraction rate (Rp) of S1 and S2 reached 55.9% and 52.3%, respectively. Moreover, the improvement in sludge dewatering performance (Dw) of S1 and S2 was 49.5% and 52.4%, respectively. Comparison of the protein, polypeptide, and amino acid contents obtained from ultrasound-assisted enzymatic hydrolysis (UEH), EH, and ultrasonic hydrolysis (UH) further demonstrated the beneficial effect of ultrasound application on enzymatic hydrolysis.

Comparison of protein extraction methods from excess activated sludge.

In this study, we used chemical methods (acid-thermal (AT) and alkaline-thermal (AKT)), enzymatic methods (single enzyme (SE) and composite enzyme (CE)) and assisted enzymatic methods (ultrasonic assisted enzyme (USE) and thermal assisted enzyme (TE)) to extract proteins from excess activated sludge. The advantages and applicability of each method were compared and analyzed in terms of their protein extraction rate (RP), energy consumption, material consumption and cost, protein hydrolysates and sludge dewatering performance. The results showed that the RP of the chemical methods were more than 75%, which were much higher than those of the enzymatic methods. Moreover, the RP of SE was significantly strengthened by physical means (ultrasonic or thermal), and the average RP was increased by more than 39% compared with that of enzymatic methods. The energy consumption analysis showed that chemical methods consumed significantly more energy than the enzymatic methods. Further analysis of enzymatic methods and assisted enzymatic methods revealed that although the energy consumption of USE was similar to that of SE, its enzyme consumption and cost were lower. In addition, the proteins extracted by USE had a high content of amino acids, which was suitable for the preparation of animal feed. The proteins extracted by AKT had a high content of polypeptides, which was beneficial to the preparation of a protein foaming agent. Furthermore, the sludge dewatering performance after hydrolyzation by the six hydrolysis methods was significantly improved, which was beneficial to the separation of proteins.

Protein extraction from excess sludge by alkali-thermal hydrolysis.

The protein in excess sludge can be extracted effectively by the alkali-thermal method, and the extracted protein can be used as a foaming agent and in other industrial raw materials to realize its resource utilization. In this paper, the factors influencing sludge protein extraction by the alkali-thermal method were optimized based on the protein extraction rate and the polypeptide content, which determine the foaming performance of the extracted protein. The results showed that the optimal conditions were a pH of 12, a temperature of 120 °C, a reaction time of 4 h, and a sludge moisture content of 92%. Under these optimized conditions, the extraction rate of protein and the concentration of polypeptides were 88.3% and 6599 mg/L, respectively. Additionally, the foaming performance of the extracted protein solution was tested, and the foamability and foam stability were close to 450% and 88.8%, respectively. Therefore, the sludge protein extracted by the alkali-thermal method can meet the relevant standards of foam extinguishing agents and concrete foaming agents in China. In addition, the dewatering performance of the hydrolyzed sludge was improved by 93.1%, which provided favorable conditions for the subsequent separation of the protein solution.

Ammonium removal characteristics of heterotrophic nitrifying bacterium Pseudomonas stutzeri GEP-01 with potential for treatment of ammonium-rich wastewater.

A heterotrophic nitrifying bacterium was isolated from the activated sludge and identified as Pseudomonas stutzeri GEP-01. Strain GEP-01 exhibited an efficient heterotrophic nitrification capability and a high nitrogen utilization rate, 48 mg/L NH4+-N was removed after culturing for 24 h without NO2--N or NO3--N accumulation, and 64.7% of the NH4+-N was removed by heterotrophic nitrification. Single-factor experiments indicated that factors such as the carbon source, temperature, NH4+-N load, and inoculum size had significant effects on the ammonium removal efficiency of strain GEP-01. The preferred conditions for heterotrophic nitrification were sodium citrate, 30 °C, 40 mg/L NH4+-N, and 5% inoculum size. When the initial NH4+-N amounts were 100, 200, 500 and 1000 mg/L, the removal rates were approximately 100%, 93%, 90.4%, and 78.9%, respectively, and higher ammonium concentrations require longer culture time. Nitrogen balance demonstrated that 40% of the initial nitrogen was lost, which was probably removed in the form of gas products under optimum culture conditions, and 36.3% of NH4+-N was converted to biomass. When incubated (adding a small amount of sodium citrate as carbon source and no carbon source) in swine wastewater containing 835 mg/L of ammonium, the removal ratio reached 56.3% and 24.8%. Strain GEP-01 has potential applications in the treatment of ammonium-rich wastewater.

Preparation of sustainable non-combustion filler substrate from waterworks sludge/aluminum slag/gypsum/silica/maifan stone for phosphorus immobilization in constructed wetlands.

In this study, an artificial wetland filler matrix capable of effectively fixing phosphorus was prepared using a non-combustion process to save energy. To evaluate the adsorption performance of this filler, adsorption experiments were performed and the phosphorus adsorption mechanism characterization was studied. An alkaline environment was found to be conducive to the increase of adsorption capacity, but excessive alkalinity was not conducive to adsorption. Static adsorption experiments showed that the phosphorus removal rate could reach 95% in the simulated phosphorus-containing wastewater after adsorption completion. The adsorption process is closely simulated by the pseudo-second-kinetic adsorption model. The isothermal adsorption experiment data were consistent with the Langmuir and the Freundlich adsorption isotherms. The characterization results showed a large number of micropores and adsorption binding sites inside and on the surface of the filler. Speciation analysis on the adsorbed phosphorus revealed that chemisorption by calcium in this filler was the dominant adsorption mechanism. The research results of this study provide the basis and reference for the development of high-efficiency phosphorus removal filler in constructed wetlands.

Research about DoS Attack against ICPS.

This paper studies denial-of-services (DoS) attacks against industrial cyber-physical systems (ICPSs) for which we built a proper ICPS model and attack model. According to the impact of different attack rates on systems, instead of directly studying the time delay caused by the attacks some security zones are identified, which display how a DoS attack destroys the stable status of the ICPS. Research on security zone division is consistent with the fact that ICPSs' communication devices actually have some capacity for large network traffic. The research on DoS attacks' impacts on ICPSs by studying their operation conditions in different security zones is simplified further. Then, a detection method and a mimicry security switch strategy are proposed to defend against malicious DoS attacks and bring the ICPS under attack back to normal. Lastly, practical implementation experiments have been carried out to illustrate the effectiveness and efficiency of the method we propose.

Enhancing sludge dewatering and heavy metal removal by bioleaching with Na2S2O3 as substrates.

Bioleaching has been demonstrated to be an effective technology for the removal of heavy metals and sludge dewaterability. Since bacteria gain nutrients by diffusion of soluble compounds, the insolubility of elemental sulfur may slow the growth of bacteria. Thus, it is very important to find an energy substance quickly become available to Acidithiobacillus thiooxidans. This paper studies the improvement of sludge dewaterability and heavy metal removal with sodium thiosulfate as the source of energy for Acidithiobacillus thiooxidans. Through orthogonal experiments with specific resistance to filtration (SRF) as the target index, four factors (FeSO4 dosage, Na2S2O3 dosage, sludge reflux ratio and sludge moisture content) were identified to be the important influencing parameters. The optimal conditions were: FeSO4 dosage, 8 g/L; Na2S2O3 dosage, 1.5 g/L; sludge reflux ratio, 30%; sludge moisture content, 97%. Results indicated that the SRF of the sludge decreased from 9.89 × 1012 to 1.03 × 1011 m/kg. The removal efficiencies of heavy metals Cu, Zn, Pb and Cr could reach 83%, 78%, 31% and 38% within 3 days, respectively. These results confirm the potential of sodium thiosulfate as an alternative energy substance in bioleaching to improve sludge dewaterability as well as removal of metals.