Green Synthesis of Magnetic Adsorbent Using Groundwater Treatment Sludge for Tetracycline Adsorption

Groundwater treatment sludge is an industrial waste that is massively produced from groundwater treatment plants.Conventional methods for treatment of this sludge,such as discharge into deep wells or the sea,or disposal at landfills,are not environmentally sustainable.Here,we demonstrate an alternative strategy to recycle the sludge by preparing a magnetic maghemite adsorbent via a one-step hydrothermal method with NaOH solution as the only solvent.With this method,the weakly magnetized sludge,which contained 33.2%iron(Fe)and other impurities(e.g.,silicon(Si),aluminum(Al),and manganese(Mn)),was converted to magnetic adsorbent(MA)with the dissolution of Si/Al oxides(e.g.,quartz and albite)into the liquid fraction.At a NaOH concentration of 2 mol L^-1,approximately 18.1%of the ferrihydrite in the Fe oxides of the sludge was converted into 11.2%maghemite and 6.9%hematite after the hydrothermal treatment.MA2(i.e.,MA produced by a 2 mol L^-1 NaOH concentration)exhibited a good magnetic response of 8.2 emu g^-1(1 emu=10^-3 A m^2),and a desirable surface site concentration of 0.75 mmol g^-1.The synthesized MA2 was used to adsorb the cationic pollutant tetracycline(TC).The adsorption kinetics of TC onto MA2 fitted well with a pseudo-second-order model,and the adsorption isotherms complied well with the Langmuir model.The maximum adsorption capacity of MA2 for TC was 362.3 mg g^-1,and the main mechanism for TC adsorption was cationic exchange.This study is the first to demonstrate the preparation of an MA from recycled sludge without a reductant and/or exogenous Fe source.The prepared adsorbent can be used as a low-cost adsorbent with high capacity for TC sorption in the treatment of TC-containing wastewater.

Recent Advances and Perspective on Design and Synthesis of Electrode Materials for Electrochemical Sensing of Heavy Metals

The increase in release of toxic heavy metals into natural water attracts much attention due to its devastating effect on ecology and human health.The design and implementation of green electrode materials is pivotal for improving the electrochemical performance of in situ heavy metal monitoring.

Recent Advances on the Development of Functional Materials in Microbial Fuel Cells:From Fundamentals to Challenges and Outlooks

Microbial fuel cells(MFCs),as a sustainable and promising technology to solve both environmental pollution and energy shortage,have captured tremendous attention.The conversion efficiency of chemical energy contained in organic waste or wastewater to electricity via microbial metabolism strongly depends on the performance of each functional unit,including the anode,cathode and separator/membrane used in MFCs.Therefore,significant attention has been paid toward developing advanced functional materials to enhance the performance of each unit or provide new featured functions.This review paper provides a comprehensive review on recent achievements and advances in the modification and development of functional materials for MFC systems,including 1)the development of functional anode materials for enhanced microbial compatibilities as well as electron transfer capabilities,2)the development of cost-effective separators/membranes such as ion exchange membrane,porous membrane,polymer electrolyte membrane and composite membrane,and 3)the development of functional cathode catalysts to decrease the over-potential and enhance the electrocatalytic efficiency for oxygen reduction reaction in order to substitute the common costly Pt catalyst.The challenges and outlooks of functional materials for MFC applications are also discussed.

Recycling of Mud Derived from Backwash Wastewater Coagulation as Magnetic Sodalite Sphere for Zn^(2+) Adsorption

Herein,we reported a method to prepare magnetic sodalite sphere by using the mud from backwash wastewater after polyaluminum chloride(PAC)coagulation.The results showed that approximately 100%of Fe in the wastewater was precipitated as flocculent iron mud(FM)by adding PAC.FM was converted to spherical magnetic sodalite(FMP)with a diameter of 3μm via a facile alkali hydrothermal method without adding Al/Si resources or reductant.The product FMP had the saturated magnetization of 10.9 emu g^(-1) and high Zn^(2+)adsorption capacity of 50.6 mg g^(-1).Without coagulation with PAC,the removal rate of Fe from the wastewater was only 92.7%,and the precipitated mud(RM)was converted to irregular particles(RMP),which had weak magnetic response and low capacity of Zn^(2+)adsorption comparing with FMP.With the method,the Fe in backwash wastewater was effectively recycled,and the generated sludge was converted to well-formed sodalite sphere without generating any secondary waste.

A potential threat from biodegradable microplastics: mechanism of cadmium adsorption and desorption in the simulated gastrointestinal environment

It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.

Insights into the changes of amino acids,microbial community,and enzymatic activities related with the nutrient quality of product during the composting of food waste

This study systematically investigated the changes of amino acids as the composting process of food waste proceeded.It is found that the addition of 0.3 g/g total solids of food waste achieved the highest seed germination index of the product(268%).The microbial community results indicated that the abundance of amino acid metabolism sequences remained at high levels during the whole composting process.Proline was identified as the key amino acid related with the nutrient quality of product during the composting of food waste.Further plant germination and hydroponic experiments found,that compared with those without the addition of proline,the addition of 50 mg/L proline increased seed germination rate by 20%,increased shoot length by 3%,increased root biomass of seedlings by 82%,and increased leaf biomass of seedlings by 76%,respectively.Firmicutes,γ-Pseudomonadota,Chloroflexi and Planctomycetes were the key identified bacteria related with the increase of proline during the composting of food waste.Meanwhile,the enzymatic tests of the activities of superoxide dismutase,peroxidase and malondialdehyde indicated that proline did not cause oxidative damage on the growth of plants.This study provided novel insights into the changes of amino acids,microbial community,and enzymatic activities related with the nutrient quality of product during the composting of food waste.

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H_2SO_4-NaCl-H_2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization（FGD） gypsum.When purified FGD gypsum was used as raw material,the morphology and phase structure of the hydrothermal products grown in pure water,H2SO4-H2O,NaCl-H2O,and H2SO4-NaCl-H2O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated.The results indicate that calcium sulfate whiskers grow favorably in the H2SO4-NaCl-H2O system.When prepared using 10-70 g NaCl/kg gypsum-0.01 M H2SO4-H2O at 130 ℃ for 60 min,the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 ｜xm and lengths from 200 to 600 ｜xm,and their phase structure was calcium sulfate hemihydrate（HH）.Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed.With the co-presence of sulfuric acid and sodium chloride in the reaction solution,the concentrations of Ca2＋ and SO42- can be kept relatively stable,which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.

Performance evaluation of microbial fuel cell for landfill leachate treatment: Research updates and synergistic effects of hybrid systems

Over half of century,sanitary landfill was and is still the most economical treatment strategy for solid waste disposal,but the environmental risks associated with the leachate have brought attention of scientists for its proper treatment to avoid surface and ground water deterioration.Most of the treatment technologies are energy-negative and cost intensive processes,which are unable to meet current environmental regulations.There are continuous demands of alternatives concomitant with positive energy and high effluent quality.Microbial fuel cells(MFCs)were launched in the last two decades as a potential treatment technology with bioelectricity generation accompanied with simultaneous carbon and nutrient removal.This study reviews capability and mechanisms of carbon,nitrogen and phosphorous removal from landfill leachate through MFC technology,as well as summarizes and discusses the recent advances of standalone and hybrid MFCs performances in landfill leachate(LFL)treatment.Recent improvements and synergetic effect of hybrid MFC technology upon the increasing of power densities,organic and nutrient removal,and future challenges were discussed in details.

Anaerobic digestion of sludge by different pretreatments:Changes of amino acids and microbial community

Many studies have investigated the effects of different pretreatments on the performance of anaerobic digestion of sludge.However,the detailed changes of dissolved organic nitrogen,particularly the release behavior of proteins and the byproducts of protein hydrolysis-amino acids,are rarely known during anaerobic digestion of sludge by different pretreatments.Here we quantified the changes of three types of proteins and 17 types of amino acids in sludge samples solubilized by ultrasonic,thermal,and acid/alkaline pretreatments and their transformation during anaerobic digestion of sludge.Tryptophan protein,aromatic protein I,aromatic protein II,and cysteine were identified as the key dissolved organic nitrogen responsible for methane production during anaerobic digestion of sludge,regardless of the different pretreatment methods.Different from the depletion of other amino acids,cysteine was resistant to degradation after an incubation period of 30 days in all sludge samples.Meanwhile,the“cysteine and methionine metabolism(K00270)”was absent in all sludge samples by identifying 6755 Kyoto Encyclopedia of Genes and Genomes assignments of genes hits.Cysteine contributed to the generation of methane and the degradation of acetic,propionic,and n-butyric acids through decreasing oxidation-reduction potential and enhancing biomass activity.This study provided an alternative strategy to enhance anaerobic digestion of sludge through in situ production of cysteine.

Comparison of different valent iron on anaerobic sludge digestion:Focusing on oxidation reduction potential,dissolved organic nitrogen and microbial community

This study compared effects of three different valent iron(Fe^(0),Fe(II)and Fe(III))on enhanced anaerobic sludge digestion,focusing on the changes of oxidation reduction potential(ORP),dissolved organic nitrogen(DON),and microbial community.Under the same iron dose in range of 0−160 mg/L after an incubation period of 30 days(d),the maximum methane production rate of sludge samples dosed with respective Fe^(0),Fe(II)and Fe(III)at the same concentration showed indiscernible differences at each iron dose,regardless of the different iron valence.Moreover,their behavior in changes of ORP,DON and microbial community was different:(1)the addition of Fe^(0) made the ORP of sludge more negative,and the addition of Fe(II)and Fe(III)made the ORP of sludge less negative.However,whether being more or less negative,the changes of ORP may show unobservable effects on methane yield when it ranged from−278.71 to−379.80 mV;(2)the degradation of dissolved organic nitrogen,particularly proteins,was less efficient in sludge samples dosed with Fe^(0) compared with those dosed with Fe(II)and Fe(III)after an incubation period of 30 d.At the same dose of 160 mg/L iron,more cysteine was noted in sludge samples dosed with Fe(II)(30.74 mg/L)and Fe(III)(27.92 mg/L)compared with that dosed with Fe^(0)(21.75 mg/L);(3)Fe^(0) particularly promoted the enrichment of Geobacter,and it was 6 times higher than those in sludge samples dosed with Fe(II)and Fe(III)at the same dose of 160 mg/L iron.