Novel electrodes for cathode electro-Fenton oxidation coupled with anodic oxidation system for advanced treatment of livestock wastewater

Experimental study of microwave-catalytic oxidative degradation of COD in livestock farming effluent by copper-loaded activated carbon

The problem of massive discharge of livestock wastewater is becoming more and more severe, causing irreversible damage to the ecological environment, and how to treat livestock wastewater efficiently and rapidly deserves to be studied in depth. In this work, CuO/granular activated carbon (GAC) loaded catalysts were prepared and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption techniques, and X-ray energy spectroscopy (EDS). The results showed that CuO was successfully attached to the GAC surface with good adsorption performance. The effects of catalyst dosage, H2O2 dosage, initial pH, microwave power and microwave irradiation time in different reaction systems on the degradation efficiency of chemical oxygen demand (COD) in wastewater were investigated, and the orthogonal experiments were used to explore the importance ranking of these factors. The highest degradation rate of COD was found to be enhanced by 12.1% in the reaction system of CuO/GAC, and the initial pH had the greatest effect on the COD removal rate. The combined MW/catalyst/H2O2 method used in this work provided a rapid and effective degradation of COD in wastewater, which can be helpful for reference in other microwave catalytic oxidation studies.

Response surface methodology for process optimization in livestock wastewater treatment: A review

With increasing demand for meat and dairy products, the volume of wastewater generated from the livestock industry has become a significant environmental concern. The treatment of livestock wastewater (LWW) is a challenging process that involves removing nutrients, organic matter, pathogens, and other pollutants from livestock manure and urine. In response to this challenge, researchers have developed and investigated different biological, physical, and chemical treatment technologies that perform better upon optimization. Optimization of LWW handling processes can help improve the efficacy and sustainability of treatment systems as well as minimize environmental impacts and associated costs. Response surface methodology (RSM) as an optimization approach can effectively optimize operational parameters that affect process performance. This review article summarizes the main steps of RSM, recent applications of RSM in LWW treatment, highlights the advantages and limitations of this technique, and provides recommendations for future research and practice, including its cost-effectiveness, accuracy, and ability to improve treatment efficiency.

From "resistance genes expression" to "horizontal migration" as well as over secretion of Extracellular Polymeric Substances: Sludge microorganism's response to the increasing of long-term disinfectant stress

Glutaraldehyde-Didecyldimethylammonium bromides (GDs) has been frequently and widely employed in livestock and poultry breeding farms to avoid epidemics such as African swine fever, but its long-term effect on the active sludge microorganisms of the receiving wastewater treatment plant was keep unclear. Four simulation systems were built here to explore the performance of aerobic activated sludge with the long-term exposure of GDs and its mechanism by analyzing water qualities, resistance genes, extracellular polymeric substances and microbial community structure. The results showed that the removal rates of CODCr and ammonia nitrogen decreased with the exposure concentration of GDs increasing. It is worth noting that long-term exposure to GDs can induce the horizontal transfer and coordinated expression of a large number of resistance genes, such as qacE, sul1, tetx, and int1, in drug-resistant microorganisms. Additionally, it promotes the secretion of more extracellular proteins, including arginine, forming a "barrier-like" protection. Therefore, long-term exposure to disinfectants can alter the treatment capacity of activated sludge receiving systems, and the abundance of resistance genes generated through horizontal transfer and coordinated expression by drug-resistant microorganisms does pose a significant threat to ecosystems and health. It is recommended to develop effective pretreatment methods to eliminate disinfectants.

Integrating anodic sulfate activation with cathodic H2O2 production/activation to generate the sulfate and hydroxyl radicals for the degradation of emerging organic contaminants

Conventional electrocatalytic degradation of pollutants involves either cathodic reduction or anodic oxidation process, which caused the low energy utilization efficiency. In this study, we successfully couple the anodic activation of sulfates with the cathodic H₂O₂ production/activation to boost the generation of sulfate radical (SO₄^·-) and hydroxyl radical (·OH) for the efficient degradation of emerging contaminants. The electrocatalysis reactor is composed of a modified-graphite-felt (GF) cathode, in-situ prepared by the carbonization of polyaniline (PANI) electrodeposited on a GF substrate, and a boron-doped diamond (BDD) anode. In the presence of sulfates, the electrocatalysis system shows superior activities towards the degradation of pharmaceutical and personal care products (PPCPs), with the optimal performance of completely degrading the representative pollutant carbamazepine (CBZ, 0.2 mg L^-1) within 150 s. Radicals quenching experiments indicated that ·OH and SO₄^·- act as the main reactive oxygen species for CBZ decomposition. Results from the electron paramagnetic resonance (EPR) and chronoamperometry studies verified that the sulfate ions were oxidized to SO₄^·-radicals at the anode, while the dissolve oxygen molecules were reduced to H₂O₂ molecules which were further activated to produce ·OH radicals at the cathode. It was also found that during the catalytic reactions SO₄^·-radicals could spontaneously convert into peroxydisulfate (PDS) which were subsequently reduced back to SO₄^·-at the cathodes. The quasi-steady-state concentrations of ·OH and SO₄^·-were estimated to be 0.51×10^-12 M and 0.56×10^-12 M, respectively. This study provides insight into the synergistic generation of ·OH/SO₄^·- from the integrated electrochemical anode oxidation of sulfate and cathode reduction of dissolved oxygen, which indicates a potential practical approach to efficiently degrade the emerging organic water contaminants.

Cow manure simultaneously reshaped antibiotic and metal resistome in the earthworm gut tract by metagenomic analysis

Earthworm conversion is an eco-friendly biological process that converts livestock waste into a benign nutrient-rich organic fertilizer. However, little is known about the impacts of earthworm-converted livestock manure on the antibiotic resistome in the earthworm gut microbiota. Herein, lab-scale vermicomposting was performed to comprehensively evaluate the shift of antibiotic resistance genes (ARGs) in the earthworm gut-feeding on cow manure (CM)-by metagenomic analysis. The effects of copper (Cu) as a food addictive were also evaluated. CM substantially enriched the antibiotic resistome in the foregut and midgut, while it decreased in the hindgut. A similar trend was observed for metal resistance genes (MRGs). Notably, Cu in the CM had little effect on composition of ARGs and MRGs in earthworm gut. The earthworm gut microbiome altered by CM was responsible for the shift of ARGs and MRGs. In wormcast, Cu (100 and 300 mg/kg) significantly increased the abundance of ARGs and MRGs. Our study provides valuable insight into the response of ARGs and MRGs to CM in earthworm gut, and underscores the need for the judicious use of heavy metals as feed additives in livestock and poultry farming.

PbO2 materials for electrochemical environmental engineering: A review on synthesis and applications

Lead dioxide (PbO₂) materials have been widely employed in various fields such as batteries, electrochemical engineering, and more recently environmental engineering as anode materials, due to their unique physicochemical properties. Key performances of PbO₂ electrodes, such as energy efficiency and space-time yield, are influenced by morphological as well as compositional factors. Micro-nano structure regulation and decoration of metal/non-metal on PbO₂ is an outstanding technique to revamp its electrocatalytic activities and enhance environmental engineering efficiency. The aim of this review is to comprehensively summarize the recent research progress in the morphology control, the structure constructions, and the element doping of PbO₂ materials, further with many environmental application cases evaluated. Concerning electrochemical environmental engineering, the lead dioxide employed in chemical oxygen demand detection, ozone generators, and wastewater treatment has been comprehensively reviewed. In addition, the future research perspectives, challenges and the opportunities on PbO₂ materials for environmental applications are proposed.

Determinants of Sick and Dead Pig Waste Recycling-A Case Study of Hebei, Shandong, and Henan Provinces in China

Improper handling of sick and dead pigs may seriously affect public health, socio-economic conditions, and eventually cause environmental pollution. However, effective promotion of sick and dead pig (SDP) waste recycling has become the prime focus of current rural governance. Therefore, the study explores the impact of commitment, rewards, and punishments to capture the recycling behavior of farmers' sick and dead pig waste management. The study employs factor analysis, the probit model, and the moderating effect model to craft the findings. The study's empirical setup comprises the survey data collected from the Hebei, Shandong, and Henan provinces, representing the major pig-producing provinces in China. The study found that the commitment, reward, and punishment mechanisms are essential factors affecting the farmers' decision-making on recycling sick and dead pig waste. The marginal effect analysis found that the reward and punishment mechanism is more effective than the farmers' commitment. The study confirmed that in the recycling treatment of sick and dead pig waste, the farmers' commitment and the government's reward and punishment policy are the main factors that influence farmers to manage sick and dead pig waste properly. Therefore, the government should highlight the importance of effective waste management, and training facilities should also be extended firmly. The government should impose strict rules and regulations to restrict the irresponsible dumping of farm waste. Monitoring mechanisms should be put in place promptly.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS₂ (DMS) of TiO₂ nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Extracellular polymeric substances excreted by anammox sludge act as a barrier for As(III) invasion: Binding property and interaction mechanism

The arsenic in livestock wastewater would induce adverse impact on the biological treatment technology such as anaerobic ammonium oxidation (anammox) process. Extracellular polymeric substances (EPS) play an important role in resisting such toxicity. Unfortunately, the role of EPS in protecting anammox from As(III) and the mechanisms underlying the protection still remains unclear. This work comprehensively evaluated the acute toxicity of arsenic on anammox sludge and investigated the binding property and interaction mechanism. The results revealed that the half maximal inhibitory concentration (IC₅₀) of As(III) on anammox sludge was estimated to be 408 mg L^-1, which decreased to 41.97 mg L^-1 when EPS was exfoliated. Complexation and hydrophobic interactions were the leading forces in preventing arsenic invasion. Protein was the main component that complexes with As(III), and O-H, -NH, -CO were binding sites. The response sequence of organic component in EPS to As(III) was ordered as hydrocarbons-proteins-polysaccharides-aliphatic amines.

Anodic oxidation of ciprofloxacin using different graphite felt anodes: Kinetics and degradation pathways

Ciprofloxacin (CIP) is ubiquitous in the environment which poses a certain threat to human and ecology. In this investigation, the physical and electrochemical properties of graphite felt (GF) anodes which affected the anodic oxidation (AO) performance, and the CIP removal effect of GF were evaluated. The GFs were used as anodes for detection of ·OH with coumarin (COU) as molecule probe and removal of CIP in a 150 mL electrolytic cell with Pt cathode (AO-GF/Pt system). The results showed that hydrophilic GF (B-GF) owned higher sp³/sp² and more oxygen-containing and nitrogen-containing functional groups than the hydrophobic GF (A-GF). Moreover, B-GF possessed higher oxygen evolution potential (1.12 V), more active sites and stronger ·OH generation capacity. Above mentioned caused that B-GF exhibited more superior properties for CIP removal. The best efficiencies (96.95%, 99.83%) were obtained in the AO-B-GF/Pt system at 6.25 mAcm^-2 after 10 min (k₁, 0.356 min^-1) and 60 min (k₂, 0.224 min^-1), respectively. Furthermore, nine degradation pathways of CIP in AO-B-GF/Pt system were summarized as the cleavage of the piperazine ring, cyclopropyl group, quinolone ring and F atom by ·OH. It provides new insights into the removal and degradation pathways of CIP with GF in AO system.

Self-Enhanced Decomplexation of Cu-Organic Complexes and Cu Recovery from Wastewaters Using an Electrochemical Membrane Filtration System

Heavy metals in industrial wastewaters are typically present as stable metal-organic complexes with their cost-effective treatment remaining a significant challenge. Herein, a self-enhanced decomplexation scenario is developed using an electrochemical membrane filtration (EMF) system for efficient decomplexation and Cu recovery. Using Cu-EDTA as a model pollutant, the EMF system achieved 81.5% decomplexation of the Cu-EDTA complex and 72.4% recovery of Cu at a cell voltage of 3 V. The ^•OH produced at the anode first attacked Cu-EDTA to produce intermediate Cu-organic complexes that reacted catalytically with the H₂O₂ generated from the reduction of dissolved oxygen at the cathode to initiate chainlike self-enhanced decomplexation in the EMF system. The decomplexed Cu products were further reduced or precipitated at the cathodic membrane surface thereby achieving efficient Cu recovery. By scavenging H₂O₂ (excluding self-enhanced decomplexation), the rate of decomplexation decreased from 8.8 × 10^-1 to 4.1 × 10^-1 h^-1, confirming the important role of self-enhanced decomplexation in this system. The energy efficiency of this system is 93.5 g kWh^-1 for Cu-EDTA decomplexation and 15.0 g kWh^-1 for Cu recovery, which is much higher than that reported in the previous literature (i.e., 7.5 g kWh^-1 for decomplexation and 1.2 g kWh^-1 for recovery). Our results highlight the potential of using EMF for the cost-effective treatment of industrial wastewaters containing heavy metals.

Kinetics and mechanisms of oxytetracycline degradation in an electro-Fenton system with a modified graphite felt cathode

The removal of trace antibiotics from the aquatic environment has received great interest. In this investigation, NaOH activated graphite felt (NaOH-GF) was characterized by multiple-methods, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle, linear sweep voltammetry (LSV) and electron paramagnetic resonance (EPR). The NaOH-GF was then used as the cathode in the electro-Fenton process for oxytetracycline (OTC) degradation, the experiment was carried out in an undivided and light-proof beaker with a Pt anode and a NaOH-GF cathode at pH 3. The results showed that the modification with NaOH enhanced the antibiotics degradation efficiency of graphite felt by increasing the oxygen reduction capacity and hydroxyl radicals yielding rate. Complete OTC removal was achieved at 5.17 mA cm^-2 after 40, 60 and 90 s with initial OTC concentration of 22, 44, and 66 μM, respectively. With an initial OTC concentration of 44 μM, after 30 min the removal rates of chemical oxygen demand (COD) by Raw-GF and NaOH-GF were 59.18% and 83.75%, respectively. The proposed degradation mechanism of OTC was an EF process, which consisted of hydroxylation, secondary alcohol oxidation, demethylation, decarbonylation, dehydration and deamination. This study demonstrates that NaOH activated GF cathode possesses high degradation capacity and good stability. It provides insight into the removal of non-biodegradable antibiotics and may shed light on future to its practical application.