The demands for high-efficient and green activation of peracetic acid (PAA) have triggered research in exploring carbon catalysis. Nevertheless, the efforts in designing reaction-oriented and high-performance carbon catalysts are largely impeded by an ambiguous understanding of the fundamental carbon structure–PAA activation performance relationship. Herein, we investigated the quantitative structure–activity relationship (QSAR) of carbon nanotubes (CNTs) for PAA activation and micropollutant (MP) removal, by tuning the physiochemical properties of CNT via thermal annealing. The CNT/PAA system was dominated by the nonradical direct electron transfer (DET) oxidation pathway, showing high MP removal rates under complex water matrices. By conducting QSAR analysis, improved catalytic efficacy of the surface-regulated CNTs was attributed to the reinforced DET via the elevated oxidative potential of the CNT–PAA complex and the enhanced electrical conductivity of CNT. Furthermore, the larger specific surface area and lower oxygen content of CNT gave rise to the elevated oxidative potential of the CNT–PAA complex, while the electrical conductivity of CNT was positively correlated with the graphitization degree of CNT. Overall, this work sheds light on the influence cascade of the physicochemical properties of CNT for MP removal and PAA activation, providing guidelines for the fit-for-purpose design of the DET-mediated carbon catalysts for PAA oxidation.

The oxygen reduction reaction (ORR) was an unavoidable side reaction in the electro-activating persulfate (PS) process, especially on the ORR-active carbon materials, which has usually been ignored in previous reports. In this work, the O2/N2-involved electro-activation of the PS system was constructed to confirm the role of side-reactive ORR on oxidized carbon black (OCB) for sulfamethoxazole (SMX) degradation. With O2 involvement, 820.8 μM •OH was produced by PDS electro-activation, over 7 times more than 115.8 μM under N2 aeration, leading to a high SMX removal of 90.6% (only 67.8% under N2 aeration). Such a huge difference in •OH yield and SMX removal performance was mainly attributed to side-reactive 2e– ORR, in which as-generated H2O2 was electro-activated to produce abundant •OH and form an advanced homogeneous •OH/SO4•– oxidation system via mutual transformation with gradual acidification. Meanwhile, the introduction of oxygen functional groups and defects on the surface of carbon black calcined at 600 °C (CB600) also contributed to the improvement of SMX removal performance, attributing to their enhancing effects on SMX electro-adsorption, PDS electro-activation, and O2 electro-reduction. Thus, side-reactive oxygen reduction played the spontaneous and synergistic oxidation roles in the O2-involved electro-activating PS process, helping to design highly effective advanced oxidation systems in the future.

One method that can help slow the spread of coronaviruses is disinfection with UV light. The Delta and Omicron variants of the COVID-19 virus (SARS-CoV-2) have come to dominate the later stages of the pandemic due to their higher rates of transmission. In this work, it is shown that a 17% higher UV254 dose is required for the disinfection of Delta and Omicron variants when compared to the ancestral strain of SARS-CoV-2. The UV254 disinfection rate constants for SARS-CoV-2 and the Delta and Omicron variants were found to be 1.4 ± 0.3, 1.1 ± 0.2, and 1.1 ± 0.2 cm2/mJ, respectively. The rate constants of Delta and Omicron were statistically different from the ancestral strain of SARS-CoV-2 at the 95% confidence level based on at least three replicate experiments. It is suggested that the reason for this difference is the absence of repeating uracil (U) bases in the genome of the two variants. The UV254 sensitivity of repeating pyrimidine bases is well-established. There are 2.6 and 3.7% fewer uracil triplets (UUU) in the Delta and Omicron variants, respectively, when compared to SARS-CoV-2. This difference in UV254 sensitivity is relevant to a range of UV disinfection applications including upper-room disinfection, air handling equipment, aircraft sanitization, and others.

Ferrate [Fe(VI)] has been widely applied due to its multifunctional effects of flocculation, disinfection, and decontamination in wastewater treatment. To achieve an enhancement for Fe(VI) activity under alkaline conditions, 1-hydroxybenzotriazole (HBT), as an emerging redox mediator, promotes electron transfer to assist Fe(VI) to achieve more excellent decontamination. In this study, the introduction of HBT increases the degradation rate of sulfamethoxazole (SMX) from 53 to 98% at pH 8.0 within 5 min. Surprisingly, quenching and probe experiments indicated that active species are all high-valent iron species rather than radicals (HO· and HBT·) by the Fe(VI)/HBT process. Further research disclosed that the enhancement for SMX degradation with the Fe(VI)/HBT system was driven by the enhancement of Fe(VI) self-decomposition and the formation of more Fe(V) via single-electron transfer by HBT. Moreover, a kinetic model is developed for fitting SMX degradation to reveal that the dominant active species shifts from Fe(IV) to more active Fe(V), reaching nearly 100% SMX degradation as the HBT dosage increased. Furthermore, 12 SMX degradation intermediates are detected using an ultrahigh performance liquid chromatography quadrupole time-of-flight mass spectrometer, and three possible removal pathways are proposed, including oxidation, hydroxylation, and hydrolysis. More importantly, the Fe(VI)/HBT system manifests a great decontamination performance on the coexisting anions, cations, and actual water such as lake, river, and tap water. In summary, this work establishes a new system for the effective removal of pollutants and provides crucial information on the application of ferrate in wastewater treatment.

Activation of persulfate is a hot topic in environmental remediation via generating reactive species such as SO4•– and 1O2. This study investigated the activation of peroxydisulfate (PDS) by HA with respect to the formation mechanisms of reactive species and their roles in contaminant transformation. SO4•–, HO•, and reactive nitrogen species (RNS, e.g., •NO, •NO2, and NH2O•) were proved to be predominant reactive species in the HA/PDS system by electron paramagnetic resonance analysis and radical scavenging tests. The reaction stoichiometric ratio of HA to PDS was about 0.63, involving two major steps: HA initially reacted with PDS to generate SO4•– and NH2O•, and NH2O• further reacted with PDS to form SO4•– and HNO. Ultimately, N2O was the major product of HA via the dimerization of HNO. •NO was formed via the reactions of HNO with O2 and HO•, and •NO2 could be formed via the reaction of SO4•– and NO2–. In the HA/PDS system, SO4•– and HO• primarily contributed to the degradation kinetic of carbamazepine, while RNS also played important roles in the transformation pathways of carbamazepine, resulting in the formation of nitroso compounds. As pH increased from 2 to 7, the removal rate of carbamazepine was highest at pH 3–4 (66–69% at 60 min), which is mainly due to NH2OH showing higher activation efficiency for PDS but faster consumption for SO4•– and HO• compared to NH3OH+. This study broadens the understanding of peroxide activation by HA and demonstrates the important roles of formed RNS in contaminant transformation.

Abundant and diverse functional groups of adsorbents are essential for their adsorption performances. Herein, we report a strategy to construct highly efficient ammonia nitrogen adsorbents by installing multiple ion-exchange complexation coordination-hydrogen bonding sites onto covalent organic frameworks (COFs). As a proof of concept, we prepared a COF (TpPa-SO3H) via a modified mechanical grinding synthetic method and then obtained a sulfonated COF bearing single Cu sites (TpPa-SO3Cu0.5) by post-loading. Benefiting from the highly exposed active sites and ordered COF channels, TpPa-SO3Cu0.5 exhibited the highest adsorption kinetics among reported ammonia nitrogen adsorbents proven by the highest pseudo-second-order adsorption rate constant (k2) of 8.97 g mg–1 min–1 with its maximum adsorption capacity (30.45 mg N g–1) higher than most adsorbents (<0.001–0.994 g mg–1 min–1 and 0–25 mg N g–1). Furthermore, TpPa-SO3Cu0.5 exhibited excellent adsorption selectivity with its selective coefficient 328 times as high as that of TpPa-SO3H in real water (10 mg N L–1, pH = 10). It also showed good stability and recyclability with a high ammonia recycle ratio (95.1%) after 5 adsorption–regeneration cycles. These findings pave a new way to develop unique COFs as platforms for ultrafast and selective pollutants in water and wastewater treatment.

In recent years, conductive membranes have attracted significant attention and have been extensively studied for their unique antifouling mechanisms and regenerative properties. The current strategy primarily focuses on enhancing the conductivity of membranes. Yet, the resulting antifouling performance enhancement is limited due to lack of capacitance-tuning. Herein, we constructed hierarchical-nanostructure membrane carbon nanotubes–polyaniline–graphene quantum dots (CNT-PANI-GQDs), first demonstrating a capacitance-tuning strategy for enhancing the membrane’s antifouling performance. PANI covers the CNTs’ surface and cross-links them, forming a conductive 3D structure polymer substrate. GQDs assisted with PANI are used for tuning the membrane capacitance. The CNT-PANI-GQDs had the highest capacitance among all the membranes and exhibited the highest water flux, the best antifouling performance, and mechanical stability. Cross-flow filtration experiments were conducted with the organic model foulants. After treating a 100 ppm bovine serum albumin (BSA) solution with a voltage of −2.5 V and running continuously for one h, the CNTs-PANI-GQDs membrane maintained a normalized flux of over 97%. Electrochemical measurement and Derjaguin–Landau–Verwey–Overbeek (DLVO) analysis revealed that PANI and GQDs simultaneously enhance the pseudocapacitance and double-layer capacitance, and the hierarchical nanostructure membrane possesses excellent charge transfer ability and a large electrochemically active surface area. Increased capacitance leads to greater accumulation of surface charges and enhances the electrostatic repulsion against impurities. This work may offer valuable references to guide the design of electric antifouling membranes to favor water purification applications.

Compared to a conventional membrane bioreactor (MBR) with a porous microfiltration (MF) membrane (MBRMF), a nanofiltration (NF)-based MBR (MBRNF) shows highly attractive features such as high permeate water quality. However, the practical applications of MBRNF are often hindered by the high driven pressures and severe membrane fouling. To address these two critical issues, this study investigated the feasibility of operating MBRNF at an ultralow flux (ULF, e.g., <5 L·m–2·h–1) toward the reuse of municipal wastewater in a single step. We operated the ULF MBRNF at a flux of 2 L·m–2·h–1 and benchmarked its performance against a conventional system using a MBRMF followed by a subsequent NF treatment (MBRMF + NF, both at a constant flux of 20 L·m–2·h–1). The results show that the ULF MBRNF achieved substantial removal of most pollutants, with low negative impacts of ultralow fluxes on pollutant rejections. Besides, the ultralow-flux operation led to a very low fouling rate (0.18 kPa·d–1). More importantly, the ULF MBRNF reduced carbon emissions by 45.2% compared with the MBRMF + NF, mainly due to less energy consumption by pumping. Our findings highlight the simplicity and great potential of ULF MBRNF for wastewater reuse.

Short- and long-term changes in electricity generating unit (EGU) emissions were observed during COVID-19 public health interventions in the United States. In a generalized synthetic control framework, we employ weekly EGU SO2, NOx, and CO2 emissions data from EPA’s Clean Air Markets Database and location-specific meteorology from 2010 to 2019 to estimate each EGU’s hypothetical business as usual (BAU) emissions throughout 2020. We find that over 60% (covering >50% of total electricity generation) of EGUs saw SO2, NOx, and CO2 emissions increases relative to BAU, with most of the increases occurring in the eastern U.S. We find increases relative to BAU in the March–April stringent lockdown period for SO2, NOx, and CO2 of 44% (4500 tons/week), 23% (2200 tons/week), and 14% (2.3 million tons/week), respectively, with similar results from March to December 2020. We find that EGUs using coal as primary fuels are the main driver of increased emissions due to increased operations, and SO2 emissions increases at coal EGUs led to a 28% increase in PM2.5 related to coal SO2 emissions relative to BAU across March–December. We find increases in SO2 and NOx emissions factors at coal EGUs in 2020 relative to 2019 that likely played a role in these increases, and we identify changes in coal fuel consumption and price that may have played a role.

This study explored the oxidative transformation of atrazine (ATZ) by an aqueous iron(IV)–oxo complex (Fe(IV)) formed through ozonation of Fe(II) and compared it to ATZ oxidation by •OH and SO4•– generated by ultraviolet (UV) irradiation of H2O2 and peroxydisulfate (PDS), respectively. The second-order rate constant between Fe(IV) and ATZ was estimated to be greater than (5.18 ± 0.3) × 105 M–1 s–1 at pH 3, which was markedly higher than the reactivity of Fe(IV) toward various water matrices. Consequently, Fe(IV) achieved the most effective selective abatement of ATZ, compared with •OH- and SO4•–-mediated processes. Moreover, in the Fe(II)/O3 system, we identified six products of ATZ and grouped them into three types: dealkylation (desethyl-atrazine [DEA] and desisopropyl-atrazine), alkylic-oxidation (atrazine amide [CDIT] and 2-hydroxy-4-(2-hydroxy-ethylamino)-6-isopropylamino-s-triazine), and dechlorination-hydroxylation (N-(4-hydroxy-6-(isopropylamino)-1,3,5-triazin-2-yl) acetamide and deethylhydroxyatrazine) products. These products also constituted the primary outcomes of ATZ in the UV/H2O2 and UV/PDS systems. Mechanism analysis revealed that Fe(IV) and SO4•– triggered the dealkylation of ATZ by electron transfer, whereas •OH initiated dealkylation by H-atom abstraction, which resulted in the reactive oxidant nature-dependent distribution of specific ATZ oxidation products. Specifically, the [CDIT]/[DEA] ratio was quantified as 0.2, 0.7, and 2.3 in Fe(IV)-, •OH-, and SO4•–-mediated oxidation processes, respectively. Accordingly, this ratio was developed as a sensitive internal probe for evaluating the relative contribution of Fe(IV) and •OH/SO4•– during ATZ oxidative abatement.

The stability and activity of microbial communities directly diagnose the health of leachate biological treatment processes, and unveiling the ecological drivers of microbial assembly could identify the critical factors resulting from the influent disturbances and improve operational performance. Hereby, we conducted a meta-analysis of microbial diversity, ecological mechanisms based on a full-scale working leachate treatment plant (LTP) around one year, and co-occurrence for shaping their communities to screen the critical microbial responses to the variations of influent loadings in practical operation. A significant difference was observed in the treatment process under the low and high-loading periods (p < 0.001) with 0.71 ± 0.09 and 0.95 ± 0.09 mg CODCr/mg MLSS, respectively, with 60.6%, 95.4%, and 64.1% of CODCr, NH4+-N, and TN removal under the low-loading period. The microbial diversity was 6.75 and 5.68 under the low- and high-loading periods in terms of the Shannon index, which was the most limiting factor influencing the operation performance (r = 0.618). The deterministic processes had a dominant role in the microbial assembly during the high-loading period, and they had little effect on the system performance. Low loadings led to over 20% of microorganism species from five bins dominating from homogeneous selection (HoS, deterministic process) to ecological drift (DR, stochastic processes), as the 2456 observed OTUs were divided into 94 phylogenetic bins, which increased microbial stability with a large average clustering coefficient of 0.192 and 15 connectors based on a complex network structure analysis. CODCr loadings rather than nitrogen loadings were critical to affecting the diversity (r = −0.771), leading to the pollutant removal rates decreasing by 11.4–14.3%. norank_f_Saprospiraceae could be the indicator microorganism for excessive organic loadings, and on-site monitoring of microbial ecology evolution should be developed to provide clues about the operational performance of the leachate treatment process in advance.

Plant-derived carbon dots have superior light absorption and intrinsic fluorescence properties. In this work, we have prepared nitrogen-doped carbon dots (N-CDs) from Piper betle leaves using a simple hydrothermal method. The synthesized N-CDs were characterized by various techniques such as high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, and photoluminescence. The N-CDs further proved to have systemic effects on the growth of strawberries compared with irrigating the strawberry plants with water and regular nutrients. The strawberry plants treated with N-CDs exhibited an increase in chlorophyll content of about 24.7%, which was reflected in increased carbohydrate content of approximately 48.61% compared to control plants. Also, N-CD-treated strawberry plants showed increased secondary metabolites (phenolics) compared to control plants. Moreover, at the end of harvesting, the comparison was reflected in significant amounts of strawberries and in an increase in the leaf area of strawberry plants obtained by the N-CD growth. The results demonstrate that biomass-based betel leave-derived N-CDs can be an effective fertilizer for global agricultural production applications.

Blue TiO2 exhibited excellent electrocatalytic activity for degrading various organic pollutants in wastewater. However, its crystal structure and morphology considerably affected the electrocatalytic activity of blue TiO2. In this study, a blue hierarchical TiO2 nanotube array (B-HTNA) was synthesized utilizing Ti foam by ice–water bath anodic oxidation and cathodic reduction. Benefiting from a higher concentration of doped Ti3+, the prepared B-HTNA exhibited greater electron transport capability. B-HTNA effectively degraded tetracycline with a high removal rate of more than 90% within 60 min under 20 mA cm–2. The results of free radical quenching experiments revealed the effects induced under different experimental conditions, wherein the electrochemical oxidation of pollutants with B-HTNA mainly relied on the oxidation of hydroxyl radicals. In addition, B-HTNA exhibited a longer service life of up to 85.4 h, surpassing other anodes with a bare and fragile nanotube array. B-HTNA displayed enhanced stability owing to the hierarchical structure with uniform nanoparticles adhering to a porous layer, which could prevent chemical erosion of the anode and charge leakage from the top of the nanotube during cathodic polarization, thereby enhancing self-doping and stability.

Sulfur dioxide (SO2) can significantly improve the selective catalytic reduction (SCR) performance of some metal oxide catalysts. Although extensively studied, understanding the promotional nature of SO2 at the molecular and atomic levels is still a great challenge. Herein, we demonstrate that the redox and acid properties of Ce1Cr3Ox could be successfully balanced via the sulfation, and its SCR activity is, therefore, significantly enhanced. More specifically, large-sized oxygen vacancies with a better oxidizing ability were covered by the formed sulfate ions (SO42–) during the sulfation process. At the same time, both small-sized oxygen vacancies and Lewis acid sites were introduced around the sulfated interface due to the reverse oxygen spillover from CeOx-S to sulfite-like ion (SO3–) on CrOx-S, thus resulting in forming an active pair to promote two critical reaction steps of NH3-SCR reaction, i.e., the adsorption and activation of NH3 molecules and the dissociation of the N–O bond in NHNO species. This work may fill the urgent need to solve the SO2 poisoning problem of SCR catalysts.

The use of human excreta in agricultural settings has the potential to meet crop nutrient requirements and improve soil health, while also providing a sustainable end use for fecal material. Previous reviews have focused on sewage sludge biosolids from wastewater treatment plants, but with on-site sanitation systems overtaking sewers as the leading sanitation system worldwide, greater attention to fecal sludge is warranted. This systematic Review is the first to compile the results of crop trials which utilized fecal amendments from on-site sanitation systems and includes 47 experiments. Overall, fecal amendments increased crop growth compared to unamended control plots and also produced comparable yields to synthetic fertilizers. Biological and physical soil parameters were underrepresented in the literature, which made a holistic assessment of soil health impossible. However, some improvements in chemical characteristics were observed, most notably for soil organic carbon. Inconsistent experimental design made aggregation of results and detailed statistical analysis difficult, highlighting the need for a more standardized approach for testing the efficacy of amendments and reporting results. Regardless, this Review compiles our collective existing knowledge to provide tentative results for the effect of fecal amendments on crop growth and soil health and offers recommendations for future work.

Knowledge of the spatial distribution of heavy metals is indispensable for successful risk analysis of contaminated sites. The common practice is to obtain soil samples for spatial interpolation through site investigation, which generally involves preliminary and detailed surveys. In this study, we propose an information entropy-based site investigation (IESI) method in which an optimal design step is implemented to guide soil sampling at the detailed survey stage. Two types of information entropy (i.e., relative entropy and Shannon entropy) are used to design the optimal sampling strategy. The results show that, within the IESI method, relative entropy is superior to Shannon entropy in guiding soil sampling. Combined with ordinary kriging, the IESI method outperforms conventional surveys for hypothetical and actual heavy metal-contaminated sites as it can identify new polluted and clean areas. For quantitative comparisons, the IESI method coupled with ordinary kriging, logarithmic ordinary kriging, and universal kriging with linear and quadratic trends can improve the interpolation accuracy by 16–43% at the actual heavy metal-contaminated site. Upon further examination of the IESI method, informative sampling points are mainly distributed around the polluted areas identified by the preliminary survey with soil pollution probabilities between 0.75 and 0.95. This work provides an effective tool for delineating the spatial distribution and valuable insights into identifying encryption areas at heavy-metal sites.

We present the mass balances associated with carbon dioxide (CO2) removal (CDR) using seawater as both the source of reactants and as the reaction medium via electrolysis following the “Equatic” (formerly known as “SeaChange”) process. This process, extensively detailed in La Plante, E.C.; ACS Sustain. Chem. Eng. 2021, 9, (3), 1073–1089, involves the application of an electric overpotential that splits water to form H+ and OH– ions, producing acidity and alkalinity, i.e., in addition to gaseous coproducts, at the anode and cathode, respectively. The alkalinity that results, i.e., via the “continuous electrolytic pH pump” results in the instantaneous precipitation of calcium carbonate (CaCO3), hydrated magnesium carbonates (e.g., nesquehonite: MgCO3·3H2O, hydromagnesite: Mg5(CO3)4(OH)2·4H2O, etc.), and/or magnesium hydroxide (Mg(OH)2) depending on the CO32– ion-activity in solution. This results in the trapping and, hence, durable and permanent (at least ∼10 000–100 000 years) immobilization of CO2 that was originally dissolved in water, and that is additionally drawn down from the atmosphere within: (a) mineral carbonates, and/or (b) as solvated bicarbonate (HCO3–) and carbonate (CO32–) ions (i.e., due to the absorption of atmospheric CO2 into seawater having enhanced alkalinity). Taken together, these actions result in the net removal of ∼4.6 kg of CO2 per m3 of seawater catholyte processed. Geochemical simulations quantify the extents of net CO2 removal including the dependencies on the process configuration. It is furthermore indicated that the efficiency of realkalinization of the acidic anolyte using alkaline solids depends on their acid neutralization capacity and dissolution reactivity. We also assess changes in seawater chemistry resulting from Mg(OH)2 dissolution with emphasis on the change in seawater alkalinity and saturation state. Overall, this analysis provides direct quantifications of the ability of the Equatic process to serve as a means for technological CDR to mitigate the worst effects of accelerating climate change.

Nitrogen, an essential nutrient for plant growth, is commonly added to food crops in the form of manure and synthetic fertilizers. Fertilizer use has significantly increased in the past decades to meet the food demands from a rising population. Although this has boosted food production, it has come at a cost to the environment. Indeed, excess fertilizer ends up in water bodies, a pollution that causes losses in aquatic biodiversity. Better fertilizer management is therefore essential to maintaining water sustainability. Here, we develop and evaluate a nitrogen water quality trading scheme to address this challenge. Nitrogen trading incentivizes farmers to work together to invest in pollution reduction measures in order to keep nitrogen water pollution levels within a standardized limit. We build a mathematical model to represent the nitrogen trading and use it to assess the pollution reduction, the effect on the crop yield, and economical outcomes. The model is applied among local farms in the agricultural county of Suffolk, eastern England. We calculate the nitrogen load to the river from each farm and incorporate the abatement cost into the model. The results show how nitrogen water pollution could be reduced cost-effectively while simultaneously increasing the benefit for the whole catchment. Although the benefit does not increase for all the farms, the increase in benefit for the whole catchment is enough to compensate for this loss. The surplus benefit is equally distributed between all the farms, thus increasing their overall benefit. We discuss how the proposed trading model can create a platform for farmers to participate and reduce their water pollution.

It has been widely accepted that oxygen vacancies are critical to catalytic oxidation activities. However, the effects of Ce–O bond strength on the formation of oxygen vacancies and the oxidation rate of styrene remain ambiguous. Herein, a series of CeO2 (CeO2-100, CeO2-140, CeO2-180) were synthesized to uncover the effects of Ce–O bond strength on surface chemical properties and unravel the oxidation mechanism of styrene via comprehensive characterization techniques and theoretical calculations. DFT calculations showed a positive correlation between the Ce–O bond strength and the formation of oxygen vacancies. The CeO2-100 catalyst exhibited a lower styrene degradation temperature (T100 = 223 °C) and the lowest apparent activation energy (Ea = 19.12 kJ/mol). This is due to the fact that weakening the Ce–O bond strength would make it easier to generate oxygen vacancies. More oxygen vacancies facilitate the adsorption of styrene and the formation of surface adsorbed oxygen, thereby accelerating styrene oxidation. In situ DRIFTS demonstrated that more oxygen vacancies can accelerate the oxidation of important intermediate products and further promote the deep oxidation of styrene to CO2 and H2O. Furthermore, the CeO2-100 catalyst showed better activity stability at 223 °C and good water resistance in the presence of 10 vol % water.

As a byproduct of sewage treatment in wastewater treatment plants, sludge has dual attributes with pollution and resource, and its research is important to ecological environment and energy security. Therefore, it is of great significance to analyze and summarize the development of research in the field of sludge treatment and disposal. Based on a bibliometric analysis, this paper analyzed the worldwide research process and trend of sludge treatment and disposal among 49,300 research articles and reviews from 1975 to 2021, which were divided into six time periods for a more detailed analysis. In this analysis, countries, institutions, authors, and keywords were discussed respectively through visual maps. The United States (before 2007–2011) and China (after 2007–2011) were the countries that published the most papers, and cooperation between China and other countries became more frequent after 2007–2011. Research institutions and authors from developed countries and China accounted for the largest proportion. As the main research objects, activated sludge and sewage sludge appeared most frequently in keywords analysis. In terms of the overall trend, sludge treatment and disposal gradually developed from harmless treatment and reduction of sludge to the control of emerging pollutants, recycling of sludge and multidisciplinary research. The analysis of cited authors (W. W. Eckenfelder, M. Henze, and Y. Liu) reflected the recognition of worldwide researchers. The top 10 cited journals were classified as Q1 and Q2 according to journal citation reports, and they were favored by researchers.