A comprehensive study of the chemical composition of rainwater was carried out from October 2016 to September 2017 in the equatorial tropical rainforest region of northwestern Borneo. Monthly cumulative rainwater samples were collected from different locations in the Limbang River Basin (LRB) and were later categorized into seasonal samples representing northeast monsoon (NEM), southwest monsoon (SWM), and inter-monsoon (IM) periods. Physical parameters (pH, EC, TDS, DO, and turbidity), major ions (HCO₃⁻, Cl⁻, Ca²⁺, Mg²⁺, Na⁺, and K⁺) and trace metals (Co, Ni, Cd, Fe, Mn, Pb, Zn, and Cu) were analyzed from collected rainwater samples. Rainwater is slightly alkaline with mean pH higher than 5.8. Chloride and bicarbonate are the most abundant ions, and the concentration of major ions in seasonal rainwater has shown slight variation which follows a descending order of HCO₃⁻> Cl⁻> Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ in NEM and Cl⁻ > HCO₃⁻ > Na⁺ > Ca²⁺ > K⁺ > Mg²⁺ in SWM and Cl⁻ > HCO₃⁻ > Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ in IM period. Trace metals such as Fe and Ni have shown dominance in seasonal rainwater samples, and all the metals have shown variation in concentration in different seasons. Variation in chemical characteristic of seasonal rainwater samples identified through piper diagram indicates dominance of Ca²⁺-Mg²⁺-HCO₃⁻ and mixed Ca²⁺-Mg²⁺-Cl⁻ facies during NEM, SWM, and IM periods. Statistical analysis of the results through two-way ANOVA and Pearson’s correlation also indicates significant variation in physico-chemical characteristics. This suggests a variation in contributing sources during the monsoon seasons. Factor analysis confirmed the source variation by explaining the total variance of 79.80%, 90.72%, and 90.52% with three factor components in NEM, SWM, and IM rainwater samples with different loading of parameters. Enrichment factor analysis revealed a combined contribution of marine and crustal sources except K⁺ which was solely from crustal sources. Sample analysis of backward air mass trajectory supports all these findings by explaining seasonal variation in the source of pollutants reaching the study area. Overall, the results show that the chemical composition of seasonal rainwater samples in LRB was significantly influenced by natural as well as anthropogenic processes. These include (long-range and local) industrial activities, fossil fuel combustion, forest burning, transportation activities including road transport and shipping activities, and land-derived soil dust along with chemical constituents carried by seasonal wind.

Determining alternative water sources to meet municipal water demands is important when availability is limited. The purpose of this study was to demonstrate a means for water planners to estimate the amount of combined sanitary wastewater and storm water that they might already be capturing through open air oxidation ponds. Increased understanding of the quantity of water that is already available could help water planners to better envision optimal water reuse scenarios. Using water and climate data on oxidation ponds in these three cities within the Texas Panhandle from 2010 to 2014, we evaluated water quantities which would be available for potential reuse. From the net monthly wastewater volumes values, the study also considered if per capita demand could have been met by reusing the wastewater. The study found wastewater volumes were lower in fall and winter months and much higher in spring and summer months. If a city considers reusing wastewater, blue water (groundwater) extraction could be reduced by as low as 45–50% in one city to as high as 100% in another. Water planners in similar environments and wastewater treatment systems may find this demonstration of potential reuse water quantity encouraging for better meeting their own water demands and enhancing water supply resiliency.

This paper investigates the interaction effects of income inequality and democracy on CO₂ emissions. The spatial panel model, which accounts for the spatial spillover effects across countries, is used. Using the panel data covering 41 Belt and Road initiative countries, the results indicate significant positive spatial spillovers effect to country-level CO₂ emission activity. The Kuznets Curve hypothesis, which assumes that reverse U relation presents between income and CO₂ emissions, is identified. Empirical results provide evidence that democracy levels promote the nonlinear nexus between income inequality and CO₂ emissions. High levels of inequality, ceteris paribus, in conjunction with poor democratic institutions are likely to result in higher pollution. The findings are robust to various robustness tests.

The levels of metals in sediments of urban river ecosystems are crucial for aquatic environmental health and pollution assessment. Yet little is known about the interaction of nutrients with metals for environmental risks under contamination accumulation. Here, we combined hierarchical cluster, correlation, and principal component analysis with structural equation model (SEM) to investigate the pollution level, source, toxicity risk, and interaction associated with metals and nutrients in the sediments of a river network in a city area of East China. The results showed that the pollution associated with metals in sediments was rated as moderate degree of contamination load and medium-high toxicity risk in the middle and downstream of urban rivers based on contamination factor, pollution load index, and environmental toxicity quotient. The concentration of mercury (Hg) and zinc (Zn) showed a significant correlation with toxic risks, which had more contribution to toxicity than other metals in the study area. Organic nitrogen and organic pollution index showed heavily polluted sediments in south of the study area. Though correlation analysis indicated that nutrients and metals had different input zones from anthropogenic sources in the urban river network, SEM suggested that nutrient accumulation indirectly intensified toxicity risk of metals by 13.6% in sediments. Therefore, we suggested the combined consideration of metal toxicity risk with nutrient accumulation, which may provide a comprehensive understanding to identify sediment pollution. Graphical abstract Toxicity rate of metals in sediments from urban river network indirectly intensified by nutrients accumulation

In this work, Mn-doped ZnS quantum dots capped by L-cysteine (Mn@ZnS/L-cyst) and polyethylene glycol (Mn@ZnS/PEG) and also Mn-doped ZnS on zeolite NaY (Mn@ZnS/Y) were synthesized. These compounds were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and ultraviolet-visible and fluorescence spectroscopy. Then, the photodegradation ability of these three photocatalysts was investigated for degradation of 4′,5′-dibromofluorescein dye under ultraviolet irradiation. In the next stage, the different effective parameters on degradation performance, such as pH, catalyst dosage, and initial dye concentration, were studied. Results demonstrated that the optimum initial concentration was 40 mg L⁻¹ for all three catalysts. The optimum catalyst dosage for both Mn-doped ZnS quantum dots capped by L-cysteine and Mn-doped ZnS on zeolite NaY was 0.017 g L⁻¹ and for Mn-doped ZnS quantum dots capped by polyethylene glycol was 0.033 g L⁻¹. The degradation efficiency of 97% for all three photocatalysts was achieved; therefore, by considering the higher production yield of quantum dots onto zeolite and also the more convenient recovery of the Mn-doped ZnS on zeolite NaY from the solution, it seems synthesis of quantum dots onto the zeolites is a reasonable strategy.

This study examined the influence of biochar addition on fungal community during composting of cow manure using high-throughput sequencing. Two treatments were set up, including compost of cow manure plus 10% biochar (BC) and cow manure compost without biochar (CK). Fungal community composition varied obviously during composting in both treatments, and main fungi included Aspergillus, Myriococcum, Thermomyces, Mycothermus, Scedosporium, Cladosporium, and unclassified Microascaceae. Fungal community composition was altered by biochar during composting, especially during the thermophilic and the cooling phase, promoting Aspergillus and Myriococcum while inhibiting unclassified Microascaceae and Thermomyces. Based on linear discriminant analysis effect size analysis, common indicator groups were detected in both composts; however, specific indicator groups were also found in BC treatment, including Clavicipitaceae, Tremellales, Gibberella, and Coprinopsis. Canonical correspondence analysis (CCA) indicated that moisture content, organic matter, C/N, and pH had significant correlation (p < 0.05) with fungal composition in both treatments. However, in compost added with biochar, temperature was not an important factor affecting fungal community (p > 0.05).

The rapidly growing interest in using graphene-based nanoparticles in a wide range of applications increases human exposure and risk. However, very few studies have investigated the genotoxicity and mutagenicity of the widely used graphene oxide (GO) nanoparticles in vivo. Consequently, this study estimated the possible genotoxicity and mutagenicity of GO nanoparticles as well as possible oxidative stress induction in the mice liver and brain tissues. Nano-GO particles administration at the dose levels of 10, 20, or 40 mg/kg for one or five consecutive days significantly increased the DNA breakages in a dose-dependent manner that disrupts the genetic material and causes genomic instability. GO nanoparticles also induced mutations in the p53 (exons 6&7) and presenilin (exon 5) genes as well as increasing the expression of p53 protein. Positive p53 reaction in the liver (hepatic parenchyma) and brain (cerebrum, cerebellum, and hippocampus) sections showed significant increase of p53 immunostaining. Additionally, induction of oxidative stress was proven by the significant dose-dependent increases in the malondialdehyde level and reductions in both the level of reduced glutathione and activity of glutathione peroxidase observed in GO nanoparticles administered groups. Acute and subacute oral administration of GO nanoparticles induced genomic instability and mutagenicity by induction of oxidative stress in the mice liver and brain tissues.

To ensure microbial activity and a reaction equilibrium with efficiency and energy saving, it is important to know the factors that influence microbiological nitrogen removal in wastewater. Thus, it was investigated the microorganisms and their products involved in the treatment of kennel effluents operated with different aeration times, phase 1 (7 h of continuous daily aeration), phase 2 (5 h of continuous daily aeration), and phase 3 (intermittent aeration every 2 h), monitoring chemical and physical parameters weekly, monthly microbiological, and qualitative and quantitative microbiological analyzes at the end of each applied aeration phase. The results showed a higher mean growth of nitrifying bacteria (NB) (10⁶) and denitrifying bacteria (DB) (10²²) in phase with intermittent aeration, in which better total nitrogen (TN) removal performance, with 33%, was achieved, against 21% in phase 1 and 17% in phase 2, due to the longer aeration time and lower carbon/nitrogen ratio (15.7), compared with the other phases. The presence of ammonia-oxidizing bacteria (AOB), the genus Nitrobacter nitrite–oxidizing bacteria (NOB), and DB were detected by PCR with specific primers at all phases. The analysis performed by 16S-rRNA DGGE revealed the genres Thauera at all phases; Betaproteobacteria and Acidovorax in phase 3; Azoarcus in phases 2 and 3; Clostridium, Bacillus, Lactobacillus, Turicibacter, Rhodopseudomonas, and Saccharibacteria in phase 1, which are related to the nitrogen removal, most of them by denitrifying. It is concluded that, with the characterization of the microbial community and the analysis of nitrogen compounds, it was determined, consistently, that the studied treatment system has microbiological capacity to remove TN, with the phase 3 aeration strategy, by simultaneous nitrification and denitrification (SND). Due to the high density of DB, most of the nitrification occurred by heterotrophic nitrification-aerobic. And denitrification occurred by heterotrophic and autotrophic forms, since the higher rate of oxygen application did not harm the DB. Therefore, the aeration and carbon conditions in phase 3 favored the activity of the microorganisms involved in these different routes. It is considered that, in order to increase autotrophic nitrification-aerobic, it is necessary to exhaust the volume of sludge in the secondary settlers (SD), further reducing the carbon/nitrogen ratio, through more frequent cleaning, whose periodicity should be the object of further studies. Graphical abstract

Environmental considerations require disposal of the contaminants in a safe manner without causing any harm. Accordingly, the contaminants should be removed and recovered as value or disposed without any burden to the environment. In this context, natural biodegradable adsorbents could possibly be an answer as they get biodegraded along with the organic contaminants including phenol. Having observed from literature that the natural guava leaf powder (NGLP) can be used as an adsorbent, experimental studies were carried out to investigate the potential of NGLP to remove phenol from aqueous solutions. Batch experiments were carried out using NGLP and the effect of different variables such as pH, NGLP dosage, contact time and agitation speed was studied using response surface methodology (RSM) with Box–Behnken approach and the significant parameters were optimized by subsequent experimentation. The optimized parameters obtained in our studies correspond to pH 5.85 for a NGLP dosage of 2.15 g/L, at an agitation speed of 140 rpm and a contact time of 9 h for the initial phenol concentrations ranging from 50 to 250 mg/L. The absorption of phenol onto NGLP was confirmed using FTIR and SEM-EDX. Thermodynamic, kinetic and equilibrium isotherm studies were conducted using the optimal parameters. The adsorption data fitted well with Langmuir isotherm (R²= 0.9982) for the batch equilibrium studies and the pseudo-second-order type model (R²= 0.9743–0.9921) depicted the phenol adsorption kinetics. The maximum adsorption capacity of NGLP for phenol was 10.85 mg/g. The results inferred the feasibility of using NGLP as a phenol adsorbent and Box–Behnken design as an effective tool for the optimization of process conditions. Even though the studies are not intended to reuse the adsorbent in view of abundance and biodegradability, the preliminary experiments have indicated the possible potential of desorption and reusability.

Pyrolysis processes were investigated using expanded polystyrene waste (EPW) with a catalyst synthesized from rice husk (RH). Biomass was treated with different acids, i.e., sulfuric acid, oxalic acid, and hydrochloric acid. The effect of normality on the oxalic acid-treated catalyst and the effects of polymer to catalyst ratio on (i) oil, gas, and residues yields; (ii) temperature; and (iii) time for the complete reaction were investigated for the effective use of oil for fuel production. The catalyst treated with 0.25 N (RHOA₀.₂₅) resulted in a high oil yield of 96 wt% and a residue yield of 3.47 wt%. The oil produced contained mainly aromatic compounds, which contributed 67.86% in an area-based GC-MS analysis. The synthesized catalyst showed a stable capacity for three regeneration runs. The significant factor is that the synthesized catalyst decreased the activation energy during the pyrolysis of EPW. Graphical abstract