Despite attempts to enhance the recycling of waste printed circuit boards (WPCBs), the simultaneous recovery of major metals of WPCBs using an efficient approach is still a great challenge. This study mainly concerned with applying an effective statistical tool to optimize the recovery of metal content (i.e., Cu, Fe, Zn, Pb, Ni, Sn, and Al) embedded in WPCBs using a leaching agent without any additive or oxidative agent. Another target was to optimize a multi-response recovery process by minimizing time, energy, and acid consumption during the leaching. Effective parameters and their levels, including leaching time (20–60 min), temperature (25–45 °C), solid to liquid (S/L) ratio (1/8–1/20 g/ml), and acid molarity (1–2.7 M), were optimized. A well-established statistical approach (i.e., response surface methodology (RSM)) was applied to precisely quantify and interpret the effects. General optimum conditions for nine responses were introduced with the desirability of ≈ 85%. Finally, the solid residue of leaching was characterized and results showed the morphology, structure, and composition of the residue content (i.e., polymers and ceramics) remained the same after the leaching, indicating the neutral behavior of the leaching process on these two materials. Also, thermal behavior and phase analysis of the original WPCBs and leaching residue were compared and analyzed. Graphical abstract

Organophosphate esters (OPEs), as re-emerging contaminants considered to be a potential health concern, are ubiquitous in the environment and have been widely investigated. However, little is known on the safe OPE concentrations in the water quality criteria for the protection of the aquatic environment, which is an indispensable part of environmental management. In the present study, aquatic acute and chronic predicted no-effect concentrations (PNECs) of six frequently detected OPEs were derived from the hazardous concentrations for 5% of species (HC₅s), respectively. The acute PNECs for the selected OPEs ranged from 17.70 to 3562 μg/L, while the chronic PNECs ranged from 4.6 × 10⁻⁴ to 61.85 μg/L. Among these OPEs, tricresyl phosphate (TCrP) exhibited the lowest acute PNEC, while tris(1,3-dichloro-2-propyl) phosphate (TDCPP) presented chronic PNEC, which indicated that it has a higher toxicity effect on the aquatic environment. Furthermore, the aquatic ecological risks of individual OPEs (except for TDCPP) were deemed to be relatively low in Chinese surface water; however, the aquatic ecological risks of TDCPP and ΣOPEs indicated that they have potential adverse effects and should be considered as a potential health concern. The probability of 5% of aquatic organisms being affected by ΣOPEs was in the range of 0.21 to 17.39% based on the joint probability curve method.

Novel and efficient animal wastewater treatment technologies of bacteria reduction are needed for preventing disease outbreak in animal herds and safeguarding environmental health. Zero-valent iron (ZVI) has been used to treat bacteria contaminated water for the past decades, but its passivation issue has been a major challenge. In this study, batch tests were performed to evaluate the effect of a hybrid zero-valent iron (h-ZVI) or a mixed ZVI/Fe₃O₄ media system on reduction of Escherichia coli (E. coli) levels. The h-ZVI media was created through a wet chemical process that uses nitrate to oxidize ZVI in the presence of externally added Fe²⁺ (aq.). Transforming ZVI into a h-ZVI system could overcome the passivation of ZVI and increase the reactivity of the media. The results demonstrated that E. coli cells in the bulk phase were removed rapidly by h-ZVI media. Majority of E. coli was attached (or adsorbed) to the surface of h-ZVI media within a few minutes, which suggested that adsorption was the dominant mechanism for bacterial removal in the initial phase. This adsorption was confirmed by fluorescence microscopy with CTC-DAPI double staining and transmission electron microscopy (TEM). Increasing contact time steadily inactivated E. coli; all cells were inactivated after 120 min of contact. The TEM results indicated that h-ZVI inactivated E. coli by causing direct damage on bacterial cell membrane. The results of this study strongly suggest that h-ZVI treatment can be used in water treatment industry where bacterial contamination is concerned.

The endogenous release of nutrients from sediments contributes to the eutrophication of landscape water to a certain degree, which depends on the characteristics of sediments. The study explored the characteristics of nitrogen (N) and phosphorus (P) released from two different sediments, which were deposited from reclaimed water (SRW) or surface water (SSW) respectively in Xi’an moat. This paper aimed to compare the effects of nutrient release from SRW and SSW on the water quality. Results showed that the maximum increase rates reached 1.21 mg TN/(L·day) and 0.11 mg TP/(L·day), respectively, in the overlying water of SRW, which were 1.6 and 2.8 times those of SSW. The released amounts of SRW were 0.192 mg TN/g and 0.038 mg TP/g, which were 4.1 and 12.7 times those of SSW. Meanwhile, the densities of benthic algae in SRW and SSW were 5.605 × 10⁹ and 2.846 × 10⁸ cells/L, respectively. Moreover, the species number and individual sizes of benthic algae in SRW were also larger than those in SSW, which played an important role in the nitrogen circulation. Unexpectedly, oxidation reduction potential (ORP) level of SRW was lower than that of SSW, although SRW has a higher dissolved oxygen level. Therefore, the N and P concentrations in the overlying water of SRW were considerably higher than those of SSW, which was mainly attributed to the higher nutrient contents and lower ORP in SRW.

Fish are important in constructed wetland (CW) ecosystem. An 80-day experiment was conducted by exposing juvenile grass carp (Ctenopharyngodon idellus) to 0, 0.5, 2.0, 4.5, 9.0, and 18.0 mg L⁻¹ total ammonia nitrogen (TAN) stress to determine the severity of physiological changes in fish organs (liver, gills, and muscle) in CW. Specific growth rate results indicated that low TAN (≤ 2.0 mg L⁻¹) help maintain or enhance grass carp growth. Fish physiological indexes did not significantly change during exposure, except for the gill’s reactive oxygen species (ROS) level that is susceptible to TAN exposure. Under high TAN (≥ 4.5 mg L⁻¹), physiological changes and organ-specific responses were revealed. The ROS and malondialdehyde levels were higher in the gills than in the liver. At 9.0 mg L⁻¹ TAN, the muscle cells manifested toxicity. The antioxidant system of different organs responded differently because the gills were more susceptible to low TAN than other organs. After TAN removal from the low TAN system, the antioxidative enzymes and antioxidants were increased to scavenge extra ROS and reverted to the normal level. However, grass carp cannot recover from the oxidative damage at ≥ 9.0 mg L⁻¹ external TAN, resulting in organ dysfunction and failed ROS scavenging. This study provides information in maintaining CW sustainability.

To investigate the effects of antibiotics on nitrogen removal and uptake by wetland plants, four typical macrophyte species, Cyperus alternifolius L., Typha angustifolia L., Lythrum salicaria L., and Acorus calamus L., were grown in hydroponic cultivation systems and fed wastewater polluted with 10 μg L⁻¹ Ofloxacin (OFL) and Tetracycline (TET). Biomass production, nitrogen mass concentration, chlorophyll content, root exudates, and nitrogen removal efficiency of hydroponic cultivation were investigated. The results indicated that in all hydroponic systems, NH₄⁺–N was entirely removed from the hydroponic substrate within 1 day and plant nitrogen accumulation was the main role of the removed NO₃⁻. OFL and TET stimulated the accumulation of biomass and nitrogen of A. calamus but significantly inhibited the NO₃⁻–N removal ability of L. salicaria (98.6 to 76.2%) and T. augustifolia (84.3 to 40.2%). This indicates that A. calamus may be a good choice for nitrogen uptake in wetlands contaminated with antibiotics. OFL and TET improved the concentrations of total organic carbon (TOC), total nitrogen (TN), organic acid, and soluble sugars in root exudates, especially for oxalic acid. Considering the significant correlation between TOC of root exudates and nitrogen removal efficiency, the TOC of root exudates may be an important index for choosing macrophytes to maintain nitrogen removal ability in wetlands contaminated with antibiotics.

The effects of different concentrations of phosphorus (P) on absorption and transfer of selenium (Se) in rice seedlings were studied by hydroponics experiment. The interaction between iron plaque and phosphorus on absorption and transport of selenium were studied by adding a large amount of iron-induced iron plaque, to provide a theoretical basis for rational application of phosphate fertilizer in the selenium bio-strengthening process of rice. The results showed that phosphorus deficiency may result in the formation of reddish brown iron oxide coating on the root surface of rice. The formation of root iron plaque of rice is related to concentration of phosphorus, and low concentration of phosphorus (0–1.5 mmol L⁻¹) can increase the amount of root iron plaque. Compared P deficiency culture and 2 mmol L⁻¹ P culture, Se content in the shoots and roots decreased by 76 and 47%, respectively. Addition of Fe²⁺ significantly reduced biomass of shoot and had no significant effect on the roots; when the P concentration increased from 0.1 to 0.3 mmol L⁻¹, transfer coefficient of Se decreased. Therefore, both root iron plaques induced by phosphorus deficiency and iron addition have a strong adsorption effect on selenium, which reduces the transport of selenium from the rice roots to the shoots. In the lower range of phosphorus concentration, low phosphorus can promote selenium content of rice shoot, while higher on the contrary. In the practice of rice production, proper management of phosphorus nutrient is of great significance to control selenium content in rice grain.

On December 19, 2017, China’s National Development and Reform Commission (NDRC) announced the official launch of the much-anticipated national emissions trading system (ETS), which is a critical period for the transition from the eight carbon emission trading pilot projects to the national market at this stage. Comprehensively evaluating the efficiency of China’s eight carbon trading pilots is vital for strengthening the construction of its national ETS. This paper investigates the weak-form efficiency of eight carbon trading markets in China. We use a series of variance ratio tests to identify the efficiency from the market set up to the May 4, 2018, of all markets. The results indicate that the majority of the carbon trading markets are inefficient and only Beijing, Hubei, and Fujian markets are efficient. The China’s carbon trading market is gradually maturing and implemented. In addition, we analyze the factors have impact on the market efficiency. It shows that the liquidity, volume, allocation allowance, and transparency in information are significant factors; meanwhile, the regional policy and cross cooperation also are important factors. Finally, this paper puts forward several policy recommendations on how to strengthen the effectiveness of China carbon trading markets based on the empirical results.

The presence of tetracycline antibiotics (TCS) in the water and wastewater has raised growing concern due to its potential environmental impacts; thus, their removal is of high importance. In this study, a novel aluminum-based MOF/graphite oxide (Al-MOF/GO) granule was prepared as an adsorbent for the removal of TCS including oxytetracycline (OTC) and chlortetracycline (CTC). The adsorbent was characterized via XRD, FTIR, BET, SEM, and XPS methods. The granules exhibited similar crystal structure and some new mesopores appearing compared to the parent Al-MOF/GO powder. In addition, the adsorption behavior of OTC and CTC on samples was explored as a function of initial concentration, contact time, pH, and ionic strength by means of batch experiments. The adsorption capacity reached to 224.60 and 240.13 mg·L⁻¹ for OTC and CTC, at C₀ = 60 mg·L⁻¹ as well as ambient temperature respectively. Moreover, the adsorption process of OTC and CTC on Al-MOF/GO samples can be better delineated by pseudo-second-order kinetics and Freundlich isotherm models. Besides, the adsorption mechanism over Al-MOF/GO granules was proposed, which could be ascribed to π-π interaction, cation-π bonding, and hydrogen bond. Finally, the great water stability, separation performance, and regeneration efficiency of these novel granules indicated their potential application in the OTC and CTC removals from aqueous solution.

The extensive extraction activity of mercury ores in Asturias (northwest Spain), also rich in As and Sb, has impacted the Nalón river estuary. The objective of this research was to assess the historical evolution of As-Hg-Sb accumulation in the salt marsh sediments of this area. For this purpose, sediment cores were collected from two different salt marshes (eastern and western river banks) in the estuarine environment to evaluate the degree of anthropogenic enrichment and the geochronology of As-Hg-Sb accumulation. Core subsampling was performed by cutting 2-cm-thick slices of sediments. The subsamples were then analysed for several physical and chemical parameters. Sedimentation rate was assessed by measuring short-lived radionuclides (excess ²¹⁰Pb and ¹³⁷Cs). Pre-mining levels of As-Hg-Sb were observed at core depths below 50 cm. In the less extended salt marsh (eastern river bank), maximum As-Hg-Sb concentrations of 87.48, 3.66, and 5.75 μg·g⁻¹, respectively, were found at the core top as a consequence of long-term mining activity in the area. The vertical distribution of As-Hg-Sb was influenced by the single-point contamination sources, whereas grain-size variability and diagenetic remobilisation did not seem affected. Geochronological measurements showed that the depositional fluxes of As-Hg-Sb were influenced by anthropogenic input after 1900, when mining activity in the area was most intense. Hg mining ceased in 1969; however, the corresponding core profiles did not show a drastic decreasing trend in element fluxes, implying that the river drainage basin retains some “memory” of contamination which affects riverine sediments. A preliminary gross estimation of total As-Hg-Sb “trapped” in the Nalón river salt marsh sediments amounted to approximately 18.7, 1.0, and 0.7 t, respectively. These morphological structures suffer erosive processes, thus representing a potential source of these elements associated with sediments; consequently, management conservation and monitoring of salt marshes should be taken into consideration from this environmental point of view.