Discharge Standards Research Articles

Evaluation of Treated Wastewater Quality for Reuse in the Northern Region of Minas Gerais

Objective: This study aims to analyze the quality of effluents treated at three Wastewater Treatment Plants (WWTPs) in the northern region of Minas Gerais, evaluating reuse potential and proposals. Theoretical framework: The practice of reusing sanitary effluents holds significant economic and environmental importance. It conserves water resources allocated for higher priority uses. When assessed and compliant with regulations, effluents become potential water sources for agriculture and urban squares. The trend towards reusing treated effluents presents an alternative to meet water demands that could be satisfied with lower-quality water. Method: The study conducted laboratory analyses of three COPASA MG sewage treatment plants, referred to as WWTPs I, II, and III, between January 2021 and September 2022. Parameters crucial for effluent reuse, including Biochemical Oxygen Demand (BOD), Electrical Conductivity (EC), Hydrogen Potential (pH), Escherichia coli, Sodium Adsorption Ratio (SAR), and viable helminth eggs, were monitored and evaluated. The feasibility of proposed water reuse methods was assessed by analyzing the quality of treated effluents from the three WWTPs, considering that the treatments adhered to the conditions and effluent discharge standards outlined in Joint Normative Decision COPAM and CERH-MG No. 01 of May 5, 2008 (Minas Gerais, 2008), as well as the reuse parameters defined in Normative Decision CERH-MG No. 65/2020 of June 18, 2020 (CERH-MG, 2020). Results and Conclusion: The findings indicate that the effluents treated in the studied WWTPs are suitable for reuse, with potential corrective measures for non-compliant parameters. This allows for irrigation of urban squares, subject to approval by local authorities, and internal irrigation within interested businesses. Research Implications: This approach is highly relevant for fostering discussions on expanding reuse practices and shaping regulations through legislation, norms, and deliberations. Originality: This study stands out due to its in-depth investigation, ensuring a viable water reuse source for localities facing water scarcity, particularly in the northern region of Minas Gerais. This innovative topic, though less explored in literature, is gaining momentum in environmental discourse, thanks to the potential of effluents for agricultural purposes.

DETERMINATION OF ECOTOXIC SUBSTANCES IN WASTEWATER FORMED IN THE PURIFICATION PROCESS OF PETROLEUM OILS WITH HYDROGEN BY SPECTRAL METHODS

The article analyzes the determination of the amount of dissolved ecotoxicants in the sample taken from the industrial wastewater obtained during the process of hydrogen treatment of petroleum oils. During the hydrogenation process, different types of wastes are formed, depending on the nature of each compound contained in petroleum distillates. Every gas, liquid, solid waste formed during the process of hydrogen purification of petroleum distillates by the oil refining industry has a negative impact on the environment in various ways. One of the main directions of our scientific research is the ecological assessment of the environmental impact of wastewater formed in the process of hydrogen treatment of petroleum distillates.Based on the results obtained, the environmental impact of the wastewater was assessed. The amount of volatile ecotoxicants in the wastewater sample was determined by spectral methods and is shown in the table. We used gas chromatography-mass spectrometry method for the polycyclic aromatic hydrocarbons; optical emission spectrometry method for metals; spectrometry method for phenols, dyes and fluorine; nephelometry method for turbidity; the gravimetry method for total suspended particles. Based on the results obtained, it is possible to assess the environmental impact of wastewater generated during the technological process at the hydrogen treatment plant. According to the results of the research, it can be noted that the industrial wastewater discharged from the oil refinery's facility № 501 has a content that will damage the ecosphere and biosphere, despite the fact that the discharge standards meet the permissible discharge limits

Mxene-based ceramic nanofiltration membranes for selective separation of primary contaminants in semiconductor wastewater

Ceramic membranes, known for their exceptional chemical stability, have found practical applications in the treatment of semiconductor wastewater. In this study, we have developed an innovative ceramic nanofiltration membrane featuring a nanochannel network created by two-dimensional (2D) nanomaterials, enabling high-performance separation and permeation. This accomplishment is realized through precise control of the size and thickness of MXene nanomaterials, which can be tailored using various coating conditions. The repeated stacking of MXene nanosheets onto the ceramic membrane substrate resulted in the formation of additional nanochannels and surface chemistry modifications, leading to significant enhancements in pollutant removal. These MXene-coated ceramic nanofiltration (NF) membranes significantly improved the removal efficiency of representative organic contaminants in semiconductor wastewater when compared to the pristine ceramic membrane. It enhanced the removal efficiencies by 4.2 times for dissolved silica, 3.7 times for dimethyl sulfoxide (DMSO), and 2.5 times for isopropyl alcohol (IPA). Furthermore, the MXene ceramic NF membrane exhibited exceptional fluoride removal capability, achieving approximately 99.1% removal, in addition to organic solvents. These findings not only help meet regulatory standards for wastewater discharge but also provide valuable insights into the transport behaviors of contaminants and their separation mechanisms. This innovative approach brings us one step closer to efficient and sustainable solutions for semiconductor wastewater treatment.

Practice assessment of integrated marine pond aquaculture for increasing benefits and reducing environmental pollution using an ecosystem modeling approach

The transformation from semi-intensive and intensive aquaculture to integrated aquaculture is an effective way to upgrade the aquaculture process. Integrated aquaculture is better able to maintain a healthy environment and a balanced ecosystem for the cultured species as well as producing high quality commodities at a high yield. In this study, we demonstrate that ecosystem modeling can be used to help optimize and promote the integrated aquaculture model. First, the aquaculture management and main biochemical processes were parametrized according to the biological populations present, the physical environment, and the management practices for the integrated aquaculture marine pond of Portunus trituberculatus– Penaeus japonicus– Sinonovacula constricta. The ecosystem model of the pond unit was constructed by coupling the individual growth models of the three cultured animals. The goodness-of-fit indicators showed that this model accurately reproduced the dynamics of the cultured animals, plankton, and nutrients. After the ecosystem model was constructed and validated, the carrying capacity of the integrated aquaculture pond was evaluated by adjusting the stocking density and management practices based on the tailwater discharge standards. The economic benefits of the system and the ecological benefits of polyculture razor clams were quantitatively compared under two scenarios: the current stocking density and reaching the maximum capacity. The assessment results show that the aquaculture pond reached the carrying capacity when the stocking density was 1.8 times the current scenario (18 ind m−2, 27 ind m−2, 22 ind m−2 for P. trituberculatus, P. japonicus and S. constricta). At 1.8 times stocking density scenario, the profit increased by 51.59 %, and nitrogen and phosphorus removal increased by 51.48 % and 55.55 %, respectively. These results provide a theoretical basis for this integrated aquaculture model, which offers a promising way forward for sustainable industrial development. Possible applications and beneficial contributions of this aquaculture model in China are discussed.

Insight into the application of micro-nano bubbles combined with heat-activated persulfate oxidation for removing dissolved organic matter from printing and dying wastewater

The effluent quality of printing and dyeing wastewater after secondary treatment does not meet industry discharge standards, which poses serious environmental risks. In this work, micro-nano bubbles and a heat-activated persulfate advanced oxidation process were innovatively combined to thoroughly treat industrial printing and dyeing wastewater. Under the optimal reaction conditions (a reaction time of 60 min, persulfate concentration of 20 mM, and temperature of 40 °C), the effluent quality met the discharge standards. Furthermore, the degradation and transformation mechanisms of dissolved organic matter during the wastewater treatment process were investigated by three-dimensional fluorescence spectroscopy and Fourier ion transform spin resonance mass spectrometry. The results showed that organic compounds in the wastewater were clearly degraded by the treatment process, and this was accompanied by a significant increase in molecular diversity. In summary, this work provides insight into the practical application of micro-nano bubbles in the advanced oxidation treatment of industrial wastewater as well as the degradation mechanism responsible for removing pollutants from this wastewater.

Effect of HRT on nitrogen removal from low carbon source wastewater enhanced by slurry and its mechanism

Insufficient carbon sources in low-carbon wastewater have consistently hindered nitrogen removal performance. This work utilized slurry after anaerobic digestion as an additional carbon source, and the optimal hydraulic retention time (HRT) parameters were obtained through adjustment. The findings revealed that, under HRT conditions of 24–12 h, the discharge standards of wastewater treatment plants (WWTPs) could be met. It had been proven that HRT 12 h was the more cost-effective parameter for application in WWTPs, and the removal efficiencies for COD, NH4+-N, NO3–-N, and TN reached impressive levels of 82.43%, 95.24%, 77.49%, and 86.70%, respectively. However, the HRT 6 h struggled to achieve efficient wastewater treatment. Mechanistic analysis demonstrated that shortening the HRT resulted in considerably higher microbial richness, diversity, and evenness, causing notable shifts in microbial community structure. Additionally, a shortened HRT reduced the enrichment abundance of key bacterial phyla (Proteobacteria, Bacteroidetes) and genera (Hydrogenophaga, Filimonas, Meganema) that played an important role in nitrogen and organic matter removal. Furthermore, a shortened HRT increased hydraulic shear forces, impeding the enrichment of carbon and nitrogen metabolism pathways, and reducing the abundance of essential genes associated with glycolysis (HK, pfkA, FBA, GAPDH) and nitrogen metabolism processes (narG, narH, narI, norB, nirS, nosZ). It was noteworthy that the microbial community under the HRT 6 h condition carried the highest risk of microbial pathogenicity. This work revealed the optimal parameters, and carbon and nitrogen metabolism mechanism of wastewater treatment systems with slurry as a carbon source for the first time, and provided novel ideas and insights for low-carbon wastewater treatment.

Hydrogen peroxide assisted advanced electrocoagulation for reducing the organic content of leachate nanofiltration concentrate

Integrated biological treatment-membrane filtration is widely applied in leachate treatment to ensure discharge standards. The most important waste of this integrated application is high volumes of membrane concentrate. In this study, the treatment of leachate nanofiltration concentrate (NFC) with high resistive organic matter content was investigated by hydrogen peroxide (HP) assisted advanced electrocoagulation process (EC-HP) using Al electrodes. To achieve maximum pollutant removal efficiencies, process optimization was carried out using the Box-Behnken design (BBD). Statistically, the fit of the model was evaluated by analysis of variance. Correlation coefficients (R2) of all mathematical models developed for system responses (COD, UV254, TOC, and color removal efficiency) with EC-HP process were close to 1, adjusted R2 values were close to R2 values, and the difference between adjusted R2 and predicted R2 values was less than 0.2. These values indicate that the BBD method is effective, appropriate, and meaningful in explaining the pollutant removal from leachate NFC with the EC-HP process. Under the optimized conditions (27.3 mM HP, 0.6 A, pH 5, and 45 min) 62.2 %, 55.3 %, 73.9 %, and 85.9 % COD, TOC, UV254, and color removal efficiencies, respectively were predicted by the model and by validation study, 57.3 % COD, 52.0 % TOC, 68.3 % UV254, and 85.0 % color removal yields were achieved. SEC and SECCOD values were calculated as 7.65 kWh/m3 and 2.78 kWh/kgCOD, respectively at optimum conditions. Moreover, ENC, ELC, CC, and TC values were 0.55 $/m3, 0.82 $/m3, 8.0 $/m3, and 9.37 $/m3, respectively. The results of the study showed that the EC-HP process is an effective method for pollutant removal from leachate NFC.

Mercury Levels in Groundwater near Artisanal Small-Scale Gold Mines in Migori County, Kenya

In Migori County, artisanal and small-scale gold mining (ASGM) is an economic activity that uses mercury during the amalgamation process to obtain gold. The waste generated in the form of soil tailings and pan-pond water contains mercury and is located close to community boreholes. The proximity may predispose groundwater to mercury contamination. Boreholes are one of the main water sources in Migori County. Ingestion is one of the ways mercury can get into the human body. This study was conducted to establish mercury concentration in groundwater from boreholes, soil tailings and pan-pond water located near five mine sites in Migori County during dry and wet seasons in comparison with drinking water standards required by KEBS and NEMA effluents discharge standards. The five mines were: -Masara, Osiri Matanda, Macalder, Kitere and Kehancha. The study used a cross-sectional-analytical study design and focused on boreholes found within a distance of 6 km from each of the five mines. Fifteen boreholes were proportionately sampled to obtain groundwater samples. 20 pan-pond water and soil tailing samples were collected in both dry and wet seasons as per the respective sampling protocols applied. Inductively Coupled Plasma –Mass Spectroscopy (7900 ICP-MS) was used to measure mercury levels. A paired t-test was used to compare the means of the levels of mercury in groundwater obtained within the two seasons. The study established that during the dry season, all of the boreholes had groundwater mercury levels higher than the recommended limit by KEBS of 0.001 mg/L. There was a decrease in the levels of mercury in groundwater as distances from the mine increased. However, during the wet season, all of the boreholes had mercury levels below the limit of detection. The study established a significant difference in the levels of mercury in groundwater between wet and dry seasons at a 95% confidence level. Mercury levels in soil tailings and pan-pond water were above the NEMA effluents discharge standards of 0.05 mg/kg and 0.05 mg/L, respectively, in the dry season. During the wet season, all pan-pond water achieved the recommended mercury level of NEMA effluent discharge limits, while the soil tailings had mercury levels above the recommended limit. This study recommends that there is a need to implement mine waste remediation. Communities near the mines continuously conduct groundwater heavy metal analysis during the dry season to protect their health

Fates of nutrients, bacteria community, and antibiotic resistance genes during membrane separation of biogas slurry at industrial scale

The swine wastewater was rich in nutrients, microbes, and antibiotic resistance genes (ARGs), thus the discharge without treatment could inevitably pose numerous harms to environment. Multistep membrane separation has been developed as a promising strategy to achieve nutrient recovery and harmful contaminants removing. Here, an integrated membrane separation system including ultrafiltration and reverse osmosis was used to treat the biogas slurry produced from swine wastewater, and samples were gathered from different points. Then, a series of physicochemical parameters were analyzed, and 16S rRNA gene amplicon sequencing and real-time qPCR was used to research the bacteria communities and the abundance of ARGs in each sample, respectively. Results showed that the integrated membrane filtration could reject most of conventional pollutants, and the final permeate, which has extremely low levels of nutrients and metal elements, could be reused to wash the piggery or meet the Chinese national discharge standard. Moreover, the membrane filtration also could reduce 99.99 % of the detected ARGs, and the bacterial abundance and diversity in the final permeate significantly decreased compared with the feed biogas slurry. Redundancy analysis and network analysis indicated that the size exclusion and the adaptation to the different water quality were the common driving forces for the variation of bacterial community and ARGs during the membrane separation processes. In addition, our results also revealed the variety of putative pathogen and abundance of ARGs except for nutrients in the reverse osmosis concentrate, thus further disinfection procedures should be implemented before resource utilization of the concentrate.

Research on Legal Risk Identification, Causes and Remedies for Prevention and Control in China’s Aquaculture Industry

Aquatic products fulfill the protein needs of people and play an important role in food safety. And aquaculture is prized for its high productivity, sustainability and environmental friendliness. Considering the importance of aquaculture, the legal risks exposed during the aquaculture process deserve attention in order to prevent them from hindering the development of the aquaculture industry. Through online research, literature analysis and practical communication, it is shown that the current legal risks with commonalities include land use violations, lack of legal documents, failure to meet tailing water criteria, unquarantined fry and misuse of prohibited agricultural pharmaceuticals through online research, literature analysis and practical communication. By analyzing the reasons for the formation of legal risks and combining the experiences in sustainable development of three major aquaculture countries, which are Korea, Norway and Chile, this paper provides targeted preventive remedies and suggestions for aquaculture operators, administrative parties, legislators and other parties on legal risks. It includes promoting the improvement of the rule of law in multiple aspects, clarifying the positioning of the aquatic breeding certificates, improving and propagating the standards for wastewater discharge, increasing the self-sufficiency rate of aquatic fry and fingerlings, as well as making use of the synergy of soft law and hard law.

Hydraulic circulation technology remediates the contaminated groundwater with petroleum hydrocarbon: Evidence from laboratory and field tests

Removal of contaminants in groundwater in situ conditions is still a challenging problem, with tailing and rebound issues occurring. This study presents a systematic in-situ remediation case by hydraulic circulation in petroleum hydrocarbon-contaminated groundwater in a historically industrial-used site in China. Lab-scale experiments of soil column leaching and in-situ remediation trials were conducted to show the effectiveness of this technology. It has been found that through regulation and optimization of operational measures in five stages, the clean-up goal (1140 μg/L) of the targeted contaminant in groundwater based on the former risk assessment of human health and the intervention value (600 μg/L) in the ‘Dutch Target and Intervention Values (2000)’ were both achieved, and the tailing rebound effect of traditional pump-and-treatment technology was well solved. The combination of groundwater monitoring by ways of pumping pipelines and groundwater monitoring wells could enable workers to timely and effectively grasp the temporal and spatial dynamic variation of pollutants in groundwater in response to the restoration activities, which played an important role in improving the pertinence of pumping-and-injection measures and efficiency of the hydraulic circulation. Discharge standards of wastewater can be reached after being treated with the mass content of added coagulants (Ferrous sulfate) reaching 0.4 g/L and adsorbents (activated carbon) reaching 0.2 g/L. The results demonstrated that it is feasible to conduct in-situ remediation of the contaminated groundwater through hydraulic circulation based on pumping and injection measures and process-monitoring activities, with a competitive operating cost of approximately Rmb 23/m³ and a measured GHG emissions level of 7.12 kg CO2-eq/m³. Overall, the results in this study provide a useful reference case for the realistic remediation of similar sites.

Construction and operation characteristics of a fully quantified low-carbon treatment process for old landfill leachate

The feasibility of utilizing a coagulation-flocculation/sedimentation-denitrification (DN)/partial nitrification (PN)-anaerobic ammonium oxidation (Anammox)-electrochemical oxidation was investigated to achieve cost-effective and fully quantified treatment of leachate from old landfills, which contains lower C/N, higher NH4+-N and refractory chemical oxygen demand (CODr). The results indicated that the coagulation-flocculation/sedimentation, which aimed to remove the CODr, not only improved the nitrogen conversion efficiencies of the following PN and Anammox by 17.5 % and 105 %, respectively, but also benefited the solid phase enrichment of PO43− and the energy consumption of subsequent advanced treatment. The optimal dose of perfluorochemical (PFC) was found to be 1200 mg/L. The optimal electrode plate spacing and current density of the electrochemical oxidation process were 25 mm and 350 A/m2, respectively, and advanced treatment of the chemical oxygen demand (COD) and total nitrogen (TN) in the wastewater was achieved within 2 h. After 190 d of operation, the effluent quality met the required discharge standards. This process has the advantage of realizing full quantified treatment of wastewater and has significant environmental benefits.

Study on the removal of iron (II) and manganese (II) in acidic mine drainage by red mud: Performance and mechanism.

Red mud is an environmental burden during the alumina production process. To mitigate the hazards associated with red mud storage, this study investigated the utilization of alkaline red mud as a treatment agent for acidic mine drainage (AMD) with high concentrations of Fe(II) and Mn(II). This study explored the influence of reaction times, addition amounts of red mud, and pH values on the removal efficiency of Fe (II) and Mn(II) from high-concentration AMD. Various parameters such as suspended solids levels, effluent pH, and zeta potentials were measured to meet discharge standards. The adsorption mechanism of red mud was examined using SEM, XRD, EDX, XPS, and 3D-EEM analysis. Optimal conditions were determined as a reaction time of 2 h, pH value of 5.01 and the addition of 100 g/L red mud, achieving effective removal of Fe(II) (reduced from 1000 to 0.224 mg/L) and Mn (II) (reduced from 20 to 1.03 mg/L). The treated AMD meets discharge standards with reduced suspended matter content of 37.4 mg/L. These findings provided valuable insights for the utilization of red mud waste in engineering applications.

A novel approach to treating nickel-containing electroplating sludge by solidification with basic metallurgical solid waste

Nickel-containing electroplating sludge is a solid waste generated during the treatment of electroplating wastewater, often managed through solidification with materials such as cement and lime. This paper presents a novel approach for solidifying nickel-containing electroplating sludge using basic metallurgical solid waste. A mathematical model was employed to determine the kinetics of Ni2+ leaching, yielding the kinetic equation α(t) = 0.97∗(1-exp (-0.19∗t)). Rapid leaching occurred in the initial 10 min, reaching a concentration of 86.78 mg/L, followed by a slower release, peaking at 104.54 mg/L within 40 min. Through the solidification of electroplating sludge with basic waste materials, it was found that the inclusion of 2.0 % lime, 12.2 % sintering dust, and 2.5 % steel slag resulted in Ni2+ leaching concentrations of 0.28, 0.41, and 0.61 mg/L, respectively, all meeting the discharge standard of <1.00 mg/L. Phase analysis indicated that the main constituents of the solidified products were C–S–H and CaSO4, with no detectable change in the crystallinity of Ni2+ before and after solidification. Thermodynamic calculations further demonstrated that under basic solidification conditions, Ni2+ transforms from NiSO4 to Ni(OH)2. Microscopic morphology analysis revealed that the encapsulation of Ni2+ by C–S–H and CaSO4 led to the densification of the porous microstructure of the electroplating sludge, achieving effective solidification.

Multi-Walled Carbon Nanotubes Modified NiCo2S4 for the Efficient Photocatalytic Reduction of Hexavalent Chromium

Hexavalent chromium (Cr(VI)) compounds are considered to be occupational carcinogens, which can be transferred from the environment to the human body and pose a significant threat to human health. It is particularly urgent to explore a more efficient catalyst for removing Cr(VI) to comply with discharge standards. The addition of CNTs enables the separation and transfer of photogenerated charges. Thus, we synthesized a range of NiCo2S4 hybrid materials with different multi-walled carbon nanotube (MWCNTs) contents using a two-step hydrothermal method. The composites had significant advantages compared to pure NiCo2S4, such as an enhanced visible light absorption, increased specific surface area, high electron–hole pair separation, and fast electron transport. Thus, MWCNT addition enabled efficient photocatalytic performances in terms of reducing hexavalent chromium (Cr(VI)). Among all the composite samples, the MWCNT/NiCo2S4 with 0.050 g of MWCNTs achieved the highest efficiency in reducing Cr(VI) under light irradiation, which showed a removal rate close to 100% within 40 min. Such CNT-based composite photocatalysts could be used to reduce the highly toxic Cr(VI) in environmental applications.

Improved reduction efficiency, cycling performance, and removal rate of hexavalent chromium by adding water-soluble salts.

Recently, the reaction speed and cycle performance of hexavalent chromium reduction over microsized zero-valent iron (ZVI) with an Fe0 core and iron oxide (FeOx) shell structure have been improved by activating the Fe0-core electrons through electromagnetic coupling between Fe0-core electrons and charges (hexavalent chromium in solution, double-charge layers of the ZVI/solution interface). Herein, the abovementioned electromagnetic coupling was greatly increased by adding salt (CH3COONa, NaCl, NaNO3, and Na2SO4) in the hexavalent chromium solution to increase the charge response. Adding salt greatly improved the reaction speed and cycle performance of hexavalent chromium reduction. It took 8 min to reduce hexavalent chromium with CH3COONa to below the discharge standard of wastewater in the first cycle and 20 min after reducing for 20 cycles. The best apparent rate of constant value (0.416 (min)-1) is nearly four times larger than those without salts. X-ray diffraction and X-ray photoelectron spectroscopy revealed the production of amorphous iron oxide shell with salt. The salt improves the hexavalent chromium reduction speed and cycle performance and impedes the Fe0-core-electron transfer via the produced Fe2O3, resulting in existence of an optimized salt dosage. This work aims to provide an effective route for enhancing the removal efficiency and cycle performance of heavy-metal-ion reduction via Fe0. And this work also proposes a novel viewpoint that adding salt in waste water would increase the electromagnetic coupling between the charges in solution and Fe0-core electrons which could finally activate the redox reaction.

Efficient treatment of recalcitrant biologically treated coking wastewater using Cu-doped LaFeO3/peroxymonosulfate activator: Performance evaluation and response surface methodology modeling

Biologically treated coking wastewater (BTCW) frequently contains many kinds of refractory and toxic organic pollutants, which is far from meeting the discharge standard of GB16171–2012. In the present work, the peroxymonosulfate (PMS) activation processes via Cu-doped LaFeO3 (LFC) prepared with Bis (hexamethylene triaminepenta(methylenephosphonic acid) (BHMTMP) as the complexing agent was first utilized to degrade BTCW. The degradation reaction rate constant (kobs) of LaFe0.5Cu0.5O3 (LFC5)/PMS for CODCr and NH3-N was 3.65 times and 3.63 times for LFO (LaFeO3)/PMS. Moreover, the kobs of LFC5/PMS system prepared using BHMTMP as the complexing agent surpassed that of the LFCC/PMS system prepared with citric acid (CA) as the complexing agent, and the former was 2.3 times and 1.8 times greater than that of the latter for the removal of CODCr and NH3-N, respectively. The leaching of Cu and Fe of LFC5 was much less than that of LFCC, the strong chelation performance of BHMTMP with various metal ions can greatly reduce the leaching of metal ions and improve the stability of the catalyst. Hydroxyl radicals, sulfate radicals, and singlet oxygen were generated in the LFC5/PMS system, with singlet oxygen playing a dominant role. HPLC, UV absorption spectra, and 3D-EEM fluorescence spectra were used to analyze pollutant components in BTCW before and after degradation, demonstrating the effective removal of certain residual contaminants. In addition, the degradation process of BTCW was modeled using a 3-factor-3-level Response Surface Methodology (RSM) model. RSM model fitted the true experimental results well. This research offers a new approach for the comprehensive treatment of BTCW to meet standard discharge requirements and promote a more cost-effective operating process.

Treatability of high-strength real sheep slaughterhouse wastewater using struvite precipitation coupled Fenton's oxidation: The MAPFOX process

Struvite (MAP, magnesium ammonium phosphate hexahydrate, MgNH4PO4.6H2O) precipitation-aided Fenton's OXidation (MAPFOX process) was explored in the treatment of high-strength real sheep slaughterhouse wastewater (RSSW) for the first time under a comprehensive soft-computing-based modeling study. The experimental results showed that under the highest-efficiency conditions (chemical combination of MgCl2.6H2O + NaH2PO4.2H2O, a molar ratio of Mg2+:NH4+-N:PO43–P = 1.2:1:1, a reaction pH of 9.0 ± 0.10, [NH4+-N]0 = 240 ± 20 mg/L, and a reaction time of 15 min), MAP precipitation could effectively remove more than 80 %, 60 %, 55 %, and 70 % of color, total chemical oxygen demand (TCOD), soluble COD (SCOD), and ammonium nitrogen (NH4+-N) from the raw RSSW. The results of the Fenton's oxidation used as the post-treatment unit of the proposed MAPFOX system indicated that the integrated advanced oxidation process (AOP) was able to reduce the residual pollutant levels in the MAP-pretreated RSSW to the relevant discharge standards. Under the subsequent condition of [Fe2+]0 = 90 mmol/L, [H2O2]0 = 180 mmol/L, reaction pH = 3.25, and total reaction time = 60 min, more than 97 % of color, TCOD, SCOD, and NH4+-N could be removed from the RSSW via the Fenton's oxidation after the MAP-based physicochemical treatment. According to SEM micrographs, surface morphology of dehydrated struvite exhibited irregular-shaped and overlapping sharp-edged particles of various sizes with an average size of about 50.9 μm. The Fourier Transform Infrared (FTIR) spectroscopy confirmed the active functional groups and type of bonds for the high-strength RSSW-oriented struvite (heated) within the spectral range of 4000–450 cm−1. Thermogravimetric Analysis (TGA), Derivative Thermogravimetry (DTG), Differential Thermal Analysis (DTA), and Differential Scanning Calorimetry (DSC) of the dehydrated struvite revealed that the weight loss occurred in three temperature zones, the maximum weight loss rate of 0.252 mg/min was recorded at around 224 °C and at time of 20.83 min, and the sample had strong endothermic and medium exothermic peaks at about 241 °C and 679 °C, respectively. The predictive successes of the implemented soft-computing approaches were benchmarked in terms of various statistical goodness-of-fit parameters. The performance assessment indices corroborated the superiority of the support vector machines-Pearson VII universal kernel function (SVM-PUKF)-based model (correlation coefficient (CC) = 0.9999–1.0000), mean absolute error (MAE) = 0.0222–0.0389 %, mean absolute percentage error (MAPE) = 0.0270–0.0506 %, root mean squared error (RMSE) = 0.0258–0.0415 %, coefficient of variation of RMSE (CV(RMSE) = 0.0003–0.0008, Nash–Sutcliffe efficiency (NSE) = 0.9998–1.000, Legates and McCabe's index (LMI) = 0.9894–0.9952) over other data-intelligent models in predicting the pollutant removal efficiencies. The computational results also indicated that the narrowest uncertainty bands (±1.96Se = 0.0537–0.1483 %) and the lowest amounts of expanded uncertainty (U95 = 3.1224–5.3124 %) values for all efficiency sets were achieved for the applied SVM-PUKF-based strategy. This study demonstrated the first-ever and successful application of the proposed MAPFOX process in treatability of the RSSW and capability of the implemented soft-computing strategy in modeling a highly nonlinear treatment system.

Insights into simultaneous adsorption of orthophosphate (PO43−) and 1-hydroxyethane 1,1-diphosphonic acid (HEDP) by kaolin/lanthanum carbonate composites: Experimental analysis and DFT calculations

Orthophosphate and phosphonate often co-exist in industrial wastewater, and it is a challenge to remove the above inorganic and organic phosphorus simultaneously to meet the stringent total phosphorus (TP) discharge standard. The kaolin-based lanthanum carbonate (LC) composites have been demonstrated to decontaminate TP (PO43− and HEDP) from reverse osmosis (RO) concentrate effectively, while the individual and simultaneous adsorption behavior and mechanisms are still not clear. In this study, the individual and simultaneous PO43− and HEDP adsorption were compared. The adsorption kinetics, isotherms, initial pH and matrix effects were performed. The results showed that PO43− exhibited a nice adsorption performance, and was severely suppressed in the presence of HEDP. The maximum adsorption capacities were obtained at initial pH of 4.0, and the co-existing Ca2+ significantly enhanced both PO43− and HEDP removal, while HCO3−/CO32− markedly interfered with their adsorption process. LaCO3OH was the main composition in the composites for PO43− and HEDP adsorption, and no La-P compounds formed after adsorption. A variety of characterization methods were adopted to explore the adsorption mechanisms, and electrostatic attraction, inner-sphere complexation and hydrogen bond were responsible for PO43− and HEDP adsorption. The density functional theory (DFT) calculations were applied to distinguish the PO43− and HEDP adsorption from the molecular level, and the binuclear bidentate complexation configuration of H2HEDP2− species (H2HEDP-BB) with higher adsorption energy (-165.42 KJ/mol) resulted in the predominant species of HEDP in the competitive adsorption. In the fixed-bed column experiments, both PO43− and HEDP adsorption performance also matched the results of batch experiments and DFT calculations. This study provides insights into the competitive adsorption of orthophosphate and phosphonate by LC-based adsorbent.

Treatment technology of shale gas fracturing flowback fluid: a mini review

Shale gas fracturing flowback fluid, characterized by its large volume, complex composition, and potential adverse environmental impacts, has gradually become one of the problems affecting the large-scale development of shale gas resources. Failure to effectively address the treatment of fracturing flowback fluid will severely constrain shale gas development. This paper focuses on the treatment technologies for shale gas fracturing flowback fluid, discussing its water quality characteristics and summarizing the research progress in physical technology, chemical technology, biological technology, and combined technology. Development recommendations are also provided. The results show that shale gas fracturing flowback fluid exhibits characteristics such as complex composition, high viscosity, and high emulsification, and difficult to treat. Individual physical technology, chemical technology, or biological technology is effective in removing certain pollutants from the flowback fluid. Moreover, the combined use of these treatment technologies prove more effective in achieving reuse or discharge standards. With the continuous expansion of shale gas development and increasingly stringent environmental protection requirements worldwide, the volume of flowback fluid requiring treatment is continuously rising. By developing energy-efficient and emission-reduction treatment technologies, and actively recycling and utilizing resources and energy, and adopting clean fracturing fluid system, efficient, energy-saving, environmentally friendly, and economically viable treatment for shale gas fracturing flowback fluid can be achieved.