Wastewater Discharge Limits Research Articles

Removal of heavy metals from mine water using a hybrid electrocoagulation-ceramic membrane filtration process

Mining operations must account for increasingly stringent wastewater discharge limits for various contaminants, such as heavy metals and suspended solids. In the treatment of metal-bearing wastes, electrochemical processes, including electrocoagulation (EC), are gaining popularity. At large scales, EC processes can be hindered by considerable amounts of flocculants and by sedimentation tank sizes required to properly operate. This work sought to address these concerns by evaluating EC in mine water treatment using a pilot system coupled with ceramic membrane microfiltration (MF) and ultrafiltration (UF). The use of MF and UF after EC allows for the removal of suspended solids without needing a flocculation-sedimentation process. EC evaluation was performed using field samples of mine water from a North American concentrator. Under optimal conditions, EC removed over 95 % of Cr, Co, Cu, Fe, Mn, Ni, Pb, Ti and Zn from the mine water. Effluent from EC was used as feed in MF and UF processes with ceramic membranes. The tested membranes rejected 100 % of suspended solids from the EC effluent. Permeate from the membranes was free of solids and possessed turbidities of 0.05–0.15 NTU. Filtrate from the hybrid process satisfied environmental regulations for heavy metal concentrations, offering new opportunities for reuse or discharge. The hybrid process applied in this work can thus be used in mining operations to safely discharge their water, and/or to increase their water recirculation due to environmental concerns and water shortage.

Towards sustainable water management for Galdieria sulphuraria cultivation

The red microalga Galdieria sulphuraria has emerged as a promising biotechnological platform for large-scale cultivation and production of high-value compounds, such as the blue pigment phycocyanin. However, a large amount of freshwater and a substantial supply of nutrients challenge both the environmental and the economic sustainability of algal cultivation. Additionally, the extremophilic nature of Galdieria sulphuraria requires cultivation in an acidic culture medium that directly leads to strongly acidic wastewater, which in turn generally exceeds legal limits for industrial wastewater discharge. This research aims to address these challenges, by investigating cultivation water reuse as a strategy to reduce the impacts of Galdieria sulphuraria management. The results indicated that a 25 % water reuse may be easily implemented and showed to be effective at the pilot scale, providing no significant changes in microalgae growth (biomass productivity ~0.21 g L−1 d−1) or in phycocyanin accumulation (~ 10.8 % w/w) after three consecutive cultivation cycles in reused water. Moreover, a single cultivation cycle with water reuse percentages of 71 and 98 %, achieved with membrane filtration and with centrifugation, respectively, was also successful (biomass productivity ~0.24 g L−1 d−1). These findings encourage freshwater reuse implementations in the microalgae sector and support further investigations focusing on coupling cultivation and harvesting in continuous, real-scale configurations. Centrifugation and membrane filtration required substantially different specific electrical energy consumption for water reuse and biomass concentration: in real applications, the former technique would roughly span from 1 to 10 kWh m−3 while the latter is expected to fall within the ample range 0.1–100 kWh m−3, strongly dependent on system size. For this reason, the most suitable separation train should be chosen on a case-by-case basis, considering the prevailing flow rate and the target biomass concentration factor targeted by the separation process.

Evaluation of batch and fed-batch rotating drum biological contactor using immobilized Trametes hirsuta EDN082 for non-sterile real textile wastewater treatment

White rot fungi, in both free and immobilized forms, excel in degrading dyes through adsorption and enzyme degradation. However, existing studies often focus on synthetic wastewater within sterile lab conditions. This study extends the application of Trametes hirsuta EDN082 immobilized in light-expanded clay aggregates (myco-LECAs) packed in a rotating drum biological contactor (RDBC) for treating real textile wastewater under non-sterile conditions to simulate industrial treatment scenarios. Experiments included batch and fed-batch RDBC to assess the impact of additional glucose and stepwise dilution on quality indicators like pH, chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), color, and solids. In fed-batch RDBC with 0.5 % additional glucose, myco-LECAs achieved a maximum of 94 % COD removal (day 15), 99 % NH4+-N reduction (day 33), and 39 % decolorization without additional glucose. In comparison, myco-LECAs in batch RDBC highlighted 89 % NH4+-N reduction in 9 days without pH adjustment or additional nutrients. The pH maintained between 6−9, with no toxicity in Artemia salina, and 97−100 % removal of E. coli. Compared to Indonesian textile wastewater discharge limits, the technology achieved effective ammonia removal below 8 mg/L. This suggests that immobilized T. hirsuta EDN082 in LECAs presents a viable, non-sterile treatment for real textile wastewater.

Pondering performance of hybrid microfiltration and membrane distillation (MF-MD) process for purifying chromium-contaminated groundwater: Optimization, fouling control, and long-term operation

Nowadays, a hazardous compound such as Chromium (Cr) in groundwater is an emerging issue worldwide due to its environmental and health impacts. Membrane distillation (MD) is a promising technique to purify Chromium-contaminated groundwater (CCG). Assisted microfiltration (MF) is lodged to overcome a major problem in MD, specifically membrane fouling. In this work, a hybrid MF-MD process is proposed with fouling control incorporated into long-term operation. Derived from the results, mixed cellulose ester with 0.1 μm of pore size (MCE0.1) at 3-min ultrasonication cleaning is chosen as the optimal parameter in the MF process, because of superior flux recovery ratio (FRR) with negligible flux deficiency of approximately 10 %. Permeate flux and total suspended solids (TSS) rejection of MCE0.1 was achieved around 440 Lm−2h−1bar−1 and > 90 %, respectively. The optimized parameters in MD were selected accordingly: feed temperature of 80 °C, and feed and coolant flow rates at 4 L/min. Eventually, the long-term batch operation was executed by obtaining average flux and permeate conductivity was 7.5 LMH and around 10 μs/cm, respectively. The Cr concentration in permeate was relatively stable around 0.05 mg/L, which meets the wastewater discharge limit of 0.5 mg/L.

Analysis of nutrient loads, heavy metals and physicochemical properties of wastewater, wetland grass, and papaya samples: Gondar Malt factory, Ethiopia with global implication

Robust attention was brought to researchers due to deterioration of wastewater quality of lakes and reservoirs as major global concerns by industrial release. The uncontrolled releases of effluents impose serious impacts for both aquatic and terrestrial environments. In the current study, many parameters like nutrient loads, heavy metals and physicochemical properties of wastewater, wetland grass, and papaya samples were analysed. The investigated nutrients, alkalinity, and total hardness in fresh water samples were within the allowable limits except for phosphate in fresh wastewater and alkalinity in wastewater. The detected levels of heavy metals (mg/L) in wastewater samples were:- Cd (0.386–0.905), Cr (ND-0.074), Cu (0.064–0.096), Mn (0.184–1.528), Fe (0.167–4.636), Zn (0.175–0.333), and Pb (0.044–0.892) (mg/L). The studied metals in the wastewater sample, except Cd, Fe, and Pb were lower than the allowable limit. The level of heavy metals in the grass and papaya samples ranged from Cd (37.14–147.62), Cr (ND-8.82), Cu (3.14–8.33), Mn (2.89–85.46), Fe(5.0–65.15), Zn (3.44–36.84), and Pb (ND-60.36) (mg/kg). The detected metals were below the permissible limits, except Cd, Cr, and Pb. The findings of the physicochemical characteristics in wastewater samples were computed: pH (6.61–8.54), temperatures (21.63–26.57 °C), TDS (205.9–1896 mg/L), EC (359.9–3226.67 μs/cm), BOD (12.0–732.67 mg/L), COD (3.67–1691.33 mg/L). Except for temperature and pH, all levels in the wastewater were above the recommended limit for wastewater discharge by USEPA.

Improving Tannery Wastewater Treatments Using an Additional Microbial Treatment with a Bacterial-Fungal Consortium.

Environmental pollutants such as toxic heavy metals and oxygen-demanding solids are generated by leather manufacturing. In most tanneries, wastewaters are treated with physico-chemical methods but overly high levels of pollutants remain in surface waters. The efficiency of tanning wastewater treatment with conventional techniques was evaluated in four tanneries in Saudi Arabia. It was observed that the wastewaters contained high amounts of pollutants, needing further treatment. We isolated microorganisms from the wastewaters and carried out experiments to treat the effluents with different bacteria, fungi, and their consortia. We hypothesized that a consortium of microorganisms is more efficient than the single microorganisms in the consortium. The efficiency of five single bacterial and five fungal species from different genera was tested. In a consortium experiment, the efficiency of nine bacterial-fungal consortia was studied. The bacterium Corynebacterium glutamicum and the fungus Acremonium sp. were the most efficient in the single-microbe treatment. In the consortium treatment, the consortium of these two was the most efficient at treating the effluent. The factory wastewater treatment reduced total dissolved solids (TDS) from 1885 mg/L to 880 mg/L. C. glutamicum treatment reduced TDS to 150 mg/L and Acremonium sp. to 140 mg/L. The consortium of these two reduced TDS further to 80 mg/L. Moreover, the factory treatment reduced BOD from 943 mg/L to 440 mg/L, C. glutamicum to 75 mg/L, and Acremonium sp. 70 mg/L. The consortium reduced BOD further to 20 mg/L. The total heavy-metal concentration (Cd, Cr, Cu, Mn, and Pb) was reduced by the factory treatment from 43 μg/L to 26 μg/L and by the consortium to 0.2 μg/L. The collagen concentration that was studied using hydroxyproline assay decreased from 120 mg/L to 39 mg/L. It was shown that the consortium of the bacterium C. glutamicum and the fungus Acremonium sp. was more efficient in reducing the pollutants than the single species. The consortium reduced almost all parameters to below the environmental regulation limit for wastewater discharge to the environment in Saudi Arabia. The consortium should be studied further as an additional treatment to the existing conventional tannery wastewater treatments.

Influence of Various Accessories Upstream Large Water Meters

The focus of this study is on large flow meters, for which there is limited information due to their large size, making testing and research challenging. This research was conducted to quantify the effects of various accessories located upstream of these meters. Even a small percentage of variation in error can correspond to a significant volume of water. Accurate meters are crucial in many applications that involve large volumes of water as precise flow measurements are necessary for smooth and efficient processes while avoiding costly errors and downtime. Inaccurate large water meters can have far-reaching implications, such as overbilling or underbilling and production inefficiencies, which result in wasted resources and energy. Furthermore, inaccurate flow measurements can lead to environmental consequences as industries must comply with strict regulations regarding wastewater discharge limits. Uncertainty about the economic impact of an accessory installed upstream of a medium-sized water meter leads many water utilities to oversize the meter chambers to mitigate potential negative errors. In this study, six types of elements were tested upstream of ten brand-new water meters from six different manufacturers, constructed using four different metering technologies: single-jet, Woltmann, electromagnetic, and ultrasonic. Each meter unit was tested at five flow rates, ranging from the minimum to overload. The tests were conducted with accessories set in different orientations and distances upstream of the water meters under study. The research shows that the accessories used can cause significant deviations in measuring errors compared to the regular errors found under undisturbed working conditions.

Separation of butyl acetate and propyl acetate from wastewater by liquid-liquid extraction and molecular dynamics simulation

Pharmaceutical production processes produce ester-containing wastewater, and the concentration of esters must be reduced to a specific limit for wastewater discharge. Therefore, this study investigated a synthetic menthol eutectic solvent to separate the ester-water mixture and meet industrial discharge standards. A deep eutectic solvent (DES) composed of menthol as the hydrogen bond acceptor and lauric acid as the hydrogen bond donor in a molar ratio of 2:1 was synthesized to study the liquid–liquid extraction experiment by separating mixtures of water and propyl acetate (PA) and water and butyl acetate (BA) at 1 atm. In addition, a temperature range of 273.15–318.15 K was used to measure the influence of temperature on the experimental results within a 5 K interval. The experimental results indicated that the increase in temperature promoted the extraction efficiency of ester to some extent, but the fluctuation range was unclear. The DES had a high distribution coefficient (β) and selectivity (S) for ester, enabling a better separation of ester and water. Thereafter, molecular dynamics (MD) simulations were performed to ascertain the mechanism of the DES extraction of esters, and the molecular simulations were used to calculate the interaction energy, radial distribution function (RDF), spatial distribution function (SDF), and self-diffusion coefficient (D). The results of the MD simulations illustrated that menthol played an important role in the extraction process, and the hydrogen bond force between menthol and ester was the main force in the extraction process. Both BA and PA were effectively removed from the water by the DES. In general, the excellent extraction ability of the DES for esters was verified by experiments and simulation, which provides solid theoretical support for ester separations in other fields.

Environmental impacts of an unlined municipal solid waste landfill on groundwater and surface water quality in Ibadan, Nigeria.

Environmental and public health concerns grow on the interaction of municipal solid waste (MSW) leachates from unlined waste disposal sites with aquifers in many developing countries. This study investigated the environmental pollution impacts of an unlined MSW landfill at Ajakanga area, Ibadan, southwest Nigeria. Analytical studies indicated that the concentrations of NO3-, SO42-, PO43-, NH4-, Cl-, Na, Fe, Mn, Cr, and Mo in the leachate samples exceeded the WHO wastewater discharge limits. Hydrochemical parameters of the groundwater and surface water were within WHO allowable thresholds, except for EC, TDS, Fe, Mn, and Pb in the groundwater and Pb, Cd, and Cu in the surface water, indicating major geogenic and minor MSW leachate impacts on the groundwater and surface water chemistry. Bacteria found in the leachate include Enterobacter cloacae (16.67%), Pseudomonas spp. (14.28%) and Bacillus spp. (9.52%). The geoelectrical imaging data indicated substratum leachate infiltration greater than 10m deep, which is consistent with the low resistivity values of the topsoil-weathered basement layers. The health risk assessment showed high hazardous index values, indicating health risks of Mn, Cd and Pb in the surface water for the residents around Ajakanga landfill. Hydrochemical data indicated greater impact of the MSW leachates on the surface water than the groundwater, while geophysical data showed greater propensity of the surrounding aquifer to leachate interaction through fractured basement zone with increasing abstraction. Waste site closure and hydrochemical monitoring are suggested measures to mitigate environmental pollution in the study area.

Evaluation of the treatment performance and reuse potential in agriculture of organized industrial zone (OIZ) wastewater through an innovative vermifiltration approach

Vermifiltration (VF) is a natural and sustainable biofilter that has many advantages, including being energy-free, cost-effective, and allowing ease of application and maintenance. In this study, the effectiveness of a lab-scale VF system was assessed by the removal efficiency of total suspended solids, electrical conductivity, chemical oxygen demand, total nitrogen, total phosphorus, fecal coliform, and heavy metals in organized industrial zones (OIZ) and domestic wastewater (DW) for the first time. Additionally, the reuse suitability of the treated wastewater was determined by comparing different countries' and global irrigational criteria. The lab systems were built with four layers: one worm-bed and three varying filtering materials, and operated at an optimum hydraulic loading rate of 1.8–2 m3/m2/day for 45 days with Eisenia fetida as the earthworm species. The results demonstrated that removal efficiencies of total suspended solids and chemical oxygen demand were found to be 95% and 80% in OIZ wastewater and 90% and 88% in DW, respectively. Total nitrogen and total phosphorus were removed at rates of 69% and 67% in OIZ wastewater, respectively, and 84% and 74% in DW. Besides, the VF system has shown satisfactory removal performance for heavy metals ranging from 51% to 77% in OIZ wastewater that has met Turkish national wastewater discharge limits. Although the final characterization of treated wastewater was suitable, heavy metal and fecal coliform levels have not met many countries' irrigation water quality criteria. To meet global irrigation standards and to enhance the VF performance, further experimental studies should be carried out, including parameters such as bed material type in the reactor, worm type, and different operating conditions.

Screening and identification of some selected fungi species from Abattior waste water

This study was carried out to screen and identify some selected fungi species from abattoir waste water in Makurdi metropolis. Abattoirs Waste water samples were collected from different locations which include Modern Market, Wadata, Wurukum, North bank, new bridge. The samples were transported to the Microbiology laboratory, Federal University of Agriculture, Makurdi. Standard microbiological tests were carried out to identify the organisms from abattoir waste water. The fungi species identified were, Aspergillus spp, Mucor, Absidia, Fusaruim, Rhizopus spp, Saccharomyces. Rhizopus and Mucor spp had the highest prevalence accounting for 21.05%, while Fusaruim spp had the lowest prevalence accounting for 10.52%. From the statistical analysis using ANOVA, there was significant difference between the colony counts in the different locations. Wurukum had the highest fungi count (20.40± 3.20 CFU/ml), followed by Wadata market (18.40± 9.62 CFU/ml), New bridge had the lowest fungi count of (8.20 ± 8.49 CFU/ml). The Physicochemical characteristics of abattoir waste water. Physicochemical analysis of waste water from abattoir shows that the temperature of wastewater ranges from 28.9°C to 29.8°C. The temperature was within the limit for wastewater discharge of <40°. The pH of the wastewater was near neutral (8.0-9.4), which plays a major role in determining the qualitative and quantitative abundance of microorganisms in the wastewater. From the findings of this study, it is recommended that there is need for regulatory authorities to enforce strict compliance to environmental safety rules.

Analyzing greenhouse gas emissions from municipal wastewater treatment plants using pollutants parameter normalizing method：a case study of Beijing

Wastewater treatment plants (WWTPs) contribute increasing amounts of greenhouse gases (GHGs), due to rapid development and increasingly stringent wastewater discharge limits in China. In this study, GHG emissions from 38 WWTPs in Beijing were estimated using the pollutants parameter normalizing method (PPNM) and the effects of various factors were analyzed. The result showed that, the total GHG emissions of Beijing WWTPs in 2017 were 1 045 661.5 t CO2-eq (tons of CO2-equivalent), the direct and indirect emissions were 186 366.0 and 859 295.5 t CO2-eq, respectively. The average emission intensity was 0.603 kg CO2-eq/m3. Direct and indirect GHG emissions were influenced by various factors, such as treatment process, influent parameters and treatment scale. The anaerobic-anoxic-oxic (AAO) process demonstrated low emission intensities (0.092 kg CO2/m3), while biofilm processes (MBBR) obtained relatively high emission intensities (0.277 kg CO2/m3). Direct GHG emission has a positive correlation with the amount of pollutant removed and low influent pollutant concentrations (chemical oxygen demand [COD]<300 mg/L and total nitrogen [TN] <20 mg/L) can lead to high indirect GHG emission intensities. The low power utilization efficiency of small-scale WWTPs (<1 × 107 t/a; 6.60 kWh/kg COD; 30.54 kWh/kg TN) contributed to additional GHG emissions. Compared with the GHG emissions in Shanghai in 2016, higher influent pollutant concentrations and stricter discharge limits contributed to higher GHG emission intensity in Beijing for both direct (0.108 kg CO2/m3) and indirect (0.496 kg CO2/m3) emissions. The comparison results between cities indicated that the PPNM method achieved a more accurate account of GHG emissions, and the analysis results provided support for carbon emission reduction.

Assessment of the Pollution Load of Effluents Discharged from Higher Institutions in Ethiopia: The Case of Bahir Dar University Zenzelma Campus.

Waste from industries, universities, and other institutions makes water a scarce resource. Although higher institutions have an honorable and principled responsibility to the environment, most higher institutions are not performing sensibly; they discharge untreated solid and liquid wastes into the environment. The objective of this study was, thus, to assess the pollution load of effluents from Bahir Dar University Zenzelma campus, Ethiopia. Wastewater samples were collected and analyzed for physicochemical and biological qualities and heavy metal levels. The phosphate (17.2–216.17 mg/L), BOD5 (51–86 mg/L), ammonia (0.02–10.29 mg/L), turbidity (22–580 NTU), total suspended solids (230–1293.33 mg/L), electrical conductivity (241–1492.03 μS/cm), and total hardness (111.67–490 mg/L) levels surpassed the wastewater discharge limit stated by WHO, environmental protection authority, Compulsory Ethiopian Standard, and Environmental Health and Safety guidelines and did not fit wastewater reuse standard for irrigation and livestock drinking. 100% of the samples were not fit for livestock drinking as the coliform bacterium count exceeded the threshold level. Copper (0.006–1.75 mg/L), lead (0.019–0.18 mg/L), and cadmium (0.007–0.196 mg/L) levels crossed the wastewater discharge limit and were not fit for irrigation and livestock drinking, while the level of manganese (nill–0.01 mg/L) was under the threshold limit. Values of the water quality parameters were higher on the downstream site than at the upstream site showing the pollution load of Zenzelma campus effluents on the local environment (Ch'imbil River); wastewater used for irrigation and livestock drinking is unsafe. Thus, it requires immediate waste management interventions and appropriate waste treatment before being released into the environment.

Utilization of natural polysaccharide from Tamarindus indica L. seeds for the effective reduction of pollutants in cheese processed wastewater

The present study was targeted to treat the cheese factory processed wastewater by using natural coagulants. The results were compared with the CPCB wastewater discharge limit and most of the parameters were exceeded the standard limit. In the present investigation, the processed wastewater was subjected to treatment with Tamarindus indica L. plant seed as a coagulating agent. The processed wastewater was treated with Tamarindus indica L. seed powder which is rich in polysaccharides. The proximate analysis confirmed the presence of higher content of carbohydrates, protein, and fiber. Different dosages were used for the treatment. Accurately 0.4 gm was recorded as optimum dosage for the effective removal of pollutants includes 71% of TDS and 75% of COD from the cheese processed wastewater. The GC-MS analysis of raw and treated cheese processed wastewater was carried out and the results showed the degradation of toxic compounds and reduction of pollutants from the processed wastewater. FTIR analysis of T.indica L. seed powder disclosed various chemical group presence and proved higher efficiency in seed treatment.

The Influence of Internal Monitoring on Compliance with Effluent Limits

Using unique data on chemical manufacturing facilities regulated under the Clean Water Act (CWA), this paper analyzes the effect of one particular environmental management practice — internal monitoring — on regulated facilities’ compliance with wastewater discharge limits. To deepen our understanding of the role played by internal monitoring, we extend our analysis by exploring the interaction between internal monitoring and self-audits, which should share a similar purpose to internal monitoring by providing systematic information to regulated facilities on their pollution abatement efforts. Baseline empirical results robustly demonstrate that increases in the extent of internal monitoring significantly improve facilities’ environmental compliance. The extended empirical results offer moderate evidence that audits complement internal monitoring (and vice versa): as facilities audit more frequently, the productive effect of increased internal monitoring grows.

Managing water sustainability in textile industry through adaptive multiple stakeholder collaboration

Textile manufacturing poses pressing challenges on water sustainability characterized by intensive chemical consumption and waterborne pollution. Industrial clustering is a hallmark of textile industry development, featuring a two-stage wastewater treatment system consisting of in-plant and centralized treatment facilities. Driven by increasingly stringent wastewater discharge limits, three pillar stakeholders in textile industrial clusters, the local government, enterprises and environmental utility operators, seek for systematic countermeasures by balancing contradictory interests. This study presents a trilateral game model to uncover the economic and environmental tradeoffs among the three stakeholders targeting the optimization of wastewater systems. The model is solidified by a representative textile industrial cluster and is then extrapolated to 242 large-scale Chinese textile clusters to quantify the benefits. The key finds are (1) the in-use wastewater systems in many clusters function with low eco-efficiency; (2) the optimal paradigm is to adaptively leave room at half- to onefold for discharge limits from in-plant to centralized treatment facilities; (3) the environmental and economic benefits thereof are 24∼x223C61% and 6%, respectively, after retrofitting to the optimal paradigm for the Chinese textile clusters.

Fenton and photo-Fenton processes integrated with submerged ultrafiltration for the treatment of pulp and paper industry wastewater

Excessive amounts of wastewater produced by the paper industry, often containing a wide range of toxic and recalcitrant pollutants based on raw materials used, should be subjected to efficient treatment processes before discharging to the environment. This experimental work examined hybrid Fenton and photo-Fenton enhanced (UVC254 and UVA365) UF system performances in treating raw wastewater from pulp and paper industry by membrane oxidation reactor (MOR). By response surface analyses of Taguchi experimental design, the systems were compared onto hybrid efficiencies, in settings optimized for maximal responses with minimum chemical needs, regarding the performance metrics of TOC and COD removal efficiencies and UF water flux. Organics were removed slightly better than Fenton in both photo-Fenton, and H2O2 and Fe2+ spends per TOC were accomplished as more efficient than anticipated in every MOR system. Optimal TOC-COD removals were found as 64.0–74.9% by 85.2 L/m2h at Fenton system, and as 66.5–76.1% by 138.1 L/m2h at UVA-Fenton, while 69.7–82.1% by 90.0 L/m2h at UVC-Fenton with the lowest chemical spending. Hybrid MORs studied were at desirable operational costs of 2.11, 4.15 and 3.13 $/kg removed COD in Fenton, UVA-Fenton and UVC-Fenton systems, respectively, corresponding to the demineralisation costs of 0.0075–0.0143 $/g TOC removed. This study revealed that by synergistic MOR performances, effluents, after pH adjustment, are directly dischargeable in sewage infrastructure ending with complete treatment. In a near future, such innovative approaches towards industrial wastewater treatments, at less resource demands, will unambiguously gain importance, as pressures to reuse wastewater increase and discharge limits become stricter.

Effects of audit frequency, audit quality, and facility age on environmental compliance

ABSTRACT This study explores the effect of environmental self-audits (‘audits’), which represent an important type of environmental management system practice, on the extent of facilities’ compliance with wastewater discharge limits. Previous studies of environmental audits explore either the presence or frequency of audits only, while ignoring the quality of audits and heterogeneous effects across facility types. Our study contributes to the economic literature by examining the role of audit quality, as measured by the comprehensiveness of the audit protocol, and the influence of facility age on the effectiveness of more frequent auditing. These two features prove important especially in combination. Our study empirically examines the U.S. chemical manufacturing sector using survey and publicly available EPA data. Empirical results reveal that more frequent audits improve the extent of compliance but only for older facilities and only when these facilities conduct high quality audits. In contrast, for newer facilities, more frequent high quality audits fail to improve compliance; worse yet, more frequent low quality audits sadly undermine compliance. Both sets of results are consistent with our hypotheses.

The fate of heavy metals and salts during the wet treatment of municipal solid waste incineration bottom ash

Bottom ash contains unfavorable contaminants that could leach into the circulating water used for wet treatment, and its improper disposal of bottom ash could cause ecological pollution. This study was to discuss the partition of heavy metals and salts of bottom ash into circulating water and ash stockpile runoff in wet treatment plants in southern China. The leachability of bottom ash before and after the wet treatment was also investigated. The checked heavy metals Pb, Cu, and Ni and dissolved salts Cl− and SO42− show lower available fractions in leachate from the treated bottom ash than that in raw bottom ash. Circulating water is contaminated by target heavy metals, which the contents of Cu and Pb is higher than its limit for urban wastewater discharge. The circulating water owned the highest concentration of Cl− and SO42−, above10000 mg/L, and 1100 mg/L, which is far higher than the limits. The detected heavy metals, Cl− and SO42− in runoff also exceed the limits for urban wastewater discharge. Locations for bottom ash processing and storage sites should be selected to control and prevent any leaching and runoff impacts. Any runoff and circulation water should be discharged to the lined landfill’s leachate collection system or suitable industrial wastewater treatment facilities.

PH tunable anionic and cationic heavy metal reduction coupled adsorption by thiol cross-linked composite: Physicochemical interpretations and fixed-bed column mathematical model study

Over the past, extensive works executed to treat anionic and cationic heavy metal ions from wastewater. Although very few adsorbents were developed to adsorb anionic and cationic heavy metal ions from the same system. In this study, we explored the pH tunable complete reduction plus adsorption mechanism of Pb2+ and Cr2O72− by dithiocarbamate-based composite. The pH study recommended that; adsorption of Pb2+ occurred at pH 5.5, besides Cr2O72− reduction coupled adsorption executed at pH 3. Furthermore, quick adsorption occurred within 60 min with adsorption capacities of 228.69 and 219.75 mg g−1 for Pb2+ and Cr2O72−, respectively. Adsorption isotherm well described by the Redlich-Peterson model, also adsorption processes were fitted by pseudo-second-order kinetics model. Interestingly, characteristic techniques, a physical monolayer model and thermodynamic models were applied to the experimental results to further understand the adsorption mechanisms. The results indicated that the physical model with two types of interaction energies was more appropriate to interpret the adsorption mechanism. Based on the physical model, three thermodynamic functions were calculated and interpreted to attribute new macroscopic interpretations at the molecular level of the adsorption systems. Inspiringly, the metal-composite system highly effective for 5 regeneration cycles and fixed-bed column could decontaminate 17.2 L of ~10 mg L−1 Pb2+ and 7.3 L of ~10 mg L−1 Cr2O72− to the EPA’s wastewater discharge limit by 5 g of CSC@SDBC with the yielding of 400 and 346 mL of eluent, respectively. Theoretically, a liter of CSC@SDBC column may efficiently adsorb 145,646 mg of Pb2+ and 57,518 mg of Cr2O72− from industrial effluent, these were calculated from the Bohart-Adams model. These collective batch and fixed-bed systems were cost-effective and environmentally tolerable techniques to remove anionic and cationic heavy metal ions from industrial wastewater.