Discharge Standards Research Articles

Acute effects of antimony exposure on adult zebrafish (Danio rerio): From an oxidative stress and intestinal microbiota perspective

The rapid development of the textile industry has resulted in a large influx of wastewater production. The “national discharge standards of water pollutants for dyeing and finishing of textile industry (GB4287-2012)” stipulates that the discharge of total Sb from textile industry effluent must be < 0.10 mg/L, but it is difficult to meet the standard at present. Antimony is potentially carcinogenic, and the pathogenic mechanism of antimony is poorly understood. In this study, the acute toxic effects of various concentrations of antimony on adult zebrafish (Danio rerio) were investigated, including effects on oxidative stress, neurotransmitters and intestinal microbiota. The activities of catalase (CAT), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), superoxide dismutase (SOD), total antioxidant capacity (T-AOC) and acetylcholinesterase (AChE) were measured in zebrafish muscle and intestine tissue samples. In addition, intestinal microbial community composition and diversity of zebrafish were also analyzed. The results demonstrated that SOD, CAT and GSH-Px activities in the zebrafish gut showed a decreasing and then increasing trend with antimony concentration increasing. SOD, CAT and MDA in zebrafish muscle decreased with increasing exposure time. GSH-Px activities increased with increasing exposure time. T-AOC increased and then decreased. In addition, antimony exposure was neurotoxic to zebrafish, and a significant decrease in AChE activity was found in the intestine with increased exposure time. The neurotoxicity caused by antimony in the high concentration group (40 mg/L) was stronger than that in low concentration groups (10 mg/L and 20 mg/L). Notably, antimony exposure caused increases in the relative abundance of phyla Fusobacteriota and Actinomycetes, but decreases in the relative abundance of the phyla Firmicutes and Proteobacteria in zebrafish intestine. These outcomes will advance our understanding of antimony-induced biotoxicity, environmental problems, and health hazards. In conclusion, this study shows that acute exposure of antimony to zebrafish induces host oxidative stress and neurotoxicity, dysregulates the intestinal microbiota, showing adverse effects on the health and gut microbiota of zebrafish.

Mineralization of High-Concentration Aqueous Aniline by Hybrid Process

The efficient mineralization of high-concentration aqueous aniline (HCAA) is an issue needing to be resolved. In this study, a hybrid process of ozonation and electrochemical oxidation (ECO) was proposed for improving the mineralization of HCAA (1000 mg·L−1). The results indicated that chemical oxygen demand (COD) removal by the hybrid process was far greater than that of a single ozonation or ECO process, revealing that the hybrid process might avoid low efficiency in late ozonation and initial ECO. Thus, a subsequent combination effect clearly existed. In this hybrid process, ozonation stage time was selected as 60 min for optimal COD removal. The main products of the ozonation stage were maleic and succinic acids, with declining pH which was beneficial to the following ECO stage. Nitrite and nitrate formed during ozonation, which acted as electrolytes for the ECO stage, in which maleic and succinic acids were fully degraded and pH thus increased. Moreover, the aniline degradation mechanism of the hybrid process was deduced, demonstrating the superiority of this hybrid process. Finally, more than 95% COD removal was achieved, which met the COD limit requirement and achieved pH control simultaneously, according to the discharge standards of water pollutants for dyeing and finishing of the textile industry in China (GB 4287–2012).

A visible-light-driven photocatalytic fuel cell/peroxymonosulfate (PFC/PMS) system using blue TiO2 nanotube arrays (TNA) anode and Cu-Co-WO3 cathode for enhanced oxidation of organic pollutant and ammonium nitrogen in real seawater

Antibiotics (or pharmaceuticals) and inorganic nitrogen may coexist in mariculture wastewater, adversely affecting food safety and coastal ecology. Advanced treatment of marine wastewater is of great significance. In this study, simultaneous removal of refractory berberine chloride (BC) and ammonium nitrogen (NH4+-N) was firstly achieved in a visible-light-driven marine photocatalytic fuel cell/peroxymonosulfate (PFC/PMS) system. The modified blue TiO2 nanotube arrays (TNA) anode and Cu-Co-WO3 cathode bridged photo-electrocatalysis, sulfate radical-based oxidation and catalytic chlorination, benefiting both pollutant removal and fuel cell electricity generation. Under optimized conditions (double photoelectrodes, 2.5 mM PMS, R = 500 Ω), the system had an open circuit voltage of 0.57 V, removing 95% of BC and NH4+-N, meeting the discharge standard of mariculture. Natural-sourced CODMn, and inorganic nitrogen in simulated mariculture wastewater were also efficiently removed with power generation. The mechanism involving (photo-)electrocatalytic chlorination and PMS-chlorination theoretically supports the application/optimization of integrated electrochemical technologies for marine pollution control.

Calcium-modified granular attapulgite removed phosphorus from synthetic wastewater containing low-strength phosphorus

Traditional biological processes combined with chemical precipitation methods can effectively reduce phosphate concentration in wastewater. However, discharge standards required additional advanced treatment technologies, and the removal of low phosphorus concentration is complicated and expensive. This study proposes application of a simple and recyclable adsorbent to remove low-concentration phosphorus from water. The removal efficiency of phosphorus from low-strength synthetic wastewater was investigated and the adsorption mechanism was analyzed. When the initial phosphorus concentration was 2.0 mg/L, the phosphorus adsorption capacity of Ca-GAT increased to 0.891 mg/g from 0.074 mg/g for GAT at 298 K and pH of 7. Phosphorus adsorption on Ca-GAT performs well when the solution pH is in the range of 5–10, and it is not conducive to the adsorption reaction when the solution pH exceeds 11. The competing anions (such as NO3−, SO42−, HCO3− and F−) existed, Ca-GAT still performed better in removing phosphorus. Then, the saturated absorbents could be effectively regenerated with a 0.5 mos/L NaOH solution, while desorption efficiency was reduced from 97.11% to 33.06% after fifth regeneration cycle. Finally, Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the Ca2+ content on the Ca-GAT surface played an important role in capturing phosphate ions from wastewater. Phosphorus was mainly removed via the formation of Ca-phosphorus precipitation. To some extent, ligand exchanges of CO32− and OH- with HPO42− and H2PO4− were also beneficial for phosphorus removal. The present work shows that attapulgite has sustainable and beneficial potential in the removal of low-strength phosphorous in wastewater, and the phosphorus loaded adsorbent can be used in the agriculture as slow-release fertilizer.

Potential Impacts of Oil and Grease on Algae, Invertebrates and Fish in the Bujagali Hydropower Project Area

This study determined the concentration of oil and grease and inferred its impacts on algae, invertebrates and fish. Water samples were collected in April and September from 2012 to 2018 at the upstream and downstream transects and in the reservoir, and analysed for oil and grease following standard procedures. Environmental compliance was compared to NEMA’s discharge standard of 10 mg/l, and its PAH effluent discharge standard of ≤ 0.1 mg/l. At all sites, average concentrations of oil and grease were below 10 mg/l throughout the sampling period. Out of the 14 data sets for each transect, only 3 along the upstream transect, and 2 at each of the downstream transect and the reservoir were compliant with the effluent discharge standard. Although impacts of oil and grease on aquatic biota were not assessed, their relatively high concentration compared to total Polycyclic Aromatic Hydrocarbon (&gt; 0.1 µg/l) is considered hazardous to most aquatic organisms. The diverse activities around the project area implied that sources of oil and grease were proportionately diverse. Hence, the observed trends may not solely be attributed to the hydropower project. Accordingly, assessment of the various sources of oil and grease and their impact on aquatic biota in the area is recommended.

Cost of raising discharge standards: A plant-by-plant assessment from wastewater sector in China

China has implemented increasingly stringent effluent standards for wastewater treatment plants (WWTPs) to protect the aquatic environment, but at the cost of more resource consumption and greenhouse gas emissions. To elaborate tradeoffs between the elevated standard and the additional burden, we compile a 10-year inventory of 6032 WWTPs across China to estimate the impacts of changes in effluent pollutant concentration on operating costs and electricity consumption. Coupled with the increasing demand for wastewater treatment, upgrading standards to the Special Discharge Limit (SDL) by 2030 would increase electricity consumption and operating costs of the wastewater treatment sector by 86.59% and 70.44% compared to the status quo in 2015. The electricity consumption-induced GHG emissions would also increase by 72.21%, which accounts for 29.16% of total emissions in the domestic wastewater treatment sector. Substantial regional differences exist in terms of upgrade-induced resource burden. Less developed regions generally suffer more stress when encountering similar standards elevation. With large-scale microdata, our findings deepen the understanding of the potential cost of raising standards and provide insights into region-customized pollutant effluent standards implementation.

Efficient advanced treatment of coking wastewater using O3/H2O2/Fe-shavings process

Catalytic oxidation is widely used in the treatment of refractory wastewater. However, catalytic oxidation has some problems such as high cost and limited production of radicals. To improve these, in this study, a new process of O3/H2O2/Fe-shavings which coupled catalytic ozonation and Fenton-like oxidation with Fe-shaving wastes reused, was used in the treatment of coking wastewater secondary biochemical effluent (CWSBE). The effects of the environmental conditions on the degradation of CWSBE were studied and the response surface method was used to optimise the parameters. The performances in organic pollutant removal from CWSBE were systematically analysed by a couple of methods such as gas chromatography mass spectrometry and three-dimensional fluorescence. The results showed that macromolecular organics were degraded into small molecules pollutants after treatment by the O3/H2O2/Fe-shavings process. At an ozone concentration of 27.5 mg/L, with the hydrogen peroxide concentration being 10.7 mmol/L, the reaction time 60 min, the initial pH value 3.6, and the pump speed 150 rpm, the COD removal degradation efficiency was 77.5%, and the effluent COD met relevant wastewater discharge standards in China (GB 16171-2012). The mechanism research showed that·OH plays an important role in the degradation of organic pollutants.

Treatment of vegetable oil wastewater by a conventional activated sludge process coupled with electrocoagulation process.

The present work aims to study chemical oxygen demand (COD), oil-grease, and color removal from vegetable oil wastewater by combined electrocoagulation and activated sludge processes. For this purpose, the sample was pretreated using electrocoagulation by various optimization parameters such as electrode type (Al-Al and Fe-Fe), current density (100-400 A/m2 ), pH (2-8), and electrolysis time (15-180 min). The results showed that 89.3% of COD, 100% of oil-grease, and 66.2% of color were removed by electrocoagulation under the conditions of 300-A/m2 current density, pH 2, and 180-min reaction time with Al-Al electrode pairs. Then, the effluent of electrocoagulation was treated by an activated sludge process. The results depicted that the activated sludge process was also effective for vegetable oil wastewater treatment and it enhanced 98.9% COD and 79.2% color removal efficiency. The effluent of the combined process was very clear, and its quality exceeded the direct discharge standard of the water pollution control regulation. The laboratory-scale test results indicate that the combined electrocoagulation and activated sludge process is feasible for the treatment of vegetable oil wastewater. PRACTITIONER POINTS: Vegetable oil wastewater was treated by combination of electrocoagulation and activated sludge processes. The combined electrocoagulation and activated sludge processes supplied 99.9% COD, 100% oil-grease, and 93.0% color removal efficiency. The laboratory-scale test results indicate that the combined EC-SBR processes were feasible for the treatment of vegetable oil wastewater.

Nitrogen Advanced Treatment of Urban Sewage by Denitrification Deep-Bed Filter: Removal Performance and Metabolic Pathway.

This study aimed to explore the performance of denitrification deep-bed filter (DN-DBF) to treat municipal sewage for meeting a more stringent discharge standard of total nitrogen (TN) (10.0 mg L–1). A lab-scale DN-DBF was conducted to optimize operation parameters and reveal the microbiological mechanism for TN removal. The results showed that more than 12.7% TN removal was obtained by adding methanol compared with sodium acetate. The effluent TN concentration reached 6.0–7.0 mg L–1 with the optimal influent carbon and nitrogen ratio (C/N) and hydraulic retention time (HRT) (3:1 and 0.25 h). For the nitrogen removal mechanism, Blastocatellaceae_Subgroup_4 and norank_o_JG30-KF-CM45 were dominant denitrification floras with an abundance of 6–10%. Though large TN was removed at the top layer of DN-DBF, microbial richness and diversity at the middle layer were higher than both ends. However, the relative abundance of nitrite reductase enzymes (EC1.7.2.1) gradually increases as the depth increases; conversely, the relative abundance of nitrous oxide reductase gradually decreased.

Uranium removal from waste water of the tailings with functional recycled plastic membrane

Plastic pollution has become one of the most pressing environmental issues. Meanwhile, developing highly efficient adsorbents for uranium removal from the wastewater of its tailings is also of great significance in environmental protection. In this study, wastes of the plastic membrane in daily life were recycled and functionalized to treat uranium pollution in the environment. Membrane adsorbent with amidoxime (AO) group was successfully prepared using recycled plastic membranes through two-step polymerization. A network of nano-holes and nanostructured particles were observed on the surface of the AO modified membrane (AO-membrane) adsorbent. The adsorption performances from uranium solution and uranium tailings wastewater were evaluated in batch and column adsorption experiments. AO-membrane exhibited good removal performance in a wide pH range from 2 to 8. After adsorption in uranium tailings wastewater, the equilibrium concentrations of uranium in solution were lower than 50 μg/L, meeting the national standard of uranium solution discharge (50 μg/L). AO-membrane could reach adsorption equilibrium within 5 h in uranium tailings wastewater and present uranium removal ratio of nearly 100%. These indicated that this AO-membrane could be used for deep purification of wastewater, especially with low uranium concentration. AO-membrane exhibited a remarkable reuse performance and long service life. During the 10 cycles of adsorption and desorption, AO-membrane exhibited almost 100% uranium removal ratio even after ten adsorption and desorption cycles. This work provides new insights into the technology of waste control by waste.

Mechanism of Removal of Hexavalent Chromium from Aqueous Solution by Fe-Modified Biochar and Its Application

This study discussed the mechanism of Fe-modified biochar (FeBC) derived from rice straw biochar (BC) as an adsorbent for removing Cr(VI) from aqueous solution and assessed its applicability in actual industrial wastewater. The Cr(VI) removal percentage increased with the FeBC dose, which achieved a removal of 99.5% at 8.0 g/L FeBC. Increasing the solution pH from 2 to 10 slightly reduced Cr(VI) adsorption by 6.6%. Coexisting ions such as Ca2+, Na+ and Cl− inhibited the removal of Cr(VI); the removal rate decreased to 60% at their concentration of 0.25 mol/L. The adsorption isotherm and kinetics were better described by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Through scanning electron microscopy with energy dispersive X-ray, the Brunauer–Emmett–Teller method, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy, the analysis revealed that FeBC with iron oxides loaded onto its surface had more active sites than BC; the surface functional groups changed; the removal of Cr(VI) by FeBC was mainly attributed to electrostatic adsorption; the redox reaction of Cr, and Fe loaded onto BC enhanced Cr(VI) reduction process. FeBC showed a good removal performance on actual industrial wastewater with the concentration of both total Cr and Cr(VI) meeting the integrated wastewater discharge standard of China.

Study on the application and optimization of domestic sewage treatment demonstration based on a novel biofilter-constructed wetland coupling system

A novel biofilter-constructed wetland coupling system has been applied more than 160 domestic sewage treatment projects in different cities of Zhejiang province, China. The performance of a randomly selected project (flux rate was 27.0 m3/d) based on the coupling system was evaluated in long-term, and the effluent monitoring by big data analysis showed a relatively stable and good water quality. The effluent concentrations of CODCr, NH4+-N and TP were 37.57 ± 11.17 mg/L, 5.64 ± 1.69 mg/L and 0.82 ± 0.16 mg/L, respectively, which met the first-class of "Standards for Discharge of Water Pollutants from Rural Domestic Sewage Treatment Facilities" (DB33/973–2015). The concentrations of effluent TP showed a strong polynomial curve fitting with effluent NH4+-N concentrations (R2 = 0.9329) according to the big data analysis. Besides, the concentrations of effluent CODCr had a strong positive linear correlation with the concentrations of effluent NH4+-N (R2 = 0.9297), which increased with the increase of effluent TP concentrations (R2 = 0.6957). Results also showed pH ranged from 6.46 to 6.57, and C/N (CODCr/NH4+-N) had stronger correlation with pH (R2 = 0.6441), while the concentration of effluent NH4+-N and effluent TP had weak correlation with pH (R2 = 0.3348 and R2 = 0.4834, respectively). The findings might have very important guiding significance for the future monitoring methods of water effluent quality of treatment facility and the cost reduction of monitoring management. Moreover, a demonstration and experiments were carried out for a contrast study of the enhanced system (b) and original system (a). The removal efficiency of CODCr, NH4+-N and TP of the enhanced system (b) was 81.33, 90.22 and 75.44%, respectively, which increased by 4.33, 9.11 and 13.77%, respectively, compared to the original system (a).

Study of domestic wastewater treatment using Moringa oleifera coagulant coupled with vertical flow constructed wetland in Kibera Slum, Kenya.

The domestic wastewater collection and treatment rate of Nairobi, Kenya are not high. The wastewater in the Kibera slum on the outskirts of the city that is directly discharged to the environment and pollution of the surrounding water body is a serious problem. This paper takes the domestic wastewater in the slum area as the research objective and researches on the wastewater characteristics, collection, and treatment, therefore providing the reference for the wastewater collection and treatment technology in the region. In this paper, domestic wastewater in the Kibera slum of Nairobi was sampled and investigated to find out the characteristics of wastewater discharged, the way of discharge of the household wastewater, and the management in this area. The study shows that there are differences in the concentration of main pollutants such as nutrients and organic matter in the wastewater from the household discharged to the residential river in the slum area. The domestic wastewater in this slum area contained a high concentration of nutrients such as nitrogen and phosphorus and other organics, total suspended solids (TSS), total coliforms and color, and with no treatment methods. Therefore, economic and feasible treatment technology needs to be developed. A pilot study was conducted on the treatment of domestic wastewater in the slum area by combining the seed extract of the natural plant Moringa oleifera as a coagulant and vertical flow constructed wetland (VFCW) at Tongji University, Shanghai, China. The VFCW system was efficient in chemical oxygen demand (COD), TSS, turbidity, total phosphorus (TP), and phosphates (PO4-P) removal, but the removal efficiency of nitrogen (total nitrogen (TN), ammonium nitrogen (NH4-N), and nitrate (NO3-N)) was poor, and the effluent pH reached the required discharge country's standard of the water. The average removal efficiencies for COD (79.99%), TSS (86.84%), turbidity (87.35%), TP (61.29%), PO4-P (65.66%), TN (14.11%), NH4-N (18.17%), and NO3-N (93%) were achieved by the treatment system. Furthermore, the removal efficiencies of pollutants such as TP, PO4-P, TN, and NH4-N were carried out by using the fruit extract of Moringa oleifera as raw material and zeolite as an auxiliary agent. The comprehensive effect of zeolite combined with VFCW and natural coagulant in the treatment of domestic wastewater was investigated. The COD removal efficiency was increased by (9%). TN by (46%), NH4-N by (67%), TP by (19%), and turbidity improved by (9%). In short, the domestic wastewater in the Kibera slum was collected and pretreated with natural plant coagulant, and then purified by vertical flow constructed wetland, which can not only significantly reduce the pollutant concentration but also basically meet the discharge standards. It is a low-cost sewage treatment technology suitable for poor areas.

Determination and seasonal analysis of physicochemical characterization and metal(oid)s of landfill leachate in Bushehr port along the Persian Gulf

This study focused on the investigation of physicochemical characterization and metal(oid)s in landfill leachate of Bushehr port along the Persian Gulf. TDS, BOD5, COD, Hg, and Cd concentrations in fresh leachate were above leachate discharge standards. Significant differences were detected among alkalinity, EC, COD, and Na+ levels in various seasons. Furthermore, the high leachate pollution index (LPI) value showed a significant amount of pollutants present in landfill leachate. The results of this study help in understanding the pollution potential of landfill leachate of Bushehr port along the Persian Gulf. Thus, decision-makers should manage landfill leachate to reduce further environmental pollution.

Behaviour of 27 selected emerging contaminants in vertical flow constructed wetlands as post-treatment for municipal wastewater

Six substrates (i.e. sand enriched with activated or non-activated biochar or zeolite in different ratios) were tested in Vertical Flow Constructed Wetlands (VFCWs) planted with Phragmites australis and Iris pseudacorus for the removal of 27 emerging contaminants from municipal wastewater. The laboratory investigation under controlled conditions (spiked constant concentrations in synthetic wastewater) lasted 357 days and proved VFCWs being able to provide excellent effluent quality in terms of both macro - and micropollutant elimination. Because overall removal efficiencies exceeded 90% in most of the cases, significant differences among the substrates were not detectable. For compounds with medium elimination (i.e. AMPA) the type of substrate seemed to play a strong role and the maximum amount of active ingredient adsorbed per amount of substrate has been quantified (i.e. 0.77 μg of AMPA per g of 30% biochar mixed with sand). Three of the most promising substrates from laboratory where thus selected to be tested under real conditions (fluctuation in concentration, variable temperature). As result, VFCWs with 15% activated biochar mixed with sand proved to be effective in the removal of 18 emerging contaminants and complying with national discharge standards for 4 selected compounds.

A first attempt for using of combined sorption and anaerobic processes for handling source separated human urine

Processing human urine with clinoptilolite results in a solid phase upon which majority of nutrients are concentrated, which may be used as fertilizer; in addition to a liquid residue to be disposed of which is saline, rich in organics and contains residual nutrients. Despite several work regarding nutrients recovery from human urine, the fate of organic matter in the liquid residue is yet to be revealed. This study aims to investigate the combination of sorption and anaerobic processing (ANA) to accomplish concurrent nutrient recovery, and organic matter removal from hydrolyzed human urine (HHU) for environmental protection. Fixed bed clinoptilolite columns were used for nutrient recovery from HHU and an anaerobic expanded granular sludge bed reactor (AnEGSB) was used for removal of organic matter from residue of the former process. Furthermore, the effluent of AnEGSB was subjected to post treatment using stage-wise sorption to enhance the effluent quality before disposal. Majority of nutrients were removed by the sorption process with 80% of ammonium and almost all of phosphorus. Sorption removed 35% of orgnic matter while ANA was responsible for the rest. Post treatment helped to polish the quality of the AnEGSB effluent to the permissible level of domestic wastewater discharge standards of EU.With the proposed combination, almost 100% of nitrogen and phosphorus were recovered for further use as fertilizer providing benefits for sustainability. Also, 97% of organic matter could be removed from HHU to provide environmental protection, which was accompanied by methane (CH4) production of 0.4 L CH4/day which is equivalent to 0.113 L CH4/g COD removed. Successful implementation of the proposed combination helps improve management of domestic wastewater.

Synergistic light irradiation and circuital current for efficient mineralization of recalcitrant organics and sequential recovery of heavy metals from etching terminal wastewater using photo-assisted bioelectrochemical systems

Practical application of photo-assisted bioelectrochemical systems (BESs) requires its treatment for actual wastewaters. Herein photo-assisted BESs fed with actual etching terminal wastewater (ETW), achieve sequentially recovering copper (85.8 ± 2.3%) in one microbial fuel cell (MFCCu), nickel (71.6 ± 0.2%) in one microbial electrolysis cell (MECNi) and zinc (67.7 ± 1.3%) in the other MEC (MECZn) with simultaneous efficient mineralization of recalcitrant organics in each units (MFCCu: 34.1 ± 0.8%; MECNi: 22.8 ± 1.3%; MECZn: 13.7 ± 2.7%) and the effluent meeting China wastewater discharge standard. Light irradiation and circuital current play synergistic roles in recalcitrant organics mineralization and heavy metals recovery, 1.9–4.2 folds (organics mineralization) and 1.2–1.4 times (heavy metals recovery) of sole circuital current, and 3.5–7.1 times (organics mineralization) and 35.8–112.8 folds (heavy metals recovery) of light irradiation only. Oxidative active species (˙OH, O2·-, holes and H2O2) variably contribute to recalcitrant organics mineralization whereas heavy metals recovery is mainly ascribed to circuital current. This study provides an alternative and environmentally benign approach for recovery and separation of multiple heavy metals with simultaneous efficient mineralization of recalcitrant organics in ETW, moving photo-assisted BESs closer to applicable ETW treatment.

Advanced treatment of hydraulic fracturing flowback water using a novel combined process

A novel process was proposed for treating heavily polluted hydraulic fracturing flowback water from oil/gas production with an initial chemical oxygen demand (COD) of 8850 mg/L. The process was comprised of gel breaking, cavitation-impinging stream/iron-carbon micro-electrolysis (CIS/ICME) and electro-Fenton. The viscosity of the wastewater was reduced from 6.20 to 1.09 mPa•s after 90 min of gel breaking treatment using sodium hypochlorite at a dosage of 3.0 g/L. The CIS technology solved the passivation and hardening problems of traditional ICME technology, enhancing COD abatement by 48.2% points and increasing iron utilization from 36.8% to 82.4%. The results show that, under the optimum conditions, the effluent COD was reduced to around 170 mg/L with a removal efficiency of 98.1%, and the reduction ratios of oil, color, corrosion rate and suspended solids reached 100%, 95.2%, 94.0% and 97.7%, respectively. The quality of final effluent could meet the national discharge standard of China. The CIS/ICME process removed a considerable proportion of COD and oil, while the electro-Fenton unit played an important role in post-polish of final effluent. This study shows that the hybrid system has the potential to be applied for the advanced treatment of high-strength oilfield wastewater.

Physico-chemical monitoring of biodegradation of furfural from oil industry effluents from the Arzew refinery (Oran) Algeria

Furfural is one of the petroleum products posing a potential danger to the environment and human health. However, the decontamination of these pollutants released into the environment is primarily governed by biodegra-dation processes. This study is based on biodegradation kinetics at increasing concentrations of furfural by natural mixed culture in order to assess the potential of this process in the elimination of furfural from petrochemical effluents from the ARZEW refinery. This biodegradation was measured through physicochemical parameters such as pH, electrical conductivity, con-centration of hydrocarbons, the chemical oxygen demand (COD), biochemi-cal oxygen demand (BOD5) and the concentration of furfural. The results obtained show at a concentration of 250ppm of injected furfural: a decrease in pH 4.9 and an increase in other parameters (conductivity 3450 μS.cm-1, HC 102 mg / l; furfural 210 ppm, COD 327mg / l, BOD5 98mgO2 / l. The study findings indicated that the injection of these effluents with concentrations greater than 180 ppm leads to values of pH, EC, HC, Furfural, COD, BOD5 which do not comply with direct discharge standards and disrupt biological treatment. The high levels of furfural not only cause a pollution problem but can also disrupt the functioning of bacteria at the biological treatment level. Therefore, dilution with the filtration wash water before switching to biologi-cal treatment is recommended in order to reduce the concentrations below 180 ppm.

Resource Utilization of Biogas Waste as Fertilizer in China Needs More Inspections Due to the Risk of Heavy Metals

The utilization of livestock waste has attracted increasing attention in recent years. The presence of high levels of heavy metals is a major obstacle to the utilization of biogas as a fertilizer resource. In this study, the heavy metal contents in biogas residue, slurry, and discharged sewage from three representative farms of gooseries, henneries, and dairy farms in the Yangtze River Basin were investigated and assessed. The results demonstrated that heavy metals, including Cd, Mn, As, Cu, Pb, Cr, Zn, etc., could be detected in all biogas residues, with significantly different contents between farm types (p &lt; 0.005). Specifically, biogas residues from the goosery and the dairy farms met “China’s Organic Fertilizer Standards” (COF Standards); however, Cd concentrations in biogas residues from hennery farms exceeded the limits by five times. The concentrations of Cd and Pb in biogas slurries from all of the farms exceeded the limits of the “China Farmland Irrigation Water Quality Standard” (CFIWQ Standard). In particular, the Pb concentrations in biogas slurry from the dairy farms exceeded the limits by 29 times, and the discharged sewage from all three farm types complied with the comprehensive sewage discharge standards in China; however, only that from the goosery farms was suitable for irrigation. Thus, it is recommended to increase the feed selection, biogas engineering, and biological-purification-supporting technology, and to carry out regular sampling inspections of the biogas residue, slurry, and discharged sewage for heavy metals, so that environmental and crop pollution risks can be reduced when they are used as sources of nutrients for eco-friendly agriculture.