Treatment Of Toxic Wastewater Research Articles

Enhanced degradation of Rhodamine B through activating peroxydisulfate by humic acid-Fe incorporated biochar: Kinetics and mechanism studies

Sulfate radical advanced technologies (SR-AOPs) has been increasingly applied for chemical oxidation of toxic wastewater treatment, while the sluggish kinetics of Fe(III)/Fe(II) cycling remains a serious problem in its application. In this study, a novel co-catalyst of humic acid-Fe incorporated biochar (HA-Fe@BC) was successfully synthesized that can greatly accelerate the Fe(II) regeneration. More than 95 % organic pollutants could be degraded in HA-Fe@BC/peroxydisulfate (PDS) system, especially for the model pollutant Rhodamine B (an almost 8.0-fold kinetic increase). More excitingly, the superior catalytic activity of HA-Fe@BC for PDS activation may be attributed to the ample surface C-OH and C=O groups, accelerated electron transfer and formed surface HA-Fe@BC-PDS* complex with efficient oxidation activity. Radical capture, quenching experiments and electrochemical analysis confirmed that the HA-Fe@BC/PDS was caused by radicals (SO4•-+ O2•-+•OH = 68.13 %) and non-radical (surface-mediated electron transfer and 1O2 = 26.33 %) pathways. Besides, it also exhibited anti-interference performance against anions and organic matter (eg. Cl-, Br-, NO3–, and PO43-). Furthermore, the degradation pathways were proposed by LC-MS assisted with density functional theory (DFT) calculations, and the mechanism was proposed comprehensively. This work demonstrates the PDS activation by HA-Fe@BC through free radical and non-free radical pathways, which provides insight into application of biochar-based materials for wastewater treatment.

Fabrication of copper molybdate nanoflower combined polymeric graphitic carbon nitride heterojunction for water depollution: Synergistic photocatalytic performance and mechanism insight

In the scope, developed a novel copper molybdate decorated polymeric graphitic carbon nitride (CuMoO4@g-C3N4 or CMC) heterojunction nanocomposite in an easy solvothermal environment for the first time. The synthesized CMC improved the photocatalytic degradation of an antibiotic drug [ciprofloxacin (CIP)] and organic dye [Rhodamine B (RhB)]. Consequently, the CMC demonstrates a marvelous crystalline nature with ∼26 nm size, as obtained from XRD analysis. Besides, the surface morphology studies confirm the large-scale construction of flower-like CMC with a typical size of 10–15 nm. The CMC showed efficient catalytic activity for both the pollutants, achieving the degradation of 98% for RhB and 97% for CIP in 35 and 60 min, respectively. The reaction parameters including the concentration of pollutants, catalyst dosages, and scavengers are optimized for the best photocatalytic results. Notably, the trapping tests showed that the •OH and O2•− radicals are the primary oxidative species liable for the photocatalytic process. The recyclability test of the photocatalyst infers that the photocatalyst is highly stable up to the fifth recycle. Our work affords an efficient and ideal path to constructing the new g-C3N4-based architected photocatalyst for toxic wastewater treatment in the near future.

Triclocarban-contaminated wastewater treatment by innovative hybrid moving entrapped bead activated sludge reactor (HyMER): Continuous performance and computational dynamic simulation analysis

Triclocarban (TCC) has been used in consumer products and is a widespread contaminant in municipal wastewater treatment systems that ultimately accumulates in natural receiving water and soil. This work aims to apply an innovative hybrid moving entrapped bead activated sludge reactor (named “HyMER”) that integrates entrapped TCC-degrading microbes and freely suspended activated sludge to treat TCC-contaminated wastewater. A previously isolated TCC-degrading bacterium (Pseudomonas fluorescens strain MC46, called MC46) and barium alginate entrapment were applied. The synthetic TCC-contaminated wastewater treatment (with TCC concentration of 10 mg/L) was performed using 20-cycle fed-batch reactor operation with feeding times of 12 and 24 h and cycle times of 13 and 25 h. The results indicated that the HyMER effectively reduced chemical oxygen demand by up to 80 and 95 % and TCC by up to 53 and 83 %, respectively, with feeding times of 12 and 24 h. Three TCC degradation intermediate products were found—3,4-dichloroaniline, 4-chloroaniline, and aniline. Scanning electron microscopic analysis revealed shorter cells and bacterial appendage development as cell adaptations against TCC and its intermediates. The live/dead assay indicated high survival of entrapped MC46 in toxic conditions, with up to 84 % viable cells. Based on computational fluid dynamic analysis, no entrapped cell agglomeration showed in the reactor, indicating the potential application of HyMER for real wastewater treatment. These results exhibit the feasibility of HyMER and its applicability for future toxic wastewater treatment.

Trace phenolic acids simultaneously enhance degradation of chlorophenol and biofuel production by Chlorella regularis

Coupling the cultivation of microalgae with wastewater treatment is a promising technology to recover bioresources from wastewater. However, toxic pollutants in wastewater seriously inhibit the growth of microalgae and the removal of pollutants. Phenolic acids are similar to phytohormones, could potentially relieve the toxicity to microalgae and simultaneously promote pollutant degradation and lipid accumulation. Chlorella and 4-chlorophenol (4-CP) were utilized to simulate the toxic wastewater treatment, and the roles of two typical phenolic acids, such as p-hydroxybenzoic acid (p-HBA) and caffeic acid (CA), were explored. The 0.2 μM concentration of p-HBA or CA improved the specific growth rate by 7.6% by enhancing photosynthesis and DNA replication. The oxidative damage caused by 4-CP was reduced by 30.3–49.7% via the synthesis of more antioxidant enzymes and the direct scavenging of free radicals by phenolic acids. Furthermore, the 4-CP removal rate increased by 27.0%, and toxic 4-CP was degraded into non-toxic compounds. The phenolic acids did not change the 4-CP degradation pathway but accelerated its removal and detoxification by enhancing the expression of 4-CP degradation enzymes. Simultaneously, lipid production increased by 20.5–23.1% due to the upregulation of enzymes related to fatty acid and triacylglycerol synthesis. Trace phenolic acids stimulated the mitogen-activated protein kinase signaling cascade and the calcium signaling pathway to regulate the physiology of the microalgae and protect cells from toxic stress. This study provides a promising new strategy for toxic wastewater treatment and bioresource recovery.

The used automobile catalytic converter as an efficient catalyst for removal of malathion through wet air oxidation process

The automobile catalytic converter (ACC) contains a huge number of precious metals as catalysts. When an ACC fails to meet standards, it is removed from the exhaust of an automobile but retains some catalytic activity. However, the recovery and/or activation of this waste is a high-cost process and includes several chemical treatments. Catalytic wet air oxidation (CWAO) has been reported as an effective wastewater treatment method. The most important disadvantage of CWAO is cost-nonefficiency. Herein, to overcome these problems, the simple recovery of catalysts from waste ACC for reuse in CWAO was investigated. The optimum conditions of reaction were investigated through response surface methodology (RSM). The optimum removal efficiency was 88% when the reaction conditions were set on the 20 bar of pressure at 111.5 °C over 77 min and using 0.41 g of recovered catalyst. In addition, toxicity testing was performed on a model of malathion-contaminated wastewater before and after CWAO treatment. Final product identification was performed which showed that CWAO eliminated the toxicity of wastewater and was determined to be malaoxon, present at acceptable concentrations, and tributyl phosphate. In conclusion, there may be important potential for the use of recovered ACC catalyst in the treatment of toxic wastewater.

BiOCOOH Microflowers Decorated with Ag/Ag2CrO4 Nanoparticles as Highly Efficient Photocatalyst for the Treatment of Toxic Wastewater

A novel flower-like Ag/Ag2CrO4/BiOCOOH heterojunction photocatalyst was synthesized by a facile in-situ precipitation strategy combined with photoreduction treatment. Morphological studies revealed that numerous Ag/Ag2CrO4 nanoparticles were evenly anchored on BiOCOOH microflowers, producing a novel heterojunction with the compactly interfacial contact. Optical absorption characterization demonstrated that Ag/Ag2CrO4/BiOCOOH possessed much better sunlight harvesting ability than Ag2CrO4/BiOCOOH and BiOCOOH. Photocatalytic experiments verified that compared with BiOCOOH, Ag2CrO4, Ag/Ag2CrO4, and Ag2CrO4/BiOCOOH, Ag/Ag2CrO4/BiOCOOH achieved remarkable efficiency by eliminating 100% of rhodamine B (RhB), 82.6% of methyl orange (MO) or 69.4% of ciprofloxacin (CIP) within 50 min at a catalyst dosage of 0.4 g/L. The high photocatalytic performance is likely owing to the improved sunlight response and the distinctly suppressed recombination of charge carriers arising from the formation of the novel 3D hierarchical heterostructure. The quenching test signified that h+, and •O2− were detected as the prevailing active species in wastewater treatment. This study may provide a viable strategy for enhancing the photocatalytic performance of wide band-gap semiconductors.

Fabrication of biobeads expressing heavy metal-binding protein for removal of heavy metal from wastewater.

Heavy metals, being toxic in nature, are one of the most persistent problems in wastewater. Unabated discharge of large amount of heavy metals into water bodies are known to cause several environmental and health impacts. Biological remediation processes like microbial remediation and phytoremediation are proved to be very effective in the reduction of heavy metal pollutants in wastewater. To circumvent the issues involved several peptides and proteins are being explored. Metal-binding capacity, accumulation, and tolerance of heavy metals in bacteria can be upsurge by overexpressing the genes which code for metal-binding proteins. In the present study, an attempt has been made to bioremediate heavy metal toxicity by overexpressing metal-binding proteins. Two expression cassettes harboring top4 metal-binding protein (T4MBP) and human metallothionein 3 (HMP3) were designed under the control of constitutive CaMV 35S promoter and transformed into E.coli TBI cells. E.coli over expressing HMP3 and T4MBP were immobilized in biobeads which were explored for the detoxification of water contaminated with copper and cadmium. Effects on the concentration of heavy metal before and after treatment with beads were estimated with the help of ICP-OES. Noteworthy results were obtained in the case of copper with 87.2% decrease in its concentration after treatment with biobeads. Significant decrement of 32.8% and 27.3% was found in case of zinc and cadmium, respectively. Mechanisms of binding of proteins with heavy metals were further validated by molecular modeling and metal-binding analysis. HMP3 protein was found to be more efficient in metal accumulation as compared with T4MBP. The fabricated biobeads in this study definitely offer an easy and user-handy approach towards the treatment of toxic wastewater.

Reductive recovery of manganese from low-grade manganese dioxide ore using toxic nitrocellulose acid wastewater as reductant

The hydrometallurgical strategy of extracting Mn from low-grade Mn ores has attracted attention for the production of electrolytic manganese metal (EMM). In this work, the reductive dissolution of low-grade MnO2 ores using toxic nitrocellulose acidic wastewater (NAW) as a reductant was investigated for the first time. Under the optimized conditions of an MnO2 ore dosage of 100 g·L−1, an ore particle size of −200 mesh, concentrated H2SO4-to-NAW volume ratio of 0.12, reaction temperature of 90°C, stirring speed at 160 r·min−1, and a contact time of 120 min, the reductive leaching efficiency of Mn and the total organic carbon (TOC) removal efficiency of NAW reached 97.4% and 98.5%, respectively. The residual TOC of 31.6 mg·L−1 did not adversely affect the preparation of EMM. The current process offers a feasible route for the concurrent realization of the reductive leaching of Mn and the treatment of toxic wastewater via a simple one-step process.

Earthworms: nature’s chemical managers and detoxifying agents in the environment: an innovative study on treatment of toxic wastewaters from the petroleum industry by vermifiltration technology

Earthworms are justifying the beliefs of Great Russian scientist Dr. Anatoly Igonin who said they are—“disinfecting, detoxifying, neutralizing, protective and productive”. Studies indicate that some species of earthworms can “bio-accumulate, biodegrade or bio-transform” any toxic chemicals including “heavy metals”, “organochlorine pesticide”, “herbicides”, and the lipophilic organic micro-pollutants like “polycyclic aromatic hydrocarbons” (PAHs). Worm vermicasts, due to the presence of “hydrophilic” groups in the “lignin contents” and “humus”, also provide wonderful sites for “adsorption” of heavy metals and chemical pollutants in wastewater. Vermifiltration of wastewater using waste-eater earthworms is a newly conceived novel technology with several economic and environmental advantages. The earthworm’s body and the their “vermicast” work as a “biofilter” removing BOD5 by over 90 %, COD by 60–80 %, TDSS by 90–95 %, and toxic chemicals and pathogens from wastewater. This was a pioneering work done on an extremely “toxic wastewater” from the petroleum industry. It contained mixture of “aliphatic” and “aromatic” volatile petroleum hydrocarbons (C 10–C 36) and “organochlorines” originating from the cooling liquids, waste engine and gear oil, waste transmission and brake fluid, grease, spilled petrol, and diesel oil. The aliphatic fraction contained cycloalkanes as well as a complex mixture of saturated toxic hydrocarbons. The aromatic fraction mainly consisted of PAHs, which are more toxic and persistent than the aliphatic part. The chemicals of concern were the total petroleum hydrocarbons (TPH), dichloromethane (DCM), dichloroethane (DCE), and t-butyl methyl ether (tBME). The tBME compound has raised global concern recently due to its high mobility and persistence in the environment and possible carcinogenicity. About 1,000 earthworms (species Eisenia fetida) were released in the soil of vermifilter bed. They not only tolerated and survived in the toxic petroleum environment but also bio-filtered and bio-remediated the dark-brown petroleum wastewater with a pungent smell into pale-yellow and odorless water indicating disappearance of all toxic hydrocarbons. The hydrocarbons C 10–C 14 were reduced by 99.9 %, the C 15–C 28 by 99.8 %, and the C 29–C 36 by 99.7 % by earthworms.

Practical automatic control of a sequencing batch reactor for toxic wastewater treatment

This paper investigates the application of a practical and robust control strategy for the operation of a sequencing batch reactor (SBR) used for toxic wastewater treatment. The strategy sets the operational conditions of the SBR based on the on-line information collected during the previous batch. In particular, it sets the exchange volume of the reactor, as well as the batch reaction duration by optimizing the amount of mass of substrate in the influent treated per time unit. The optimization uses an experimentally calibrated mathematical model of the previous SBR cycle, found using the on-line dissolved oxygen concentration measurement data. The results show the applicability of the methodology to treat synthetic wastewater containing 4-chlorophenol as model toxic compound as sole source of carbon and energy. It correctly detects changes in the influent concentration and appropriately sets the operational parameters of the process.

Time-Optimal Output Feedback Controller for Toxic Wastewater Treatment in a Fed-batch Bioreactor

AbstractAerobic processes using sequencing fed-batch bioreactors are an effective technology to treat wastewater with toxic compounds. In order to implement optimal control schemes it is convenient to assess the biodegradation rate on-line. In this work, the dissolved oxygen concentration is used as output variable from the process to estimate this rate using a robust observer based on the generalized supertwisting algorithm. It does not require complete knowledge of the system dynamics or its parameters and is capable of estimating the biodegradation rate despite uncertainties and significant sensor and signal conditioning dynamics. The observer is then used for the implementation of a time-optimal output feedback controller that regulates the feed rate in a sequencing batch bioreactor used to treat toxic wastewater. This is tested using numerical simulations with promising results, while discussing the trade-off between allowed signal noise and convergence speed of the observer and how this affects the controller performance.

Removal of ammonia nitrogen in wastewater by microwave radiation: A pilot-scale study

A large removal of ammonia nitrogen in wastewater has been achieved by microwave (MW) radiation in our previous bench-scale study. This study developed a continuous pilot-scale MW system to remove ammonia nitrogen in real wastewater. A typical high concentration of ammonia nitrogen contaminated wastewater, the coke-plant wastewater from a Coke company, was treated. The output power of the microwave reactor was 4.8 kW and the handling capacity of the reactor was about 5 m 3 per day. The ammonia removal efficiencies under four operating conditions, including ambient temperature, wastewater flow rate, aeration conditions and initial concentration were evaluated in the pilot-scale experiments. The ammonia removal could reach about 80% for the real coke-plant wastewater with ammonia nitrogen concentrations of 2400–11000 mg/L. The running cost of the MW technique was a little lower than the conventional steam-stripping method. The continuous microwave system showed the potential as an effective method for ammonia nitrogen removal in coke-plant water treatment. It is proposed that this process is suitable for the treatment of toxic wastewater containing high concentrations of ammonia nitrogen.

Acclimatization model of an aerobic bioreactor for the treatment of toxic wastewater

This work proposes a mathematical model for the acclimatization process of a bioreactor treating toxic wastewater. Experimental data was used to identify the changing kinetic parameters of the model as acclimatization progresses. It was found that only one key parameter, the specific biomass growth rate function, changed during the acclimatization process. Therefore, an acclimatization model was proposed to explain the changes of this parameter.

Automation of the acclimation phase in a sequencing batch reactor using dissolved oxygen regulation

In this work, an automatic strategy for acclimation of biomass to toxic wastewater biodegradation in a sequencing batch reactor (SBR) is proposed and evaluated. It is based on monitoring the airflow needs for regulating the dissolved oxygen concentration at a desired set point. The regulation is achieved by using a PID controller with an input/output linearizing feedforward part, using the airflow rate as input variable. A simple algorithm to detect the end of the reaction phase using this manipulated signal is proposed. The strategy was tested on a laboratory bioreactor using 4-chlorophenol as model toxic compound and two inocula from different sources. The results show that it is a viable alternative for automatic acclimation of biomass for toxic wastewater treatment in a SBR. Furthermore, the strategy is also suitable for the operation of the reactor after acclimation.

Controlled backwashing in a membrane sequencing batch reactor used for toxic wastewater treatment

A new control algorithm for performing filtration in a membrane sequencing batch reactor (MSBR) to prevent fouling is presented. Based on continuous measurements of the transmembrane pressure (TMP) and the permeate flux, the algorithm decides when to initiate backwashing. The algorithm was tested on a laboratory scale bioreactor treating synthetic wastewater containing 4-chlorophenol (4CP) as model toxic compound and filtration was carried out using a submerged tubular membrane module and a diaphragm pump. Several controller configurations were tested for different MSBR cycles. The results showed that the proposed algorithm was robust against the highly varying mixed liquor characteristics and was able to keep the TMP below critical values and maintain the flux at a maximum for most of the filtration time. Therefore, despite possible frequent backwashes, the total filtration time was minimized.

AUTOMATION OF THE ACCLIMATION PHASE IN A SEQUENCING BATCH REACTOR DEGRADING INHIBITORY COMPOUNDS

An automatic strategy for acclimation of biomass to 4-chlorophenol in a sequencing batch reactor was evaluated. It combines an I/O linearizing plus PID controller to regulate the dissolved oxygen within the reactor at a given setpoint using the airflow rate, and a simple algorithm for establishing the end of the reaction phase using the manipulated airflow signal. The strategy was tested experimentally obtaining results that indicate that itis a viable alternative for automatic acclimation of biomass for toxic wastewater treatment in a SBR.

Comparison of two types of inocula during acclimation and stable operation for nitrophenol biodegradation in an anaerobic-aerobic SBR

This work presents a comparison of two inocula used for the acclimation of two anaerobic-aerobic sequencing batch bioreactors used for toxic wastewater treatment. The bioreactors were acclimated with different types of sludge: one coming from an anaerobic wastewater treatment plant and the other one from a conventional aerobic activated sludge plant. The model toxic compound was p-nitrophenol, which is reduced to p-aminophenol during the initial anaerobic phase of the reaction, and later mineralized during a posterior aerated reaction phase. Biodegradation of the compounds was monitored using UV/Vis spectrophotometry. After acclimation stabilization of the sludge and of the process was also monitored. Results show that there is no significant difference in acclimation times and stability of the process between the two employed inocula, and thus an originally anaerobic inoculum presents no apparent advantage over a more easily accessible aerobic one.

Laboratory scale and pilot plant study on treatment of toxic wastewater from the petrochemical industry by UASB reactors

This research concentrates on the development of an integrated approach to evaluate the possibility of treating very concentrated (COD = 15-20 g/l) and toxic wastewater (nitro-organic effluent) from the petrochemical industry in UASB reactors. A newly developed method utilising a modified Micro-Oxymax respirometer was used to (1) evaluate the inhibitory effects of varying concentrations of nitro-organic effluent on anaerobic granular sludge and (2) to make the proposal of operational parameters for the start up of the continuous process. Subsequently, the continuous tests were undertaken using laboratory scale upflow anaerobic sludge bed reactors to test gradual adaptation of anaerobic biomass to nitro-organic effluent. Practical application of the experimental results of the laboratory-scale continuous tests was evaluated by running the UASB pilot plant. Acceptable COD removal efficiencies were obtained when nitro-organic effluent was diluted with a readily biodegradable substrate up to 80 vol % of nitro-organic effluent in the inlet. The COD removal was 90% and the methane production rate was 4.5 l/d. Wastewater was detoxified and no acute toxicity of the treated wastewater to the anaerobic biomass was detected. This research indicates that anaerobic digestion of the undiluted nitro-organic effluent was not feasible. However, it is possible to blend the nitro-organic effluent with another effluent stream and co-treat these effluents.

Wet air oxidation: past, present and future

Wet air oxidation (WAO) is a liquid-phase reaction between organic material in water and oxygen. The WAO process is used around the world to treat industrial wastewaters and sludges, at moderate temperatures (180–315°C), and at pressures from 2 to 15 MPa. Under these conditions, complex organic compounds are mostly oxidized into carbon dioxide and water along with simpler forms which are biodegradable. Unlike other thermal processes, WAO produces no NO x , SO 2, HCl, dioxins, furans and fly ash. The efficiency of aqueous phase oxidation can be largely improved by the use of catalysts, either heterogeneous or homogeneous. However, key points to be solved are stability of heterogeneous catalysts and recycling of homogeneous catalysts. This paper presents an update on the development of commercial catalytic WAO (CWAO) processes, which started as early as the mid-fifties in the United States. Several Japanese companies developed CWAO technologies relying on heterogeneous catalysts based on precious metals deposited on titania or titania–zirconia. Conversely, the focus in Europe was more on homogeneous CWAO, where three processes are already commercial and one under development. Compared to conventional WAO, CWAO offers lower energy requirements and much higher oxidation efficiencies. Further developments of this technology should include high durability/low cost catalysts. Catalytic wet air oxidation would, thus, provide an environmentally attractive option to manage the growing organic sludge and toxic wastewater treatment problems.

Development of a new process for treatment of a pharmaceutical wastewater

In this study a process for biological treatment of toxic wastewater from a pharmaceutical company was developed. By simulations on a laboratory scale, the contribution of organic material and toxicity in wastewater from different sources was determined and the degradability of specific compounds were studied. The information obtained from these tests was used to improve the treatability of the wastewater at the sources. As an example a persistent organic phosphorous compound could be degraded after pre-treatment with chemical hydrolysis. By further simulations on a laboratory scale it was possible to screen through a large number of process configurations to determine the best working biological treatment. A combination of fungal and bacterial treatment was found to remove toxicity from the wastewater more than a conventional bacterial treatment. The results from the laboratory studies were confirmed in pilot tests. A full scale treatment plant, which design is based on the results from these studies are presently under construction.