Subsequent Biological Treatment Research Articles

Modeling and optimization of the coagulation of highly concentrated coking wastewater by ferrous sulfate using a response surface methodology

The coagulation process by ferrous sulfate was used to pretreat coking wastewater prior to a subsequent biological treatment. The central composite Box–Behnken experimental design and response surface method were applied to evaluate and optimize the interactive effects of three operating variables, namely the initial pH, dosage of ferrous sulfate, and interaction time, on the physical and chemical performances of coagulation. Four dependent parameters, namely COD removal, cyanide removal, sulfide removal, and total oil removal, were either directly measured or calculated as responses. According to analysis of variances results, the four models proposed in this work can be used to navigate the design space, with the high regression coefficient R2 varying from 0.9158 to 0.9877. The initial pH, ferrous sulfate dosage, and interaction time had significant effects on the COD removal, cyanide removal, sulfide removal, and total oil removal due to their respective effects on chemical precipitation and coagulation removal. The synergies effect of chemical precipitation and coagulation during ferrous sulfate coagulation process controlled the treatment. A visual search of the overlaying critical response contours plot was carried out, and the results indicated the optimum conditions to an initial pH 11, ferrous sulfate dosage of 1.5 g/L, and reaction time of 120 min. The experimental date and models’ predictions agreed well. COD removal, cyanide removal, sulfide removal, and total oil removal of 15.25, 93.82, 73.36, and 4.73%, respectively, were demonstrated. The results of a B/C analysis and cost evaluation show that FeSO4 coagulation is an appropriate technology for coking wastewater pretreatment.

Hydrophobicity Distribution of Landfill Leachates and Evaluation of Organic Constituents That Affect Publicly Owned Treatment Works

AbstractLandfill leachates are often discharged through sewers or by trucks to publicly owned treatment works (POTWs) after on-site biological treatment. This discharge of landfill leachate is widely accepted because of its cost-effectiveness and reliability, but potential impacts of this practice include additional nutrient loading and interference with ultraviolet (UV) disinfection during subsequent biological treatment. Leachate was fractionated into humic acid (HA), fulvic acid (FA), and hydrophilic (Hpi) fractions based on chemical composition and solubility to determine the hydrophobicity distribution. The analysis showed that the specific UV254 absorbance (SUVA254) of the humic substances (HA and FA) was significantly higher than the Hpi fraction. The UV quenching materials were found to be resistant to biological treatment for the majority of leachates studied. Removal of humic substances was associated with decreased UV quenching and the aromatic content of landfill leachates after biological tre...

Treatment of oilfield produced water using Fe/C micro-electrolysis assisted by zero-valent copper and zero-valent aluminium

In this study, the Fe/Cu/C and Fe/Al/C inner micro-electrolysis systems were used to treat actual oilfield produced water to evaluate the feasibility of the technology. Effects of reaction time, pH value, the dosage of metals and activated carbon, and Fe:C mass ratio on the treatment efficiency of wastewater were studied. The results showed that the optimum conditions were reaction time 120 min, initial solution pH 4.0, Fe dosage 13.3 g/L, activated carbon dosage 6.7 g/L, Cu dosage 2.0 g/L or Al dosage 1.0 g/L. Under the optimum conditions, the removal efficiencies of chemical oxygen demand (COD) were 39.3%, 49.7% and 52.6% in the Fe/C, Fe/Cu/C and Fe/Al/C processes, respectively. Meanwhile, the ratio of five-day biochemical oxygen demand to COD was raised from 0.18 to above 0.35, which created favourable conditions for the subsequent biological treatment. All these led to an easy maintenance and low operational cost.

Electrochemical treatment of cork boiling wastewater with a boron-doped diamond anode

Anodic oxidation at a boron-doped diamond anode of cork boiling wastewater was successfully used for mineralization and biodegradability enhancement required for effluent discharge or subsequent biological treatment, respectively. The influence of the applied current density (30–70 mA/cm2) and the background electrolyte concentration (0–1.5 g/L Na2SO4) on the performance of the electrochemical oxidation was investigated. The supporting electrolyte was required to achieve conductivities that enabled anodic oxidation at the highest current intensities applied. The results indicated that pollutant removal increased with the applied current density, and after 8 h, reductions greater than 90% were achieved for COD, dissolved organic carbon, total phenols and colour. The biodegradability enhancement was from 0.13 to 0.59 and from 0.23 to 0.72 for the BOD/COD ratios with BOD of 5 and 20 days’ incubation period, respectively. The tests without added electrolyte were performed at lower applied electrical charges (15 mA/cm2 or 30 V) with good organic load removal (up to 80%). For an applied current density of 30 mA/cm2, there was a minimum of electric conductivity of 1.9 mS/cm (corresponding to 0.75 g/L of Na2SO4), which minimized the specific energy consumption.

Remediation of the effect of adding cyanides on an algal/bacterial treatment of a mixture of organic pollutants in a continuous photobioreactor.

The effect of inorganic pollutants on the treatment of organic pollutants using algal/bacterial microcosm was investigated in a continuous photobioreactor. The microcosm was composed of Chlorella vulgaris MM1 and Pseudomonas MT1 and was able to efficiently treat artificial waste-water contaminated with 6.4 salicylate and 2.2mM phenol at a hydraulic retention time of 4days. No negative effect was recorded when the waste-water was supplemented with 1.6mM thiocyanate; however, the treatment efficiency severely deteriorated when the system was challenged with 0.74mM cyanide. Addition of 2g NaHCO3 l(-1) did not improve the efficiency of the treatment. Toxicity of the pollutants to the alga was cyanide > thiocyanate > phenol > salicylate. The high toxicity of the waste-water was eliminated either by a 25-fold dilution or by photocatalytic pre-treatment which allowed the subsequent efficient biological treatment.

Electrochemical Disintegration of Activated Sludge Using Ti/RuO<sub>2</sub> Anode

Electrochemical process is one of the most effective methods to enhance sludge disintegration. In this study, Ti/RuO2 anodes were prepared by Pechini’s method and the electrode surface morphology was characterized by FESEM and EDAX. The effects of various operating conditions were investigated including initial pH value of sludge, sludge concentration, electrolysis time and current density. The study showed that the removal efficiencies of TS, VS, TSS and VSS increased with the increase of pH in the alkaline range, electrolysis time and current density but decreased with the increase of initial sludge concentration. The application of electrochemical process using Ti/RuO2 electrodes enhanced the sludge disintegration for possible subsequent biological treatment.

Sequential ozone advanced oxidation and biological oxidation processes to remove selected pharmaceutical contaminants from an urban wastewater

Sequential treatments consisting in a chemical process followed by a conventional biological treatment, have been applied to remove mixtures of nine contaminants of pharmaceutical type spiked in a primary sedimentation effluent of a municipal wastewater. Combinations of ozone, UVA black light (BL) and Fe(III) or Fe3O4 catalysts constituted the chemical systems. Regardless of the Advanced Oxidation Process (AOP), the removal of pharmaceutical compounds was achieved in 1 h of reaction, while total organic carbon (TOC) only diminished between 3.4 and 6%. Among selected ozonation systems to be implemented before the biological treatment, the application of ozone alone in the pre-treatment stage is recommended due to the increase of the biodegradability observed. The application of ozone followed by the conventional biological treatment leads high TOC and COD removal rates, 60 and 61%, respectively, and allows the subsequent biological treatment works with shorter hydraulic residence time (HRT). Moreover, the influence of the application of AOPs before and after a conventional biological process was compared, concluding that the decision to take depends on the characterization of the initial wastewater with pharmaceutical compounds.

Photocatalytic oxidation process used as a pretreatment to improve hexane vapors biofiltration

AbstractBACKGROUNDPhotolytic and photocatalytic oxidation processes were used as pretreatments for the purpose of producing more soluble and easily degradable byproducts that were subsequently treated in a biofiltration system for VOC treatment. n‐Hexane was chosen as a model hydrophobic VOC, and ZnO was used as a photocatalyst.RESULTSThe potential of this technology was evaluated at an inlet load of 200 g m−3 h−1 and a residence time of 94.2 s for the coupled system. The results showed that the photocatalytic pretreatment had a greater impact on the removal of hexane than the photolytic pretreatment with elimination capacities (EC) of 43 g m−3 h−1 and 24 g m−3 h−1, respectively. The EC of hexane and the CO2 production reached in the coupled system increased by at least 20%. This behavior was directly related to the high biodegradability of byproducts produced in the photocatalytic system, such as alcohols and ketones.CONCLUSIONPhotocatalytic oxidation used as a pretreatment system for hexane vapors using ZnO as photocatalyst enabled the generation of byproducts with high solubility that could be easily degraded in subsequent biological treatment. © 2014 Society of Chemical Industry

Electrocoagulation pretreatment of wet-spun acrylic fibers manufacturing wastewater to improve its biodegradability

The electrocoagulation (EC) process was used to pretreat wastewater from the manufacture of wet-spun acrylic fibers, and the effects of varying the operating parameters, including the electrode area/wastewater volume (A/V) ratio, current density, interelectrode distance and pH, on the EC treatment process were investigated. About 44% of the total organic carbon was removed using the optimal conditions in a 100min procedure. The optimal conditions were a current density of 35.7mAcm−2, an A/V ratio of 0.28cm−1, a pH of 5, and an interelectrode distance of 0.8cm. The biodegradability of the contaminants in the treated water was improved by the EC treatment (using the optimal conditions), increasing the five-day biological oxygen demand/chemical oxygen demand ratio to 0.35, which could improve the effectiveness of subsequent biological treatments. The improvement in the biodegradability of the contaminants in the wastewater was attributed to the removal and degradation of aromatic organic compounds, straight-chain paraffins, and other organic compounds, which we identified using gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy. The EC process was proven to be an effective alternative pretreatment for wastewater from the manufacture of wet-spun acrylic fibers, prior to biological treatments.

Removal of Total Dissolved Solids in Spent Caustic Using Biochar: Pretreatment for Subsequent Biological Treatment

Biological oxidative treatment of spent caustic, a liquid waste generated from a refinery plant, is limited due to high concentrations of total dissolved solids (TDS). In this study, we investigated the possibility of using biochar as a sorbent to remove TDS in spent caustic to enhance the subsequent biological treatment. Compared to inefficient removal of TDS with granular activated carbon, biochar can effectively remove TDS from spent caustic, resulting in up to 65% removal of TDS as biochar dosage was increased in batch reactors. With 51.8 min of retention time, 59% of TDS was removed in a column reactor. After TDS removal, chemical oxygen demand removal in biological reactors was markedly enhanced. Our results suggest that biochar may have potential as a sorbent to remove TDS from spent caustic before biological treatment.

Improvement of the activated sludge treatment by its combination with electro Fenton for the mineralization of sulfamethazine

A combined process coupling an electro-Fenton pretreatment and a biological degradation in order to mineralize sulfamethazine (SMT) was investigated. The electro-Fenton pretreatment of SMT was first examined and the intermediates products were identified for an initial SMT amount of 0.36 mM, after 1 h electrolysis at pH 3, 18 °C, 200 mA. 94.2% SMT was degraded but the level of mineralization remained low (6.5%), ensuring significant residual organic content for a subsequent biological treatment. Two possible degradation reaction pathways involving all the identified and quantified intermediates are proposed. In a second part, biological treatments with fresh activated sludge were performed to complete the mineralization of the electrolyzed solution of SMT, showing an increase of the mineralization yield with time duration of the pretreatment. For an initial SMT concentration of 0.2 mM, a ferrous ions concentration of 0.5 mM, at pH 3, 18 °C and 500 mA, the mineralization yield during the biological treatment increased as follows: 61.4, 78.8 and 93.9% for 0.5, 1 and 4 h pretreatment, confirming the relevance of the proposed combined process.

Coupling Fenton and biological oxidation for the removal of nitrochlorinated herbicides from water

The combination of Fenton and biological oxidation for the removal of the nitrochlorinated herbicides alachlor, atrazine and diuron in aqueous solution has been studied. The H2O2 dose was varied from 20 to 100% of the stoichiometric amount related to the initial chemical oxygen demand (COD). The effluents from Fenton oxidation were analyzed for ecotoxicity, biodegradability, total organic carbon (TOC), COD and intermediate byproducts. The chemical step resulted in a significant improvement of the biodegradability in spite of its negligible or even slightly negative effect on the ecotoxicity. Working at 60% of the stoichiometric H2O2 dose allowed obtaining highly biodegradable effluents in the cases of alachlor and atrazine. That dose was even lower (40% of the stoichiometric) for diuron. The subsequent biological treatment was carried out in a sequencing batch reactor (SBR) and the combined Fenton-biological treatment allowed up to around 80% of COD reduction.

Ozonation products of carbamazepine and their removal from secondary effluents by soil aquifer treatment – Indications from column experiments

Ozonation is known as an efficient treatment to reduce the concentration of many trace organic compounds from WWTP effluents, but the formation of unknown and possibly persistent and toxic transformation products has to be considered. In this paper tertiary treatment of wastewater by the combination of ozone and soil aquifer treatment was investigated with respect to the removal of the antiepileptic drug carbamazepine (CBZ, 10 μg/L) and its transformation products. Batch tests and pilot experiments confirmed efficient removal of carbamazepine from secondary effluent by ozone. With typical ozone consumption of 0.7 mg O3/mg DOC0, approx. 50% of the transformed CBZ was detected as its primary product 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM). Structure proposals and a formation pathway were elaborated for a total of 13 ozonation products of CBZ. In subsequent biological treatment BQM turned out to be more effectively biodegraded than CBZ. Its aldehyde group was quickly oxidized to a carboxylic acid (BaQM), which was removed in sand column experiments. Most of the minor ozonation products of CBZ persisted in sand column experiments with residence times of 5–6 days. Non-target screening of column effluent revealed no formation of persistent biotransformation products.

Degradation of Landfill Leachate by Ultrasound/Ultraviolet - Aged Refuse Bioreactor Combined Process

The biodegradability of aged landfill leachate is low, and the treatment effects of common processes are very poor. This paper explored the effects of the Ultrasound/Ultraviolet - Aged Refuse Bioreactor combined process on aged landfill leachate. The main results were as follows: 1The optimum power of ultrasound was 100 W, and the optimum wavelength of ultraviolet was 254 nm. The removal rate of COD was 27.33% and the value of BOD/COD ratio was increased from 0.1 to 0.35 after the treatment of Ultrasound/Ultraviolet process. Therefore, the biodegradability of the leachate was improved, which might meet the demand of subsequent biological treatment. 2The COD removal rates of the two-stage series aged refuse bioreactor were both kept above 50% during the experiment and this process had a strong capacity of resistance to impact load. 3The COD removal rate of the combined process was over 80% as a whole without any pretreatment, and it has positive significance for the treatment of aged leachate.

Simulation and Operation Cost Estimate for Phenol Extraction and Solvent Recovery Process of Coal-Gasification Wastewater

To further reduce the total phenols of coal-gasification wastewater which comes from the Lurgi pressurized coal-gasification process, methyl isobutyl ketone (MIBK) instead of diisopropyl ether (DIPE) is used as the extraction solvent in the process to remove the phenols. To obtain process parameters for an industrial trial, process simulations with a treatment capacity of 100 ton/h wastewater are carried out. The simulation results show that with the use of MIBK as an extraction solvent, the total phenol concentration of coal-gasification wastewater can be reduced from 5410 ppm to less than 200 ppm. The operation cost estimate shows that using MIBK as an extraction solvent to extract and remove phenols from coal-gasification wastewater has good economic feasibility. With the process parameters obtained from the simulation, an industrial trial is implemented and satisfactory agreement is found. With the total phenol concentration reduced to below 200 ppm in the pretreatment, the coal-gasification wastewater can be decontaminated in the subsequent biological treatment.

Degradation of chlorophenoxy herbicides by coupled Fenton and biological oxidation

A combined treatment for the degradation of the chlorophenoxy herbicides 2,4-D and MCPA in water by means of Fenton and biological oxidation has been studied. The chemical oxidation step was necessary to achieve an efficient removal of these pollutants due to their toxicity and low biodegradability. Aqueous herbicide solutions (180mgL−1) were subjected to Fenton oxidation upon different H2O2 doses (from the theoretical stoichiometric amount referred to initial COD to 20% of this value). The toxicity and biodegradability tests of the Fenton effluents suggested that the ones resulting upon treatment with 80% and 60% of stoichiometric H2O2 were the optimal for subsequent biological treatment dealing with 2,4-D and MCPA, respectively. These effluents were treated in a sequencing batch reactor achieving nearly 90% conversion of organic matter measured as COD.

Membrane-integrated hybrid bioremediation of industrial wastewater: a continuous treatment and recycling approach

A new membrane-integrated hybrid treatment system was investigated to turn highly hazardous coke wastewater reusable. This could protect both air and surface water bodies from toxic contaminants such as ammonia, phenol, cyanide, thiocyanate and other carcinogenic aromatic compounds which are normally released into the environment during discharge of coke wastewater and during quenching of coke by wastewater. Apart from these hazardous substances, oil, grease, other organics and even trace elements could be very effectively removed from wastewater by logical sequencing of chemical, biological and finally nanomembrane-based treatments in an integrated hybrid plant. After almost 99% removal of highly toxic cyanide compounds in a well-optimized Fenton's treatment unit, subsequent biological treatment units could be very effective. All these pretreatments helped achieve microbial nitrification and denitrification of more than 98% of ammonia. Composite nanofiltration membranes selected through investigation could separate ionic trace contaminants from water with a high degree of purification permitting recycling and reuse of the treated water. A selected cross flow membrane module allowed long hours of largely fouling-free operation under a reasonably low transmembrane pressure of only 15 bars while yielding an industrially acceptable flux of 80 L of pure water per hour per square meter of membrane surface.

Pretreatment of Herbicides Production Wastewater by Spherical Micro-Electrolysis Media

[Objective] The aim is to study the pretreatment effect of herbicides production wastewater by spherical micro-electrolysis media. [Method] Spherical micro-electrolysis media is preferred for the pretreatment of herbicides production wastewater and effects of PH, amount of media and reaction time on the pretreatment was investigated. The change of pre- and post-processing herbicides production wastewater was determined; the operation cost was also analyzed. [Result]The optimum reaction conditions are as follows: the PH was 3; the amount of media was 1.0kg/L wastewater; and the reaction time was 3.0h. Under the optimum reaction conditions, the removal of COD, Chromaticity and TP reached 26.3%, 86.4% and 95.6% respectively; BOD5/COD varied from 0.10 to 0.35, and the biodegradability was improved greatly; the cost of pretreatment was 1.0yuan/t, and it was lower than that of electrolysis. [Conclusion] The pretreatment of herbicides production wastewater by spherical micro-electrolysis media has good effect, low cost and no soiling hardening, so it provides a good foundation for subsequent biological treatment.

Effect of Synthetic Wastewater by Electrochemical Pretreatment on <i>Chlorella vulgaris</i> Growth and Nutrients Removal

Electrochemical processing combined with the system of microalgaeChlorella vulgariswas used to treat the synthetic organic wastewater in this paper. The effect of wastewater concentration on the biomass growth and nutrients removal was investigated. Three levels of the wastewater concentrations were ranked as Low, Mid and High, respectively. After 2 h of electrolysis pretreatment and 10 d of microalgae cultivation, TOC, NH4-N, and TP concentrations in the group Low were reduced by 83.7%, 99.3% and 95.0%, respectively. TheChlorella vulgarisin the groups Mid and High without electrolysis pretreatment did not survive longer than 24 h, whereas it grown well in the wastewater pretreated by electrolysis. The dry weight (DW) ofChlorella vulgarisin the group Low with electrolysis pretreatment was increased from 0.048 g/l to 1.087 g/l by 10 d cultivation. Results indicate that electrolysis pretreatment for wastewater can provide appropriate conditions for the subsequent biological treatment and efficiently promote the biomass growth ofChlorella vulgaris.

Nanofiltration of partial oxidation products and copper from catalyzed wet peroxidation of phenol

The aim of this work is to study the combination of Catalytic Wet Peroxide Oxidation (CWPO) and nanofiltration processes in the treatment of phenol solutions. A home-made Cu-chitosan/Al2O3 catalyst was applied for this purpose. The effluent from CWPO usually contains some metal leached from the catalyst in addition to latter oxidation intermediates (short chain organic acids). Downstream nanofiltration is used to retain the metal leached from the catalyst, which would result in secondary pollution and negatively impact on a possible subsequent biological treatment step.The CWPO was performed in a batch recycle trickle bed reactor packed with the catalyst. The final distribution of intermediates was identified by HPLC. Cross flow filtration experiments using either model solutions containing phenol and the main intermediates (succinic, malonic, maleic and oxalic acid), with and without Cu(II) or the effluent of the CWPO reaction were performed using a NF90 membrane. When all intermediates were combined, the rejection of copper reached over 95% while an acceptable maximum of 10% of permeate flux loss, compared with the initial flux, was maintained.Nanofiltration of a real CWPO effluent gave a higher copper recovery of 97%. Thus, the permeate toxicity was highly reduced. In addition, after 4h of filtration, only a 5% of flux loss was observed, which guarantees a stable filtration for days.