Biodegradability Index Research Articles

Electro-catalytic ozonation for improving the biodegradability of mature landfill leachate

Landfill leachate contains complex, resistant, and diverse compounds that are considered as an environmental health problem. This study aims to investigate the efficacy of integrated homogeneous catalytic ozonation and electrochemical process for improving the biodegradability of landfill. This experimental study was conducted on real landfill leachate on the laboratory scale. The variables were current density (O3/H2O2-42.1 mA/cm2), ozone concentrations (100–400 mg/h), the initial pH (3–9), and the reaction times (1–6 h). The optimum operating condition was obtained at 1.42 mA/m2, 400 mg/h of ozone concentration, initial pH of 3, during 3 h. In the proposed integrated catalytic ozonation-electrochemical process, the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) concentrations were removed to 3381.9 and 1521.8 mg/L, respectively. Under the optimum condition, the biodegradability index increased from 0.27 to 0.45. The results showed that the electro-catalytic ozonation process has a significant effect on the biodegradability index and could improve the removal efficiency of landfill leachate treatments.

Treatment of vegetable oil refinery wastewater with biodegradability index improvement

The vegetable oil refinery wastewater (VORWW) creates an environmental problem in terms of threat to aquatic life due to high organic and inorganic content. These refinery plants produce a large quantity of wastewater with high chemical oxygen demand (COD) and biological oxygen demand (BOD). In this research, HC was evolved as a recent treatment option for the treatment of VORWW. Various parameters like inlet pressure, pH, temperature and H2O2 dose were tested during experimentation to determine BOD, COD, and BI (BOD/COD ratio). Using the hydrodynamic cavitation (HC) reactor biodegradability index (BI) of 0.69 and COD reduction up to 71.8% were obtained. In this same condition BOD increases by 14.4%, which helps to increase BI at optimum conditions of 120 min reaction time, operating temperature 20 °C, inlet pressure 8 bar, pH-4 and H2O2 dose of 25 g/L. It was found that the operating pressure of 8 bar in the HC reactor gives the maximum BI (BOD/COD ratio). The obtained optimum conditions of HC were used in the Ultrasonic cavitation reactor for the degradation of VORWW. In the 80 min of treatment COD reduced by 73.2%, which is highest as compared to HC. Similarly, BOD increases by 12.7% in just 80 min of treatment. The final obtained BI is 0.71, COD of 5984 mg/L and BOD 4270 mg/L which seems good as compared to HC.

Hydrogen production from coffee pulp by dark fermentation.

Coffee pulp (C.P.) is a waste of coffee production that needs to be controlled. Due to its high moisture and sugar content, a diagnostic study that characterizes the pulp was conducted and the potential for hydrogen production was evaluated. Subsequently, the kinetics of hydrogen production in a bioreactor were evaluated. A biodegradability index of 0.91 (DBO5/DQO) was calculated, initial pH of the sample was 4.16 ± 0.05, a concentration of total volatile solids (TVS) of 58.1 ± 0.94 [g/L], and total sugar of 19.6 ± 0.79 [g Dextrose/L]. The yield was at 49.2 [NmL H2/g DQOInitial], the hydrogen production per fresh coffee pulp kilogram was 4.18 [L H2/kg C.P.], the energy density was determined at 0.045 [MJ/kg C.P.]. Modified Gompertz parameters were 585 [NmL] for Hmax, 4.1 [NmL H2/g DQO-h] for Rmax and a lag phase (λ) of 92.70 [h]. Because the yield of hydrogen production of coffee pulp estimated was similar to complex substrates like tequila vinasses, and there was a DQO reduction of 13.58%, based on some substrate restrictions, dark fermentation could be a stage of pretreatment of wastewater with coffee pulp in a biogas process to produce two relevant economic and energy products (hydrogen and biogas).

Optimized electro-Fenton process with sacrificial stainless steel anode for degradation/mineralization of ciprofloxacin

In this study, an electro-Fenton (EF) process with auto generation of Fenton`s catalyst (Fe2+) was proposed and its applicability in degradation and mineralization of Ciprofloxacin (CIP) antibiotic was examined. A graphite-felt sheet was used as cathode for continuous electro-generation of H2O2 and a trifle stainless steel plate (AISI 304) was used as sacrificial anode to provide ferrous catalyst. Effect of various operating parameters including current intensity (5–100mA), reaction time (5–25min), initial CIP concentration (10–150mg/L) and initial pH (2–7) was investigated using Response Surface Methodology (RSM). Central Composite Design (CCD) under RSM was utilized to model the two main responses, namely, CIP and COD removals. Simultaneous optimization of responses under current intensity of 75mA, treatment time of 20min, initial CIP concentration of 45mg/L and initial pH of 5 showed that 95.1% and 57.4% of CIP and COD removal efficiency could be achieved, respectively. High coefficients of determination (R2), for CIP and COD removal efficiency (0.92 and 0.94, respectively) indicated strong predictive capability of the models. BOD5/COD ratio, as an index of biodegradability, increased sharply from 0 to 0.42 under optimal condition. Two energy models, Electrical Energy Consumption (EEC) and EEC per unit COD removal, were introduced and the effect of operating parameters on them was evaluated. The intermediates of CIP degradation in aqueous solution were identified using ion chromatography and liquid chromatography coupled with mass spectrometry (LC–MS).

Optimization of the heterogeneous electro-Fenton process assisted by scrap zero-valent iron for treating textile wastewater: Assessment of toxicity and biodegradability

In this work, the heterogeneous electro-Fenton process assisted by scrap zero-valent iron (SZVI) and with graphite electrodes (as anode and cathode) is studied as an alternative way to treat wastewater from a textile plant located in Medellín, Colombia. The effects of the initial pH, SZVI load, and current density in the SZVI-assisted electro-oxidation process (EO/SZVI) are analyzed and optimized using multivariable regression models generated using the Box–Behnken experimental design and convex nonlinear optimization. The EO/SZVI process leads to maximum reductions of approximately 100%, 67%, and 59% in color, chemical oxygen demand (COD), total organic carbon (TOC), respectively, under the optimal operating conditions of pH of 3.5. Further, it leads to an SZVI concentration of 0.6 g/L, and a current density of 20 mA/cm2 during 30 min of electrolysis. The post-process pollutants are characterized further using molecular weight distribution measurements, ultraviolet–visible spectroscopy, high-performance liquid chromatography, biodegradability, and toxicity. The results show that the treated effluent is polluted mostly by carboxylic acids of low molecular weight. A remarkable enhancement of the biodegradability of the effluent is evidenced by an increase in the BOD5/COD ratio (biodegradability index) from 0.15 to 0.54. Although the EO/SZVI process does not improve the toxicity (as measured by the mortality of Artemia salina), the latter is reduced subsequently from 100% to 20% through adsorption using activated carbon (AC). The findings of this study indicate that the EO/SZVI process is an effective and promising alternative for treating textile wastewater.

Fenton oxidation and adsorption pretreatment for superior biogas recovery from biomethanated spent wash

A key task in alcohol distilleries is the effective treatment of biomethanated spent wash after biogas recovery. This colored washwater exhibits low biodegradability index (BI < 0.2), high chemical oxygen demand (30,000 < COD < 40,000 mg/L), and recalcitrance to aerobic treatment. In this work, pretreatment of biomethanated distillery wastewater by Fenton oxidation was proposed for improved biogas recovery. The effects of temperature, solution pH, and H2O2 dosage on the efficacy of the oxidation process were studied. Using ferrous sulfate catalyst (36 mg/L) for diluted wastewater (BOD5 = 81; COD = 400 mg/L), 54% reduction in COD was achieved within 1 h in acidic medium (pH = 3) at ambient temperature (T = 30 °C). Post-oxidation, the BI value improved (0.33). After subsequent adsorption over activated carbon (loading 5%) for 1 h, COD reduction (70%), and BI value (0.43) improved further. Upon anaerobic treatment with 1% acclimatized biomass, 1 Nm3 of biogas (47% CH4) was additionally formed per m3 of treated wastewater; without pretreatment, this value was 0.9 Nm3 (just 11% CH4). Lastly, aerobic treatment was performed and the results were encouraging: BI = 0.51 and COD reduction = 94%. Many oxidation products were identified and first-order kinetic plots were made to describe COD conversion kinetics. In this way, useful insight on a plausible technique for valorization of biomethanated washwater was provided.

Relationships between the physical properties and biodegradability and bacteria toxicity of fatty acid-based ionic liquids

This work is focused on the correlation between several physical properties (kinematic viscosity, viscosity index, refractive index, density and water solubility) and biodegradability and bacteria toxicity of a family of ionic liquids synthesized from fatty acids as anion precursor (FAILs): methyltrioctylammonium hexanoate [N8881][C6:0], methyltrioctylammonium octanoate [N8881][C8:0], methyltrioctylammonium laurate [N8881][C12:0], methyltrioctylammonium palmitate [N8881][C16:0], methyltrioctylammonium stearate [N8881][C18:0] and methyltrioctylammonium oleate [N8881][C18:1]. To that end, new values of these physical properties, biodegradability and bacteria toxicity were determined, although literature data for the [N8881][C8:0], [N8881][C12:0] and [N8881][C16:0] FAILs were also needed. It was found a good linear relationship (r2>0.90) between the biodegradability index (BOD5/COD) and the logarithm of kinematic viscosity, refractive index and water solubility for the saturated FAILs. Besides, the toxicity on both Vibrio fischeri and Escherichia coli can be successfully predicted using the logarithm of kinematic viscosity and viscosity index. Therefore, kinematic viscosity, which is an essential parameter for a lubricant, is the most promising physical property to estimate both biodegradability and bacteria toxicity of a family of ionic liquids. The double bond in the structure of the unsaturated FAIL ([N8881][C18:1]) is responsible for the worsening of the linear dependence between physical and environmental properties.

Biodegradability index enhancement of landfill leachates using a Solar Galvanic-Fenton and Galvanic-Fenton system coupled to an anaerobic–aerobic bioreactor

Mature landfill leachate is among the most difficult effluents to treat because of its complex composition, low biodegradability index and high toxicity. In this study the performances of Galvanic Fenton (GF) and solar Galvanic Fenton (SGF) systems coupled to a biological reactor were evaluated for the remediation of landfill leachate. The SGF and GF systems showed an increase in biodegradability from 0.0022 to 0.1388 and 0.1014, respectively, at 1500 mg hydrogen peroxide (H2O2) L−1 and 30 min of hydraulic retention time (HRT). The GF/biological coupled treatment showed the best performance in chemical oxygen demand (COD) (66.6%), biochemical oxygen demand (BOD) (86.5%), toxicity (90.1%) and organic nitrogen (ON) (93.7%) removal. The GF and SGF effluent characterization by UV–Visible (Uv–Vis), infrared (IR) and fluorescence spectroscopy showed the breaking of aromatic rings and conjugated double bond via the oxidation process. The GF system can be applied to improve the biodegradability index (BI) of leachates and integrated in wastewater treatment prior to a conventional biological treatment.

Wet air oxidation of leachate containing emulsified and solubilized hydrocarbons from crude oil-contaminated soil

The present research work is focussed on the treatment of leachate generated from crude oil-contaminated soil sites using wet air oxidation as an advanced oxidation process. The factors affecting the wet air oxidation (WAO) process, viz. temperature, pressure and time of treatment were optimized using central composite design and response surface methodology. The significant factors were optimized to maximize % COD removal from the leachate. The linear effects of pressure and temperature (p = 0.000); the square effects of pressure (p = 0.019) and time (p = 0.007) and the interaction effect of temperature–pressure (p = 0.002) were found to be significantly governing the % COD removal. The maximum COD removal of 76% was obtained at temperature = 244 °C, time = 30 min and pressure = 5 bar. Further, the biodegradability index (BOD5/COD) increased from 0.14 ± 0.007 of the untreated leachate to 0.48 ± 0.02 of the wetox-treated leachate. Moreover, the degradation of recalcitrant hydrocarbons in initial leachate by WAO treatment was confirmed using GC–MS analysis.

Thermophilic ligno-cellulolytic fungi: The future of efficient and rapid bio-waste management

To accelerate the process of decomposition using consortia of thermophilic ligno-cellulolytic fungi, different crop residues viz. sorghum (SG), soybean (SS), maize (MS), sugarcane (SC), cotton (CS) and pigeon pea (PS) with a varied C:N ratio and sawdust (SD) having high lignin content were collected and used for decomposition process. Compost quality assessed by evaluating different maturity and stability indices at five succeeding stages [first mesophilic (M1), thermophilic (T), second mesophilic (M2), cooling (C) and humification (H)]. A significant reduction was observed in the C:N ratio, biodegradability index, nitrification index, ratio of water-soluble carbon to organic nitrogen (WSC/Org.N) with an increase in concomitant over time while Ash (%), organic matter loss (%), CEC/TOC ratio, cellulose biodegradation ratio (BR) and lignin/cellulose ratio were significantly increased with time. By correlation study, biodegradability index (BI) and fluorescein diacetate (FDA) hydrolysis emerged as the most suitable compost maturity and stability parameters, respectively. Principal component analysis (PCA) results confirmed that BI, BR, WSC/Org. N and FDA can be regarded as key indicators for assessing compost quality. Our findings conclude that fungal consortia of Tricoderma viride, Rhizomucor pusillus, Aspergillus awamori and Aspergillus flavus can accelerate decomposition time from 8 to 12 months (which is normal farming practice) to 120 days.

Nano catalytic ozonation of biomethanated distillery wastewater for biodegradability enhancement, color and toxicity reduction with biofuel production

The effectiveness of O3, O3/Fe2+, and O3/nZVI processes on biomethanated distillery wastewater (BMDWW) was evaluated in terms of biodegradability index (BI) enhancement, biofuel production, COD, color & toxicity reduction. A significant increase in biodegradability, COD, color and toxicity reduction was observed in O3/nZVI compared with O3, O3/Fe2+ due to more hydroxyl radical production. The O3/nZVI pretreated wastewater with enhanced BI (up to 0.71) showed 60% COD removal with additional biogas generation (64% methane content). From the Gas Chromatography Mass Spectrometry (GC-MS) analysis, 18 foremost organic compounds were predominantly detected in the raw distillery wastewater. The disappearance of the corresponding FTIR (Fourier Transform Infrared Spectroscopy) & GC-MS spectra during pretreatment processes signified the degradation or transformation of the recalcitrant present in the distillery wastewater. Subsequent (AnO + AO, AO) of pretreated BMDWW resulted in biodegradation rate enhancement by (1.83, 1.67), (3.5, 2.4) and (4.7, 2.9) times for O3, O3/Fe2+ and O3/nZVI processes respectively.

Assessing the efficiency in assisted depuration of coffee processing wastewater from mixed wild microbial selected inoculum.

This work evaluated the efficiency of bacterial bio-augmentation to the biological treatment of coffee processing wastewater (CPWW) in a pilot wastewater treatment plant (WTP). Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) values were the basis for the treatment efficiency. Serratia marcescens CCMA 1010 and CCMA 1013, Corynebacterium flavescens CCMA 1006 and Acetobacter indonesiensis CCMA 1002 were previously selected. The microbial cocktail was inoculated and persisted in CPWW during all treatments. The richness of wild species was a little altered over time and up to nine species were found in each sampled season. The microbiota composition presented variation of a total of 13 species, despite the inoculation of the microbial inoculum. The biodegradability index of effluent, close to 0.5, was favourable to biological treatment. The pollution parameters of CPWW were decreased in function of the variation of community composition and microbial activity. The greatest reduction of BOD (~ 33%) and COD (~ 25%) was observed between 72h and 8days of the biological treatment. The CPWW toxicity in Allium cepa seeds was lower by up to 60%, and the germination index (GI) exceeded 100% in the treated CPWW. The results of the CPWW biological treatment by bio-augmentation from native micro-organisms in the pilot-scale WTP indicated the greatest efficiency relating to the spontaneous biological treatment of CPWW. After this treatment, the discharge of effluent in the environment would not have toxic effects on the plants.

Effects of green waste participation on the co-digestion of residual sludge and kitchen waste: A preliminary study

Anaerobic co-digestion has been extensively applied in treating residual sludge (RS) and kitchen waste (KW). However, some problems still occur in co-digestive system. This study tries to add green waste (GW) as co-substrate into RS/KW co-digestive system to improve methane production and system stability. The results showed that K4 group (RS:KW:GW = 2:1:0.5, based on VS addition, similarly hereinafter) presented the highest specific methane yield (SMY) of 303.4 mL/g VS, as well as the highest acetic acid (HAc) concentration at the primary stage. An appropriate amount of GW addition into co-substrate mixture was conducive to guaranty continuous degradation and conversion of the organics, and it could also improve the stability of the digestive system and optimize volatile fatty acids (VFAs) composition structure. Buswell formula was used and showed that the highest biodegradability index (BI) was obtained in K4 (97.0%) and K5 (98.2%). Besides, the fitting results of kinetic models were used to analyze methane production and hydrolytic process. The enzymes activity and microbial diversity results of K4 group can also verify the results above.

A kinetic study on the degradation and biodegradability of silver nanoparticles catalyzed Methyl Orange and textile effluents

The present study includes the Azadirachta indica (neem) induced Silver nanoparticles (AgNPs) by green synthesis as reducing and capping agent. Synthesized AgNPs were characterized by different instrumental techniques such as XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), Zetasizer, UV-Visible and FT-IR (Fourier Transformation Infra-Red) spectroscopy. The result of XRD reveals that nanoparticles were crystalline in nature and pure, stability was determined by Zeta potential and SEM, TEM analysis indicates that AgNPs was monodisperse in a spherical shape with average size 9 nm. These synthesized AgNPs were applied as the catalyst in the degradation process of Methyl Orange (MO) and wastewater samples in presence of peroxodisulphate (PDS). Effect of different experimental conditions such as initial pH, concentration of PDS, Dye, and AgNPs was studied on the degradation process. The obtained kinetic result shows that AgNPs/PDS system induces 1.1 × 10−4 to 15.9 × 10−4 s-1 folds in presence of the small concentration of AgNPs (1 × 10−8 mol dm−3). The degradation of MO and real wastewater samples in AgNPs/PDS system is followed pseudo-first order kinetics and maximum degradation of MO reached 88% in 40 min and real wastewater samples in 80 min. Liquid chromatography-mass spectrometry (LC-MS) analysis and UV-Visible spectral changes were used to analyze the structure of intermediate and end products (CO2, H2O, NO3−, and O3S−) during the degradation process. Furthermore, the result of biodegradability index (greater than 0.3) implies that advanced oxidation process enhances the biodegradability of wastewater.

Rapid and high purification of olive mill wastewater (OMV) with the combination electrocoagulation-catalytic sonoproxone processes

Background and purpose: Olive Mill Wastewater (OMW) is one of the most problematic wastewater in the food industry. Thus, its ineffective treatment causes severe pollution in the environment. In this study, the treatment of OMW by combining electrocoagulation (EC) and catalytic sonoperoxone processes was investigated. Materials and methods: The efficiency of turbidity removal and mineralization of OMW using EC was investigated by applying the following operation variables: type of electrode (iron and aluminum), reaction time (0- 60 min) and current density (0.08�0.77 A/dm 2 ). Then, a single ozonation process (SOP), a catalytic ozonation process (COP), an ultrasonic process (US), H 2 O 2 , COP/US, a peroxone process (H 2 O 2 /O 3 ) and a catalytic sonoperoxone process (H 2 O 2 /COP/US) were performed. Finally, the biodegradability of OMW was measured by using BOD 5 /TOC index. Results: Maximum removal efficiency of the turbidity, Total Organic Carbon (TOC) and consumed electrode in the EC were 82, 75 and 634 mg of iron electrode/L of OMWW, respectively. The TOC removal efficiency of the pretreated OMW by using the following oxidation processes of US, H 2 O 2 , SOP, O 3 /H 2 O 2 , COP, COP/US and H 2 O 2 /COP/US was 8, 15, 20, 25, 61, 68 and 75, respectively. In addition, the biodegradability index (BOD 5 /TOC) in the catalytic sonoperoxone process increased by as much as 32 compared to raw OMWW. Conclusion: The EC process caused an effective per-treatment of OMW and combined by sonoperoxone process improved its biological biodegradability. So, this process can be used for the efficient treatment of OMWW and the wastewater produced by similar industries. © 2019 Taiwan Institute of Chemical Engineers

Evaluation of inoculum acclimatation and biochemical seasonal variation for the production of renewable gaseous fuel from biorefined Laminaria sp. waste streams

Laminaria. sp. seaweeds have been recognised the potential to greatly contribute to the generation of renewable gaseous fuel via anaerobic digestion. Seaweed feedstock has been documented to consistently vary its biochemical composition with seasons, which affects stability of biomethane production. As currently seaweeds are too costly for use as third generation feedstock for biofuels, this paper investigates the biogas potential of the algal waste streams from the existing bio-industry. Analytical tests identified an improved digestibility of extracted residues (C:N > 20). Fermentation with and without inoculum acclimatation revealed the interaction between compositional seasonality and inoculum type to significantly affect methane production from the extracted samples. Summer’s composition has the most significant impact on methane production, with best results achieved with acclimatised inoculum (433 ml CH4 gVS−1 and final biodegradation of about 90%). Organics concentration (tCOD) and ash:volatile (A:V) ratio also play a major role in the bioconversion process. In particular, digestion with acclimatised inoculum better responds to A:V fluctuations across seasons, which produced the highest average methane yield of 334 ml gVS−1. Pretreatments are required to increase the biodegradation index in spring and summer when not using acclimatation.

Treatment of biodigester effluent through EC followed by MFC: Pollutants removal and energy perspective

The present work deals with the treatment of bio digester effluent (BDE) using electrocoagulation (EC) followed by continuous membrane less microbial fuel cell (CML‐MFC). BDE with high organic load and low biodegradability index (BI) is first treated with EC process, which removes organic load and improves the BI of treated BDE. Further the EC treated BDE with relatively low organic load 1000 mg/L and considerable BI (~0.42) is used as a substrate solution for the CML‐MFC process. It is noted that the BDE with initial organic load of 2500 mg/L can be successfully treated using only EC process, whereas, only CML‐MFC operation can successfully teat EC treated BDE with low organic load (1000 mg/L). However, in combined study of EC followed by CML‐MFC, the BDE with initial organic load of 7450 mg/L can be successfully treated to achieve effluent composition below permissible limit as per Central Pollution Control Board (CPCB) norm. It is also computed that under the experimental conditions, during the EC process, approximately 2.466 and 0.537 kJ/g of energy can be generated from sludge and scum, respectively, whereas, approximately 48 mV voltage and 0.02 mA current can be generated from the CML‐MFC process. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13139, 2019

Electro-oxidation of landfill leachate using boron-doped diamond: role of current density, pH and ions.

Electro-oxidation using a boron-doped diamond (BDD) anode can be used as an alternative to leachate treatment. Aside from the hydroxyl radical, BDDs are capable of generating chloride and sulfate radical species that play significant roles in the oxidation of pollutants. This research investigated the role of Cl-:SO4 2- ions at molar ratios of 237:1, 4:1 and 18:1, and the influence of applied current density (i.e. 50, 75 and 100 mA cm-2) on the removal of organic and ammonium contaminants. The results show that current density had considerable effects on chemical oxygen demand (COD) and colour removal, while ion composition of Cl-:SO4 2- at pH 3, 5 and 8.5 (original pH) gave different effects on COD and ammonium removal. The pH had a significant effect on the COD removal at the ratio of 237:1, but showed no dramatic effect at the ratio of 18:1, giving ∼40% of COD removal at all pHs tested. This indicates that electro-oxidation at the ratio of 18:1 could be effectively conducted at a wide range of pH. Furthermore, the optimum ammonium removal was obtained at pH 8.5 with the ratio of 237:1. This process was found to be ineffective in increasing the biodegradability index of the leachate; instead, it exhibited mineralization of organic content.

Degradation and COD removal of trichlorophenol from wastewater using sulfite anion radicals in a photochemical process combined with a biological reactor: Mechanisms, degradation pathway, optimization and energy consumption

This study proposes the combination of UV/sulfite with a biological reactor (USPB) for the degradation, dechlorination and mineralization of 2, 4, 6-trichlorophenol (TCP). The effects of pH, sulfite dosage, co-existing water anions and quenchers on the performance of the UV/sulfite process (USP) were investigated. The rate of degradation, dechlorination and mineralization of TCP under optimum experimental conditions of pH, 7.0; [sulfite]/[TCP] = 3.13; UV irradiation, 87 μW cm−2; dissolved oxygen (DO), 2 mg L-1 and an 80 min reaction time, were 100, 98 and 30.2%, respectively (initial TCP concentration was 250 mg L-1 and initial COD was 363 mg L-1). Investigation of the reaction mechanism revealed the superiority of sulfite radicals (SO3-) in the degradation and dechlorination of TCP. The co-existing water anions did not significantly affect the performance of TCP degradation. The intermediates derived from TCP degradation included: 1,3-cyclohexadiene, 2-chloro-1-benzoquinone, 2-chlorophenol, benzene, 2-hydroxy benzoquinone and cyclohexene. The (BOD5)/(COD) ratio (the solution biodegradability index) was obtained as 0.57 after 80 min of UV/sulfite reaction time. The effluent obtained from UV/sulfite after 80 min of reaction time (with COD of 253 mg L-1) was efficiently post-treated in a batch biological reactor (MLSS = 5000 mg L-1), and the COD reduced to 37 mg L-1 after 720 min (12 h) of aeration. Therefore, it was found that the combination of the UV/sulfite with a biological process might be an efficient method for the treatment of wastewater containing high concentrations of toxic compounds.

Degradation of nitrobenzene by synchronistic oxidation and reduction in an internal circulation microelectrolysis reactor.

The degradation of nitrobenzene by synchronistic oxidation and reduction was investigated using an internal circulation microelectrolysis (ICE) reactor with an active volume of 0.018 m3. Compared with a conventional fixed bed reactor with and without aeration, the ICE reactor exhibited a markedly higher nitrobenzene degradation efficiency. The effects of various operational parameters such as reaction time, aeration rate, initial nitrobenzene concentration, initial pH, and a volume ratio of iron and carbon (Fe/C) were also investigated. The optimal operating conditions (reaction time = 60 min, aeration rate = 5 × 10-4 m3/s, initial concentration of nitrobenzene = 300 mg/L, pH = 3.0, Fe/C = 1:1) gave removal efficiencies of nitrobenzene and chemical oxygen demand of 98.2% and 58%, respectively. The biodegradability index of the treated nitrobenzene solution was 0.45, which is 22 times that of the original solution. The reaction intermediates were identified through high-performance liquid chromatography, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and ion chromatography. The primary intermediates were determined to be aniline, phenol, and carboxylic acids, indicating that nitrobenzene was synchronously oxidized and reduced in the ICE reactor. Based on the identified intermediates, a possible pathway for nitrobenzene degradation in the ICE reactor is proposed.