Ozonation of NSAID: A Biodegradability and Toxicity Study

This work deals with the biodegradability and toxicity of three non-steroidal anti-inflammatory drugs (NSAID) (diclofenac, ibuprofen and naproxen) treated by ozonation. The results show that the total removal of 200 mg L^?1 of diclofenac and 100 mg L^?1 of naproxen is possible using an ozone dose of 0.20 and 0.04 g L^?1, respectively. For 200 mg L^?1 of ibuprofen, 90% removal is achieved using an ozone dose of 2.3 g L^?1. The BOD₅/COD ratio, the Zahn-Wallens test and EC₅₀ toxicity test (Microtox) are chosen as biological and toxicity indicators of NSAID intermediates. The evolution of BOD₅/COD ratio during 1 hour of treatment is evaluated and the results show that ozonation improves the biodegradability for the three NSAID treated solution. The Zahn-Wellens test for diclofenac and ibuprofen solutions shows that biological mineralization, after 28 days, is higher for diclofenac than for ibuprofen solution. According to the Microtox test, the treatment with ozone removes the toxicity of the naproxen solution. Taking into account the results obtained with the biocompatibility tests it could be assumed that ozonation is an adequate treatment for removal NSAID in aquatic medium, and the ozonated effluents could be post-treated in a biological wastewater facility.     

Ozone treatment of textile effluents and dyes: effect of applied ozone dose,pH and dye concentration

The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye‐bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi‐batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD₅ (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm^?3 ozone consumption. Ozonation of acid dyes was a pseudo‐first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR‐183) dye solution with a concentration of 50 mg dm^?3 rose from 0.32 to 0.72 mg‐O₃ per mg dye decomposed as the dye concentration was increased to 500 mg dm^?3. © 2002 Society of Chemical Industry     

pH Effect on Ozonation of Ampicillin: Kinetic Study and Toxicity Assessment

Ampicillin (AP) is a penicillin-type antibiotic and one of the most widely used bacteriostatic antibiotics in human and veterinary medicine. A kinetic study was performed under different pH conditions (5, 7.2, and 9) to determine the degradation efficiency of AP by ozonation. The second-order rate constants for the direct reaction of AP with ozone were measured to be 2.2 ?5.4×10⁵ M^?1s^?1 under the pH conditions tested. The rate constants were greater at higher pH. The potential toxicity of the AP intermediates formed after ozonation under the various pH conditions were examined using a bioluminescence assay on Vibrio fischeri species. The biodegradability of the AP degraded products was also determined by measuring the BOD₅/COD of the ozonated samples under the different pH conditions. A lower biodegradability and acute toxicity was observed at the lowest pH (pH 5). These results suggest that higher pH conditions are needed for the removal of AP by ozonation in order to mitigate the residual toxicity that can remain even after complete removal of the parent compound by ozonation.     

Decolorization,mineralization, and toxicity reduction of acid orange 6 by iron‐sacrificed plates in the electrocoagulation process

In this study, electrocoagulation (EC) was used to investigate the decolorization and mineralization of an azo dye solution, as well as biodegradation enhancement and toxicity reduction. Initial pH, flow rate, and acid orange 6 concentration were investigated, and the optimum operational parameters were found to be pH = 4, flow rate (Q) = 0.3 to 0.5 L min^?1, and current density = 68.3 A dm^?2. With these optimal parameters, total organic carbon and color removal efficiencies of 40% and 98% were achieved, respectively. Biodegradation was evaluated using the ratio of the 5‐day biological oxygen demand (BOD₅) and the chemical oxygen demand (COD), which was 0.19 to 0.25 initially and increased to the range 0.25 to 0.4 after EC treatment, indicating that biodegradability was significantly enhanced. The mean effective concentration (EC₅₀) was measured to represent the toxicity of the solution. Initial EC₅₀ values ranged from 25 to 6.6%, which represent extremely toxic to very toxic solutions. After EC treatment, the toxicity levels were reduced significantly, suggesting that the EC process could be a promising method for reducing the toxicity of textile wastewater. Copyright © 2007 Society of Chemical Industry     

Toxicity and Biodegradability Behavior of Xenobiotic Chemicals Before and After Ozonation: A Case Study with Commercial Textile Tannins

Ozonation of a natural tannin (NT; COD_o?=?1195 mg/L; TOC_o?=?342 mg/L; BOD_5,o?=?86 mg/L) and a synthetic tannin ST; COD_o?=?465 mg/L; TOC_o?=?55 mg/L; BOD_5,o?=?6 mg/L) being frequently applied in the polyamide dyeing process was investigated. Synthetic wastewater samples containing these tannins individually were prepared and subjected to ozonation at varying ozone doses (625– 1250 mgO₃/L wastewater), at pH?=?3.5 (the application pH of tannins) and pH?=?7.0 at an ozone dose of 1125 mgO₃/L wastewater. The collective environmental parameters COD, TOC, BOD₅, UV₂₅₄ and UV₂₈₀ (UV absorbance at 254 nm and 280 nm, representing aromatic and unsaturated moieties, respectively) were followed during ozonation. Changes in the biodegradability of the tannins were evaluated in terms of BOD₅ measurements conducted before and after ozonation. In addition, activated sludge inhibition tests employing heterotrophic biomass were run to elucidate the inhibitory effect of raw and ozonated textile tannins towards activated sludge biomass. Partial oxidation (45% COD removal at an ozone dose of 750 mg O₃/L wastewater and pH?=?3.5) of ST was sufficient to achieve elimination of its inhibitory effect towards heterotrophic biomass and acceptable biodegradability improvement, whereas the inhibitory effect and biodegradability of NT could not be reduced via ozonation under the same reaction conditions.     

Chemical treatment of cork‐processing wastewaters for potential reuse

The chemical treatment of cork‐processing wastewater by ozonation, alone and in combination with hydrogen peroxide and UV radiation was investigated. A reduction of the chemical oxygen demand (COD) ranging from 42% to 76% was obtained during ozonation after 3 h of reaction, depending on the experimental conditions. The additional presence of hydrogen peroxide and UV radiation enhanced the efficiency of the ozonation treatment due to the contribution of the OH radicals formed in the decomposition of ozone. Thus, final reductions of the COD higher than 90% and a complete elimination of phenolic compounds and absorbance at 254 nm were achieved in both Advanced Oxidation Processes (AOPs), O₃/H₂O₂ and O₃/UV. Therefore the effluent resulting from the ozonation treatments can be reused in the cork‐processing industry. In a second step, the chemical treatment was conducted by means of UV radiation alone and by the action of hydroxyl radicals, which were generated by the following AOPs: UV/H₂O₂, Fenton's reagent, and photo‐Fenton system. The single photochemical process resulted in 9% of the organic matter present being removed, while the AOPs significantly enhanced this reduction with values in the range 20–75%. Kinetic studies for both groups of treatments were performed, and apparent kinetic rate constants were evaluated. In the ozone‐based experiments, the rate constants ranged from 1846 to 10922 dm³ mol^?1 O₃ h^?1, depending on the operating conditions. In the oxidation experiments using oxidants other than ozone, the rate constants varied between 0.06 and 1.19 h^?1. Copyright © 2004 Society of Chemical Industry     

Ozonation of complex industrial park wastewater: effects on the change of wastewater characteristics

BACKGROUND: Ozonation of complex industrial park wastewater was carried out in a semi‐batch reactor. The variation of wastewater characteristics was evaluated based on the analysis of 5‐day biochemical oxygen demand (BOD₅) concentration, BOD₅/chemical oxygen demand (COD) ratio, COD fractionation, and dissolved organic carbon (DOC) molecular size distribution before and after ozonation. RESULTS: The experimental results indicated that low efficiency of COD removal with increasing tendency of BOD₅ concentration generally appeared after ozonation. Also, the BOD₅/COD ratio increased from an initial of 0.27 to a maximum of 0.38. The COD fractionation tests revealed that most of the inert soluble COD was transformed to biodegradable soluble COD at 30 min of reaction time. Additionally, the DOC molecular size distribution tests showed that the fraction larger than 500 kDa was significantly decreased and the fraction smaller than 2 kDa was increased when the reaction time was prolonged to 240 min. CONCLUSION: This study verified that partial oxidation of the complex industrial park wastewater by ozonation could enhance wastewater biodegradability. The biodegradability enhancement was primarily because the inert soluble COD fraction was converted to the biodegradable soluble COD and the high molecular weight fraction of DOC was shifted toward the low molecular weight fraction. Copyright © 2009 Society of Chemical Industry     

Ozonation of Anionic and Non-ionic Surfactants in Aqueous Solutions: Impact on Aquatic Toxicity

The objective of this study was to investigate the influence of ozonation of anionic and non-ionic surfactants on their aquatic toxicity. Toxicity values of various commercially important anionic and non-ionic surfactants have been determined using the luminescent bacterium Vibrio fischeri. Surface tension measurements were made to study the interfacial activity. The behavior depends on the chemical structure. Some intermediate ozonation products were found to be more toxic than the base surfactant and others were found to be less. Surfactants with aromatic rings such as linear alkyl benzene sulfonates, or surfactants with glycosidic groups such as alkylpolyglucosides, exhibit a lower toxicity after ozonation. On the other hand, ether groups present in the fatty-alcohol ethoxylates and ether carboxylic derivative surfactants, and carboxylic acid derivates present in the ether carboxylic derivative surfactants lead to increasing toxicity after ozonation. Surfactants with ether groups probably formed short-chain polyethoxylated compounds and carboxylic acids, which are possibly responsible for the surface-tension decrease that promotes the toxicity increase.     

Advanced oxidation of raw and biotreated textile industry wastewater with O3, H2O2 /UV‐C and their sequential application

The advanced chemical oxidation of raw and biologically pretreated textile wastewater by (1) ozonation, (2) H₂O₂ /UV − C oxidation and (3) sequential application of ozonation followed by H₂O₂ /UV − C oxidation was investigated at the natural pH values (8 and 11) of the textile effluents for 1 h. Analysis of the reduction in the pollution load was followed by total environmental parameters such as TOC, COD, UV–VIS absorption kinetics and the biodegradability factor, f_B. The successive treatment combination, where a preliminary ozonation step was carried out prior to H₂O₂ /UV − C oxidation without changing the total treatment time, enhanced the COD and TOC removal efficiency of the H₂O₂ /UV − C oxidation by a factor of 13 and 4, respectively, for the raw wastewater. In the case of biotreated textile effluent, a preliminary ozonation step increased COD removal of the H₂O₂ /UV − C treatment system from 15% to 62%, and TOC removal from 0% to 34%. However, the sequential process did not appear to be more effective than applying a single ozonation step in terms of TOC abatement rates. Enhancement of the biodegradability factor (f_B) was more pronounced for the biologically pretreated wastewater with an almost two‐fold increase for the optimized Advanced Oxidation Technologies (AOTs). For H₂O₂ /UV − C oxidation of raw textile wastewater, apparent zero order COD removal rate constants (k_app), and the second order OH· formation rates (r_i) have been calculated. © 2001 Society of Chemical Industry     

Biodegradability of slaughterhouse wastewater with high blood content under anaerobic and aerobic conditions

In this work, the biodegradability of wastewater from a slaughterhouse located in Ke?an, Turkey, was studied under aerobic and anaerobic conditions. A very high total COD content of 7230 mg dm^?3 was found, due to an inefficient blood recovery system. Low BOD₅/COD ratio, high organic nitrogen and soluble COD contents, were in accordance with a high blood content. A respirometry test for COD fractionation showed a very low readily biodegradable fraction (S_S) of 2%, a rapidly hydrolysable fraction (S_H) of 51%, a slowly hydrolysable fraction (X_S) of 33% and an inert fraction of 6%. Kinetic analysis revealed that hydrolysis rates were much slower than these of domestic sewage. The results underlined the need for an anaerobic stage prior to aerobic treatment. Tests with an anaerobic batch reactor indicated efficient COD degradation, up to around 80% removal. Further anaerobic degradation of the remaining COD was much slower and resulted in the build up of inert COD compounds generated as part of the metabolic activities in the anaerobic reactor. Accordingly, it is suggested that an appropriate combination of anaerobic and aerobic reactors would have to limit anaerobic degradation to around 80% of the tCOD and an effluent concentration above 1000 mg dm^?3, for the optimum operation of the following aerobic stage. © 2003 Society of Chemical Industry     

Anaerobic and aerobic treatment of a simulated textile effluent

A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this effluent contained one reactive azo dye, PROCION Red H‐E7B (1.5 g dm⁻³); sizing agent, Tissalys 150 (1.9 g dm⁻³); sodium chloride (1.5 g dm⁻³) and acetic acid (0.53 g dm⁻³) together with nutrients and trace elements, giving a mean COD of 3480 mg dm⁻³. An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic effluent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77–247 68% of the true colour of PROCION Red H‐E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (B _v) 1.24 g COD dm⁻³day⁻¹) and the UASB at a 2 day HRT (B _v 1.74 g COD dm⁻³day⁻¹) gave comparable COD removals but the UASB gave better true colour removal. Effluent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm⁻³, and further treatment would be required to meet consent standards. © 1999 Society of Chemical Industry     

Impact of Ozonation on Decolorization and Mineralization of Azo Dyes: Biodegradability Enhancement,By-Products Formation,Required Energy and Cost

In the present study ozonation process was implemented to analyze the effect of ozonation time on the rate of chemical oxygen demand (COD) removal, mineralization and rate of decolorization of azo dyes. Three types of azo dyes i.e. Acid Red 14, Direct Red 28 and Reactive Black 5 were selected. Decolorization and mineralization of samples were conducted in batch scale. The COD and color removal efficiency were found to be increasing at a certain time of ozonation. The results with Acid Red 14, Congo Red and Reactive Black 5 dyes solutions lead to maximum COD reduction of 75%, 67% & 50% respectively. 93%, 92% and 94% color removal were achieved after 25 min of ozonation time of the same dyes which highlighted that ozonation process was found to be more efficient for reactive dye decolorization. Ozonation by-products analyzed by ion chromatography resulted that it partially mineralized with the formation of chloride, fluoride, sulphate, nitrate and oxalate ions. During ozonation process a rapid decrease in pH value indicated the acidic nature of by-products. The effect of buffered dye solutions on the ozonoation process highlighted that the decolorization efficiency decreases in comparison to unbuffered dye solutions. Ozonation led to enhancement of biodegradability ratio (BOD₅/COD) and increased electrical conductivity of the dye solutions. Optimum ozonation time required for degradation of dye solutions reflected the evaluation of energy consumption and cost of the treatment after ozonation.     

Abatement of 4-Chlorophenol in Aqueous Phase by Ozonation Coupled with a Sequencing Batch Biofilm Reactor (SBBR)

The aim of this work was to assess the mineralization of 100 and 200 mg L^?1 4-chlorophenol (4-CP) solutions by ozonation-biological treatment. The results show that starting from a 4-CP initial concentration from 100 to 500 mg L^?1 and using an ozone flow rate of 5.44 and 7.57 g h^?1, 4-CP was completely removed. A kinetic constant around 9·10^?2 min^?1 was calculated for the ozone direct attack. The biodegradability (BOD₅/COD) of the pre-ozonated solutions increased from 0 until a range between 0.2–0.37. The combination of the ozonation and aerobic biological treatment in an aerobic sequencing batch biofilm reactor (SBBR) gave an abatement of more than 90% of the initial TOC.     

Enhancing Agro-Industrial Wastewaters Depuration by Ozone Oxidation

This article explores the application of several ozone-based technologies on the abatement of a bio-refractory stream coming from an elderberry juice plant (BOD₅/COD = 0.26). The impact of ozone inlet concentration and pH was addressed firstly, followed by the analysis of the O₃+H₂O₂ combined system. Finally, the activity and stability of two solid catalysts (Mn-Ce-O and Fe-Mn-O) was assessed. None of the approaches produced values within the legal thresholds for direct discharge into water-courses. It is advisable to integrate the chemical treatment with a bio-reactor. Thus, single ozonation at pH = 3 (BOD₅/COD = 0.48), O₃+[H₂O₂] = 32.5 mM (BOD₅/COD = 0.46) and O₃+Mn-Ce-O at pH = 3 (BOD₅/COD = 0.44) are promising strategies.     

Ozonation of Two Acidic Azo Dyes with Different Substituents

The ozonation of two differently substituted azo dyes (Schwarz GRS and Orange Acid 8) in water media is studied. The influence of pH on the effectiveness of the ozonation at various initial concentrations of each dye is explored. It was found out that the rates of decolorization for amino-group substituted dyes reflect the considerable influence by the widely varying initial pH from 4.5 to 10. Specifically, the highest effect of decolorization of this dye was obtained at the highest pH studied (pH 10) for all initial concentrations of the solutions. Considering the dye without an amino-group substitute, the rates of color disappearance in ozonation reflected to a lower degree the variations of the initial pH. Pseudo-first-order trends of decolorization were observed in all the experimental runs. Regarding the kinetic results obtained, an attempt to explain the different dyes reactivity was made based on the absolute electronegativity (E_lumo + E_homo) of both dyes. The COD/BOD analysis shows that the ozonation of both azo dyes can reduce the sample COD but it could not improve the biodegradability ratio (BOD₅/COD). BOD decrease with ozonation time indicates that the intermediates of the ozonation are of lower biodegradability. Oxalic acid was found as the final product of ozonation of both dyes.     

Effect of surfactants on phenol removal by the method of polymerization and precipitation catalysed by Coprinus cinereus peroxidase

The removal of phenol by peroxidase‐catalysed polymerization was examined using Coprinus cinereus peroxidase in the presence of surfactants. The non‐ionic surfactants with poly(oxyethene) residues, Triton X‐100, Triton X‐405 and Tween 20, enhanced the phenol removal efficiency at a level similar to high relative molecular mass poly(ethylene glycol) (relative molecular mass 3000). Although the improvement in the removal efficiency was less than that of Triton X‐100, Span 20, sodium lauryl sulfate (SDS) and lauryl trimethylammonium bromide (DTAB) also enhanced the removal efficiency. The requirement of the enzyme for almost 100% removal of 100 mg dm^?3 phenol decreased to one‐fourth by the addition of 30 mg dm^?3 Triton X‐100. Triton X‐100, Triton X‐405, Tween 20 and DTAB could reactivate the enzyme precipitated with the phenol polymer, leading to the restarting of the phenol removal reaction. Copyright © 2003 Society of Chemical Industry     

An investigation on the optimal location of ozonation within biological treatment for a tannery wastewater

The objective of this study was to evaluate the optimal location of ozonation within biological treatment for a typical tannery wastewater by giving special attention to biodegradability‐based chemical oxygen demand (COD) characterization. As treating the raw tannery effluent solely by biological treatment is not adequate to meet the discharge standards owing to the high level of biorecalcitrant COD at the outlet, the application of chemical oxidation, i.e. ozone together with biotreatment (pre‐ozonation or in mid‐ozonation or post‐ozonation) was investigated. The tannery effluent under investigation had initially inert soluble COD (S_I1) and particulate COD (X_I1) fractions corresponding to 9% and 13% of the total COD (C_T1), respectively, whereas each component of the biodegradable part—readily biodegradable COD (S_S1), rapidly hydrolysable COD (S_H1), and slowly hydrolysable COD (X_S1)—accounted for around 26% of the total COD (C_T1). Pre‐ozonation, undesirably competing with biotreatment for the removal of degradable organics, was shown to be insufficient both in terms of total COD (C_T1) and inert COD (C_I1) removal efficiencies. The scheme of biological treatment + ozonation + biological treatment could be applied successfully when 42.8 mg O₃ min^?1 was introduced for 5 min with a utilized ozone percentage of 76% at a point in biological treatment where the readily biodegradable COD (S_S1) was depleted through biochemical reactions. Such an alternative yielded satisfactory outcomes when both total COD (C_T) and inert COD (C_I) removal efficiencies per utilized ozone ratios were considered. With post‐ozonation, on the other hand, the highest inert COD (C_I) removal efficiencies together with an effluent quality meeting the discharge standards could be obtained. Copyright © 2006 Society of Chemical Industry     

Effect of organic surfactant additives on gas holdup in the pseudo-homogeneous regime in bubble columns equipped with fine pore sparger

New experimental data concerning the gas holdup in bubble columns equipped with porous sparger were acquired. The effect of surfactant additives on gas holdup in the pseudo-homogeneous regime has been studied. Three different commercial surfactants (Triton X-100^®, SDS^®, CTAB^®) were used and four aqueous solutions of each one were employed, in order to study the effect of the surfactant concentration and type (i.e., non-ionic, anionic, cationic). A general correlation, which includes dimensionless numbers (i.e., Froude, Archimedes and Bond) as well as the geometric characteristics of the column and the sparger, can predict the gas holdup in various systems (i.e., pure substances, ionic surfactants, non-ionic surfactants) with reasonable accuracy.     

Remediation of phenolic wastewaters by advanced oxidation processes (AOPs) at ambient conditions: Comparative studies

The efficiency of two AOPs operating at room conditions of pressure and temperature, ozonation (single and catalytic over the laboratorial Mn–Ce–O and the commercial N-150—Fe₂O₃/MnO_x) and Fenton's process (homogeneous and over Fe–Ce–O), was simultaneously checked for the remediation of a phenolic mixture. Gathering up former individual results pointing out as most suitable treatments those involving solid catalysts, either for ozonation or Fenton's, a global conclusion elects this last process as the more interesting for industrial applications. In fact, the lower retention time required by H₂O₂+Fe–Ce–O 70/30 to attain an easily biodegradable effluent makes this technology truly attractive for in-situ remediation of this specific wastewater. These findings were mostly driven by the comparative ability to transform the non-biodegradable raw effluent into streams more amenable to further bio-processing. In this regard, biological parameters superposed chemical COD degradation within the ultimate selection reasons. Indeed, in all cases COD limits were not reached and a subsequent biological treatment is required. Despite COD removal for catalytic ozonation showed to be higher than for heterogeneous Fenton's (63% and 50%), BOD₅/COD was contrarily favorable to Fenton's, which immediately conducted to a biodegradable mixture in the first minutes (0.78 in 10 min) while ozonation took more than 1 h to impart a biodegradable character.     

Degradation of Two Persistent Surfactants by UV-Enhanced Ozonation

In this study the treatment efficiency of different ultraviolet (UV)-enhanced ozonation processes for degradation of two surfactants, sodium dodecylbenzene sulfonate [200 mg/L or 0.3 critical micelle concentration (CMC)] and a nonylphenol ethoxylate with 40 oxyethylene units (200 mg/L ~0.5 CMC), were investigated in laboratory-scale experiments at ambient temperature. The absorbance band of the aromatic ring of the surfactants was monitored during the oxidation process. The reduction in chemical oxygen demand (COD) and total organic carbon (TOC) of the surfactant solution was evaluated. The results showed that a combination of UV irradiation and ozonation was considerably more efficient than the individual processes (at least two times more efficient in terms of COD and TOC reductions). The synergistic effect of ozonation and UV irradiation was particularly pronounced when medium-pressure UV irradiation was used. By adding alkali to the solution, the efficiency of the UV-enhanced ozonation increased with respect to COD reduction but decreased with respect to TOC reduction. This indicates partial oxidation with lower degree of mineralization of the surfactants.