Natural pH conditions with phenol concentrations in the range of 180–733 mg/L. The photochemical treatment was mediated with ferrioxalate and peroxide in two photoreactors of different volumes and operation conditions (batch and with closed flow).
Wastewater
Phenol transformation efficiencies of 100% and total COD reduction percentages of 85% were reached within the first hour of phototreatment, with an aromatic free effluent as the final product in both types of reactor. The ferrioxalate type complexes using mass ratios of oxalate/phenol = 1.5, oxalate/Fe3+ = 15, and H2O2/phenol > 5.0 were shown to be very effective in the treatment of these effluents, even at pH conditions close to neutral, the pH region in which Fenton type processes begin to lose efficiency due to the precipitation of iron as a hydroxide.
Photo-Fenton process in a CPC solar photoreactor. The effect of solar activated photo-Fenton reagent at pH 5.0 before and after a slow sand filtration (SSF) process in waters containing natural iron species was investigated.
Natural organic matter (NOM) model compounds (dihydroxy-benzene)
The results showed that the total transformation of dihydroxybenzene compounds was obtained with a mineralization of over 80%. The mineralization of organic compounds dissolved in natural water was higher than in Milli-Q water, suggesting that the aqueous organic and inorganic components (metals, humic acids, and photoactive species) positively affect the photocatalytic process. When 1.0 mg/L of Fe3+ was added to the system, photo-Fenton degradation improved.
Two laboratory scale photo-Fenton experiments were performed with the solar simulator and SMX dissolved in diluted water (DW) and in seawater (SW) at the same concentration (50 mg/L; DOC = 23.75 mg/L) as in the pilot plant experiments for their comparison with natural solar radiation. The initial DOC of SW was 2.6 mg C/L. The experiments were performed at three different initial concentrations of FeSO4·7H2O (2.6, 5.2, and 10.4 mg/L). Initial H2O2 concentrations ranged from 30 to 210 mg/L. The solar pilot plant reactor consisted of a compound parabolic collector (CPC) with a 3.0 m2 irradiated surface and total volume of 39 L.
Antibiotic sulfamethoxazole (SMX)
The photo-Fenton degradation of SMX was strongly influenced by the seawater matrix when compared to distilled water. Indeed, in seawater it is proposed that degradation occurs mainly through and Cl1− (or ) and not through HO−. The increased iron concentration showed a slight improvement on the pollutant degradation and mineralization rate. The increase of H2O2 concentration up to 120 mg/L in distilled water reduced the sample toxicity during the photo-Fenton process, which demonstrates that this is a feasible technology for the treatment of wastewater containing this compound.
Photo-Fenton oxidation was carried out using a cylindrical Pyrex thermostatic cell with a 300 mL capacity (°C), equipped with a magnetic stirrer. The dye solution volume was 250 mL. A 6 W Philips black light fluorescent lamp which basically emits at 350 nm was used as an artificial light source. The incident light intensity, measured with a uranyl actinometer, was Einstein s−1. A few Fenton reagent doses were tested in the present work (a series of three experiments): 5 mg/L Fe(II) and 125 mg/L H2O2, 10 mg/L Fe(II) and 125 mg/L H2O2 10 mg/L Fe(II) and 250 mg/L H2O2. Contaminants with a ratio of BOD5/COD ≥ 0.4 are generally accepted as biodegradable, while those with ratios between 0.2 and 0.3 units were partially biodegradable.
Homo-bireactive dye (Procion Red H-E7 B)
The results demonstrated that a photo-Fenton reaction can be used successfully as a pretreatment process to biocompatibilize Procion Red H-E7B reactive dye solutions. The best pretreatment results were obtained with 60 min of photo-Fenton irradiation time and 10 mg/L Fe(II) and 125 mg/L H2O2 of initial reagent concentration. Under these conditions, the BOD5/COD index increased from 0.10 to 0.35 units with 39% mineralization and 16.5 mg/L of residual H2O2. The use of photo-Fenton type reactions as a pretreatment allows the SBR system to remove Procion Red H-E7B Reactive Dye from aqueous solution, which improves the low success rate of aerobic biological removal of dye colour.
This study explored the application of the solar photoFenton process to the degradation of PNA in water. The operating pH value was varied in the range of 3–6. The effect, of H2O2 and Fe2+ dosage on the degradation of PNA by solar photo-Fenton process were investigated between 2.5–40 and 0.025–0.1 mM, respectively. Also the effect, of temperature and initial pollutant concentration were investigated in the range of 20–50°C and mM.
P-Nitroaniline (PNA)
The optimum conditions for the degradation of PNA in water were considered to be pH 3.0, 10 mmol/L H2O2, 0.05 mmol/L Fe2+, 0.072–0.217 mmol/L PNA, and temperature 20°C. Under optimum conditions, the degradation efficiencies of PNA were more than 98% within a 30 min reaction time. The degradation characteristic of PNA showed that the conjugated systems of the aromatic ring in the PNA molecules were effectively destroyed. The experimental results indicated that the solar photo-Fenton process has advantages over the classic Fenton process, such as higher oxidation power, a wider working pH range, and a lower ferrous ion usage.
During the experiment, H2O2 was added continuously to the reactor at a flow rate of 1 mL/min with a syringe pump. Two 8 W monochromatic UV lamps of 312 nm (with an emission range between 280 and 360 nm) were placed axially in the reactor and kept in place with a quartz sleeve. The UV intensity of one 8 W UV lamp is 60 W/cm. The reaction temperature was maintained at °C using a water bath. A two factor CCD was carried out using H2O2 dosage rate ranging from 1 to 10 mg/L min and Fe3+ dosage from 1 to 100 mg/L to investigate their influence on carbofuran degradation under the photo-Fenton process.
Carbofuran
Under these conditions, the toxicity unit measured by Microtox test with 5 min exposure was decreased from 47 to 6 and the biodegradability evaluated by BOD 5/COD ratio was increased from 0 to 0.76 after a 60 min reaction. The results obtained in this study demonstrate that the photo-Fenton process is a promising pretreatment to biological treatment for carbofuran removal from contaminated water or wastewater.
Experiments were carried out in a Pyrex glass cylindrical reactor of 0.10 m diameter and 0.20 m height. The working volume was 1 L and all experiments were conducted in batch mode. The initial solution pH was adjusted to 3 which is the optimal value for the Fenton and photo-Fenton reactions using sulphuric acid. All experiments except those in the dark and at night were carried out between 10 am and 4 pm. The mean solar radiation during the experiments from October to January was in the range of 2.55–3.01 kWh (m2 day)−1. The effects of solar light, initial Fe concentration, and initial H2O2 concentration were investigated.
Acid Orange 7
With increasing Fe dosage the decolourization rate increased, but the enhancement was not pronounced beyond 10 mg/L. Although the addition of H2O2 increased the decolourization rate up to around 1000 mg/L of H2O2, further additions of H2O2 did not enhance colour removal. At excess dosages of Fenton reagents, colour removal was not improved, due to their scavenging of hydroxyl radicals. It was found that the pseudo first-order decolourization kinetic constant based on the accumulated solar energy is the sole parameter unifying solar photo-Fenton decolourization processes under different weather conditions.
