Fenton’s reagent and combinations

Several studies are available in the scientific literature dealing with the Fenton’s treatment of pharmaceuticals and the effect of pretreatment on the biotreatability of advanced oxidation products. Tekin et al. (2006) investigated the applicability of Fenton’s oxidation to improve the biodegradability of effluents originating from a medium scale drug manufacturing plant producing various antiseptics and disinfectant solutions. The total number of products is 10 including an antiseptic gargle and an antiseptic liquid soap formulated with the same active ingredient as well as several other antiseptic solutions with different active ingredients and disinfectant solutions for medical use. The intermittent cleaning of the tanks used in the production processes and domestic utilisation of the tap water make up the wastewater of the plant. Typically, wastewater originating from the washing of

equipments amount to 2–3 m³/day and that from the washing of bottles increases this volumetric flow rate to approximately 6-7 m³/day. Domestic wastewater from the plant is around 5 m³/day, making up a total wastewater flow rate of 11–12 m³/day. Due to the fact that not all of the products were produced during the treatability studies, Fenton’s oxidation was carried out with synthetically prepared wash waters (SPWWs) made up by diluting each product. The synthetically prepared wash waters were thereafter mixed with domestic wastewater at a rate of domestic/pharmaceutical = 3.5/1.5 to mimic daily average discharge rates.

The COD and BOD₅ values of the mixed wastewaters were in the range of 900–7000 mg/L and 85–3600 mg/L, respectively. Accordingly, the BOD₅/COD ratios varied between 0.09–0.59. Communication with the plant and an analysis of the flow records, though scarce, indicated that the wash waters contained the product with an average of 1/100 dilution. In the preparation of SPWWs, three different dilution factors, 1/50, 1/100 and 1/500, were used to account for the variations in pharmaceutical wastewater flows. The effects of temperature, initial pH, coagulation pH, initial COD (at 3 different dilutions), H₂O₂ and Fe²⁺

dosages (at optimised pH and temperature; for H₂O₂ concentrations between 0.8 and 5.0 M and Fe²⁺ doses between 0.002 and 0.033 M) were studied. The Fe²⁺

concentrations were kept constant at 0.033 M while studying the effect of H₂O₂ dosage, and H₂O₂ concentration was fixed at 2.5 M in the tests for optimum Fe²⁺

dosage. The experiments were conducted at 50°C. The pH of the heated samples was adjusted and required amounts of FeSO₄·7H₂O and H₂O₂ were added to the samples. The reaction solutions were stirred for 30 min and then another 30 min were allocated for precipitation. The pH of the decanted supernatant was then adjusted to initiate coagulation. Two hours were allowed for precipitation. COD was measured in all treated samples whereas the BOD₅ test was conducted only for selected runs. Since no significant differences were observed in the treatment efficiency for room temperature and 50°C all further experiments were carried out at room temperature due to practical and economic reasons. The optimum pH was determined as 3.5 and 7.0 for the first (Fenton’s oxidation) and second stage (based on iron removal from reaction solution by chemical precipitation) of the treatment process, respectively. The COD removal efficiency was relatively higher for lower initial COD values (dilution rate = 1/500); however, at the lower dilution ratios (1/50 to 1/100), average COD removals did not differ considerably.

The optimal H₂O₂/Fe²⁺ ratio varied highly with type of waste to be oxidised. In addition, on the condition that the H₂O₂/Fe²⁺ ratio is optimum, the required H₂O₂ and FeSO₄ doses can be reduced or tuned up significantly. In the present study, COD removal efficiency was highest when the molar ratio of H₂O₂/Fe²⁺ was 150–

250 for all pharmaceutical chemicals. At a H₂O₂/Fe²⁺ ratio of 155, e.g. 0.3 M H₂O₂ and 0.002 M Fe²⁺, provided 45–65 % COD removal. Keeping the ratio

constant at 155 thereby increasing H₂O₂ to 5 M and Fe²⁺ to 0.032 M, resulted in COD removal efficiencies ranging from 77 % to 95 %. In general, treatment with Fenton’s oxidation was found to improve the biodegradability of the wash waters. The COD removal efficiency attained in this unit was between 45 % and 50 %. After Fenton’s oxidation, the BOD₅/COD ratio of the wastewater increased by a factor of about 3–5. The wastewater treatment plant employing Fenton’s oxidation followed by aerobic degradation in sequencing batch reactors (SBR), built after the treatability studies provided an overall COD removal efficiency of 98 %, and compliance with the discharge limits. The efficiency of the Fenton’s oxidation was around 45–50 % and the efficiency in the SBR system which has two reactors each having a volume of 8 m³ and operated with a total cycle time of one day, was around 98 %, regarding the COD removal. The BOD₅ values measured at the outlet of the treatment plant by the competent authority, during this 2-month period were in the order of 15–20 mg/L which corresponded to an overall BOD₅ removal efficiency of 98 %. This was well below the discharge limit of 50 mg/L set in the discharge standards. This was also reflected in the toxicity dilution factor (TDF) measurements by the Provincial Authority, which indicated that toxicity was greatly reduced. The TDF is defined as the minimum dilution factor required for the survival of all 10 specimens of Lebistes reticulatus after 48 h. The TDF values measured by the Provincial Authority consistently reduced to 2, after the new system was put to operation from its earlier value of 5–10.

Badawy et al. (2009) studied the treatability of pharmaceutical wastewater from El-Nasr Pharmaceutical and Chemical Company, located in South-East of Cairo.

Chloramphenicol, diclofenac, salicylic acid and paracetamol were produced and obtained from El-Nasr Company in a pure form. During the study, a continuous monitoring program was carried out for almost one year. Six composite samples from end-of-pipe treatment were collected over the working hours. The company discharges both industrial (6000 m³/d) and municipal wastewater (128 m³/d) into a nearby evaporation pond without any pretreatment. The generated wastewater was characterised by high values of COD (4100–13,023 mg/L), TSS (20–330 mg/L) and oil&grease (17.4–600 mg/L). In addition, the presence of refractory compounds decreases the BOD₅/COD ratio (0.25–0.30), with an average value of 0.27. Analysis of raw wastewater confirmed that pretreatment is required prior to discharge into public sewers to comply with the Egyptian Environmental laws and regulations.

Fenton’s treatment process was carried out at room temperature by adding various doses of FeSO₄·7H₂O. The pH was adjusted at 3.0 ± 0.2 using 1N H₂SO₄ and kept at that value during the reaction. The required amount of H₂O₂ was fed by a dosing pump during a period of 15 min, and then the coagulation experiments were conducted with the Jar Test apparatus that was preceded with rapid mixing of the Fenton-treated effluent at 100 rpm for 5 min, slow mixing at 40 rpm for

30 min, and then standstill for 30 min. After settling the supernatant was filtered through 0.45 μm, treated with enzyme Catalase to remove residual H₂O₂. The pH values for oxidation and coagulation experiments were controlled at 3.0 ± 0.2 and 8.5 ± 0.2, respectively with 0.1N sulphuric acid or sodium hydroxide. Raw and Fenton-treated wastewaters were subjected to biological treatment in two-litre plexiglass laboratory columns. Air was fed continuously at a rate of 120 mL/min to ensure sufficient dissolved oxygen. Biomass taken from an activated sludge process of a municipal wastewater treatment plant was acclimated to both raw wastewater conditions and Fenton-treated effluent for a period of 4 weeks. During this period, nutrients was added to raw wastewater and Fenton-treated effluent to keep the ratio 100:5:1 for the parameters COD:N:P, respectively. In order to study the effect of aeration time and the sludge loads on the treatment process, the system was operated for 24 h at a MLSS of 3–4 g/L. Samples were withdrawn at regular intervals to follow COD and TOC. Diclofenac, chloramphenicol, paracetamol drugs and their by-products p-aminophenol, phenol, benzoic acid, nitrobenzene and salicylic acid were detected in all biologically treated effluents and their mean concentrations were 5.60, 38.84, 69.68, 62.94, 130.18, 2.51, 32.84 and 1.03 mg/L, respectively. Phenylacetic acid, a by-product of diclofenac, was not detected in any of treatment effluents. COD and TOC removal efficiencies obtained during biological treatment depended mainly on the characteristics of the wastewater, especially on the presence of non-biodegradable substances and the BOD/COD ratio (= 0.25). COD and TOC removal efficiencies were 51 % and 56 % as well as 48 % and 36 % for wastewater at an initial COD of 11,987 and 4100 mg/L, respectively. These low COD removal efficiencies were attributed to the presence of refractory organic compounds. A high removal efficiency of 76 % was obtained for initial COD of 13,023 mg/L due to the fact that for this wastewater sample the BOD₅/COD ratio increased to 0.30. The efficiency of Fenton process as a pretreatment step of wastewater was also investigated in terms of pH and hydrogen peroxide concentration. The highest COD and TOC removals were obtained as 64 % and 62 %, respectively, within1.5 h at a pH 3. The effect of hydrogen peroxide on oxidation efficiency was investigated under the following operating conditions: reaction time = 1.5 h, pH = 3, Fe²⁺/H₂O₂ = 1:100, and a COD/H₂O₂ ratio varying from 1:1.1 to 1:4.4. It was found that TOC and COD removal efficiency increased with increasing peroxide concentration. Maximum removal efficiency was attained at a COD/H₂O₂ ratio of 1:2.2. In order to obtain the optimal Fe²⁺ dose, experiments were carried out at different Fe²⁺/H₂O₂ molar ratios being equivalent to 1:10, 1:25, 1:50 and 1:100. The results indicated that the maximum TOC and COD removal were found at a Fe²⁺/H₂O₂ molar ratio of 1:50.

Further increase of this ratio decreased the extent of oxidation as a consequence of the recombination of HO^● radicals with Fe²⁺. Fenton treatment of wastewater

collected from the company’s end-of-pipe was carried for 1.5 h, with a COD/H₂O₂ ratio of 1:2.2, at pH 3 and a Fe²⁺/H₂O₂ ratio of 1:50. Under these conditions, COD abatement ranged from 67 % to 87 %. These results revealed that the quality of treated effluent is satisfactory and parameter values complied with the Egyptian Law for discharge of industrial wastewater into the public sewage system. Fenton as a pretreatment process prior to biological activated sludge treatment increased the biodegradability of the wastewater by converting persistence compounds in the wastewater into more easily biodegradable ones. Results have indicated that complete removal of chloramphenicol, diclofenac, p-aminophenol, benzoic acid, nitrobenzene and salicylic acid was achieved in the final effluent when coupling Fenton’s oxidation with a biological activated sludge processes. The obtained results have also showed that the refractory compounds and their by-products cannot be readily removed by biological treatment and always remain in the treated effluent or adsorbed on the sludge flocs. The application of Fenton oxidation process as a pretreatment improved the removal of pharmaceuticals from wastewater and appears to be an effective solution to achieve compliance with the law legislation with respect to discharge in a determined receptor medium.

Combined treatment of pharmaceutical effluent generally is more effective than single stage operations. Attempts were made in a study conducted by Xin and Sun (2009) to examine the combined coagulation, Fenton and sedimentation process for the treatment of non-degradable antibiotic fermentation wastewater. The antibiotic fermentation wastewater containing cefpirome, latomoxef, aztreonam, cefoperazone, cefatridine, ropylene glycol, and ceftazidime was obtained from a pharmaceutical company located in Harbin, China. The characterisation of the effluent was as follows; COD = 3279 mg/L; BOD₅/COD < 0.1; pH = 3–4;

TOC = 1296 mg/L; TN = 221 mg/L; SS = 195 mg/L; NH₄⁺–N = 54 mg/L. The coagulation experiments were conducted with a Jar Test apparatus and using polyferric sulphate (PFS) as the coagulant. During a coagulation experiment, pH was adjusted in the range of 2–10, thereafter PFS was added in the range 50–800 mg/L with rapid mixing at 300 rpm for 1 min, followed by slow mixing at 50 rpm for 15 min and then standstill for 30 min. In Fenton’s oxidation reaction reagents were added and thereafter the water sample was mixed rapidly for 30–60 min, depending on the designated oxidation time. In the coagulation step, the above oxidised sample was mixed slowly for 15 min at a pH of 7 and then allowed to standstill for 30 min. The efficacy of combined wastewater treatment was mainly evaluated in terms of the parameters colour and COD removal. The experimental results indicated that 67 % colour and 72 % COD were removed under optimised conditions of coagulation (PFS dosage 200 mg/L and pH 4.0).

In addition, optimal parameters of the Fenton process were determined to be 150 mg/L H₂O₂, 120 mg/L FeSO₄ and 1 h of reaction time at pH 4. In order

to simplify the Fenton’s oxidation kinetic model, it was assumed that the major oxidation action was attributed to HO^● and was provided instantaneously. The kinetics of COD removal for antibiotic fermentation wastewater in the Fenton’s oxidation system showed pseudo-first order behaviour with respect to COD. It could be concluded that there was no marked effect of the initial COD (= 213, 599 and 905 mg/L) on the obtained abatement rate coefficients and the average reaction rate constant was found to be 0.0047 s^–1. The half life of pseudo-first order reaction was only 147 s, so it demonstrated that the degradation of organic pollutants in Fenton system was quite fast. When Fenton-treated effluent pH was adjusted to 7.0, the pollutants could be further removed by a coagulation and sedimentation process. The overall colour, COD and SS removals reached 97 %, 97 %, and 87 % under the selectedoptimum coagulation and Fenton’s treatment (oxidation+sedimentation) conditions, respectively.

Among several advanced oxidation processes, Fenton’s oxidation or Fenton-like reaction appeared to be the most promising one in terms of cost-effectiveness and ease of operation. In recent years, more and more reports have been appearing concerning the use of microwave radiation to promote the oxidative degradation of biorefractory wastes due to its advantages of swiftness, high-efficiency and environmentally friendliness (Kawala and Atamańczuk 1998; Abramovitch et al. 1999; Lai et al. 2006; Quan et al. 2007). These investigations suggested that microwave radiation was in favour of promoting the degradation efficiency of traditional treatment methods. Wang et al. (2009) explored microwave enhanced Fenton-like process to treat high concentration pharmaceutical wastewater with an initial COD of 49,913 mg/L. The pharmaceutical wastewater sample was collected from Harbin pharmaceutical manufacturing group in China.

The effluent contained ferment ramification, remnant penicillin and several of remnant menstrum, acetone, amyl butyric ester as well as formaldehyde. The characteristics of the wastewater sample were as follows: TOC = 11,540 mg/L, pH = 4.42, UV₂₅₄ absorbance (100 fold dilution) = 1.491 and a BOD₅/COD ratio of 0.165, respectively. The morphology of the sediment sludge was observed with a transmission electron micrograph with accelerated voltage of 80 kV. The liquid/

solid ratio (L/S) was measured as the following steps: transportation of treated effluent to a 50 mL cylinder and allowing standstill for 1 h. Then the volume of supernatant and precipitated sludge was measured. The ratio between the two values was denoted as the L/S value. Settlement rate (SR) was used as an indicator for the settling quality of sludge and to optimise the treatment performance. The SR index was measured as follows: transportation of treated effluent to a 50 mL cylinder and determination of the increasing supernatant volume after a standstill period of 10 min. The ratio of the increasing volume versus time was denoted as the SR value. The parameters L/S, SR and BOD₅/COD were followed for treatment

process optimisation. In addition ferric iron concentration was determined in treated samples by using ICP-OES (Optima 5300 DV, PerkinElmer). Operating parameters were investigated and the optimal conditions were established as follows: a microwave power of 300 W (studied range = 100–500 W), a radiation time of 6 min (studied range: 2–10 min), initial pH of 4.4 (range of study: 2–11), a H₂O₂ dosage of 1300 mg/L (range = 3200–19,000 mg/L) and a Fe₂(SO₄)₃ dosage of 4900 mg/L (range of study = 2000–8000 mg/L). Within the present experimental conditions employed, the COD and UV₂₅₄ removals reached to 58 % and 55 %, respectively, and the BOD₅/COD ratio was enhanced from 0.165 to 0.470 under these reaction conditions. The variation of molecular weight distribution indicated that both macromolecular substances and micromolecular substances were eliminated quite well but mainly via different removal mechanisms, namely Fenton’s oxidation for micromolecules and coagulation for macromolecules. The structure of flocs revealed that ferric hydroxide ions seemed to connect with ferric hydroxides and/or organic molecules to form large-size particles by means of Van der Waals force and/or hydrogen bonds. Subsequently, these particles aggregated to form flocs and settled down. Comparing with traditional Fenton-like reaction (55 % COD removal; final BOD₅/COD ratio = 0.38) and conventional heating assisted Fenton-like reaction (52 % COD removal, final BOD₅/COD ratio = 0.29), microwave-enhanced Fenton-like process displayed superior treatment efficiency in terms of biodegradability enhancement, L/S ratio and COD removal efficiency.

Microwave was in favour of improving the degradation efficiency, the settling quality of sludge, as well as reducing the yield of sludge and enhancing the biodegradability of effluent. Microwave enhanced Fenton-like process is believed to be a promising treatment technology for high concentration and biorefractory wastewater.