Continuous solar photo-Fenton for wastewater reclamation in operational environment at demonstration scale.

For the first time, a continuous flow solar photo-Fenton demonstration plant has been assessed for wastewater reclamation according to the EU 2020/741 regulation. The treated water qualities achieved under two operating strategies (acidic and neutral pH) in a 100-m2 raceway pond reactor were explored in terms of liquid depth, iron source, reagent concentrations, and hydraulic residence time over three consecutive days of operation. The results obtained at acidic pH showed removal percentages of contaminants of emerging concern (CECs) > 75% and water quality classes B, C and D according to EU regulation at both assessed operating conditions, with treatment capacities up to 1.92 m3 m-2 d-1. At neutral pH with ferric nitrilotriacetate (Fe3+-NTA), 50% of CEC removal and only water quality class D were achieved with the most oxidizing condition assessed, giving a treatment capacity of 0.80 m3 m-2 d-1. The treatment capacities obtained in this work, which have never been achieved with solar water treatments, demonstrate the potential of this technology for commercial-scale application.

Neutral or acidic pH for the removal of contaminants of emerging concern in wastewater by solar photo-Fenton? A techno-economic assessment of continuous raceway pond reactors.

As far as the authors know, no in-depth comparison has been made between the different performances of the solar photo-Fenton process for the removal of contaminants of emerging concern (CECs) as a function of pH. To this end, real WWTP secondary effluents were treated in continuous flow mode at pilot plant scale. The effect of hydraulic residence time (HRT), liquid depth and percentage of CEC removal on treatment capacity was studied. At acidic pH (2.8), the iron source was FeSO4 and at neutral pH (7.0), it was Fe(III)-EDDS. At both pH values, 2250 L m-2 d-1 can be treated in 15-cm deep raceway pond reactors at 30 min HRT with 0.1 mM iron and 0.88 mM H2O2 in order to achieve 80% CEC removal. Treatment costs were 0.25 € m-3 and 0.56 € m-3 at acidic and neutral pH, respectively. This study paves the way for the solar photo-Fenton process to be employed on a commercial scale.

Pyrimethanil degradation by photo-Fenton process: Influence of iron and irradiance level on treatment cost.

This study evaluates the combined effect of photo-catalyst concentration and irradiance level on photo-Fenton efficiency when this treatment is applied to industrial wastewater decontamination. Three levels of irradiance (18, 32 and 46W/m2) and three iron concentrations (8, 20 and 32mg/L) were selected and their influence over the process studied using a raceway pond reactor placed inside a solar box. For 8mg/L, it was found that there was a lack of catalyst to make use of all the available photons. For 20mg/L, the treatment always improved with irradiance indicating that the process was photo-limited. For 32mg/L, the excess of iron caused an excess of radicals production which proved to be counter-productive for the overall process efficiency. The economic assessment showed that acquisition and maintenance costs represent the lowest relative values. The highest cost was found to be the cost of the reagents consumed. Both sulfuric acid and sodium hydroxide are negligible in terms of costs. Iron cost percentages were also very low and never higher than 10.5% while the highest cost was always that of hydrogen peroxide, representing at least 85% of the reagent costs. Thus, the total costs were between 0.76 and 1.39€/m3.

Ecotoxicity evaluation of a WWTP effluent treated by solar photo-Fenton at neutral pH in a raceway pond reactor.

Some pollutants can be resistant to wastewater treatment, hence becoming a risk to aquatic and terrestrial biota even at the very low concentrations (ng L-1-µg L-1) they are commonly found at. Tertiary treatments are used for micropollutant removal but little is known about the ecotoxicity of the treated effluent. In this study, a municipal secondary effluent was treated by a solar photo-Fenton reactor at initial neutral pH in a raceway pond reactor, and ecotoxicity was evaluated before and after micropollutant removal. Thirty-nine micropollutants were identified in the secondary effluent, mainly pharmaceuticals, with a total concentration of ≈80 µg L-1. After treatment, 99 % microcontaminant degradation was reached. As for ecotoxicity reduction, the assayed organisms showed the following sensitivity levels: Tetrahymena thermophila > Daphnia magna > Lactuca sativa > Spirodela polyrhiza ≈ Vibrio fischeri. The initial effluent showed an inhibitory effect of 40 % for T. thermophila and 20 % for D. magna. After 20 min of photo-Fenton treatment, no toxic effect was observed for T. thermophila and toxicity dropped to 5 % for D. magna. Graphical abstract Ecotoxicity removal by solar photo-Fenton at neutral pH. ᅟ.

Low cost UVA-LED as a radiation source for the photo-Fenton process: a new approach for micropollutant removal from urban wastewater.

Light Emitting Diode (LED) technology has matured sufficiently to be considered as an alternative UVA radiation source in photoreactors. Currently, low energy consuming LEDs with a wide range of wavelengths and radiant flux are readily available. In this study, UVA-LEDs were used as a radiation source for the photo-Fenton process as tertiary treatment. The water matrix used was a simulated secondary effluent doped with 200 µg L-1 of the pesticide acetamiprid (ACTM) due to its recalcitrant nature. All experiments were carried out in a LED-box reactor at pH 2.8. The main purpose of this research was to gain some insight into the relationships among energy supply, LED consumption, UVA irradiance and reaction rate. The effect of LED wavelength on energy efficiency for ACTM degradation was studied by varying the iron concentration and liquid depth. Three wavelengths (365, 385 and 400 nm) and two iron concentrations (5 and 11 mg L-1) for two different liquid depths (5 and 15 cm) were evaluated in order to obtain more energy efficient conditions. The results suggest that while the wavelength of 365 nm with 11 mg Fe2+ L-1 was the best condition for ACTM degradation, the wavelength of 385 nm had slower kinetics, but higher energy efficiency.

Automatic dosage of hydrogen peroxide in solar photo-Fenton plants: development of a control strategy for efficiency enhancement.

The solar photo-Fenton process is widely used for the elimination of pollutants in aqueous effluent and, as such, is amply cited in the literature. In this process, hydrogen peroxide represents the highest operational cost. Up until now, manual dosing of H(2)O(2) has led to low process performance. Consequently, there is a need to automate the hydrogen peroxide dosage for use in industrial applications. As it has been demonstrated that a relationship exists between dissolved oxygen (DO) concentration and hydrogen peroxide consumption, DO can be used as a variable in optimising the hydrogen peroxide dosage. For this purpose, a model was experimentally obtained linking the dynamic behaviour of DO to hydrogen peroxide consumption. Following this, a control system was developed based on this model. This control system - a proportional and integral controller (PI) with an anti-windup mechanism - has been tested experimentally. The assays were carried out in a pilot plant under sunlight conditions and with paracetamol used as the model pollutant. In comparison with non-assisted addition methods (a sole initial or continuous addition), a decrease of 50% in hydrogen peroxide consumption was achieved when the automatic controller was used, driving an economic saving and an improvement in process efficiency.

Economic evaluation of the photo-Fenton process. Mineralization level and reaction time: the keys for increasing plant efficiency.

The use of the solar photo-Fenton process is proposed to degrade Paracetamol in water in order to form biodegradable reaction intermediates which can be finally removed with a downstream biological treatment. Firstly, biodegradability enhancement with photo-Fenton treatment time has been evaluated; the minimum mineralization level should be at least 18.6% where Paracetamol has been degraded and biodegradability efficiency is higher than 40%. 20 mg L(-1) of Fe(2+) and 200 mg L(-1) of H(2)O(2) were selected in a lab-scale study looking at Paracetamol's degradation rate and organic carbon mineralization rate. As a result of scaling up the process at a pilot plant, 157.5 mg L(-1) of Paracetamol (∼1 mM) was treated in 25 min of photo-Fenton treatment achieving the desired biodegradability. A further economic evaluation shows how the proposed treatment strategy markedly increases plant efficiency, resulting in an 83.33% reduction in reagent cost and a 79.11% reduction in costs associated with reaction time. Total cost is reduced from 3.4502 €/m(3) to 0.7392 €/m(3).

An analysis of the bacterial community in a membrane bioreactor fed with photo-Fenton pre-treated toxic water.

A photo-Fenton-membrane bioreactor (MBR) coupled system is an innovative tool for the treatment of wastewater containing high quantities of contaminants. In this paper, wastewater with 200 mg l(-1) of dissolved organic carbon (DOC) of a selected mixture of five commercial pesticides: Vydate®, Metomur®, Couraze®, Ditimur-40®, and Scala® was treated by combining photo-Fenton and MBR. The effect of photo-treated pollutants on MBR operation was investigated by studying the population changes that occurred with time in the activated sludge of the biological system. Pre-treatment with photo-Fenton was carried out (only up to 34% of mineralization of DOC) and, after MBR treatment, 98% of biodegradation efficiency was obtained. During the biological treatment, little changes in the activated sludge population were detected by DGGE analysis, maintaining acceptable biodegradation efficiency, which points out the robustness of the MBR treatment versus changes in feed composition.

A comparative study of different tests for biodegradability enhancement determination during AOP treatment of recalcitrant toxic aqueous solutions.

Four biodegradability tests (Pseudomonas putida bioassay, Zahn-Wellens test, BOD5/COD ratio and respirometry assay) have been used to determine the biodegradability enhancement during the treatment of wastewater containing 200 mg L(-1) of dissolved organic carbon (DOC) of a five commercial pesticides mixture (Vydate, Metomur, Couraze, Ditumur and Scala) by an advanced oxidation process (AOP). A comparative study was carried out taking into account repeatability and precision of each biodegradability test. Solar photo-Fenton was the AOP selected for pesticide degradation up to three levels of mineralization: 20%, 40% and 60% of initial DOC. Intra- and interday precisions were evaluated conducting each biodegradability test by triplicate and they were applied three times on different dates over a period of three months. Fisher's least significant difference method was applied to the means, P. putida and Zahn-Wellens tests giving higher repeatability and precision. The P. putida test requires a shorter time to obtain reliable results using a standardized inoculum and constitutes a worthwhile alternative to estimate biodegradability in contrast to other less accurate or more time consuming methods.

Effect of pesticide concentration on the degradation process by combined solar photo-Fenton and biological treatment.

The influence of pesticide concentration, expressed as dissolved organic carbon (DOC), on combined solar photo-Fenton and biological oxidation treatment was studied using wastewater containing a mixture of five commercial pesticides, Vydate, Metomur, Couraze, Ditumur and Scala. Two initial DOC concentrations, 200 mg L(-1) and 500 mg L(-1) were assayed. Variation in biodegradability with photocatalytic treatment intensity was tested using Pseudomonas putida. Thus the mineralisation required for combining with biodegradation of intermediates by activated sludge was 33% and 55% at 200 mg L(-1) and 500 mg L(-1), respectively. Biotreatment was carried out in a stirred tank in sequencing batch reactor (SBR) mode. As revealed by the biodegradation kinetics, intermediates generated at the higher pesticide concentration caused lower carbon removal rates in spite of the longer photo-Fenton treatment time applied. One strategy for treating water with high concentrations of pesticides and overcoming the low biodegradability of photo-Fenton intermediates is to mix it with a biodegradable carbon source before biological oxidation. This combination of photo-Fenton and acclimatized activated sludge in several SBR cycles led to complete biodegradation of a concentrated pesticide solution of 500 mg L(-1) DOC in approximately 5h with a carbon removal efficiency of 90%.

Degradation of a four-pesticide mixture by combined photo-Fenton and biological oxidation.

Complete degradation of a pesticide mixture by a combination of a photo-Fenton pretreatment and an activated-sludge batch reactor is demonstrated. Four commercial pesticides, Laition, Metasystox, Sevnol and Ultracid were chosen for this experiment. The active ingredients are, respectively, dimethoate, oxydemeton-methyl, carbaryl and methidathion. The original pesticide concentration was 200 mg L(-1). Biotreatment began after 31% photocatalytic mineralization, which after 5 h in a 6-L stirred batch-mode tank reactor with non-acclimated activated sludge, leaves the photo-Fenton effluent completely degraded. This biotreatment time is shorter than commonly found in municipal wastewater treatment plants (approximately 8-10 h). Therefore, the combined process is effective for rapid pesticide degradation in wastewater with complete removal of parent compounds and the associated DOC concentration. Nonetheless, assessment of this technology should take into account higher pesticide concentrations and how this factor affects both the photocatalytic and the biological oxidation.

Degradation of alachlor and pyrimethanil by combined photo-Fenton and biological oxidation.

Biodegradability of aqueous solutions of the herbicide alachlor and the fungicide pyrimethanil, partly treated by photo-Fenton, and the effect of photoreaction intermediates on growth and DOC removal kinetics of the bacteria Pseudomonas putida CECT 324 are demonstrated. Toxicity of 30-120 mg L(-1) alachlor and pyrimethanil has been assayed in P. putida. The biodegradability of photocatalytic intermediates found at different photo-treatment times was evaluated for each pesticide. At a selected time during batch-mode phototreatment, larger-scale biodegradation kinetics were analysed in a 12 L bubble column bioreactor. Both alachlor and pyrimethanil are non-toxic for P. putida CECT 324 at the test concentrations, but they are not biodegradable. A approximately 100 min photo-Fenton pre-treatment was enough to enhance biodegradability, the biological oxidation response being dependent on the pesticide tested. The different alachlor and pyrimethanil respiration and carbon uptake rates in pre-treated solutions are related to change in the growth kinetics of P. putida. Reproducible results have shown that P. putida could be a suitable microorganism for determining photo-Fenton pre-treatment time.

Combined photo-Fenton and biological oxidation for pesticide degradation: effect of photo-treated intermediates on biodegradation kinetics.

Biodegradability of a partially photo-oxidized pesticide mixture is demonstrated and the effect of photo-Fenton treatment time on growth and substrate consumption of the bacteria Pseudomonas putida CECT 324 is shown. Four commercial pesticides, laition, metasystox, sevnol and ultracid, usually employed in citric orchards in eastern Spain, were chosen for these experiments. The active ingredients are, respectively, dimethoate, oxydemeton-methyl, carbaryl and methidathion. Judging by biomass measurements, dissolved organic carbon measurements and biodegradation efficiency, it may be concluded that 90min

Pellet morphology, culture rheology and lovastatin production in cultures of Aspergillus terreus.

Pellet growth of Aspergillus terreus ATCC 20542 in submerged batch fermentations in stirred bioreactors was used to examine the effects of agitation (impeller tip speed u(t) of 1.01-2.71 ms(-1)) and aeration regimens (air or an oxygen-enriched mixture containing 80% oxygen and 20% nitrogen by volume) on the fungal pellet morphology, broth rheology and lovastatin production. The agitation speed and aeration methods used did not affect the biomass production profiles, but significantly influenced pellet morphology, broth rheology and the lovastatin titers. Pellets of approximately 1200 microm initial diameter were reduced to a final stable size of approximately 900 microm when the agitation intensity was >/=600 rpm (u(t)>/=2.03 ms(-1)). A stable pellet diameter of approximately 2500 microm could be attained in less intensely agitated cultures. These large fluffy pellets produced high lovastatin titers when aerated with oxygen-enriched gas but not with air. Much smaller pellets obtained under highly agitated conditions did not attain high lovastatin productivity even in an oxygen-enriched atmosphere. This suggests that both an upper limit on agitation intensity and a high level of dissolved oxygen are essential for attaining high titers of lovastatin. Pellet size in the bioreactor correlated equally well with the specific energy dissipation rate and the energy dissipation circulation function. The latter took into account the frequency of passage of the pellets through the high shear regions of the impellers. Pellets that gave high lovastatin titers produced highly shear thinning cultivation broths.

Lovastatin inhibits its own synthesis in Aspergillus terreus.

Lovastatin suppresses its own synthesis in the microfungus Aspergillus terreus. The inhibitory effect was documented by spiking identical batch cultures with pure lovastatin (0, 50, 100 and 250 mg/l) 24 h after initiation from spores.