Initial Neutral pH Research Articles

Mechanistic investigation of the electricity and gallic acid synergistically accelerated Fe(III)/Fe(II) cycle for the degradation of carbamazepine

This study investigated the application of a natural plant polyphenol, gallic acid (GA) to form complex with iron to promote the redox cycle of Fe(III)/Fe(II) under neutral initial pH conditions in the electrochemical (EC) system for activation of peroxymonosulfate (PMS) to efficiently degrade carbamazepine (CBZ). Results demonstrated that the synergistic effects of GA and EC significantly improved the removal efficiency, and the EC/GA/Fe(III)/PMS system effectively removed 100% of CBZ within a wide initial pH range of 3.0–7.0. The optimum stoichiometric ratio of GA to Fe(III) was found as 2:1. Investigations including quenching experiment, chemical probe analysis, and electron paramagnetic resonance (EPR) analysis were conducted to identify the primary reaction radicals as •OH, SO4•−, along with the 1O2 and Fe(IV). In the EC/GA/Fe(III)/PMS system, the synergistic effect of GA and electrochemistry led to a remarkable enhancement in the generation of •OH. Furthermore, the complexation reduction mechanism of GA and Fe(III) was proposed based on experimental and instrumental analyses, which demonstrated that the semi-quinone products of GA were the main substances promoting the Fe(III)/Fe(II) cycle. Mass spectrometry results showed that CBZ generated 27 byproducts during degradation, with formic acid as the main product of GA. The degradation efficiency of the EC/GA/Fe(III)/PMS system remained stable and excellent, exhibiting remarkable performance in the presence of various inorganic anions, including Cl− and NO3−, as well as naturally occurring organic compounds such as fulvic acid (FA). Overall results indicated that the EC/GA/Fe(III)/PMS system can be applied to effectively treat practical wastewater treatment without requirement of pH adjustment.

Abiotic aerobic oxidation pathways of stibnite revealed by oxygen and sulfur isotope systematics of sulfate

The environmental threat posed by stibnite is an important geoenvironmental issue of current concern. To better understand stibnite oxidation pathways, aerobic abiotic batch experiments were conducted in aqueous solution with varying δ18OH2O value at initial neutral pH for different lengths of time (15-300 days). The sulfate oxygen and sulfur isotope compositions as well as concentrations of sulfur and antimony species were determined. The sulfur isotope fractionation factor (Δ34SSO4-stibnite) values decreased from 0.8‰ to -2.1‰ during the first 90 days, and increased to 2.6‰ at the 180 days, indicating the dominated intermediate sulfur species such as S2O32−, S0, and H2S (g) involved in Sb2S3 oxidation processes. The incorporation of O into sulfate derived from O2 (∼100%) indicated that the dissociated O2 was only directly adsorbed on the stibnite-S sites in the initial stage (0-90 days). The proportion of O incorporation into sulfate from water (27%-52%) increased in the late stage (90-300 days), which suggested the oxidation mechanism changed to hydroxyl attack on stibnite-S sites promoted by nearby adsorbed O2 on stibnite-Sb sites. The exchange of oxygen between sulfite and water may also contributed to the increase of water derived O into SO42−. The new insight of stibnite oxidation pathway contributes to the understanding of sulfide oxidation mechanism and helps to interpret field data.

Utilization of Fe-Ethylenediamine-N,N'-Disuccinic Acid Complex for Electrochemical Co-Catalytic Activation of Peroxymonosulfate under Neutral Initial pH Conditions.

The ethylenediamine-N,N'-disuccinic acid (EDDS) was utilized to form Fe-EDDS complex to activate peroxymonosulfate (PMS) in the electrochemical (EC) co-catalytic system for effective oxidation of naphthenic acids (NAs) under neutral pH conditions. 1-adamantanecarboxylic acid (ACA) was used as a model compound to represent NAs, which are persistent pollutants that are abundantly present in oil and gas field wastewater. The ACA degradation rate was significantly enhanced in the EC/PMS/Fe(III)-EDDS system (96.6%) compared to that of the EC/PMS/Fe(III) system (65.4%). The addition of EDDS led to the formation of a stable complex of Fe-EDDS under neutral pH conditions, which effectively promoted the redox cycle of Fe(III)-EDDS/Fe(II)-EDDS to activate PMS to generate oxidative species for ACA degradation. The results of quenching and chemical probe experiments, as well as electron paramagnetic resonance (EPR) analysis, identified significant contributions of •OH, 1O2, and SO4•- in the removal of ACA. The ACA degradation pathways were revealed based on the results of high resolution mass spectrometry analysis and calculation of the Fukui index. The presence of anions, such as NO3-, Cl-, and HCO3-, as well as humic acids, induced nonsignificant influence on the ACA degradation, indicating the robustness of the current system for applications in authentic scenarios. Overall results indicated the EC/PMS/Fe(III)-EDDS system is a promising strategy for the practical treatment of NAs in oil and gas field wastewater.

Floating TiO2/expanded perlite prepared for degradation of sulphadiazine and sulphamethoxazole

ABSTRACT Photocatalysis treatment is a promising technology to eliminate antibiotic pollution. In this study, a floating TiO2/expanded perlite (TiO2/EP) catalyst was successfully prepared using a simple dip-coating method. The photocatalytic degradation effects of sulphadiazine (SDZ) and sulphamethoxazole (SMZ) were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements demonstrated that TiO2 has been immobilised on the surface of EP. The TiO2/EP with TiO2 dip-coating three layers displayed the best degradation effect of SDZ and SMZ and the loading amount of TiO2 was 20wt%. The photocatalytic degradation rates of SDZ and SMZ were above in the TiO2/EP+UV system reached over 92% within 75 min, and followed a pseudo-first-order kinetic model. Low initial concentration (<10 mg L−1) and neutral pH water environment were found to be favourable for the photocatalytic degradation of SDZ and SMZ. Additionally, electrolyte ions (SO4 2- and Cl−) and humic acid (HAc) showed inhibitory effects on the degradation of SDZ and SMZ. However, HCO3 − inhibited the degradation of SDZ and SMZ at low concentration and had the opposite effect at high concentrations. This study provides valuable data for the designing of composite photocatalysts for efficient removal of SDZ and SMZ in real water systems.

Efficient removal of recalcitrant naphthenic acids with electro-cocatalytic activation of peroxymonosulfate by Fe(III)-nitrilotriacetic acid complex under neutral initial pH condition

This work investigated the activation of peroxymonosulfate by electrochemical (EC) system assisted with Fe(III)-nitrilotriacetic acid (NTA) complex for degradation of persistent naphthenic acids (NAs) under neutral initial pH conditions. As NAs are a complicated mixture, 1-adamantanecarboxylic acid (ACA) was selected as the model NA compound for degradation experiment. The addition of NTA is to chelate with Fe(III), gaining stability under neutral pH condition to facilitate the circulation of Fe(II)/Fe(III) by the electrochemical process to activate PMS. The EC/Fe(III)-NTA/PMS system was explored with applicable pH range of 3–9 and an optimized molar ratio 1: 2 for Fe: NTA. Results of quenching and chemical probe experiment together with results of electron paramagnetic resonance (EPR) analysis revealed the main reactive species of the system, including •OH, SO4•−, 1O2 and possibly Fe(IV). With the addition of NTA, the yields of •OH, SO4•−, 1O2 were enhanced. Results of mass spectrometry analysis and DFT calculations indicated the formation of 9 degradation byproducts of ACA via three primary degradation pathways such as hydroxyl substitution, carbonyl substitution, and decarboxylation. Furthermore, the EC/Fe(III)-NTA/PMS system could achieve excellent removal efficiency of ACA with different anions such as Cl-, HCO3-, NO3- and H2PO4- in the background. The practical applicability of the system was also verified with the high removal of commercial NAs mixture standard. Overall results have indicated the EC/Fe(III)-NTA/PMS system could be utilized for efficient reclamation of authentic oil and gas industrial wastewater under natural pH conditions.

Application of iron-activated persulfate for municipal wastewater disinfection

To address the increasing contamination of aquatic environments and incidence of waterborne diseases, advanced oxidation processes with activated persulfate have emerged as tools to inactivate wastewater microorganisms and contaminants. In this work, the disinfection of a secondary effluent from a wastewater treatment plant by iron-based persulfate activation was studied. Experiments in a batch stirred tank reactor were carried out to evaluate the performance along reaction time and the effect of operational parameters in the oxidative process efficiency (oxidant and iron concentration, pH and temperature). After 60 min of reaction, persulfate and iron concentrations of 3 mM and 0.75 mM, respectively, combined with a neutral initial pH (7.5) and a temperature of 40 °C, allowed to reach values below the detection limit (<10 CFU/100 mL) of enterococci and enterobacteria with and without ciprofloxacin resistance, as well as a 91% inactivation of total heterotrophic organisms and a 70% removal of total organic carbon. Regrowth of microorganisms was evaluated 72 h after treatment and it was only noticed a slight increase in total heterotrophs. Evaluation of physico-chemical characteristics of the treated water showed that it meets the requirements imposed by European and Portuguese legislation for its reuse in irrigation and most urban utilities.

Simultaneous removal of heavy metals from drinking water by banana, orange and potato peel beads: a study of biosorption kinetics

Banana, orange and potato peels (BP, OP and PP, respectively) were immobilised to produce biosorbent beads that were employed for the biosorption of heavy metals from a cocktail solution containing As(V), Cd(II), Cr(VI), Cu(II), Hg(II) and Ni(II) ions. Drinking water conditions were maintained with neutral initial pH and low concentration of the ions. Batch experiments were performed for evaluating the effect of pH in the drinking water range (6.5–8.5). Results showed a significant increase in the biosorption capacity of the beads with respective to the uptake of As and Pb, whereas it decreased significantly for Cd, Cu, Hg and Ni ions at basic pH values. Approximate equilibrium biosorption of Cd, Cu, Hg and Ni was 89–92%, 79–87%, 84% and 71–80% by BP, OP and PP beads. The physisorption-based PFO model was the most suitable for the ions with biosorption capacities closer to the experimental values. BP and OP beads had better biosorption efficiencies relative to PP bead due to the higher surface heterogeneity observed by scanning electron microscopy coupled with energy-dispersive spectroscopy. An increase in the biosorbent concentration from one to ten BP beads significantly increased the biosorption percentage of the ions. The biosorption capacities of Cd, Hg and Ni uptake by one BP bead from a 1 mgL−1 cocktail solution were 3.4 ± 0.0, 5.3 ± 0.1 and 3.0 ± 0.0 mgg−1, respectively. Thus, BP beads were the most effective than for the simultaneous removal of heavy metals from drinking water.

Heterogeneous Catalytic Ozonation of Aqueous p-nitrophenol over MIL-100(Fe) Metal–Organic Framework

ABSTRACT Metal–organic frameworks have been extensively studied in catalysis owing to their unique physicochemical properties. However, this class of materials has not yet been directly applied to the catalytic ozonation of organic pollutants. In this study, MIL-100(Fe) was synthesized by a solvothermal method and characterized by powder X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, N2 adsorption–desorption and scanning electron microscopy. A range of reaction conditions such as pH, solute concentration and catalyst content were applied to investigate the catalytic activity of our MIL-100(Fe) sample for the ozonation of p-nitrophenol in water. According to the experimental results, at a neutral initial pH, the catalytic ozonation of p-nitrophenol proceeded mainly through radical reactions, whereas in the absence of the MIL-100(Fe) catalyst, ozone could react with p-nitrophenol via the direct reaction pathway. The catalyst achieved a conversion of up to 98% and chemical oxygen demand removal of up to 75%. Moreover, our MIL-100(Fe) catalyst retained this performance for seven cycles of operation, which offers potential applications for metal–organic frameworks as catalysts in wastewater treatment.

Impact of organic acids and sulfate on the biogeochemical properties of soil from urban subsurface environments

Urban subsurface environments are often different from undisturbed subsurface environments due to the impacts of human activities. For example, deterioration of underground infrastructure can introduce elevated levels of Ca, Fe, and heavy metals into subsurface soils and groundwater. Likewise, leakage from sewer systems can lead to contamination by organic C, N, S, and P. However, the impact of these organic and inorganic compounds on biogeochemical processes including microbial redox reactions, mineral transformations, and microbial community transitions in urban subsurface environments is poorly understood. Here we conducted a microcosm experiment with soil samples from an urban construction site to investigate the possible biotic and abiotic processes impacted when sulfate and acetate or lactate were introduced into an urban subsurface environment. In the top-layer soil (0–0.3 m) microcosms, which were highly alkaline (pH > 10), the major impact was on abiotic processes such as secondary mineral precipitation. In the mid-layer (2–3 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were greatly impacted by the specific organic acid added, and sulfate-reduction was not observed until after Fe(III)-reduction was complete. Near the end of the incubation, some genera related to syntrophic acetate oxidation and methanogenesis were observed in the lactate-amended microcosms. In the bottom-layer (7–8 m) soil microcosms, the rate of Fe(III)-reduction and the amount of Fe(II) produced were affected by the concentration of amended sulfate. Sulfate-reduction was concurrent with Fe(III)-reduction, suggesting that Fe(II) production was likely due to abiotic reduction of Fe(III) by sulfide produced by microbial sulfate reduction. The slightly acidic initial pH (~5.8) of the mid-soil system was a major factor controlling sequential microbial Fe(III) and sulfate reduction versus parallel Fe(III) and sulfate reduction in the bottom soil system, which had a neutral initial pH (~7.2). 16S rRNA gene-based community analysis revealed a variety of indigenous microbial groups including alkaliphiles, dissimilatory iron and sulfate reducers, syntrophes, and methanogens tightly coupled with, and impacted by, these complex abiotic and biogeochemical processes occurring in urban subsurface environments.

Recycling of iron and aluminum from drinking water treatment sludge for synthesis of a magnetic composite material (ALCS-Fe-Al) to remove fluoride from drinking water

In this study, a novel investigation for recovery of Al and Fe from drinking water treatment sludge (DWTS) has been conducted, which are used for the synthesis of a magnetic composite material (ALCS-Fe-Al) by loading Al/Fe oxides onto acid-leached carbonized sludge (ALCS). The low-cost magnetic adsorbent which can be easily separated from water by a magnet was tested for the ability to remove fluoride from drinking water. The most effective adsorbent ALCS-Fe-Al was prepared under the following conditions: ALCS:Fe = 1:1 & (ALCS-Fe):Al = 1:2. While the preparation conditions of the adsorbent ALCS-Fe-Al* prepared according to the actual iron and aluminum contents in the sludge are: ALCS:Fe = 1:1 & ALCS-Fe:Al = 2:1. Both of the two adsorbents could reduce the fluoride concentration to below 1.5 mg/L in aqueous solution at pH = 7, T = 25 °C with a adsorbent ratio of 3g/L, which meets the level of drinking water standard recommended by the World Health Organization (WHO). In addition, it had a relatively high selectivity for fluoride versus common competitive co-existing ions and high fluoride removal efficiency in a wide range of initial pH of 4-9. At neutral initial pH, the adsorption isotherm was well fitted with the Langmuir model. The maximum adsorption capacity reached 30.49 mg/g. The adsorption kinetics followed the pseudo-second-order model. Furthermore, the adsorption performance, composition and adsorption mechanism of the adsorbent can be proved by SEM, BET, VSM, XRD and XPS. This work provides a new idea for full utilization of DWTS as adsorbent for fluoride removal from drinking water.

Novel Fenton-biological combined process at neutral pH by virtue of endogenous acidification and fungal degradation: Performance and cost analysis in the lab-scale study

In this study, a novel cost-effective Fenton-biological combined process performing at initial neutral pH was proposed to avoid or reduce the chemicals for acidification and neutralization, its performance and preliminary operational cost were evaluated in the lab-scale. By virtue of acidic intermediates, Fenton oxidation was performed at initial neutral pH without acidification by adding acid. After removing the dissolved Fe by ion exchange resins, acidic Fenton effluent was treated by a fungal consortium without pre-neutralization. Our results demonstrate that several phenolic compounds, representing target pollutants, could be effectively oxidized by Fenton at initial neutral pH through endogenous acidification by formed carboxylic acids; in some cases, phenolic complexation with Fe3+ also played an important role. When Fenton treatment was conducted in a continuous-flow reactor similar to anaerobic baffled reactor (ABR), the effect of H2O2 dosage in terms of COD removal efficiency, H2O2 utilization efficiency, acidity and BOD5/COD was assessed. From an economic perspective, the optimal H2O2 dosage was in the range of 0.6 to 0.7 times the theoretical H2O2 dosage. Additionally, the acidic Fenton effluent was further purified in a biofilm reactor inoculated with a specially screened fungal consortium, and effective COD removal and pH increase to near neutral were achieved. This novel Fenton-biological combined process was further validated by treatment of real tannery wastewater. By comparison with classical Fenton-biological combined process, this novel technology could reduce the operational cost by at least 20%, showing a significant economic advantage.

Kinetic and mechanistic investigation of water taste and odor compound 2-isopropyl-3-methoxy pyrazine degradation using UV-A/Chlorine process

The present study was launched as a continuation of global efforts to tackle problems associated with two important aesthetic characteristics, taste and odor (T&O), of drinking water. The UV-A/Chlorine process, a promising advanced oxidation process (AOP), was evaluated for the first time for the removal of 2-isopropyl-3-methoxy pyrazine (IPMP), a widely reported compound in the literature that causes unpleasant taste and odor when present in water at or below the ng L−1 level. It was found that the studied process was efficient for the removal of IPMP in both ultrapure and drinking water. The initial chlorine dosage influenced significantly the degradation efficiency under initial neutral pH values. Degradation efficiency of IPMP was slightly inhibited by using drinking water as matrix. Scavenging experiments highlighted the significant role of various reactive species (e.g. HO, ClO, Cl, Cl2−) generated during the process that have not been studied comprehensively until now. In addition, the significant role of HO was further verified by Electron paramagnetic resonance spectroscopy (EPR) experiments. Overall, the formation of diverse radicals during the UV-A/Chlorine treatment enhanced the degradation of IPMP, promoting mainly the formation of hydroxy, hydroperoxy and dealkylated derivatives. In contrast, chlorinated by-products were only identified in traces.

Photo-Fenton process at natural conditions of pH, iron, ions, and humic acids for degradation of diuron and amoxicillin.

Effect of ferric ions at concentrations typically found in natural waters (0.05 to 1.06mgL-1) and low H2O2 concentrations (between 0.5 and 17.9mgL-1) on simulated sunlight-induced (300Wm-2) photo-Fenton degradation at initial neutral pH (7.0) of amoxicillin and diuron in Milli-Q water was studied using an rotatable central composite experimental design 22 with a central and two axial points. H2O2 concentration was the parameter playing the key role on the degradation of both pollutants. Despite that initial pH was 7.0 in Milli-Q water, this latter decreased rapidly in the first minutes, reaching values of 3.5 and 5.0 for diuron and amoxicillin respectively after 15min of simulated sunlight irradiation. In contrast, in presence of bicarbonate/carbonate (HCO3-/CO3=), fluoride (F-), and humic acids (HAs) at concentrations found often in surface and well waters with ferric ion and H2O2 concentrations of 0.3 and 9.7 and 15.2mgL-1 respectively, both pollutants exhibited a strong degradation keeping the circumneutral pH. Amoxicillin and diuron degradation byproducts found by HPLC/MS were compatible with HO• and/or CO3-• radical attack. Several photo-induced processes such as photo-Fenton (by dissolved ferric-HA complexes), heterogeneous photocatalysis (by colloidal iron), UV-B H2O2 photolysis, irradiated-dissolved organic matter, and their reactions with pollutants would be the main oxidative route responsible of degradations. These findings demonstrated that it could be possible using iron concentrations often found in natural waters to oxidize via photo-Fenton processes among other events, organic pollutants at natural pH conditions.

Inactivation of Human Norovirus and Tulane Virus by High Pressure Processing in Simple Mediums and Strawberry Puree

Human norovirus (NoV) is a major cause of fresh produce associated outbreaks. In this study a non-thermal process, high pressure processing (HPP), was evaluated for efficacy against a human NoV GII.4 strain and Tulane virus (TV). Virus survival following HPP treatment was determined using direct RT-qPCR, the PGM-MB binding assay followed by RT-qPCR, and plaque assay. HPP (400 MPa) inactivation of human NoV and TV was enhanced in simple mediums at a low initial temperature (4°C) and neutral pH (pH 7). HPP treatment of human NoV and TV in strawberry puree at 400 MPa did not significantly affect the level of RNA detected using the PGM-MB binding assay; increasing the pressure level to 600 MPa lead to inactivation of both human NoV and TV. Overall, HPP inactivation of human NoV GII.4 and TV is enhanced at lower initial temperature and neutral pH, and viruses can be inactivated in the food matrix at commercially acceptable pressure levels.

Hybrid microbial electrolytic/UV system for highly efficient organic pollutants removal

This study for the first time proposed an efficient microbial electrolyte/UV system for Methyl Orange decomposition. With an external applied voltage of 0.2 V and cathode aeration of 20 mL/min, H2O2 could be in-situ generated from two-electron reduction of oxygen in cathode, reaching to 8.1 mg/L in 2 hr and continued to increase. The pollutant removal efficiency of approximate 94.7% was achieved at initial neutral pH, with the activation of •OH in the presence of UV illumination. Although the nature of its guiding principles remain on the vista of practical exploration, this proof-of-concept study provides an alternative operation pattern of solar–microbial hybrid technology for future wastewater treatment from a basic but multidisciplinary view.

Hydroxyl and sulfate radicals formation in UVA/FeIII-NTA/S2O82− system: Mechanism and effectiveness in carbamazepine degradation at initial neutral pH

Ferrous ion (FeII)-induced activation of persulfate (S2O82−), reference to the generation of sulfate radical (SO4−), has attracted considerable attention in water treatment for refractory organic contaminants removal. However, two major challenges, i.e., the required acidic pH condition and the extremely slow FeIII/FeII redox cycle, limit the application of FeII/S2O82− process. Herein, the present work addresses S2O82− activation in aqueous solutions at neutral pH by a ferric-nitrilotriacetic (FeIII-NTA) complex under low pressure UVA irradiation. The results showed that UVA irradiation-induced FeIII-NTA reduction could effectively enhance FeIII/FeII redox cycle for the S2O82− activation under neutral pH condition. Electron spin resonance spectroscopy (ESR) and radicals quenching tests indicated that the major reactive species included SO4− and hydroxy radicals (HO) in UVA/FeIII-NTA/S2O82− process, which contributed more than 80% degradation of a model compound carbamazepine (CBZ). In addition, comprehensive investigations were conducted on the important parameters including NTA:FeIII molar ratio, initial pH, FeIII-NTA and S2O82− dosages and their impacts on CBZ degradation kinetics. The critical NTA:FeIII molar ratio was determined at 1:1, above this ratio the excess NTA would act as a scavenger of SO4−/HO thereby inhibiting the degradation of CBZ. The secondary reaction rate constant of NTA with SO4− was determined at 5.89 × 107 M−1 s−1. Moreover, the degradation of CBZ by UVA/FeIII-NTA/S2O82− process in real water matrix (lake water, groundwater and tap water) with environmentally relevant concentration were conducted, and the efficacies were compared with UVA/FeIII-NTA/H2O2 (i.e., photo-Fenton-like) process. The degradation mechanism and pathway of CBZ were proposed on the basis of the identified intermediates by using LC-QTOF-MS technique.

Volatile fatty acids production from protease pretreated Chlorella biomass via anaerobic digestion.

Volatile fatty acids (VFAs) produced via anaerobic digestion (AD) are regarded as a low cost production process of building blocks of interest for the chemical industry. In this study, VFAs and methane production were assessed in batch reactors at different temperature ranges (psychrophilic 25°C, mesophilic 35°C, thermophilic 50°C) and different pH values (5.5 and 7.5) using protease pretreated Chlorella sp. biomass as substrate. Acetic acid and propionic acid were the most abundant products (up to 73% of the total VFAs) during the first days independently of the conditions. VFAs concentration decreased over time as methane was produced after a lag phase of 7-10 days. Results showed that best conditions for VFAs production were mesophilic temperature ranges (35°C) at neutral initial pH values (7.5), and psychrophilic temperature ranges (25°C) at low initial pH values (5.5) which resulted in a conversion of the initial COD into VFAs of 48%, respectively. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1363-1369, 2018.

Comparison between Fenton and Fenton-like reactions for l-proline degradation

Fe/H2O2 and Co/PMS reactions were compared for l-proline degradation under different initial pH values, various transition metal salt and oxidant agent concentrations, as well with and without irradiation. The Fenton reaction took 60 min to degrade 90% of the l-proline, whereas the Fenton-like reaction achieved the same degradation after only 15 min. The best conditions for the Fenton-like reaction resulted from using 0.8 mM of cobalt salt with low PMS concentration (20 mM) at a neutral initial pH and without irradiation. Further experiments were performed using the Co/PMS system to estimate the effects of the other reaction conditions. The results of these experiments showed that pH, reagent concentration, and UV (λ = 365 nm) radiation had no significant effect on the degradation. Additionally, the Fenton-like reaction was made in heterogeneous phase, showing that the reaction proceed equally at same pH than homogeneous phase reaction with no significant effect of phase type used. Significant amount of cobalt was found being leached from the solid media to the water at acidic pH values during the heterogeneous process so the best process conditions were found at neutral pH where the amount of cobalt being leached was found negligible. The heterogeneous Fenton-like process was found feasible to be used for different contaminants degradation with no risk of increased toxicity related with cobalt leachate. The results of this work provide a good evaluation of heterogeneous and homogeneous Fenton-like reaction and suggest that high reagent concentrations are unnecessary for efficient contaminant removal in aqueous phase.

Solid Base MgO/Ceramic Honeycomb Catalytic Ozonation of Acetic Acid in Water

MgO/ceramic honeycomb (MgO/CH) composite material was prepared by the excessive impregnation method, and its catalytic activity in ozonation of acetic acid at initial neutral pH value was investigated. It was found that the efficiency of ozonation in the presence of MgO/CH (81.6% acetic acid removal in 30 min) was greatly enhanced compared to that (only 18.7%) in the absence of MgO/CH under the same conditions. Besides the increase in pH value of the solution caused by MgO/CH, the surface active sites of MgO/CH also accelerated ozone decomposition, thus bringing about the further high efficiency of ozonation. Therefore, MgO/ceramic honeycomb is a potential catalyst in ozonation process.

Volatile fatty acids production during mixed culture fermentation – The impact of substrate complexity and pH

Volatile fatty acids (VFAs) are obtained during chemical routes from non-renewable petrochemicals. Intensive exploitation of oil resources have renewed the idea of VFAs production during biological routes, mainly throughout anaerobic mixed culture fermentation (MCF). We carried out MCF trials at initial acidic (5.0), neutral (7.0, with addition of specific methanogenesis inhibitor) and alkaline (11.0) pH conditions for four different substrates i.e. maize silage, cheese whey, microalgae biomass and glucose. The goal of the study was to investigate the impact of the substrate complexity on the produced VFAs’ quality and quantity. The highest VFAs concentration occurred in neutral pH proceeded by initial alkaline pH (0.83gVFAs/gSCOD for microalgae biomass, 0.78gVFAs/gSCOD for maize silage and 0.71gVFAs/gSCOD for cheese whey, respectively). In the fermentation of glucose, the highest VFAs concentration was achieved in neutral pH. We demonstrated that the alkaline pH was favorable for hydrolysis of complex organic matter (acidification yield over 71% for maize silage fermentation), while the neutral pH was beneficial for the acidogenesis and the overall VFAs production. Our findings showed that it was possible to carry out efficient and stable MCF process without using a large amounts of acid or base for pH adjustment and that the distribution of VFAs only merely depended on the substrate type.