Enhanced biodegradation of petrochemical wastewater using ozonation and BAC advanced treatment system

Bubbleless aerated-biological activated carbon as a superior process for drinking water treatment in rural areas

Drinking water supply in rural areas remains a substantial challenge due to complex natural, technical and economic conditions. To provide safe and affordable drinking water to all, as targeted in the UN Sustainable Development Goals (2030 Agenda), low-cost, efficient water treatment processes suitable for rural areas need to be developed. In this study, a bubbleless aeration BAC (termed ABAC) process is proposed and evaluated, involving the incorporation of a hollow fiber membrane (HFM) assembly within a slow-rate BAC filter, to provide dissolved oxygen (DO) throughout the BAC filter and an increased DOM removal efficiency. The results showed that after a 210-day period of operation, the ABAC increased the DOC removal by 54%, and decreased the disinfection byproduct formation potential (DBPFP) by 41%, compared to a comparable BAC filter without aeration (termed NBAC). The elevated DO (> 4 mg/L) not only reduced secreted extracellular polymer, but also modified the microbial community with a stronger degradation ability. The HFM-based aeration showed comparable performance to 3 mg/L pre-ozonation, and the DOC removal efficiency was four times greater than that of a conventional coagulation process. The proposed ABAC treatment, with its various advantages (e.g., high stability, avoidance of chemicals, ease of operation and maintenance), is well-suited to be integrated as a prefabricated device, for decentralized drinking water systems in rural areas.

Efficient Removal of Cr(VI) Ions in Petrochemical Wastewater Using Fe3O4@Saccharomyces cerevisiae Magnetic Nanocomposite

Saccharomyces cerevisiae (SC) is a widely available biobased source for function material. In this work, a kind of new efficient magnetic composite adsorbent containing Fe₃O₄ and SC was prepared successfully and used for the removal of Cr(VI) ions in petrochemical wastewater. The morphology and structure of this magnetic adsorbent were characterized with FT-IR, TG, XRD, VSM, SEM and XPS. The effect of the different factors such as pH, adsorption time, initial Cr(VI) ions concentration and adsorption temperature on the adsorption behavior were investigated. The results showed that 10%-Fe₃O₄@SC exhibited high removal rate, reutilization and large removal capacity. The corresponding removal capacity and removal rate could reach 128.03 mg/g and 96.02% when the pH value was 2, adsorption time was 180 min, and initial Cr(VI) ions concentration were 80 mg/L at 298 K. The kinetics followed the pseudo-first-order, which indicated that the adsorption behavior of 10%-Fe₃O₄@SC for Cr(VI) ions belonged to the physical adsorption and chemical adsorption co-existence. The thermodynamic study showed that the adsorption process was spontaneous and exothermic. It still showed better adsorption performance and reutilization after the fifth adsorption-desorption experiment. The possible mechanism of Cr(VI) ions adsorption onto the 10%-Fe₃O₄@SC magnetic adsorbent has been discussed. Hence, this new adsorbent will be a candidate for industry-level applications in petrochemical wastewater containing Cr(VI) ions.

Fenton process for the treatment of wastewater effluent from the edible oil industry

The present study intends to investigate the performance of the Fenton reaction as one of the most efficient (AOPs) in a batch mode for treating wastewater effluent from the edible oil industry, as well as the parameters that influence the reaction, such as pH, hydrogen peroxide (H₂O₂), and ferrous sulfate heptahydrate (FeSO₄.7H₂O) doses at various reaction times. The response surface methodology (RSM) was applied with a central composite design (CCD) for optimizing the responses of pollutant removals. The obtained results indicated that the authenticated response to the chemical oxygen demand (COD) removal was 93.52%, at optimum values of pH, FeSO₄.7H₂O dose, H₂O₂ dose, and reaction time of 3, 1 g/L, 8.38 g/L, and 50 min, respectively. Furthermore, the authenticated response to oil and grease (O&G) removal was 99.8%, at optimum values of pH, FeSO₄.7H₂O dose, H₂O₂ dose, and reaction time of 3, 0.71 g/L, 8.7 g/L, and 37.4 min, respectively. Under these conditions, the residual COD and O&G after Fenton oxidation become 155.4 mg/L and 10 mg/L, respectively.

Comparison of Fenton and Ozone Oxidation for Pretreatment of Petrochemical Wastewater: COD Removal and Biodegradability Improvement Mechanism

Cost-effective pretreatment of highly concentrated and bio-refractory petrochemical wastewater to improve biodegradability is of significant importance, but remains challenging. This study compared the pretreatment of petrochemical wastewater by two commonly used chemical advanced oxidation technologies (Fenton and ozone oxidation), and the mechanisms of biodegradability improvement of pretreated wastewater were explored. The obtained results showed that in the Fenton oxidation system, the COD removal of petrochemical wastewater was 89.8%, BOD5 decreased from 303.66 mg/L to 155.49 mg/L, and BOD5/COD (B/C) increased from 0.052 to 0.62 after 60 min under the condition of 120 mg/L Fe2+ and 500 mg/L H2O2, with a treatment cost of about 1.78 $/kgCOD. In the ozone oxidation system, the COD removal of petrochemical wastewater was 59.4%, BOD5 increased from 127.86 mg/L to 409.28 mg/L, and B/C increased from 0.052 to 0.41 after 60 min at an ozone flow rate of 80 mL/min with a treatment cost of approximately 1.96 $/kgCOD. The petrochemical wastewater treated by both processes meets biodegradable standards. The GC–MS analysis suggested that some refractory pollutants could be effectively removed by ozone oxidation, but these pollutants could be effectively degraded by hydroxyl radicals (•OH) produced by the Fenton reaction. In summary, compared with ozone oxidation, petrochemical wastewater pretreated with Fenton oxidation had high COD removal efficiency and biodegradability, and the treatment cost of Fenton oxidation was also lower than that of ozone oxidation.

New directions and challenges in engineering biologically-enhanced biochar for biological water treatment

Cost-effective, efficient, and sustainable water treatment solutions utilising existing materials and technology will make it easier for low and middle-income countries to adopt them, improving public health. The ability of biochar to mediate and support microbial degradation of contaminants, combined with its carbon-sequestration potential, has attracted attention in recent years. Biochar is a possible candidate for use in cost-effective and sustainable biological water treatment, especially in agrarian economies with easy access to abundant biomass in the form of crop residues and organic wastes. This review evaluates the scope, potential benefits (economic and environmental) and challenges of sustainable biological water treatment using 'Biologically-Enhanced Biochar' or BEB. We discuss the various processes occurring in BEB systems and demonstrate the urgent need to investigate microbial degradation mechanisms. We highlight the need to correlate biochar properties to biofilm development, which can eventually determine process efficiency. We also demonstrate the various opportunities in adopting BEB as a cheaper and more viable alternative in Low and Middle Income Countries and compare it to the current benchmark, 'Biological Activated Carbon'. We focus on the recent advances in the areas of data science, mathematical modelling and molecular biology to systematically and sustainably design BEB filters, unlike the largely empirical design approaches seen in water treatment. 'Sequential biochar systems' are introduced as specially designed end-of-life techniques to lower the environmental impact of BEB filters and examples of their integration into biological water treatment that can fulfil zero waste criteria for BEBs are given.

Pilot-scale microaerobic hydrolysis-acidification and anoxic-oxic processes for the treatment of petrochemical wastewater

Microaerobic hydrolysis and acidification (MHA), as a promising pre-treatment method of industrial wastewater, is drawing increasing attention to enhance the hydrolysis-acidification rate and inhibit the production of toxic gas H₂S. In the present work, a pilot-scale MHA reactor coupled with anoxic-oxic (A/O) processes for treating the petrochemical wastewater was established and the mechanism and application of the MHA reaction were explored. The results showed that the ratio of VFA/COD was increased by 43-90% and low effluent S^2- concentration (less than 0.2 mg/L) was obtained after MHA treatment with 5.5-13.8 L air m^-3 h^-1 supply. The MHA sludge exhibited a good settleability, a higher protease activity and plentiful community diversity. In addition to the dominant anaerobic bacteria responsible for hydrolysis and acidification such as Clostridiales uncultured, Anaerovorax, Anaerolineaceae uncultured and Fastidiosipila, the sulfate reducing bacteria involving Desulfobacter, Desulfomicrobium and Desulfobulbus, the sulphur oxidizing bacteria involving Thiobacillus, Arcobacter and Limnobacter, the nitrifies such as Nitrosomonadaceae uncultured and Nitrospira, and denitrifies Thauera were also identified. MHA pre-treatment guaranteed the efficacy and stability of the following A/O treatment. The removal efficiency of COD and ammonium of the MHA-A/O system remained at around 78.3% and 80.8%, respectively, although the organic load fluctuated greatly in the influent.

Toxicity evaluation and by-products identification of triclosan ozonation and chlorination

Triclosan (TCS) has attracted increasing concern due to its ubiquitous occurrence in aquatic environments as well as its potential adverse effects on human health. This study investigated the toxicity and transformation characteristics of triclosan ozonation and chlorination. The results showed that two hydroxylated by-products were formed via nucleophilic substitution during ozonation, while three chlorinated compounds were generated via electrophilic substitution during chlorination. The toxicity results demonstrated that the parent compound, triclosan, exhibited mild genotoxicity and anti-estrogenic activity. The chlorination of triclosan resulted in a 30-fold increase in anti-estrogenic activity owing to the generation of toxic polychlorinated transformation by-products. In addition, the chlorination by-products were found to be genotoxic like the parent compound. Fortunately, in contrast to chlorination, ozonation could mitigate the genotoxicity and anti-estrogenic activity of triclosan-containing water.

Effective oxidative degradation of coal gasification wastewater by ozonation: A process study

Coal gasification wastewater (CGW) has attracted considerable industrial attention because of its high toxicity and poor biodegradability. Ozonation is a promising process for CGW treatment. In this study, the effects of ozone concentration, pH, and ozonation time on CGW treatment were investigated. The results confirmed that CGW was degraded effectively and that the chemical oxygen demand (COD) was reduced from 1057 to 362 mgL^-1, utilizing 50 mgL^-1 ozone for 90 min. Further, the color of CGW changed from brown to clear and colorless, and the pH decreased from 8.5 to 4.7. Importantly, molds were observed in the oxidized CGW after 14 d at room temperature (23 ± 2 °C), indicating that CGW is significantly biodegradable by ozonation. The CGW components were extracted with three different organic solvents (chloroform, n-hexane, and benzene), and their compositions were analyzed by gas chromatography-mass spectrometry (GC-MS) before and after ozonation. The results proved that considerable amounts of highly toxic refractory compounds in CGW, such as phenolic compounds, polynuclear aromatic hydrocarbons (PAHs), and nitrogenous heterocyclic compounds (NHCs), were degraded to compounds that included olefins, carboxylic acids, and cycloalkanes, or minerals, which are relatively environmentally benign. Moreover, the number of substances in CGW decreased significantly from 127 to 74 after ozonation. Summarily, ozonation is a promising approach for the treatment of highly toxic refractory wastewater, such as CGW.

Treatment of wastewater from petroleum industry: current practices and perspectives

Petroleum industry is one of the fastest growing industries, and it significantly contributes to economic growth in developing countries like India. The wastewater from a petroleum industry consist a wide variety of pollutants like petroleum hydrocarbons, mercaptans, oil and grease, phenol, ammonia, sulfide, and other organic compounds. All these compounds are present as very complex form in discharged water of petroleum industry, which are harmful for environment directly or indirectly. Some of the techniques used to treat oily waste/wastewater are membrane technology, photocatalytic degradation, advanced oxidation process, electrochemical catalysis, etc. In this review paper, we aim to discuss past and present scenario of using various treatment technologies for treatment of petroleum industry waste/wastewater. The treatment of petroleum industry wastewater involves physical, chemical, and biological processes. This review also provides scientific literature on knowledge gaps and future research directions to evaluate the effect(s) of various treatment technologies available.

ANN model for predicting acrylonitrile wastewater degradation in supercritical water oxidation

The discharged acrylonitrile wastewater had aroused more and more attention due to the increasingly serious water pollution. Supercritical water oxidation (SCWO) was an effective and fast way to degrade it completely without secondary pollution. To better illustrate the performances of SCWO of acrylonitrile wastewater, the experimental research covered the effects of different operation conditions on TOC reduction, such as reduced temperature (T/Tc), reduced pressure (P/Pc), initial total organic carbon concentration (TOC₀), stoichiometric ratio (SR) and residence time (t). For a more accurate prediction of the emissions, two kinds of artificial neural network (ANN) models were adopt to simulate the TOC reductions in the processes of SCWO of acrylonitrile wastewater, including the Cascade-forward back propagation neural network (CFBPNN) and Feed-forward back propagation neural network (FFBPNN). The input parameters of ANN models were T/Tc, P/Pc, TOC_0, SR and t. The output parameter was TOC reduction (η). The mean square error (E²) and the coefficient of determination (R²) were used to evaluate the model performances, respectively. Both the model and the experiment results had shown the TOC reduction could be greatly improved by reduced temperature, reduced pressure, initial TOC concentration, stoichiometric ratio and residence time. The FFBPNN model with the hidden neurons numbers of 12 was shown much better performances than the CFBPNN model.

Enhanced ozonation degradation of petroleum refinery wastewater in the presence of oxide nanocatalysts

The catalytic activity of Mn₂O₃, FeOOH and CeO₂ nanoparticles was evaluated in the treatment of a synthetic petroleum refinery wastewater (SPRW) using O₃ in a discontinuous reactor at 25°C and pH 5.5. The mineralization and partial chemical oxidation rates of SPRW using these metal oxides are in the same order of magnitude, and the catalytic activity in the mineralization of SPRW decreased in the order Mn₂O₃>CeO₂> FeOOH. The mineralized fraction progressively increased with time in the catalytic process while in the non-catalytic process it remained constant. The effect of the operational conditions on the mineralization and partial chemical oxidation rates using Mn₂O₃ was investigated in detail. The mineralization rate was found to be lower than the partial oxidation rate due to the formation of partially oxidized by-products, and this is dependent on the solids dosage and pH. An investigation of the mechanism demonstrated that the enhancement effect could be attributed to the introduction of the manganese oxide nanoparticles, which could promote the utilization of O₃ and/or enhance the formation of free radicals (•OH, •O₂H and •O₂^-) on the solid surface and further accelerate the degradation of the organic compounds present in the wastewater.

Dynamic membrane bioreactor performance enhancement by powdered activated carbon addition: Evaluation of sludge morphological, aggregative and microbial properties

The effects of powdered activated carbon (PAC) addition on sludge morphological, aggregative and microbial properties in a dynamic membrane bioreactor (DMBR) were investigated to explore the enhancement mechanism of pollutants removal and filtration performance. Sludge properties were analyzed through various analytical measurements. The results showed that the improved sludge aggregation ability and the evolution of microbial communities affected sludge morphology in PAC-DMBR, as evidenced by the formation of large, regularly shaped and strengthened sludge flocs. The modifications of sludge characteristics promoted the formation process and filtration flux of the dynamic membrane (DM) layer. Additionally, PAC addition did not exert very significant influence on the propagation of eukaryotes (protists and metazoans) and microbial metabolic activity. High-throughput pyrosequencing results indicated that adding PAC improved the bacterial diversity in activated sludge, as PAC addition brought about additional microenvironment in the form of biological PAC (BPAC), which promoted the enrichment of Acinetobacter (13.9%), Comamonas (2.9%), Flavobacterium (0.31%) and Pseudomonas (0.62%), all contributing to sludge flocs formation and several (such as Acinetobacter) capable of biodegrading relatively complex organics. Therefore, PAC addition could favorably modify sludge properties from various aspects and thus enhance the DMBR performance.

Residue-based iron oxide catalyst for the degradation of simulated petrochemical wastewater via heterogeneous photo-Fenton process

Iron oxide with a high degree of purity was recovered from waste and used as an environmentally friendly, low-cost catalyst in the application of the photo-Fenton process to simulated petrochemical wastewater (SPW). Iron oxide nanoparticles were characterized by X-ray powder diffraction, transmission electron microscopy, N₂ adsorption/desorption isotherms, zeta potential, toxicity and atomic absorption spectrometry. The experiments were performed in a batch photochemical reactor, at 20 ± 2.0°C and pH 3.0. The SPW was efficiently mineralized and oxidized using a low catalyst dosage. The results showed that the organic compounds present in the wastewater were not adsorbed onto the solid surface. The solid was found to be stable with negligible leaching and low toxicity. The k_TOC/k_COD ratios were calculated and varied according to the process: for a homogeneous reaction, the ratio obtained was 0.31 and for the heterogenous photo-Fenton process, it was closer to 1. The chemical oxygen demand and total organic carbon removal values were very close, indicating that the SPW is immediately mineralized, without producing partially oxidized compounds. The residue-based goethite studied represents a good alternative to commercially available catalysts in terms of sources and availability.

Data on investigating the quantitative and qualitative status of effluent in a petrochemical complex in Iran

The aim of this data was investigating the quantity and quality of the produced effluent by different petrochemical industry units in Iran and comparison of effluent with the present standards. In the present data, 5 effluent channel of the complex with interval of 12 h (in two shifts) were sampled and 28 physical and chemical parameters were analyzed according to the standard methods. These parameters are pH, Temperature, DO, Conductivity, Color, TDS, TSS, TP, PO₄^3-, Oil, BOD₅, COD, Turbidity, TKN, Fe, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, Si⁴⁺, CO₃^2-, HCO_3, NO₂^-, NO₃^-, NH₃, Na, K⁺, Mn²⁺. Then, the average of each parameter was obtained for each channel, and finally, values of these parameters were compared with the standard set by Iranian Environmental Protection Agency for discharge to surface water resources. Gathered Data showed that many of these parameters, including Oil, BOD₅, COD, Turbidity, PO₄^3-, SO₄^2-, TSS, in effluent of industrials are higher than the permitted amount. Therefore, regarding discharge of the to the surface water (seawater) and in accordance with Environment Protection Agency standards for effluent disposal, it should be purified to about 90% prior to discharge. Due to high concentration of solutes in petrochemical wastewater, it is not possible to use it for agricultural purpose. In this data, due to ethical considerations, we did not mention the name of petrochemical complex.

Pretreatment technologies for industrial effluents: Critical review on bioenergy production and environmental concerns

The implementation of different pretreatment techniques and technologies prior to effluent discharge is a direct result of the inefficiency of several existing wastewater treatment methods. A majority of the industrial sectors have known to cause severe negative effects on the environment. The five major polluting industries are the paper and pulp mills, coal manufacturing facilities, petrochemical, textile and the pharmaceutical sectors. Pretreatment methods have been widely used in order to lower the toxicity levels of effluents and comply with environmental standards. In this review, the possible environmental benefits and concerns of adopting different pretreatment technologies for renewable energy production and product/resource recovery has been reviewed and discussed.

A review: Potential and challenges of biologically activated carbon to remove natural organic matter in drinking water purification process

The use of biologically activated carbon (BAC) in drinking water purification is reviewed. In the past BAC is seen mostly as a polishing treatment. However, BAC has the potential to provide solution to recent challenges faced by water utilities arising from change in natural organic matter (NOM) composition in drinking water sources - increased NOM concentration with a larger fraction of hydrophilic compounds and ever increasing trace level organic pollutants. Hydrophilic NOM is not removed by traditional coagulation process and causes bacterial regrowth and increases disinfection by-products (DBPs) formation during disinfection. BAC can offer many advantages by removing hydrophilic fraction and many toxic and endocrine compounds which are not otherwise removed. BAC can also aid the other downstream processes if used as a pre-treatment. Major drawback of BAC was longer empty bed contact time (EBCT) required for an effective NOM removal. This critical review analyses the strategies that have been adopted to enhance the biological activity of the carbon by operational means and summarises the surface modification methods. To maximize the benefit of the BAC, a rethink of current treatment plant configuration is proposed. If the process can be expedited and adopted appropriately, BAC can solve many of the current problems.

Treatment of petrochemical wastewater by microaerobic hydrolysis and anoxic/oxic processes and analysis of bacterial diversity

Microaerobic hydrolysis-acidification (MHA)-anoxic-oxic (A/O) processes were developed to treat actual petrochemical wastewater. The results showed that the overall COD removal efficiency was 72-79% at HRT=20h, and MHA accounted for 33-42% of COD removal, exhibiting good efficiency of acidogenic fermentation. Ammonium removal was more than 94%. The main pollutants in the influent were identified to be benzene, ketone, alcohols, amine, nitrile and phenols by GC-MS, and the majority of pollutants could be removed by MHA-A/O treatment. Proteobacteria was the most dominant bacteria in the system, accounting for more than 55% of the reads. The predominant genera in MHA, anoxic and oxic reactors were Anaerolineaceae and Sulfuritalea, Lactococcus and Blastocatella, and Saprospiraceae uncultured and Nitrosomonadaceae, respectively. This treatment system exhibited good performance in degrading the complex compounds in the petrochemical wastewater.

Scale-up of electrochemical oxidation system for treatment of produced water generated by Brazilian petrochemical industry

Scale-up of anodic oxidation system is critical to the practical application of electrochemical treatment in bio-refractory organic wastewater treatment. In this study, the scale-up of electrochemical flow system was investigated by treating petrochemical wastewater using platinized titanium (Ti/Pt) and boron-doped diamond (BDD) anodes. It was demonstrated that flow cell was successfully scaled-up because when it was compared with batch mode (Rocha et al. 2012b), higher performances on organic matter removal were achieved. Under the suitable operating conditions and better anode material, the chemical oxygen demand (COD) of petrochemical wastewater was reduced from 2,746 to 200 mg L(-1) within 5 h with an energy consumption of only 56.2 kWh m(-3) in the scaled-up BDD anode system. These results demonstrate that anode flow system is very promising in practical bio-refractory organic wastewater treatment.

Optimization of membrane bioreactors by the addition of powdered activated carbon

It was found that with replenishment, powdered activated carbon (PAC) in the membrane bioreactor (MBR) would develop biologically activated carbon (BAC) which could enhance filtration performance of a conventional MBR. This paper addresses two issues (i) effect of PAC size on MBR (BAC) performance; and (ii) effect of sludge retention time (SRT) on the MBR performance with and without PAC. To interpret the trends, particle/floc size, concentration of mixed liquor suspended solid (MLSS), total organic carbon (TOC), short-term filtration properties and transmembrane pressure (TMP) versus time are measured. The results showed improved fouling control with fine, rather than coarse, PAC provided the flux did not exceed the deposition flux for the fine PAC. Without PAC, the longer SRT operation gave lower fouling at modest fluxes. With PAC addition, the shorter SRT gave better fouling control, possibly due to greater replenishment of the fresh PAC.

Biological treatment and ozone oxidation: Integration or coupling?

Wastewaters generated by many economically relevant industrial activities contain recalcitrant organic compounds which pass unaltered through biological stage of the treatment plant making it difficult to meet the discharge limits currently in force. Therefore, an additional treatment is usually required to remove these compounds. In this study, the application of ozonation together with biological treatment was investigated. In particular, the effectiveness of biological degradation followed by or integrated with ozonation for treating the effluents produced by three environmentally relevant activities (i.e., leather and textile processing and municipal waste landfilling) are compared in the present paper. The results show that biological treatment followed by ozonation does not guarantee depurative levels sufficient for discharge for landfill leachates and tannery wastewater. On the contrary, thanks to the synergy between biological degradation and ozonation, integrated treatment significantly improves the process performance for all the investigated wastewaters, thus allowing the discharge limits to be met.

Kinetics of styrene biodegradation in synthetic wastewaters using an industrial activated sludge

Kinetics of styrene biodegradation in synthetic wastewaters, containing either styrene or styrene together with ethanol, by an industrial activated sludge obtained from the wastewater treatment unit of a petrochemical complex was studied. The kinetic data could be fitted using the Haldane kinetic model. This model was previously used to predict kinetic data for biodegradation of styrene by pure or mixed microbial cultures isolated from biofilters, but the values of the model parameters reported in these studies was substantially different from that obtained for the industrial activated sludge. The presence of ethanol did not affect the kinetics of styrene biodegradation by the industrial activated sludge; however, it increased the rates of styrene biodegradation due to the resulting higher microbial growth rates. Styrene concentration was found to affect the specific growth rate in a manner similar to its effect on the styrene degradation rate. No lag phase was observed in styrene biodegradation by industrial activated sludge for styrene concentrations up to 100mg/L. Lag phase was observed for municipal activated sludge even at 50mg/L styrene concentration but the rate of styrene biodegradation after the lag phase was similar to that achieved by the industrial activated sludge.

Treatment of phenol wastewater using hydroxyl radical produced by micro-gap discharge plasma technique

Hydroxyl radical produced by non-equilibrium plasma, which was induced by micro-gap dielectric barrier discharge, was used for the treatment of phenol wastewater. The advantage of this method was that chemicals and catalysts were not involved when hydroxyl radical was generated from water and oxygen. A proportional efficiency of phenol removal was observed with the hydroxyl radical increasing. The removal efficiency was higher in a basic condition than in an acidic condition, which was enhanced with the pH value of the solution increasing from 3.6 to 11.2. It was rational to adjust the pH value between 9.0 and 10.0. The removal efficiency of phenol was reduced when the conductivity of the solution increased from 0 to 200 micros x cm(-1); the highest was found in the solution without Na2CO3. The UV spectral absorption in the process indicated that few organic compounds with a conjugated structure were included in the treated wastewater.

Theoretical analysis of physicochemical processes occurring during water treatment by ozone and ultraviolet radiation

The paper presents a kinetic model developed for ozone dissolution in water and taking into account convective and diffusion processes occurring in the vicinity of floating bubbles that contain an ozone-air mixture. It was shown that the gradient of ozone concentration in a convective-diffusion layer and consequently the rate of ozone transfer from bubbles to the solution depended on the rate of ozone decomposition both in its reaction with organic admixtures and in the conditions of exposure to ultraviolet radiation. The obtained kinetic curves of destruction of organic compounds and changes of ozone concentration in water and ozone-air mixture are compared with experimental data for humic acids. The paper also analyzes additional factors affecting the kinetics of ozone dissolution and the rate of resultant reactions.

Biofilm processes in biologically active carbon water purification

This review paper serves to describe the composition and activity of a biologically active carbon (BAC) biofilm used in water purification. An analysis of several physical-chemical, biochemical and microbiological methods (indicators) used to characterize the BAC biofilm's composition and activity is provided. As well, the ability of the biofilm to remove and biodegrade waterborne organic substances and pollutants will be reviewed, with context to other industrial processes such as pre-ozonation and post-membrane filtration. Strategies to control the growth of the BAC biofilm, such as varying the nutrient loading rate, manipulating influent DO and pH levels, altering the frequency of BAC filter backwashing and applying oxidative disinfection, will be described in detail along with their respective process control challenges.

Ozonation of oil sands process water removes naphthenic acids and toxicity

Naphthenic acids are naturally-occurring, aliphatic or alicyclic carboxylic acids found in petroleum. Water used to extract bitumen from the Athabasca oil sands becomes toxic to various organisms due to the presence of naphthenic acids released from the bitumen. Natural biodegradation was expected to be the most cost-effective method for reducing the toxicity of the oil sands process water (OSPW). However, naphthenic acids are poorly biodegraded in the holding ponds located on properties leased by the oil sands companies. In the present study, chemical oxidation using ozone was investigated as an option for mitigation of this toxicity. Ozonation of sediment-free OSPW was conducted using proprietary technology manufactured by Seair Diffusion Systems Inc. Ozonation for 50min generated a non-toxic effluent (based on the Microtox bioassay) and decreased the naphthenic acids concentration by approximately 70%. After 130min of ozonation, the residual naphthenic acids concentration was 2mgl(-1): <5% of the initial concentration in the filtered OSPW. Total organic carbon did not change with 130min of ozonation, whereas chemical oxygen demand decreased by approximately 50% and 5-d biochemical oxygen demand increased from an initial value of 2mgl(-1) to a final value of 15mgl(-1). GC-MS analysis showed that ozonation resulted in an overall decrease in the proportion of high molecular weight naphthenic acids (n> or = 22).

Adsorption thermodynamics and kinetic investigation of aromatic amphoteric compounds onto different polymeric adsorbents

The adsorption behavior of p-aminobenzoic acid and o-aminobenzoic acid onto the different polymeric adsorbents was systematically investigated as a function of the solution concentration and temperature. Experimental results indicated that the equilibrium adsorption data of the four polymeric adsorbents fitted well in the Freundlich isotherm. The adsorption capacity of multi-functional polymeric adsorbent NJ-99 was the highest, which might be attributed to the strong hydrogen-bonding interaction between the amino groups on the resin and the carboxyl group of aminobenzoic acid. The adsorption capacity of o-aminobenzoic acid onto any adsorbent was higher than p-aminobenzoic acid. Thermodynamic studies suggested the exothermic, spontaneous physical adsorption process. Adsorption kinetics results showed that the adsorption followed the pseudo-second-order kinetics model and the intraparticle mass transfer process was the rate-controlling step.

Comparison of AC/O3-BAC and O3-BAC processes for removing organic pollutants in secondary effluent

AC (activated carbon)/O3-BAC (biological activated carbon) process was employed to treat secondary effluent and compared to O3-BAC process. The effects of ozone dosages and empty bed contact time (EBCT) in BAC on dissolved organic carbon (DOC) removal were investigated. The results showed that the presence of AC improved ozone utilization and biodegradability of the effluent. DOC removal increased with ozone dosage and EBCT in BAC, however, 3 mg l(-1) ozone dosage with 15 min oxidation time and 15 min EBCT in BAC were more economical and efficient. For DOC removal, AC/O3-BAC was more efficient than O3-BAC and its synergetic effect was more than that in O3-BAC process. The biomass of the subsequent BAC unit in AC/O3-BAC process was more than that in O3-BAC process and much more than that in BAC alone. Except for organic pollutants with molecular weight (MW) >10 kDa, those of other MW range were decomposed much more by AC/O3 process than by O3 process. GC/MS analysis showed that dibutyl phthalate, bis(2-ethylhexyl) phthalate, 4-bromo-3-chloroaniline, 2-propanone-ethylhydrazone and phenol derivatives were prevalent organic compounds in the secondary effluent. Some aromatic compounds, such as 4-bromo-3-chloroaniline and 2,4-dichloro-benzenamine disappeared after AC/O3 treatment. However, some small molecules were generated, after further biological treatment by BAC, the kinds and concentration of organic compounds were greatly reduced.

Improvement of oxidative decomposition of aqueous phenol by microwave irradiation in UV/H2O2 process and kinetic study

2.5GHz of microwave irradiation can cause a considerable improvement of oxidative decomposition of aqueous phenol in a UV/H2O2 system. The experimental results showed that the microwave irradiation can raise both the phenol conversion and the TOC removal efficiency up to or above 50%. Also, the microwave irradiation could considerably enhance the oxidative degradation of phenol in the UV/H2O2 system even under a suppression of thermal effect. Addition of hydrogen peroxide by more than a stoichiometric amount was critical to mineralize aqueous phenol to create a short reaction time. Also, microwave irradiation can accelerate the degradation rate of intermediates, hydroquinone and catechol, produced in the course of phenol oxidative decomposition. From the kinetic study, the disappearance rate of phenol can be expressed as dX/dt = kPH[M]0(alpha - X)(1 - X), where alpha equivalent [H2O2]0/[M]0 + kOH[OH*]/kPH[M]0, shows a good correlation with the experimental data. The kinetic analysis showed that an indirect reaction of phenol with OH radical might be dominant in the absence of microwave irradiation, meanwhile a direct reaction of phenol with hydrogen peroxide might be dominant in the presence of microwave irradiation except for low concentrations of hydrogen peroxide.