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When desalinating an industrial stream like polymer-flooding produced water via electrodialysis (ED), high water recoveries, low energy consumption, and reduced membrane area are all desirable. However, little effort has been done until now to experimentally achieve these goals. Encouraged by recent and promising results obtained using aliphatic membranes and pulsed electric field, this study experimentally evaluated different strategies and operational conditions to increase the water recovery while keeping a low energy consumption. The results obtained were analyzed to understand the trade-offs in operative time, water recovery, and energy consumption. Finally, the experimental data was employed to perform an economic analysis, which indicated that although further optimization should be possible, current conditions already make ED desalination of polymer-flooding produced water a sound case from an economical point of view.

When performing electrodialysis (ED) to desalinate a stream, both the energy for desalination and the energy for pumping contribute to the total energy consumption, although under typical working conditions (e.g., brackish water desalination) the latter is usually negligible. However, the energy penalty might increase when desalinating viscous mixtures (i.e., viscosity of 2–20 cP). In this work, we experimentally investigate the desalination performance of an ED-unit operating with highly viscous water-polymer mixtures. The contribution of desalination and pumping energy to the total energy consumption was measured while varying diverse parameters, i.e., salinity and viscosity of the feed, and geometry and thickness of the spacer. It was found that the type of spacer did not significantly influence the energy required for desalination. The pumping energy was higher than predicted, though in most cases minimal compared to the energy for desalination. Only when using thin spacers (300 μm) and/or highly viscous feeds (12 cP), the pumping energy accounted for 50% of the total energy for low salinity feeds. Therefore, the main contributor to the energy consumption of viscous solutions is the desalination energy, provided that large spacer thicknesses (at least 450 μm) and adequate operating conditions are utilized to limit pumping energy losses.

Micropollutants (MPs) are organic chemicals that are present in the environment at low concentrations (ng/L-μg/L), for example pharmaceuticals. A constructed wetland (CW) is a promising post-treatment technique to remove MPs from wastewater effluent. Selecting a suitable material for support matrix is important when designing such a CW. Nine materials were studied as potential support matrices: Light Expanded Clay Aggregates (LECA), compost, bark, granulated activated carbon (GAC), biochar, granulated cork, lava rock, sand and gravel. Batch experiments were conducted to study MP removal by nine materials in phosphate buffer with 5 or 50 μg/L MPs, or wastewater effluent with 50 μg/L of MPs. GAC and biochar removed almost all MPs in both phosphate buffer and wastewater effluent, followed by bark, compost, granulated cork. Sand, gravel, LECA and lava rock removed less than 30% of most MPs in both matrixes. Based on set criteria (e.g. removal efficiency), biochar, bark, compost, LECA and sand were selected, and used in combinations in column studies to test their overall performance. A combination of bark and biochar performed the best on MP removal, as 4 MPs were highly (70%–100%) removed, 4 MPs were moderately (30%–70%) removed while only 3 MPs were hardly removed. The main flow regime of this combination was both plug flow and dispersive flow. Moreover, we hypothesized to apply bark and biochar in a CW. Based on the assumptions and calculations, some benefits are expected, such as increasing MP removal and extending operation time.

Microbial extracellular polymeric substances (EPS) were produced in two membrane bioreactors, each separately treating fresh and saline synthetic wastewater (consisting of glycerol and ethanol), with the purpose of applying them as sustainable bioflocculants. The reactors were operated under nitrogen-rich (COD/N ratios of 5 and 20) and limited (COD/N ratios of 60 and 100) conditions. Under both conditions, high COD removal efficiencies of 87–96% were achieved. However, nitrogen limitation enhanced EPS production, particularly the polysaccharide fraction. The maximum EPS recovery (g EPS−COD/g CODinfluent) from the fresh wastewater was 54% and 36% recovery was obtained from the saline (30 g NaCl/L) wastewater. The biopolymers had molecular weights up to 2.1 MDa and anionic charge densities of 2.3–4.7 meq/g at pH 7. Using kaolin clay suspensions, high flocculation efficiencies of 85–92% turbidity removal were achieved at EPS dosages below 0.5 mg/g clay. Interestingly, EPS produced under saline conditions proved to be better flocculants in a saline environment than the corresponding freshwater EPS in the same environment. The results demonstrate the potential of glycerol/ethanol-rich wastewater, namely biodiesel/ethanol industrial wastewater, as suitable substrates to produce EPS as effective bioflocculants.

The reuse of polymer flooding produced water (PFPW) generated in oil and gas industry is limited by its salt content, making desalination by electrodialysis a promising treatment option. Therefore, this study aimed to 1) assess the technical feasibility of employing electrodialysis to desalinate PFPW generated in assorted scenarios, and 2) evaluate the reuse of the electrodialysis-desalted water to confect polymer-flooding solution. The experimental work involved desalting two kinds of synthetic PFPW solutions, one with relatively low salinity (TDS=5000 mg/L, brackish PFPW), and another with high salinity (TDS=32,000 mg/L, sea PFPW), at two different temperatures, and later reusing the desalted solution to prepare viscous solutions. For the electrodialysis runs, the effects of feed composition and temperature on water transport, energy consumption and current efficiency were analyzed. It was found that the presence of polymer did not significantly influence the water transport rate or the specific energy consumption for the seawater cases, but had a measurable effect when desalting brackish water at 20 °C. It was also found that some polymer remained in the stack, the loss occurring faster for the brackish PFPW. Still, both kinds of reused PFPW probed adequate to be employed as a basis for preparing n polymer solution.

This research aimed at studying the oxidation process, to verify the effectiveness of coliform inactivation and to evaluate the formation of ozonation disinfection byproducts (DBP) in anoxic sanitary wastewater treated with ozone/hydrogen peroxide applied at doses of 2.6 mg O3 L-1 and 2.0 mg H2O2 L-1 with contact time of 10 min and 8.1 mg O3 L-1 and 8.0 mg H2O2 L-1 with contact time of 20 min. The mean chemical oxygen demand (COD) reductions were 7.50 and 9.40% for applied dosages of 2.5 – 2.8 and 6.4 – 9.4 mg O3 L-1 + 2.0 and 8.0 mg H2O2.L-1, respectively. The Escherichia coli (E. coli) inactivation range was 2.98 – 4.04 log10 and the total coliform inactivation range was 2.77 – 4.01 log10. The aldehydes investigated were formaldehyde, acetaldehyde, glyoxal and methylglyoxal. It was observed only the formation of acetaldehyde that ranged 5.53 to 29.68 µg L-1. Keywords: Ozone, hydrogen peroxide, disinfection, byproducts, sanitary wastewater, anaerobic effluent. RESUMO Esta pesquisa visou estudar o processo de oxidacao, verificar a eficacia da inativacao de coliformes e avaliar a formacao de subprodutos da ozonizacao em efluente sanitario anoxico tratado com ozonio/peroxido de hidrogenio aplicado em doses de 2.6 mg O3 L-1 e 2.0 mg H2O2 L-1 com tempo de contato de 10 min e 8,1 mg O3 L-1 e 8,0 mg H2O2 L-1 com tempo de contato de 20 min. As reducoes medias da demanda quimica de oxigenio (DQO) foram 7,50 e 9,40% para dosagens aplicadas de 2,5 – 2,8 e 6,4 – 9,4 mg O3 L-1 + 2,0 e 8,0 mg.H2O2.L-1, respectivamente. O intervalo de inativacao de Escherichia coli (E. coli) foi 2,98 – 4,04 log10 e o intervalo de inativacao de coliformes totais foi 2,77 – 4,01 log10. Os aldeidos investigados foram o formaldeido, acetaldeido, glioxal e metilglioxal. Foi observada apenas a formacao de acetaldeido que variou de 5,53 ate 29,68 µg L-1. Palavras-Chaves: Ozonio, peroxido de hidrogenio, desinfeccao, subprodutos, esgoto sanitarior, efluente anaerobio.

The reuse of cooling tower blowdown (CTBD) in the cooling tower itself requires CTBD deionization and a pre-treatment before deionization to remove organic compounds (OCs) that induce membrane fouling. This study assesses the potential of electrochemical oxidation (EO) with a boron-doped diamond (BDD) and a Ti/RuO2 mixed-metal oxide (MMO) anode for CTBD pre-treatment. Also, the influence of the applied current density (j), initial pH, hydrodynamic conditions, and supporting electrolyte on the process performance was evaluated. Results show that COD and TOC removal were 85 and 51%, respectively, with the BDD-anode; however, they were 50 and 12% with MMO-anode at a j-value of 8.7 mA cm−2 and neutral pH. An increased j-value increased the COD and TOC removal; however, different pHs, hydrodynamic conditions, and the addition of supporting electrolytes had a minor impact on the removal with both anodes. Liquid chromatography-organic carbon detection analysis showed that the OC in CTBD mainly consisted of humic substances (HS). EO with the BDD-anode resulted in 35% HS mineralization, while the rest of the HS were partially oxidized into low molecular weight compounds and building blocks. However, HS mineralization was limited with the MMO-anode. The mineralization and oxidation were accompanied by the formation of organic and inorganic chlorinated species. These species increased the toxicity to Vibrio fischeri 20-fold compared to the initially low-toxic CTBD. Thus, EO with a BDD-anode is a promising pre-treatment technology for the removal of OCs before CTBD deionization, but measures to minimize the chlorinated species formation are required before its application.

A substantial part of the freshwater used in the industry is consumed in cooling towers. Cooling towers discharge saline cooling tower blowdown (CTBD), and the reuse of CTBD in the cooling tower can lower the industrial freshwater footprint. This reuse requires CTBD desalination and a pre-treatment that removes organic chemicals before physico-chemical desalination technologies to be applied efficiently. In the present study, the pre-treatment of CTBD by a combination of electrochemical oxidation (EO) with a boron-doped diamond (BDD) or mixed-metal oxide (MMO) anode and a vertical flow constructed wetland (VFCW) was assessed in both possible configurations. The integrated VFCW-EO systems removed more organic chemicals, such as COD, TOC, and the corrosion inhibitor benzotriazole than the EO-VFCW systems. However, the EO resulted in highly toxic effluent to Vibrio fischeri and the plants in the VFCW. This toxicity was the result of the production of unwanted chlorinated organic compounds and ClO3− and ClO4− by both the BDD- and MMO-anode during EO. These toxic EO by-products were removed substantially in the VFCW during EO-VFCW treatment but did impact the removal efficiency and viability of the VFCW. Moreover, significant water loss was observed in the VFCW due to evapotranspiration. In conclusion, the negative impact of EO effluent on the VFCW and evapotranspiration of the VFCW should be considered during application.

Domestic (household) biogas plants constitute a growing sub-sector of the anaerobic digestion industry worldwide but have received low interest for improvements. The Chinese dome digester (CDD 1), a major type of domestic biogas plants, is a naturally mixed, unheated and low technology reactor mainly used in rural and pre-urban areas for cooking using animal manure. In this study, a multiphase Computational Fluid Dynamics (CFD) model was applied to evaluate an optimized CDD design and outcomes were compared with results of pilot scale experiments. The optimized digester (CDD2) under goes self-agitating cycles created by the pressure variation from the produced biogas with the aid of a baffle at the top of the reactor, whereas the blank (CDD 1) does not self-agitate. The optimized digester has two pressure zones to improve mixing viz. the self-agitation cycles. The optimized digester is characterized by more, stable and improved hydraulic characteristics and mixing.

Household digesters are anaerobic reactors applied mostly in rural areas of developing countries with tropical climate. The Chinese dome digester is the most popular household digester type in Asia and Africa, and has become the basis for contemporary developments in the household digester sector around the world. Household digesters are operated at ambient temperatures and have no internal mixing device, making them simple to operate. In the absence of internal mixing mechanism, the Chinese dome digester is mixed via pressure variation during gas production, gas use and feeding. Since mixing is limited in household digesters, they are operated at low organic loading rates and long hydraulic retention time when compared with forced mixed reactors. This review analyses and presents the various types of domestic biogas plants and operating parameters, with emphasis on mixing. Experimental results of household reactors, forced mixed reactors with different mixing modes and intensities were also reviewed and compared.

The Residence Time Distribution (RTD) technique was applied to evaluate mixing of liquid and solid phases in laboratory scale Chinese dome digesters mixed via hydraulic variation. To achieve this purpose, six laboratory scales digesters with different mixing modes and two total solids (TS) concentrations using appropriate tracers were studied over a theoretical hydraulic retention time (HRT) of 30 days. The three different mixing modes were impeller, unmixed and hydraulic mixing, each at influent concentration of ca. 7.5 and 15% TS concentrations. The mode of mixing strongly affected the effective or actual residence time (ta) and directly influenced the percentage of dead zones. The Chinese dome digesters had more dead volumes than the impeller mixed reactors and less than the unmixed reactors. This implied that mixing was more efficient in the impeller mixed reactors followed by the hydraulic mixed reactors and then the unmixed reactors, irrespective of the TS concentration. There was a clear relation between the RTD results and anaerobic digestion performance viz. methane production. There is need to optimize the hydraulic variation in the Chinese dome digester to reduce dead zones while also optimizing the effective residence time (ta).

A model based on three equations was developed and validated for the design of the inlet and outlet of the Chinese dome digester (CDD) to prevent biogas emission or leakage. The model was implemented in MATLAB software and validated with results from a pilot study. Biogas and temperature data from the pilot experiment were used to validate the model and the results fitted well with the experimental data at low gas volume (20 mols). The model can be used to predict the optimal size of the CDD for daily biogas storage based on different reactor and expansion chamber sizes, in order to mitigate the emission of surplus biogas from the inlet and outlet pipes.

Poor nitrogen removal efficiency (mainly nitrate, NO3 −-N) at low temperatures strongly limits application of subsurface wastewater infiltration systems (SWISs). Seven psychrophilic strains (heterotrophic nitrifying bacteria and aerobic denitrifying bacteria) were isolated and added to SWISs to investigate the effect of embedding and direct-dosing bioaugmentation strategies on sewage treatment performance at low temperature. Both bioaugmentation strategies improved ammonium (NH4 +-N) removal efficiencies, and the embedding strategy also exhibited satisfactory NO3 −-N and total nitrogen (TN) removal efficiencies. Pyrosequencing results of the bacterial 16S rRNA gene indicated that the embedding strategy significantly decreased the indigenous soil microbial diversity (p

Microbial extracellular polymeric substances (EPS) have gained increasing attention for various water treatment applications. In this study, EPS produced from nitrogen-limited glycerol/ethanol-rich wastewater were used to recover Cu2+ and Pb2+ from aqueous solutions. Continuous flow-through tests were conducted on a column packed with silica gel coated with polyethyleneimine, to which EPS were irreversibly attached as shown by optical reflectometry. These immobilised EPS excellently adsorbed Cu2+ and Pb2+, with 99.9% of influent metal adsorbed before the breakthrough points. Metal desorption was achieved with 0.1M HCl, with an average recovery of 86% for Cu2+ and 90% recovery for Pb2+. For the first time, we successfully showed the possibility to regenerate and reuse the immobilised EPS for five adsorption-desorption cycles (using Cu2+ as an example) with no reduction in the adsorbed amount at the breakthrough point (qbp). Based on the mass balance of the associated metal ions participating in the adsorption process, ion exchange was identified as the major mechanism responsible for Cu2+ and Pb2+ adsorption by EPS. The results demonstrate the potential of wastewater-produced EPS as an attractive and perhaps, cost-effective biosorbent for heavy metal removal (to trace effluent concentrations) and recovery (86–99%).

Strong electric fields for disinfection of wastewaters have been employed already for several decades. An innovative approach combining low strength (7 V/cm) alternating electric fields with a granular activated carbon fluidized bed electrode (FBE) for disinfection was presented recently. For disinfection performance of FBE several pure microbial cultures were tested: Bacillus subtilis, Bacillus subtilis subsp. subtilis, Enterococcus faecalis as representatives from Gram positive bacteria and Erwinia carotovora, Pseudomonas luteola, Pseudomonas fluorescens and Escherichia coli YMc10 as representatives from Gram negative bacteria. The alternating electric field amplitude and shape were kept constant. Only the effect of alternating electric field frequency on disinfection performance was investigated. From the bacteria tested, the Gram negative strains were more susceptible and the Gram positive microorganisms were more resistant to FBE disinfection. The collected data indicate that the efficiency of disinfection is frequency and strain dependent. During 6 h of disinfection, the decrease above 2 Log units was achieved with P. luteola and E. coli at 10 kHz and at dual frequency shift keying (FSK) modulated signal with frequencies of 10 kHz and 140 kHz. FBE technology appears to offer a new way for selective bacterial disinfection, however further optimizations are needed on treatment duration, and energy input, to improve effectiveness.

This research studied the sequential ozone and chlorine process with respect to, the inactivation of indicator bacteria and the formation of ozone disinfection byproducts in sanitary wastewater effluent. The applied ozone doses were 5, 8 and 10 mg.O3.L(-1), followed by chlorine doses of 10, 20 and 30 mg.L(-1), respectively. After the sequential ozone/chlorine process, the mean reduction in chemical oxygen demand ranged from 9 to 37%. Total coliform inactivation ranged from 1.59 to 3.73 log10, and E. coli was always

At the high-rate anaerobic treatment of domestic sewage, both biological and physical processes play an important role. Therefore, the anaerobic biodegradability of raw, paper-filtered and membrane-filtered sewage and black water has been investigated in batch experiments. Additionally, the effect of anaerobic digestion on physical characteristics, like particle size, surface tension and zeta-potential, of the present particles is studied. The biodegradability of domestic sewage and black water at 30 degrees C is almost similar (71-74%). Moreover, a high methanogenesis of the colloidal fraction in domestic sewage (86 +/- 3%) is achieved, showing that the low removal of colloidal particles in continuous high-rate anaerobic reactors is due to low physical removal rather than biodegradability. The lowest biodegradability is demonstrated for the dissolved fraction (62%). The results show that after anaerobic digestion the average radius of particles with diameter4.4 and0.45 microns increased for domestic sewage, while it decreased for black water. Part of the surface-active components in domestic sewage is not biodegraded during anaerobic batch digestion, as indicated by the development of the surface tension. The negative zeta-potential of all particles hardly changes during digestion, showing that colloidal interactions were not affected by anaerobic digestion.

The metallization of TiO 2 photocatalyst with 1%Pt gave increasing rates of alcohol conversions and carbon dioxide production. A new porous powder micro-cell model was proposed. Heterogeneous reactions of photocatalytic oxidation, and final mineralizing to CO 2 , of methanol, ethanol in dilute (50–400 pm) aqueous solution should take place on the solid–liquid interface of the photocatalyst. It has similar kinetic behavior as reactions on the solid–gas interface of a heterogeneous catalyst. The process can be described by the Langmuir adsorption isotherm. These photocatalytic degradations can be expressed as a first-order reaction. Maximum rates of photocatalytic reactions and efficiencies can be estimated according to the calculation of surface coverage of certain compounds on TiO 2 . Because ethanol have the double coverage of methanol at same concentration, it is presumed that methanol and ethanol have the same adsorption state of the end-group on catalyst surfaces. In a closed reactor, if oxygen pressure was controlled at 76 cm H 2 O, its reduction rate was nearly of zero order.

The removal of pathogens from effluents is important to promote the reuse of these water resources and safeguarding human health, especially in water scarce areas worldwide. Previously a proof-of-principle of a method for water disinfection consisting of fluidized bed electrodes (FBE) with RX3 EXTRA granular activated carbon (GAC) and a low strength alternating electric field (AC field) in radio frequency range (80–200 kHz) was published. In the study presented here we investigated the mechanistic role of 10 different types of GAC in radio frequency FBE disinfection with Escherichiacoli YMc10 as the model microorganism. The disinfection performances with only GAC, and GAC combined with an AC field were quantified. Seven GACs showed poor to intermediate and three GACs (Norit RB3 (2.7 Log CFU E. coli decrease), Sorbonorit 3 (2.8 Log CFU E. coli decrease) and RX3 EXTRA (3.4 Log CFU E. coli decrease)) showed substantial disinfection in FBE. The results suggest a relation between the pHpzc of the GAC and the disinfection performance. Disinfection performance increased with bigger particle size and decreasing conductivity of tested GACs. We conclude that these physico-chemical and physical properties of GAC are important factors controlling the disinfection performance of these type FBE systems.

In Advanced oxidation processes (AOPs) radicals are considered to play an important role. Organic contaminations can in AOPs generally be converted to carbon dioxide, water, etc. The most important limitation to the application of AOPs, however, is their high costs, especially when complete mineralisation of the pollutants is pursued. The costs can be reduced by using the oxidant more efficiently, which can be achieved by introducing selectivity. Kinetic and mechanistic data are the basic requirements for optimization of the process. In this work, the influence of several different parameters (temperature, pH, UV irradiation and carbonate concentration) on the kinetics of the degradation ofortho -chlorophenol and para-chlorophenol by ozone was investigated. The pH is the most important parameter. Strongly related to the pH is the degree of ionisation of the phenol, which might be of importance since the shift from a slow to a fast reaction occurs at a higher pH in the case of para-chlorophenol as compared to the case with the more acidic ortho-chlorophenol. A strong indication for a radical mechanism is found in the decrease of the reaction rate in the presence of carbonate, a well known radical scavenger. A further indication is seen in the first step of the reaction, which is dechlorination of the aromatic compound.

Nitrogen recovery through NH(3) stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid-gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 g(N) d(-1) m(-2) (vs. membrane surface area) was achieved at a current density of 0.50 A m(-2) (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ g(N)(-1), which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.

Ammonium recovery using a two chamber microbial fuel cell (MFC) was investigated at high ammonium concentration. Increasing the ammonium concentration (from 0.07 to 4 g ammonium–nitrogen/L) by addition of ammonium chloride did not affect the performance of the MFC. The obtained current densities by DC-voltammetry were higher than 6 A/m 2 for both operated MFCs. Also continuous operation at lower external resistance (250 Ω) showed an increased current density (0.9 A/m 2 ). Effective ammonium recovery can be achieved by migrational ion flux through the cation exchange membrane to the cathode chamber, driven by the electron production from degradation of organic substrate. The charge transport was proportional to the concentration of ions. Nonetheless, a concentration gradient will influence the charge transport. Furthermore, a charge exchange process can influence the charge transport and therefore the recovery of specific ions.

This research was aimed at studying oxidation processes, coliform inactivation effectiveness and disinfection byproducts (DBPs) associated with the disinfection of anaerobic sanitary wastewater effluent with ozone applied at doses of 5.0, 8.0 and 10.0mg O(3)L(-1) for contact times of 5, 10 and 15 min. The wastewater used in this research was generated by the wastewater treatment plant (WWTP), University of São Paulo - Brazil. The total coliform inactivation range was 2.00-4.06 log(10), and the inactivation range for Escherichia coli was 2.41-4.65 log(10). Mean chemical oxygen demand (COD) reductions were 37.6%, 48.8% and 42.4% for doses of 5.0, 8.0 and 10.0mg O(3)L(-1), respectively. Aldehyde formation varied with dosage only when the ozone dose was increased from 5.0 to 8.0mg O(3)L(-1) for acetaldehyde and from 5.0 to 8.0 and from 8.0 to 10.0mg O(3)L(-1) for glyoxal.

Much research on ozone oxidation is performed using model wastewaters, containing a number of organic compounds to be degraded. In some cases they contain low concentrations of inorganic buffers to stabilize the pH during the experiments. In practical applications, however, salts and detergents may be present as well. The effect of such compounds on the process has to be investigated to prevent unexpected results in pilot- or full-scale applications. To quantify these effects, experiments have been performed on model waste waters in the absence and the presence of high concentrations of several inorganic salts. The oxidation selectivity in these experiments was interpreted using Hammett free-energy relationships. The effect of the different salt concentrations on the oxidation selectivity when considering reactions in the bulk of the liquid was seen to be small. This implicates the design of an ozone-based oxidation system can often be based on literature or calculated data regarding reaction rates. However, the effect of increased salt concentrations on ozone solubility and bubble size distribution may have implications for the reactor design, as these factors affect the mass transfer efficiency.

Ozonation can be a suitable technique for the pre-treatment of wastewater containing low concentrations of toxic or non-biodegradable compounds that cannot be treated with satisfactory results when only the traditional, less expensive biological techniques are applied. In this case, the oxidation process has to be made as efficient as possible, in order to reduce the costs of ozone addition and energy use. An efficient oxidation process with ozone can be obtained by focusing the oxidation with ozone selectively on the direct oxidation of toxic pollutants and to minimize ozone losses due to the decay of ozone in water. Supported by data of the rate constants of the reactions involved, a mathematical model was developed. It quantifies the ozone consumption by the process, and the share of ozone consumption by undesired side reactions, in several different reactor systemsOzonation can be a suitable technique for the pre-treatment of wastewater containing low concentrations of toxic or non-biodegradable compounds that cannot be treated with satisfactory results when only the traditional; less expensive biological techniques are applied. In this case, the oxidation process has to be made as efficient as possible, in order to reduce the costs of ozone addition and energy use. An efficient oxidation process with ozone can be obtained by focusing the oxidation with ozone selectively on the direct oxidation of toxic pollutants and to minimize ozone-losses due to the decay of ozone. in water. Supported by data of the rate constants of the reactions involved, a mathematical model was developed. It quantifies the ozone consumption by the process, and the share of ozone consumption by undesired side reactions, in several different reactor systems. Results obtained with this model indicate that a plug flow reactor (PFR) will be the most efficient design for the oxidation reactor. As an alternative, the cascaded tank reactor system (CTR), in which the ozone feed may be realized with less practical problems, might be considered: The traditional continuous flow stirred tank reactor (CFSTR) is shown to be the least efficient system.

This paper reports on the chemical extraction efficiency in the removal of heavy metals from sludge from an activated-sludge system, which receives as influent both industrial and municipal wastewater. Utilizing a series of chemical extractants in a sequential order comprised the first phase of the research, called sequential chemical extraction (SCE). The work started with the well-known Tessier method followed by Veeken and by Sims and Kline SCE schemes. Afterwards, modified versions of Tessier and Veeken schemes were applied. The second phase, named chemical extraction using pH progressive changes, concerns an alternative to the extraction process. Four acids were tested: nitric, hydrochloric, oxalic and citric and the pH values as well as the time were varied. Some conclusions reveal that although modifying Tessier and Veeken schemes provides more consistent results, SCE is still an imperfect method regarding specificity and selectivity. Besides, it is not advisable to apply one SCE scheme developed for one specific situation to another one, once the accurateness of the method depends on several factors such as sort of material and chemicals, contact time, temperature, etc. The extraction efficiency increases using nitric or hydrochloric acids at low pH values, promoting high extraction efficiency level.

A column packed with clean sheets of reticulated polyurethane foam was fed with either raw sewage, synthetic sewage or skimmed milk for a short time to evaluate the mechanism of physical entrapment and filtration of particles. The results revealed that clean media were effective in the removal of suspended chemical oxygen demand (COD) (>75%) even with hydraulic retention time (HRT) as low as 0.5 h or upflow velocity as high as 10 m/h. However, the removal of colloidal COD remained poor under all experimental conditions. The treatment of raw sewage and paper-filtered sewage in a fed-batch recirculation system under anaerobic conditions resulted in average removal efficiencies for colloidal COD of 63% and 81%, respectively at a temperature of 24 ± 1°C. Therefore, the presence of an anaerobic biofilm and the removal of suspended solids (SS) from the influent increased the removal efficiency of colloidal COD in the treatment of domestic sewage in an anaerobic polyurethane-foam filter.

A detailed description of various mechanisms for the photocatalytic oxidation of alcohols and organochlorides in an aerated or a deaerated system is given. This description includes mechanisms of surface reactions and radical reactions based on our experimental data presented. A surface mechanism of direct oxidation of substrates in photocatalyst surfaces is proposed as a favorable pathway for photocatalytic oxidations of methanol and ethanol, also a possible pathway for chloroform, trichloroethylene (TCE) and dichloropropionic acid (DCP) in M/TiO2 aqueous slurries.

Photocatalytic oxidations of methanol, ethanol and chloroform, trichloroethylene (TCE), and dichloropropionic acid (DCP) in M/TiO2 aqueous slurries are studied. In the presence of oxygen, the intermediates of methanol oxidation, such as formaldehyde and formic acid, were not detected by GC in the slurries of TiO2, Pt/TiO2, or Pd/TiO2, and CO2 was the only product detected. The distribution of intermediates for ethanol photocatalytic oxidation varies with different catalysts: under the same reaction conditions, the ratio of acetaldehyde:acetic acid is 30:1 on TiO2, and 0.23:1 on Pt/TiO2, with the acetaldehyde concentration being 130 times higher on TiO2 than on Pt/TiO2. Thus, a further oxidation is achieved easily on the Pt/TiO2. The CO2 production depends on the initial reaction pH: Acidic pH produces CO2 immediately in alcohol oxidation, but alkaline pH retards the mineralization substantially. Little effect of Pd metallization on TiO2 was observed for photocatalytic oxidation of chloroform, TCE or DCP. Pt/TiO2 only enhances DCP dechlorination and has no effect on its decarboxylation.

The treatment of sewage at a temperature of 13°C was investigated in three reactors (each 3.84 litre) a UASB and two anaerobic hybrid (AH) reactors with small sludge granules with an average diameter of 0.73 mm. The media used in the AH reactors were vertical polyurethane foam sheets. The reactors were operated at a HRT of 8 h. The use of small sludge granules and operating the reactors at low upflow velocity (1.8 m/d) improved suspended COD removal efficiencies for the UASB reactor. Moreover, the use of sheets in the AH reactors significantly increased suspended COD removal efficiencies as compared to the UASB and reached to 87% for pre-settled sewage treatment. The treatment of pre-settled sewage instead of raw sewage in AH reactors significantly increased colloidal and dissolved COD removal efficiencies with 13% and 12% respectively and colloidal COD removal efficiency for the UASB reactor with 13%. At ‘steady state’ for pre-settled sewage treatment, the AH reactors removed 64% of the total COD which is significantly higher by 4% than the UASB reactor. Therefore, the anaerobic treatment of domestic sewage at low temperature can be improved by treating pre-settled sewage in shallow AH reactors containing small sludge granules.

Solvent extraction is one of the possibilities to clean-up polluted sediments. It is especially attractive when the sediment mainly consists of clay particles polluted with contaminants which are not, or not easily, biodegradable. Using acetone as extracting agent the extraction process has been investigated at laboratory scale for treating sediment of the Petroleum Harbour in Amsterdam. This sediment is characterised by a substantial percentage of particles with diameter

Surfactants are compounds that generally prefer interfaces above bulk solution (Gibbs-adsorption) and prefer some interfaces above others (selectivity). It is this combination of properties that can make them useful tools in the hands of environmental technologists.