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Water reuse is one of the possible solutions to prevent depletion of freshwater resources; however, it is often limited by the accumulation of specific ions in the recirculating water. Ion selective desalination technologies can increase the potential for water reuse. Electrodialysis is a water treatment technology that is able to selectively remove ions from water. In order to enhance and further develop the selectivity of the process, a fundamental understanding of the various mechanisms governing multi-ion transport in electrodialysis is essential. In the present study, a theoretical model for multi-ionic (Na+ and K+) mass transport in electrodialysis was developed including ion-water and ion-membrane frictions, and water transport. General properties and the selectivity of ion exchange membranes towards K+ over Na+ ions were experimentally determined and included in the model. The theory was successfully validated for ion flux through the membranes, ion concentrations in the solutions, and water transport by comparing theory with batch-mode electrodialysis experiments. Contributions of different ion transport mechanisms to the selective transport of Na+ and K+ ions were evaluated by model calculations. It was found that electromigration has the largest contribution to ion transport followed by convection, and that diffusion controls the selectivity of ion transport in electrodialysis under constant voltage operation.

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.

The reuse instead of discharge of cooling tower water can significantly lower the industrial fresh water footprint. The reuse of cooling tower water requires the removal of different chemical fractions from the cooling tower water, such as dissolved minerals, phosphate, organic carbon and industrial chemicals. However, there is no stand-alone water treatment technology that can remove all these fractions simultaneously. Therefore, the aim of this study was to assess the removal of these fractions with an innovative pilot-scale technology train that was fed with real cooling tower water consisting of green and grey technologies: constructed wetlands, nanofiltration, electrochemical oxidation and reverse osmosis. In addition, attention was paid to the fate of emerging industrial contaminant benzotriazole, the performance of the nanofiltration membranes and potential production of unwanted by-products by electrochemical oxidation. The experiments showed that 1) The treatment-train was capable of reaching the desired water quality; 2) Benzotriazole was completely removed by the constructed wetlands that acted as pre-treatment before nanofiltration as a result of biodegradation; 3) the production of inorganic carbon species in the constructed wetlands resulted in increased fouling of the subsequent nanofiltration membranes; 4) these membranes mainly retained divalent ions and did not retain monovalent ions, which resulted in a permeate stream whose EC was too high for reuse applications and therefore required further treatment by reverse osmosis; 5) electrochemical oxidation of the nanofiltration concentrate was more efficient than direct electrochemical oxidation of cooling tower water in terms of degradation of recalcitrant humic acids. In addition, less unwanted chlorinated by-products were produced as a result of different ions ratios due to retention of ions by the nanofiltration membranes. Before the full-scale application of the studied treatment train for cooling tower water treatment, it is recommended to identify strategies to improve the water recovery, to include innovative new nanofiltration membranes that can make the use of reverse osmosis redundant and to adopt new insights in preventing unwanted by-product formation during electrochemical oxidation.

Electrochemical oxidation is an effective technique for treating persistent organic pollutants, which are hardly removed in conventional wastewater treatment plants. Sulfate and chloride salts commonly used and present in natural wastewater influence the electrochemical degradation process. In this study, the effect of electrolyte composition on the active sulfate species (SO4●⁻ and S2O82⁻) formation, benzotriazole degradation-a model organic compound, and chlorinated by-products distribution have been investigated while using a boron-doped diamond (BDD) anode. Different Na2SO4:NaNO3 and Na2SO4:NaCl ratios with constant conductivity of 10 mS/cm were used in the experiments and applied anode potential was kept constant at 4.3 V vs. Ag/AgCl. The electrogenerated SO4●⁻ and S2O82⁻ formation were faster in 10:1 and 2:1 Na2SO4:NaNO3 ratios than in the 1:0 ratio. The ●OH-mediated SO4●⁻ production has prevailed in 10:1 and 2:1 ratios. However, ●OH-mediated SO4●⁻ production has hindered the 1:0 ratio due to excess chemisorption of SO42⁻ on the BDD anode. Similarly, the faster benzotriazole degradation, mineralization, and lowest energy consumption were achieved in the 10:1 Na2SO4:NaNO3 and Na2SO4:NaCl ratio. Besides, chlorinated organic by-product concentration (AOX) was lower in the 10:1 Na2SO4:NaCl ratio but increased with the increasing chloride ratio in the electrolyte. LC-MS analysis shows that several chlorinated organic transformation products were produced in 0:1 to 2:1 ratio, which was not found in the 10:1 Na2SO4:NaCl ratio. A comparatively higher amount of ClO4⁻ was formed in the 10:1 ratio than in 2:1 to 0:1 ratio. This ClO4⁻ formation train evidence the effective ●OH generation in a sulfate-enriched condition because the ClO4⁻ formation is positively correlated to ●OH concentration. Overall results show that sulfate-enriched electrolyte compositions are beneficial for electrochemical oxidation of biorecalcitrant organic pollutants.

One of the major challenges in reusing cooling tower blowdown water (CTBD) utilizing membrane processes is its remaining organic compounds, e.g., humic substances leading to biofouling. Besides, the possible abundance of chloride in CTBD imposes the concern of the formation of chlorinated by-products. To choose a pre-treatment process for the studied CTBD composition, various advanced oxidation processes (AOPs), including electrooxidation (EO), photocatalytic degradation (PCD), heat-activated persulfate oxidation (PS), UVC/vacuum UV (UVC/VUV), and UVC processes, were evaluated and compared based on two main targets: i) highest removal and mineralization of the organics, especially humic substances; and ii) lowest formation of chlorinated by-products including adsorbable organic halides and oxychlorides. All the processes were conducted in the natural condition of the real CTBD, while solution pH was monitored. Based on results of chemical oxygen demand, total organic carbon, dissolved organic carbon, UV254 absorbance, liquid-chromatography–organic carbon detection (LC-OCD), and fluorescence excitation-emission matrices (FEEM), it is concluded that PS leads to complete removal of organic compounds along with the lowest formation of low molecular weight organic acids and organic neutrals. FEEM and LC-OCD data also indicated that EO, PCD, and UVC/VUV processes brought about substantial removal of organic compounds and broke down the humic substances into low molecular weight building blocks and organics. Besides, EO exhibited the highest AOX and oxychlorides formation, while these were limited when using the other AOPs. Summarizing, PS, PCD, and UVC/VUV were efficient processes for the degradation and mineralization of organics without generating significant amounts of chlorinated by-products.

Hypothesis Microbial extracellular polymeric substances (EPS) produced from wastewater are generally heterodispersed, which is expected to influence their flocculation performances and mechanism, particularly in mixed particle systems. The different molecular weight (MW) fractions should contribute to the overall adsorption affinity and flocculation mechanism of EPS in single and dual clay systems. Experiments EPS harvested from bioreactors were size-fractionated into high, medium and low MW fractions (HMW, MMW, LMW, respectively). The harvested mixed EPS and its fractions were characterised by diverse analytical techniques coupled with optical reflectometry to investigate the role of each EPS fraction in the overall flocculation mechanism of EPS in kaolinite and montmorillonite clay systems. Findings In single clay systems, both the harvested mixed EPS and the HMW-EPS fraction showed comparable flocculation performances. However, mixed EPS proved to be more efficient than the HMW-EPS fraction for dual clay flocculation. Site blocking effects were observed in mixed EPS: the LMW and MMW EPS first adsorbed to the surface due to higher diffusivities and faster mass transfer to the interface, while the HMW-EPS were slowly transported but were attached to the surface irreversibly and stronger than the LMW/MMW-EPS. We propose from this, a mixed EPS adsorption mechanism: extended anionic polymer tails in solution, thereby enhancing particle flocculation.

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.

Constructed wetlands could be improved with novel substrata to enhance the removal efficiency of micropollutants from wastewater and reduce the spatial footprint. Use of hydroponic substrata like mineral wool, pumice, wood - and coconut fibre is both novel for wastewater treatment, and potentially suitable, due to their hydraulic compatible texture. Since sorption is a key removal process for pollutants in constructed wetlands, this study investigates sorption to novel substrata by six priority micropollutants, caffeine, carbamazepine, ibuprofen, naproxen, sulfamethoxazole and trimethoprim, with diverse Log Kow and pKa values. We found that higher sorption was positively related to substrata's organic matter content. Organic substrata, namely wood - and coconut fibre, demonstrated higher sorption affinity compared with the inorganic substrata mineral wool and pumice, notably regardless of the micropollutants’ Log Kow. Carbamazepine efficiently and rapidly sorbed onto organic substrata, which is particularly noteworthy considering the recalcitrance of carbamazepine in conventional treatment plants. The sorption isotherms were best described by the Freundlich model rather than Langmuir or linear models. We determined that using wood fibre in constructed wetlands would require around 35–66% less area to remove the selected micropollutants, compared to soil as matrix. Thus our results show the potential of using hydroponic substrata such as wood - and coconut fibre to both remove micropollutants in, and reduce the footprint of constructed wetlands.

Hypothesis Cation exchange membranes (CEMs) are subject to fouling when utilized to desalinate wastewater from the oil and gas industry, hampering their performance. The kind and extent of the fouling are most likely dependent on the composition of the stream, which in practical applications can vary significantly. Experiments Fouling experiments were performed on commercial cation exchange membranes, which were used in electrodialysis runs to desalinate solutions of varying composition. The variations included ionic strength, type of ions, amount of viscosifying polyelectrolyte (partially hydrolyzed polyacrylamide), presence of crude oil, and surfactants. Performance parameters, like electric potential and pH, were monitored during the runs, after which the membranes were recovered and analyzed. Findings Fouling was detected on most CEMs and occurred mainly in the presence of the viscosifying polyelectrolyte. Under normal pH conditions (pH ~ 8), the polyelectrolyte fouled the concentrate side of the CEMs, as expected due to electrophoresis. However, by applying a current in the opposite direction, the polyelectrolyte layer could be removed. Precipitation occurred mostly on the opposite side of the membrane, with different morphology depending on the feed composition.

Anaerobic digestion is an attractive treatment technology for concentrated waste streams. However, high ammonia concentrations cause inhibition of methanogenesis, especially when operated at elevated temperatures like (hyper-)thermophilic (55 and 70 °C) anaerobic digestion. These emerging (hyper-)thermophilic technologies are beneficial due to high conversion rates and pathogen removal, but are more susceptible for ammonia toxicity as consequence of a temperature-induced pKa shift. Determination of NH3-N (free ammonia nitrogen (FAN); toxic form) concentrations is conventionally based on an equilibrium model and the total ammonia nitrogen concentration (TAN). However, the conventional equilibrium model overestimates the FAN concentration and therefore we developed an Ionic Activity Model which takes the ionic strength and organic matter interactions into account. The difference between the two models could mainly be attributed to the high ionic strength of the waste stream, whereas interactions with organic matter had a smaller effect. Based on this Ionic Activity Model and batch experiments at hyper-thermophilic conditions, we found that acetoclastic methanogenesis was completely inhibited at FAN concentrations exceeding 588 mg/L, whereas hydrogenotrophic methanogenesis could produce methane up to 925 mg/L. During thermophilic and hyper-thermophilic black water treatment, the ionic strength and organic matter interactions resulted in NH3 concentrations below the inhibitory threshold.

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 TiO2 nanotube array (TNA) is a promising photocatalyst for removal of micropollutants from water, but better understanding on its applicability in complex water matrices is still desired. Therefore this study investigates the effect of dissolved natural organic matter (NOMs) on 4-chloro-2-methylphenoxyacetic acid (MCPA, a typical micropollutant found in many water bodies) removal performance of TNA. The present study shows that although in bulk liquid phase NOMs would undergo photosensitization that can contribute to MCPA removal, the overall effect of NOMs on MCPA removal is detrimental due to the interaction between NOMs and the TNA surface: the total removal of MCPA decreased from 94.3% to 62.0% and 61.8%, in the presence of only 5 mg/L SWR-NOM and UMR-NOM respectively. Acidic pH was found to be able to mitigate the detrimental effect of NOMs (the total removal of MCPA was only decreased from 94.5% to 83.3% and 88.8% under acidic pH, in the presence of 15 mg/L SWR-NOM and UMR-NOM respectively), and the photosensitization effect of NOMs was strengthened; while under alkaline pH conditions the detrimental effect of NOMs completely vanished (the total removal of MCPA increased from 45.7% to 55.7% and 60.5% in the presence of 15 mg/L SWR-NOM and UMR-NOM respectively). Two commonly present co-existing anions, i.e. phosphate and bicarbonate, also mitigate the detrimental effect of NOMs. With 15 mg/L SWR-NOM: the presence of 100 mg/L bicarbonate increased the total removal of MCPA from 49.1% to 65.1%; the presence of 100 mg/L phosphate increased the total removal of MCPA from 49.1% to 62.5%. With 15 mg/L SWR-NOM, the presence of 100 mg/L bicarbonate increased the total removal of MCPA from 45.2% to 56.1%; the presence of 100 mg/L phosphate increased the total removal of MCPA from 45.2% to 62.9%. The photocurrent measurement support that the presence of such anions greatly suppresses the h + scavenging effect of NOMs; while other anions, i.e. chloride, nitrate, sulfate, showed no notable effect.

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.

Research on employing advanced oxidation processes (AOPs) for pharmaceuticals removal is gaining interests. However, detrimental effects of background water constituents in complex water matrices are limiting their implementation. In this study, we report red light induced methylene blue photosensitization (MB/Red-light) as a promising alternative for pharmaceuticals removal from wastewater, because of its potential to overcome detrimental effects of background water constituents as experienced in other AOP technologies. In this study, the efficacy of MB/Red-light on degradation of four pharmaceutical compounds, i.e. diclofenac (DFN), metoprolol (MTP), propranolol (PRP) and sulfamethoxazole (SFZ), was investigated. The MB/Red-light photosensitization enabled degradation of three model compounds, i.e. DFN, PRP and SFZ. Degradation rates followed the order of DFN ＞ PRP ＞ SFZ. Singlet oxygen was found to be crucial in pharmaceuticals degradation, and another additional mechanism, i.e. a direct reaction with triplet MB, also contributed to DFN degradation. The presence of two DFN degradation mechanisms were confirmed by UV–vis light absorbance spectra measurement as well as the identification of degradation products by LC–MS/MS. Effects of three common back ground water constituents were examined to assess the applicability of MB/red-light system in complex water matrices, which suggests that the MB/red-light system has great potential to be used in real wastewater. Higher pH was found to impose positive impact on the efficacy of the proposed system. Last but not least, red light LED is an optimum light source for the proposed MB/Red-light system, because the light emission spectrum of the LED used in this study fits well with the light absorption spectrum of the photosensitizer-methylene blue.

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.

Concentration polarization and fouling hamper the desalination of polymer-flooding produced water (PFPW) via electrodialysis (ED). This water is an abundant by-product from the oil and gas industry. A common technique to mitigate both problems is the application of pulsed electric field (PEF), which consists in supplying a constant current during a short time (pulse) followed by a time without current (pause). Accordingly, this work evaluated the application of PEF during the ED of PFPW to improve the process performance and to reduce fouling incidences. The experimental work consisted in performing ED batch runs in a laboratory-scale stack containing commercial ion exchange membranes. Synthetic PFPW was desalinated under different operating regimes until a fixed number of charges were passed. After each experiment, a membrane pair was recovered from the stack and analyzed through diverse techniques. The application of PEF improved the ED performance in terms of demineralization percentage and energy consumption, the latter having reductions of 36% compared to the continuous mode. In general, the shorter the pulses, the higher the demineralization rate and the lower the energy consumption. Regarding the application of different pause lengths, longer pauses yielded lower energy consumptions, but also lower demineralization. Amorphous precipitates composed of polymer and calcium fouled most on the anion and cation exchange membranes, independently of the applied current regime, but in a moderate amount. Finally, the present study relates the observed effects of PEF application to the electrophoresis and diffusion of HPAM, and shows that PEF is a sound option to enhance the desalination of PFPW.

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.

Ferric based coprecipitation–low pressure membrane filtration is a promising arsenic (As) removal method, however, membrane fouling mechanisms are not fully understood. In this study we investigated the effect of feed water composition and membrane pore size on arsenate [As(V)] removal and membrane fouling. We observed that As removal efficiency was independent of the membrane pore size because the size of the Fe(III) particles was larger than the pore size of the membranes, attributed to a high calcium concentration in the feed water. Arsenic coprecipitation with Fe(III) (oxyhydr)oxides rapidly reached equilibrium before membrane filtration, within 1 min. Therefore, As removal efficiency was not improved by increasing residence time before membrane filtration. The removal of As(V) was strongly dependent on feed water composition. A higher Fe(III) dose was required to reduce As(V) to sub-µg/L levels for feed water containing higher concentration of oxyanions such as phosphate and silicate, and lower concentration of cations such as calcium. Cake-layer formation was observed to be the predominant membrane fouling mechanism.

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.

Desalination is known to have considerable energy, economic, and environmental impacts. Treatment trains are receiving increased interest for their potential to meet produced water standards while both minimizing impacts and increasing the range of eligible input salinities. However, determining which technologies to combine and predicting their performance is both difficult and case specific. This research will present a unique hybrid-modelling framework (DESALT) for evaluating and comparing desalination treatment trains based on the same customizable inputs. This comprehensive discrete-based approach generates treatment trains and then systematically evaluates them using physics-based evaluation methods that are reflective of changes in operating conditions. DESALT also accounts for technology limitations, product water requirements, and user preferences. The modelling outputs are filtered using a combination of a Pareto front analyses and DEA decision support. The result is a list of eligible and preferred treatment trains with their corresponding operating conditions. The framework's performance was tested by applying two different technologies (electrodialysis and brackish water reverse osmosis) to a brackish water case study. While the methodology was able to capture the trade-offs between treatment trains and individual technologies, the results are highly reliant on the accuracy of the evaluation methods used.

This study examines the effect of mixing on the performance of anaerobic digestion of cow manure in Chinese dome digesters (CDDs) at ambient temperatures (27−32 °C) in comparison with impeller mixed digesters (STRs) and unmixed digesters (UMDs) at the laboratory scale. The CDD is a type of household digester used in rural and pre-urban areas of developing countries for cooking. They are mixed by hydraulic variation during gas production and gas use. Six digesters (two of each type) were operated at two different influent total solids (TS) concentration, at a hydraulic retention time (HRT) of 30 days for 319 days. The STRs were mixed at 55 rpm, 10 min/hour; the unmixed digesters were not mixed, and the Chinese dome digesters were mixed once a day releasing the stored biogas under pressure. The reactors exhibited different specific biogas production and treatment efficiencies at steady state conditions. The STR 1 exhibited the highest methane (CH4) production and treatment efficiency (volatile solid (VS) reduction), followed by STR 2. The CDDs performed better (10% more methane) than the UMDs, but less (approx. 8%) compared to STRs. The mixing regime via hydraulic variation in the CDD was limited despite a higher volumetric biogas rate and therefore requires optimization.

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 presence of multivalent ions in polymer-flooding produced water (PFPW) hampers its recycling mainly because i) they increase the risk of scaling and reservoir souring (sulfate), ii) they interfere with the viscosifying effect of the fresh polyelectrolyte. It is desirable to achieve the removal of most multivalent ions without completely desalting the stream. With the adequate process conditions, electrodialysis could help to achieve this goal, so this work focused on evaluating the removal of divalent ions from synthetic PFPW through varying operational conditions. The experimental work consisted on batch experiments run in an electrodialysis-stack composed of strong Neosepta ion-exchange membranes. Synthetic PFPW solutions containing a mixture of monovalent and divalent ions were desalted at four different current densities, and three different temperatures. Additionally, the effect of the dissolved polymer on the removal was assessed by performing half of the experiments on polymer-containing solutions and half of them on solutions without it. Our results demonstrate that it is possible to achieve preferential removal of divalent cations (calcium and magnesium) through electrodialysis, especially when employing low current densities (24 A/m2) and high temperature (40 °C). The removal of sulfate, a divalent anion, is also accelerated in these conditions. The presence of polyelectrolyte did not significantly affect the removal rate of divalent ions. Thus, it is concluded that meticulous application of ED to minimize concentrations of divalent ions in PFPW is a potential effective way for water and polymer recycling in enhanced oil recovery situations, as an alternative to the use of other non-selective desalination technologies.

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).

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%).

Removal of arsenic (As) from water by co-precipitation with Fe(III) (oxyhydr)oxides is a widely used technique in water treatment. Nevertheless, As removal efficiency appears to be sensitive to the composition of the water matrix. The aim of this study was to gain a deeper understanding of the independent and combined effects of silicate (Si), phosphate (P), natural organic matter (NOM) and calcium (Ca) on arsenate [As(V)] co-precipitation efficiency and the size of Fe(III) precipitates. We found that, in complex solutions, containing multiple solutes and high levels of Ca, (variations in) Si and P concentrations reduce As(V) removal to some extent, mainly due to a decreased adsorption of As(V) onto Fe(III) precipitates. On the other hand, NOM concentrations reduced As(V) removal to a much greater extent, due to possible formation of mobile Fe(III)–NOM complexes that were difficult to remove by filtration. These findings have a great significance for predicting As(V) removal as a function of seasonal and process-related water quality changes at water treatment plants.

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.

Natural flocculants, due to their eco-friendliness, have gained increasing attention for (waste) water treatment and are promising alternatives to oil-based synthetic flocculants. We systematically investigated simultaneous industrial wastewater treatment with the production of microbial extracellular polymeric substances (EPS) as natural flocculants. EPS were produced in two membrane bioreactors, respectively treating fresh and saline synthetic wastewater from biodiesel and (bio)ethanol industries. From each reactor, soluble and bound EPS fractions were extracted, purified and characterised for their functionalities, molecular weights and charge densities using Fourier transform infrared (FTIR), size exclusion chromatography and colloid titration, respectively. High removal of chemical oxygen demand (COD) was achieved in both reactors (93–95%), with 5.8–7.6% of the inlet COD recovered as EPS. FTIR spectroscopy reveals these EPS as a mixture of proteins and polysaccharides, possessing carboxyl, hydroxyl and amine groups. These functional groups, which provided a net anionic charge density (1.5–2.9 meq/g at neutral pH), coupled with EPS mixed molecular weight (MW) distribution: high (> 1000 kDa), medium (1000–100 kDa) and low (< 100 kDa) MW fractions, make them promising flocculants. Extracted EPS showed good flocculation of non-saline kaolin suspension (74–89% turbidity reduction) and excellent flocculation of saline kaolin suspension (88–97%), performances comparable to anionic polyacrylamide. The results show the possibility for wastewater treatment plants to combine wastewater treatment with the production of valuable flocculants.

The aim of this study was to evaluate the use of self-organized TiO2 nanotube arrays (TNAs) as immobilized catalyst and UV-LED as light source (UV-LED/TNAs) for photocatalytic degradation of the β-blocker metoprolol (MTP) from aqueous solution. Firstly we employed electrochemical anodization to synthesize self-organized TNAs, and the effect of anodization potential and annealing temperature was examined. Characterization by SEM demonstrated a linear relation between the diameter of TiO2 nanotubes produced and the anodization potential, while Raman measurement revealed the vital role of annealing on crystallographic composition of the anodic produced TiO2 nanotubes. Regarding their performance in photocatalytic MTP degradation, surface morphology and crystallographic composition of the TNAs were found to impose crucial influence: only TNAs with diameter not smaller than 53 nm enabled rapid MTP degradation, and highest MTP degradation was obtained when a mixture of anatase and rutile were present in the TNAs. Secondly, the effect of operational parameters, i.e initial MTP concentration, pH, was investigated. Initial MTP concentration at low level had no detrimental effect on the process performance. Rapid MTP degradation and high total removal were achieved in a wide pH range (3–11). To evaluate the applicability of TNAs for water treatment, experiments were first carried out in the presence of three different commonly present water constituents, i.e bicarbonate ions, phosphate ions, and natural organic matters (NOMs). The results show that bicarbonate and phosphate ions have no inhibitory effect at concentration levels up to 200 mg/L, and NOMs exhibit detrimental effect when their concentration exceeds 5 mg/L. The total removal MTP degradation reduced from 87.09 ± 0.09% to 62.05 ± 0.08% when tap water samples were applied, demonstrating reasonable efficacy for practical applications. Regarding the degradation mechanism, formic acid and tert-butanol were added as scavenger for photo-generated holes (h+) and hydroxyl radicals (·OH), respectively. The obtained results demonstrate that primary degradation process occurred in liquid phase with participation of hydroxyl radicals in the liquid phase (·OH liquid), while smaller portion of MTP were degraded on the catalysis surface via reaction with h+ and hydroxyl radicals adsorbed on the catalyst surface (·OH surface). Other reactive species, e.g photo generated electrons and superoxide radical anions, did also play a minor role in MTP degradation. The mechanistic aspect was further confirmed by identification of degradation products by LC–MS/MS. The TNAs exhibited good stability after repeated use under varied operation conditions.

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

This study evaluated the application of a membrane-free photocatalytic fuel cell composed of a TiO2 nanotube array photoanode and a Cu cathode, i.e. TNA-Cu PFC system, for micropollutant removal from water. Significantly enhanced removal of a commonly present aqueous micropollutant 4-chloro-2-methylphenoxyacetic acid (MCPA) was obtained in this TNA-Cu PFC system: the TNA-Cu PFC system achieved better MCPA degradation compared to the conventional photocatalytic method using the same catalyst. In the TNA-Cu PFC system, the MCPA degradation was largely promoted under acidic conditions, indicating this as an important operational condition. The enhancement of MCPA degradation in the TNA-Cu PFC system involved better e−/h+ separation and generation of other oxidants: in conventional photocatalytic process, hydroxyl radicals in liquid phase contributed to 93.7% MCPA degradation while only 2.4% MCPA degradation was mediated by other oxidants like [rad]O2 −, H2O2, [rad]HO2; for MCPA degradation in the TNA-Cu PFC system, the contribution of hydroxyl radicals in the liquid phase decreased to 83.6%, while contribution of other oxidants like [rad]O2 −, H2O2, [rad]HO2 increased to 15.3%. This change in MCPA degradation mechanisms was confirmed via degradation intermediates analysis by LC-MS/MS. The study on the effect of electrolyte concentration suggests that when operated under acidic conditions, addition of electrolyte is not required. The TNA-Cu PFC system was shown to work well in the presence of up to 15 mg/L natural organic matter (originating from two large rivers), high amounts of common inorganic ions, and even in WWTP effluent. The TNA-Cu PFC system also exhibited relatively good stability after several cycles of repeated use. The obtained results demonstrated that this is an adequate system for micropollutant removal from water at various places in the water cycle, i.e. as polisher of WWTP effluents before discharge or for cleaning intake water before producing drinking water.

A method is presented to distribute small scale light sources in a photocatalytic slurry reactor. The goal of distributing the light sources is to increase photon transfer efficiency, and thereby increasing the reaction rate, compared to using one single light source. The light sources used in this study were ultraviolet light emitting diodes with a wavelength of 375 nm. An up-flow of air into the photocatalytic reactor distributes the UV-LEDs throughout the reactor, mixes the reaction solution and saturates the solution with molecular oxygen. To make distribution of the UV-LEDs possible, the UV-LEDs were powered wirelessly by resonant inductive coupling. This article shows that UV-LEDs distributed throughout the reactor show a 30% higher removal rate of methylene blue compared to the UV-LEDs concentrated on one plane in the reactor. The removal rate increased linearly with increasing numbers of UV-LEDs. The size of the UV-LEDs determined that up to 32 UV-LEDs could be wirelessly powered in a reactor volume of 500 ml. To increase the reactivity, a higher amount of UV-LEDs per reaction liquid volume and higher radiant power of the UV-LED can be used, bringing use of photocatalytic reactors closer to industrial applications.

Granular activated carbon (GAC) is used in water treatment systems, typically to remove pollutants such as natural organic matter, volatile organic compounds, chlorine, taste, and odor. GAC is also used as a key component of a new technology that combines a fluidized bed reactor with radio frequency electric fields for disinfection. So far, the effects of GAC on bacteria in these fluidized bed reactors are unclear. This paper describes a systematic study of the physico-chemical changes in five microbial media compositions caused by different concentrations (23–350?g/L) of GAC, and the effects of these physico-chemical changes on the metabolic activity and survival of a model microorganism (Escherichia coli YMc10) in a fluidized bed reactor. The chemical adsorption taking place in suspensions with specific GAC changed nutritional, osmotic, and pH conditions in the investigated microbial media (LB, diluted LB, PBS, diluted PBS, and tap water), leading to a decay of the metabolic activity and survival of E. coli. Especially media that are poor in organic and mineral compounds (e.g., PBS) with suspended GAC showed a concentration decay of 3.5?Log CFU/mL E. coli after 6?h. Organic compounds depletion and severe pH variation were enhanced in the presence of higher GAC concentrations. Biotechnol. Bioeng. 2014;111: 2009–2018.

Properties of water-filled inductors are relevant for underwater wireless energy transfer. The influence of the relative permittivity and resistivity of the core material on the impedance of an inductor can be modeled with a lumped parameter circuit. The relative permittivity of the core material has influence on the turn-to-core capacitance of the inductor. The resistivity of the core material has a linear relation with the resistance of the turn-to-turn capacitance. With this model, the influence of the conductivity on the quality factor of an inductor can be predicted. This is a helpful tool to find the optimal frequency at which the quality factor is maximum.

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.

Household or domestic biogas plants constitute a growing sub-sector of the anaerobic digestion industry worldwide, but had received low research attention for improvements. The Chinese dome digester (CDD), a major type of domestic biogas plant, is a naturally mixed, unheated and low tech system that is mainly used in rural areas. In this study, a multiphase computational fluid dynamics (CFD) model was applied to evaluate and subsequently improve mixing in a lab scale Chinese dome digester. The normal Chinese dome digester (CDD1) and two baffle configurations were investigated to improve the hydraulic mixing in the digester (CDD2 and CDD3 respectively) . 2-D time dependent numerical simulations were done with the three-phase, phase field model in COMSOL Multiphysics in a CDD geometry. Residence time distribution (RTD) curves were derived for all the configurations to evaluate and compare performances. In addition, three hydraulic indicators were also studied to evaluate mixing improvement. The Anaerobic digestion model No. 1 (ADM1) was used to evaluate biogas production. The effects of the addition of baffles to the CDDs did not significantly improve mixing, however about 16 % of dead zones was reduced in the two-baffle configuration.

The methylene blue photosensitization under red light irradiation (MB/Red-light) is a promising and powerful tool for removal of pharmaceuticals from wastewater. To further develop this new technology, the present work aimed at studying the effect of operational parameters on the performance of MB/Red-light pharmaceuticals removal processes. Three pharmaceuticals, i.e. diclofenac (DFN), propranolol (PRP), and sulfamethoxazole (SFZ), were used as model compounds, and degradation rate constants and total compound removal were examined. The three operational parameters studied were initial MB concentration (0–5.0 mg/L), initial pharmaceutical concentration (0.1–2.0 mg/L), aeration rate (0–5.0 L/min), and for DFN also the pH. The results show that degradation of pharmaceuticals was promoted with increasing initial MB concentration at values of [MB] below 0.5 mg/L, and leveled off to constant values at [MB] values higher than 2.0 mg/L. Initial pharmaceutical concentration and aeration rate were found to have no significant impact. Moreover, rapid degradation of pharmaceuticals can take place even at low initial dissolved oxygen concentrations (2.0 mg/L, i.e. situations without aeration). In order to better understand the effect of pH on the MB/Red-light pharmaceutical degradation processes, DFN was chosen for more detailed investigation, with identification of the degradation products formed under neutral and alkaline conditions identified by LC–MS/MS. The pH was found to play an important role on the transformation pathways and formation of degradation products.

Anaerobic methanethiol (MT) degradation by mesophilic (30 degrees C) alkaliphilic (pH 10) communities was studied in a lab-scale Upflow Anaerobic Sludge Bed (UASB) reactor inoculated with a mixture of sediments from the Wadden Sea (The Netherlands), Soap Lake (Central Washington), and Russian soda lakes. MT degradation started after 32 days of incubation. During the first 252 days, complete degradation was achieved till a volumetric loading rate of 7.5 mmol MT/L/day, and sulfide, methane, and carbon dioxide were the main reaction products. Temporary inhibition of MT degradation occurred after MT peak loads and in the presence of dimethyl disulfide (DMDS), which is the autooxidation product of MT. From day 252 onwards, methanol was dosed to the reactor as co-substrate at a loading rate of 3-6 mmol/L/day to stimulate growth of methylotrophic methanogens. Methanol was completely degraded and also a complete MT degradation was achieved till a volumetric loading rate of 13 mmol MT/L/day (0.77 mmol MT/gVSS/day). However, from day 354 till the end of the experimental run (day 365), acetate was formed and MT was not completely degraded anymore, indicating that methanol-degrading homoacetogenic bacteria had partially outcompeted the methanogenic MT-degrading archea. The archeal community in the reactor sludge was analyzed by DGGE and sequencing of 16S rRNA genes. The methanogenic archea responsible for the degradation of MT in the reactor were related to Methanolobus oregonensis. A pure culture, named strain SODA, was obtained by serial dilutions in medium containing both trimethyl amine and dimethyl sulfide (DMS). Strain SODA degraded MT, DMS, trimethyl amine, and methanol. Flow sheet simulations revealed that for sufficient MT removal from liquefied petroleum gas, the extraction and biological degradation process should be operated above pH 9.

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.