Sustainable engineering of sewers and sewage treatment plants for scenarios with urine diversion.

Urine diversion (UD) has been studied for decades as a way to enable distributed sanitation and to recycle nutrients onto land to fuel circular economies. No study to date has attempted a quantitative technical and economic analysis of the downstream effects of UD on sewage transport and treatment. This work used the SeweX model to reveal for the first time that through UD, hydrogen sulfide concentration in sewer headspaces can be reduced, and consequently sewer corrosion can be reduced. For a long rising main of 5 km, sewer headspace H2S can be reduced from 280 ppm to 200 ppm by diverting 75% of the urine. The same scenario enables the reduction of sewer corrosion from 12 to 10 mm/yr. Modeling sewage treatment plants with BioWin showed that sewage treatment responds to UD with a sharp reduction of the anoxic volume and a decrease of energy requirement by up to 50% at 75% UD. An upgrade of bioreactors to increase capacity by 20% can be completely avoided if 7% of the catchment's urine is diverted. Reductions in upgrade expenditure by up to 75% can provide the economic incentive for the uptake of UD.

Performance of titanium salts compared to conventional FeCl3 for the removal of algal organic matter (AOM) in synthetic seawater: Coagulation performance, organic fraction removal and floc characteristics.

During algal bloom periods, operation of seawater reverse osmosis (SWRO) pretreatment processes (e.g. ultrafiltration (UF)) has been hindered due to the high concentration of algal cells and algal organic matter (AOM). The present study evaluated for the first time the performance of titanium salts (i.e. titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC)) for the removal of AOM in seawater and results were compared with the conventional FeCl3 coagulant. Previous studies already demonstrated that titanium salts not only provide a cost-effective alternative to conventional coagulants by producing a valuable by-product but also minimise the environmental impact of sludge production. Results from this study showed that both TiCl4 and PTC achieved better performance than FeCl3 in terms of turbidity, UV254 and dissolved organic carbon (DOC) removal at similar coagulant dose. Liquid chromatography - organic carbon detection (LC-OCD) was used to determine the removal of AOM compounds based on their molecular weight (MW). This investigation revealed that both humic substances and low MW organics were preferentially removed (i.e. up to 93% removal) while all three coagulants showed poorer performance for the removal of high MW biopolymers (i.e. less than 50% removal). The detailed characterization of flocs indicated that both titanium coagulants can grow faster, reach larger size and present a more compact structure, which is highly advantageous for the design of smaller and more compact mixing and sedimentation tanks. Both titanium coagulants also presented a higher ability to withstand shear force, which was related to the higher amount of DOC adsorbed with the aggregated flocs. Finally, TiCl4 had a better recovery after breakage suggesting that charge neutralization may be the dominant mechanism for this coagulant, while the lower recovery of both PTC and FeCl3 indicated that sweep flocculation is also a contributing mechanism for the coagulation of AOM.

Evaluating the mobility of polymer-stabilised zero-valent iron nanoparticles and their potential to co-transport contaminants in intact soil cores.

The use of zero-valent iron nanoparticles (nZVI) has been advocated for the remediation of both soils and groundwater. A key parameter affecting nZVI remediation efficacy is the mobility of the particles as this influences the reaction zone where remediation can occur. However, by engineering nZVI particles with increased stability and mobility we may also inadvertently facilitate nZVI-mediated contaminant transport away from the zone of treatment. Previous nZVI mobility studies have often been limited to model systems as the presence of background Fe makes detection and tracking of nZVI in real systems difficult. We overcame this problem by synthesising Fe-59 radiolabelled nZVI. This enabled us to detect and quantify the leaching of nZVI-derived Fe-59 in intact soil cores, including a soil contaminated by Chromated-Copper-Arsenate. Mobility of a commercially available nZVI was also tested. The results showed limited mobility of both nanomaterials; <1% of the injected mass was eluted from the columns and most of the radiolabelled nZVI remained in the surface soil layers (the primary treatment zone in this contaminated soil). Nevertheless, the observed breakthrough of contaminants and nZVI occurred simultaneously, indicating that although the quantity transported was low in this case, nZVI does have the potential to co-transport contaminants. These results show that direct injection of nZVI into the surface layers of contaminated soils may be a viable remediation option for soils such as this one, in which the mobility of nZVI below the injection/remediation zone was very limited. This Fe-59 experimental approach can be further extended to test nZVI transport in a wider range of contaminated soil types and textures and using different application methods and rates. The resulting database could then be used to develop and validate modelling of nZVI-facilitated contaminant transport on an individual soil basis suitable for site specific risk assessment prior to nZVI remediation.

Analytical characterisation of nanoscale zero-valent iron: A methodological review.

Zero-valent iron nanoparticles (nZVI) have been widely tested as they are showing significant promise for environmental remediation. However, many recent studies have demonstrated that their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Both the mobility and reactivity of nZVI mainly depends on properties such as particle size, surface chemistry and bulk composition. In order to ensure efficient remediation, it is crucial to accurately assess and understand the implications of these properties before deploying these materials into contaminated environments. Many analytical techniques are now available to determine these parameters and this paper provides a critical review of their usefulness and limitations for nZVI characterisation. These analytical techniques include microscopy and light scattering techniques for the determination of particle size, size distribution and aggregation state, and X-ray techniques for the characterisation of surface chemistry and bulk composition. Example characterisation data derived from commercial nZVI materials is used to further illustrate method strengths and limitations. Finally, some important challenges with respect to the characterisation of nZVI in groundwater samples are discussed.

Agglomeration behaviour of titanium dioxide nanoparticles in river waters: A multi-method approach combining light scattering and field-flow fractionation techniques.

Titanium dioxide nanoparticles (TiO2 NPs) are currently one of the most prolifically used nanomaterials, resulting in an increasing likelihood of release to the environment. This is of concern as the potential toxicity of TiO2 NPs has been investigated in several recent studies. Research into their fate and behaviour once entering the environment is urgently needed to support risk assessment and policy development. In this study, we used a multi-method approach combining light scattering and field-flow fractionation techniques to assess both the aggregation behaviour and aggregate structure of TiO2 NPs in different river waters. Results showed that both the aggregate size and surface-adsorbed dissolved organic matter (DOM) were strongly related to the initial DOM concentration of the tested waters (i.e. R(2) > 0.90) suggesting that aggregation of TiO2 NPs is controlled by the presence and concentration of DOM. The conformation of the formed aggregates was also found to be strongly related to the surface-adsorbed DOM (i.e. R(2) > 0.95) with increasing surface-adsorbed DOM leading to more compact structures. Finally, the concentration of TiO2 NPs remaining in the supernatant after sedimentation of the larger aggregates was found to decrease proportionally with both increasing IS and decreasing DOM concentration, resulting in more than 95% sedimentation in the highest IS sample.

Aggregation behaviour of engineered nanoparticles in natural waters: characterising aggregate structure using on-line laser light scattering.

Adsorption of natural organic matter, aggregation and disaggregation have been identified as three of the main processes affecting the fate and behaviour of engineered nanoparticles (ENPs) in aquatic environments. However, although several methods have been developed to study the aggregation behaviour of ENPs in natural waters, there are only a few studies focusing on the fate of such aggregates and their potential disaggregation behaviour. In this study, we proposed and demonstrated a simple method for characterising the aggregation behaviour and aggregate structure of ENPs in different natural waters. Both the aggregate size of ENPs and their adsorption capacity for dissolved organic matter (DOM) were strongly related (R(2)>0.97, p<.05) to the combined effect of initial concentration of dissolved organic matter (DOM) and the ionic strength of the natural waters. The structure of the formed aggregates was strongly correlated (R(2)>0.95, p<.05) to the amount of DOM adsorbed by the ENPs during the aggregation process. Under high ionic strength conditions, aggregation is mainly governed by diffusion and the aggregates formed under these conditions showed the lowest stability and fractal dimension, forming linear, chain-like aggregates. In contrast, under low ionic strength conditions, the aggregate structure was more compact, most likely due to strong chemical binding with DOM and bridging mechanisms involving divalent cations formed during reaction-limited aggregation.

Comparison of a novel polytitanium chloride coagulant with polyaluminium chloride: coagulation performance and floc characteristics.

Polymerized inorganic coagulants are increasingly being used in the water supply and wastewater treatment process, yet there is limited research on the development of polytitanium coagulants. The aim of this study is to synthesize polytitanium chloride (PTC) coagulants and investigate their coagulation behavior and floc characteristics for humic acid removal in comparison to polyaluminum chloride (PAC). The PTC samples with different B (molar ratios of OH/Ti) values were prepared using an instantaneous base-feeding method, employing sodium carbonate as the basification agent. The coagulation efficiency was significantly influenced by different B values. The results suggest that the humic acid removal increased with the increasing B value for PAC, while the inverse trend was observed for PTC. The optimum B value was chosen at 1.0 and 2.0 for PTC and PAC, respectively. Under the optimum coagulant dose and initial solution pH conditions, the PTC coagulant performed better than the PAC coagulant and the floc properties were significantly improved in terms of floc growth rate and floc size. However, the PAC coagulants produced flocs with better floc recoverability than the PTC coagulants.

Stability of Fe-oxide nanoparticles coated with natural organic matter under relevant environmental conditions.

Manufactured nanoparticles (MNPs) are increasingly released into the environment and thus research on their fate and behaviour in complex environmental samples is urgently needed. The fate of MNPs in the aquatic environment will mainly depend on the physico-chemical characteristics of the medium. The presence and concentration of natural organic matter (NOM) will play a significant role on the stability of MNPs by either decreasing or exacerbating the aggregation phenomenon. In this study, we firstly investigated the effect of NOM concentration on the aggregation behaviour of manufactured Fe-oxide nanoparticles. Then, the stability of the coated nanoparticles was assessed under relevant environmental conditions. Flow field-flow fractionation, an emerging method which is gaining popularity in the field of nanotechnology, has been employed and results have been compared to another size-measurement technique to provide increased confidence in the outcomes. Results showed enhanced stability when the nanoparticles are coated with NOM, which was due to electrosteric stabilisation. However, the presence of divalent cations, even at low concentration (i.e. less than 1 mM) was found to induce aggregation of NOM-coated nanoparticles via bridging mechanisms between NOM and Ca(2+).

Forward osmosis for the treatment of reverse osmosis concentrate from water reclamation: process performance and fouling control.

While high quality water reuse based on dual membrane filtration (membrane filtration or ultrafiltration, followed by reverse osmosis) is expected to be progressively applied, treatment and sustainable management of the produced reverse osmosis concentrate (ROC) are still important issues. Forward osmosis (FO) is a promising technology for maximising water recovery and further dewatering ROC so that zero liquid discharge is produced. Elevated concentrations of organic and inorganic compounds may act as potential foulants of the concentrate desalting system, in that they consist of, for example, FO and a subsequent crystallizer. The present study investigated conditions under which the FO system can serve as concentration phase with the focus on its fouling propensity using model foulants and real ROC. Bulk organics from ROC consisted mainly of humic acids (HA) and building blocks since wastewater-derived biopolymers were retained by membrane filtration or ultrafiltration. Organic fouling of the FO system by ROC-derived bulk organics was low. HA was only adsorbed moderately at about 7% of the initial concentration, causing a minor flux decline of about 2-4%. However, scaling was a major impediment to this process if not properly controlled, for instance by pH adjustment or softening.

Removal of natural organic matter by titanium tetrachloride: The effect of total hardness and ionic strength.

This study is the first attempt to investigate the effect of total hardness and ionic strength on coagulation performance and the floc characteristics of titanium tetrachloride (TiCl4). Membrane fouling under different total hardness and ionic strength conditions was also evaluated during a coagulation-ultrafiltration (C-UF) hybrid process. Coagulation experiments were performed with two simulated waters, using humic acid (HA, high molecular weight) and fulvic acid (FA, relatively low molecular weight), respectively, as model natural organic matter (NOM). Results show that both particle and organic matter removal can be enhanced by increasing total hardness and ionic strength. Floc characteristics were significantly influenced by total hardness and ionic strength and were improved in terms of floc size, growth rate, strength, recoverability and compactness. The results of the UF tests show that the pre-coagulation with TiCl4 significantly improves the membrane permeate fluxes. Under different total hardness and ionic strength conditions, the membrane permeate flux varied according to both NOM and floc characteristics. The increase in total hardness and ionic strength improved the membrane permeate flux in the case of HA simulated water treatment.

Preparation and characterization of novel polytitanium tetrachloride coagulant for water purification.

Polymeric metal coagulants are increasingly being used to improve coagulation efficiency, yet the research on the development of titanium and particularly polytitanium salts remains limited. This study is the first attempt in the synthesis, characterization, and application of polytitanium salts as coagulants. Polytitanium tetrachloride (PTC) solutions with different basicity values B (OH/Ti molar ratio) were prepared using a slow alkaline titration method. Jar tests were conducted to assess coagulation performance using both synthetic and real raw water samples, and the floc characteristics were monitored online using a laser diffraction particle size analyzer. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) was utilized to identify various Ti species, with the results providing strong evidence of the presence of various hydrolyzed Ti species in the titanium aqueous phase. Compared to titanium tetrachloride (TiCl4), higher or comparable turbidity and organic matter removal efficiency could be achieved by PTC with improved floc characteristics in terms of size, growth rate, and structure. Besides, the water pH after PTC coagulation was significantly improved toward neutral pH. This study indicates that PTC is an effective and promising coagulant for water purification. Besides, the PTC flocculated sludge was able to recycle and produce functional TiO2 photocatalyst.

Cationic polyacrylamide as coagulant aid with titanium tetrachloride for low molecule organic matter removal.

This is the first attempt to use cationic polyacrylamide (PAM) as coagulant aid with titanium tetrachloride (TiCl4) to improve the coagulation performance and floc properties. Coagulation-flocculation treatment was applied to simulated water (with fulvic acid (FA) as model organic matter) for both coagulation behavior investigation and floc characterization. The effect of PAM on floc reformation properties after cyclic breakage/regrowth was also investigated. Ultrafiltration experiments were performed to investigate the influence of PAM aided TiCl4 coagulation on the membrane fouling. The results showed that organic removal was enhanced by PAM addition at low TiCl4 doses. Floc growth rate and floc size were significantly affected by dosing sequence. TiCl4-PAM significantly improved the floc strength factors (Sf) and recovery factors (Rf). The dosing sequence of TiCl4 and PAM significantly influenced the floc structure. Characterization of the flocculated sludge indicated that TiO2 with anatase structure and high photocatalytic activity could be obtained from the TiCl4-PAM flocculated sludge.

How to optimize hollow-fiber submerged membrane bioreactors.

Membrane fouling is linked to reversible or irreversible accumulation of macromolecules and solids on membrane surfaces and to the irreversible adsorption inside pores. If reversible accumulation can be controlled by filtering in subcritical conditions, then adsorption could also be minimized by reducing the soluble organic matter [extracellular polymeric substances, soluble microbial products (SMP)]. This research shows how the choice of operating parameters related to biological reaction (solid retention time and the organic loading rate) can influence the process rate and the by-product (SMP) production. It also illustrates how suspension characteristics and membrane aeration can influence membrane fouling control according to the hollow fiber configuration and to the different scales of observation. The investigations were based on the definition of different fouling level and fine-tuning of a model to better understand the effects of operating parameters on membrane bioreactor filtration.

Anionic polymer compound bioflocculant as a coagulant aid with aluminum sulfate and titanium tetrachloride.

The objectives of this study are to investigate the impacts of anionic polymer compound bioflocculant (CBF) as a coagulant aid on coagulation performance and floc characteristics with titanium tetrachloride (TiCl(4)) and aluminum sulfate (Al(2)(SO(4))(3)). The effect of dosing sequence was also investigated. Floc size, breakage, regrowth and floc fractal dimension were examined using a laser diffraction instrument. The results showed that CBF with TiCl(4) or Al(2)(SO(4))(3) coagulants exhibited synergistic effects by promoting dissolved organic carbon (DOC) removal. For both TiCl(4) and Al(2)(SO(4))(3), the floc recoverability was improved by CBF addition, and the flocs formed by TiCl(4) and the corresponding dual-coagulants showed weaker recovery ability than those by Al(2)(SO(4))(3) and the corresponding dual-coagulants. Fractal dimension analysis demonstrated that the floc fractal dimension values increased with the increasing coagulant dose. The effect of CBF on fractal dimension of the flocs generated by TiCl(4) was different from that of Al(2)(SO(4))(3).

The effect of second coagulant dose on the regrowth of flocs formed by charge neutralization and sweep coagulation using titanium tetrachloride (TiCl4).

Characteristics of flocs formed by charge neutralization and sweep coagulation using titanium tetrachloride (TiCl(4)) were investigated with humic acid-kaolin suspension by continuous optical monitoring. This paper focused on the regrowth ability of broken flocs after addition of second TiCl(4) dose. Variation of floc size and the fractal dimension of flocs versus second TiCl(4) dose after regrowth were investigated. Second TiCl(4) dose was added during the floc breakage period, and addition time of second TiCl(4) dose was also investigated. The results showed that, when coagulated by charge neutralization at pH 6, an appropriate second TiCl(4) dose improved regrowth ability of broken flocs at low initial TiCl(4) doses. While for high initial TiCl(4) doses, second TiCl(4) dose lowered floc re-growth ability. When coagulated by sweep coagulation at pH 10, second TiCl(4) dose made regrown flocs larger than those without second TiCl(4) dose. Floc structure analysis showed that it was determined by not only the fractal dimension of flocs, but also the chemical characteristics of floc surface. Addition time of second TiCl(4) dose had a great effect on floc regrowth ability, suggesting that the broken flocs had better regrowth when second TiCl(4) dose was added at the end of the breakage period.

Preparation and characterisation of TiO2 nanoparticle and titanate nanotube obtained from Ti-salt flocculated sludge with drinking water and seawater.

This study aimed to prepare and characterise titanium dioxide (TiO2) nanoparticles and titanate nanotubes produced from Ti-sat flocculated sludge with drinking water (DW) and seawater (SW). The Ti-salt flocculated sludge from DW and SW was incinerated at 600 degrees C to produce TiO2 nanoparticles. XRD results showed that the anatase TiO2 structure was predominant for TiO2 from DW (TiO2-DW) and TiO2 from SW (TiO2-SW), which were mainly doped with carbon atoms. Titanate nanotubes (tiNT) were obtained when TiO2-DW and TiO2-SW were hydrothermally treated with NaOH solution. Structure phase, shape, crystallisation and photocatalytic activity of tiNT were affected by the incineration temperature and the amount of sodium present in different tiNT. The tiNT doped with thiourea incinerated at 600 degrees C presented anatase phase, showing a high increase of the degree of crystallisation with nanotube-like structures. The photocatalytic activity of these photocatalysts was evaluated using photooxidation of gaseous acetaldehyde. Thiourea doped tiNT-DW and tiNT-SW showed similar photocatalytic activity compared to commercially available TiO2-P25 under UV light and indicated a photocatalytic activity under visible light.

Effect of shear force, solution pH and breakage period on characteristics of flocs formed by Titanium tetrachloride (TiCl4) and Polyaluminum chloride (PACl) with surface water treatment.

The growth, breakage and regrowth nature of flocs formed by Titanium tetrachloride (TiCl(4)) and polyaluminum chloride (PACl) was comparatively evaluated with surface water treatment. A series of jar experiments were conducted to investigate the impacts of different operating parameters such as shear force, solution pH and a breakage period on floc strength and re-aggregation potential. Results indicated that the responses of flocs to different operating parameters depend on the coagulant used. The ability of floc to resist breakage decreased with the increase of shear force and breakage period. Floc strength properties were also measured in response to increasing shear force, with the results suggesting that the order of floc strength was TiCl(4)>PACl. Floc regrowth of the two coagulants after exposure to high shear was limited, and flocs formed by TiCl(4) displayed weaker recoverability. The flocs generated in acid conditions were more recoverable than those generated in alkaline conditions no matter which coagulant was used.

Seasonal variation in the properties of titania photocatalysts produced from Ti-salt flocculated bioresource sludge.

Ti-salt flocculation of biologically treated sewage effluent (BTSE) was carried out on monthly basis during one year to trace the seasonal variation in the properties of BTSE, Ti-salt flocculated BTSE and titania photocatalysts. Titania photocatalysts were produced from incineration of Ti-salt flocculated sludge at 600°C. The physio-chemical properties of BTSE, Ti-salt flocculated BTSE and titania photocatalysts were investigated. The photocatalytic activity of titania was examined using different substrates of rhodamine B and humic acid under UV light irradiation. Results indicated that the flocculation performance of Ti-salt was not affected by the seasonal variation of BTSE. BTSE characteristics resulted in marginal effect in titania characterisation and photocatalytic activity. Titania photocatalysts produced from Ti-salt flocculated sludge in different seasons showed constant anatase phase, high BET surface area and high photocatalytic activity.

Coagulation characteristics of titanium (Ti) salt coagulant compared with aluminum (Al) and iron (Fe) salts.

In this study, the performance of titanium tetrachloride (TiCl(4)) coagulation and flocculation is compared with commonly used coagulants such as aluminum sulfate (Al(2)(SO(4))(3)), polyaluminum chloride (PACl), iron chloride (FeCl(3)), and polyferric sulfate (PFS) in terms of water quality parameters and floc properties. TiCl(4) flocculation achieved higher removal of UV(254) (98%), dissolved organic carbon (DOC) (84%) and turbidity (93%) than other conventional coagulants. Charge neutralization and physical entrapment of colloids within coagulant precipitates and adsorption, seemed to play a significant role during TiCl(4) flocculation, while the main mechanism for conventional coagulants was bridge-aggregation and adsorption. The aggregated flocs after TiCl(4) flocculation showed the fastest growth rate compared to the other coagulants, with the largest floc size (801 µm) occurring within 8 min. The floc strength factor of PACl, Al(2)(SO(4))(3), PFS, FeCl(3) and TiCl(4) was 34, 30, 29, 26 and 29, respectively, while the floc recovery factor of the TiCl(4) coagulant was the lowest. Based on the results of the above study, it is concluded that the TiCl(4) flocculation can reduce the hydraulic retention time of slow and rapid mixing, however, careful handling of sludge is required due to the low recoverability of the aggregated floc.

Preparation of titanium dioxide nanoparticles from electrocoagulated sludge using sacrificial titanium electrodes.

A comprehensive investigation of electrocoagulation using sacrificial titanium (Ti) electrodes in wastewater was carried out. The effects of specific process variables, such as initial pH, mixing, current density, initial organic loading, and ionic/electrolyte strength were first optimized to produce recyclable Ti-based sludge. The sludge was incinerated at 600 degrees C to produce functional TiO(2) photocatalyst. X-ray diffraction analysis revealed that TiO(2) produced at optimum electrocoagulation conditions was mostly anatase structure. The specific surface area of the synthesized TiO(2) photocatalyst was higher than that of the commercially available and widely used Degussa P-25 TiO(2). Furthermore, energy dispersive X-ray and X-ray photoelectron spectroscopy analyses showed that in additional to titanium and oxygen, this photocatalyst is also composed of carbon and phosphorus. These elements were mainly doped as a substitute site for the oxygen atom. Transmission electron microscopy images exhibited sharply edged nanorods, round nanoparticles, and nanotubes with nonuniform shapes showing some structural defects. Photodecomposition of gaseous acetaldehyde by this photocatalyst was also conducted under UV and visible light irradiation to study the photocatalytic properties of the doped TiO(2) photocatalyst. While no photocatalytic activity was observed under visible light irradiation, this doped TiO(2) photocatalyst exhibited high photocatalytic activity under UV light.