•Literature assessing in situ fluorescence probes for cyanobacteria monitoring were reviewed.•Published information on probes' performance in laboratory and field conditions were investigated.•Chla ...from other phytoplankton was identified as the key source of interference with probe readings.•Range of error varies based on sources of interferences.•Published methods to reduce the error associated with probes were explored.
The frequency and intensity of potentially toxic cyanobacterial blooms in water sources are increasing. Currently, the water industry relies on laboratory analysis of cyanobacteria that can take two-five days; there is therefore a need to improve response time. Online fluorometric probes (also called “fluorescence probes” in some publications) are available for the rapid detection of cyanobacteria cells via measurement of specific pigmentation; however, water quality interferences with probe measurements in natural environments hinder their wider application. This review aims to investigate the sources of interference and bias, and assess the applicability of these probes for measurement of water supplies. Reported laboratory and field validation of these probes showed that their readings were sufficiently accurate. Correction procedures have been investigated for the identified sources of interferences but require field validation. Fluorometric probes can help with decision making during plant operation and have the potential to be applied as a management technique; however, probe users should be fully aware of the sources of interferences when interpreting the in situ probe measurements.
Algae and cyanobacteria frequently require separation from liquid media in both water treatment and algae culturing for biotechnology applications. The effectiveness of cell separation using a novel ...dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) has recently been of interest but has been shown to be dependent on the algae or cyanobacteria species tested. Previously, it was hypothesised that algal organic matter (AOM) could be impacting the separation efficiency. Hence, this study investigates the influence of AOM on cell separation using PosiDAF, in which bubbles are modified using a commercially available cationic polyelectrolyte poly(N, N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). The separation of Chlorella vulgaris CS-42/7, Mychonastes homosphaera CS-556/01 and two strains of Microcystis aeruginosa (CS-564/01 and CS-555/1), all of which have similar cell morphology but different AOM character, was investigated. By testing the cell separation in the presence and absence of AOM, it was determined that AOM enhanced cell separation for all the strains but to different extents depending on the quantity and composition of carbohydrates and proteins in the AOM. By extracting AOM from the strain for which optimal separation was observed and adding it to the others, cell separation improved from <55% to >90%. This was attributed to elevated levels of acidic carbohydrates as well as glycoprotein-carbohydrate conjugations, which in turn were related to the nature and quantity of proteins and carbohydrates present in the AOM. Therefore, it was concluded that process optimisation requires an in-depth understanding of the AOM and its components. If culturing algae for biotechnology applications, this indicates that strain selection is not only important with respect to high value product content, but also for cell separation.
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•Algal organic matter was required to enhance flotation of all species in PosiDAF•PosiDAF efficiency varied with proportion of acidic carbohydrates in the species•Glycoprotein and carbohydrate conjugation may enhance effectiveness of PosiDAF
A wide range of cyanobacterial species and their harmful metabolites are increasingly detected in water bodies worldwide, exacerbated by climate change and human activities. The resulting bloom ...conditions represent significant challenges to production of safe drinking water and cost effective water reuse, therefore their removal is a priority to ensure public safety. While current microscopic taxonomy identification methods provide valuable information about cell numbers during treatment, these methods are incapable of providing information about the fate of cells during treatment. The objectives of this study were to (1) identify the critical control points for breakthrough and accumulation of cells by investigating the fate of cells during treatment processes using a combination of taxonomy, cell integrity and next-generation sequencing (NGS), and (2) assess the impact of pre-treatment processes on breakthrough prevention at critical control points, and the benefits of cell integrity and NGS analysis for improved management purposes. This paper presents the results of an unprecedented cyanobacterial monitoring program conducted in four full scale water treatment plants located in three different climate zones. Cyanobacterial cell integrity and accumulation during operation process were assessed for the first time using next generation of gene sequencing methods. NGS analysis led to detection of cyanobacterial and melainabacteria orders in water samples that were not identified by microscopy. 80 ± 5% of cells were completely lysed post pre-oxidation (for both ozone and potassium permanganate). However unlike pre-ozonation, the remaining cells were undamaged cells with the potential to accumulate and grow within the plants post-KMnO4 treatment, particularly in clarifier sludge. To effectively monitor water quality, this study presents a synergistic approach coupling new and traditional analytical methods and demonstrates the importance of identifying critical points for managing accumulation of cyanobacteria within plants.
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•Studied performance of treatment barriers for removal of cyanobacterial cells.•Applied combination of taxonomy, cell integrity & next-generation sequencing (NGS).•NGS detected new cyanobacterial & melainabacteria orders in water samples.•80 ± 5% of cells were completely lysed after pre-oxidation (O3 & KMnO4).•Viable cells with potential to accumulate & grow within plants remained post-KMnO4.
The impact of fouling on N-nitrosamine rejection by nanofiltration (NF) and reverse osmosis (RO) membranes was investigated in this study. Membrane fouling was simulated using tertiary treated ...effluent and several model fouling solutions (that contained sodium alginate, bovine serum albumin, humic acid or colloidal silica) to elucidate the changes in rejection behaviour of N-nitrosamines. In general, the rejection of N-nitrosamines increased when the membranes were fouled by tertiary effluent. The rejection of small molecular weight N-nitrosamines was most affected by membrane fouling. In particular, the rejection of N-nitrosodimethylamine (NDMA) by the ESPA2 membrane increased from 34% to 73% after membrane fouling caused by tertiary effluent. The results also indicate that the impact was less apparent for the lowest permeability membrane (i.e., ESPAB), and the rejection of N-nitrosamines by the ESPAB membrane was over 82% regardless of membrane fouling. The effect of membrane fouling caused by model foulants on N-nitrosamine rejection was considerably less than that caused by tertiary effluent. Size exclusion chromatography analyses revealed that the tertiary effluent contains a high fraction of low molecular weight (<500g/mol) organic substances. It appears that these low molecular weight foulants present in the tertiary effluent can restrict the solute pathway within the active skin layer of membranes, resulting in the observed increase of solute rejection.
► Membrane fouling can affect the rejection of low molecular weight N-nitrosamines. ► Tertiary effluent (TE) contains a large fraction of low molecular weight organics. ► Fouling caused by TE leads to an increase in N-nitrosamine rejection. ► Fouling caused by model foulants leads to smaller increase in rejection. ► The ESPAB membrane shows high NDMA removal and the effect of fouling is negligible.
Abstract
The occurrence and severity of cyanobacterial and algal blooms in water supplies has been increasing due to the effects of eutrophication and climate change, resulting in more frequent taste ...and odour (T&O) events. Conventional treatment processes have been found to be inefficient in removing the two most commonly detected algal T&O compounds, geosmin and 2-methylisoborneol (MIB), though granular activated carbon (GAC) and biological activated carbon (BAC) contactors have achieved high T&O removal rates. Literature on the performance of GAC and BAC for T&O removal in full-scale treatment plants, however, is limited. This review collates and assesses pilot-scale and full-scale studies which focus on removal of geosmin and MIB, with the aim of understanding the factors which influence T&O removal and determining knowledge gaps in the use of GAC and BAC. Age and empty bed contact time (EBCT) were found to have a significant impact on GAC performance, with removal efficiency decreasing with increased age and increasing with longer EBCTs. BAC contactors have achieved higher removal rates than non-biologically active GAC contactors and were not impacted by age, EBCT and/or carbon type. From these observations, implementation of BAC for T&O removal would be favourable; however, further investigations are required to understand full-scale performance of BAC and service life modelling.
Membrane fouling in reverse osmosis (RO) systems caused by organic matter (OM) remains a significant operational issue during desalination. Dissolved air flotation (DAF) has recently received ...attention as a pre-treatment option for seawater OM removal; however, only a limited number of studies have been undertaken. This may be because it is difficult to characterise OM in seawater due to the high salt content and low carbon concentration. In this study, DAF pre-treatment experiments were conducted using a model seawater solution, and real seawater and brackish water samples. DAF performance was determined via conventional water quality parameters as well as fluorescence excitation–emission matrix (FEEM) spectroscopy and liquid chromatography with organic carbon detection (LC-OCD). Biopolymers and humic substances were the major organic fractions removed between 38 and 84% and 20–61% depending on the sample, respectively. The optimal normalised coagulant dose (Fe3+ to DOC ratio) was observed to be 0.5–4 at pH5.5 increasing to 4–12 at pH7.5. At pH5.5, the optimum coagulant dose increased with increasing humic character of the feed water. Overall, the OM removal efficiency by DAF observed in this study was higher than reported for other membrane-based processes; a combination of DAF and biofiltration is likely to be complementary.
•Use of DAF for organic matter removal is a good option in desalination systems•High removal of biopolymers and humic substances were observed using coagulation- DAF•Optimal coagulant dose was dependent on humic substance concentration
► Ultrafiltration treatment was undertaken for five tertiary wastewater effluents. ► Advanced techniques were used for better characterisation of foulant layers. ► Biopolymer fraction was the most ...significantly reduced by UF treatment. ► The majority of rinsing layer comprised predominantly protein-enriched biopolymers. ► Tyrosine fluorescence intensity correlated well with associated hydraulic resistance.
Membrane fouling remains an operational challenge in the ultrafiltration (UF) membrane treatment of wastewater effluent and research is on-going to improve understanding of the organic character of foulants. Two advanced organic characterisation techniques that have potential to lend insight into membrane fouling are size exclusion chromatography with organic carbon, UV
254 and nitrogen detection (LC-OCD) and fluorescence excitation–emission matrix (EEM) spectroscopy. In this study, UF treatment was undertaken for five tertiary wastewater effluents. The total hydraulic resistance was determined as well as that contributed by foulant layers fractionated by rinsing, backwashing and chemically desorbing. Organic characterisation for UF feed samples, permeates and each foulant layer was then performed using LC-OCD and FEEM spectroscopy with the aim of improving understanding of the character of foulants present in effluent organic matter (EfOM) and to determine the potential for the use of FEEM spectroscopy as a foulant indicator in such systems. It was determined that the biopolymer fraction was most significantly reduced on UF treatment, as anticipated due to its high molecular size. This was supported by the observation that the majority of the foulant layer comprised predominantly protein-enriched biopolymers (38–60% of total foulant layer DOC) that could be removed by rinsing. The resistance attributed to rinsing was directly related to the combined DOC concentration associated with proteins and low molecular weight neutral compounds as defined by LC-OCD analysis. Furthermore, tyrosine-like fluorescence intensity (
λ
ex/em
=
250/304
nm) of both the rinsing solutions and UF feed samples showed good correlation with associated hydraulic resistance for EfOM originating from domestic wastewater, suggesting that fluorescence has potential to be used as a foulant indicator for these systems.
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•PosiDAF cell separation was comparable for all modified polymers tested.•Zeta potential of treated effluents remained highly negative for only two polymers.•Polymer orientation on ...the bubble changed depending on base polymer used.•Effluent polymer concentration was quantified for the first time in PosiDAF trials.
The novel dissolved air flotation (DAF) process that uses hydrophobically-modified polymers (HMPs) to generate positively charged bubbles (PosiDAF) has been shown to separate negatively charged algal cells without the need for coagulation-flocculation. Previous research has been limited to HMPs of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and, while they were effective at bench-scale, performance at pilot-scale was better using commercial poly(N,N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). Hence, the aim of this research was to compare the effectiveness of PDADMAC modified with aliphatic and aromatic moieties in comparison to previously tested PDMAEMA HMPs in respect to algal cell separation and minimisation of effluent polymer concentration, as well as defining the underlying polymer-bubble interaction mechanisms. Polymer-bubble adhesion properties were measured using atomic force microscopy (AFM) while polymer concentration was monitored via zeta potential and, where possible, assays using fluorescence spectroscopy. Both PDADMAC functionalised with a fluorinated aromatic group (PDADMAC-BCF) and PDMAEMA modified with 1-bromodecane respectively, gave effective cell separation, while the treated effluent zeta potential values at maximum cell removal were lower than the other polymers trialled. The effluent polymer concentration when using PDADMAC-BCF was four times lower in comparison to another aromatically modified PDADMAC polymer. AFM studies indicated that, in contrast to the PDMAEMA-based polymers, the PDADMAC-based polymers did not adsorb closely to the bubble surface. The different polymer-bubble interactions indicate that separation mechanisms will also vary, potentially leading to differences in process effectiveness when explored at pilot scale.
We studied the formation of four nitrogenous DBPs（N-DBPs） classes（haloacetonitriles,halonitromethanes, haloacetamides, and N-nitrosamines）, as well as trihalomethanes and total organic halogen（TOX）, ...after chlorination or chloramination of source waters. We also evaluated the relative and additive toxicity of N-DBPs and water treatment options for minimisation of N-DBPs. The formation of halonitromethanes, haloacetamides, and N-nitrosamines was higher after chloramination and positively correlated with dissolved organic nitrogen or total nitrogen. N-DBPs were major contributors to the toxicity of both chlorinated and chloraminated waters. The strong correlation between bromide concentration and the overall calculated DBP additive toxicity for both chlorinated and chloraminated source waters demonstrated that formation of brominated haloacetonitriles was the main contributor to toxicity. Ozone–biological activated carbon treatment was not effective in removing N-DBP precursors. The occurrence and formation of N-DBPs should be investigated on a case-by-case basis, especially where advanced water treatment processes are being considered to minimise their formation in drinking waters, and where chloramination is used for final disinfection.
Dissolved Air Flotation (DAF) is a well-known coagulation–flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell ...recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99% cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95% coagulant reduction depending on the algae species and the pH conditions adopted. In terms of floc structure and strength, the inclusion of microspheres in the algae floc generated a looser aggregate, showing a more compact structure within single cell alga, than large and filamentous cells. Overall, BDAF appeared to be a more reliable and sustainable harvesting system than DAF, as it allowed equal cells recovery reducing energy inputs, coagulant demand and carbon emissions.
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•Ballasted Dissolved Air Flotation (BDAF) allowed high coagulant saving compare to conventional Dissolved Air Flotation (DAF).•The inclusion of microspheres on the algae biomass generated loser floc structure supporting post flotation algae-beads separation.•Ballasted floc formation was more influenced by the cell morphology than the extracellular algogenic organic matter (AOM).•Compare to DAF, the BDAF technology allowed significant energy, carbon and cost saving depending on the algae species adopted.
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