Impact of microalgae species and solution salinity on algal treatment of wastewater reverse osmosis concentrate.

Six common microalgal species, including freshwater microalgae Scenedesmus abundans, Chlorella vulgaris, Chlamydomonas reinhardtii and Coelastrum microporum, and marine microalgae Nannochloropsis salina and Dunaliella tertiolecta, were tested in batch treatment to identify the most promising species for remediating a municipal wastewater reverse osmosis concentrate (ROC). Selected species were then studied at different ROC salinity levels (5, 10, and 15 g TDS/L) in semi-continuous treatment to evaluate their potential for nutrient remediation, and biogas production through anaerobic digestion. S. abundans, C. vulgaris, and N. salina showed higher potential for growth and nutrient remediation under salinity stress. Further tests revealed that N. salina adapted well to ROC conditions, and S. abundans could grow better and had higher tolerance to the elevated salinity than C. vulgaris. S. abundans and N. salina performed better for removing nutrients and organic matter (11.5-18 mg/L/d TN, 7.1-8.2 mg/L/d TP, and 8.6-12.4 mg/L/d DOC). Increasing salinity led to growth inhibition and N uptake reduction for freshwater species but had no significant effect on TP removal. Biochemical methane potential tests showed the algal biomass produced a significant amount of methane (e.g., up to 422 mL CH4/g VS for N. salina), suggesting the algae generated from the ROC treatment could produce significant amounts of energy through anaerobic digestion without the need for pretreatment. This study showed the environmental and economic potential of the algal system for future applications.

Treatment of wastewater reverse osmosis concentrate using alginate-immobilised microalgae: Integrated impact of solution conditions on algal bead performance.

Alginate can be used for entrapment of microalgal cells in gel beads to achieve high-rate treatment of wastewater and can overcome the difficulties of cell separation that would occur in suspended microalgae treatment systems. The potential for alginate beads to disintegrate in the presence of high ion concentrations could limit the use of alginate entrapment for treating municipal wastewater reverse osmosis concentrate (ROC). The combined effect of the pH, alkalinity, and salinity of the ROC that impact the physical stability, chemical characteristics, biomass production, and nutrient removal performance of alginate-entrapped Chlorella vulgaris for treating the ROC was investigated. Water adsorption resulting from the loss of calcium from the alginate matrix was the initiating cause of reduction of the algal bead stability. The combination of alkalinity >400 mg/L and pH ≥9.5 led to a >65% reduction in compressive strength and thus disintegration of beads during ROC treatment. However, alginate beads of C. vulgaris were sufficiently stable and were capable of nutrient remediation (up to 100% TP and 85% TN per treatment cycle of 48 h over a 10-day period) and biomass production (up to 340 mg/L/d) when salinity, pH, and alkalinity levels were <8 g TDS/L, 7-9.5, and <400 mg/L, respectively. Empirical models that were developed and validated could enable the prediction of the performance of the algal beads for various ROC compositions. This study enhances the insight and decision-making regarding the feasibility of the alginate-immobilised microalgal system for treating municipal wastewater ROC streams.

Potential of Chlorella vulgaris and Nannochloropsis salina for nutrient and organic matter removal from municipal wastewater reverse osmosis concentrate.

Municipal wastewater reverse osmosis concentrate (ROC) poses health and environmental risks on its disposal as it contains nutrients and harmful organic compounds at elevated concentrations. This study compared a freshwater microalga Chlorella vulgaris and a marine microalga Nannochloropsis salina in suspended and alginate-immobilised cultures for batch and semi-continuous treatment of the ROC. The immobilised algae gave comparable nutrient removal rates to the suspended cells, demonstrating immobilisation had no apparent negative impact on the photosynthetic activity of microalgae. Semi-continuous algal treatment illustrated that the microalgae could remove significant amounts of nutrients (> 50% and > 80% for TN and TP, respectively), predominantly through algal uptake (> 90%), within a short period (48 h) and generate 335-360 mg DCW L-1 d-1 of algal biomass. The treatment also removed a significant amount of organic matter (12.7-13.3 mg DOC L-1 d-1), primarily (> 65%) through the biotic pathway.

Fugacity modelling of the fate of micropollutants in aqueous systems - Uncertainty and sensitivity issues.

The application of multimedia fugacity models is useful to facilitate understanding of the behaviour of emerging contaminants during wastewater treatment, as well as after their release to the environment. In this paper, twenty-two fugacity modelling applications (reported over 1995-2019) describing the distribution of organic micropollutants in wastewater treatment plants and surface water bodies were analysed in terms of model application and modelling strategy. Disparities and similarities in strategies including selection of micropollutants, data sources for internal and external model inputs, sensitivity and uncertainty analysis, as well as model validation were discussed. This review confirmed that fugacity modelling is very applicable for providing qualitative predictions of the fate and removal of organic micropollutants in the various aqueous systems. However, it was also noted that there are issues related to the uncertainties and sensitivities of fugacity models such as the sources of model inputs and selection of default settings. The issues associated with the uncertainties in the investigated fugacity models are pointed out. Recommendations are given regarding the selection of the sources of model inputs, sensitivity analysis strategies and model validation methods. This review presents the challenges and opportunities for improving multimedia fugacity models, and so paves the way for future research in this field.

A comparative study of biological activated carbon based treatments on two different types of municipal reverse osmosis concentrates.

A study was conducted to understand the impact of reverse osmosis concentrate (ROC) characteristics on the efficacy of biological activated carbon (BAC) based treatments for removing organics and nutrients from two ROC streams (ROCa derived from municipal waste input with high salinity, and ROCb derived from domestic waste plus industrial trade waste with markedly lower salinity). Fluorescence excitation and emission matrix spectra and molecular weight analysis demonstrated that ROCa and ROCb had a significantly different composition of organic compounds due to the petrochemical processing and abattoir waste compounds in ROCb. Although the sequence of coagulation, UV/H2O2 and BAC gave the highest organic removal from the two ROCs (67% DOC for ROCa and 62% for ROCb), UV/H2O2 followed by BAC achieved satisfactory removal (>55%) for both ROC types. Sequential treatment involving coagulation gave better phosphorus removal (>90%) than any single treatment (<65%). Total nitrogen (TN) removal was fairly low (<50%) for all the treatment options and the salinity level had insignificant impact on nitrogen removal. Analysis of bacterial communities suggested that higher phosphorus removal and lower total nitrogen and nitrate removal from ROCb than ROCa was related to the presence of various denitrifying or phosphorus accumulating bacteria in the BAC.

Impact of the Interaction between Aquatic Humic Substances and Algal Organic Matter on the Fouling of a Ceramic Microfiltration Membrane.

The influence of the interaction between aquatic humic substances and the algal organic matter (AOM) derived from Microcystis aeruginosa on the fouling of a ceramic microfiltration (MF) membrane was studied. AOM alone resulted in a significantly greater flux decline compared with Suwannee River humic acid (HA), and fulvic acid (FA). The mixture of AOM with HA and FA exhibited a similar flux pattern as the AOM alone in the single-cycle filtration tests, indicating the flux decline may be predominantly controlled by the AOM in the early filtration cycles. The mixtures resulted in a marked increase in irreversible fouling resistance compared with all individual feed solutions. An increase in zeta potential was observed for the mixtures (becoming more negatively charged), which was in accordance with the increased reversible fouling resistance resulting from enhanced electrostatic repulsion between the organic compounds and the negatively-charged ceramic membrane. Dynamic light scattering (DLS) and size exclusion chromatography analyses showed an apparent increase in molecular size for the AOM-humics mixtures, and some UV-absorbing molecules in the humics appeared to participate in the formation of larger aggregates with the AOM, which led to greater extent of pore plugging and hence resulted in higher irreversible fouling resistance.

Impact of biological activated carbon pre-treatment on the hydrophilic fraction of effluent organic matter for mitigating fouling in microfiltration.

The hydrophilic (HPI) fraction of effluent organic matter, which has protein and carbohydrate contents, has a high propensity to foul low-pressure membranes. Biological activated carbon (BAC) filtration was examined as a pre-treatment for reducing the fouling of a microfiltration (MF) membrane (0.1 µm PVDF) by the HPI organic fraction extracted from a biologically treated secondary effluent (BTSE). Although the BAC removed less dissolved organic carbon, carbohydrate and protein from the HPI fraction than the granular activated carbon treatment which was used for comparison, it led to better improvement in permeate flux. This was shown to be due to the removal/breakdown of the HPI fraction resulting in less deposition of these organics on the membrane, many components of which are high molecular weight biopolymers (such as protein and carbohydrate molecules) through biodegradation and adsorption of those molecules on the biofilm and activated carbon. This study established the potential of BAC pre-treatment for reducing the HPI fouling of the membrane and thus improving the performance for the MF of BTSE for water reclamation.

Direct and indirect photolysis of seven micropollutants in secondary effluent from a wastewater lagoon.

The photodegradation of seven micropollutants commonly found in municipal wastewater, namely caffeine, carbamazepine, diuron, simazine, sulfamethoxazole, triclosan and 2,4-D, was investigated in pure water and secondary effluent to understand the direct and indirect photolysis of these compounds under natural sunlight irradiation. Sulfamethoxazole and triclosan were readily photodegraded with half-lives of 5.8 and 1.8 h, respectively, whilst the others were relatively resistant towards sunlight irradiation. Enhanced degradation was observed in secondary effluent compared with in the pure water matrix for all compounds, except for triclosan. It was confirmed that hydroxyl radicals played an important role in the photodegradation of the micropollutants while singlet oxygen may also play a role. The contribution of hydroxyl radical to the overall degradation of the five compounds that were resistant to direct sunlight accounted for 32%-70%. The impact of humic acid and nitrate, two known photosensitisers and wastewater components, on the photodegradation of the seven micropollutants in pure water was investigated under simulated solar radiation. The presence of nitrate promoted the photochemical loss of all seven micropollutants, however, humic acid caused promotion or inhibition, depending on the characteristics of the micropollutant. Humic acid enhanced the photolytic degradation of caffeine, sulfamethoxazole and diuron, while it hindered the photodegradation of the other four compounds by absorbing the available irradiation energy and/or reforming the parent compound. Furthermore, it was shown that there was only a small increase (up to 15%) in photodegradation of the compounds at 25 °C compared with that at 10 °C in the simulated system.

Impact of algal organic matter released from Microcystis aeruginosa and Chlorella sp. on the fouling of a ceramic microfiltration membrane.

Algal blooms lead to the secretion of algal organic matter (AOM) from different algal species into water treatment systems, and there is very limited information regarding the impact of AOM from different species on the fouling of ceramic microfiltration (MF) membranes. The impact of soluble AOM released from Microcystis aeruginosa and Chlorella sp. separately and together in feedwater on the fouling of a tubular ceramic microfiltration membrane (alumina, 0.1 µm) was studied at lab scale. Multi-cycle MF tests operated in constant pressure mode showed that the AOM (3 mg DOC L(-1)) extracted from the cultures of the two algae in early log phase of growth (12 days) resulted in less flux decline compared with the AOM from stationary phase (35 days), due to the latter containing significantly greater amounts of high fouling potential components (protein and humic-like substances). The AOM released from Chlorella sp. at stationary phase led to considerably greater flux decline and irreversible fouling resistance compared with that from M. aeruginosa. The mixture of the AOM (1:1, 3 mg DOC L(-1)) from the two algal species showed more similar flux decline and irreversible fouling resistance to the AOM from M. aeruginosa than Chlorella sp. This was due to the characteristics of the AOM mixture being more similar to those for M. aeruginosa than Chlorella sp. The extent of the flux decline for the AOM mixture after conventional coagulation with aluminium chlorohydrate or alum was reduced by 70%.

Combining Coagulation/MIEX with Biological Activated Carbon Treatment to Control Organic Fouling in the Microfiltration of Secondary Effluent.

Coagulation, magnetic ion exchange resin (MIEX) and biological activated carbon (BAC) were examined at lab scale as standalone, and sequential pre-treatments for controlling the organic fouling of a microfiltration membrane by biologically treated secondary effluent (BTSE) using a multi-cycle approach. MIEX gave slightly greater enhancement in flux than coagulation due to greater removal of high molecular weight (MW) humic substances, although it was unable to remove high MW biopolymers. BAC treatment was considerably more effective for improving the flux than coagulation or MIEX. This was due to the biodegradation of biopolymers and/or their adsorption by the biofilm, and adsorption of humic substances by the activated carbon, as indicated by size exclusion chromatography. Coagulation or MIEX followed by BAC treatment further reduced the problematic foulants and significantly improved the flux performance. The unified membrane fouling index showed that the reduction of membrane fouling by standalone BAC treatment was 42%. This improved to 65%, 70%, and 93% for alum, ferric chloride and MIEX pre-treatment, respectively, when followed by BAC treatment. This study showed the potential of sequential MIEX and BAC pre-treatment for controlling organic fouling and thus enhancing the performance of microfiltration in the reclamation of BTSE.

Impact of salinity on organic matter and nitrogen removal from a municipal wastewater RO concentrate using biologically activated carbon coupled with UV/H2O2.

The concentrate streams generated from reverse osmosis (RO)-based municipal wastewater reclamation processes contain organic substances and nutrients at elevated concentrations, posing environmental and health risks on their disposal to confined receiving environments such as bays. The impact of salinity (TDS at 7, 10 and 16 g/L) of a RO concentrate (ROC) on the treatment efficiency of a biological activated carbon (BAC) system after pre-oxidation with UV/H2O2 was characterised in terms of removal of organic matter and nitrogen species, and the bacterial communities. Organic matter removal was comparable for the ROC over the tested salinity range, with 45-49% of DOC and 70-74% of UVA254 removed by the combined treatment. However, removal in total nitrogen (TN) was considerably higher for the ROC at the high salinity (TDS âˆ¼ 16 mg/L) compared with the low (∼7 g/L) and medium salinity (∼10 g/L). Effective nitrification with high ammonium removal (>90%) was achieved at all salinity levels, whereas greater denitrification (39%) was obtained at high salinity than low (23%) and medium salinity (27%) which might suggest that the bacterial communities contributing to the greater denitrification were more halotolerant. Microbiological characterisation using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and culture based techniques showed that diversified bacterial communities were present in the BAC system as evident from different 16S rDNA. The major bacterial groups residing on the BAC media belonged to Bacillus (Firmicutes), Pseudomonas (γ-Proteobacteria), and Rhodococcus (Actinobacteria) for all salinity levels, confirming that these microbial communities could be responsible for carbon and nitrogen removal at the different salinity levels. This has implications in understanding the effectiveness and robustness of the BAC system over the salinity range of the ROC and so would be useful for optimising the treatment efficiency of the BAC system.

Long-term operation of biological activated carbon pre-treatment for microfiltration of secondary effluent: Correlation between the organic foulants and fouling potential.

The impact of long-term (>2 years) biological activated carbon (BAC) treatment for mitigating organic fouling in the microfiltration of biologically treated secondary effluent was investigated. Correlation between the organic constituents and hydraulic filtration resistance was investigated to identify the major components responsible for fouling. Over two years operation, the removal efficiency for dissolved organic carbon (DOC) by the BAC treatment was fairly consistent (30 ± 3%), although the reduction in UVA254 gradually decreased from 56 to 34%. BAC treatment effectively decreased the organic foulants in the effluent and so contributed to the mitigation of membrane fouling as shown by reduction in the unified membrane fouling index (UMFI). BAC consistently removed biopolymers whereas the removal of humic substances decreased from 52 to 25% after two years of BAC operation, and thus led to a gradual decrease in UMFI reduction efficiency from 78 to 43%. This was due to gradual reduction in adsorption capacity of the activated carbon as confirmed by analysis of its pore size distribution. Hence humics also played an important role in membrane fouling. However, there was a good correlation between protein and carbohydrate contents with hydraulically reversible and irreversible filtration resistance, compared with UVA254, turbidity and DOC. Although the mitigation of membrane fouling decreased over time, this study demonstrated that the long-term use of BAC pre-treatment of biologically treated secondary effluent prior to microfiltration has potential to reduce the need for frequent chemical cleaning and so increase membrane life span.

Removing organic and nitrogen content from a highly saline municipal wastewater reverse osmosis concentrate by UV/H2O2-BAC treatment.

Reverse osmosis (RO) concentrate (ROC) streams generated from RO-based municipal wastewater reclamation processes pose potential health and environmental risks on their disposal to confined water bodies such as bays. A UV/H2O2 advanced oxidation process followed by a biological activated carbon (BAC) treatment was evaluated at lab-scale for the removal of organic and nutrient content from a highly saline ROC (TDS 16 g L(-1), EC 23.5 mS cm(-1)) for its safe disposal to the receiving environment. Over the 230-day operation of the UV/H2O2-BAC process, the colour and UV absorbance (254 nm) of the ROC were reduced to well below those of the influent to the reclamation process. The concentrations of DOC and total nitrogen (TN) were reduced by approximately 60% at an empty bed contact time (EBCT) of 60 min. The reduction in ammonia nitrogen by the BAC remained high under all conditions tested (>90%). Further investigation confirmed that the presence of residual peroxide in the UV/H2O2 treated ROC was beneficial for DOC removal, but markedly inhibited the activities of the nitrifying bacteria (i.e., nitrite oxidising bacteria) in the BAC system and hence compromised total nitrogen removal. This work demonstrated that the BAC treatment could be acclimated to the very high salinity environment, and could be used as a robust method for the removal of organic matter and nitrogen from the pre-oxidised ROC under optimised conditions.

Impact of green algae on the measurement of Microcystis aeruginosa populations in lagoon-treated wastewater with an algae online analyser.

Tests on the algae online analyser (AOA) showed that there was a strong direct linear correlation between cell density and in vivo Chl-a concentration for M. aeruginosa over the range of interest for a biologically treated effluent at a wastewater treatment plant (25,000-65,000 cells mL(-1), equivalent to a biovolume of 2-6 mm3 L(-1)). However, the AOA can provide an overestimate or underestimate of M. aeruginosa populations when green algae are present in the effluent, depending on their species and relative numbers. The results from this study demonstrated that the green algae (e.g., Euglena gracilis, Chlorella sp.) in the field phytoplankton population should be considered during calibration. In summary, the AOA has potential for use as an alert system for the presence of M. aeruginosa, and thus potentially of cyanobacterial blooms, in wastewater stabilization ponds.

Effect of biological activated carbon pre-treatment to control organic fouling in the microfiltration of biologically treated secondary effluent.

Biological activated carbon (BAC) filtration was investigated as a pre-treatment for reducing the organic fouling of a microfiltration membrane (0.1 µm polyvinylidene fluoride) in the treatment of a biologically treated secondary effluent (BTSE) from a municipal wastewater treatment plant. BAC treatment of the BTSE resulted in a marked improvement in permeate flux, which was attributed to the effective removal of organic foulants and particulates. Although the BAC removed significantly less dissolved organic carbon than the granular activated carbon (GAC) treatment which was used as a control for comparison, it led to a markedly greater flux. This was attributed to the effective removal of the very high molecular weight substances such as biopolymers by the BAC through biodegradation and adsorption of those molecules on the biofilm. Size exclusion chromatography showed the BAC treatment led to approximately 30% reduction in these substances, whereas the GAC did not greatly remove these molecules. The BAC treatment led to a greater reduction of loosely-attached and firmly-attached membrane surface foulant, and this was confirmed by attenuated total reflection-fourier transform infrared spectroscopy analysis. This study demonstrated the potential of BAC pre-treatment for reducing organic fouling and thus improving flux for the microfiltration of BTSE.

Potential of BAC combined with UVC/H2O2 for reducing organic matter from highly saline reverse osmosis concentrate produced from municipal wastewater reclamation.

The organic matter present in the concentrate streams generated from reverse osmosis (RO) based municipal wastewater reclamation processes poses environmental and health risks on its disposal to the receiving environment (e.g., estuaries, bays). The potential of a biological activated carbon (BAC) process combined with pre-oxidation using a UVC/H2O2 advanced oxidation process for treating a high salinity (TDS~10000 mg L(-1)) municipal wastewater RO concentrate (ROC) was evaluated at lab scale during 90 d of operation. The combined treatment reduced the UVA254 and colour of the ROC to below those for the influent of the RO process (i.e., biologically treated secondary effluent), and the reductions in DOC and COD were approximately 60% and 50%, respectively. UVC/H2O2 was demonstrated to be an effective means of converting the recalcitrant organic compounds in the ROC into biodegradable substances which were readily removed by the BAC process, leading to a synergistic effect of the combined treatment in degrading the organic matter. The tests using various BAC feed concentrations suggested that the biological treatment was robust and consistent for treating the high salinity ROC. Using Microtox analysis no toxicity was detected for the ROC after the combined treatment, and the trihalomethane formation potential was reduced from 3.5 to 2.8 mg L(-1).

The interaction between natural organic matter in raw waters and pesticide residues: a three dimensional excitation-emission matrix (3DEEM) fluorescence investigation.

This paper examines the interaction between dissolved natural organic matter and pesticide residues, both of which are found in raw water sources, using three dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. It was observed that pesticide residue at 0.1 mg L(-1) formed a complex with humic-like fluorophores that are commonly found in raw water samples. Applying 3DEEM fluorescence to investigate the humic fractions, it was found that identification of changes in water sources was possible, and, importantly, the presence of a number of pesticides was able to be determined. In addition, the formation of this complex, and the influence of soluble cations and anions upon it, was shown to impact the efficiency of analytical extraction procedures for pesticides; however, 3DEEM fluorescence could be an approach to account for such losses.

A review of the use of sonication to control cyanobacterial blooms.

The development of cyanobacterial blooms in water bodies imparts undesirable characteristics to the water such as odours, tastes and the potential presence of toxins. Several chemical and physical methods have been used to control the blooms, but have limitations in terms of pollution and application on a large scale. A more recent approach has been the use of sonication in the control of cyanobacteria (also referred to as blue-green algae). This paper reviews current advancements in research on using sonication to control cyanobacteria, particularly Microcystis aeruginosa, as it is a prevalent and a major bloom-forming toxic species. The impact of sonication on the structure and function of M. aeruginosa is discussed, including the influence of sonication parameters such as power intensity, frequency and exposure time. Alternate strategies of cyanobacterial control in combination with sonication are also reviewed.

Impact of salinity and pH on the UVC/H2O2 treatment of reverse osmosis concentrate produced from municipal wastewater reclamation.

While reverse osmosis (RO) technology is playing an increasingly important role in the reclamation of municipal wastewater, safe disposal of the resulting RO concentrate (ROC), which can have high levels of effluent organic pollutants, remains a challenge to the water industry. The potential of UVC/H(2)O(2) treatment for degrading the organic pollutants and increasing their biodegradability has been demonstrated in several studies, and in this work the impact of the water quality variables pH, salinity and initial organic concentration on the UVC/H(2)O(2) (3 mM) treatment of a municipal ROC was investigated. The reduction in chemical oxygen demand and dissolved organic carbon was markedly faster and greater under acidic conditions, and the treatment performance was apparently not affected by salinity as increasing the ROC salinity 4-fold had only minimal impact on organics reduction. The biodegradability of the ROC (as indicated by biodegradable dissolved organic carbon (BDOC) level) was at least doubled after 2 h UVC/H(2)O(2) treatment under various reaction conditions. However, the production of biodegradable intermediates was limited after 30 min treatment, which was associated with the depletion of the conjugated compounds. Overall, more than 80% of the DOC was removed after 2 h UVC/3 mM H(2)O(2) treatment followed by biological treatment (BDOC test) for the ROC at pH 4-8.5 and electrical conductivity up to 11.16 mS/cm. However, shorter UV irradiation time gave markedly higher energy efficiency (e.g., EE/O 50 kWh/m(3) at 30 min (63% DOC removal) cf. 112 kWh/m(3) at 2 h). No toxicity was detected for the treated ROC using Microtox(®) tests. Although the trihalomethane formation potential increased after the UVC/H(2)O(2) treatment, it was reduced to below that of the raw ROC after the biological treatment.

Biofouling of water treatment membranes: a review of the underlying causes, monitoring techniques and control measures.

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies. This paper highlights the underlying causes of membrane biofouling and provides a review on recent developments of potential monitoring and control methods in water and wastewater treatment with the aim of identifying the remaining issues and challenges in this area.