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

Domestic wastewater treatment towards reuse by "self-supplied" microbial electrochemical system assisted UV/H2O2 process

Domestic wastewater is a potential source of water for non-potable reuse that may help address the global water, energy, and resource challenges. Herein, a "self-supplied" process through integrating microbial electrochemical system (MES) with UV/H2O2 was developed and investigated for wastewater treatment. H2O2 was "self-supplied" from MES while the MES catholyte was "self-supplied" from the final effluent of UV/H2O2. It was found that the MES accomplished > 80 % degradation of chemical oxygen demand (COD) through bioanode degradation, and produced 18 - 20 mg L-1 H2O2 via oxygen reduction reaction in the gas diffusion cathode. The MES effluent was further treated by the UV/H2O2 process, which achieved the complete removal of recalcitrant diclofenac and > 6 log inactivation of Escherichia coli. The enhanced treatment performance of UV/H2O2 was demonstrated via a comparison with the control experiments (UV or H2O2 treatment) and benefited from ·OH generation and sulfide removal. When treating the actual wastewater, the proposed system exhibited consistent treatment performance for the organic compounds and recalcitrant contaminants, and the quality of the treated water would meet the non-potable water reuse guidelines. The results of this study encourage the further exploration of emerging contaminant removal, system coordination, and use of renewable energy by the cooperation between MES and UV/H2O2.

An overview of deploying membrane bioreactors in saline wastewater treatment from perspectives of microbial and treatment performance

The discharged saline wastewater has severely influenced the aquatic environment as the treatment performance of many wastewater treatment techniques is limited. In addition, the sources of saline wastewater are also plentiful from agricultural and various industrial fields such as food processing, tannery, pharmaceutical, etc. Although high salinity levels negatively impact the performance of both physicochemical and biological processes, membrane bioreactor (MBR) processes are considered as a potential technology to treat saline wastewater under different salinity levels depending on the adaption of the microbial community. Therefore, this study aims to systematically review the application of MBR widely used in the saline wastewater treatment from the perspectives of microbial structure and treatment efficiencies. At last, the concept of carbon dioxide capture and storage will be proposed for the MBR-treating saline wastewater technologies and considered toward the circular economy with the target of zero emission.

A critical review on diverse technologies for advanced wastewater treatment during SARS-CoV-2 pandemic: What do we know?

Advanced wastewater treatment technologies are effective methods and currently attract growing attention, especially in arid and semi-arid areas, for reusing water, reducing water pollution, and explicitly declining, inactivating, or removing SARS-CoV-2. Overall, removing organic matter and micropollutants prior to wastewater reuse is critical, considering that water reclamation can help provide a crop irrigation system and domestic purified water. Advanced wastewater treatment processes are highly recommended for contaminants such as monovalent ions from an abiotic source and SARS-CoV-2 from an abiotic source. This work introduces the fundamental knowledge of various methods in advanced water treatment, including membranes, filtration, Ultraviolet (UV) irradiation, ozonation, chlorination, advanced oxidation processes, activated carbon (AC), and algae. Following that, an analysis of each process for organic matter removal and mitigation or prevention of SARS-CoV-2 contamination is discussed. Next, a comprehensive overview of recent advances and breakthroughs is provided for each technology. Finally, the advantages and disadvantages of each method are discussed.

Pilot-scale and mechanistic study of the degradation of typical odors and organic compounds in drinking water by a combined UV/H2O2-BAC process

Odor problems are challenging issues in water treatment. Advanced oxidation has a significant degradation effect on these odors; however, some issues, such as oxidant residues and disinfection byproducts, exist in the use of advanced oxidation in actual water treatment. Because of the above issues, a combined advanced oxidation process has emerged-the UV/H₂O₂ -biological activated carbon (BAC) process can play a strong oxidizing role in advanced oxidation and uses the physical adsorption and biological effects of activated carbon. However, there have been few studies on the odor degradation mechanism and characteristics of activated carbon biofilms in actual water treatment. This paper systematically studied the organic and odor substances removal effects and mechanism of a pilot combined UV/H₂O₂-BAC process. The results showed that UV/H₂O₂-BAC technology had a good removal effect on odor substances under long-term stable operation. The concentrations of geosmin (GSM) and 2-methylisoborneol (2-MIB) after systemic treatment were below 5 ng/L. The removal rates of DOC, UV₂₅₄ and H₂O₂ by the combined process were 53.60%, 73.08% and 60.20%, respectively. The results of full-scan determination of GSM and 2-MIB degradation by gas chromatography-mass spectrometry (GC-MS) were consistent with those of front-track analysis. The diversity, richness and evenness of microorganisms in the lower activated carbon layer were higher than those in the middle and upper activated carbon layers. The greater the difference in the carbon layer height was, the greater the difference in the biological community structure.

Effects of pure oxygen aeration on organic pollutants removal performance and soluble microbial products characteristics of salt-tolerant activated sludge

The effects of pure oxygen aeration on organic pollutants removal performance and effluent soluble microbial products (SMP) characteristics of salt-tolerant sludge for the treatment of wastewater with the salinity from 1.0% to 3.5% were investigated. The results showed that the oxygen transfer efficiency of the pure oxygen aeration was higher than that of the air aeration. At the low salinities (0.5%, 1.0%, 1.5%), the total organic carbon (TOC) removal rates were 71.42%, 72.88% and 76.30%, respectively, much higher than those with air aeration. However, there were no significant differences of TOC removal efficiency between the air aeration and the pure oxygen aeration at high salinities (2.5% and 3.5%). The SMP contents showed a trend of first decline and then increase generally. The content of SMP with pure oxygen aeration was lower than that with air aeration at low salinity, whereas an opposite result was obtained for salinity above 2.5%. Five excitation-emission matrix (EEM) fluorescence peaks detected in the SMP with pure oxygen aeration and air aeration were assigned to tryptophan protein-like, tyrosine protein-like and humic acid-like substances. Humic acid-like fluorescence mainly appeared in the SMP with air aeration, which may be due to respiratory failure under air aeration conditions.

UV-based advanced oxidation of dissolved organic matter in reverse osmosis concentrate from a potable water reuse facility: A Parallel-Factor (PARAFAC) analysis approach

Disposal of reverse osmosis concentrate (ROC) from advanced water purification facilities is a challenge associated with the implementation of reverse osmosis-based treatment of municipal wastewater effluent for potable reuse. In particular, the dissolved organic matter (DOM) present in ROC diminishes the quality of the receiving water upon environmental disposal and affects the toxicity, fate, and transport of organic contaminants. This study investigates UV-based advanced oxidation processes (UV-AOPs) for treating DOM in ROC using a Parallel Factor Analysis (PARAFAC) approach. DOM composition and degradation were tested in UV-only and three UV-AOPs using hydrogen peroxide (H₂O₂), free chlorine (Cl₂), and persulfate (S₂O₈^2-). The four-component PARAFAC model consisted of two terrestrial humic-like components (C_UVH and C_VisH), a wastewater/nutrient tracer component (C_NuTr), and a protein-like (tyrosine-like) component (C_PrTy). Based on the observed loss in the maximum fluorescence intensity of the components, DOM degradation was determined to be dependent on UV fluence, oxidant dose, and dilution factor of the ROC (i.e., bulk DOM concentration). C_VisH was most the photolabile component in the UV-only system, followed by C_NuTr, C_PrTy, and C_UVH, respectively. Furthermore, UV-H₂O₂ and UV-S₂O₈^2- displayed faster overall reaction kinetics compared to UV-Cl₂. The degradation trends suggested that C_NuTr and C_PrTy consisted of chemical moieties that were susceptible to reactive oxygen species (HO^•) but not reactive chlorine species; whereas, C_VisH was sensitive to all reactive species generated in the three UV-AOPs. Compared to other components, C_PrTy was recalcitrant in all treatment scenarios tested. Calculations using chemical probe-based analysis also confirmed these trends in the reactivity of DOM components. The outcomes of this study form a foundation for characterizing ROC reactivity in UV-AOP treatment technologies, to ultimately improve the sustainability of water reuse systems.

A baseline of terrestrial freshwater and nitrogen fluxes to the Southern California Bight, USA

Time series were compiled of terrestrial nitrogen, phosphorus, carbon, iron, and silica fluxes to the Southern California Bight (SCB), a U.S. West Coast embayment (Sutula et al., 2021). Monitoring data and model output were used to construct a baseline of inputs from direct point source (PS) discharges of wastewater treatment (WWT) effluent (via ocean outfalls) and PS, non-point and natural sources from coastal rivers. The baseline covers 1971-2017 for large WWT plants discharging >50 million gallons per day (MGD) and 1997-2017 for small WWT plants and rivers. PS are the dominant nitrogen source, with contributions of 70% of the total annual freshwater discharge and 95% of nitrogen loads. WWT upgrades have reduced organic nitrogen loads by 73% since 1971. Inorganic nitrogen loads have generally held constant (35-40 Gg y^-1) for the large WWT plants. This baseline represents a period prior to extensive wastewater and stormwater recycling that is increasing in the region.

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.

Non-thermal plasma combined with zeolites to remove ammonia nitrogen from wastewater

In this work, non-thermal plasma combined with zeolites was used to remove inorganic pollutant ammonia nitrogen from wastewater. Ammonia nitrogen elimination performances at various operating parameters were investigated. Roles of active species in the removal of ammonia nitrogen were also discussed. The experimental results showed that 69.97% ammonia nitrogen can be removed from the plasma/zeolites synergistic system after 30 min treatment. The removal efficiency was 16.23% and 61.55% higher than that in sole zeolites adsorption system and that in sole discharge plasma system, respectively. Higher applied voltage, lower initial ammonia nitrogen concentration and weak acidic conditions were favorable for ammonia nitrogen removal. After the addition of zeolites, part of O₃ and H₂O₂ generated in the plasma/zeolites system were decomposed into other oxygen species (•OH and ¹O₂), which improved the oxidation degree of ammonia nitrogen. In addition, the reaction mechanism of ammonia nitrogen in water by plasma/zeolites process was discussed. After repeated use three times, the effect of the zeolites in the plasma/zeolites system remained stable. Characterization of the zeolites after reaction was analyzed through BET, SEM, XRD and FT-IR. The experiments have confirmed the applicability of the plasma/zeolites system for the further treatment of low-concentration ammonia nitrogen wastewater.

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.

A review on the application of ozonation to NF/RO concentrate for municipal wastewater reclamation

Nanofiltration (NF) and reverse osmosis (RO) technology have gained worldwide acceptance for reclamation of municipal wastewater due to their excellent efficiencies in rejecting a wide spectrum of organic pollutants, bacteria, dissolved organic matters and inorganic salts. However, the application of NF/RO process produces inevitably a large volume of concentrated waste stream (NF/RO concentrate), which is generally characterised by high levels of inorganic and organic substances, a low biodegradation and potential ecotoxicity. At present, one of the most significant concerns for this process is regarding the sustainable management of municipal NF/RO concentrate, due to a potentially serious threat to water receiving body. It should therefore be further disposed or treated by effective technologies such as ozonation in a cost-effective way, aiming to minimize the potential environmental risk associated with the presence of emerging micropollutants (ng L^-1 - μg L^-1). This paper provides an overview on the disposal of NF/RO concentrate from municipal wastewater by ozonation process. This is a first review to present entirely ozonation efficiency of NF/RO concentrate in terms of elimination of emerging micropollutants, degradation of organic matters, as well as toxicity assessment. In addition, ozone combining biological activated carbon (BAC) or other advanced oxidation processes (AOPs) is also discussed, aiming to further improve mineralization of ozone-recalcitrant substances in NF/RO concentrate. Finally, further research directions regarding the management of NF/RO concentrate are proposed.

Enhanced simultaneous removal of nitrogen, phosphorous, hardness, and methylisothiazolinone from reverse osmosis concentrate by suspended-solid phase cultivation of Scenedesmus sp. LX1

The disposal of reverse osmosis (RO) concentrate (ROC) is a critical challenge impeding the application of RO-based wastewater reclamation. Herein, we proposed an enhanced biotreatment approach for the simultaneous removal of nitrogen, phosphorous, hardness, and methylisothiazolinone (MIT) from ROC by suspended-solid phase cultivation of Scenedesmus sp. LX1. Repeated carrier addition, guided by the developed optimal carrier addition model, efficiently enhanced algal growth and contaminant removal through dynamically controlling the suspended algal density by cell attachment. The maximum algal growth rate (212.2 mg/(L∙d)) increased by 41% compared with the control, and the time needed for reaching the maximum algal biomass (906.7 mg/L) was shortened by 1 d, attributing to the mitigation of density restriction. 91.8% of nitrogen (30.2 mg/L) was removed with 5.5 mg/(L∙d) accelerating removal rate, and phosphate (3.7 mg/L) was completely removed within 1 d. Hardness precursors calcium and inorganic carbon were also removed in large amounts, 268.4 and 128.2 mg/L, respectively. Moreover, suspended-solid phase cultivation significantly mitigated the growth inhibition caused by MIT toxicity, enabled the algae to completely biodegrade MIT of extremely high concentrations (4.7 mg/L and 11.4 mg/L) in a short time. Our results demonstrate the feasibility of suspended-solid phase algal cultivation for simultaneously and effectively removing multiple main contaminants from ROC.

Ozonation mechanism of carbamazepine and ketoprofen in RO concentrate from municipal wastewater treatment: Kinetic regimes, removal efficiency and matrix effect

A relatively important disadvantage of reverse osmosis (RO) application to municipal wastewater reclamation is related to management of a concentrated waste stream containing high levels of organic contaminants. The present study investigated ozonation performance of RO concentrate from municipal wastewater treatment in a stirred semi-batch reactor. In this work, carbamazepine (CBZ, as a representative of ozone-reactive micropollutants) and ketoprofen (KET, one of ozone-resistant organic chemicals) were selected as target micropollutants. The absence of dissolved ozone within the first 60 min corresponding to initial ozone demand (IOD) complement suggested that chemical reactions took place quite fast, and ozone mass transfer was considered as a limiting step. A complete elimination of CBZ and an excellent removal of KET were observed in this period, indicating that molecular ozone was a dominated oxidant responsible for the decomposition of the target micropollutants in RO concentrate containing initial dissolved organic carbon (DOC₀, ~50.8 mg L^-1). >90% of ozone-reactive CBZ was eliminated at a low ozone dose of 0.33 g consumed ozone per g DOC₀. More ozone dose requirement for an equivalent removal of KET was ascribed to its low ozone kinetic rate constant below 10 L mol^-1 s^-1. In addition, the presence of high contents of organic matters and alkalinity in RO concentrate exhibited pronounced effects on the degradation of KET because of a competition with oxidants. Overall, ozonation appeared to be a promising alternative for disposal of RO concentrate in terms of micropollutant removal. However, additional technologies should be followed to further enhance the degradation rate of organic matters for a zero liquid discharge treatment scheme.

Electrochemical nitrate removal with simultaneous magnesium recovery from a mimicked RO brine assisted by in situ chloride ions

Electrochemical reduction is effective to remove nitrate but byproducts such as ammonia and nitrite would need chloride addition for indirect oxidation to nitrogen gas. Herein, electrochemical nitrate reduction was investigated to remove nitrate from a mimicked reverse osmosis (RO) brine containing chloride that eliminates the need for external chloride addition. Both Cu/Zn and Ti nano cathodes exhibited the best performance of nitrate removal with >97 % removal in either Na₂SO₄ or NaCl electrolyte, although with different products. Complete nitrate reduction to nitrogen gas was realized in the RO brine whose complex composition decreased the electrode efficiency, for example from 71.4 ± 0.2%-49.4 ± 0.3 % with the Cu/Zn cathode after 5 cycles of operation. Magnesium was recovered at the same time of nitrate removal and the purity of Mg(II) could reach 96.8 ± 2.0 % after proper pH pre-treatment. In a preliminary adsorption study, a key byproduct - chlorate was reduced by 49.8 ± 2.7 % after 3-h adsorption by 100 g L^-1 activated carbon. These results have demonstrated the simultaneous electrochemical nitrate removal and resource recovery from a complex water like a RO brine and provided new information such as byproduct management and electrode deterioration.

Advanced treatment of coal chemical reverse osmosis concentrate with three-stage MABR

The issue of reverse osmosis concentrate (ROC) has attracted significant attention due to its complex and toxic constituents under high salinity conditions. In this work, a three-stage membrane-aerated biofilm reactor (MABR) system was constructed to treat such wastewater without an external carbon source. The effects of operating conditions including aeration pressure, reflux ratio, temperature and hydraulic retention time on the removal performance of the integrated system were evaluated and optimized. Under the optimal operating parameters, the removal efficiencies of COD, NH4 +-N, NO3 --N, and TN reached 69.36%, 80.95%, 54.55%, and 54.36%, respectively. Three-dimensional fluorescence analysis indicated that humic acid was mostly removed from raw water. Moreover, microbial diversity analysis indicated that the microbial community structure of each reactor could be individually modulated to exert different functions and enhance the system performance. The integrated MABR system exhibits great feasibility and potential for the advanced treatment of coal chemical ROC.

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 (ROC_a derived from municipal waste input with high salinity, and ROC_b derived from domestic waste plus industrial trade waste with markedly lower salinity). Fluorescence excitation and emission matrix spectra and molecular weight analysis demonstrated that ROC_a and ROC_b had a significantly different composition of organic compounds due to the petrochemical processing and abattoir waste compounds in ROC_b. 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 ROC_b than ROC_a was related to the presence of various denitrifying or phosphorus accumulating bacteria in the BAC.

Promotion by humus-reducing bacteria for the degradation of UV254 absorbance in reverse-osmosis concentrates pretreated with O3-assisted UV-Fenton method

The primary pollutants in reverse-osmosis concentrates (ROC) are the substances with the UV absorbance at 254 nm (UV₂₅₄), which is closely related to humic substances that can be degraded by humus-reducing bacteria. This work studied the degradation characteristics of humus-reducing bacteria in ROC treatment. The physiological and biochemical characteristics of humus-reducing bacteria were investigated, and the effects of pH values and electron donors on the reduction of humic analog, antraquinone-2, 6-disulfonate were explored to optimize the degradation. Furthermore, the O₃-assisted UV-Fenton method was applied for the pretreatment of ROC, and the degradation of UV₂₅₄ absorbance was apparently promoted with their removal rate, reaching 84.2% after 10 days of degradation by humus-reducing bacteria.

Is ozonation environmentally benign for reverse osmosis concentrate treatment? Four-level analysis on toxicity reduction based on organic matter fractionation

Ozonation is a promising option to treat reverse osmosis concentrate (ROC). However, a systematic understanding and assessment of ozonation on toxicity reduction is insufficient. In this study, ROC sampled from a typical industrial park wastewater treatment plant of China was fractionated into hydrophobic acid (HOA), hydrophobic base (HOB), hydrophobic neutral (HON), and hydrophilic fraction (HI). Systematic bioassays covering bacteria, algae, fish, and human cell lines were conducted to reveal the role of ozonation in toxicity variation of the four ROC fractions. HOA in the raw ROC exhibited the highest toxicity, followed by HON and HI. Ozonation significantly reduced total organic carbon (TOC) and UV₂₅₄ values in HOA, HON, and HI and their toxicity except in HOB. Correlation analysis indicated that chemical data (TOC and UV₂₅₄) of HOA and HON correlated well with their toxicities; however, poor correlations were observed for HOB and HI, suggesting that a battery of toxicity assays is necessary. This study indicates that TOC reduction during ozonation could not fully reflect the toxicity issue, and toxicity assessment is required in conjunction with the chemical data to evaluate the effectiveness of ozonation.

A review: Potential and challenges of biologically activated carbon to remove natural organic matter in drinking water purification process

The use of biologically activated carbon (BAC) in drinking water purification is reviewed. In the past BAC is seen mostly as a polishing treatment. However, BAC has the potential to provide solution to recent challenges faced by water utilities arising from change in natural organic matter (NOM) composition in drinking water sources - increased NOM concentration with a larger fraction of hydrophilic compounds and ever increasing trace level organic pollutants. Hydrophilic NOM is not removed by traditional coagulation process and causes bacterial regrowth and increases disinfection by-products (DBPs) formation during disinfection. BAC can offer many advantages by removing hydrophilic fraction and many toxic and endocrine compounds which are not otherwise removed. BAC can also aid the other downstream processes if used as a pre-treatment. Major drawback of BAC was longer empty bed contact time (EBCT) required for an effective NOM removal. This critical review analyses the strategies that have been adopted to enhance the biological activity of the carbon by operational means and summarises the surface modification methods. To maximize the benefit of the BAC, a rethink of current treatment plant configuration is proposed. If the process can be expedited and adopted appropriately, BAC can solve many of the current problems.

Applications of microalgal biofilms for wastewater treatment and bioenergy production

BACKGROUND

Microalgae have shown clear advantages for the production of biofuels compared with energy crops. Apart from their high growth rates and substantial lipid/triacylglycerol yields, microalgae can grow in wastewaters (animal, municipal and mining wastewaters) efficiently removing their primary nutrients (C, N, and P), heavy metals and micropollutants, and they do not compete with crops for arable lands. However, fundamental barriers to the industrial application of microalgae for biofuel production still include high costs of removing the algae from the water and the water from the algae which can account for up to 30-40% of the total cost of biodiesel production. Algal biofilms are becoming increasingly popular as a strategy for the concentration of microalgae, making harvesting/dewatering easier and cheaper.

RESULTS

We have isolated and characterized a number of natural microalgal biofilms from freshwater, saline lakes and marine habitats. Structurally, these biofilms represent complex consortia of unicellular and multicellular, photosynthetic and heterotrophic inhabitants, such as cyanobacteria, microalgae, diatoms, bacteria, and fungi. Biofilm #52 was used as feedstock for bioenergy production. Dark fermentation of its biomass by Enterobacter cloacae DT-1 led to the production of 2.4 mol of H₂/mol of reduced sugar. The levels and compositions of saturated, monosaturated and polyunsaturated fatty acids in Biofilm #52 were target-wise modified through the promotion of the growth of selected individual photosynthetic inhabitants. Photosynthetic components isolated from different biofilms were used for tailoring of novel biofilms designed for (i) treatment of specific types of wastewaters, such as reverse osmosis concentrate, (ii) compositions of total fatty acids with a new degree of unsaturation and (iii) bio-flocculation and concentration of commercial microalgal cells. Treatment of different types of wastewaters with biofilms showed a reduction in the concentrations of key nutrients, such as phosphates, ammonia, nitrates, selenium and heavy metals.

CONCLUSIONS

This multidisciplinary study showed the new potential of natural biofilms, their individual photosynthetic inhabitants and assembled new algal/cyanobacterial biofilms as the next generation of bioenergy feedstocks which can grow using wastewaters as a cheap source of key nutrients.

Simultaneous nitrogen, phosphorous, and hardness removal from reverse osmosis concentrate by microalgae cultivation

While reverse osmosis (RO) is a promising technology for wastewater reclamation, RO concentrate (ROC) treatment and disposal are important issues to consider. Conventional chemical and physical treatment methods for ROC present certain limitations, such as relatively low nitrogen and phosphorus removal efficiencies as well as the requirement of an extra process for hardness removal. This study proposes a novel biological approach for simultaneous removal of nitrogen, phosphorus, and calcium (Ca(2+)) and magnesium (Mg(2+)) ions from the ROC of municipal wastewater treatment plants by microalgal cultivation and algal biomass production. Two microalgae strains, Chlorella sp. ZTY4 and Scenedesmus sp. LX1, were used for batch cultivation of 14-16 days. Both strains grew well in ROC with average biomass production of 318.7 mg/L and lipid contents up to 30.6%, and nitrogen and phosphorus could be effectively removed with efficiencies of up to 89.8% and 92.7%, respectively. Approximately 55.9%-83.7% Ca(2+) could be removed from the system using the cultured strains. Mg(2+) removal began when Ca(2+) precipitation ceased, and the removal efficiency of the ion could reach up to 56.0%. The most decisive factor influencing Ca(2+) and Mg(2+) removal was chemical precipitation with increases in pH caused by algal growth. The results of this study provide a new biological approach for removing nitrogen, phosphorous, and hardness from ROC. The results suggest that microalgal cultivation presents new opportunities for applying an algal process to ROC treatment. The proposed approach serves dual purposes of nutrient and hardness reduction and production of lipid rich micro-algal biomass.

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 ∼ 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.