Final Report Summary - ACTIWATE (Advanced concentrate treatment for integrated membrane based water reuse systems)
ACTIWATE • Advanced concentrate treatment for integrated membrane based water reuse systems
Contract No.: PIOF-GA-2010-272584
PROJECT OBJECTIVES
In the context of water scarcity mitigation, high quality water reuse based on dense membrane treatment is expected to be progressively applied to provide the additional water resources required. Many countries started to invest in double membrane reclamation plants. However environmental concerns and the high costs associated with membrane concentrate management limit the application of high quality water reuse, especially in inland locations. State-of-the-art treatment relies on evaporation ponds, brine concentrators and crystallizers, discharge to the wastewater collection system, land application, deep well injection or discharge to surface waters. All available methods have serious shortcomings either from the environmental or the economic perspective.
The project aims at the investigation of integrated reverse osmosis (RO) and nanofiltration (NF) membrane concentrate treatment concepts with minimized costs and environmental impact. The volume of the concentrate streams typically ranges from 15 to 25% of the feed stream. High salinity alongside concentrated organic and inorganic toxic compounds pose danger to many plants and animals. Applying the sustainable Zero Liquid Discharge principle, the ACTIWATE project combines treatment methods for the removal of bulk and trace organics with a subsequent desalting system. The concentrate desalination is based on a low energy consuming and low fouling concentration step, such as forward osmosis (FO) or electrodialysis (ED), to significantly increase the salt concentration of the brine for precipitation of the salts and then use simple technologies like wind aided intensified evaporation as final stage for salt production (cf. Fig. 1, attachment).
The focus of the research is on the optimum removal of micropollutants and foulants affecting the desalting system to allow a complete recycle of the concentrate to the upstream process, such as wastewater treatment or effluent filtration.
The technological activities cover experimental and theoretical studies to investigate the most promising emerging concentrate treatment concepts and identify their technical feasibility, affordability and environmental sustainability. Feasible alternatives of organics removal and desalting processes with membranes, crystallization and energy saving drying or separation processes are evaluated.
WORK PERFORMED AND MAIN RESULTS
RO concentrate (ROC) samples were taken from two advanced dual membrane water recycling plants in Sydney, Australia. The presence of organic micropollutants and bulk organics in relevant and typical concentrations was confirmed. The concentration of dissolved organic carbon was about 25 to 45 mg/L mainly consisting of humic acids and building blocks as shown by liquid chromatography and organic carbon detection (LC-OCD). Typical poorly biodegradable pharmaceuticals such as carbamazepine, diclofenac, and sulfamethoxazole were detected in the ROC in concentrations of around 0.1 to 1 µg/L using liquid chromatography with mass spectroscopy detection after enrichment of the target compounds by solid phase extraction.
Organics removal: The removal of organics can be achieved through a number of treatment technologies, e.g. ozonation, advanced oxidation processes, adsorption and biological treatment. Tests with granular activated carbon with three different carbon types (two fresh carbons and one reactivate) revealed a rapid breakthrough of bulk organics after 2000 to 4000 bed volumes irrespective of the chosen carbon type. Trace organic compounds were adsorbed to significantly higher degree. Fresh mesoporous carbon was found to provide the best performance for the majority of micropollutants. Figure 2 (attachment) illustrates the differences between typical compound classes based on key properties such as charge and hydrophobicity. Positively charged and neutral compounds were removed very stably, in particular by the fresh carbon. Negatively charged pharmaceuticals however started to break through after 5000 bed volumes. Besides compound charge, hydrophobicty seems to play the main role in Adsorption: e.g. better adsorption of diclofenac (log D at pH 7.5: 0.74) than of sulfamethoxazole (log D at pH 7.5: • 1.51). Ozonation of ROC transforms the majority of micropollutants at a dose of 0.5 mgO3/mgDOC. Some compounds such as TCEP are critical in several treatment processes. Oxidative methods to partially break down bulk organics allow extending the carbon usage. They appear to be advantageous particularly in combination with biological activated carbon. A broad range of advanced oxidation methods and biological GAC have been tested earlier in other projects.
Brine concentration: Electrodialysis (ED) and forward osmosis (FO) have been investigated regarding desalination performance and susceptibility to fouling and scaling. Both processes proved to be applicable for brine concentration when the ROC pH is properly controlled and the water is softened to avoid scaling by carbonates. Phosphates should be removed in the main wastewater treatment prior to the RO treatment to minimize scaling by phosphates. Forward osmosis seems to be more stable under changing concentrations and feed water qualities than electrodialysis.
Fouling of ED and FO was studied with model solutes containing humic acid, alginate and bovine serum albumin representing the key foulants. Tests with synthetic RO concentrate and model foulants were compared to test with real RO concentrate. It was found that in FO fouling and scaling effects increased with flux supporting the idea of a “critical flux”. While organic fouling was removable by hydraulic flushing, scaling effects impaired the membrane performance significantly and were only partially removable by chemical cleaning. ED fouling tests revealed a strong impact of bulk organics such as humic acids on the desalination performance by reducing the ion transport and increasing the energy demand. Counter ions such as calcium appear to play a key role in stabilisation of polysaccharides, which were less fouling relevant than proteins and humics. FO and ED insufficiently retained organic micropollutants. Thus organic micropollutants require pre-treatment (e.g. by GAC) or post-treatment (e.g. by RO) for blending the FO permeate or ED diluate of the brine concentration process with the main stage RO permeate. Subsequent to ROC dewatering by ED or FO, thermal processes or advanced evaporative methods such as WAIV are required to achieve Zero Liquid Discharge. Several thermal concentration processes have been evaluated for industrial applications.
CONCLUSIONS
Zero Liquid Discharge is gaining importance in handling of municipal and industrial brine streams. Concentrates from water reclamation plants with dense membrane processes can be treated with a number of market available and emerging treatment trains. The composition of reverse osmosis concentrates is complex and challenges the technologies for brine concentration such as forward osmosis or electrodialysis. Trace organic compounds and bulk organics are present in elevated concentrations in reject streams from RO and NF up to 10 µg/L of the respective trace compound and 100 mg/L of DOC in total. Organic compounds have to be removed prior to the concentration and desalting units to avoid severe fouling and performance loss of the desalting units. Combinations of oxidative and adsorptive processes appear to be most promising, in particular ozonation followed by GAC. The preferred treatment method contains the following unit processes: ozone - granular activated carbon filtration - forward osmosis (with draw solution recovery by MD or NF) - evaporation by thermal or (intensified) natural processes such as thermal vapour compression/crystallization or WAIV (in dry climatic conditions). This treatment train allows a significant reduction of the energy demand of a conventional thermal brine concentration from around 30 kWh/m3 to below 10 kWh/m3 of RO concentrate.
Contact:
Dr. Christian Kazner
Senior Researcher
University of Applied Sciences and Arts Northwestern Switzerland
University of Technology Sydney
Tel: +41 61 467 43 04
christian.kazner@fhnw.ch
Website:.
http://cfsites1.uts.edu.au/research/strengths/ctww/actiwate.html
http://www.fhnw.ch/lifesciences/iec/forschungsfelder-und-projekte-en/umweltbiotechnologie-und-umwelttechnik/actiwate?set_language=en
Contract No.: PIOF-GA-2010-272584
PROJECT OBJECTIVES
In the context of water scarcity mitigation, high quality water reuse based on dense membrane treatment is expected to be progressively applied to provide the additional water resources required. Many countries started to invest in double membrane reclamation plants. However environmental concerns and the high costs associated with membrane concentrate management limit the application of high quality water reuse, especially in inland locations. State-of-the-art treatment relies on evaporation ponds, brine concentrators and crystallizers, discharge to the wastewater collection system, land application, deep well injection or discharge to surface waters. All available methods have serious shortcomings either from the environmental or the economic perspective.
The project aims at the investigation of integrated reverse osmosis (RO) and nanofiltration (NF) membrane concentrate treatment concepts with minimized costs and environmental impact. The volume of the concentrate streams typically ranges from 15 to 25% of the feed stream. High salinity alongside concentrated organic and inorganic toxic compounds pose danger to many plants and animals. Applying the sustainable Zero Liquid Discharge principle, the ACTIWATE project combines treatment methods for the removal of bulk and trace organics with a subsequent desalting system. The concentrate desalination is based on a low energy consuming and low fouling concentration step, such as forward osmosis (FO) or electrodialysis (ED), to significantly increase the salt concentration of the brine for precipitation of the salts and then use simple technologies like wind aided intensified evaporation as final stage for salt production (cf. Fig. 1, attachment).
The focus of the research is on the optimum removal of micropollutants and foulants affecting the desalting system to allow a complete recycle of the concentrate to the upstream process, such as wastewater treatment or effluent filtration.
The technological activities cover experimental and theoretical studies to investigate the most promising emerging concentrate treatment concepts and identify their technical feasibility, affordability and environmental sustainability. Feasible alternatives of organics removal and desalting processes with membranes, crystallization and energy saving drying or separation processes are evaluated.
WORK PERFORMED AND MAIN RESULTS
RO concentrate (ROC) samples were taken from two advanced dual membrane water recycling plants in Sydney, Australia. The presence of organic micropollutants and bulk organics in relevant and typical concentrations was confirmed. The concentration of dissolved organic carbon was about 25 to 45 mg/L mainly consisting of humic acids and building blocks as shown by liquid chromatography and organic carbon detection (LC-OCD). Typical poorly biodegradable pharmaceuticals such as carbamazepine, diclofenac, and sulfamethoxazole were detected in the ROC in concentrations of around 0.1 to 1 µg/L using liquid chromatography with mass spectroscopy detection after enrichment of the target compounds by solid phase extraction.
Organics removal: The removal of organics can be achieved through a number of treatment technologies, e.g. ozonation, advanced oxidation processes, adsorption and biological treatment. Tests with granular activated carbon with three different carbon types (two fresh carbons and one reactivate) revealed a rapid breakthrough of bulk organics after 2000 to 4000 bed volumes irrespective of the chosen carbon type. Trace organic compounds were adsorbed to significantly higher degree. Fresh mesoporous carbon was found to provide the best performance for the majority of micropollutants. Figure 2 (attachment) illustrates the differences between typical compound classes based on key properties such as charge and hydrophobicity. Positively charged and neutral compounds were removed very stably, in particular by the fresh carbon. Negatively charged pharmaceuticals however started to break through after 5000 bed volumes. Besides compound charge, hydrophobicty seems to play the main role in Adsorption: e.g. better adsorption of diclofenac (log D at pH 7.5: 0.74) than of sulfamethoxazole (log D at pH 7.5: • 1.51). Ozonation of ROC transforms the majority of micropollutants at a dose of 0.5 mgO3/mgDOC. Some compounds such as TCEP are critical in several treatment processes. Oxidative methods to partially break down bulk organics allow extending the carbon usage. They appear to be advantageous particularly in combination with biological activated carbon. A broad range of advanced oxidation methods and biological GAC have been tested earlier in other projects.
Brine concentration: Electrodialysis (ED) and forward osmosis (FO) have been investigated regarding desalination performance and susceptibility to fouling and scaling. Both processes proved to be applicable for brine concentration when the ROC pH is properly controlled and the water is softened to avoid scaling by carbonates. Phosphates should be removed in the main wastewater treatment prior to the RO treatment to minimize scaling by phosphates. Forward osmosis seems to be more stable under changing concentrations and feed water qualities than electrodialysis.
Fouling of ED and FO was studied with model solutes containing humic acid, alginate and bovine serum albumin representing the key foulants. Tests with synthetic RO concentrate and model foulants were compared to test with real RO concentrate. It was found that in FO fouling and scaling effects increased with flux supporting the idea of a “critical flux”. While organic fouling was removable by hydraulic flushing, scaling effects impaired the membrane performance significantly and were only partially removable by chemical cleaning. ED fouling tests revealed a strong impact of bulk organics such as humic acids on the desalination performance by reducing the ion transport and increasing the energy demand. Counter ions such as calcium appear to play a key role in stabilisation of polysaccharides, which were less fouling relevant than proteins and humics. FO and ED insufficiently retained organic micropollutants. Thus organic micropollutants require pre-treatment (e.g. by GAC) or post-treatment (e.g. by RO) for blending the FO permeate or ED diluate of the brine concentration process with the main stage RO permeate. Subsequent to ROC dewatering by ED or FO, thermal processes or advanced evaporative methods such as WAIV are required to achieve Zero Liquid Discharge. Several thermal concentration processes have been evaluated for industrial applications.
CONCLUSIONS
Zero Liquid Discharge is gaining importance in handling of municipal and industrial brine streams. Concentrates from water reclamation plants with dense membrane processes can be treated with a number of market available and emerging treatment trains. The composition of reverse osmosis concentrates is complex and challenges the technologies for brine concentration such as forward osmosis or electrodialysis. Trace organic compounds and bulk organics are present in elevated concentrations in reject streams from RO and NF up to 10 µg/L of the respective trace compound and 100 mg/L of DOC in total. Organic compounds have to be removed prior to the concentration and desalting units to avoid severe fouling and performance loss of the desalting units. Combinations of oxidative and adsorptive processes appear to be most promising, in particular ozonation followed by GAC. The preferred treatment method contains the following unit processes: ozone - granular activated carbon filtration - forward osmosis (with draw solution recovery by MD or NF) - evaporation by thermal or (intensified) natural processes such as thermal vapour compression/crystallization or WAIV (in dry climatic conditions). This treatment train allows a significant reduction of the energy demand of a conventional thermal brine concentration from around 30 kWh/m3 to below 10 kWh/m3 of RO concentrate.
Contact:
Dr. Christian Kazner
Senior Researcher
University of Applied Sciences and Arts Northwestern Switzerland
University of Technology Sydney
Tel: +41 61 467 43 04
christian.kazner@fhnw.ch
Website:.
http://cfsites1.uts.edu.au/research/strengths/ctww/actiwate.html
http://www.fhnw.ch/lifesciences/iec/forschungsfelder-und-projekte-en/umweltbiotechnologie-und-umwelttechnik/actiwate?set_language=en