Beneficial Reuse Research Articles

BiVO<sub>4</sub>/MnO<sub>2</sub> Composite Photocatalytic Material for the Shale Gas Flowback Wastewater Treatment

The management and disposal of the shale gas flowback wastewater is one of the greatest challenges associated with the exploration and extraction of unconventional natural gas resources. High salinity and complex chemical composition of fracturing fluids are the main limiting factors for beneficial reuse of the shale gas flowback wastewater, which has become a tough problem in the global environmental field. In this study, a composite photocatalytic oxidant of MnO2 modified BiVO4 was successfully synthesized with one-step hydrothermal method, and used to treat the shale gas flowback wastewater. The synergistic effect of photocatalysis and oxidation has made a great contribution to the removal of COD value in wastewater. When catalyst dosage was 0.6 g, the pH value was controlled to 3, and visible light exposure was 4 h, the prepared BiVO4/MnO2 exhibited the optimum photocatalytic oxidation activity, and the removal efficiency of COD could reach 65.5%, which is better than that of pure BiVO4 or MnO2. Furthermore, in this case, the COD value could be decreased from 188 mg/L to 64.9 mg/L, complying with the first-level standard limit requirements in the integrated wastewater discharge standard (GB8978-1996). Moreover, in the viewpoint of dynamics, Langmuir isothermal-like equation can better describe the relationship between COD removal efficiency and illumination time.

Constructed wetlands for polishing oil and gas produced water releases.

Produced water (PW) is the largest waste stream associated with oil and gas (O&G) operations and contains petroleum hydrocarbons, heavy metals, salts, naturally occurring radioactive materials and any remaining chemical additives. In some areas in Wyoming, constructed wetlands (CWs) are used to polish PW downstream of National Pollutant Discharge Elimination System (NPDES) PW release points. In recent years, there has been increased interest in finding lower cost options, such as CWs, for PW treatment. The goal of this study was to understand the efficacy of removal and environmental fate of O&G organic chemical additives in CW systems used to treat PW released for agricultural beneficial reuse. To achieve this goal, we analyzed water and sediment samples for organic O&G chemical additives and conducted 16S rRNA gene sequencing for microbial community characterization on three such systems in Wyoming, USA. Three surfactants (polyethylene glycols, polypropylene glycols, and nonylphenol ethoxylates) and one biocide (alkyldimethylammonium chloride) were detected in all three PW discharges and >94% removal of all species from PW was achieved after treatment in two CWs in series. These O&G extraction additives were detected in all sediment samples collected downstream of PW discharges. Chemical and microbial analyses indicated that sorption and biodegradation were the main attenuation mechanisms for these species. Additionally, all three discharges showed a trend of increasingly diverse, but similar, microbial communities with greater distance from NPDES PW discharge points. Results of this study can be used to inform design and management of constructed wetlands for produced water treatment.

Ozonation-assisted electro-membrane hybrid reactor for oily wastewater treatment: A methodological approach and synergy effects

Abstract Wastewater produced from oil and gas industries contains high levels of organic and inorganic pollutants in the form of emulsions sized below 10 μm. The beneficial reuse of oily wastewater requires advanced treatment methods to remove these emulsions and promote cleaner production. This work has attempted to investigate the hybridization of electrocoagulation (EC) process, ceramic microfiltration membrane, and ozonation as a one-pot solution for the treatment of oily wastewater. The variables in this study included hydraulic retention time (HRT), aeration, current density (CD), mode of power supply, and initial pH of the sample. Aerated electro-membrane reactor contributed to a maximum COD reduction of 18.0% as opposed to 53.1% for the ozonated reactor. The effectiveness of the novel hybrid reactor could be attributed to the enhancement of electrocoagulation process by the ozone, which facilitated size-exclusion by the submerged membrane. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were performed to characterize the generated foam, electrodes, and sludge. The present findings indicate that the ozonation-assisted electro-membrane hybrid method has the potential to be employed for the treatment of oily wastewater.

Evaluation of sequencing batch bioreactor followed by media filtration for organic carbon and nitrogen removal in produced water

Produced water contains high concentrations of total dissolved solids (TDS), metals, and organic matter. In areas of high water stress, beneficial reuse of produced water needs to be considered. This study evaluates the treatment capabilities, efficiency, and limitations of a sequencing batch reactor (SBR) to remove organic material and nutrients from produced water. SBRs have been used to facilitate biological organic and nutrient removal from municipal and industrial waste streams. Although the bacteria responsible for the treatment of municipal and most industrial wastewaters cannot tolerate the high TDS concentrations in produced water, the microorganisms native to produced water have the capacity to treat produced water. In a bench scale bioreactor test using produced water from the Denver-Julesburg Basin, the produced water was determined to be nutrient limited with respect to phosphorus. By adding a phosphorus supplement, soluble chemical oxygen demand (COD) removal was increased by over 20 % and ammonia removal increased by approximately 40 %. Various supplements, including KH2PO4, centrate from an anaerobic digester, and activated sludge from a municipal SBR, were added to the bioreactors to determine which of them was more effective. A pilot scale SBR followed by media filtration was used to evaluate the effects of operating conditions on produced water treatment. The hydraulic residence time ranged from 1.67 to 8.3 days during various phases of operation, with no measured effect on treatment performance. Adding 7.5 mg-P/L of KH2PO4 as a phosphorus supplement had the most significant effect on treatment performance of the system. The majority of COD removal switched locations from the filter columns to the bioreactors. Comparing total organic carbon to COD, the biologically available portion of COD appears to be treated in the SBR while recalcitrant carbon and inorganic material may need to be removed via physical or chemical methods.

Sludge management in water treatment plants: literature review

Due to the increased environmental concern; there is a considerable pressure on the water authorities for the safe treatment and disposal of sludge. It is very important to choose a suitable sludge treatment and disposal system, which is both economical and technically feasible. In this article, sludge characteristics, quantities and sources will be outlined. A detailed sludge management and treatment methods will be presented. Sludge reuse, incineration, landfilling and disposal were also considered. The study concluded that sludge management should be considered when designing and operating WTPs, adopting beneficial reuse options of sludge will become very essential and it is necessary to investigate the appropriate options for formulating long term sludge management plans under strict environmental regulations. The study recommended that sludge must be treated and disposed of in a safe and effective manner. Great emphasis is to be enforced to minimise the quantity of generated sludge, more studies should be conducted to develop suitable sludge management plans, when applying sludge reuse in agricultural purposes it is highly recommended to investigate the long term effects of sludge reuse, and finally the environmental impacts of different of sludge disposal methods should be evaluated.

Bio-modification of coal fly ash using urease-producing bacteria

Due to its potential for metal leaching and the corresponding environmental impacts, the beneficial reuse of coal fly ash in construction has been carefully evaluated. Biological processing may provide a promising technology to modify coal ash to limit metal leaching. The goal of this study was to use urease-producing bacteria to modify coal fly ash and to evaluate the effect on metal leaching. Metal leaching was investigated through synthetic precipitate leaching processes by three types of coal fly ash before and after bio-modification. For metals like Al, Ba, and Cr, the leaching concentrations decreased after bio-modification, whereas the leaching concentrations increased for metals such as Ca, Mg, Mn and V. The increase of pH and the production of carbonate by the consumption of urea and the adsorption to precipitation compounds during the bio-modification process contributed the stabilization of Al, Ba and Cr. However, the bio-leaching induced by the organic products from bacteria and potentially the competition for carbonates promoted the leaching of Ca, Mg, Mn and V which would benefit the recycle of metals. Bioprocessed coal fly ash and sand mixtures were utilized to prepare construction materials. The unconfined compressive and flexural strength supports beneficial uses of coal fly ash with bio-modification.

Decentralised, small-scale coagulation-membrane treatment of wastewater from metal recycling villages - a case study from Vietnam.

Effective treatment of wastewaters laden with heavy metals is critical to the sustainable social and economic growth of metal recycling villages in Vietnam. Currently, most wastewaters from metal recycling villages in Vietnam are directly discharged, posing great threats to the environment and human health. In this study, a small-scale combined coagulation-membrane filtration treatment of wastewater collected from a metal recycling village in Vietnam was experimentally investigated. The experimental results manifested the technical viability of the combined coagulation-membrane filtration process for the treatment of the heavily polluted metal recycling wastewater for beneficial reuse. In this combined treatment process, coagulation using ferric chloride (FeCl2) served as a pre-treatment prior to the microfiltration (MF)/reverse osmosis (RO) process. Under the optimised conditions, coagulation at the dosage of 0.2 g FeCl2 per 1,000 ml wastewater removed more than 90% of heavy metals (i.e. most notably including aluminium and chromium) from the wastewater, reducing the aluminium and chromium concentrations in the wastewater from 548.0 to 52.3 mg/L to 32.6 and 1.7 mg/L, respectively. The MF treatment of the wastewater following the coagulation further removed suspended solids and organic matters, rendering the wastewater safe for the subsequent RO filtration with respect to membrane fouling. Given the efficient pre-treatment of coagulation and MF, the RO process at the controlled water recovery of 50% was able to effectively treat the wastewater to potable water.

Removal and formation of perfluoroalkyl substances in Canadian sludge treatment systems – A mass balance approach

Poly- and per-fluoroalkyl substances (PFAS) are an emerging class of anthropogenic contaminants whose occurrence has raised concerns with the beneficial reuse of biosolids from wastewater treatment. This study evaluated the behavior of thirteen PFAS in nine Canadian sludge treatment systems including pelletization, alkaline stabilization, aerobic and anaerobic digestion processes. The composition of the overall PFAS-fluorine (ΣPFAS-F) loading in a system fed with only primary sludge was dominated by perfluorodecanoate (PFDA), whereas systems with blended primary and waste activated sludge feeds had a mix of short and long chain PFAS in raw sludges and treated biosolids. An increase in average ΣPFAS-F mass flow was observed through pelletization (19% formation) and alkaline stabilization (99% formation) processes indicating negative removal or contaminant formation. One of the two aerobic digestion systems and three of the five anaerobic digestion systems showed modest reductions (< 40% removal) in ΣPFAS-F loading. Long chain PFAS such as perfluorodecanoate (PFDA) and perfluorooctane sulfonate (PFOS) exhibited a wide variation in behavior ranging from substantial formation (> 75% formation) to modest removal (42% removal) in the surveyed systems while short chain perfluoropentanoate (PFPeA) mass flows increased through the three systems where they occurred. Overall, the contaminant mass balances revealed that there were significant changes in mass flows of the target PFAS through all kinds of sludge treatment systems. The results of this study on PFAS fate through sludge processing can inform future global PFAS risk management activities as well as sludge treatment considerations.

Treatment of environmental contamination using sepiolite: current approaches and future potential

To evaluate the potential of sepiolite-based materials to resolve environmental pollution problems, a study is needed which looks at the whole life cycle of material application, including the residual value of material classified as waste from the exploitation of sepiolite deposits in the region or from its processing and purification. This would also maximize value from the exploitation process and provide new potential for local waste management. We review the geographical distribution of sepiolite, its application in the treatment of potentially toxic elements in soil and across the wider landscape, an assessment of modification and compositional variation of sepiolite-based applications within site remediation and wastewater treatment. The potential of sepiolite-based technologies is widespread and a number of processes utilize sepiolite-derived materials. Along with its intrinsic characteristics, both the long-term durability and the cost-effectiveness of the application need to be considered, making it possible to design ready-to-use products with good market acceptance. From a critical analysis of the literature, the most frequently associated terms associated with sepiolite powder are the use of lime and bentonite, while fly ash ranked in the top ten of the most frequently used material with sepiolite. These add improved performance for the inclusion as a soil or wastewater treatment options, alone or applied in combination with other treatment methods. This approach needs an integrated assessment to establish economic viability and environmental performance. Applications are not commonly evaluated from a cost–benefit perspective, in particular in relation to case studies within geographical regions hosting primary sepiolite deposits and wastes that have the potential for beneficial reuse.

Waterworks Sludge: An Underrated Material for Beneficial Reuse in Water and Environmental Engineering

Waterworks sludge refers to the inevitable suspended and dissolved solids produced during the water purification process when producing tap water where Al-salt and/or Fe-salt are used as coagulant worldwide. Waterworks sludge is dewatered and the resultant cakes have been treated as “waste” for landfill as their major final disposal solution for a long time in practice. As waterworks sludge is the residual of potable water treatment process, it is not harmful and without toxic elements such as heavy metals in most cases in comparison to sewage sludges for instance. Actually, waterworks sludge is an underrated material with huge potential for beneficial reuse as raw material in water and environmental engineering. However, little was significantly progressed on this topic until the last two decades. Research and development (R&D) with special interest and focus on waterworks sludge reuse was conducted in our group in the last 15 years and this paper reports and discusses the main work and its novel application profile. Overall, it is believed that the R&D of waterworks sludge is useful and will help to develop national strategy of the entire waterworks sludge management, allowing its transformation from a “waste” into value-added products, and thus contribute to sustainable development.

A Geospatial Database for Effective Mine Rehabilitation in Australia

The Australian landscape is affected by abandoned mines that pose environmental, public health and safety risks. To promote the beneficial reuse, rehabilitation and/or remediation of these sites and understand their spatial arrangement, we compiled, classified and analysed a country-wide geospatial database of all known inactive hard rock mine sites. Following extensive review and classification of disparate records of such sites that have been terminated, neglected or classified as heritage, plus those under care and maintenance in Australia, we assessed state-by-state reporting and cross-border rehabilitation requirements. This was enabled by the development of the Mining Incidence Documentation &amp; Assessment Scheme (MIDAS) that can be used to catalogue and compare active or inactive mine data regardless of reporting conventions. At a national level, and with four case studies, we performed GIS-based spatial analyses and environmental risk assessments to demonstrate potential uses of our database. Analyses considered the proximity of sites to factors such as infrastructure and sensitive environmental receptors. As Australia struggles to manage the ongoing technical, socioeconomic and environmental challenges of effective mine rehabilitation, the insights enabled by this national-level spatial database may be key to developing coordinated responses that extend beyond state boundaries. Our classification and methodology are easily transferable, thereby encouraging more formalized, systematic and widespread documentation of abandoned mines worldwide.

Algae-Based Beneficial Re-use of Carbon Emissions Using a Novel Photobioreactor: a Techno-Economic and Life Cycle Analysis

Despite the many advantages of microalgae, the feasibility of large-scale cultivation requires significant amounts of carbon dioxide (CO2) to enable high growth rates. A synergistic union typically proposed for the supply of CO2 is the coupling of algal cultivation with emissions from power plants. This study investigates the sustainability of a novel microalgae platform coupled with coal-based flue gas. The proposed system consists of a novel photobioreactor (PBR) for the production of biomass followed by a two-stage dewatering process. A systems model, which quantifies the CO2 and energy consumption of the proposed system, was developed, and the minimum biomass selling price (MBSP) was determined by a techno-economic analysis (TEA). TEA results indicate that a facility with the capacity to capture 30% of the emissions from a 1-MW power plant requires a biomass production of 1280 metric ton per year, which when scaled to a nth of kind facility can produce biomass at a MBSP of $2322 per ton. The environmental impact of the proposed facility was determined by a life cycle assessment methodology, and results indicate a carbon capture potential of 1.16 × 104 metric tons of CO2 equivalent. In addition, an energy analysis indicates a desirable net energy ratio of 0.1, which is lower than conventional PBRs. Discussion focuses on the requirements to reduce biomass production cost, including research investment areas for increasing productivity while decreasing energy requirements.

Barriers and opportunities for beneficial reuse of sediment to support coastal resilience

As urbanization and climate change alter sediment fluxes, relative sea level, and coastal erosion around the world, management of sediment as a resource is increasingly important. Sediment is needed to enhance marsh accretion rates, raise the grade elevation of development, and build up beaches and dunes. Beneficial reuse of sediment refers to the repurposing of local sources of sediment for these applications, material typically available from dredging or sediment capture infrastructure, and represents a more sustainable approach compared to the status-quo involving transport to and from distant locations. However, in many locations, beneficial reuse remains a concept or is constrained to small-scale applications. In this paper, we draw on interviews with coastal sediment managers and regulators in Southern California to identify barriers to beneficial reuse and opportunities to overcome them. Interviewees reported numerous regulatory, technical, psychological, financial, and interorganizational barriers in their watersheds and regions. By highlighting these barriers, we aim to identify systemic changes that would make beneficial reuse a realistic and accessible option for Southern California and elsewhere. Most prominently, a more flexible regulatory framework that allows sediment management practices to adapt over time, pilot studies to understand how beneficial reuse works in various settings, and educational programs for regulators and the public could make beneficial reuse a more widespread approach.

Effects of aging of ferric-based drinking water sludge on its reactivity for sulfide and phosphate removal

Recent studies demonstrated the practical potential of multiple beneficial reuse of ferric-rich drinking water sludge (ferric DWS) for sulfide and phosphate removal in wastewater applications. In practice, ferric DWS is often stored on-site for periods ranging from days to several weeks (or even months), which may affect its reuse potential through changes in iron speciation and morphology. In this study, we investigated for the first time the impact of ferric DWS ‘aging’ time on the iron speciation and morphology and its subsequent impact on its reactivity and overall sulfide and phosphate removal capacity. A series of coagulation tests were conducted to generate ferric DWS of a practically relevant composition by using raw influent water from a full-scale drinking water treatment plant (DWTP). A comparison with ferric DWS from 8 full-scale DWTPs confirmed the similitude. The presence of akaganeite (β-FeOOH) was detected in ferric DWS (through XRD analyses), independent of the DWS storage time. However, the morphology of akaganeite changed over time from a predominant poorly-crystalline phase in ‘fresh’ DWS (8 ± 0.1% of total Fe) to a highly crystalline phase (76 ± 3% of total Fe) at a sludge aging time of 30 days which was confirmed by means of Rietveld refinement in XRD analyses (n = 3). Subsequent batch tests showed that its sulfide removal capacity decreased significantly from 1.30 ± 0.02 mmol S/mmol Fe (day 1) to 0.60 ± 0.01 (day 30), a decrease of 54 % (p < 0.05). The level of crystallinity however had no impact on sulfide removal kinetics, most sulfide being removed within 10 minutes. Upon aeration of sulfide-loaded ferric DWS in activate sludge, amorphous iron oxides species were formed independent of the initial DWS crystallinity which resulted in efficient P removal at capacities similar to that of conventional FeCl3 dosing.

The Fate of Mud Nourishment in Response to Short-Term Wind Forcing

In this study, results from a realistic 3D hydrodynamic and sediment transport model, applied to a channel in the Dutch Wadden Sea, are analyzed in order to assess the effect of short-term wind forcing, the impact of fresh water effects, and the variability induced by the spring-neap cycle on the transport of suspended sediment. In the investigated region, a pilot study for sediment nourishment, the so-called Mud Motor, is executed. This project aims for the beneficial re-use of dredged harbor sediments through the disposal of these sediments at a location where natural currents are expected to transport them toward a nearby salt marsh area. The model results presented in this study advance the understanding of the driving forces that determine sediment transport in shallow, near-coastal zones, and can help to improve the design of the Mud Motor. In the investigated channel, which is oriented parallel to the coastline, tidal asymmetries generally drive a transport of sediment in flood direction. It was found that already moderate winds along the channel axis reverse (wind in ebb direction), or greatly enhance this transport, up to an export of sediment over the adjacent water shed (wind in flood direction). The most beneficial wind conditions (moderate westerly winds) can cause an accumulation of more than 90% of the initial 200 tons sediment pool on the intertidal area; during less favorable conditions (northeasterly winds), less than a third of the dumped sediment is transported onto the mudflat. On-shore winds induce a transport toward the coast. Surprisingly, sediment pathways are only sensitive to the exact disposal location in the channel during wind conditions that counteract the tidally driven transport, and freshwater effects play no significant role for the dispersal of sediment.

Process design of coal seam gas associated water treatment plants to facilitate beneficial reuse

This study used computer simulation to select appropriate process designs to make coal seam gas (CSG) associated water comply with beneficial reuse regulations. The hypothesis was that computational simulation may predict the unit operations required for treatment of CSG associated water over a wide range of salinities. AqMB software facilitated complete analysis of water treatment from initial storage pond to final pH and sodium adsorption ratio (SAR) adjustment. Three samples of CSG associated water ranging from 3650 to 22123 mg/L total dissolved solids content were evaluated. Common to each process design was a settling pond, coarse & fine filtration, softening, anti-scalant addition, and reverse osmosis. When the water hardness was very hard, then a lime softening system may be required. Both microfiltration and ultrafiltration were considered, and in both cases the level of suspended solids was reduced to close to zero. Sodium exchanged WAC resin removed the majority of alkaline earth ions and inhibited downstream scale formation. The presence of substantial alkalinity was addressed by use of acid exchanged WAC resin in combination with an air stripper. However, process economics indicated this option was not favourable. A two-stage Reverse Osmosis system not only recovered from ca. 74–79 % water with all CSG associated water types but also the water quality was compliant with beneficial reuse regulations. The computer predictions mirrored actual data from operating industry sites.

Increasing net water recovery of reverse osmosis with membrane distillation using natural thermal differentials between brine and co-located water sources: Impacts at large reclamation facilities

Maximizing water recovery and minimizing the volume of RO concentrate (i.e., brine) produced is a growing challenge, especially for inland communities that lack ocean disposal options. In such regions, transitioning towards zero liquid discharge (ZLD) can avoid detrimental impacts associated with salt disposal via regional sewer discharge or deep-well injection. On-site ZLD energy requirements are proportional to the RO brine flowrate. Thus, system-level strategies that reduce RO brine flows will lower ZLD costs while simultaneously increasing the overall water recovery for beneficial reuse in reclamation facilities. We investigated a membrane distillation (MD) system operating using co-located, cooler source water to treat warmer wastewater RO brine. Using experimentally-quantified MD fluxes based on observed monthly water temperatures of co-located water and RO brine at a facility in central Arizona, and based on the previously reported performance of large-scale MD systems, energy consumption and operating cost were estimated to evaluate the potential capabilities of MD to treat RO brine at full scale facilities. When the RO unit was combined with MD brine treatment, net water recovery at the full-scale facility can increase from 85% to up to 91% while brine flow can be reduced by 26%. A 25% lower thermal energy was required to achieve RO net water recovery of 95% when using co-located water, compared against conventional MD without using co-located water. Overall, this work demonstrates the potential to use local thermal gradients to reduce RO brine volumes, thereby reducing ZLD costs.

Techno-Economic Analysis of RO Desalination of Produced Water for Beneficial Reuse in California

There is approximately 508.7 million cubic meters (3.2 million barrels) of oilfield-produced water generated per year across the oil fields of California. While less than 2% of this produced water receives advanced treatment for beneficial reuse, changing regulations and increasing scarcity of freshwater resources is expected to increase the demand for beneficial reuse. This paper reviews onshore-produced water quality across California, relevant standards and treatment objectives for beneficial reuse, identifies contaminants of concern, and treatment process design considerations. Lastly, we evaluate the capital and operating costs of an integrated membrane system for treating produced water based on data from a field pilot conducted in the coastal region of California.

Membrane Distillation for Strategic Water Treatment Applications: Opportunities, Challenges, and Current Status

Membrane distillation (MD) has been known as a promising water treatment process for many years. However, despite its advantages, MD has never been able to compete with other processes for industrial water treatment and supply. Instead, it has been orientated towards several unique strategic water treatment applications. This review aims to uncover the opportunities and technical challenges pertinent to the MD process and the current status of its strategic water treatment applications most notably including decentralised small-scale desalination for fresh water provision in remote areas, hybridisation with forward osmosis (FO) for treatment of challenging polluted waters, regeneration of liquid desiccant solutions for air conditioning, and treatment of acid effluents for beneficial reuse. Pilot and small-scale MD systems have been demonstrated for decentralised desalination using various renewable energy sources to supply fresh water in remote, rural areas and on ships where other desalination processes are inefficient or unfeasible. For this strategic desalination application, MD is technically viable, but more works on configuration modification and process optimisation are required to reduce the process energy consumption and water production costs. For the three other strategic applications, the technical viability of the MD process has been proved by extensive lab-scale researches, but its economic feasibility is still questionable due to the lack of large-scale evaluation and the uncertain costs of MD systems. The orientation of MD towards strategic water treatment applications is clear. However, huge efforts are required to facilitate these applications at commercial and full scale.

Beneficial reuse of treated municipal wastewater and flue gas carbon dioxide via combined ion exchange

Combined ion exchange (CIX) treatment of wastewater effluent and ion-exchange regeneration using flue gas carbon dioxide (CO2) was investigated as a way of beneficially joining the water and energy sectors. CIX treatment removed calcium, magnesium, sulfate, nitrate, phosphate, and dissolved organic carbon from wastewater effluent. Regeneration of CIX using sodium chloride, sodium bicarbonate, hydrochloric acid, and CO2 was investigated. Carbon dioxide had a lower regeneration efficiency compared with the other regeneration solutions. Alternative CO2 regeneration conditions were evaluated to gain insight on the effects of increased gas pressure, increased contact time, and increased rate of CO2 dissolution on regeneration efficiency.