Removal of organic micropollutans by adsorptive membrane.

Various emerging organic micropollutants, such as pharmaceuticals, have attracted the interest of the water industry during the last two decades due to their insufficient removal during conventional water and wastewater treatment methods and increasing demand for pharmaceuticals projected to climate change-related impacts and COVID-19, nanosorbents such as carbon nanotubes (CNTs), graphene oxides (GOs), and metallic organic frameworks (MOFs) have recently been extensively explored regarding their potential environmental applications. Due to their unique physicochemical features, the use of these nanoadsorbents for organic micropollutans in water and wastewater treatment processes has been a rapidly growing topic of research in recent literature. Adsorptive membranes, which include these nanosorbents, combine the benefits of adsorption with membrane separation, allowing for high flow rates and faster adsorption/desorption rates, and have received a lot of publicity in recent years. The most recent advances in the fabrication of adsorptive membranes (including homogeneous membranes, mixed matrix membranes, and composite membranes), as well as their basic principles and applications in water and wastewater treatment, are discussed in this review. This paper covers ten years, from 2011 to 2021, and examines over 100 published studies, highlighting that micropollutans can pose a serious threat to surface water environments and that adsorptive membranes are promising, particularly in the adsorption of trace substances with fast kinetics. Membrane fouling, on the other hand, should be given more attention in future studies due to the high costs and restricted reusability.

A holistic approach for the recovery of rare earth elements and scandium from secondary sources under a circular economy framework - A review.

Limited natural resources and a continuous increase in the demand for modern technological products, is creating a demand and supply gap for rare earth elements (REEs) and Sc. There is therefore a need to adopt the sustainable approach of the circular economy system (CE). In this review, we defined six steps required to close the loop and recover REEs, using a holistic approach. Recent statistics on REEs and Sc demand and the number of waste generations are reported and studies on more environmentally friendly, economic, and/or efficient recovery processes are summarized. Pilot-scale recovery facilities are described for several types of secondary sources. Finally, we identify obstacles to closing the REE loop in a circular economy and the reasons why secondary sources are not preferred over primary sources. Briefly, recovery from secondary sources should be environmentally and economically friendly and of an acceptable standard concerning final product quality. However, current technologies for recovery from for secondary sources are limiting and technology needs will vary depending on the source type. The quality/purity of the recovered metals should be proven so that they do not result in any adverse effects on the product quality, when they are being used as secondary raw material. In addition, for industrial-scale facilities, process improvements are required that consider environmental conditions.

Separation of rare earth elements from mixed-metal feedstocks by micelle enhanced ultrafiltration with sodium dodecyl sulfate.

Micelle enhanced ultrafiltration (MEUF) is a surfactant-based membrane separation process that may be used to separate target ions from mixed metal aqueous solutions, such as leachates of coal ash and other geological wastewaters. The ability of MEUF to separate rare earth elements (REEs) was evaluated using sodium dodecyl sulfate (SDS) as the sorbent in surfactant micelle phase, which was subsequently separated using ultrafiltration, acidification, and ferricyanide precipitation. Separation experiments were performed with a synthetic coal ash leachate feedstock as an example mixed-metal feedstock. Experiments tested the influence of surfactant concentration, pH, and co-existing competitive ions on REE recoveries, and also tested methods for SDS recovery and reuse. Membrane rejection efficiencies of REEs were 97% and 71% respectively for synthetic and real leachate under optimized operating conditions. A two-step process of precipitation with CaCl2 and Na2CO3 following membrane separation was the best for recovering SDS with a yield of 99.7%.

Process optimization for acidic leaching of rare earth elements (REE) from waste electrical and electronic equipment (WEEE).

E-waste (EW) from discarded electrical and electronic devices is a potential source of rare earth elements (REEs) that might be recovered from urban and industrial wastes. REEs are essential raw materials for emerging and high technologies. China currently dominates global REE production with a proportion of 97%. To increase the independence of REE supply and eliminate the environmental impacts related to REE mining, methods for an efficient REE recovery from secondary sources like EW are needed. In this work, we examine improvements in pre-treatment and acidic leaching processes to recover REEs and other valuable metals. EW was crushed and ground prior to the sieving. The materials obtained were then subjected to acid leaching. The parameters used to optimize the conditions for leaching were as follows: acid type (HCl, HNO3, and aqua regia), particle size, and waste-to-acid ratio. The maximum leaching efficiency was obtained from the ground, sieved, and undersized part of e-waste by using HCl with a W:A of 12.5 mg/mL. The total REE concentration was 435 mg/kg. Several treatment scenarios are identified with promise for improving REE recovery at full scale in EW recovery plants and thereby advancing goals for a sustainable, circular economy.

Effect of solution chemistry on filtration performances and fouling potential of membrane processes for rare earth element recovery from red mud.

Rare earth elements or REEs are a vital and irreplaceable part of our modern technological and digital industries. Among the REEs that are the most critical to be recovered are Ce, La, and particularly, Nd, and Y, due to high demand and at a potential future supply risk. Innovative techniques must be considered to recover REEs from secondary resources. In this study, REEs are extracted from iron mining sludge from Central Anatolia in Turkey. Two different acid solutions were compared, one with a higher acid content (120 ml HCl and 80 ml HNO3 per liter) and one with lower acid content (20 ml HNO3 per liter). Nanofiltration, as a process to concentrate the acidic leachate and increase the REE concentration, was carried out at pH levels of 1.5, 2.5, and 3.5 and under 12, 18, and 24 bar operating pressures. SLM studies had been carried out using a PVDF membrane with a pore diameter of 0.45 µm, with three different carriers to separate the REEs from other major elements in the concentrated leachate. Through this analysis, the optimum operating conditions for nanofiltration are at pH 3.5 at 12 bar, using the leach with low acidity, achieving about 90% recovery efficiency of the REEs. SLM studies using 0.3M D2EHPA, with a 3-h reaction time, showed the highest mass flux values for the REEs. Nanofiltration and SLM represent novel methods of REE concentration and extraction from iron mining sludge.

Natural organic matter and sulphate elimination from rainwater with nanofiltration technology and process optimisation using response surface methodology.

In the current study, the effect of operating conditions including membrane characteristics and applied pressure on natural organic matter and sulphate removal of nanofiltration (NF) membranes for drinking water production was investigated. Water stress has been increasing all over the world due to population growth, climate change, and pollution; rainwater management stands out as one of the key solutions to this problem. Nanofiltration to treat rainwater stored in a cistern was studied. The objectives were sufficient treatment performance to overcome the taste problem and lower energy consumption. In this regard, three commercial nanofiltration membranes (NP010, NP030, and NF90) were used for the experiments carried out at 6-12 bar operating pressure regarding the response surface methodology. The correlation among the results of experiments and the model parameters were also calculated for all steps. According to the results, the effect of membrane characteristics was more abundant than the effect of the operating pressure. Finally, over 99% of natural organic matter and sulphate were eliminated in the optimum conditions. The results showed that it is possible to obtain treated rainwater with desired qualities, in a non-continuous NF plant operated at the pressure of 6 bar to reuse the rainwater and achieve water sustainability.

Long-term MBR performance of polymeric membrane modified with Bismuth-BAL chelate (BisBAL).

An ultrafiltration membrane prepared by polyethersulfone (PES) was modified with Bismuth-BAL chelate (BisBAL) and was used in submerged membrane bioreactor system. Moreover, a control membrane reactor was also tasked to evaluate the effect of BisBAL on the membrane performance. The flux profile, transmembrane pressure, the effect of chemical treatment, cake layer formation, anti-fouling properties against extracellular polymeric substances (EPS) and soluble microbial products (SMP) were studied. The UF modified membrane demonstrated a sustained permeability, low cleaning frequency, and longer filtration time. In terms of anti-EPS and SMP accumulation, the modified membrane showed a lower membrane resistance. It can be illustrated from scanning electron microscopy and confocal laser scanning microscope images that the modified membrane had presented better properties than bare PES membrane, as it was looser and thinner. Thus, the UF membrane proved to be more efficient in terms of permeability and lifetime.

Impact of salinity on the population dynamics of microorganisms in a membrane bioreactor treating produced water.

Biomass characteristics may change subject to a salinity increase when treating high strength wastewater. In this study, the impact of salinity in a membrane bioreactor (MBR) was investigated for the treatment of produced water (PW). MBR was operated as a pre-treatment prior to nanofiltration (NF) and reverse osmosis (RO). Mixed PW, that was originated from different oil, gas, and oil-gas wells, were subjected to pre-treatment for 146 days including three different operational phases: Low-salinity (~10 mS/cm), gradual increased salinity (10-40 mS/cm) and high salinity (~40 mS/cm). The results of this study showed that microorganisms could adapt using real wastewater and treat PW up to a certain level of the salinity. At high salinity levels of PW, the floc structure started to be disrupted and membrane fouling was accelerated. PCR-DGGE analysis confirmed the changes in microbial communities' composition in relation with high salinity. The results of the final treatment experiments presented that NF and RO treatment produced high-quality effluents that could be suitable for reuse.

Treatment of produced water originated from oil and gas production wells: a pilot study and cost analysis.

Produced water originated from oil and gas production wells was treated by a pilot-scale system including pre-treatment (chemical precipitation), pre-filtration, and post-filtration units. Pre-filtration unit consisted of sand filter, granulated activated carbon (GAC) filter, and ultrafiltration (UF) membrane. Post-filtration unit included reverse osmosis (RO) membrane unit. In this study, two different RO membranes including sea water (SW) and brackish water (BW) membranes were comparatively evaluated in terms of treatment and filtration performance. Besides, a cost analysis was conducted for a real scale RO membrane unit by using the data obtained from the pilot plant study. Average fluxes of 12.7 and 9.4 L/m2 h were obtained by SW and BW membrane units, respectively. Higher COD and conductivity removal efficiencies were obtained by SW membrane in comparison to BW membrane. Total cost of 0.88 €/m3 was estimated for a RO plant treating produced water with a flowrate capacity of 300 m3/d.