Reverse Osmosis Retentates Research Articles

Removal of contaminants of emerging concern from secondary-effluent reverse osmosis retentates by continuous supercritical water oxidation- parametric study and conceptual design

The continuous removal of TOC and the degradation efficiency of carbamazepine and 17β-estradiol were investigated using actual secondary municipal-effluent RO-retentate solutions. A specific set of operating parameters were applied within the supercritical water oxidizing conditions: temperature range 420–480 °C, 25.1 MPa, hydraulic retention time (HRT) of 1–2 min, excess oxidant molar-ratio of 3–10 and presence of a homogenous catalyst (IPA) at 50–100 mg/L. > 99% organic carbon mineralization, along with complete degradation of model pollutants, was observed at 450 °C/1 min/OC= 5–10 and 100 mgIPA/L. The outlet estrone concentration, 1.03 ± 1.14 ng/L, representing estrogenic pollutants, dropped to the "no effect" range. A model for a SCWO plant treating secondary-municipal-effluent-RO-retentate for a city of 100,000 capita-equivalent was developed, based on a shell & tube SCWO flow reactor, showing > 75% energy-efficiency. The model yielded that for the extreme case of a zero caloric-value feed-solution, the total OPEX and CAPEX would be < $6.0 ± 2.5 per m3 of secondary effluents, i.e., two orders of magnitude lower than the reported environmental shadow-price associated with CECs (contaminants of emerging concern). Further work is required on the continuous and efficient separation of the salt-matrix, which can lead to higher overall heat transfer coefficients and enable further reduction in capital costs.

Gypsum Seeding to Prevent Scaling

Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum crystallization before any other species. This results in gypsum scaling on the cooled surfaces of the crystallizer, which is undesirable as it retards heat transfer rates and hence reduces the yield of other products. The aim of this study was to investigate and understand gypsum crystallization and gypsum scaling in the presence of gypsum seeds. Synthetic brine solutions were used in this research because they allowed an in-depth understanding of the gypsum bulk crystallization process and scaling tendency without the complexity of industrial brines. A cooled, U-shaped stainless-steel tube suspended in the saturated solution was employed as the scaling surface. This was because a tube-shaped surface enabled the introduction of a constant temperature cold surface in the saturated solution and most industrial EFC crystallizers are constructed from stainless steel. Gypsum seeding was effective in decreasing the mass of scale formed on the heat transfer surface. The most effective seed loading was 0.25 g/L, which reduced scale growth rate by 43%. Importantly, this seed loading is six times the theoretical critical seed loading. The seeding strategy also increased the gypsum crystallization kinetics in the bulk solution, which resulted in an increase in the mass of gypsum product. These findings are relevant for the operability and control of EFC processes, which suffer from scaling problems. By using an appropriate seeding strategy, two problems can be alleviated. Firstly, scaling on the heat transfer surface is minimised and, secondly, seeding increases the crystallization kinetics in the bulk solution, which is advantageous for product yield and recovery. It was also recommended that the use of silica as a seed material to prevent gypsum scaling should be investigated in future studies.

A cascade microfiltration and reverse osmosis approach for energy efficient concentration of skim milk

Abstract To improve the efficiency of water removal from skim milk, a cascade membrane process of microfiltration and reverse osmosis (RO) was developed whereby skim milk was concentrated to 18% dry matter (DM) by RO at either 15 or 50 °C. The average flux of the RO process at 50 °C was 89% higher than that observed at 15 °C, linked to altered membrane surface fouling behaviour due to lower viscosity, higher cross-flow velocity and increased diffusivity of the solvent phase. In corollary, a ~57% energy reduction per unit volume of water removed was observed when the RO process was operated at 50 °C. Evaluation of the physicochemical properties of control (9% DM content skim milk) and RO retentates post-heating (at 80, 90 and120 °C) and post-evaporation (to 42% DM) demonstrated a clear relationship between heating at elevated DM contents and solution viscosity, an effect that was compounded at higher heating temperatures.

A novel hybrid concept for implementation in drinking water treatment targets micropollutant removal by combining membrane filtration with biodegradation

Groundwater extracted for drinking water production is commonly treated by aeration and sand filtration. However, this simple treatment is typically unable to remove pesticide residues. As a solution, bioaugmentation of sand filter units (i.e., the addition of specific degrader strains) has been proposed as an alternative “green” technology for targeted pesticide removal. However, the introduced degraders are challenged by (i) micropollutant levels of target residue, (ii) the oligotrophic environment and (iii) competition and predation by the native microorganisms, leading to loss of population and degradation potential. To overcome these challenges, we propose the introduction of a novel hybrid treatment step to the overall treatment process in which reverse osmosis filtration and biodegradation are combined to remove a target micropollutant. Here, the reverse osmosis produces a concentrated retentate that will act as a feed to a dedicated biofilter unit, intended to promote biodegradation potential and stability of an introduced degrader. Subsequently, the purified retentate will be re-mixed with the permeate from reverse osmosis, for re-mineralization and downstream consumption. In our study, we investigated the effect of reverse osmosis retentates on the degradation potential of an introduced degrader. This paper provides the first promising results of this hybrid concept using the 2,6-dichlorobenzamide (BAM)-degrading bacteria Aminobacter sp. MSH1 in batch experiments, spiked with radiolabeled BAM. The results showed an increased degradation potential of MSH1 in retentate waters versus untreated water. Colony-forming units and qPCR showed a stable MSH1 population, despite higher concentrations of salts and metals, and increased growth of native bacteria.

Processing of retentates of reverse osmosis treatment of phosphate-containing wastewater

The possibility of processing the phosphate-containing reverse osmosis retentates has been investigated. It was established that the use of NH4Cl: NH4OH mixture with 1: 4 ratio as a source of NH4 + ions and the use of magnesium chloride as a source of Mg2+ ions ensured the phosphate removal by 95.1–96.6% at the initial pH value of reaction medium equal to 10.5–11 and precipitator component ratio PO4 3–: NH4 +: Mg2+ = 1: 1: 2.

Partitioning of calcium and magnesium (total divalent cations) during membrane filtration of milk

Partitioning of total divalent cations (TDVC) during reverse osmosis (RO), nanofiltration (NF) and ultrafiltration (UF) has been investigated. During RO, there was an increase in TDVC and Ca2+, and a reduction in the ethanol stability of RO retentates. During UF of milk at its normal pH, there was an increase in total divalent cations, but only a slight increase in Ca2+ in the retentate. There was some loss of micellar calcium during UF. However, the ratio of amounts of soluble to total divalent cations in the retentate decreased as concentration factor increased. During NF, a small amount of TDVC was found in the permeate and TDVC rejection was estimated to be about 0.83.During UF of milk, the amount of TDVC in permeate increased significantly as the pH was reduced over the range 6.7–5.1 and the concentration of Ca2+ also increased both in the retentate and the permeate. However, this was not reversible, as when milk was restored to its original pH, its Ca2+ remained higher and ethanol stability was lower. In contrast, for whey and for UF permeate, changes in Ca2+ were reversible, when they were subject to similar pH changes. During UF, TDVC concentration in permeate decreased as temperature increased, due to the lower solubility of calcium phosphate at higher temperature. Ca2+ in permeate also decreased as UF temperature increased.

Pharmaceuticals and organic pollution mitigation in reclamation osmosis brines by UV/H2O2 and ozone

One significant disadvantage of using reverse osmosis (RO) for reclamation purposes is the need to dispose of the RO retentates. These retentates contain a high concentration of micropollutants, effluent organic matter (EfOM) and other inorganic constituents, which are recalcitrant to biological treatment and may impact the environment. The occurrence of 11 pharmaceuticals (concentrations ranging from 0.2 to 1.6μgL−1) and their mitigation in RO retentates by a UV/H2O2 process and ozonation was studied using a wide range of oxidant dosages. Eleven pharmaceuticals were identified at. Initial observed kinetic constants (kobs) were calculated for the different pharmaceuticals. Other typical wastewater parameters were also monitored during the UV/H2O2 and ozonation reactions.The range for kobs was found to be 0.8–12.8LmmolO3−1 and 9.7–29.9LmmolH2O2−1 for the ozonation and UV/H2O2 process, respectively. For ozonation, Atenolol, Carbamazepine, Codeine, Trimethoprim and Diclofenac showed the lowest initial kobs (in the order mentioned). Atenolol and Carbamazepine appeared as the most ozone resistant pharmaceuticals, exhibiting the lowest percentage of elimination at low ozone doses. On the other hand, despite the non-selectivity of HO, differences in the initial kobs were also observed during the UV/H2O2 process. Trimethoprim, Paroxetine and Sulfamethoxazole exhibited the lowest initial kobs values (in the order mentioned). Trimethoprim and Paroxetine also exhibited the lowest percentage removal when low H2O2 doses were assayed. The compounds that were identified as problematic during ozonation were more efficiently removed by the UV/H2O2 process. UV/H2O2 generally appeared to be a more efficient technology for removing pharmaceuticals from RO brines compared to ozonation.

Combining coagulation, softening and flocculation to dispose reverse osmosis retentates

The concentrated stream of a reverse osmosis unit was treated by coagulation, softening and flocculation to reduce conductivity and refractory organic matter content. Different polyaluminium chlorides and one ferric salt were used as coagulants, lime was added as softener, and two polymers (anionic and cationic polyacrylamides) were tested as flocculants. Coagulants reduced significantly the presence of refractory compounds by themselves, although conductivity increased. Lime addition decreased conductivity forming precipitates of CaCO3 and Mg(OH)2. When coagulation was combined with flocculation without adding lime, the anionic flocculant was more effective than the cationic one because the specific high hardness of water supplied enough Ca2+ and Mg2+ to promote the formation of bigger flocs, bridging the slightly negative coagula and anionic groups of the polymer; although they also reduced the efficiency of the cationic polyacrylamide. None of the tested flocculants showed any effect on conductivity and refractory organic matter reduction when lime was added.

Removal of Pharmaceutical and Personal Care Products from Reverse Osmosis Retentate Using Advanced Oxidation Processes

The application of reverse osmosis (RO) in water intended for reuse is promising for assuring high water quality. However, one significant disadvantage is the need to dispose of the RO retentate (or reject water). Studies focusing on Pharmaceutical and Personal Care Products (PPCPs) have raised questions concerning their concentrations in the RO retentate. Advanced oxidation processes (AOPs) are alternatives for destroying these compounds in retentate that contains high concentration of effluent organic matter (EfOM) and other inorganic constituents. Twenty-seven PPCPs were screened in a RO retentate using solid phase extraction (SPE) and UPLC-MS/MS, and detailed degradation studies for 14 of the compounds were obtained. Based on the absolute hydroxyl radical (HO•) reaction rate constants for individual pharmaceutical compounds, and that of the RO retentate (EfOM and inorganic constituents), it was possible to model their destruction. Using excitation-emission matrix (EEM) fluorescence spectroscopy, the HO• oxidation of the EfOM could be observed through decreases in the retentate fluorescence. The decrease in the peak normally associated with proteins correlated well with the removal of the pharmaceutical compounds. These results suggest that fluorescence may be a suitable parameter for monitoring the degradation of PPCPs by AOPs in RO retentates.

Design of a Eutectic Freeze Crystallization process for multicomponent waste water stream

Complex, hypersaline brines originating from the mining and extractive metallurgical industries have the potential to be treated using Eutectic Freeze Crystallization (EFC). Although EFC has been shown to be effective in separating a single salt and water, it has yet to be applied to the complex hypersaline brines that are typical of reverse osmosis retentates in South Africa. This paper focuses on the application of EFC for the purification of a typical brine containing high levels of sodium, chlorine, sulphate and ammonia that cannot be achieved with other separation techniques. The presence of ammonia prevents the application of membrane technology to treat the brine, leaving only cooling or evaporation as other possible options. Evaporation produces a mixed salt that requires further treatment. Modelling tools were applied to describe the phase behaviour of the complex saline systems under different process conditions and were experimentally validated. The results showed that Eutectic Freeze Crystallization could be used to selectively recover the sodium as a sodium sulphate salt. The simulation tools were especially useful in the design and optimisation of the process.

Vacuum membrane distillation for an integrated seawater desalination process

Seawater desalination by reverse osmosis (RO) is widely used for drinking water production. In order to reduce the volume of brines and to increase recovery, a new approach is proposed in the frame of the European MEDINA project. It lies on a combination of RO and Vacuum Membrane Distillation (VMD) in order to over concentrated RO retentates and to reduce their volume. Indeed, VMD can be used for concentrated salty solutions, because concentration polarization and temperature polarization might be non limiting even for quite high salt concentrations. The objective of this paper is to provide some first trends on the feasibility of using VMD for enhancing the global process recovery. The approach is firstly based on simulations for highly concentrated solutions using a VMD modeling based on Knudsen diffusion through the membrane which was improved to take into account highly concentrated waters. The model was validated by experimental results obtained with different salty solutions and with both flat-sheet...

Oxidation of organics in retentates from reverse osmosis wastewater reuse facilities

The use of membrane processes for wastewater treatment and reuse is rapidly expanding. Organic, inorganic, and biological constituents are effectively removed by reverse osmosis (RO) membrane processes, but concentrate in membrane retentates Disposal of membrane concentrates is a growing concern. Applying advanced oxidation processes (AOPs) to RO retentate is logical because extensive treatment and energy inputs were expended to concentrate the organics, and it is cheaper to treat smaller flowstreams. AOPs (e.g., UV irradiation in the presence of titanium dioxide; UV/TiO 2) can remove a high percentage of organic matter from RO retentates. The combination of AOPs and a simple biological system (e.g., sand filter) can remove higher levels of organic matter at lower UV dosages because AOPs produce biologically degradable material (e.g., organic acids) that have low hydroxyl radical rate constants, meaning that their oxidation, rather than that of the primary organic matter in the RO retentate, dictates the required UV energy inputs. At the highest applied UV dose (10 kWh m −3), the dissolved organic carbon (DOC) in the RO retentate decreased from ∼40 to 8 mg L −1, of which approximately 6 mg L −1 were readily biologically degradable. Therefore, after combined UV treatment and biodegradation, the final DOC concentration was 2 mg L −1, representing a 91% removal. These results suggest that UV/TiO 2 plus biodegradation of RO retentates is feasible and would significantly reduce the organic pollutant loading into the environment from wastewater reuse facilities.

Comprehensive characterization of oil refinery effluent-derived humic substances using various spectroscopic approaches

Refinery effluent-derived humic substances (HS) are important for developing refinery effluent reclamation techniques and studying the environmental chemistry of wastewater effluents. In this study, dissolved organic matter (DOM) from refinery effluent was concentrated using a portable reverse osmosis (RO) system. HS were isolated from RO retentates with XAD-8 resin. A variety of approaches such as specific UV absorbance at 254 nm (SUV 254), elemental analysis, size exclusion chromatography (SEC), solid-state cross polarization magic angle spinning 13C nuclear magnetic resonance spectrometry ( 13C CPMAS NMR), Fourier transform infrared spectrometry (FTIR), and electrospray ionization/ion trap/mass spectrometry (ESI/ion trap/MS) were employed for characterization of HS. The portable RO system exhibited high yield and recovery of DOM for concentrating refinery effluent. The concentration of dissolved organic carbon (DOC) in the refinery effluent was 9.9 mg/l, in which humic acids (HA) and fulvic acids (FA) accounted for 2.3% and 34.6%, respectively. Elemental and SUV 254 analyses indicated relative high amounts of aliphatic structures and low amounts of aromatic structures in refinery effluent-derived HS. Refinery effluent-derived HS displayed lower molecular weight than natural HS. The number-average molecular weight ( M n) and the weight-average molecular weight ( M w) of HA were 1069 and 2934, and those of FA were 679 and 1212 by SEC, respectively. By ESI/ion trap/MS, the M n and the M w of FA were 330 and 383. Four kinds of carbon structures (aliphatic, aromatic, heteroaliphatic, and carboxylic carbons) were found in refinery effluent-derived HS by 13C NMR analysis. The quantitative results support the interpretation that these HS are rich in aliphatic carbons and poor in aromatic carbons. Proteinaceous materials were identified by FTIR analysis in refinery effluent-derived HS.

Manufacture of direct acidified cheese from ultrafiltration and reverse osmosis retentates

Whole milk and retentates from ultrafiltration at 4:1 volume concentration ratio and reverse osmosis at 2.5:1 were used in the manufacture of direct acidified cheese. Yield based on component recovery was higher in cheese from milk retentates than whole milk. On a dry mass basis, an increase in cheese yield of 37.9% for reverse osmosis, and 14.7% for ultrafiltration was achieved compared with cheese from whole milk. Compositional variation in the resulting cheese affected both textural and sensory parameters. Cheese from ultrafiltration scored highest in sensory evaluation, although all cheeses were graded fair to good.

Whole Milk Reverse Osmosis Retentates for Cheddar Cheese Manufacture: Chemical Changes During Aging

Cheddar cheese was made in a commercial plant from whole milk concentrated by reverse osmosis at 5, 10, 15 and 20% reduction of volume. Reverse osmosis Cheddar cheese was compared with commercial control cheese that was made from the same lot of milk and ingredient on the same day. Proteolysis, as measured by nitrogen soluble in acetate buffer (pH 4.6) and in 12% trichloroacetic acid, were similar for both control and reverse osmosis cheese during the first 3 mo of aging. After 6 mo of aging the reverse osmosis cheese at 15 and 20% reduction of volume had 10 to 15% less soluble nitrogen than control cheese Initial lots of reverse osmosis Cheddar cheese had significantly higher free fatty acids than control cheeses. After the pressure regulation device on the reverse osmosis unit was changed, milk concentrates and subsequent reverse osmosis cheese had normal free fatty acids. Lactose content of reverse osmosis cheese was slightly higher than control cheese. After 3 mo of aging, cheese from milk 20% volume reduced by reverse osmosis had significantly greater lactose content than commercial control cheeses. Good quality aged Cheddar cheese was made from whole milk reverse osmosis retentates.

Whole Milk Reverse Osmosis Retentates for Cheddar Cheese Manufacture: Cheese Composition and Yield

The impact of concentrating whole milk by reverse osmosis prior to Cheddar cheese making was studied. Heat treated, standardized, whole milk was reduced in volume by 0, 5, 10, 15, and 20% prior to Cheddar cheese manufacture. Milk solids at various milk volume reductions were 11.98, 12.88, 13.27, 14.17, and 15.05%, respectively. Permeates contained only traces of organic matter and would not create a significant by-product handling problem for a cheese plant. Solids content of the whey from cheese making increased with increasing milk concentration. Proximate compositions of reverse osmosis cheeses were comparable to control cheeses. Fat losses decreased, and fat retained in the cheese increased with increasing milk solids concentration. Improved fat recovery in the cheese was related to the amount of mechanical homogenization of milk fat during the concentration process. Actual, composition adjusted, and theoretical cheese yields were determined. Increased retention of whey solids and improved fat recovery gave cheese yield increases of 2 to 3% above expected theoretical yields at 20% milk volume reduction. Water removal from whole milk prior to Cheddar cheese manufacture gave increased productivity and cheese yield without requiring different cheese-making equipment or manufacturing procedures.