The mechanisms of humic substances self-assembly with biological molecules: The case study of the prion protein

Humic substances (HS) are the largest constituent of soil organic matter and are considered as a key component of the terrestrial ecosystem. HS may facilitate the transport of organic and inorganic molecules, as well as the sorption interactions with environmentally relevant proteins such as prions. Prions enter the environment through shedding from live hosts, facilitating a sustained incidence of animal prion diseases such as Chronic Wasting Disease and scrapie in cervid and ovine populations, respectively. Changes in prion structure upon environmental exposure may be significant as they can affect prion infectivity and disease pathology. Despite its relevance, the mechanisms of prion interaction with HS are still not completely understood. The goal of this work is to advance a structural-level picture of the encapsulation of recombinant, non-infectious, prion protein (PrP) into different natural HS. We observed that PrP precipitation upon addition of HS is mainly driven by a mechanism of “salting-out” whereby PrP molecules are rapidly removed from the solution and aggregate in insoluble adducts with humic molecules. Importantly, this process does not alter the protein folding since insoluble PrP retains its α-helical content when in complex with HS. The observed ability of HS to promote PrP insolubilization without altering its secondary structure may have potential relevance in the context of “prion ecology”. These results suggest that soil organic matter interacts with prions possibly without altering the protein structures. This may facilitate prions preservation from biotic and abiotic degradation leading to their accumulation in the environment

Metallic anion recovery from aqueous streams and removal agent recycle in the polymer–surfactant aggregate process

In a previous contribution, a new application of the polymer–surfactant aggregate (PSA) process was developed; the removal of metallic anions from dilute aqueous solutions. A subsequent pH adjustment method has been developed to recover the metallic anions from the flocculated PSAs into a concentrated solution and then to recover the polymer (PAA) and surfactant (MTAB) for recycling. The PSA is a colloidal structure that is formed by micelle-like aggregates associating with the oppositely charged polymer chains. The PSA can then bind with metallic anions, and will eventually flocculate out of the solution under colloidal destabilisation. In the work presented, a small volume of 0.1 M NaOH is firstly added to the flocs to leach out the bound metallic anions in 15 min, and then a coarse filter is used to separate out the basic solution containing 5–20 times more concentrated metallic anions than the original effluent. After the metallic anion recovery, the flocs can be completely dissolved in a small volume of 0.05 M H 2 SO 4 . This acidic solution, containing PAA and MTAB, is then reused in the next treatment cycle; meanwhile, the pH of the feed is adjusted to 5.3 by adding NaOH. The results show that the recovery efficiency of CrO 4 2 − at an optimum pH of 12 is 94%, and the recovery efficiency of PAA–MTAB at its optimum pH of 1.4 is 94%. The kinetics of the recovery process is quick; both the basification and acidification steps can be completed within 15–20 min. In addition, the removal efficiency of 0.2 mM CrO 4 2 − solution remains at the same level when using previously recycled PAA and MTAB (with a small makeup of the MTAB to cover leakage at the metallic anion removal stage). In short, the sequential pH adjustment method is able to recover and concentrate the metallic anions from the flocculated PSAs, and then recover the removal agent for recycling into the process with little deterioration of removal ability

Removal of metallic ions at the parts per billion level from aqueous solutions using the polymer-surfactant aggregate process

The polymer-surfactant aggregate process has been developed to remove metallic ions from aqueous solutions for which the ions are typically at the mg/l (parts per million) concentration level. In some cases, such as extremely valuable or highly toxic metals, the concentration of metals may exist at the μg/l (parts per billion) level. It is, nevertheless, essential to be able to apply such a process to treat them cost-effectively. In this paper, cadmium ions are removed from a 560 ppb aqueous solution down to a concentration of 17 ppb using 2 ppm polyethylenimine (PEI) and 0.02 mM sodium dodecyl sulphate (SDS). At such a low optimum dosage of polymer and surfactant (the removal agent), the loading percentage on the removal agent increases with the concentration of Cd(II) to as high as 39%. However, at this low optimum dosage of the removal agent, the removal efficiency of Cd(II) and the usage efficiency of the removal agent both have a lower tolerance toward salinity effects. This contrasts with the higher salinity tolerance corresponding to the higher optimum dosages commensurate with higher metallic ion concentrations

Removal of metallic ions at the parts per billion level from aqueous solutions using the polymer-surfactant aggregate process

The polymer-surfactant aggregate process has been developed to remove metallic ions from aqueous solutions for which the ions are typically at the mg/l (parts per million) concentration level. In some cases, such as extremely valuable or highly toxic metals, the concentration of metals may exist at the μg/l (parts per billion) level. It is, nevertheless, essential to be able to apply such a process to treat them cost-effectively. In this paper, cadmium ions are removed from a 560 ppb aqueous solution down to a concentration of 17 ppb using 2 ppm polyethylenimine (PEI) and 0.02 mM sodium dodecyl sulphate (SDS). At such a low optimum dosage of polymer and surfactant (the removal agent), the loading percentage on the removal agent increases with the concentration of Cd(II) to as high as 39%. However, at this low optimum dosage of the removal agent, the removal efficiency of Cd(II) and the usage efficiency of the removal agent both have a lower tolerance toward salinity effects. This contrasts with the higher salinity tolerance corresponding to the higher optimum dosages commensurate with higher metallic ion concentrations

Metallic anion recovery from aqueous streams and removal agent recycle in the polymer–surfactant aggregate process

In a previous contribution, a new application of the polymer–surfactant aggregate (PSA) process was developed; the removal of metallic anions from dilute aqueous solutions. A subsequent pH adjustment method has been developed to recover the metallic anions from the flocculated PSAs into a concentrated solution and then to recover the polymer (PAA) and surfactant (MTAB) for recycling. The PSA is a colloidal structure that is formed by micelle-like aggregates associating with the oppositely charged polymer chains. The PSA can then bind with metallic anions, and will eventually flocculate out of the solution under colloidal destabilisation. In the work presented, a small volume of 0.1 M NaOH is firstly added to the flocs to leach out the bound metallic anions in 15 min, and then a coarse filter is used to separate out the basic solution containing 5–20 times more concentrated metallic anions than the original effluent. After the metallic anion recovery, the flocs can be completely dissolved in a small volume of 0.05 M H 2 SO 4 . This acidic solution, containing PAA and MTAB, is then reused in the next treatment cycle; meanwhile, the pH of the feed is adjusted to 5.3 by adding NaOH. The results show that the recovery efficiency of CrO 4 2 − at an optimum pH of 12 is 94%, and the recovery efficiency of PAA–MTAB at its optimum pH of 1.4 is 94%. The kinetics of the recovery process is quick; both the basification and acidification steps can be completed within 15–20 min. In addition, the removal efficiency of 0.2 mM CrO 4 2 − solution remains at the same level when using previously recycled PAA and MTAB (with a small makeup of the MTAB to cover leakage at the metallic anion removal stage). In short, the sequential pH adjustment method is able to recover and concentrate the metallic anions from the flocculated PSAs, and then recover the removal agent for recycling into the process with little deterioration of removal ability

Forward osmosis for sustainable water treatment

Forward osmosis (FO) as an emerging technology has been researched extensively over the past few decades for water treatment and other applications. In FO, the water in the feed solution (at low osmotic pressure) spontaneously flows through a semipermeable membrane to the draw solution (at high osmotic pressure) under the osmotic pressure difference and without applied hydraulic pressure, conferring the advantages of low energy consumption in the separation process and reduced membrane fouling. For this reason, it is a promising potential candidate for sustainable water processing. Although FO is unlikely to replace reverse osmosis in many applications, it has successfully been employed as a pretreatment process in desalination, wastewater treatment, power generation and life science applications. Some niche applications of stand-alone FO have been identified in food and fertiliser industries, but the majority of practical applications involve FO as a pretreatment process to reduce the energy cost and membrane fouling during subsequent stages of water processing. This chapter will introduce the three key parts in the FO process: the draw solutions, the membranes and the modules, and then discuss the practical applications. The associated challenges in FO are also highlighted within each part, including draw solution development, reverse solute diffusion, concentration polarisation, membrane fouling and FO membrane development. To overcome these challenges, the related developments and modifications are critically discussed with consideration of the overall performance of the FO process.</p

Osmotically assisted reverse osmosis (OARO): Five approaches to dewatering saline brines using pressure-driven membrane processes

The ability of osmotically assisted reverse osmosis to draw water from concentrated brine (>75 g/L) can be attributed to the combined effect of reducing the transmembrane osmotic pressure difference via a draw solution, and operating at high hydraulic feed pressures. This approach has been incorporated into a standard ultrafiltration and reverse osmosis desalination plant to increase the process recovery. In total, five different OARO integrated flow processes are modelled numerically to determine their technical and economical feasibility in maximising the process recovery. Three of the five presented OARO integrated flow processes are novel, and offer technical and economical advantages over the previously proposed OARO processes. At lower feed salinities, OA-5, which is a new process, is the optimal OARO integrated flow process. Recoveries of up to 72% from a 35 g/L saline feed are possible when operating at the membrane burst pressure of 48.3 bar. Furthermore, the energy consumption of OA-5 is approximately 4.00 kWh/m3, which is significantly lower than that in currently employed high recovery thermal processes, such as mechanical vapour compression. OA-3 is another original OARO integrated flow process and is the most attractive at a higher feed salinity of 70 g/L. The maximum recovery of 44% is achieved at an average energy consumption of 6.37 kWh/m3. The results presented in this article demonstrate that pressure-based membrane processes can competitively concentrate brine streams to concentrations of up to 125 g/L

Interaction among branched polyethylenimine (PEI), sodium dodecyl sulfate (SDS) and metal cations during copper recovery from water using polymer-surfactant aggregates

The application of polymer–surfactant aggregates (PSAs) to recover heavy metal ions from water is a novel treatment process for aqueous metallic effluents. To better employ this strategy, branched polyethylenimine (PEI), sodium dodecyl sulfate (SDS) and copper ions were selected to investigate their interaction in water and to improve the recyclable PSAs process for metal removal and recovery. Electrostatic association between PEI and SDS caused the formation of PSAs, and the addition of SDS to a partially protonated PEI solution caused a pH increase; however, re-dispersal of PSAs could be achieved via an increase in pH. Precipitation of PSAs depended on pH, SDS/PEI concentration ratio and the total concentration of PEI; the optimal SDS/PEI ratio decreased as pH increased, and a higher concentration of PEI showed a greater potential to precipitate. PEI formed a strong complex with Cu2+, with the most stable complex at a PEI/Cu chelation ratio of 4. Acidification decreased the chelation capacity of PEI to Cu2+, because of the competition from protons for amino groups. Complexation with Cu2+ in turn reduced the proton buffer capacity of PEI in a non-acid solution. The removal of Cu2+ increased by increasing the total PEI concentration, or by increasing pH from 1 to above 4. Ionic strength and hardness had no marked effect on Cu2+ removal using the PSAs process. Following the initial interaction among PEI, SDS and Cu2+, the Cu2+ could then be released from the PSAs by acidification and the reuse of the PSAs material could be achieved by alkalization. Copper removal and recovery were still up to 98 % and 88 % after three reuse cycles of the PSAs process, respectively