Polymer and alcohol-based three-phase partitioning systems for separation of polysaccharide and protein

BACKGROUND: Natural polymers are macromolecules produced by living organisms, and they have a wide range of applications and relevance for the development of a circular economy. However, large-scale production continues to be hindered by several factors, such as downstream processing. In this work, three-phase partitioning (TPP) systems were investigated for separation of model polysaccharide (dextran, alginate, and gum arabic) from protein [Bovine serum albumin (BSA) and lysozyme]. The recyclability of the phase-forming compounds used to form the extractive platform was assessed by ultrafiltration (UF). This study contributes to the development of production processes for biopolymers from fermented waste by proposing an effective separation technique for fractionation of biopolymers. Such biopolymers are often collected as mixtures, but with the studied approaches, fractionation of polysaccharides from proteins may also be employed. With the chosen systems, the scope of TPP systems is expanded by using another class of phase-forming compound (polymers); in addition, UF was studied as a versatile regeneration approach. RESULTS: Within the TPP approach, the best separation of dextran from BSA was achieved using TPP systems composed of 25 wt% polyethylene glycol (PEG) + 25 wt% K3C6H5O7 and 36 wt% EtOH + 10 wt% K3PO4, in which more than 95% of dextran and BSA were found as precipitate and partitioned to top phase (PEG or EtOH-rich), respectively. By using other model compounds, it was found that the molecular weight and charge of the biopolymer play a key role in the yield and selectivity of TPP systems. Finally, by using ultrafiltration/diafiltration, about 99% of the ethanol and phosphate salt used to form the extractive platform could be retrieved in the permeate stream. CONCLUSION: The high extraction yields, good selectivity, and recyclability of phase-forming compounds confirm the potential of polymer-based and alcohol-based TPP systems to fractionate biopolymer mixtures.</p

Separation of polysaccharide and protein by ionic liquid-based extraction techniques

Biopolymers are natural macromolecules obtained from animal, plant and microbial sources, with the potential to be used in a wide range of applications. A key process step, which is still underdeveloped, is the downstream processing. In this work, water immiscible and water miscible ionic liquids (ILs) were investigated regarding their ability to fractionate a mixture of polysaccharide and proteins. Alginate and bovine serum albumin (BSA) were used as model compounds to mimic natural polymer crude extract. Phosphonium ILs composed of different anions (bromide, dicyanamide and phosphinate) were used as water immiscible ILs while imidazolium ILs, combined with phosphate salts to form biphasic system, were selected as water miscible ILs. In water immiscible IL systems, the partitioning behavior of biopolymers depended on IL's anions and there was formation of insoluble precipitate. The insolubility of precipitate in diverse aqueous and organic solvents hindered the processibility of water immiscible phosphonium IL for fractionation of biopolymers. The partitioning of biopolymers in water miscible ILs systems also depended on the IL's anion, as well the concentration of IL. Separation of alginate (yield = 90% and purity = 99%) from BSA (yield = 89% and purity = 99%) was best achieved by the [C4mim]Cl-based extraction system. After fractionation, regeneration of IL and salt used was carried out by ultrafiltration, with recovery yields up to 100%. The high extraction yields and recyclability of phase-forming compounds confirm the potential of water miscible ILs systems to fractionate polysaccharide and protein

Diversity and enrichment of nitrite-dependent anaerobic methane oxidizing bacteria from wastewater sludge

Recently discovered microorganisms affiliated to the bacterial phylum NC10, named “Candidatus Methylomirabilis oxyfera”, perform nitrite-dependent anaerobic methane oxidation. These microorganisms could be important players in a novel way of anaerobic wastewater treatment where ammonium and residual dissolved methane might be removed at the expense of nitrate or nitrite. To find suitable inocula for reactor startup, ten selected wastewater treatment plants (WWTPs) located in The Netherlands were screened for the endogenous presence of M. oxyfera using molecular diagnostic methods. We could identify NC10 bacteria with 98% similarity to M. oxyfera in nine out of ten WWTPs tested. Sludge from one selected WWTP was used to start a new enrichment culture of NC10 bacteria. This enrichment was monitored using specific pmoA primers and M. oxyfera cells were visualized with fluorescence oligonucleotide probes. After 112 days, the enrichment consumed up to 0.4 mM NO2− per day. The results of this study show that appropriate sources of biomass, enrichment strategies, and diagnostic tools existed to start and monitor pilot scale tests for the implementation of nitrite-dependent methane oxidation in wastewater treatment at ambient temperature

Recovery Techniques Enabling Circular Chemistry from Wastewater

In an era where it becomes less and less accepted to just send waste to landfills and release wastewater into the environment without treatment, numerous initiatives are pursued to facilitate chemical production from waste. This includes microbial conversions of waste in digesters, and with this type of approach, a variety of chemicals can be produced. Typical for digestion systems is that the products are present only in (very) dilute amounts. For such productions to be technically and economically interesting to pursue, it is of key importance that effective product recovery strategies are being developed. In this review, we focus on the recovery of biologically produced carboxylic acids, including volatile fatty acids (VFAs), medium-chain carboxylic acids (MCCAs), long-chain dicarboxylic acids (LCDAs) being directly produced by microorganisms, and indirectly produced unsaturated short-chain acids (USCA), as well as polymers. Key recovery techniques for carboxylic acids in solution include liquid-liquid extraction, adsorption, and membrane separations. The route toward USCA is discussed, including their production by thermal treatment of intracellular polyhydroxyalkanoates (PHA) polymers and the downstream separations. Polymers included in this review are extracellular polymeric substances (EPS). Strategies for fractionation of the different fractions of EPS are discussed, aiming at the valorization of both polysaccharides and proteins. It is concluded that several separation strategies have the potential to further develop the wastewater valorization chains

Recovery Techniques Enabling Circular Chemistry from Wastewater

In an era where it becomes less and less accepted to just send waste to landfills and release wastewater into the environment without treatment, numerous initiatives are pursued to facilitate chemical production from waste. This includes microbial conversions of waste in digesters, and with this type of approach, a variety of chemicals can be produced. Typical for digestion systems is that the products are present only in (very) dilute amounts. For such productions to be technically and economically interesting to pursue, it is of key importance that effective product recovery strategies are being developed. In this review, we focus on the recovery of biologically produced carboxylic acids, including volatile fatty acids (VFAs), medium-chain carboxylic acids (MCCAs), long-chain dicarboxylic acids (LCDAs) being directly produced by microorganisms, and indirectly produced unsaturated short-chain acids (USCA), as well as polymers. Key recovery techniques for carboxylic acids in solution include liquid-liquid extraction, adsorption, and membrane separations. The route toward USCA is discussed, including their production by thermal treatment of intracellular polyhydroxyalkanoates (PHA) polymers and the downstream separations. Polymers included in this review are extracellular polymeric substances (EPS). Strategies for fractionation of the different fractions of EPS are discussed, aiming at the valorization of both polysaccharides and proteins. It is concluded that several separation strategies have the potential to further develop the wastewater valorization chains

Glocal assessment of integrated wastewater treatment and recovery concepts using partial nitritation/Anammox and microalgae for environmental impacts

This study explored the feasibility and estimated the environmental impacts of two novel wastewater treatment configurations. Both include combined bioflocculation and anaerobic digestion but apply different nutrient removal technologies, i.e. partial nitritation/Anammox or microalgae treatment. The feasibility of such configurations was investigated for 16 locations worldwide with respect to environmental impacts, such as net energy yield, nutrient recovery and effluent quality, CO2 emission, and area requirements. The results quantitatively support the applicability of partial nitritation/Anammox in tropical regions and some locations in temperate regions, whereas microalgae treatment is only applicable the whole year round in tropical regions that are close to the equator line. Microalgae treatment has an advantage over the configuration with partial nitritation/Anammox with respect to aeration energy and nutrient recovery, but not with area requirements. Differential sensitivity analysis points out the dominant influence of microalgal biomass yield and wastewater nutrient concentrations on area requirements and effluent quality. This study provides initial selection criteria for worldwide feasibility and corresponding environmental impacts of these novel municipal wastewater treatment plant configurations

Calcium effect on microbial activity and biomass aggregation during anaerobic digestion at high salinity

The potential effect of different Ca2+ additions (150, 300, 450, 600 and 1000 mg/L) on microbial activity and aggregation, during anaerobic digestion at moderate (8 g/L Na+) and high salinity (20 g/L Na+) has been investigated. Batch tests were carried out in duplicate serum bottles and operated for 30 days at 37 °C. At 8 g/L Na+, methanogenic activity and protein degradation were comparable from 150 to 450 mg/L Ca2+, and a significant inhibition was only observed at a Ca2+concentration of 1000 mg/L. In contrast, at 20 g/L Na+, 150 to 300 mg/L were the only Ca2+ concentrations to maintain chemical oxygen demand (COD) removal, protein hydrolysis and methane production. Overall, increasing Ca2+ concentrations had a larger impact on acetotrophic methanogenesis at 20 g/L than at 8 g/L Na+. Increasing Ca2+ had a negative effect on the aggregation behaviour of the dominant methanogen Methanosaeta when working at 8 g/L Na+. At 20 g/L Na+ the aggregation of Methanosaeta was less affected by addition of Ca2+ than at 8 g/L Na+. The negative effect appeared to be connected with Ca2+ precipitation and its impact on cell-to cell communication. The results highlight the importance of ionic balance for microbial aggregation at high salinity, bringing to the forefront the effect on Methanosaeta cells, known to be important to obtain anaerobic granules.</p

Membrane Bioreactor (MBR) as Alternative to a Conventional Activated Sludge System Followed by Ultrafiltration (CAS-UF) for the Treatment of Fischer-Tropsch Reaction Water from Gas-to-Liquids Industries

The potential of a membrane bioreactor (MBR) system to treat Fischer-Tropsch (FT) reaction water from gas-to-liquids (GTL) industries was investigated and compared with the current treatment system: a conventional activated sludge system followed by an ultrafiltration (CAS-UF) unit. The MBR and the CAS-UF systems were inoculated with municipal activated sludge and operated in parallel for 645 days with four interruptions using synthetic FT reaction water. Both treatment systems achieved a removal efficiency of 98 ± 0.1% within 60 days after inoculation, the COD influent concentration was 1014 ± 15 mg L−1. This suggests that MBRs form a suitable alternative to CAS-UF systems for the treatment of FT reaction water from the GTL industries. Moreover, the total fouling rates (Ft) of the membranes used from day 349 till the end were assessed. The average Ft was 7.3 ± 1.0 1010 m−1 day−1 for CAS-UF membranes and 2.8 ± 00.7 1010 m−1 day−1 for MBR-MT membranes. This indicates that MBR systems for the treatment of FT reaction water from the gas-to-liquids industries are less prone to fouling than CAS-UF systems

Co-digestion to support low temperature anaerobic pretreatment of municipal sewage in a UASB–digester

The aim of this work was to demonstrate that co-digestion improves soluble sewage COD removal efficiency in treatment of low temperature municipal sewage by a UASB-digester system. A pilot scale UASB-digester system was applied to treat real municipal sewage, and glucose was chosen as a model co-substrate. Co-substrate was added in the sludge digester to produce additional methanogenic biomass, which was continuously recycled to inoculate the UASB reactor. Soluble sewage COD removal efficiency increased from 6 to 23%, which was similar to its biological methane potential (BMP). Specific methanogenic activity of the UASB and of the digester sludge at 15°C tripled to a value respectively of 43 and 39mg CH4-COD/(gVSSd). Methane production in the UASB reactor increased by more than 90% due to its doubled methanogenic capacity. Therefore, co-digestion is a suitable approach to support a UASB-digester for pretreatment of low temperature municipal sewage.</p