This study deals with the development of antifouling ultrafiltration membranes based on polysulfone (PSF) for wastewater treatment and the concentration and purification of hemicellulose and lignin in the pulp and paper industry. The efficient simple and reproducible technique of PSF membrane modification to increase antifouling performance by simultaneous addition of triblock copolymer polyethylene glycol-polypropylene glycol-polyethylene glycol (Synperonic F108, Mn =14 × 103 g mol−1) to the casting solution and addition of polyacrylic acid (PAA, Mn = 250 × 103 g mol−1) to the coagulation bath is proposed for the first time. The effect of the PAA concentration in the aqueous solution on the PSF/Synperonic F108 membrane structure, surface characteristics, performance, and antifouling stability was investigated. PAA concentrations were varied from 0.35 to 2.0 wt.%. Membrane composition, structure, and topology were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The addition of PAA into the coagulation bath was revealed to cause the formation of a thicker and denser selective layer with decreasing its pore size and porosity; according to the structural characterization, an interpolymer complex of the two additives was formed on the surface of the PSF membrane. Hydrophilicity of the membrane selective layer surface was shown to increase significantly. The selective layer surface charge was found to become more negative in comparison to the reference membrane. It was shown that PSF/Synperonic F108/PAA membranes are characterized by better antifouling performance in ultrafiltration of humic acid solution and thermomechanical pulp mill (ThMP) process water. Membrane modification with PAA results in higher ThMP process water flux, fouling recovery ratio, and hemicellulose and total lignin rejection compared to the reference PSF/Synperonic F108 membrane. This suggests the possibility of applying the developed membranes for hemicellulose concentration and purification.
We set up a structural model to study credit risk for a portfolio containing several or many credit contracts. The model is based on a jump-diffusion process for the risk factors, i.e. for the company assets. We also include correlations between the companies. We discuss that models of this type have much in common with other problems in statistical physics and in the theory of complex systems. We study a simplified version of our model analytically. Furthermore, we perform extensive numerical simulations for the full model. The observables are the loss distribution of the credit portfolio, its moments and other quantities derived thereof. We compile detailed information about the parameter dependence of these observables. In the course of setting up and analyzing our model, we also give a review of credit risk modeling for a physics audience.
Molasses is a sugar mill by-product with low value that today is used primarily for animal feed. However, molasses contains large amounts of sucrose which, if purified, could be used for other purposes. In this study, purification by membrane filtration using ceramic tubular ultrafiltration (UF) and nanofiltration (NF) was examined. NF purifies sucrose by removing small compounds, whereas UF removes larger compounds. Based on our results, high filtration fluxes could be obtained, and it was possible to clean the membranes sufficiently from fouling compounds. Sucrose was separated from other compounds, but the separation efficiency was generally higher with diluted molasses compared with concentrated molasses. This could be explained by more severe fouling when filtering dilute molasses or potentially due to aggregate formations in the molasses as our analysis showed. Overall, this study shows the potential of ceramic UF and NF membranes for sucrose purification from molasses.
A new approach for one‐stage facile membrane modification during non‐solvent induced phase separation (NIPS)‐process is proposed. The novelty of this study is that cheap and commercially available anionic high molecular polyacrylamide‐based flocculant (AHMPF) is applied for the first time as an additive to coagulation bath (CB). The series of polyethersulfone membranes were prepared using 0.05–0.3 wt% AHMPF aqueous solution as CB at different temperatures (25–50°C) via NIPS. The effect of AHMPF concentration on the structure, composition and hydrophilicity of membranes was investigated. The separation and antifouling performance were evaluated during filtration of bovine serum albumin (BSA) solution and thermomechanical pulp mills process water (ThMP) in order to concentrate hemicellulose. The successful immobilization of AHMPF into the structure of membranes selective layer (not bottom layer) was confirmed by FTIR spectroscopy. It was established that despite the similar rejection of hemicellulose (88.8–93%) and lignin (20–21.4), modified membranes demonstrate 3–8 times higher flux and 2 times higher FRR (43.8% for reference membrane and 86.5% for modified one) in ThMP ultrafiltration. The developed membrane was found to be highly efficient in hemicellulose concentration and purification in pulp industry.
The suspended solids (SS) concentrations in effluent from moving bed biofilm reactors (MBBRs) used for secondary biological treatment can be up to 500 mg/L. Microscreens (Drumfilters or Discfilters) can be used as alternatives to traditional clarification or dissolved air flotation to remove SS and total phosphorus (TP). This study shows how a small-scale municipal WWTP for 5,700 population equivalent (PE) can be upgraded to 12,000 PE by combining MBBR with coagulation-flocculation tanks and a Discfilter with a total footprint of 160 m2. This long-term investigation demonstrated that even though influent turbidity (range 146–431 NTU) and flow (25–125 m3/h) varied considerably, very low effluent turbidities (below 10 NTU) could be achieved continuously. Furthermore, this compact treatment system can provide average reductions of ammonium (NH4-N) from 19 to 0.04 mg/L, COD from 290 to 10 mg/L, and TP from 4.5 to 0.3 mg/L. The results show that effluent requirements can be reached by combining MBBR, coagulation-flocculation and disc filtration at full scale, without a primary clarifier upstream of MBBR.
Microscreening (using Discfilters) is a widely used technology for suspended solids removal in tertiary effluent streams of wastewater treatment plants. Several pilot studies have shown the feasibility of using coagulation and flocculation in combination with microscreens for advanced phosphorus removal, but the number of full-scale references is still limited. In summer 2014, the first Scandinavian full-scale Discfilter installation with 2-stage chemical pre-treatment (coagulation and flocculation) was started up at the Arvidstorp wastewater treatment plant in Trollhättan (Sweden). The results obtained during the first year of operation proved that low suspended solids and total phosphorus effluent values could be achieved (<5 and <0.2 mg/l, respectively). These results were obtained even during heavy rainfall, when biologically and primary treated water were mixed at the influent of the Discfilter installation, before the coagulation and flocculation tanks. Further analysis of the results showed that Discfilter in combination with coagulant and polymer pre-treatment is a robust and reliable technology with low energy demand (34 Wh/m3) and a high recovery (1.9 ± 0.4% of influent flow discharged as reject).
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