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Recovery of alginate extracted from aerobic granular sludge (AGS) has given rise to a novel research direction. However, these extracted alginate solutions have a water content of nearly 100%. Alternately, ultrafiltration (UF) is generally used for concentration of polymers. Furthermore, the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials. In this study, membrane fouling mitigation by multivalent metal ions, both individually and in combination, and properties of recycled materials were investigated for UF recovery of sodium alginate (SA). The filtration resistance showed a significantly negative correlation with the concentration of metal ions, arranged in the order of Mg2+ Fe3+ + Ca2+ > Ca2+ > Mg2+. Three mechanisms were proposed in the presence of Fe3+, such as the decrease of SA concentration, change in pH, and production of hydroxide iron colloids from hydrolysis. The properties of recycled materials (filter cake) were investigated via optical microscope observation, dynamic light scattering, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The results provide further insight into UF recoveries of alginate extracted from AGS.

Traditional wastewater treatment plants cannot completely remove trace pharmaceutical and personal care products. In particular, quinolone antibiotics are mainly adsorbed on microbial cell surfaces in excess sludge and are released into the water environment during agricultural supplementation, mainly due to the exfoliation of extracellular polymeric substances (EPS) caused by changes in environmental conditions. Here, the occurrence of seven typical quinolone antibiotics from three generations in excess sludge was investigated at trace concentrations using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). EPS facilitated adsorption independent of pH and quinolone antibiotic type, and the solid-liquid distribution coefficient decreased markedly as pH increased (pH 5–9, range of municipal wastewater). Metal ions bound in EPS were predominantly responsible for the adsorption of antibiotics in sludge, rather than the macroscopic size of the sludge floc. pH affected patterns of quinolone antibiotics, the zeta potential of sludge floc, and the contents of metal ions contained in sludge. The adsorption capacity of antibiotics first increased and then decreased with increasing pH in the range of pH 3–11, reaching a maximum (20,506, 14,458, 10,689, 22,854, 20,302, 8494, and 29,547 L/kg for CIP, ENR, LOM, MOX, NOR, OFL, and SAR, respectively) near pH 5, at which the cationic bridging of Ca2+ and Mg2+ bound in EPS played a major role owing to their larger ion radius and higher contents in excess sludge. Due to high surface heterogeneity of sludge, the Freundlich model was more suitable than the Langmuir model for describing the adsorption behavior of quinolone antibiotics. These results provide further insight into the release of quinolone antibiotics adsorbed in excess sludge, with potential implications for the agricultural use of sludge.

Anaerobic digestion (AD) is a sustainable pathway towards recovering chemical energy from excess sludge, and humic substances (HSs) contained in sludge can inhibit energy (methane/CH4) conversion efficiency. This study aims to investigate the impact of humic acids (HA) on the various processes in a batch anaerobic digestion process. For this purpose, “clean” sludge was cultivated in a laboratory to avoid HSs presence. The cultivated sludge was used in a series of batch experiments, with humic acids added at different levels. A complete AD test, as well as three sub-phase tests (hydrolytic phase; acidogenic phase; methanogenic phase) was performed and analyzed with and without HA dosing. In the single-phase AD system, dosing with HA inhibited the methanogenic efficiency by 35.1% at HA:VSS = 15%. However, the effects of HA on the three sub-phases revealed something very different. HA inhibited hydrolytic efficiency by 38.2%, promoted acidogenic efficiency by 101.5%, and finally inhibited methanogenic efficiency by 52.2%. The combined efficiency of the three sub-phases without HA dosing is calculated at 15.7%; and with HA dosing (HA:VSS = 15%) at 10.2%. Overall, the combined inhibition efficiency of the three sub-phases is equal to 35.0%, which is almost identical (35.1%) to the result observed in the single-phase AD process. The possible mechanisms behind the phenomena were analyzed and summarized in the context.

The water content in the recycled alginate solutions from aerobic granular sludge was nearly 100%. Forward osmosis (FO) has become an innovative dewatering technology. In this study, the FO concentration of sodium alginate (SA) was investigated using calcium chloride as a draw solute. The reverse solute flux (RSF) of calcium ions in FO had a beneficial effect, contrary to the findings of previous literature. The properties of the concentrated substances formed on the FO membrane on the feed side were analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, verifying that calcium alginate (Ca-Alg), which can be used as a recycled material, was formed on the FO membrane on the feed side owing to the interaction between SA and permeable calcium ions. Water flux increased significantly with the increase in calcium chloride concentration, while the concentration of SA had little influence on the water flux in FO. Based on this discovery, we propose a novel method for the concentration and recovery of alginate, in which the RSF of calcium ions is utilized for recovering Ca-Alg by FO, with calcium chloride as a draw solute.

Excess sludge production by wastewater treatment plants (WWTPs) represents a serious environmental problem that necessitates the development of effective sludge treatment/disposal methods. Excess sludge contains valuable materials such as extracellular polymer substances (EPSs), and their recovery is of great practical importance. However, conventional recovery methods afford EPS solutions with moisture contents of ∼100% and the dehydration of these solutions via direct drying methods is considerably energy consuming. Here, we investigate the separation of EPSs extracted from excess sludge by microfiltration (0.5 μm) and ultrafiltration (10 kDa), revealing that Ca2+ addition reduces the extent of membrane fouling during EPS isolation since the interactions between Ca2+ and EPS carboxylate groups increase the size and reduce the concentration of colloids/polymers in EPS suspensions. Additionally, we establish an ultrafiltration-based EPS separation protocol, demonstrating that it allows highly efficient EPS recovery (>90%) irrespective of the Ca2+ concentration, and show that EPSs extracted from excess sludge samples derived from two different WWTPs exhibit similar filtration resistances at Ca2+ concentrations of 0–4 mM. Finally, we demonstrate that the EPSs recovered from excess sludge can be used as adsorbents for the removal of diverse heavy metal ions (Pb2+, Cd2+, Cu2+) from wastewater, exhibiting performances that are on par with those of commercial adsorbents and are unaffected by the employed extraction procedure. Based on the obtained results, Ca2+ addition is confirmed to be a viable method for reducing filtration resistance during the membrane recovery of EPSs, since this ion does not affect the adsorption capacity for heavy metal ions.

Excess sludge produced by wastewater treatment plants contains extracellular polymeric substances (EPSs; 10–40 dry wt%) that mainly comprise polysaccharides and proteins and can be used as bioflocculants, adsorbents for heavy metal ions, and soil conditioners. Herein, we investigated the separation of EPS constituents using unstirred and stirred dead-end microfiltration in the presence of Ca2+, with an aqueous solution of sodium alginate (SA) and bovine serum albumin (BSA) employed as an EPS model. Acceptable separation efficiencies were obtained utilizing filter papers with micropores of various sizes, which retained calcium alginate aggregates formed due to the SA-Ca2+ interaction but allowed BSA to be filtered out. Notably, a certain minimal Ca2+ concentration was required to achieve the above separation, with the separation efficiency being independent of the SA:BSA concentration ratio at Ca2+ concentrations exceeding the threshold value. The filtration resistance decreased with increasing pore size, Ca2+ concentration, and BSA content. Rather unexpectedly, variation of filtration surface shear could not be used to improve the filtration separation efficiency and reduce fouling in spite of the revolution rate, since the disturbing flow forced the aggregates into the filter pores. The polysaccharide in the EPSs was separated effectively by microfiltration with the addition of Ca2+. Thus, the obtained results provide further insight into the microfiltration-aided separation and recovery of polysaccharides and proteins in EPSs.

The recovery of polymeric substances from excess sludge is gaining significant research interest in future wastewater treatment technologies. We present a surfactant-enhanced ultrasonic method to extract mixed polymeric substances with typical functional groups from excess sludge. Four potential reasons were revealed for the higher efficiency upon ultrasonication with surfactant: low surface tension, damage of non-covalent bonds between extracellular polymeric substances and cells, enhanced dissolution of polymeric substances, and release of intracellular polymeric substances caused by cell lysis. The increase in extraction efficiency after the addition of cetyltrimethylammonium bromide and sodium dodecyl sulfate reached the maximum of 76.5% and 53.1%, respectively. The contents of polysaccharides, proteins, and DNA were approximately 50% of the total polymeric substances, and the content of protein was higher than that of polysaccharide; the concentration change of the surfactant had a minimal effect on these contents. For the polymeric substances extracted via ultrasonication with surfactant, the size was smaller than that for the non-surfactant extraction; moreover, the contents of metals decreased significantly (Al: 0.18% → 0%; Na: 0.15% → 0%; Ca: 0.24% → 0.11%), which was probably caused by the interaction between the surfactant and metal ions in the excess sludge. The surfactant had a negligible effect on the properties of polymeric substances, adsorption capacity of polymeric substances for heavy metal ions, and dewatering performance of sludge. The recycled polymeric substances may be used as a substitute for commercial adsorbents of heavy metal ions. Thus, the obtained results provide further insight into the recovery of polymeric substances from excess sludge via the surfactant-enhanced ultrasonic method.

Alginate, a sustainable product, can be synthesized by organic substances in wastewater by aerobic granules. Although chemical precipitation is effective for extraction, this typically consumes considerable amounts of chemicals, causing chemical pollution. Alternatively, membrane separation can be used as a potential separation method. Resistance reduction and fouling mechanisms were investigated by constant-pressure dead-end filtration for the membrane recovery of alginate from a suspension formed in an aqueous solution of sodium alginate (SA) by the addition of Ca 2+ . Flux decline was analyzed by the Ruth's cake filtration theory and the Ruth's filtration coefficient, which indicated that feed filterability exponentially increased as Ca 2+ was added. The increased Ruth's filtration coefficient corresponded to decreased concentrations and average specific cake resistances of the components present in the suspension, e.g., colloids and polymers. The optimal amount of Ca 2+ should be economically feasible while also affording filtration resistance. Residual Ca 2+ in the filtrate can be reused. Residual salt ions increased filtration resistance. The filter cake formed on the membrane was compressible. The effect of protein on the ultrafiltration of alginate was considered. Microfiltration or filtration with a filter paper, exhibiting a high recovery rate of alginate, was suggested.

Methane (CH4) recovery from excess sludge plays an important role in wastewater treatment aimed at achieving carbon neutrality. Besides pretreatment for excess sludge, exogenous CO2 and even H2 have already been tested in enhancing CH4 production from anaerobic digestion (AD). However, exogenous H2 injected into AD might simultaneously influence both upstream acidogenesis and downstream methanogenesis. In this study, a series of batch tests were conducted to ascertain the influences of hydrogen partial pressure ( P H 2 ) on these two processes. Interestingly, the batch tests demonstrated that injecting exogenous H2 into AD at the beginning of each batch cycle can both stimulate acidogenesis (organic conversion rate) and enhance methanogenesis (both CH4 and biogas productions) at an appropriate P H 2 (=0.33 bar) and an optimal revolution (Rs = 200 rpm) of a shaker.

With a high rejection coefficient for trace pharmaceuticals and personal care products (PPCPs), forward osmosis (FO) membrane separation has become a cutting-edge technology in water treatment owing to its low energy consumption and low membrane fouling. Wastewater contains many types of PPCPs, and one pharmaceutical molecule affects the separation behaviors of other pharmaceuticals in FO. Therefore, simultaneous FO of multiple PPCPs needs to be investigated. In this study, the separation behaviors of four trace pharmaceuticals (ciprofloxacin (CIP), sulfamethoxazole (SMX), acetaminophen (ACP), carbamazepine (CBZ)), individually (termed “single pharmaceuticals”) and in combination (termed “binary pharmaceuticals” as two pharmaceuticals were studied simultaneously), during FO were investigated at trace concentrations using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that for single pharmaceuticals, the molecular sieve dominates their retention rate—the retention rate increases with increasing Stokes radius of the molecules (29.1 → 94.8% for 0.35 → 0.47 nm). For binary pharmaceuticals, the retention rates of both pharmaceuticals without charge decrease with increasing total molecule number (for ACP + CBZ, 31.4 → 52.1% (ACP), 75.1 → 83.0% (CBZ)). Negatively charged pharmaceuticals are mutually exclusive with the negatively charged FO membrane, resulting in the increase of the retention rate of pharmaceuticals (83.1 → 90.1% (CIP) when CIP + ACP → CIP + SMX). In the presence of a positively charged pharmaceutical, the retention rate of negatively charged pharmaceuticals decreases (85.7 → 80.4% (SMX) when SMX + ACP → SMX + CIP) because the positively charged pharmaceutical neutralizes the negative charge on the FO membrane surface, resulting in the weakening of electrostatic repulsion between the negatively charged pharmaceutical and FO membrane surface. The positively charged molecule attracts the negatively charged molecule, forming a couple of molecules with larger molecule weight and increasing the retention rate of the pharmaceuticals (80.4 → 88.2% (SMX) when pH = 7 → 5 for SMX + CIP). The results suggest that the interactions between pharmaceuticals cannot be ignored in the process of removing PPCPs by FO.

To solve the difficult problem of separating extracellular polymeric substances (EPSs) with adsorbed heavy metal ions (HMIs) from aqueous solutions, EPS recovery and HMI adsorption were combined into dead-end ultrafiltration (EPS-enhanced ultrafiltration, EPS-UF). First, an EPS solution was concentrated via UF into a cake on the membrane, which was then used to filter heavy-metal-containing wastewater. EPS-UF could effectively remove HMIs in wastewater, with a 94.8% Pb2+ removal efficiency and 85.5% EPS recovery efficiency with concentrations of 0.1 g/L EPS and 10 μM Pb2+. During concentration, the filtration resistance increased with increasing filtration pressure because of the high compressibility of the EPS cake and as filtration proceeded. During removal, a high filtration pressure (200 kPa) could not increase the filtration rate, and the removal efficiency of Pb2+ decreased markedly (78.9%). Ca2+ was proposed as a strategy for controlling membrane fouling because it was completely released from the cake after adsorbing Pb2+ and barely affected the characteristic groups in EPS. Fourier transform infrared and X-ray photoelectron spectroscopy revealed that carboxyls or esters from carboxylate and uronic acids in EPS bonded with HMIs via ion exchange or complexation, and the main characteristic groups in EPS remained unchanged, while more complex proteins formed.

The filtration behaviors were examined in microfiltration of binary mixtures of particles with two different sizes. Dilute suspension of monodisperse polystyrene latexes with particle diameters of 0.522 and 0.091 μm was filtered using the microfiltration membranes with the nominal pore size of 0.3 μm, making them essentially impermeable to larger particles but permeable to smaller particles. The filter cake comprised of larger particles alone initially formed because smaller particles permeate through the membrane. However, the flux decline became gradually marked since smaller particles were trapped into the pores of the filter cake of larger particles. Eventually, smaller particles were fully rejected, and thereafter the binary cake of both larger and smaller particles grew. This filtration behavior was reflected by both data of flux decline and particle rejection. The logistic equation was employed to describe the variation of the rejection of smaller particles with the progress of filtration. The flux decline behaviors were well described using the logistic equation on the basis of the resistance-in-series model that the total cake resistance was represented by adding the increased cake resistance caused by the capture of smaller particles to the cake resistance of larger particles alone.

The improvement of concentration performance was examined extensively for freeze concentration assisted with the use of shaking of the solution. Freeze concentration experiments of vitamin B1 aqueous solution were conducted using a reciprocal shaker, thereby generating the oscillatory motion, for a variety of amplitude and frequency conditions. The increase in the amplitude and frequency caused the decrease in the average distribution coefficient and the increase in the growth rate of the ice crystal, leading to the improvement of the performance of freeze concentration. The variations of solute concentration in the solution with freezing time were well described on the basis of the empirical equations representing the growth rate of ice crystal and the average distribution coefficient as functions of the shaking conditions such as the amplitude and frequency. The average distribution coefficient was maintained substantially constant throughout the course of freeze concentration, but the local distribution coefficient evaluated from the average distribution coefficient increased with the progress of freeze concentration, resulting in the reduction in the concentration efficiency. The increase in the freezing rate brought about the increase in the concentration rate in a shaking type of freeze concentration, but the excessive increase in the freezing rate is less-helpful for the improvement in the performance of freeze concentration.

Carbon-neutral operation of wastewater treatment plants (WWTPs) requires enhancing anaerobic digestion (AD) of excess sludge for a higher energy conversion efficiency. Among others, iron has been identified to function on enhancing methane production in AD. As an industrial residual, waste iron scraps (WISs) have been reported as potentially enhancing CH4 production in AD. With this study, the mechanisms of AD enhanced by WISs are analysed in a two-phase process: acidogenic phase (AP) and methanogenic phase (MP). Semi-continuous tests substantially excluded ORP reduction and hydrogen-evolution corrosion induced by WISs in enhancing CH4 production, although WISs (10 g Fe/L) could indeed increase CH4 production by 10.1% and 21.4% when added in AP and MP respectively. Detection on both FISH and enzymatic activities of involved microorganisms revealed that the stimulating effects of WISs on anaerobes (both catabolism and anabolism) could play an important (96.3%) role in enhancing CH4 production, which would facilitate hydrolysis of refractory organics and improvement of electron transport rate (ETR).

lactic acid, inclined tube sedimentation, ultrafiltration, flow velocity Abstract This study combined inclined tube sedimentation with ultrafiltration to remove the particles and protein in lactic acid fermentation broth. The influence of flow velocity on the extract property was investigated as well as the variations of flux, protein removal rate and lactic acid recovery in ultrafiltration. The result indicated that the inclined tube sedimentation was effective to remove the particles of fermentation broth. When the flow velocity was 0.031cm/s, the percentage of particles smaller than 10μm was 77%. The flow velocity 0.143cm/s in inclined tube sedimentation was more suitable in this study. SS removal rate can achieve 45.5% while protein removal rate and lactic acid recovery can be maintained above 90% in such situation

Flocculation of lactic acid (LA) fermentation broth using chitosan and cationic polyacrylamide (CPAM) as flocculants individually was evaluated. Flocculation effects under different flocculants dosages as well as the loss of the target product LA were investigated. It was found that CPAM was more suitable in flocculation of LA fermentation broth while the optimized dosage of CPAM was 0.2g/L. The results showed that flocculants made little impact on the LA so that it was feasible to treat lactic acid by flocculation.