Effect of bioflocculation on fouling-related biofoulants in a membrane bioreactor during saline wastewater treatments

Application of Aspergillus niger in Practical Biotechnology of Industrial Recovery of Potato Starch By-Products and Its Flocculation Characteristics

This study developed a practical recovery for potato starch by-products by A. niger and applied it on a plant scale to completely solve the pollution problems. Soughing to evaluate the effect of A. niger applied towards the production of by-products recycling and analyze the composition and characteristics of flocculating substances (FS) by A. niger and advance a possible flocculation mechanism for by-product conversion. After fermentation, the chemical oxygen demand (COD) removal rate, and the conversion rates of cellulose, hemicellulose, pectin, and proteins were 58.85%, 40.19%, 53.29%, 50.14%, and 37.09%, respectively. FS was predominantly composed of proteins (45.55%, w/w) and polysaccharides (28.07%, w/w), with two molecular weight distributions of 7.3792 × 10⁶ Da and 1.7741 × 10⁶ Da and temperature sensitivity. Flocculation was mainly through bridging and ionic bonding, furthermore, sweeping effects may occur during sediment. Flocculation was related to by-products conversion. However, due to severe pollution problems and resource waste, and deficiencies of existing recovery technologies, converting potato starch by-products via A. niger liquid fermentation merits significant consideration.

Novel intertidal wetland sediment-inoculated moving bed biofilm reactor treating high-salinity wastewater: Metagenomic sequencing revealing key functional microorganisms

In this study, two lab-scale moving bed biofilm reactors (MBBR), seeded with intertidal wetland sediment (IWS) and activated sludge (AS), were constructed to compare their performances in treating high-salinity (3%) wastewater. Under a wide range of influent TOC (178-620 mg/L) and NH₄⁺-N (25-100 mg/L), both the MBBRs (R_iws and R_as) exhibited excellent TOC removal efficiencies of >95%. Regarding nitrogen reduction, R_iws exhibited a significantly superior TN removal efficiency of 90.2 ± 1.8% than that of R_as (76.8 ± 2.9%). A correlation analysis was innovatively conducted comparing the results between metagenomic sequencing and DNA pyrosequencing, and positive linear relationships were found with R² values of 0.763-0.945. Meanwhile, for illustration of different TN removal performance, nitrogen metabolic pathways were also assessed. Moreover, a list of functional oxidases (EC: 1.13.11.1, EC: 1.13.11.2, EC: 1.13.11.24, EC: 1.13.12.16, EC: 1.4.3.4, EC: 1.16.3.3, EC: 1.14.14.28) was found in IWS, revealing its potential in degradation of recalcitrant organics.

Membrane bioreactors for hospital wastewater treatment: recent advancements in membranes and processes

Discharged hospital wastewater contains various pathogenic microorganisms, antibiotic groups, toxic organic compounds, radioactive elements, and ionic pollutants. These contaminants harm the environment and human health causing the spread of disease. Thus, effective treatment of hospital wastewater is an urgent task for sustainable development. Membranes, with controllable porous and nonporous structures, have been rapidly developed for molecular separations. In particular, membrane bioreactor (MBR) technology demonstrated high removal efficiency toward organic compounds and low waste sludge production. To further enhance the separation efficiency and achieve material recovery from hospital waste streams, novel concepts of MBRs and their applications are rapidly evolved through hybridizing novel membranes (non hydrophilic ultrafiltration/microfiltration) into the MBR units (hybrid MBRs) or the MBR as a pretreatment step and integrating other membrane processes as subsequent secondary purification step (integrated MBR-membrane systems). However, there is a lack of reviews on the latest advancement in MBR technologies for hospital wastewater treatment, and analysis on its major challenges and future trends. This review started with an overview of main pollutants in common hospital waste-water, followed by an understanding on the key performance indicators/criteria in MBR membranes (i.e., solute selectivity) and processes (e.g., fouling). Then, an in-depth analysis was provided into the recent development of hybrid MBR and integrated MBR-membrane system concepts, and applications correlated with wastewater sources, with a particular focus on hospital wastewaters. It is anticipated that this review will shed light on the knowledge gaps in the field, highlighting the potential contribution of hybrid MBRs and integrated MBR-membrane systems toward global epidemic prevention.

Analysis of the Curative Effect and Influencing Factors of Collagen Sponge Combined with Autologous Skin Graft in the Treatment of Deep Burn Patients

Burn is one of the common traumatic diseases in clinics. After deep burn, the complicated changes of the condition are caused by the burn wound, which ends with the repair of the wound. For patients with deep burns, whether the wound can be repaired as soon as possible is the key to the success of clinical treatment. For patients with deep burns, due to the lack of an autologous skin source, scar hyperplasia at donor site, skin graft repair at donor site, postoperative flap necrosis, and other problems in traditional surgical procedures, the method of improving function only by an autologous skin source has been unable to perform the later function reconstruction in patients with deep burns. In this study, collagen sponge combined with autologous skin graft was used to treat patients with deep burn, and the clinical efficacy of the patients was observed, and the related factors affecting the efficacy of the patients were analyzed. The results showed that collagen sponge combined with autologous skin graft was effective in the treatment of deep burn patients, and it was worth popularizing. Deep III-IV degree burns, wound infection, and hospital stay >3 months are all risk factors affecting the postoperative curative effect of patients. Therefore, in the clinical work, we should focus on patients with deep III-IV degree burns, perform surgery as soon as possible, and actively deal with wounds to prevent infection, which is beneficial to improve the curative effect.

Biological-based control strategies for MBR membrane biofouling: a review

Membrane bioreactor (MBR) technology has been paid extensive attention for wastewater treatment because of its advantages of high effluent quality and minimized occupation space and sludge production. However, the membrane fouling is always an inevitable problem, which causes high operation and maintenance costs and prevents the wide use of MBR technology. The membrane biofouling is the most complicated and has relatively slow progress among all types of fouling. In recent years, many membrane biofouling control methods have been developed. Different from the physical or chemical methods, the biological-based strategies are not only more effective for membrane biofouling control, but also milder and more environment-friendly and, therefore, have been increasingly employed. This paper mainly focuses on the mechanism, unique advantages and development of biological-based control strategies for MBR membrane biofouling such as quorum quenching, uncoupling, flocculants and so on. The paper summarizes the up-to-date development of membrane biofouling control strategies, emphasizes the advantages and promising potential of biological-based ones, and points out the direction for future studies.

Biodegradation performance and biofouling control of a halophilic biocarriers-MBR in saline pharmaceutical (ampicillin-containing) wastewater treatment

This work develops a halophilic biocarriers-MBR for saline pharmaceutical wastewater treatment. The system has effectively treated the ampicillin-containing saline wastewater for 32 days, when the ampicillin concentration is lower than 20 mg/L. The system can tolerate the saline organic wastewater with a reasonable biodegradability (removals of COD over 75%) when the ampicillin concentration is 50 mg/L. The system has a bad performance in biodegradation (COD removals around 60-70%) and fouled within 16 days at a high ampicillin concentration of 100 mg/L. At high transmembrane pressures over 30 KPa, some ampicillin molecules may permeate through the membrane causing decreases in the ampicillin removal. The concentrations of protein and carbohydrate in EPS and SMP have increased over time and with increasing the ampicillin concentration. The method of biofouling control in MBR for the ampicillin situations has been proposed based on monitoring the concentrations of EPS and SMP. The drying-assisted monitoring of membrane biofoulants has showed a better efficiency than the monitoring of transmembrane pressure for membrane anti-biofouling in the treatment of pharmaceutical saline wastewaters where a spectroscopic detection can be hardly applied. This work may benefit relative research works for the control of biodegradation performance and membrane biofouling to better treat saline pharmaceutical wastewaters.

Application of a specific membrane fouling control enhancer in membrane bioreactor for real municipal wastewater treatment: Sludge characteristics and microbial community

The feasibility of a novel bioflocculant (GemFloc™) for membrane fouling mitigation in membrane bioreactor (MBR) was investigated during real municipal wastewater treatment. When compared to the conventional MBR (CMBR), suspended sludge in the MBR with GemFloc™ (G-MBR) showed less soluble microbial products (SMP), higher ratios of proteins to polysaccharides in SMP (SMP_P/SMP_C) and loosely bound extracellular polymeric substances (LB-EPS). Adding GemFloc™ also enlarged floc size (> 200 µm), and increased tightly bound EPS levels, zeta potential and relative hydrophobicity of sludge flocs, further reduced cake layer and pore blocking resistances. Moreover, more diverse microbial community and enrichment of fouling reduction microbes such as Arenimonas and Flavihumibacter were observed in the G-MBR, together with less abundant microbes (e.g. Sphaerotilus and Povalibacter) which could aggravate membrane fouling. Therefore, GemFloc™ has high capability in improving sludge characteristics, mitigating membrane fouling and increasing diversity of special functional bacterial community in MBR.

Influence of salinity on the biological treatment of domestic ship sewage using an air-lift multilevel circulation membrane reactor

Recently, strict standards for ship domestic sewage discharge have been implemented by the International Maritime Organization (IMO). The high salinity of ship sewage was considered a key factor influencing the removal efficiency of ship sewage treatment systems. In the present study, the salinity effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) from ship domestic sewage was investigated by using a novel air-lift multilevel circulation membrane reactor (AMCMBR). Enzyme activity analysis and wavelet neural network (WNN) models were built to determine the mechanisms of the process. The experimental results indicate that high salinity levels (> 21 g/L) had a negative impact on COD and NH₄⁺-N removal efficiencies, and low saline concentrations (≤ 21 g/L) caused a negligible effect. The COD and NH₄-N removal efficiencies were 84% and 97%, respectively, at a salinity of 21 g/L, which were higher than those at low salinities (i.e., 7 g/L and 14 g/L). Invertase and nitrate reductase had a close relationship with removal performance, and they can be considered important indicators reflecting the operation effort under saline environments. With high predictive accuracies, the constructed WNN models simulated the complex COD and NH₄⁺-N removal processes well under different saline concentrations, ensuring the long-term stable operation of the AMCMBR under different salinities.

Gaining deeper insights into the bioflocculation process occurring in a high loaded membrane bioreactor used for the treatment of synthetic greywater

In the present study, a high loaded membrane bioreactor (HL-MBR) operated at a hydraulic retention time (HRT) of 1.5 h, and three different sludge retention times (SRTs) in the range of 0.5-2 days, was used for the treatment of synthetic greywater. The chemical oxygen demand (COD) removal efficiency of the system was in the range 87-89% at all SRTs. Bioflocculation efficiency (defined as the percentage of suspended COD in the concentrate stream), COD bio-oxidation, total extracellular polymeric substances (EPS), tightly bound (TB) EPS and the ratio of EPS protein (EPS_p) to carbohydrate (EPS_c) increased when SRT was increased from 0.5 to 2 days. Sludge supernatant soluble microbial products (SMP) increased with increase in SRT from 0.5 to 2 days, while the effluent SMP was negligible. Particle size distribution analyses revealed a bimodal distribution at an SRT of 0.5 days, and normal distributions at other SRTs. Furthermore, depending on the value of the F/M ratio, different SRTs in the range of 0.5-2 days had either positive or negative effects on the mean particle size. Linear correlation analyses were performed using the data obtained during both transient and steady-state operations of the HL-MBR system. TB-EPS and EPS_p showed strong correlations with the biofloccultaion efficiency, whereas loosely bound (LB) EPS correlated with soluble COD removal. TB-EPS and EPS_c had negative correlations with the energy recovery potential of the system. The trend of change of parameters affecting membrane fouling intensity with SRT suggested that, in the range studied, the lowest rate of membrane fouling would be expected at SRT of 0.5 days.

A critical review on saline wastewater treatment by membrane bioreactor (MBR) from a microbial perspective

This work has reviewed from a microbial perspective and listed the typical studies on MBR techniques for saline wastewater treatments. When the salinity of influent is lower than 10 g/L NaCl, conventional MBR can be easily applied with adjusted operating conditions. For better biodegradation and anti-fouling ability at higher salinities (10-100 g/L), modified and hybrid MBR systems may need to be wisely designed according to the change in the microbial community and contents of EPS/SMP. To treat hypersaline wastewaters with salinities of up to 100 g/L NaCl, inoculation of halophilic bacteria has been applied in MBR works. Microbial community structures in some typical works have been discussed from a microbial perspective to benefit the identification and isolation of halophilic bacteria for future works. The following aspects are also suggested in future MBR research for saline wastewater treatment: (1) The structure design of MBR and the manufacture of advanced membranes; (2) The maintenance of the microbial biodiversity for anti-membrane fouling; (3) The metabolic mechanism for halophilic (or salt-tolerant) microorganisms against salinity shocks; (4) The revolution stage and process of microorganisms during saline wastewater treatment in MBR; (5) The effects of characteristics (cell structure, shape and metabolic pathways) of microorganisms on the salt tolerance; (6) Applying halophilic microorganisms for salinities over 150 g/L NaCl.

Enhanced removal mechanism of iron carbon micro-electrolysis constructed wetland on C, N, and P in salty permitted effluent of wastewater treatment plant

In this study, the combination of a constructed wetland (CW) with iron-carbon (Fe-C) system was used to enhance the simultaneous removal of carbon, nitrogen and phosphorus in salty permitted effluent of wastewater treatment plant (SPE-WTP). The removal mechanism of Fe-C micro-electrolysis CWs with different salinity (0.027, 0.308, and 0.511%) for treating SPE-WTP was investigated, including chemical oxygen demand (COD), phosphorus and nitrogen removal, the mass balance, as well as the changes in the microbial community structure. The results showed the salinity has a certain influence on the contaminant removals, and can enhance nitrogen removal under certain conditions. When the salinity increased from 0.308% to 0.511%, the removal of COD decreased from 68.20% to 62.69%, whereas the removal of total nitrogen (TN) increased from 72.02% to 81.21% in the ICCW-p system (including P. australis as the plant and gravel doped with 3% iron-carbon as the matrix). Microbial degradation, including the electrochemical effect (the degradation by iron-carbon micro-electrolysis) was the main N removal pathway in the ICCW-p system. The ICCW-p system always achieved higher removal rates (such as 81.21% TN and 62.69% COD removals at 0.511% salinity) than that in ICCW-n system (without plants and gravel doped with 3% iron-carbon as the matrix, 63.76% TN and 56.31% COD removals, respectively) and CW-n (without plants and gravel as the matrix, 14.90% TN and 22.39% COD removals, respectively). In addition, high-throughput sequencing analysis revealed that high salinity increased the abundance of N-removing bacteria in the ICCW-p system. Furthermore, with the introduction of iron-carbon in CWs, the removal methods in ICCW-p were diverse, which has enough ability to resist the impact of salinity. Fe electrolysis produced different valence states that acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions, which enhanced the simultaneous removal of carbon, nitrogen and phosphorus.