Sludge Membrane Bioreactor Research Articles

Enhanced performance and mechanism of adsorption pretreatment for alleviating membrane fouling in AGMBR: Impact of structural variations in carbon adsorbents

The structural variances of adsorbents play a crucial role in determining the number of effective adsorption sites and pretreatment performance. However, there is still a gap in comprehending the impact of different carbon structural adsorbents on membrane fouling. Therefore, this study aimed to compare the efficacy of granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) in mitigating membrane fouling during municipal sewage reclamation using an aerobic granular sludge membrane bioreactor (AGMBR). The results demonstrated that the utilization of PAC significantly enhanced the normalized flux and reduced fouling resistance in comparison to GAC and ACF systems. PAC effectively adsorbed low and medium-molecular-weight pollutants present in raw sewage, resulting in an increase in average particle size and a decrease in foulant content on the membrane surface. The Hermia model indicated that adsorption pretreatment minimized standard blocking while promoting the formation of a sparse and porous cake layer. Moreover, according to the extended Derjaguin–Landau–Verwey–Overbeek theory, PAC has been demonstrated as the optimal antifouling system owing to its enhanced repulsion between membrane-foulant and foulant-foulant interactions. Correlation analysis revealed that the exceptional antifouling performance of the PAC system was due to its high removal rates of chemical oxygen demand (~78 %) and suspended solids (~97 %). This research offers valuable insights into the mitigation of membrane fouling through the utilization of adsorbents featuring diverse carbon structures.

Insights into feasibility and microbial characterizations on simultaneous elimination of dissolved methane from anaerobic effluents and nitrate/nitrite reduction in a conventional anoxic reactor with magnetite

Discovery of nitrate/nitrite-dependent anaerobic methane oxidation (DAMO) challenges the conventional biological treatment processes, since it provides a possibility of simultaneously mitigating dissolved methane emissions from anaerobic effluents and reducing additional carbon sources for denitrification. Due to the slow growth of specialized DAMO microbes, this possibility has been just practiced with biofilms in membrane biofilm reactors or granular sludge in membrane bioreactors. In this study, simultaneous elimination of dissolved methane from anaerobic effluents and nitrate/nitrite reduction was achieved in a conventional anoxic reactor with magnetite. Calculations of electron flow balance showed that, with magnetite the eliminated dissolved methane was almost entirely used for nitrate/nitrite reduction, while without magnetite approximately 52 % of eliminated dissolved methane was converted to unknown organics. Metagenomic sequencing showed that, when dissolved methane served as an electron donor, the abundance of genes for reverse methanogenesis and denitrification dramatically increased, indicating that anaerobic oxidation of methane (AOM) coupled to nitrate/nitrite reduction occurred. Magnetite increased the abundance of genes encoding the key enzymes involved in whole reverse methanogenesis and Nir and Nor involved in denitrification, compared to that without magnetite. Analysis of microbial communities showed that, AOM coupled to nitrate/nitrite reduction was proceeded by syntrophic consortia comprised of methane oxidizers, Methanolinea and Methanobacterium, and nitrate/nitrite reducers, Armatimonadetes_gp5 and Thauera. With magnetite syntrophic consortia exchanged electrons more effectively than that without magnetite, further supporting the microbial growth.

Intensifying the simultaneous removal of nitrogen and phosphorus of an integrated aerobic granular sludge-membrane bioreactor by Acinetobacter junii

This work aims at intensifying the simultaneous removal of nitrogen and phosphorus of an integrated aerobic granular sludge (AGS) - membrane bioreactor (MBR) by Acinetobacter junii. After acclimation and enrichment in a sequencing batch reactor (SBR), Acinetobacter junii, a kind of denitrifying phosphate accumulating organism (DPAO), was successfully screened in the used SBR. Then it was verified to be capable of effectively enhancing the performance in the simultaneous removal of nitrogen and phosphorus of AGS-MBR. In the system, DPAO (Acinetobacter junii) mainly occurred in AGS, and the highest ratio even reached 22.8%, but its competitive advantages highly depend on the size of AGS. The presented results can cultivate AGS and enrich DPAO simultaneously to improve the removal of nitrogen and phosphorus of an AGS-MBR, which provide an environmentally friendly approach to upgrade traditional wastewater treatment processes.

Effects of granule disintegration and sludge re-aggregation on fouling behaviors and bio-cake formation in aerobic granular sludge membrane bioreactor (AGMBR)

The contribution of granules to membrane fouling alleviation in aerobic granular sludge-membrane bioreactor (AGMBR) has been increasingly investigated, yet the inoculated granules in MBR are more unstable than those in conventional AGS system and thus in-depth insight into the effects of the mutual transformation between granules and flocs on membrane fouling as well as corresponding bio-cake formation is necessary. Herein, we found that the disintegration of granules was accompanied by the release of soluble microbial products (SMP) and the increase of microbial diversity. The re-granulation phase occurred when granules gradually re-dominated the sludge system with the growth of biomass and the massive secretion of extracellular polymeric substances (EPS), corresponding to the declined microbial diversity and stable pollutants removal (COD: 93.45–98 %, TN: 21.06–36.86 %). Compared with the granule disintegration phase, less flocs deposition and fewer contents of SMP containing high molecular weight (>100 kDa) compounds in bio-cakes in the re-granulation phase resulted in the longer filtration period, as evidenced by lower attractive interaction energies between sludge foulants and membranes according to extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. Microbial community analysis demonstrated higher relative abundance of filamentous bacteria (Thiothrix) and lower relative abundance of denitrifiers (e.g, Hydrogenophag, Trichococcus, Arenimonas, Acinetobacter) in bio-cakes in the re-granulation phase. Besides, the genera Thiothrix, norank_f__env.OPS_17 and Aeromonas may be responsible for the organic foulants accumulation on membrane surface. More importantly, stronger positive correlations among microbial populations between bio-cake and suspended sludge in the re-granulation phase indicated the lower propensity of membrane fouling. The systematic insights into the effects of granules disintegration and sludge re-aggregation on fouling layer may have important implications for the future development of membrane fouling control in AGMBR system.

Anti-biofouling performance and microbial communities of an integrated fixed-film activated sludge membrane bioreactor with a fibrous carrier material: Pilot-scale demonstration

Widespread use of membrane bioreactors for high-performance wastewater treatment depends on the prevention of biofouling during membrane filtration, which can reduce operating costs. Biofouling is usually prevented using mechanical and chemical membrane treatment methods, which can be time-consuming and expensive. In this study, we developed bio-capsules as a fluidizing carrier material in an integrated fixed-film activated sludge membrane bioreactor (IFAS-MBR). The bio-capsules were prepared from moniliform polyvinylidene chloride fibrous balls enclosed in a spherical plastic basket, and could harbor protozoa and metazoa. A pilot-scale anoxic–oxic IFAS-MBR system with a total volume of 132 m3 was operated to remove organic carbon and nitrogen from municipal wastewater at a high permeate flux (0.84 m3/m2/day). The efficacy of the bio-capsules and the prokaryotic/eukaryotic community structures in the system were investigated. After operation for 1 year, the system demonstrated stable removal of organic carbon (76.0 % ± 15.5 % as total organic carbon, 93.1 ± 5.3 % as BOD, and 88.5 ± 5.2 % as CODMn) and nitrogen (71.3 % ± 9.3 %) despite fluctuations in the influent concentrations. Increases in transmembrane pressure (TMP) were retarded from its increase rates from 0.56 kPa/day to 0.149–0.224 kPa/day by the bio-capsules, and the TMP was kept constant at around 20 kPa throughout the operational period. High-throughput sequencing of 16S rRNA gene amplicons showed that the prokaryotic family Pirellulaceae was metabolically active and correlated with the TMP. According to the 18S rRNA gene sequencing, the eukaryotic metazoan Bdelloidea was more abundant in the bio-capsules than in activated sludge, which was supported by microscopic observations. These results suggest that the application of bio-capsules prevents increases in the TMP by harboring the procaryotes and eukaryotes responsible for biofouling mitigation in the IFAS-MBR system.

Simultaneous nitrogen and phosphorus removal from black water: Effects of dissolved oxygen level and sludge concentration on full-scale performance and bacterial community dynamics

Removal of nutrients from pretreated black water is difficult during the biological nutrient removal process, owing to the lack of carbon sources. To improve nitrogen and phosphorus removal, this study explored optimal operating strategies in a plant-scale multistage activated sludge-membrane bioreactor system for black water treatment. The results showed that the nutrient removal efficiency was highly dependent on the regulation of dissolved oxygen (DO) levels and sludge concentrations. The decreased DO levels (0.6–0.7 mg O2/L) in aerobic zones O3–O5 and the increased sludge concentrations (10.5 g/L) enhanced simultaneous nitrification and denitrification (SND), thereby improving the nitrogen removal efficiency from 82.4 % to 94.3 %. Additionally, when the nitrates were mostly reduced in the aerobic zones, phosphorus removal significantly increased from 29.6 % to 75.7 %. High-throughput sequencing analyses revealed a continuous increase in bacterial diversity during the entire operation period to adapt to the black water properties. Although the proportion of nitrogen- and phosphorus-removing bacteria decreased under oxygen-limited conditions, nitrogen removal efficiency was guaranteed via the SND pathway. The bacterial relative abundances could be partially or fully recovered by appropriately adjusting the DO levels and sludge concentrations.

Insights into the alleviation of membrane fouling in AGMBR through thermal/Fe2+-activated persulfate pre-oxidation: Performance and mechanisms

Aerobic granular sludge membrane bioreactors (AGMBRs) are a viable option for municipal sewage reuse; however, the issue of membrane fouling remains a significant obstacle to overcome to achieve large-scale implementation. Therefore, a novel thermal/Fe2+/persulfate (PDS) system was proposed to investigate its alleviation effect on membrane fouling in AGMBR. The findings indicated that the thermal/Fe2+/PDS system demonstrated superior efficacy in eliminating pollutants from raw sewage. Radical scavenging experiments demonstrated that sulfate radicals and coagulation were the primary contributors to mitigating membrane fouling in the thermal/Fe2+/PDS system, effectively reducing fouling resistance and retarding the decline in membrane flux. Analysis of interfacial interaction energy indicated that increasing the electrostatic double-layer repulsion between foulant–membrane and foulant–foulant could mitigate membrane fouling. Additionally, the interfacial characteristics (membrane surface morphology and foulant content) of the fouled membranes were characterized to further validate the efficacy of this system in alleviating membrane fouling. The correlation analysis revealed a positive association between the mitigation of membrane fouling and the substantial elimination of various pollutants, such as chemical oxygen demand, polysaccharides, and suspended solids. This study highlights the exceptional performance of the thermal/Fe2+/PDS system and provides novel insights into alleviating AGMBR membrane fouling.

Integrating eco-environmental assessment with energy recovery for petrochemical wastewater treatment technologies: A transition towards green and sustainable management

The petrochemical industry is a significant source of hazardous waste, leading to widespread environmental pollution. For the first time, an integrated approach was employed in the current study to combine life cycle assessment (LCA) coupled life cycle cost (LCC) analysis with waste sludge disposal scenarios to evaluate trickling filter (TF), membrane bioreactor-reverse osmosis (MBR-RO), and integrated fixed-film activated sludge-membrane bioreactor (IFAS-MBR) performance at the individual unit level for the treatment of petrochemical wastewater. The midpoint LCA modeling indicated that the main environmental burdens in the studied systems were freshwater eutrophication (<5.31 kg P eq) and toxicity potentials (<263.16 kg 1,4-DCB). These impacts were primarily attributed to the emissions of zinc, copper, nickel, and the processing of heat and gas. Furthermore, the results of the LCC analysis revealed that the TF system was more cost-effective than the MBR-RO and IFAS-MBR systems. By utilizing the produced biogas for energy provision in the TF system, significant reductions in toxicity potentials and ecosystem impact categories ranging from 26.72 % to 56.69 % were observed. Additionally, the biowaste scenario exhibited lower environmental concerns (<50 %) compared to incineration or landfill. In conclusion, this investigation provides valuable perspectives and a sustainable strategy for future policymaking regarding petrochemical wastewater treatment.

Dispersive biofilm from membrane bioreactor strains: effects of diffusible signal factor addition and characterization by dispersion index.

Biofilm occurs ubiquitously in water system. Excessive biofilm formation deteriorates severely system performance in several water and wastewater treatment processes. Quorum sensing systems were controlled in this study with a signal compound cis-2-Decenoic acid (CDA) to regulate various functions of microbial communities, including motility, enzyme production, and extracellular polymeric substance (EPS) production in biofilm. The addition of CDA to six strains extracted from membrane bioreactor sludge and the Pseudomonas aeruginosa PAO1 strain was examined for modulating biofilm development by regulating DSF expression. As the CDA doses increased, optical density of the biofilm dispersion assay increased, and the decrease in EPS of the biofilm was obvious on membrane surfaces. The three-dimensional visual images and quantitative analyses of biofilm formation with CDA proved thinner, less massive, and more dispersive than those without; to evaluate its dispersive intensity, a dispersion index was proposed. This could compare the dispersive effects of CDA dosing to other biofilms or efficiencies of biofouling control practices such as backwashing or new cleaning methods.

A comparison study of heat-assisted Fe2+/persulfate and powdered activated carbon/persulfate wastewater pre-treatment for membrane fouling alleviation

Heat/Fe2+/persulfate (PS) and heat/powdered activated carbon (PAC)/PS exhibit oxidation, coagulation, and adsorption effects, respectively. However, no studies have been conducted to discuss and compare the synergistic contribution to membrane fouling mitigation under thermal synergy. Herein, heat/Fe2+/PS and heat/PAC/PS systems were used to alleviate membrane fouling during municipal wastewater recycling in an aerobic granular sludge membrane bioreactor (AGMBR), and the effects of oxidation, coagulation, and adsorption on the membrane fouling mitigation were analyzed. The results showed that heat/Fe2+/PS and heat/PAC/PS effectively increased the filtration flux, decreased the fouling resistance, and maintained the membrane surface morphology. Compared to heat/PAC/PS, the heat/Fe2+/PS exhibited better control of membrane fouling owing to the generation of sulfate radicals and Fe3+. The non-radical effect is an important way to mitigate membrane fouling by heat/PAC/PS. Moreover, the pretreatment systems were effective in decomposition and removal of large-particle-size pollutants owing to their excellent oxidation capacity. According to the extended Derjaguin–Landau–Verwey–Overbeek theory, the heat/Fe2+/PS system had the higher energy barrier values of foulant–membrane (155.31 kT) and foulant–foulant (113.75 kT). The cake filtration and intermediate blocking models were the major mechanisms of membrane fouling, and efficient removal of chemical oxygen demand (R2>0.93) and suspended solids (R2>0.92) were beneficial to the membrane fouling mitigation. This study elucidates the differences in the mechanisms of heat/Fe2+/PS and heat/PAC/PS in mitigating AGMBR membrane fouling.

Effect of superficial gas velocity on membrane fouling behavior and evolution during municipal wastewater treatment

Aerobic granular sludge membrane bioreactor (AGMBR) is a promising technology for wastewater reuse and membrane fouling mitigation. Superficial gas velocity (SGV) plays an important role in the efficient and stable operation of AGMBR. However, the effect of SGV on the membrane fouling behavior and evolution of AGMBR has not been reported, which was systematically investigated in this study. AGMBR with various SGVs was used to treat synthetic municipal wastewater, and more than 94.5% and 60.5% of organics and total nitrogen, respectively, were removed at all SGVs. Further, a larger SGV prolonged the AGMBR overall operation. Contents and physiochemical properties of foulants varied with SGV and transmembrane pressure (TMP). Micro-level analyses revealed that the proportion of pore-blocking resistance in total fouling resistance as well as the microbial community diversity in the sludge mixture or on the membrane surface increased with TMP and SGV. The correlation analyses demonstrated that decreasing the polysaccharide content of soluble microbial products, increasing the protein content of tight extracellular polymeric substances in the sludge mixture, and enhancing the relative abundance of Bacteroidia and Gammaproteobacteria were beneficial for mitigating membrane fouling. This study reveals membrane fouling evolution and provides theoretical guidance for the large-scale application of AGMBR in wastewater reuse.

Biofouling mitigation by D-tyrosine in membrane bioreactor: Short-term performance

D-amino acids can inhibit the formation of biofilm without affecting bacterial growth, which is a new strategy to control membrane biofouling. This paper investigated the effects of D-tyrosine on the performance of membrane bioreactor (MBR) during short-term operation. The results showed that the critical flux of activated sludge in MBR increased with the existence of D-tyrosine. The removal efficiencies of wastewater were not affected by D-tyrosine. The fouling propensities of soluble microbial products (SMP) in both MBRs were almost the same. Extracellular polymeric substance (EPS) in D-tyrosine group exhibited weaker fouling propensity. Further research indicated that the addition of D-tyrosine did not have a significant impact on SMP. D-tyrosine lead to the reduction of EPS polysaccharides and the great fluctuation of EPS protein. Microbial community analysis demonstrated that the addition of D-tyrosine changed the microbial community structure in MBR, which might be one of the reasons for the change of EPS.

Application of Encapsulated Quorum Quenching Strain Acinetobacter pittii HITSZ001 to a Membrane Bioreactor for Biofouling Control

Quorum quenching (QQ) is a novel anti-biofouling strategy for membrane bioreactors (MBRs) used in wastewater treatment. However, actual operation of QQ-MBR systems for wastewater treatment needs to be systematically studied to evaluate the comprehensive effects of QQ on wastewater treatment engineering applications. In this study, a novel QQ strain, Acinetobacter pittii HITSZ001, was encapsulated and applied to a MBR system to evaluate the effects of this organism on real wastewater treatment. To verify the effectiveness of immobilized QQ beads in the MBR system, we examined the MBR effluent quality and sludge characteristics. We also measured the extracellular polymeric substances (EPS) and soluble microbial products (SMP) in the system to determine the effects of the organism on membrane biofouling inhibition. Additionally, changes in microbial communities in the system were analyzed by high-throughput sequencing. The results indicated that Acinetobacter pittii HITSZ001 is a promising strain for biofouling reduction in MBRs treating real wastewater, and that immobilization does not affect the biofouling control potential of QQ bacteria.

The impact of sunlight on fouling behaviors and microbial communities in membrane bioreactors

Membrane fouling is a significant obstacle to applying membrane bioreactors (MBRs) for wastewater treatment. Here we report the impact of sunlight irradiation on membrane fouling, biopolymers, signal molecules, and microbial communities in MBRs. The degradation of signal molecules, which induce membrane biofouling, occurred through solar photolysis in batch tests. However, MBR sludge exposed to sunlight exhibited different biological behaviors creating more soluble microbial products (SMP) and signal molecules (particularly autoinducer-2). Cell lysis and deflocculation occurred when the MBR mixed liquor was exposed to sunlight. MBR fouling rates coincided with the temporal concentration profiles of SMP and signal molecules. Sunlight caused drastic changes in the MBR microbial community, stimulating the preferential growth of specific bacteria (e.g., Deinococcus Runella, Flavitalea, Glaiimonas, and Rurimicrobium). The nonmetric multidimensional scaling analysis of the MBR community structures with and without sunlight irradiation showed two distinct microbial community clusters and their reversibility. Network analysis based on Spearman's rank correlations revealed that with sunlight irradiation, fouling rates had significant positive connections with SMP proteins and the Flavitalea genus. The findings of this study demonstrate that sunlight is a considerable factor affecting membrane fouling and microbial ecology in MBRs, needing shade for fouling mitigation and sustainable operation.

New insights into mycelial pellets for aerobic sludge granulation in membrane bioreactor: Bio-functional interactions among metazoans, microbial communities and protein expression

Direct cultivation of aerobic granular sludge (AGS) in membrane bioreactor (MBR) has gained increasing attention. Mycelial pellets (MPs) has been shown capable of promoting rapid granulation of aerobic sludge in MBR, yet mechanisms remain unclear and in-depth insight into cross-scale interactions between MPs and indigenous microbiota as well as the corresponding protein expression functions is necessary. Herein, we found that the addition of MPs in MBR resulted in massive growth of metazoans with 40–400 /mL for rotifers, 20–140 /mL for nematodes and 2–420 /mL for oligochaetes in the initial phase of granulation. This facilitated the MPs to rapidly aggregate with bacteria to form defensive granules for physical protection from predation by metazoans, which inhibited the overgrowth of filamentous bacteria Thiothrix and promoted the reproduction of functional bacteria related to nitrogen removal (Nitrospira, Trichococcus and Acinetobacter). Proteomic analysis demonstrated that the upregulation of functional proteins was mainly ascribed to the decrease of Thiothrix and the increase of Nitrospira, resulting in the enhancement of metabolic pathways involved in glycolysis/gluconeogenesis, citrate (TCA) cycle, oxidative phosphorylation, pyruvate metabolism, nitrogen metabolism and biosynthesis of amino acids, which was responsible for MPs-induced AGS with denser structure, more abundant proteins and β-polysaccharides, higher species diversity, significant nitrogen removal (33.12–42.33%) and lower membrane fouling potential. This study provided a novel and comprehensive insight into the enhanced granulation of aerobic sludge by MPs and the functional superiority of MPs-induced AGS in MBR system.

Removal performance and biodegradation mechanism of sulfonamides antibiotic contained wastewater by IFAS-MBR bioreactor

Sulfonamides (SAs) have been extensively detected in drinking water sources and warrant further studies on the removal of them in water treatment processes. Sulfadiazine (SDZ), sulfamethoxazole (SMX) and sulfathiazole (STZ) were investigated using Fixed-film activated sludge membrane bioreactors (IFAS-MBRs). The research indicates that addition of SAs has obvious inhibit the removal of COD and NH4+-N in three reactors while the average removal efficiencies of SDZ, SMX and STZ were all over 94 %. The degradation mechanism of three SAs were concluded as follows: the fracture of multiple cleavage sites to form new intermediates, breaking of bonds in different R substituents to generate new substances, hydroxylation, amino nitration, and recombination between these cleavage substances. The microbial community results showed that at the phylum level, Proteobacteria was the dominant, followed by Bacteroidetes, Patescibacteria and Acidobacteria. At the genus level, Rhodanobacter may be the characteristic bacteria in SAs degradation.

A Review on Development of Aerobic Granular Sludge Membrane Bioreactor for the Industrial Effluent Treatment

The technology of aerobic granular sludge and Membrane Bioreactor (MBR) were combined to develop an Aerobic Granular Sludge Membrane Bioreactor (AGMBR). Biomass content is high, higher the retention time of biomass, and the capacity of phosphorus and nitrogen removal has been shown by aerobic granular sludge; now a day it is a promising option for wastewater treatment. Reclaiming wastewater one of the favourite choices is Membrane technology in removing organic and inorganic impurities they have recognised as moderately operative with biological entities removal from wastewater. Consequently, the wastewater treatment membrane bioreactor and aerobic granular sludge technology are dynamic and new trending cost-efficient technologies. This article aims to review all the potential applications and principles in AGMBR technology.

The granular sludge membrane bioreactor: A new tool to enhance Anammox performance and alleviate membrane fouling

Anammox process has be widely concerned as a novel biological nitrogen removal technology because of reduced operating costs and environmental friendliness. However, the long start-up time and operational instability of Anammox process has hindered its wide applications. A new-type hybrid granular sludge membrane bioreactor (GSMBR) combining sludge granulation with membrane filtration was developed for accelerating start-up of Anammox process and stabilizing its operation as well as alleviating the membrane fouling. Anammox start-up period was shortened to 43 days, the maximum nitrogen removing rate and efficiency reached 0.83 kg N m−3 d−1 and 97 % respectively on 115 d. Moreover, the membrane fouling is relatively light. The maximum transmembrane pressure only reached 32 kPa on 115 d, when there were still several visible micropores and channels on the fouled membrane surface. The mature brownish-red Anammox granular sludge mostly sized at 0.5–1.0 mm. The specific population shift from norank Alphaproteobacteria to Candidatus Brocadia was found. Three Anammox species were present in the mature sludge and uncultured Candidatus Brocadia sp. was the predominated bacteria. GSMBR was proven to be a robust reactor for enhancing Anammox performance. This study was helpful to promote the engineering applications of Anammox process in treating the high-strength nitrogenous wastewaters.

Municipal wastewater treatment and fouling in microalgal-activated sludge membrane bioreactor: Cultivation in raw and treated wastewater

Since the advent of conventional activated sludge biological treatment plants, their low efficiency in nitrogen and phosphorus removal has become a significant concern. Therefore, in this study, the performance of microalgal-activated sludge membrane bioreactor (MAS-MBR) as a self-biological treatment or as a post-treatment for conventional biological treatments was investigated. A continuous MAS-MBR with two ratios of algae/sludge (only microalgae and 5:1) was used to treat raw and treated wastewater. The optimum case was achieved with the cultivation of mixed algae/sludge in raw wastewater (R2 case). In this case, the ammonium and phosphorus removal efficiencies were 94.36 ± 3.5 and 88.37 ± 3 %, respectively. Furthermore, the highest oxygen production rate (OPR) and oxygen uptake rate (OUR) values were obtained in this case (145.58 ± 3 and 68.43 ± 1.5 mgO2/lit.d, respectively). In addition, membrane fouling was adversely increased in R2 compared with other cases, indicating the necessity of membrane cleaning for high-performance bioreactors in nutrient removal. Transmembrane pressure (TMP) jump in R2 was captured after 14 days, while the results supported that the membrane fouling was influenced by raised production of carbohydrate fraction of soluble microbial products (SMPc) and protein fraction of extracellular polymeric substances (EPSp) at first and last stages, respectively. Therefore, although the MAS-MBR is a potential candidate as a self-biological treatment, the membrane fouling is high in this case.

Acute Inhibition of Hospital and Medical Laboratory Wastewater on Activated Sludge

Sustainable operation is an essential challenge in many municipal wastewater treatment plants. Among many types of wastewater mixed in a sewer, healthcare wastewaters need special attention due to their hazardous substance content, which can be toxic to activated sludge. This study compared the acute inhibitory effects of healthcare wastewaters (HW) and medical laboratory wastewater (MLW) on conventional activated sludge (CAS) and membrane bioreactor (MBR). The sensitivity test showed that nitrifying bacteria (NBs) in MBR sludge have higher resistance to acute toxicity than the CAS. Compared with HW, MLW caused much higher inhibition on both sludges. When the ratio of HW in the tested domestic wastewater was 10%, inhibition of NBs was 39% in AS, while it was 31% in MBR. When the ratio of MLW in the tested domestic wastewater was only 10%, 72% of NBs in AS and 57% of NBs in MBR were already inhibited. The higher resistance of NB in MBR may be explained by the diversity of microorganisms in the MBR operated at high sludge ages. The findings of this study may be used to estimate the acute inhibition effect of HW and MLW discharged directly to the sewage at higher loads.