Towards physicochemical and biological effects on detachment and activity recovery of aging biofilm by enzyme and surfactant treatments

Comparing biofilm reactors inoculated with Shewanella for decolorization of Reactive Black 5 using different carrier materials

This study assessed the performance of biofilm reactors inoculated with azo dye degrading Shewanella for the decolorization of Reactive Black 5 (RB5), using three different carrier materials, namely almond shell biochar, moving bed biofilm reactor (MBBR), and polypropylene carrier (PPC). The reactors were fed with low-nutrient artificial wastewater containing RB5, and all three carriers showed good RB5 decolorization performance, with varying efficiencies. Liquid Chromatography-Mass Spectrometry analysis revealed distinct RB5 degradation pathways associated with each carrier, influenced by carrier materials and microbial communities. The MBBR carrier exhibited good stability due to its rough surface and microbial aggregates. Sequencing results highlighted differences in the microbial community structures among the carriers. Shewanella predominated the functional bacteria in the MBBR and PPC carriers, while the biochar carrier fostered highly efficient degrading microbial communities. The physicochemical properties of carrier materials significantly influenced the microbial community and RB5 degradation efficiency. These findings provide valuable insights for optimizing biofilm reactors for dye-containing wastewater treatment.

The influence of different nitrate concentrations on aerobic sludge granulation and the role of extracellular polymeric substances

This study investigated the influence of nitrate on aerobic granular sludge (AGS) granulation. The introduction of nitrate at 5, 15 and 20 mg L-1 promoted AGS granulation, and the promoting effect was positively correlated with nitrate concentrations. Meanwhile, exogenous nitrate significantly increased denitrification rate in the AGS system. However, granular disintegration appeared at a long-term addition of nitrate. An in-deep analysis showed that nitrate stimulated the secretion of extracellular polymeric substances (EPS), especially the content of proteins, which might be the main reason for the AGS granulation. However, the rapid and excessive increase in EPS might cause granular disintegration, as excessive EPS blocked the transmission of substrates, leading to the increase of dead cells in the granules. Besides, nitrate also altered the hydrophobicity of EPS and the content of α-helix, 3-turned helix and polymeric chain that favored aggregation, which also affected AGS granulation. From the microbial community level, nitrate induced the enrichment of denitrifying bacteria, including those that also functioned as EPS producers, such as Micropruina and Flavobacterium, resulting in the rapid increase of functional enzymes associated with amino acid synthesis, thereby promoting the secretion of proteins in EPS. Conversely, disintegration caused by mass transfer blockage might lead to the loss of EPS producing bacteria and subsequent decrease in EPS content, further accelerating granular disintegration.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

Bio-clogging mitigation in constructed wetland using microbial fuel cells with novel hybrid air-photocathode

Excessive accumulation of extracellular polymeric substances (EPS) in constructed wetland (CW) substrate can lead to bio-clogging and affect the long-term stable operation of CW. In this study, a microbial fuel cell (MFC) was coupled with air-photocathode to mitigate CW bio-clogging by enhancing the micro-electric field environment. Because TiO₂/biochar could catalyze and accelerate oxygen reduction reaction, further promoting the gain of electric energy, the electricity generation of the tandem CW-photocatalytic fuel cell (CW-PFC) reached 90.78 mW m^-3. After bio-clogging was mitigated in situ in tandem CW-PFC, the porosity of CW could be restored to about 62.5 % of the initial porosity, and the zeta potential of EPS showed an obvious increase (-14.98 mV). The removal efficiencies of NH₄⁺-N and chemical oxygen demand (COD) in tandem CW-PFC were respectively 31.8 ± 7.2 % and 86.1 ± 6.8 %, higher than those in control system (21.1 ± 11.0 % and 73.3 ± 5.6 %). Tandem CW-PFC could accelerate the degradation of EPS into small molecules (such as aromatic protein) by enhancing the electron transfer. Furthermore, microbiome structure analysis indicated that the enrichment of characteristic microorganisms (Anaerovorax) for degradation of protein-related pollutants, and electroactive bacteria (Geobacter and Trichococcus) promoted EPS degradation and electron transfer. The degradation of EPS might be attributed to the up-regulation of the abundances of carbohydrate and amino acid metabolism. This study provided a promising new strategy for synergic mitigation and prevention of bio-clogging in CW by coupling with MFC and photocatalysis.

Insight into the effect of nitrate on AGS granulation: Granular characteristics, microbial community and metabolomics response

As a promising wastewater treatment technology, aerobic granular sludge (AGS) process is still hindered by slow granule formation and easy disintegration in the application. While nitrate, one of the target pollutants in wastewater, showed a potential effect on AGS granulation process. Herein, this study attempted to reveal the role of nitrate in AGS granulation. By adding exogenous nitrate (10 mg L^-1), the AGS formation was markedly improved and accomplished at 63 d, while the control group achieved AGS formation at 87 d. However, a disintegration was observed under a long-term nitrate feeding. A positive correlation was observed among granule size, extracellular polymeric substances (EPS) and intracellular c-di-GMP level in both formation and disintegration phases. The subsequent static biofilm assays indicated that nitrate might upregulate c-di-GMP via denitrification-derived NO, and c-di-GMP further upregulated EPS, thereby promoting AGS formation. However, excessive NO probably caused disintegration by downregulating c-di-GMP and EPS. Microbial community showed that nitrate favored the enrichment of denitrifiers and EPS producing microbes, which were responsible for the regulation of NO, c-di-GMP and EPS. Metabolomics analysis showed that amino acid metabolism was the most affected metabolism by nitrate. Some amino acids, such as Arg, His and Asp, were upregulated in the granule formation phase and downregulated in the disintegration phase, indicating the potential contribution to EPS biosynthesis. This study provides metabolic insight into how nitrate promotes/inhibits granulation, which may contribute to unwrapping the mystery of granulation and overcoming the limitations of AGS application.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

Morphological image analysis of biofilm evolution with quantitative analysis in a moving bed biofilm reactor

The quantitative analysis of biomass is essential for the research and application of moving bed biofilm reactors (MBBRs). However, the difficulty in measuring the attached growing biomass hinders the quantitative analysis of biofilm processes. In this study, a pilot-scale MBBR system was established to investigate biofilm evolution. The quantity of active heterotrophic and autotrophic biomass was measured throughout the entire culturing process. The total active biomass reached 250 mg COD/m² when the biofilm attachment and detachment were balanced, and the corresponding autotrophic biomass contributes to as high as 17 % of the total biomass. Furthermore, quantitative image analysis was performed to obtain the thickness and morphological data of the biofilm evolution. Multivariate regression models were constructed based on the morphological data, which provided satisfactory prediction accuracy for the biofilm thickness and maturation. The most suitable carrier spots for biomass quantification and biofilm maturation were suggested. This work provided the life-cycle information of biofilm quantity and morphology of the MBBR, which contributes to the quantitative understanding of biofilm evolution at MBBRs.

Acceleration of start-up of moving bed biofilm reactor at low temperature by adding specialized quorum sensing bacteria

This study aims to accelerate biofilm formation and operational performance of moving bed biofilm reactor (MBBR) at 5 ℃ by adding specialized Quorum Sensing bacteria (sphingomonas rubra BH3^T). Results showed that bio augmented MBBR (R_S) achieved a higher chemical oxygen demand and NH₄⁺-N removal rate (93% and 75%), which in accordance with its increased biofilm thickness, higher biofilm activity, and nitrifying bacteria abundance (Nitrospira). The increased biofilm thickness (60.23 %) during the whole operating time, accompanied by more potent adhesion force (61.59 %), was related to increased polysaccharides and proteins in the biofilm. Pyrosequencing analysis indicated that BH3^T contributed to higher species richness and triggered the rapid growth of precursor microorganisms (Nakamurella, Micropruina, and Zoogloea) and the enrichment of multifunctional microorganisms (Pseudomonas, Aeromonas, Arcobacter, Dechloromonas, and Flavobacterium) at low temperatures. This study provides an economical and practical new insight into accelerating start-up of MBBR system at low temperature.

A review on the physicochemical and biological applications of biosurfactants in biotechnology and pharmaceuticals

Biosurfactants are the chemical compounds that are obtained from various micro-organisms and possess the ability to decrease the interfacial tension between two similar or different phases. The importance of biosurfactants in cosmetics, pharmaceuticals, biotechnology, agriculture, food and oil industries has made them an interesting choice in various physico-chemical and biological applications. With the aim of representing different properties of biosurfactants, this review article is focused on emphasizing their applications in various industries summarizing their importance in each field. Along with this, the production of recently developed chemically and biologically important biosurfactants has been outlined. The advantages of biosurfactants over the chemical surfactants have also been discussed with emphasis on the latest findings and research performed worldwide. Moreover, the chemical and physical properties of different biosurfactants have been presented and different characterization techniques have been discussed. Overall, the review article covers the latest developments in biosurfactants along with their physico-chemical properties and applications in different fields, especially in pharmaceuticals and biotechnology.

Ni(II), Cr(VI), Cu(II) and nitrate removal by the co-system of Pseudomonas hibiscicola strain L1 immobilized on peanut shell biochar

At present, the improvement of nitrate and mixed heavy metals removal in wastewater by microorganism are urgently needed. Previous studies have shown that Pseudomonas hibiscicola strain L1 exhibited Ni(II) removal ability under aerobic denitrification. In this study, the characteristics of the free strain L1, peanut shell biochar (PBC) and further the co-system of strain L1 immobilized on PBC were investigated for the removal of Ni(II), Cr(VI), Cu(II) and nitrate in mix-wastewater. The results illustrated that strain L1 could remove 15.51% - 32.55% of Ni(II) (20-100 mg·L^-1), and removal ratios by co-system were ranked as Ni(II) (81.17%) > Cu(II) (45.84%) > Cr(VI) (38.21%). Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) images indicated that the strain L1 immobilized well on PBC and had vigorous biological activity; the crystals of Ni(OH)₂, Cu(OH)₂ and CrO(OH) etc. were formed on surface of co-system with various functional groups participated in. In Sequential Batch Reactor (SBR), the pollutant removal ratios by co-system were higher than that by free strain L1. This study illustrated that the co-system of strain L1 immobilized on PBC was qualified to be applied for practical scenarios of effective heavy metal removal of electroplating mix-wastewater.

Insight into synergies between Acinetobacter sp. AL-6 and pomelo peel biochar in a hybrid process for highly efficient manganese removal

The manganese contamination of groundwater is a global issue that needs to be solved urgently. In this study, a hybrid process between pomelo peel biochar(BC) and Acinetobacter sp. AL-6 (strain AL-6) was established to remove manganese from water. The results showed that microbe-biochar composite had removed 98.19% of manganese (800 mg L^-1) within 48 h. Compared with two separate systems (biochar, strain AL-6), the co-system (strain AL-6 and BC composite) had an excellent synergy effect on manganese removal. The average removal rate of manganese in the synergistic system was 14.08 mg L^-1 h^-1, which was 6.41 times higher than strain AL-6, 3.45 times higher than biochar, and even at 2.24 times their sum. In addition, the scanning electron microscope (SEM) and the bioassay indicated that many strains were attached to biochar and had vigorous biological activity. The FTIR results showed that the functional groups of OH, CO, CO, CH₂, and CH played a vital role in removing manganese. And the correlation analysis shows that biochar with strains AL-6 has a highly synergistic effect on manganese removal. Meanwhile, the composite material can maintain excellent manganese removal efficiency under different pH conditions. Besides, in the sequence batch reactor (SBR) inoculating with the microbe-biochar composite, more than 96% of manganese was removed, which far exceeded the treatment efficiency of free bacteria in the SBR. Hence, biochar-immobilized AL-6 has great potential and can be applied to degrade manganese polluted wastewater.

Microbial Biosurfactant: A New Frontier for Sustainable Agriculture and Pharmaceutical Industries

In the current scenario of changing climatic conditions and the rising global population, there is an urgent need to explore novel, efficient, and economical natural products for the benefit of humankind. Biosurfactants are one of the latest explored microbial synthesized biomolecules that have been used in numerous fields, including agriculture, pharmaceuticals, cosmetics, food processing, and environment-cleaning industries, as a source of raw materials, for the lubrication, wetting, foaming, emulsions formulations, and as stabilizing dispersions. The amphiphilic nature of biosurfactants have shown to be a great advantage, distributing themselves into two immiscible surfaces by reducing the interfacial surface tension and increasing the solubility of hydrophobic compounds. Furthermore, their eco-friendly nature, low or even no toxic nature, durability at higher temperatures, and ability to withstand a wide range of pH fluctuations make microbial surfactants preferable compared to their chemical counterparts. Additionally, biosurfactants can obviate the oxidation flow by eliciting antioxidant properties, antimicrobial and anticancer activities, and drug delivery systems, further broadening their applicability in the food and pharmaceutical industries. Nowadays, biosurfactants have been broadly utilized to improve the soil quality by improving the concentration of trace elements and have either been mixed with pesticides or applied singly on the plant surfaces for plant disease management. In the present review, we summarize the latest research on microbial synthesized biosurfactant compounds, the limiting factors of biosurfactant production, their application in improving soil quality and plant disease management, and their use as antioxidant or antimicrobial compounds in the pharmaceutical industries.

Ecological Linkages between a Biofilm Ecosystem and Reactor Performance: The Specificity of Biofilm Development Phases

In biofilm-based engineered ecosystems, the reactor performance was closely linked to interspecies interactions within a biofilm ecosystem, whereas the ecological processes underpinning such linkage were still unenlightened. Herein, the principles of community succession and assembly were integrated to capture the ecological laws of biofilm development by molecular ecological networks and assembly model analysis based on the 16S rRNA sequencing analysis and metagenomics in a well-controlled moving bed biofilm reactor. At the initial colonization phase (days 0-2, driven by initial colonizers), interspecific cooperation (74.18%) facilitated initial biofilm formation, whereas some pioneers, and keystone species disappeared at later phases. At the accumulation phase (days 3-30, rapid biofilm development), interspecific cooperation (81.41 ± 5.07%) contributed to rapid biofilm development and keystone species were mainly involved in quorum sensing or positively correlated with extracellular polymeric substance production. At the maturation phase (days 31-106, a well-adapted quasi-equilibrium state), increased interspecific competition (32.74 ± 4.77%) and higher small-world property facilitated the rapid information transportation and pollutant treatment, and keystone species were positively correlated with the removal of COD and NH₄⁺-N. Homogenizing dispersal diminished the contemporary community dissimilarities, while turnover but rather nestedness governed the temporal variations in the biofilm succession period. This study highlighted the specificity of ecological processes at distinct biofilm development phases, which would advance our understanding on the development-to-function linkages in biofilm-based treatment processes.

Effects of chronic exposure to different sizes and polymers of microplastics on the characteristics of activated sludge

Wastewater treatment plants (WWTPs) have become an important source of microplastics (MPs) contamination and most MPs remain in the sludge inducing potential impacts on sludge disposal. However, little is known about the influence of MPs on the characteristics of sludge, which is essential for sludge disposal. In this study, the dewaterability of activated sludge in response to chronic exposure (60 days) to MPs of different sizes (213.7 nm ~ 4.2 mm) and polymers (polystyrene, polyethylene, and polyvinyl chloride) were investigated. Overall, different particle sizes caused more evident effects on sludge dewatering than different polymer types did. Millimeter MPs (~4 mm) dramatically reduced the dewaterability of sludge by 29.6% ~ 47.7%. These effects were mainly caused by the physical crushing of MPs on sludge flocs, except polyvinyl chloride (PVC)-MPs, possibly containing additives, induced toxicity on sludge. Moreover, 100 mg/L nano-size MPs (213 nm) also reduced the dewatering performance of sludge. The potential mechanism is that nano-size MPs inhibited sludge activity and decreased the abundance of key microorganisms, which subsequently altered the composition and spatial distribution of extracellular polymeric substances (EPS), and finally impeded sludge dewatering. Our results highlight the impacts of different sizes of MPs on the characteristics of sludge, affecting the final disposal of sludge.

Changes in bacterial diversity of activated sludge exposed to titanium dioxide nanoparticles

The rapid growth of the use of nanomaterials in different modern industrial branches makes the study of the impact of nanoparticles on the human health and environment an urgent matter. For instance, it has been reported that titanium dioxide nanoparticles (TiO₂ NPs) can be found in wastewater treatment plants. Previous studies have found contrasting effects of these nanoparticles over the activated sludge process, including negative effects on the oxygen uptake. The non-utilization of oxygen reflects that aerobic bacteria were inhibited or decayed. The aim of this work was to study how TiO₂ NPs affect the bacterial diversity and metabolic processes on an activated sludge. First, respirometry assays of 8 h were carried out at different concentrations of TiO₂ NPs (0.5-2.0 mg/mL) to measure the oxygen uptake by the activated sludge. The bacterial diversity of these assays was determined by sequencing the amplified V3-V4 region of the 16S rRNA gene using Illumina MiSeq. According to the respirometry assays, the aerobic processes were inhibited in a range from 18.5 ± 4.8% to 37.5 ± 2.0% for concentrations of 0.5-2.0 mg/mL TiO₂ NPs. The oxygen uptake rate was affected mainly after 4.5 h for concentrations higher than 1.0 mg/mL of these nanoparticles. Results indicated that, in the presence of TiO₂ NPs, the bacterial community of activated sludge was altered mainly in the genera related to nitrogen removal (nitrogen assimilation, nitrification and denitrification). The metabolic pathways prediction suggested that genes related to biofilm formation were more sensitive than genes directly related to nitrification-denitrification and N-assimilation processes. These results indicated that TiO₂ NPs might modify the bacteria diversity in the activated sludge according to their concentration and time of exposition, which in turn impact in the performance of the wastewater treatment processes.

Development of simultaneous nitrification-denitrification and anammox and in-situ analysis of microbial structure in a novel plug-flow membrane-aerated sludge blanket

This study proposed a novel one-stage plug-flow microaerobic sludge blanket (PMSB) with membrane aerated for treating low carbon to nitrogen (C/N) ratio municipal sewage. The performance of simultaneous nitrification, denitrification, and anammox in the reactor was investigated. The results illustrated that the removal efficiencies of ammonium and total nitrogen (TN) were 93.2% and 87.1% with a C/N ratio of 4. High throughput sequencing revealed that aerobic bacteria, anaerobic bacteria and facultative anaerobe could co-exist at the same time in the sludge blanket. Meanwhile, a notable correlation between the oxygen concentration and the distance of the membrane module was analyzed. It was shown that the microbial community of functional bacteria developed in different aeration sites due to the oxygen concentration gradient. Microbial community structure was analyzed depending on the sludge stratification in the sludge blanket.

Mass transfer of nanobubble aeration and its effect on biofilm growth: Microbial activity and structural properties

It is necessary to improve the performance and reduce the aeration cost is of wastewater treatment by aerobic biofilm systems. Nanobubble aeration is supposed to be a promising method to achieve these goals. Compared with coarse bubbles, dissolved oxygen profiling showed that the nanobubbles provided more oxygen to biofilms, offering superior oxygen supply capacity and 1.5 times higher oxygen transfer efficiency. Nanobubble aeration accelerated the growth of the biofilm and achieved better removal efficiencies of chemical oxygen demand and ammonia, with as maximum as six times higher dehydrogenase activity, and more extracellular polymeric substance content than when using the traditional aeration mode. This is attributed to the enhancement of metabolism and the proliferation of microorganisms. Confocal laser-scanning microscopy imaging confirmed that nanobubble aeration affected the components of biofilm by shifting the microbial community and changing its metabolic pathways of biofilms, such as carbohydrate synthesis. Nanobubble aeration resulted in an energy saving of approximately 80%. The assessment of nanobubble aerated biofilm growth suggests that this technique can offer a rapid-initiation, high efficiency, and low-cost strategy for aerobic biofilm systems in wastewater treatment.

A novel start-up strategy for mixotrophic denitrification biofilters by rhamnolipid and its performance on denitrification of low C/N wastewater

A novel start-up strategy for sulfur-based mixotrophic denitrification biofilters (mDNBFs) by rhamnolipid was investigated for the first time. Rhamnolipid with gradient concentrations (0-120 mg/L) was added into five lab-scale mDNBFs. Results showed that rhamnolipid could promote biomass yield and nitrogen removal rate (NRR) by 71.7% and 68.7%, respectively, while its effect on EPS and adhesion force was concentration-dependent. The spatial distribution characteristics of microbial communities demonstrated the enrichment of main heterotrophic denitrifying bacteria outcompeted that of the autotrophs, with a more pronounced difference in high concentration rhamnolipid-treated mDNBFs. Furthermore, highest abundance of napA, narG, nirK and nosZ genes was observed in 80 mg/L rhamnolipid-treated mDNBF. Interfacial processes including solubilizing effect and hydration repulse and variations of organics were discussed to explicate the underlying mechanism. The study enlightened that an appropriate concentration (∼80 mg/L) of rhamnolipid may be a good solution for accelerating biofilm formation and enriching denitrifying bacteria to promote denitrification performance of mDNBFs treating low C/N wastewater.

Start-up of aerobic granular biofilm at low temperature: Performance and microbial community dynamics

Low temperature is a great challenge for the biological treatment of wastewater. In this study, the rapid start-up of aerobic granular biofilm (AGF) reactor was realized by adding micro-sized polyurethane (PU) sponges as matrices at 10 °C. The results showed that the granulation process of AGF was different from that of traditional aerobic granular sludge and biofilms, which was formed by using the sludge intercepted in PU matrix instead of sponge skeletons as granulation carriers. During the 5-month operation period, stable pollutants removal performance was achieved within 70 days, besides, the corresponding ammonium, total nitrogen, and total phosphorus removal efficiencies were 98%, 70%, and 95%, respectively. The addition of PU matrices inhibited the growth of filamentous bacteria and provided support for high structural stability of AGF. With the operation of the reactor, the relative abundance of traditional denitrifying bacteria (genera Thauera and Acidovorax, etc.) decreased gradually, and the putative denitrifying phosphorus accumulating genus, Dechloromonas, occupied a dominant position in the system. This experiment showed that AGF system could be successfully started-up and operated with efficient pollutants removal performance under low temperature when using micro-sized PU sponges as matrices.

Undesirable effects of exogenous N-acyl homoserine lactones on moving bed biofilm reactor treating medium-strength synthetic wastewater

Exogenous AHLs are gradually reported to facilitate biofilm growth, however, whether they play a universal role in promoting biofilm formation and pollutants removal remains to be investigated. The pollutant removal, biofilm properties, microbial community and the distribution of AHLs were investigated in three lab-scale MBBRs by continuous dosing 100 nM N-Hexanoyl-L-homoserine lactone (C6-HSL) and N-Octanoyl-L-homoserine lactone (C8-HSL) in synthetic wastewater under normal nutrition (40 mg/L NH₄⁺-N with C/N = 20). Results showed that adding AHLs didn't affect organics removal and exogenous C6-HSL even significantly suppressed NH₄⁺-N removal by 0.44-20.29% after 16 days (p < 0.05). The introduction of AHLs both facilitated biofilm growth and extracellular polymeric substances secretion while suppressed ATP production especially during the stable operation period, with 48.96% by C6-HSL (p < 0.05) and 27.25% by C8-HSL, respectively. Exogenous AHLs inhibited the proliferation of Chryseobacterium, resulting in improvement in biofilm growth and it probably mediated ATP synthesis through regulating the release of 3OHC12-HSL in aqueous phase. Organics removal and biofilm growth were mainly attributed to the combined actions of multitudinous AHLs in biofilm phase rather than that in aqueous phase. The counterintuitive conclusions obtained in this study highlighted the importance of legitimately applying exogenous AHLs to accelerate biofilm formation and the start-up of MBBR in wastewater treatment.

Overcoming the instability of aerobic granular sludge under nitrogen deficiency through shortening settling time

This study investigated the short settling time strategy to overcome the instability of aerobic granular sludge (AGS) under nitrogen deficiency. AGS variations in its physical and chemical characteristics and microbial community were investigated. Results showed that nitrogen deficiency led to the instability of AGS, while short settling time strategy could overcome the instability of AGS under nitrogen deficiency. Extracellular polymeric substances (EPS), especially, the increased secretion of polysaccharide and proteins with amide III groups at the short settling time enhanced the stability of the granules under nitrogen deficiency. Unclassified_f_Microbacteriaceae shifted to be the major bacteria group at short settling time, along with the decrease of Meganema and Rhodobacter and the increase of Lysobacter, which may play an important role in enhancing AGS stability. Therefore, shortening settling time supports an effective strategy for applications of AGS under nitrogen deficiency.

Enhanced biofilm formation and denitrification in biofilters for advanced nitrogen removal by rhamnolipid addition

Denitrification biofilters (DNBFs) are widely used in advanced nitrogen removal of wastewater with low C/N and effective biofilm formation is critical to their long-term operation. Hereby the influence of rhamnolipid addition in DNBFs was investigated for the first time. Gradient concentrations (0, 20, 40, 80, 120 mg/L) of rhamnolipid were applied to investigate nitrogen removal, biofilm properties and microbial community of lab-scale DNBFs. A significant increase of nitrogen removal was observed in rhamnolipid-treated DNBFs (p < 0.05). Total solid (TS), extracellular polymeric substances (EPS) and adhesion force of biofilms in DNBF with 120 mg/L rhamnolipid reached the maximum, which were 2.17, 2.15 and 3.36 times of those in the control, respectively. Moreover, rhamnolipid exhibited an improvement in abundance of Simplicispira and Gemmatimonas which were responsible for enhanced biofilm formation and denitrification. The results suggested that rhamnolipid addition can be a novel strategy to improve the start-up and denitrification performance of DNBFs.

Autotrophic nitrogen removal in an integrated fixed-biofilm activated sludge (IFAS) reactor: Anammox bacteria enriched in the flocs have been overlooked

In this study, an autotrophic nitrogen removal process was established using an integrated fixed-biofilm activated sludge (IFAS) reactor treated with high ammonium wastewater. A nitrogen removal rate (NRR) of 2.78 kg N/(m³·d) was obtained during the 206-day operation. Moreover, during the stable period, the large flocs (D > 0.2 mm) had a significantly higher abundance of anammox bacteria than the small flocs (D < 0.2 mm) and biofilm, resulting in 51% of the anammox bacteria being located in the flocs. The result indicates that anammox bacteria can be enriched in the flocs and in the biofilm, which has been rarely reported for IFAS reactors. In addition, the large flocs are likely formed through biofilm detachment since the microbial community was similar for the two kinds of biomass. Overall, the role of flocs in IFAS reactors are complicated and their contribution to the anammox reaction have been overlooked thus far.

Enhanced simultaneous nitrification and denitrification in treating low carbon-to-nitrogen ratio wastewater: Treatment performance and nitrogen removal pathway

Simultaneous nitrification and denitrification (SND) is an energy-saving wastewater treatment process, however, the nitrogen removal pathways are not clear. An enhanced SND sequencing batch biofilm reactor with a SND ratio above 97.3% was built to treat low carbon to nitrogen ratio wastewater. When traditional nitrification was inhibited, ammonia removal efficiency still reached 45% in 8 h while the NO₃^- and NO₂^- concentration was less than 3 mg/L and 0.01 mg/L during the complete process, respectively. The pathways that could not be suppressed by the inhibitors (ATU and ClO₃^-) were stimulated by heterotrophic nitrifiers and aerobic denitrifiers with periplasmic nitrate reductase and contributed 55% of the total removed NH₄⁺ and produced 51% of the emitted N₂O. The contributions of different nitrogen removal pathways indicate that the unconventional pathways are important in wastewater treatment system and inhibitors should be carefully used in nitrogen removal pathway assays.

Effects of biomass pyrolysis derived wood vinegar on microbial activity and communities of activated sludge

The effects of wood vinegar (WVG) on microbial activity and communities of activated sludge were investigated in a sequencing batch reactor (SBR) process. Results showed that the optimal WVG concentration was 4 μL/L when the pollutants removal efficiency and microbial activity were promoted by a WVG dilution factor of 1000. WVG could reduce the increase in microbial species richness, which led to a more notable variety of microbial species diversity. The enhanced microbial activity and communities were addressed to the promotion of 7 main classes of microbes in Proteobacteria, Bacteroidetes, Acidobacteria, and Nitrospirae phyla. The growth of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and main genera of denitrifying bacteria (DNB), phosphorus-accumulating organisms (PAOs), and glycogen-accumulating organisms (GAOs) could be promoted by WVG, which improved the sewage treatment effectiveness in a SBR.

Highly synergistic effects on ammonium removal by the co-system of Pseudomonas stutzeri XL-2 and modified walnut shell biochar

Pseudomonas stutzeri strain XL-2 presented efficient ammonium removal due to heterotrophic nitrification-aerobic denitrification. The modified walnut shell biochar also showed ammonium adsorption due to chemical interaction. The complex of modified biochar and strain XL-2 exhibited excellent synergistic effects on ammonium removal, especially in unfavorable environment. The maximum average ammonium removal rate of the complex was 4.40 mg·L^-1·h^-1, which was 3.01 times higher than that of pure bacteria and 5.57 times higher than that of biochar. A large number of irregular pores and hydrophilic functional groups promoted the immobilization of strain XL-2 on biochar. Adsorption of ammonium, high specific surface area and release of Mg²⁺ by biochar enhanced biodegradation of strain XL-2. Approximately 96.34%-98.73% of ammonium was removed in a sequencing batch reactor (SBR) inoculating with the complex of strain XL-2 and biochar, which was much higher than the treatment efficiency of free bacteria in SBR.

Effect of continuous and intermittent electric current on lignin wastewater treatment and microbial community structure in electro-microbial system

In this study, complex structured soluble lignin wastewater was treated by electro-microbial system (EMS) using different direct current (DC) application modes (CR (continuous ON), IR_12h (12 h-ON/12 h-OFF) and IR_2h (2 h-ON/2 h-OFF)), and physiological characteristics and microbial communities were investigated. Results showed that CR, IR_12h and IR_2h had higher lignin removals, which were almost two times that of the control reactor (R₀′, no current), and IR_2h performed best and stably. Furthermore, IR_2h exhibited the lowest ohmic resistance (Rs) of electrode biofilms, which could be explained by its higher abundance of electroactive bacteria. In the activated sludge of EMS, the concentration of dehydrogenase activity (DHA) and electronic transport system (ETS) in IR_2h were the highest (1.48 and 1.28 times of R₀′), which contributed to its high content of adenosine triphosphate (ATP). The viability of activated sludge was not affected by different DC application modes. Phospholipid fatty acids (PLFA) analysis indicated that IR_2h had the maximum content of C15:1 anteiso A, C16:0 and C18:0; CR increased the content of C15:0 anteiso and decreased the content of saturated fatty acids. Genus-level results revealed that lignin-degrading bacteria, Pseudoxanthomonas and Mycobacterium, could be enriched in IR_2h and CR, respectively.

Enzyme treatment improves the performance of laboratory-scale vertical flow constructed wetland

An enzyme treatment was developed and evaluated for its effectiveness in alleviating bioclogging through a laboratory-scale vertical-flow constructed wetland (VFCW) experiment in this study. The enzyme preparation was a combination of α-glucoamylase and β-glucanase. The results show that the enzyme treatment greatly reduced bioclogging, and the peak hydraulic conductivity after treatment increased by a factor of 16, mainly because polysaccharides in the clogging matter were decomposed and the gelatinous clogging matter was dissolved and dispersed. The results also show that the abundance of Proteobacteria microbes increased by 89.4% after the enzyme treatment, although the diversity of the microbial community within the substrate decreased slightly. These microbes can increase the capability of the constructed wetland to purify influent water, and thus the rate of reduction of COD improved. It offers a solution to the problem of bioclogging in constructed wetlands.

Effect of adding low-concentration of rhamnolipid on reactor performances and microbial community evolution in MBBRs for low C/N ratio and antibiotic wastewater treatment

This study aims to explore the potential of low-concentration of rhamnolipid in efficient treatment of wastewater with poor biodegradability. Six lab-scale moving bed biofilm reactors (MBBRs) were applied to investigate the effect of rhamnolipid concentration (0, 20, 50 mg/L) on pollutants removal, biomass accumulation, microbial morphology and community evolution in synthetic low C/N ratio (3:1) and antibiotic (50 μg/L tetracycline) wastewater. 20 mg/L rhamnolipid treated groups exhibited significant increase (p < 0.05) of chemical oxygen demand (COD) removal and volatile solid (VS) content in both synthetic wastewater. Hydrogenophaga and Aeromonas were dominant in all reactors in which Aeromonas was positively correlated with the removal of COD and ammonia nitrogen (NH₄⁺-N). Besides, Methyloversatilis became dominant only in 20 mg/L rhamnolipid treated groups and was positively correlated with VS. This study provides a novel and feasible strategy for treating poorly biodegradable wastewater by biofilm process with moderate amount of rhamnolipid.