Acceleration of biofilm formation in start-up of sequencing batch biofilm reactor using carriers immobilized with Pseudomonas stutzeri strain XL-2

Enhanced simultaneous removal of sulfamethoxazole and zinc (II) in the biochar-immobilized bioreactor: Performance, microbial structures and gene functions

Biochar-immobilized functional bacteria Bacillus SDB4 was applied for sulfamethoxazole (SMX) and zinc (Zn2+) simultaneous removal in the bioreactor. Under the optimal operating conditions of HRT of 10 h, pH of 7.0, SMX concentration of 10 mg L-1 and Zn2+ concentration of 50 mg L-1, the removal efficiencies of SMX and Zn2+ by the immobilized reactor (IR) were 97.42% and 96.14%, respectively, 20.39% and 30.15% higher than those by free bioreactor (FR). SEM-EDS and FTIR results revealed that the functional groups and light metals on the carrier promoted the biosorption and biotransformation of SMX and Zn2+ in IR. Moreover, the improvement of SMX and Zn2+ removal might be related to the abundance enhancement of functional bacteria and genes. Bacillus SDB4 responsible for SMX and Zn2+ removal was the main strain in IR and FR. Biochar increased the relative abundance of Bacillus from 32.12% in FR to 38.73% in IR and improved the abundances of functional genes (such as carbohydrate metabolism, replication and repair and membrane transport) by 1.82%-11.04%. The correlations among the physicochemical properties, microbial communities, functional genes and SMX-Zn2+ co-contaminant removal proposed new insights into the mechanisms of biochar enhanced microbial removal of antibiotics and heavy metals in biochar-immobilized bioreactors.

Organic carbon source excites extracellular polymeric substances to boost Fe0-mediated autotrophic denitrification in mixotrophic system

Fe⁰-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe⁰ corrosion. The mixotrophic denitrification (MDN) coupling Fe⁰-mediated ADN with heterotrophic denitrification (HDN) can circumvent the weakening of Fe⁰-mediated ADN over operation time. But the interaction between HDN and Fe⁰-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO₃^--N ratio increased from 0.0 to 1.8-2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe⁰-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO₃^--N removal significantly, while accelerated the electron release originating from Fe⁰ corrosion. The bioorganic-Fe complexes were generated on Fe⁰ surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe⁰-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe⁰-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.

Enhancement of biological nitrogen removal performance from low C/N municipal wastewater using novel carriers based on the nano-Fe3O4

The aim of this work was to study the effects of the magnetic microparticles (MMP) on nitrogen removal under low C/N conditions. A 30-day anaerobic/oxic progress illustrated that nitrification and denitrification were promoted in the presence of MMP. MMP could facilitate the production of extracellular polymeric substances (EPS) and act as pH buffering in aerobic conditions. The high-throughput sequencing displayed that, compared with the sludge without MMP, the relative abundance of Dokdonella and Comamonas which are capable of both nitrifying and denitrifying were 8.7% and 1.29% higher in anaerobic sludge and 7.11% and 0.97% higher in aerobic sludge with MMP, respectively. The relative abundance of Pseudomonas with the excellent capability of EPS secretion was also observed 4.33 times higher than that without MMP in the aerobic sludge. Based on the superior performance above, MMP is a promising additive to enhance nitrogen removal efficiency for low C/N wastewater.

Bio-augmentation of the filler-enhanced denitrifying sulfide removal process in expanded granular sludge bed reactors

Sulfur- and nitrogen-containing organic industrial wastewaters, which primarily result from several processes, including pharmaceutical, slaughter, papermaking, and petrochemical processes, are typical examples of refractory wastewaters. To ensure resource utilization, sulfur compounds at high concentrations in such wastewaters can be converted to elemental sulfur through specific methods. Specifically, the denitrifying sulfide removal (DSR) process can be employed to effectively recover elemental sulfur via biological sulfide oxidation, and reportedly, bio-augmentation presents as an effective strategy by which the challenges that limit the application of the DSR process can be overcome. However, the bacterial loss resulting from microorganism activity inhibition owing to toxic effect of high sulfide concentration as well as the complexity of the organic matter (carbon source) in actual wastewater environments reduce the actual elemental sulfur production rate. In this regard, the bio-augmentation effect of adding fillers under complex carbon source conditions was studied. The structure and function of the microbial community on the surface of the fillers were also analysed to reveal the internal factors that contributed to the increased efficiency of elemental sulfur generation. The results obtained showed that relative to the control, elemental sulfur generation increased 1.5- and 2-fold following the addition of fillers and fillers with microbial inoculants, respectively. Further, in the reactor with the added filler, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Azoarcus, while in reactor with added fillers plus microbial inoculates, the dominant bacteria in the biofilm on the filler surface were Pseudomonas and Arcobacter. These findings indicated that bio-augmentation promoted the expression of sulfur oxidation functional genes. Furthermore, adding Pseudomonas sp. gs1 for bio-augmentation improved the impact load resistance of the biofilm on the surface of the filler, leading to the rapid restoration of the elemental sulfur generation rate after the impact.

Bifunctional lighting/supporting substrate for microalgal photosynthetic biofilm to bio-remove ammonia nitrogen from high turbidity wastewater

Treatment technologies based on microalgal biofilms have an enormous potential for dealing with water pollution because they can efficiently redirect nutrients from wastewater to renewable biomass feedstock. However, poor light transmittance is caused by the high turbidity of wastewater, which hinders the commercial application of microalgal biofilm-based wastewater treatment. Here, a bifunctional substrate with lighting and biofilm support functions was constructed using a light guide plate. In a biofilm photobioreactor (bPBR) with a bifunctional lighting/supporting substrate (BL/S substrate), light can directly irradiate the biofilm to avoid attenuation by the turbid wastewater. Direct irradiation of light onto the biofilm led to a 93.0% enhancement of microalgal photoconversion efficiency when compared to that of a supporting substrate without lighting (SO substrate). Meanwhile, the maximum growth rate of the microalgal biofilm on the BL/S substrate was 8.7 g m^-2 d^-1, which was increased by 60.3%. The removal rate of ammonia nitrogen (NH₄⁺-N) from the digested wastewater contributed by the microalgal biofilm reached 22.6 mg L^-1 d^-1, which was higher than the previously reported that of NH₄⁺-N from turbid digested wastewater by the biofilms. Furthermore, the BL/S substrate can facilitate the secretion of abundant extracellular polymeric substrates, which results in the stable adhesion of the biofilm onto the BL/S substrate. The optical density of the microalgae cells at the outlet of the bPBR with BL/S substrate was below 0.1, which was 94% lower than that of the bPBR with the SO substrate. The results indicated the BL/S substrate may avoid the loss of microalgal biomass, and almost all biomass could be easily harvested from the biofilm for algae-based biomass resources. Consequently, this study can offer a promising alternative with efficient treatment technologies for wastewater with high turbidity.

Simultaneously pollutant removal and S0 recovery from composite wastewater containing Cr(VI)-S2- based on biofilm enhancement

Bioaugmentation of extracellular polymeric substances-producing bacteria was applied in pollutant removal and S⁰ recovery from composite wastewater in a mixotrophic denitrification system. In the presence of 200 mg·L^-1 S^2- and 50 mg·L^-1 Cr(VI), the removal efficiencies of chemical oxygen demand, NO₃^-, S^2- and Cr(VI) were 86.38%, 91.82%, 95.75%, and 100.00% respectively, while S⁰ recovery efficiency reached 79.17%. Increased contents of protein and polysaccharide, especially the high ratio of protein/polysaccharide verified the structural stability of biofilm was promoted by biofilm enhancement. The widespread distribution of bacteria/extracellular polymeric substance (EPS) revealed the more obvious biofilms formation in biofilm-enhanced group. High-throughput sequencing analysis showed that EPS-producing bacteria (Flavobacterium, Thauera, Thiobacillus and Simplicispira) were dominant bacteria in the biofilm-enhanced group. Moreover, by comprehensive considering of redundancy analysis, the colonization of selected bacteria improved the robustness of the reactor and treatment performance to wastewater contained toxic pollutions.

Promoted removal of phosphate by layered double hydroxides combined with bacteria: Application of novel carriers in biofilm reactor

Layered double hydroxides (LDHs) were used as carriers for the microbial consortium in sequencing biofilm batch reactor (SBBR) without inoculation to promote the removal of phosphate. The adsorption capacity of [Zn-Al]-LDH was significantly better than that of [Mg-Al]-LDH. The pollutants removal performance and behavior of microorganisms in LDH-SBBRs were also investigated. LDH-SBBRs showed improved removal efficiencies of COD, phosphate and TP with a low C/N ratio. Microscopic images show that biofilm formed rapidly in LDH-SBBRs. SEM-EDS detected abundant carbon and phosphorus, implying that biomass and phosphorus accumulate on LDH carriers. The microbial compositions of the three SBBRs indicate that the LDHs carriers improved the biodiversity of biofilm in the bioreactors. Synergistic effects of adsorption and biodegradation between well-structured LDHs and microorganisms led to an improved phosphate removal performance of LDH-SBBR. The results also demonstrate that [Zn-Al]-LDH carrier is the best for improving SBBR phosphate removal.

Rapid recovery of mixed culture polyhydroxyalkanoate production system from EPS bulking using azithromycin

The long-term stable operation of the mixed culture polyhydroxyalkanoate (PHA) enrichment stage is the guarantee for the continuous synthesis of PHA, however extracellular polymeric substances (EPS) sludge bulking occurred from time to time may cause the operation fail. In order to solve this problem, as a quencher of signal molecules and antibiotic, azithromycin (AZM) was used in the two systems with different modes to recover the sedimentation capacity of the sludge. The results showed that AZM addition resulted in the reduction of polysaccharide /protein (PS/PN) ratio in EPS and significant improvement of the sedimentation capacity of the sludge. Quorum quenching of AZM or aiiA gene maintained the sedimentation ability of the sludge in a relay mode. By adding AZM, the growth of Thauera and Flavobacterium, which caused sludge bulking, was inhibited. Paracoccus, a strong PHA producer, has been enriched to ensure that the maximum PHA synthesis of the system.