Suspended Carriers Research Articles

Intensified microalgae production and development of microbial communities on suspended carriers and municipal wastewater

Wastewater represents an alternative source of nutrients in which to grow microalgae, whilst improving the quality of the wastewater, and reducing the downstream treatment required. However, commercialisation of microalgal cultures for such duties faces a number of challenges, predominantly high cost and low productivity. Suspended-solid reactors (ssPBR) can reduce the operational costs, while promoting attached and suspended microalgae growth. In the present study, a novel approach was developed by integrating microalgal wastewater treatment with carrier systems to favour the growth of both attached and suspended cells of T. obliquus. This study found that T. obliquus was able to uptake nutrients from municipal wastewater, achieving removals of 99.3–99.9 % NH3-N, 54.5–88.5 % PO43− and 92.8–94.5 % DTC. The addition of a 12.5 % volumetric fill ratio of carriers in ssPBRs produced higher microalgal cell productivity (1.2·106 ± 2.5·105 cell ml−1 d−1) than the control (4.3·105 ± 2.8·105 cell ml−1 d−1). MinION nanopore sequencing was conducted to assess the impact of microalgal and carrier treatment on wastewater bacterial communities. It was found not only that bacterial communities had changed after the treatment but also the ones attached differed from the ones suspended. Untreated wastewater was characterised by the abundance of sewer bacteria genera such as Aliarcobacter and Arcobacter, whilst, after treatment, microbial communities were characterised by the presence of photosynthetic freshwater (Limnococcus, Stanieria) and bioremediation-like bacteria genera (Pseudomonas, Rheinheimera). In conclusion, the addition of 12.5 % fill carrier ratio increased microalgal productivity, while stimulating changes in the algal microbiome, and creating distinctly different populations in the free and attached environments.

Moving Bed Sequenced Batch Reactor System in Tetracycline Antibiotic Removal from Real Hospital Wastewater

Background: Water contamination by synthetic organic chemicals like antibiotics is a major environmental issue. Tetracycline (TC), an antibiotic in a wide family, is notable. A moving bed sequenced batch reactor (MBSBR) is tested for treating hospital raw wastewater containing TC. Methods: A 35-L pilot system was constructed, with 30 L usable. PVC suspended carriers (Kaldnes K3) with 584.3 m2 /m3 specific surface area made about 70% of the functional volume. The independent variables in this study were hydraulic retention duration (1, 1.5, 2, and 2.5 hours) and starting TC concentration (5, 10, and 15 mg/L). Results: The findings of the study demonstrated satisfactory performance under the conditions of an initial TC concentration of 5 mg/L and an organic load of 350 mg/L. The overall removal efficiencies for TC, chemical oxygen demand (COD), and biological oxygen demand (BOD5 ) were 72.8%, 83%, and 93.9%, respectively. The optimal performance of the system was primarily observed during the initial phase, characterized by a TC concentration of 5 mg/L and a hydraulic retention time (HRT) of 2.5 hours. The experimental results also indicated that the maximum removal efficiency was 1.8 kg COD/m2 .day, as determined by a fitted surface loading rate (SLR). Furthermore, the food-tomicroorganism (F/M) ratio decreased from 0.101 to 0.038 as the HRT increased from 1 to 2.5 hours. Conclusion: The results of the study indicate that the MBSBR exhibits a high level of efficiency in removing TC from hospital wastewater.

Methanogenesis performance and microbial characteristics in An-IFFAS process filled with conductive suspended carriers at ambient temperature

Direct interspecies electron transfer (DIET) has been proven to be established efficiently on conductive suspended carriers, and thus enhances methane production at thermophilic condition. However, the methanogenesis performance and relevant microbial characteristics in the anaerobic integrated floating-film activated sludge (An-IFFAS) reactor filled with conductive suspended carriers when feeding different substrates at ambient temperature are still unclear. In this study, An-IFFAS was fed by different substrates including ethanol, sodium propionate, glucose, sucrose and starch at ambient temperature (11.7–23.6°C). The experimental An-IFFAS reactor always exhibited significant advantages in COD removal (removal efficiency increased by 9.73 ± 4.36%) and methane production (methane production rate increased by 72.6 ± 49.1%) compared with the control reactor filled with conventional carriers regardless of the feeding substrate types. Abundant nano-wire structures were observed on conductive carriers, implying potential DIET pathway. The abundance of syntrophic electroactive bacteria (Smithella, Syntrophobacter, Thauera, Pseudomonas) and methanogens (Methanobacterium, Methanosaeta) increased by 3.79 and 4.08 times respectively on the novel carriers. Besides, the hydrolytic acidification bacteria (Endomicrobium, Treponema, Lentimicrobium) and hydrogen-producing acetogens (Acinetobacter) were enriched. This study provides a reference for DIET establishment and enhanced anaerobic digestion performance at ambient temperature.

Simultaneous denitrification enhancement and sludge reduction based on novel suspended carrier modified using activated carbon and magnetite at low carbon/nitrogen ratio

A novel suspended carrier was prepared by sticking activated carbon (AC) and magnetite (Fe3O4) onto polypropylene slices. Although this carrier could not reverse the decreased denitrification capacity trends under anoxic conditions at an influent carbon/nitrogen (C/N) ratio of 2, it enhanced denitrification by stimulating sludge reduction and accelerating electron transfer to certain extent. The carrier stuck by mixed AC/Fe3O4 exhibited better performance in terms of sludge reduction, extracellular polymeric substances (EPS) secretion, and denitrification than that merely stuck by AC and Fe3O4 at an influent C/N ratio of 2. The carrier stuck by mixed AC/Fe3O4 increased the total nitrogen removal efficiency by 24.6 % ± 12.5 % in a 72-h denitrification batch experiment compared to the common polypropylene carrier. Moreover, the carrier improved EPS secretion and nitrogen metabolism and promoted the growth of Trichococcus and some denitrifying genera. This study provides a reference for the treatment of low C/N ratio sewage.

Effect of aeration on low-substrate CANON process

The completely autotrophic nitrogen removal over nitrite (CANON) is a new type of nitrogen removal process developed in recent years. The control of dissolved oxygen (DO) in this process is relatively stringent, especially in low-substrate wastewater treatment. However, the results of studies on the operation of the process in different aeration modes are still controversial, and investigations on biofilm type CANON reactors are limited. In this study, a pilot-scale CANON bioreactor filled with suspended carriers was investigated on the treatment of wastewater at low ammonium concentrations, and the effect of the aeration mode on autotrophic nitrogen removal was evaluated. Seven conditions with various aeration on/off times and DO levels were tested. The results showed that an intermittent aeration with a 20-min/20-min aeration on/off time and DO concentrations of 1.0–1.3 mg/L at the end of the aeration period was appropriate, potentially inhibiting nitrite oxidizing bacteria (NOB) and keeping the total nitrogen (TN) removal rate at a relatively high level of 76.7% ± 2.5%. In the optimal aeration mode, the reactor achieved effluent TN and NH4+-N concentrations of (11.1 ± 3.3) mg/L and (3.6 ± 2.3) mg/L, respectively, with a hydraulic retention time of 12 h and an influent NH4+-N concentration of (48.6 ± 9.4) mg/L at 30.1°C ± 2.2°C. The results of metagenomic sequencing for microorganisms on carriers indicated that the main nitrogen removal bacteria in the reactor were Proteobacteria, Planctomycetes, and Nitrospirae. The NOB genus Nitrospira was completely inhibited by intermittent aeration. Candidatus Kuenenia had strong adaptability to low-concentration wastewater.

Pilot-scale Evaluation of an Anaerobic/Anoxic/Oxic Process for Nitrogen Removal from Sewage Using Metagenomic Sequencing

A modified pilot plant with two sequencing batch reactors on the strength of utilizing the inner carbon supply and adding suspended carriers was operated for 280 d to analyze nitrogen removal performance and microorganism community. Despite a low chemical oxygen demand (COD)/total nitrogen (TN) ratio of 3.5, the TN in the effluent decreased from 37.2 to 10.4 mg N/L. High-throughput sequencing indicated significant differences in the abundance of the phylum Actinobacteria (p<0.0001), Firmicutes (p<0.0001), Bacteroidetes (p<0.001), Uroviricota (p<0.0001) and Planctomycetes (p<0.0001) between the anoxic-carrier biofilms and flocculent sludge. Quantitative PCR revealed that denitrification and anammox genes were additional abundant in the anoxic-carrier biofilms than flocculent sludge (narG: p<0.0001; nirS: p<0.01; narH: p<0.01; norB: p<0.0001; hzsB: p<0.01; hdh: p<0.01). Thus, enrichment with denitrification and anammox bacteria might improve nitrogen removal; this was supported by KEGG pathway annotation. Collectively, this study suggests that anoxic-carrier biofilms might enhance nitrogen removal through partial denitrification and anammox process in CWWTPs.

Simultaneous removal of refractory organic pollutants and nitrogen using electron shuttle suspended biofilm carriers in an integrated hydrolysis/acidification-anoxic/aerobic process

Azo dyes wastewater contains refractory pollutant and nitrogen, which threatens human health and ecological environment when discharged into environment directly. Electron shuttle (ES) is able to participate in the extracellular electron transfer, and thus enhances the removal efficiency of refractory pollutant. However, the continuous dosing of soluble ES would rise operation cost and cause contamination inevitably. In this study, a type of insoluble ES (carbonylated graphene oxide (C-GO)) was developed and melt blended into polyethylene (PE) to prepare novel C-GO-modified suspended carriers. Compared to those of conventional carrier (31.60%), the surface active sites of novel C-GO-modified carrier increased to 52.95%. An integrated hydrolysis/acidification (HA, filled with C-GO-modified carrier) - anoxic/aerobic (AO, filled with clinoptilolite-modified carrier) process was applied to remove azo dye acid red B (ARB) and nitrogen simultaneously. ARB removal efficiency was significantly improved in the reactor filled with C-GO-modified carriers (HA2) compared to the reactor filled with conventional PE carriers (HA1) or activated sludge (HA0). Total nitrogen (TN) removal efficiency of the proposed process increased by 25.95–32.64% compared to the reactor filled with activated sludge. Moreover, the intermediates of ARB were identified by liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway of ARB through ES was proposed. C-GO-modified carriers induced ARB-removal-related bacterial enrichment (such as Chloroflexi, Lactivibrio, Longilinea, Bacteroidales and Anaerolineaceae). Besides, the relative abundance of denitrifiers and nitrifiers in the AO reactor filled with clinoptilolite-modified carrier was increased by 11.60% compared with activated sludge. Copy numbers of genes related to membrane transport, carbon/energy metabolism and nitrogen metabolism increased significantly on the surface-modified carriers. This study proposed an efficient approach for simultaneous azo dyes and nitrogen removal, showing potential in actual application.

Superior nitrogen removal and efficient sludge reduction via partial nitrification-anammox driven by addition of sludge fermentation products for real sewage treatment

Efficient retention and enrichment of anammox bacteria (AnAOB) are essential for the application of municipal wastewater anammox. Herein, an innovative process for highly enriching AnAOB within suspended carrier was developed in a single-stage anaerobic/oxic/anoxic reactor with 5.5 % carrier filling ratio for real sewage. Addition of sludge fermentation products promoted stable maintenance of partial nitrification (nitrite accumulation rate > 90.0 %) and achieved efficient external sludge reduction (27.6–37.9 %). Continuous nitrite supply and carrier addition promoted AnAOB enrichment (2.4 × 1011 gene copies/g dry sludge). Candidatus Brocadia was the predominant bacteria in carriers (18.6 %). The average effluents of total inorganic nitrogen (TIN) and NH4+-N were 1.9 and 0.8 mg/L with removal rates of 97.0 % and 98.7 %. In the anoxic stage, TIN removal rate reached 71.5 %, and the proportion of anammox to nitrogen removal accounted for 82.7 %. This study broadens the application of mainstream sewage anammox and the resource utilization of waste activated sludge.

Integration of a pure moving bed biofilm reactor process into a large micro-polluted water treatment plant.

The pure-MBBR process was applied to remove ammonia in a full-scale micro-polluted-water treatment plant with a daily treatment capacity of 260 × 104 m3/d, Guangdong, China. The relationship between treatment efficiency, physical and chemical properties and microbial diversity in the process of biofilm growth was explored, and the oxygen transfer model of biofilm was established. The results show that the effluent of two-stage pure MBBR process is stable and up to standard after 10 days' incubation. The nitrification loads of two-stage biofilm was stable on the 14th day. The biomass and biofilm thickness lagged behind the nitrification load, and reached a relatively stable level on the 28th day. The species richness of biofilm basically reached a stable level on the 21st day, and the microbial diversity of primary biofilm was higher. In the primary and secondary stage at different periods, the relative abundance of dominant nitrifying bacteria Nitrospira reaches 8.48-13.60%, 6.48-9.27%, and Nitrosomonas reaches 2.89-5.64%, 0.00-3.48%. The pure MBBR system mainly adopts perforated aeration. Through the cutting and blocking of bubbles by suspended carriers, the oxygen transfer rate of the system was greatly improved.

Enhanced nitrogen removal at low temperature with mixed anoxic/oxic process

Different hydraulic retention times (HRTs) were tested in a mixed anoxic/oxic (A/O) system at 5°C and 10°C to investigate the effects of HRT and carrier on nitrogen removal in wastewater at low temperatures. The results showed that the addition of the fillers improved the treatment effect of each index in the system. With an optimal HRT of 7.5 h at 5°C, the removal efficiencies of NH4+-N and total nitrogen (TN) reached 91.2% and 75.6%, respectively. With an HRT of 6 h at 10°C, the removal efficiencies of NH4+-N and TN were 96.7% and 82.9%, respectively. The results of high-throughput sequencing showed that the addition of the suspended carriers in the aerobic zone could improve the treatment efficiency of nitrogen at low temperatures. The microbial analysis indicated that the addition of the suspended carriers enhanced the enrichment of nitrogen removal bacteria. Nitrospira, Nitrotoga, and Nitrosomonas were found to be the bacteria responsible for nitrification, and their relative concentrations on the biofilm at 5°C and 10°C accounted for 98.11%, 92.79%, and 69.98% of all biological samples, respectively.

Combined application analysis of MBBR and magnetic coagulation process in a full-scale project

The combined application of moving bed biofilm reactor (MBBR) and magnetic coagulation (MC) is a new method of enhancing nitrogen and phosphorus removal of wastewater treatment plants with limited land occupation. This had been successfully used in a full-scale 30,000-m3/d wastewater treatment plant in Guangdong Province, China. The effluent concentrations of COD, NH4+–N, total phosphorus (TP), and suspended solid (SS) stabilized at 11.6 ± 3.9, 1.4 ± 1.3, 0.28 ± 0.11, and 2.2 ± 1.2 mg/L when the corresponding influent concentrations were 81.7 ± 27.5, 15.2 ± 3.0, 1.40 ± 0.29, and 42 ± 19 mg/L, respectively, which could steadily meet the designed discharge standard even though the land occupation was merely at 2000 m2. Regarding the MBBR effluent, the MC process sufficiently removed residual SS, TP, and some COD within 3 min of sedimentation, which ensured that the discharge reached the designed standard. The relative abundance of nitrifying genera of the secondary MBBR was higher than that of the primary MBBR, leading to a greater NH4+–N removal ability for the secondary MBBR. Meanwhile, the primary MBBR was superior to the secondary MBBR in terms of organic matter removal. The suspended carrier was more competent in enriching nitrifiers than the activated sludge, highlighting the significant advantage of MBBR. However, the suspended carrier was insufficient in enriching phosphorus removal bacteria as compared with the activated sludge, leading to a poor biological TP removal efficiency of the MBBR process. Further research is needed to improve the biological phosphorus removal ability of MBBR.

A Novel Anaerobic Gravity-Driven Dynamic Membrane Bioreactor (AnGDMBR): Performance and Fouling Characterization.

Despite numerous studies undertaken to define the development and significance of the dynamic membrane (DM) formed on some coarse materials, the optimization of reactor configuration and the control of the membrane fouling of anaerobic dynamic membrane bioreactor (AnDMBR) need to be further investigated. The aim of this study was to design a novel anaerobic gravity-driven dynamic membrane bioreactor (AnGDMBR) for the effective and low-cost treatment of municipal wastewater. An 800 mesh nylon net was determined as the optimal support material based on its less irreversible fouling and higher effluent quality by the dead-end filtration experiments. During the continuous operation period of 44 days, the reactor performance, DM filtration behavior and microbial characteristics were studied and compared with the results of recent studies. AnGDMBR had a higher removal rate of chemical oxygen demand (COD) of 85.45 ± 7.06%. Photometric analysis integrating with three-dimensional excitation–emission matrix fluorescence spectra showed that the DM effectively intercepted organics (46.34 ± 16.50%, 75.24 ± 17.35%, and 66.39 ± 17.66% for COD, polysaccharides, and proteins). The addition of suspended carriers effectively removed the DM layer by mechanical scouring, and the growth rate of transmembrane pressure (TMP) and the decreasing rate of flux were reduced from 18.7 to 4.7 Pa/h and 0.07 to 0.01 L/(m2·h2), respectively. However, a dense and thin morphological structure of the DM layer was still observed in the end of reactor operation and plenty of filamentous microorganisms (i.e., SJA-15 and Anaerolineaceae) and the acidogens (i.e., Aeromonadaceae) predominated in the DM layer, which was also embedded in the membrane pore and led to severe irreversible fouling. In summary, the novel AnGDMBR has a superior performance (higher organic removal and lower fouling rates), which provides useful information on the configuration and operation of AnDMBRs for municipal wastewater treatment.

A Class-E Power and Data Transmitter With Improved Data Rate to Carrier Frequency Ratio for Medical Implants

In this brief, a new wireless power transfer and data telemetry circuit for biomedical implants is proposed that increases the data-rate without compromising power transmission efficiency. The power and data are transferred through an inductive link driven by a class-E amplifier. In addition to the proposed modulation, this transmitter can be used for a variety of amplitude modulations such as ON-OFF keying and carrier-width modulation. Based on the suspended carrier modulation idea, the data rate to carrier frequency (DRCF) ratio is improved in the proposed transmitter. In comparison with the conventional suspended carrier transmitter, our design is more efficient and less complex. The DRCF ratio in the proposed transmitter is 50 percent. A proof-of-concept prototype of the proposed transmitter has been implemented on printed circuit board. At 1 MHz carrier frequency, the transmitter power efficiency is close to 61% for the power delivered to the load of 32.3 mW and the data rate of 0.5 Mbps.

Numerical simulation and experimental research of fractal suspended carrier based on nonlinear equation.

The geometric structure of the suspended carrier is an important factor that directly affects the effluent quality of the moving bed biofilm reactor, and it should be a valuable mathematical solution to solve the nonlinear equation through numerical simulation and experimental research. Therefore, this study has designed and prepared a coral-shaped fractal suspension carrier based on nonlinear equations and verified the effectiveness of the new carrier for sewage treatment through FLUENT numerical simulation and domestic sewage treatment experiments. The experimental results show that the coral-shaped fractal suspension carrier has a significant effect on the velocity, vortex distribution, and gas-phase distribution of the flow field in the reactor. The mass transfer dead area in the reactor is reduced, the number of vortices is significantly increased, and the fractal dimension of the carrier is negatively correlated with the flow velocity and pressure drop of the fluid. After stabilization, the average removal rates of COD and NH4+-N by the reactor are 89.5% and 93.21%, respectively; the effluent quality reaches the national first-class A standard; and the sewage treatment performance is good. At the same time, this research provides a preliminary research basis for the method of solving nonlinear equations through numerical simulation and experimental research.

Enhancing anaerobic methane production in integrated floating-film activated sludge system filled with novel MWCNTs-modified carriers

Conductive materials can enhance anaerobic methane production by accelerating interspecies electron transfer between electroactive bacteria and methanogens. However, the daily loss or less specific surface area of small/big size of conductive materials always limits their application in anaerobic digestion. In this study, the conductive multi-walled carbon nanotubes (MWCNTs) (15 wt% and 20 wt%) were mixed with high-density polyethylene (HDPE) and novel conductive suspended carriers were prepared. Results showed the conductivity of the novel conductive suspended carriers increased by 1–2 orders of magnitude comparing with HDPE carriers, as well as the attached biomass improved from 3.93 g/m2 (HDPE carriers) to 5.82 g/m2 (15 wt% MWCNTs-modified carriers) and 6.67 g/m2 (20 wt% MWCNTs-modified carriers). Integrated floating-film activated sludge (IFFAS) filled with MWCNT-modified carriers showed significant advantages in chemical oxygen demand (COD) removal (removal efficiency increased by 3.6–37.2%) and methanogenic performance (cumulative methane increased by 12.28–62.91%) compared with the control reactor filled with conventional HDPE carriers when treating sodium propionate wastewater at the organic loading rates (OLR) of 11.3–26.3 kg COD/(m³∙d). SEM images and high-throughput sequencing results proved potential direct interspecies electron transfer (DIET) had been established successfully on the MWCNTs-modified carriers. The syntrophic electroactive bacteria (Geobacter, Thauera) and Methanotrix were enriched by 2.28–4.58% and 9.41–16.80% respectively owning to the addition of novel conductive carriers. This study proved IFFAS process filled with novel MWCNTs-modified suspended carriers showed great potential in establishing DIET to enhance anaerobic digestion in practical application.

Enhancing the formation of simultaneous nitrification and denitrification (SND) biofilm and nitrogen removal performance using two-units IFFAS process filled with surface-modified carriers

Moving-bed biofilm reactor (MBBR) and integrated floating-film activated sludge (IFFAS) are considered as well-established technologies for simultaneous nitrification and denitrification (SND). However, SND biofilm formation and nutrient removal performance are generally limited by the innate physico-chemical properties of conventional suspended carriers and/or insufficient carbon source available for denitrification. In this study, novel surface-modified carriers were developed via introducing mixed functional materials (natural zeolite, cationic polyquaternium-10, insoluble biodegradable organic polybutylene succinate/bamboo powder) into polyethylene. The modified carrier revealed enhanced hydrophilicity, positive surface charge, higher surface free energy and carbon source slow release capacity. Biofilm growth feature showed that the surface-modification resulted in more biofilm formation and more polysaccharide and protein in extracellular polymeric substances (EPS), which was structural and functional beneficial for substrate capture, transfer and intercellular interactions between nitrifiers and denitrifiers. IFFAS reactor filled with novel modified carriers was upgraded by dividing into two vertical units, where alternate feeding and aeration was conducted to create an anoxic unit to enhance the utilization of influent carbon source for denitrification as well as an aerobic unit to strengthen nitrification. The two-units IFFAS reactor exhibited highly efficient SND performance with TN removal efficiency of 59.9–65.9%, increased by 12.3–13.5% compared with control group. This study proposed an approach towards enhancement of functional biofilm formation and SND performance, and had fascinating potential in actual applications.

Study on the effect of new type of suspended carrier on oxygen mass transfer characteristics.

Based on the characteristic that the air can form a vortex around the carrier after passing through the suspended carrier, a new layered fan-like carrier and a wave multi-channel carrier were prepared by designing the spatial structure of the suspension carrier and combining 3D printing technology. Compared with commercially available multi-faceted hollow sphere carrier, clear water oxygenation experiment was carried out in a transparent organic glass reactor, and the aeration volumetric flow rate was 0.28, 0.42, 0.56, 0.70, and 0.84 VVM, respectively. The results show that the growth rate of dissolved oxygen, the saturation value of dissolved oxygen, and the oxygen mass transfer coefficient in the new type of carrier reactor are higher than those of commercially available multi-faceted hollow spheres and blank reactors at various aeration intensities. Under the condition of aeration volumetric flow rate at 0.56 VVM, the reactor can reach dissolved oxygen saturation at a faster rate of dissolved oxygen growth. Combined with the FLUENT numerical simulation and sewage treatment experiments, it is proved that changing the spatial structure of the carrier can accelerate the reoxygenation of the water body, increase the value of dissolved oxygen saturated in the water, and create ideal mass transfer conditions for the MBBR (moving bed biofilm reactor).

Enhancing anoxic denitrification of low C/N ratio wastewater with novel ZVI composite carriers

External organic carbon sources are needed to provide electron donors for the denitrification of wastewater with a low COD/NO3−-N (C/N) ratio, increasing the treatment cost. The economic strategy is to enhance the bioactivity and/or biodiversity of denitrifiers to efficiently utilize organic substances in wastewater. In this study, novel zero-valent iron (ZVI) composite carriers were prepared and implemented in a suspended carrier biofilm reactor to enhance the bioactivity and/or biodiversity of denitrifiers. At the influent C/N ratio of 4 (COD was 179.5 ± 5.0 mg/L and TN was 44.2 ± 0.8 mg/L), COD and TN removal efficiencies were 85.1% and 66.4%, respectively, in the reactors filled with 3 wt% ZVI composite carriers. In contrast, COD and TN removal efficiencies were 70.4% and 55.3%, respectively, in the reactor filled with conventional high-density polyethylene (HDPE) biofilm carriers. The biofilm formation on the 3 wt% ZVI composite carriers was optimized due to its higher roughness (surface square roughness increased from 76.0 nm to 93.8 nm) and favorable hydrophilicity (water contact angle dropped to 72.5° ± 1.4° from 94.3° ± 3.2°) compared with the HDPE biofilm carriers. In addition, heterotrophic denitrifiers, Thauera and Dechloromonas, were enriched, whereas autotrophic denitrifiers, Raoultella and Thiobacillus, exhibited high relative abundance in the biofilm of ZVI composite carriers. The coexistence of heterotrophic denitrifiers and autotrophic denitrifiers on the surface of ZVI composite carriers provided mixotrophic metabolism of denitrification (including heterotrophic and iron-based autotrophic), thereby ensuring effective denitrification for wastewater with a low C/N ratio without external organic carbon source addition.

Microbial community structure analysis in a hybrid membrane bioreactor via high-throughput sequencing

Compared to the suspended culture (sludge) of a conventional bioreactor, hybrid membrane bioreactors (HMBRs) are more effective at removing pollutants owing to the addition of fillers addition of fillers that facilitate biofilm formation. However, the microbial community structure and composition in an HMBR remain unclear. We ran three laboratory-scale HMBRs at room temperature under different sludge retention times (SRTs; 10d, 20d, and 30d) to compare the microbial diversity and community structure among the membrane surface, suspended filler surface, and mixed liquor using high-throughput sequencing. The results showed that SRT can markedly affect microbial community structure in the HMBR, and different trends appeared in the three functional units. The largest number of mutual operational taxonomic units was found in the activated sludge mixture and suspended carrier with an SRT of 20d and 30d. Species belonging to Proteobacteria in the 10d SRT group had the greatest contribution to between-group differences. A longer SRT could mitigate membrane fouling by decreasing the relative abundance of Thauera and Sphaerotilus attached on the membrane surface. Comamonadaceae, a family of denitrifying bacteria, offer high denitrification potential for bioreactors operating under a long SRT.

Simultaneous nitrification and denitrification in moving bed bioreactor and other biological systems.

Moving bed bioreactor (MBBR), used for treatment of municipal and industrial wastewater, is a completely mixed attached growth type system that involves microorganisms which grow as biofilm on the surface of the suspended carriers within the reactor. If the biofilm is thick enough, dissolved oxygen in the reactor would not diffuse into deeper strata and thus anoxic/anaerobic condition develops in those regions facilitating growth of heterotrophic denitrifying bacteria. Autotrophic nitrifiers colonize the outer surface of biofilm in biocarriers as usual. Thus, development of aerobic nitrifying and anoxic denitrifying microorganisms facilitates nitrification and denitrification simultaneously within different zones of the same biofilm. The present paper summarizes the feasibility of nitrogen removal in MBBR systems via autotrophic nitrification followed by heterotrophic denitrification, including various aspects of simultaneous nitrification and denitrification (SND) process in other biofilm units as well. Apart from that, the areas for further investigation are briefly narrated from studies conducted earlier.