Treatment Of Low-strength Wastewater Research Articles

Anaerobic fluidized membrane bioreactors with low strength wastewater: A long-term study on the impact of conductive polyaniline modified fluidized biocarrier on biomethane production

Polyaniline (PANI) is used as a coating material to create a conductive surface on polyvinylidene fluoride (PVDF) substrate. This was implemented as a biocarrier in an anaerobic fluidized membrane bioreactor (AFMBR) to treat low-strength wastewater consisting of glucose. The results of parallel operation using AFMBRs indicate that the fouling rate was invariably similar in both AFMBR 1 and AFMBR 2 throughout the operation of 400 days for uncoated and PANI coated PVDF pellet as substrate, respectively. The conductive coating in AFMBR 2 enhanced the electron transfer between organic matter and microbes. The AFMBR 2 with PANI-PVDF biocarrier exhibited a methane yield that was 62 % more per gram soluble chemical oxygen demand (SCOD) removed at 12 h HRT than its uncoated counterpart in AFMBR 1. The results of the surface analysis of the biocarrier indicated the enhanced biomass attachment on the conductive surface owing to the roughness (which is 1.6 times more) created by PANI coating over PVDF supporting material. The findings of our study indicate that the utilization of conductive polymeric-based biocarrier has the potential to significantly enhance the kinetics of AFMBR during the treatment of low-strength wastewater.

Anaerobic treatment of low-strength municipal wastewater with electroactive magnetite-embedded granules under mainstream conditions

This study examined the potential for the anaerobic treatment of low-strength wastewater (250mg chemical oxygen demand/L) using expanded granular sludge bed (EGSB) with conductive magnetite-embedded granules (MEGs) under mainstream conditions (25℃). The inclusion of magnetite, with high specific gravity and conductivity, enhanced the settleability, structural stability, and electron transfer capability of MEGs compared to granules without it. Within the hydraulic retention time (HRT) range of 4–12h, the MEG-EGSB reactors maintained superior treatment performance, along with comparable or higher methane production, compared to the control EGSB reactors lacking MEGs. This performance enhancement was more pronounced under conditions of higher hydraulic and organic loading. The MEG-EGSB reactors achieved approximately 90% organic removal efficiency at 8–12-h HRTs, a range comparable to that of the aerobic activated sludge process, with minimal loss of magnetite. The results from RNA-based microbial community analysis, alone with the consistently higher methane content in the biogas from MEG-EGSB reactors, supported the potential development of electric syntrophy between exoelectrogenic bacteria and electrotrophic methanogens in electroactive MEGs. This capability of MEGs to promote electro-syntrophic methanogenesis could potentially enhance methanogenic degradation of organic matter. The overall findings suggest that the MEG-EGSB process is a promising candidate for anaerobic municipal wastewater treatment.

The superiority of hydrophilic polyurethane in comammox-dominant ammonia oxidation during low-strength wastewater treatment

Carriers have been extensively employed to enhance nitrification performance during low-strength wastewater treatment by retaining slow-growing ammonia oxidizing microorganisms (AOMs). Still, there is a dearth of systematic understanding of biofilm properties and microbial community structure formed on different carriers. In this study, hydrophilic polyurethane foam (PUF) carriers were prepared and compared with five widely used commercial carriers, namely Kaldness 3, Biochip, activated carbon, volcanic rock, and zeolite. The results indicated that the biofilms formed on carriers enhanced microbial ammonia oxidation activity. Additionally, the biofilm developed on the PUF demonstrated the most superior performance among all selected carriers, not only exhibiting the highest abundant and the most active AOMs, with amoA gene abundance of 1.41 × 1013 copies/m3 and specific ammonia oxidation rate of 9.84 g NH4+-N/(m3 × h), but also possessing a compact structure, with 3.41 kg VSS/m3 and 46.83 mg extracellular polymeric substances/g VSS. The high-throughput sequencing analysis revealed that the comammox (CMX) Nitrospira dominated on biofilm due to the intrinsically low apparent half-saturation constant for substrate. A unique ecological community structure was established on PUF, characterized by low species diversity and high homogeneity in alignment with community characteristics of CMX. The biofilms on PUF contributed to the proliferation of CMX Nitrospira dominated by Nitrospira nitrosa, achieving the highest proportion among colonial three AOMs at 86.58 %. The appropriate average pore size, superior hydrophilicity, and large specific surface area of PUF carriers provided a robust foundation for the exceptional ammonia oxidation performance of the formed biofilms.

Fe(II)-driven spatiotemporal assembly of heterotrophic and anammox bacteria enhances simultaneous nitrogen and phosphorus removal for low-strength municipal wastewater

The mainstream anaerobic ammonium oxidation (anammox) faces considerable challenges with low-strength municipal wastewater. A Fe(Ⅱ)-amended partial denitrification coupled anammox (PD/A) process was conducted and achieved a long-term and efficient nitrogen and phosphorus removal, yielding effluent total nitrogen and phosphorus concentrations of 1.97 ± 1.03 mg/L and 0.23 ± 0.13 mg/L, respectively, which could well meet more stringent effluent discharge standard of some wastewater treatment plants in specific geographical locations, e.g., estuaries. Fe(Ⅱ)-driven vivianite formation provided key nucleuses for the optimization of the spatial distribution of heterotrophic and anammox bacteria with enhanced extracellular polymeric substances as key driving forces. Metagenomics analysis further revealed the increase of key genes, enhancing anammox bacteria homeostasis, which also bolstered the resistance to environmental perturbations. This study provided a comprehensive sight into the function of Fe(Ⅱ) in mainstream PD/A process, and explored a promising alternative for synergetic nitrogen and phosphorus removal for low-strength municipal wastewater treatment.

Unravelling the optimal strategy on the stable mineralized anammox granular systems in treating low-strength wastewater

Effective retention of anammox bacteria (AnAOB) is the prerequisite for the application of anammox process, especially in treating low-strength wastewater. The employment of anammox granules coupled with phosphorus minerals has gained extensive attention as retaining biomass. To achieve the stability of mineralized anammox system for low-strength wastewater treatment, two switching strategies (cascade strategy and plunging strategy) were compared in terms of nitrogen removal performance, physicochemical properties and microbial community. Results showed cascade strategy significantly implemented the nitrogen removal rate of 0.86 ± 0.05 kg N/m3/d at hydraulic retention time of 1.6 h, with higher phosphorus removal via the hydroxyapatite formation. The cross-section observation indicated mineralized anammox granules exhibited a unique spatially heterogeneous structure with distinct zoning. Moreover, the granules displayed dense structure, excellent settleability, superior mechanical strength and outstanding biomass retention based on cascade strategy. Microbial analysis revealed the dominant populations were shifted from Ca. Kuenenia to Ca. Brocadia after switching to low-strength conditions. Further investigation is warranted to explore effective methods for phosphorus recovery from hydroxyapatite. Overall, the study provided a reference for promoting and understanding the synergistic nitrogen removal and phosphorus recovery in actual applications.

Iron-electrolysis assisted anammox/denitrification system for intensified nitrate removal and phosphorus recovery in low-strength wastewater treatment

Two iron-electrolysis assisted anammox/denitrification (EAD) systems, including the suspended sludge reactor (ESR) and biofilm reactor (EMR) were constructed for mainstream wastewater treatment, achieving 84.51±4.38 % and 87.23±3.31 % of TN removal efficiencies, respectively. Sludge extracellular polymeric substances (EPS) analysis, cell apoptosis detection and microbial analysis demonstrated that the strengthened cell lysate/apoptosis and EPS production acted as supplemental carbon sources to provide new ecological niches for heterotrophic bacteria. Therefore, NO3−-N accumulated intrinsically during anammox reaction was reduced. The rising cell lysis and apoptosis in the ESR induced the decline of anammox and enzyme activities. In contrast, this inhibition was scavenged in EMR because of the more favorable environment and the significant increase in EPS. Moreover, ESR and EMR achieved efficient phosphorus removal (96.98±5.24 % and 96.98±4.35 %) due to the continued release of Fe2+ by the in-situ corrosion of iron anodes. The X-ray diffraction (XRD) indicated that vivianite was the dominant P recovery product in EAD systems. The anaerobic microenvironment and the abundant EPS in the biofilm system showed essential benefits in the mineralization of vivianite.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in anaerobic/anoxic/oxic + nitrification system

A two-sludge anaerobic/anoxic/oxic + nitrification system with simultaneous nitrogen and phosphorus removal was studied for enhanced low-strength wastewater treatment. After 158 days of operation, excellent NH4+-N, chemical oxygen demand (COD) and PO43−-P removal (99.0 %, 90.0 % and 92.0 %, respectively) were attained under a low carbon/nitrogen ratio of 5, resulting in effluent NH4+-N, COD and PO43−-P concentrations of 0.3, 30.0 and 0.5 mg/L, respectively. The results demonstrate that the anaerobic/anoxic/oxic sequencing batch reactor (A2-SBR) and nitrification sequencing batch reactor (N-SBR) had favorable denitrifying phosphorus removal and nitrification performance, respectively. High-throughput sequencing results indicate that the phosphate-accumulating organisms Dechloromonas (1.1 %) and Tetrasphaera (1.2 %) were enriched in the A2-SBR, while the ammonia-oxidizing bacteria Nitrosomonas (7.8 %) and the nitrite-oxidizing bacteria Nitrospira (18.1 %) showed excellent accumulation in the N-SBR. Further analysis via functional prediction revealed that denitrification is the primary pathway of nitrogen metabolism throughout the system. Overall, the system achieved low carbon and high efficiency nutrient removal.

Expansive microbial metabolic versatility and spatial biodiversity of anammox coupling with denitrification granular sludge under different feeding strategies

Anammox coupling with denitrification has attracted increasing attention in low-strength wastewater treatment. However, its wide application in continuous-flow process is seriously restricted by insufficient anammox capacity due to the failed biomass retention. The functional capacities of communities inhabiting the fluctuating habitat has been little understood. This study developed a novel granular sludge-based partial denitrification coupling with anammox (PD/A) process with the feeding strategy shifting from sequencing to continuous flow in a Continuous Stirred Tank Reactor (CSTR), treating low-strength wastewater containing ammonia (NH4+-N) of 46.1 mg/L and nitrate (NO3−-N) of 60.7 mg/L. Significantly enhanced specific anammox activity was demonstrated, attributed to the robust nitrite (NO2−-N) generation with NO3−-N to NO2−-N transformation ratio (NTR) averaged 84.1 %. Remarkable total nitrogen (TN) removal of 95.4 % was thus achieved with anammox pathway contribution as high as 88.3 %. Interestingly, a dynamic and stratified microbial structure was obtained in CSTR, in which anammox migrated to outer layer together with Thauera capable of partial denitrification (PD) in big granules, resulting in more efficient cross-feeding and strengthening the cooperation between anammox and heterotrophic PD bacteria in CSTR. Metagenomic-based metabolic inferences provide first insight into the versatile microbial metabolic potential of anammox bacteria for reducing NO3−-N with acetate as electron donor in PD/A process. They were successfully enriched and retained with the relative abundance of 8.4 %, being attributed to the enhanced mass transfer efficiency. On the contrary, dominant denitrifier Thauera decreased sharply to 4.2 %. This study provides a new alternative of anammox coupling with heterotrophics granular sludge for efficient low-strength wastewater treatment under continuous feeding, and open up new perspectives for selecting distinctive communities that stand out by expansive metabolic versatility and excellent microbial collaboration.

Rapid start-up strategy and microbial population evolution of anaerobic ammonia oxidation biofilm process for low-strength wastewater treatment

The implementation of the anaerobic ammonium oxidation (anammox) process in treating low-strength wastewater is limited by the difficulty in enriching anammox bacteria (AnAOB). Here, the first enrichment of AnAOB at a high nitrogen (N) loading rate (NLR) as a strategy was proposed to achieve the rapid start-up of the anammox biofilm process treating low-strength wastewater. The long-term stability of the anammox biofilm process after start-up operating at a low NLR of 0.2–0.4 kg N/(m3⋅d) was evaluated. Results showed that the N removal efficiency was up to 75 % under a low NLR of 0.2 kg N/(m3⋅d) condition. Low-strength organic matter promoted the metabolic coupling between partial denitrifying bacteria (PDB) and AnAOB. The genus Candidatus Brocadia as AnAOB (18 %-27 %) can coexist with Limnobacter (PDB, 9 %-12 %) for efficient N removal. This study offers a rapid start-up strategy of anammox biofilm process in treating low-strength wastewater.

Hydraulic retention time optimization achieved unexpectedly high nitrogen removal rate in pilot-scale anaerobic/aerobic/anoxic system for low-strength municipal wastewater treatment

Applications of post-denitrification processes are subjected to low reaction rates caused by a lack of carbon resources. To offer a solution for reaction rate promotion, this research found a pilot-scale anaerobic/aerobic/anoxic bioreactor treating 55–120 m3/d low-strength municipal wastewater for 273 days. A short hydraulic retention time (HRT, 5–6 h) and a high nitrogen removal rate (63.2 ± 9.3 g-N/m3·d) were achieved using HRT optimization. The effluent total nitrogen concentration was maintained at 5.8 ± 1.4 mg/L while operating at a high nitrogen loading rate of 86.2 ± 12.8 g-N/m3·d. The short aeration (1.25–1.5 h) minimized the Glycogen loss. The endogenous denitrification rate increased to above 1.0 mg/(g-VSS·h). The functional genus Ca. Competibacter enriched to 2.3 %, guaranteeing the efficient post-denitrification process. Dechloromonas rose to 1.1 %, aiding in the synchronous phosphorus removal. These findings offered fresh insights into AOA processes to achieve energy/cost-saving wastewater treatment.

Rapid static feeding combined with Fe2+ addition for improving the formation and stability of aerobic granular sludge in low-strength wastewater

Aerobic granular sludge (AGS) needs a long start-up time and always shows unstable performance when it is used to treat low-strength wastewater. In this study, a rapid static feeding combined with Fe2+ addition as a novel strategy was employed to improve the formation and stability of AGS in treating low-strength wastewater. Fe-AGS was formed within only 7 days and showed favorable pollutant removal capability and settling performance. The ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) concentration in the effluent were lower than 5 mg/L and 50 mg/L after day 23, respectively. The sludge volume index (SVI) and mixed liquid suspended solids (MLSS) was 37 mL/g and 2.15 g/L on day 50, respectively. Rapid static feeding can accelerate granules formation by promoting the growth of heterotrophic bacteria, but the granules are unstable due to filamentous bacteria overgrowth. Fe2+ addition can inhibit the growth of filamentous bacteria and promote the aggregation of functional bacteria (eg. Nitrosomonas, Nitrolancea, Paracoccus, Diaphorobacter) by enhancing the secretion of extracellular polymeric substances (EPS). This study provides a new way for AGS application in low-strength wastewater treatment.

Rapid enrichment of anammox bacteria for low-strength wastewater treatment: Role of influent nitrite and nitrate ratios in sequencing batch reactors (SBRs)

Anaerobic ammonium oxidation (Anammox) bacteria (AnAOB) have a long doubling time, which represents one of the key challenges for starting up anammox-based reactors. This study investigated the effect of varied nitrite/nitrate ratios on the anammox reactor startup process using five lab-scale anammox sequencing batch reactors (SBRs) (R1-R5). Nitrate addition significantly accelerated AnAOB enrichment startup, particularly during nitrite accumulation phase. The total start-up time was shortened by 55–71 days, compared to the reactor without nitrate. In R1 (nitrite/nitrate=10:0), anammox contributed the highest nitrogen removal percentage (91%), while R2 (nitrite/nitrate=7:3), with nitrate added, exhibited the highest anammox activity (53.84 mg NH4+-N/g VSS/day) in the steady-state phase. As nitrate proportions increased (R3-R5), anammox activity gradually declined due to limited available COD required for the conversion of NO3- to NO2-. Furthermore, it was found that nitrate-added improved the sludge settleability, with lower SVI30. 16S rRNA gene revealed that Ca. Brocadia was the predominant AnAOB in R1, R2 and R3, where nitrite was the primary NOx--N species (≥50%) in the influent. While in the reactor with low concentration of nitrite (R4: nitrite/nitrate=3:7), Ca. Kuenenia was the dominant AnAOB. This study successfully established a complex and balanced ecosystem with multi-species coexistence, where AnAOB served as the primary functional group on nitrogen removal, supported by denitrification bacteria and dissimilatory nitrate reduction to ammonium (DNRA) bacteria. This study proposes a rapid start-up strategy for the anammox process, which overcomes the bottleneck of long start-up time and helps to promote the application of anammox in wastewater treatment.

Acceleration of the startup process of an anaerobic baffled reactor utilizing electrolyte regeneration

The objective of this study was to examine the performance of an electrolytic anaerobic baffled reactor (EABR) that contained five rectangular compartments in the treatment of low-strength synthetic wastewater. The effect of integration of electrolysis into an anaerobic baffled reactor (ABR) on the startup process, removal of chemical oxygen demand (COD), production of volatile fatty acids (VFAs), and profile of the pH of the EABR were investigated. With a low-strength influent (COD = 600 mg/L), the results indicated that COD removal was 92 % and that the VFAs were negligible by the third compartment. Also, VFA analysis showed that propionic acid was found in the first two compartments. This finding is aligned with compartment-wise profiles of COD removal, which was the highest in the initial compartments and which decreased longitudinally down the reactor. Monitoring the pH profile elucidated that the largest drop in pH was observed in the first two compartments, which is attributed to acidogenesis and acetogenesis activities. The proposed integration could decrease the startup process time to 12 d or less for low-strength feed of synthetic wastewater. This study demonstrated the significance of maintaining a stable pH for the optimal functioning of a diverse bacterial community by integrating bioelectrochemical processing in anaerobic digestion, as well as the application of the potential strategies to optimize the startup process of ABR. The optimization of the startup process of ABR through the integration of bioelectrochemical processing can contribute to Sustainable Development Goal 9 (Industry, Innovation, and Infrastructure) by promoting sustainable technological advancements and fostering sustainable industrialization.

Sludge floc characteristics and microbial community in high-rate activated sludge and high-rate membrane bioreactor for organic recovery

High-rate activated sludge (HRAS) and high-rate membrane bioreactor (HRMBR) are considered as potential processes for organic recovery through bioflocculation and biosorption of particulate COD and colloidal COD with sludge flocs. In this study, bioflocculation and biosorption, in terms of sludge floc characteristics and microbial community, in HRAS and HRMBR was investigated in relation to organic recovery performance for low strength wastewater treatment. HRAS and HRMBR were operated at two different solids retention times (SRTs) of 2 and 0.8 days. Reducing the SRT of HRAS from 2.0 to 0.8 days resulted in failure in total COD (tCOD) removal efficiency (from 79 ± 2 to 34 ± 13 %) and lowering organic recovery (from 40.8 to 15.7 %). This contrasted with HRMBR, which showed high tCOD removal efficiency (84 ± 2 and 84 ± 1 %) and organic recovery (43.4 and 46.3 %) at both SRTs of 2.0 and 0.8 days. Analysis of sludge floc characteristics showed that the lower organic recovery of the HRAS operated at an SRT of 0.8 days could be associated with poor bioflocculation and biosorption, as evidenced by relatively larger floc size, higher extracellular polymeric substance, higher protein/polysaccharide ratio, and higher zeta potential value of the sludge. These characteristics were in contrast to the HRMBR operated at an SRT of 0.8 days, that exhibited the highest organic recovery among the reactors studied. The microbial taxa Bdellovibrio, Clostridium sensu stricto 9, Hyphomicrobium, and Ideonella could play a role in the poor bioflocculation and biosorption in HRAS. Rhodanobacter, Enterobacter, Terrimonas, Nakamurella, and Mizugakiibacter may be associated with bioflocculation and biosorption and organic recovery in HRMBR. The results of this study enhanced our understanding on the relationships between the microbial community, sludge floc characteristics, and organic recovery performance of HRAS and HRMBR for future optimization of the systems.

Toward Integrating EBPR and the Short-Cut Nitrogen Removal Process in a One-Stage System for Treating High-Strength Wastewater.

Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal. Excellent EBPR performance of effluent 0.8 ± 1.0 mg P/L and >99% removal efficiency was achieved fed with synthetic high-strength phosphorus wastewater. Long-term sludge acclimation proved that the dominant polyphosphate accumulating organisms (PAOs), Candidatus Accumulibacter, could evolve to a specific subtype that can tolerate the nitrite inhibition as revealed by operational taxonomic unit (OTU)-based oligotyping analysis. The EBPR kinetic and stoichiometric evaluations combined with the amplicon sequencing proved that the Candidatus Competibacter, as the dominant glycogen accumulating organisms (GAOs), could well coexist with PAOs (15.3-24.9% and 14.2-33.1%, respectively) and did not deteriorate the EBPR performance. The nitrification activity assessment, amplicon sequencing, and functional-based gene marker quantification verified that the unexpected nitrite accumulation (10.7-21.0 mg N/L) in the high-strength EBPR system was likely caused by the nitritation process, in which the nitrite-oxidizing bacteria (NOB) were successfully out-selected (<0.1% relative abundance). We hypothesized that the introduction of the anaerobic phase with high VFA concentrations could be the potential selection force for achieving nitritation based on the literature review and our preliminary batch tests. This study sheds light on developing a new feasible technical route for integrating EBPR with short-cut nitrogen removal for efficient high-strength wastewater treatment.

Towards a better understanding of the anaerobic/oxic/anoxic-aerobic granular sludge process (AOA-AGS) for simultaneous low-strength wastewater treatment and in situ sludge reduction from ambient to winter temperatures

The new anaerobic/oxic/anoxic-aerobic granular sludge (AOA-AGS) merits the advantages of effective carbon utilization and low-carbon treatment. However, low temperature poses stressing concerns and the resisting mechanism remains much unknown. Herein, an AOA-AGS process was configured for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) with low-strength wastewater from ambient (>15 °C) to winter temperatures (<15 °C). Results showed that simultaneously advanced nutrients removal, and dramatic in situ sludge reduction (Yobs of 0.093 g MLSS/g COD) were gained regardless of seasonally decreasing temperatures. Winter temperatures even amplified Candidatus Competibacter predominating from 20.11% to 34.74%, which laid the core basis for endogenous denitrification, sludge minimization and temperature resistance. A removal model was thus proposed given the observed functional groups, and doubts were also raised for future investigations. This study would aid a better understanding on the microbial ecology and engineering aspects of the new AOA-AGS process treating low-strength wastewater at low temperatures.

Advanced low-strength wastewater treatment, side-stream phosphorus recovery, and in situ sludge reduction with aerobic granular sludge

Modern paradigm has upgraded wastewater treatment plants (WWTPs) to water resources recovery facilities (WRRFs), where aerobic granular sludge (AGS) is a sewage treatment technology with promising phosphorus recovery (PR) potential. Herein, the AGS-based simultaneous nitrification, denitrification, and phosphorus removal coupling side-stream PR process (AGS-SNDPRr) was developed with municipal wastewater. Results revealed that AGS always maintained good structural stability, and pollutant removal was unaffected and effective after 40 days of anaerobic phosphorus-rich liquid extraction (fixed rate of 30%). The AGS-SNDPRr achieved a stable phosphorus recovery efficiency of 63.40%, and the side-stream PR further exaggerated in situ sludge reduction by 7.7–10%. Apart from responses of extracellular polymeric substances (EPS), the Matthew effect of typical denitrifying glycogen accumulating organisms (DGAOs) Candidatus_Competibacter up to 67.40% mainly contributed to enhanced performance of this new process. This study demonstrated a new approach for simultaneous advanced wastewater treatment, phosphorus recovery, and excess sludge minimization.

A novel enhanced bio-ecological combined reactor for rural wastewater treatment: Operational performance and microbial communities

Due to the low efficiency and high energy consumption of conventional rural wastewater bio-ecological processes, a novel multi-compartment enhanced hydrolysis-composite media ecological filter bed combined reactor (EH-CMEFB) was constructed. The combined reactor's start-up, operational performance, and microbial communities were studied for low-strength rural wastewater treatment. The results showed that EH-CMEFB could achieve synchronous start-up quickly, with the average removal efficiencies of chemical oxygen demand (COD) and total phosphorus (TP) reaching 87.20 % and 87.98 %, respectively, during the stable period. The multi-compartment partition hydrolysis of the enhanced hydrolysis unit (EH) increased the hydrolysis of tryptophan-like protein and soluble microbial products (SMPs), thereby improving the biodegradability of wastewater. The synergistic effect of Acorus calamus root and filling materials on pollutant absorption, adsorption, and precipitation in the composite media ecological filter bed (CMEFB) achieved the main removal of pollutants. High-throughput sequencing technology assessments indicated that the population and relative abundance of dominant functional bacteria in the different compartments of EH were different, and the partitioning hydrolysis function enhanced the hydrolysis of different types of pollutants in different compartments. This novel combined reactor has a competitive advantage in rural wastewater treatment owing to its economic benefits.

Responses of straw foam-based aerobic granular sludge to atrazine: Insights from metagenomics and microbial community variations

Atrazine (ATZ) has caused serious environmental pollution, but the biodegradation of ATZ is relatively slow and inefficient. Herein, a straw foam-based aerobic granular sludge (SF-AGS) was developed, the spatially ordered architectures of which could greatly improve the drug tolerance and biodegradation efficiency of ATZ. The results showed that, in the presence of ATZ, chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total phosphorus (TP), and total nitrogen (TN) were effectively removed within 6 h, and the removal efficiencies were as high as 93.37%, 85.33%, 84.7%, and 70%, respectively. Furthermore, ATZ stimulated microbial consortia to secrete three times more extracellular polymers compared to without ATZ. Illumina MiSeq sequencing results showed that bacterial diversity and richness decreased, leading to significant changes in microbial population structure and composition. ATZ-resistant bacteria including Proteobacteria, Actinobacteria, and Burkholderia laid the biological basis for the stability of aerobic particles, efficient removal of pollutants, and degradation of ATZ. The study demonstrated that SF-AGS is feasible for ATZ-laden low-strength wastewater treatment.

Aerobic granular sludge development using diatomite for low-strength wastewater treatment

This paper presents an assessment of the start-up performance of aerobic granular sludge (AGS) for the treatment of low-strength (chemical oxygen demand, COD < 200mg/L) domestic wastewater by the application of a diatomite carrier. The feasibility was evaluated in terms of the start-up period and stability of the aerobic granules as well as COD and phosphate removal efficiencies. A single pilot-scale sequencing batch reactor (SBR) was used and operated separately for the control granulation and granulation with diatomite. Complete granulation (granulation rate ≥ 90%) was achieved within 20days for the case of diatomite with an average influent COD concentration of 184mg/L. In comparison, control granulation required 85days to accomplish the same feat with a higher average influent COD concentration (253mg/L). The presence of diatomite solidifies the core of the granules and enhances physical stability. AGS with diatomite recorded the strength and sludge volume index of 18 IC and 53mL/g suspended solids (SS) which is superior to control AGS without diatomite (19.3 IC, 81mL/g SS). Quick start-up and achievement of stable granules lead to an efficient COD (89%) and phosphate removal (74%) in 50days of bioreactor operation. Interestingly, this study revealed that diatomite has some special mechanism in enhancing the removal of both COD and phosphate. Also, diatomite has a significant influence on microbial diversity. The result of this research implies that the advanced development of granular sludge by using diatomite can provide promising low-strength wastewater treatment.