Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor

Bed expansion behavior and sensitivity analysis for super-high-rate anaerobic bioreactor （SAB） were performed based on bed expansion ratio （E）, maximum bed sludge content （Vpmax）, and maximum bed contact time between sludge and liquid （Tmax）. Bed expansion behavior models were established under bed unfluidization, fluidization, and transportation states. Under unfluidization state, Ewas 0, Vprnax was 4867 ml, and rmax was 844-3800 s. Under fluidization state, E, Vpmax, and Tmax were 5.28%-255.69%, 1368-4559 ml, and 104-732 s, respectively. Under transportation state, washout of granular sludge occurred and destabilized the SAB. During stable running of SAB under fluidization state, E correlated positively with superficial gas and liquid velocities （Ug and ul）, while Vpmax and Tmax correlated negatively. For E and Vpmax, the sensitivities of ug and ul were close to each other, while for Tmax, the sensitivity of ur was greater than that of Ug. The prediction from these models was a close match to the experimental data.

Achieving simultaneous removal of carbon and nitrogen by an integrated process of anaerobic membrane bioreactor and flow-through biofilm reactor

In this study,a combined system consisting of an anaerobic membrane bioreactor(AnMBR)and flow-through biofilm reactor/CANON(FTBR/CANON)was developed to simultaneously remove carbon and nitrogen from synthetic livestock wastewater.The average removal efficiencies of total nitrogen(TN)were 64.2 and 76.4%with influent ammonium(NH4+-N)concentrations of approximately 200 and 500 mg/L,respectively.The COD removal efficiencies were higher than 98.0%during the entire operation.Mass balance analysis showed that COD and TN were mainly removed by the AnMBR and FTBR/CANON,respectively.The anammox process was the main nitrogen removal pathway in the combined system,with a contribution of over 80%.High functional bacterial activity was observed in the combined system.Particularly,an increase in the NH4+-N concentration considerably improved the anammox activity of the biofilm in the FTBR/CANON.16S rRNA high-throughput sequencing revealed that Methanosaeta,Candidatus Methanofastidiosum,and Methanobacterium were the dominant methanogens in the AnMBR granular sludge.In the CANON biofilm,Nitrosomonas and Candidatus Kuenenia were identified as aerobic and anaerobic ammonium-oxidizing bacteria,respectively.In summary,this study proposes a combined AnMBR and FTBR/CANON process targeting COD and nitrogen removal,and provides a potential alternative for treating high-strength wastewater.

Methanation and chemolitrophic nitrogen removal by an anaerobic membrane bioreactor coupled partial nitrification and Anammox

An AnMBR-PN/A system was developed for mainstream sewage treatment.To verify the efficient methanation and subsequent chemolitrophic nitrogen removal,a long-term experiment and analysis of microbial activity were carried out.AnMBR performance was less affected by the change of hydraulic retention time(HRT),which could provide a stable influent for subsequent PN/A units.The COD removal efficiency of AnMBR was>93%during the experiment,85.5%of COD could be recovered in form of CH4.With the HRT of PN/A being shortened from 10 to 6 h,nitrogen removal efficiency(NRE)of PN/A increased from 60.5%to 80.4%,but decreased to 68.8%when the HRTPN/A further decreased to 4 h.Microbial analysis revealed that the highest specific ammonia oxidation activity(SAOA)and the ratio of SAOA to specific nitrate oxidation activity(SNOA)provide stable NO_(2)^(−)-N/NH_(4)^(+)-N for anammox,and anammox bacteria(mainly identified as Candidatus Brocadia)enriched at the bottom of Anammox-UASB might play an important role in nitrogen removal.In addition,the decrease of COD in Anammox-UASB indicated partial denitrification occurred,which jointly promoted nitrogen removal with anammox.

Degradation and mineralization of 2-chlorophenol in a single-stage anaerobic fixed-bed bioreactor

Chlorophenols(CPs) have drawn great attention due to their high toxicity and ubiquitous presence in the environment. However,the practical application of anaerobic biodegradation to remove CPs is limited by low degradation rate and incomplete mineralization. This work aims to apply a single-stage anaerobic fixed-bed bioreactor(An FBR) for complete anaerobic dechlorination and mineralization of CPs. Results showed that 2-CP removal efficiency of 99.4%, chemical oxygen demand(COD)removal efficiency of 93.0%, and methane yield of 0.22 L-CH4/g-COD could be obtained for a wide range of 2-CP loading rates(3.6–18.2 mmol L–1 d–1). Nearly complete anaerobic mineralization of 2-CP was achieved even in the absence of co-substrates,thereby greatly reducing the operation cost. This may be partly related to the attached-growth microorganisms in An FBR,allowing a higher biomass concentration and longer biomass retention time for enhanced 2-CP removal. Moreover, 16 S r RNA gene sequence analysis suggests that the An FBR harbored the potential dechlorinators(e.g., Anaeromyxobacter), phenoldegrading microbes(e.g., Comamonas and Syntrophobacter), and methanogens(e.g., Methanobacterium and Methanosaeta)after acclimation, which could cooperate effectively for 2-CP dechlorination and mineralization. Based on the identified intermediates, the possible mineralization pathway of 2-CP was proposed. These findings should be valuable to facilitate the engineering applications of An FBRs for removing CPs from wastewater.

Microbial characteristics in anaerobic membrane bioreactor treating domestic sewage:Effects of HRT and process performance

Two anaerobic membrane bioreactors(AnMBRs)equipped with different membrane pore size(0.4 or 0.05μm)were operated at 25℃and fed with domestic wastewater.The hydraulic retention time(HRT)of the reactors was shortened.The microbial communities of the two AnMBRs were investigated by 16S rRNA gene amplicon sequencing to see the effects of HRT.The predominant Archaea was an aceticlastic methanogen Methanosaeta.The composition of hydrogenotrophic methanogens changed with the HRTs:the population of Methanobacterium was higher for longer HRTs,whereas the population of unclassified Methanoregulaceae was higher for shorter HRTs.The Anaerolineae,Bacteroidia and Clostridia bacteria were dominant in both of the reactors,with a combined relative abundance of over 55%.The relative abundance of Anaerolineae was proportional to the biogas production performance.The change in the population of hydrogenotrophic methanogens or Anaerolineae can be used as an indicator for process monitoring.The sum of the relative abundance of Anaerolineae and Clostridia fluctuated slightly with changes in the HRT in both AnMBRs when the reactor was stably operated.The co-occurrence analysis revealed the relative abundance of the operational taxonomic units belonging to Anaerolineae and Clostridia was functionally equivalent during the treatment of real domestic sewage.A principal coordination analysis revealed that the changes in the microbial community in each reactor were consistent with the change of HRT.In addition,both the HRT and the stability of the process are important factors for maintaining microbial community structures.

Membrane fouling control by ultrasound in an anaerobic membrane bioreactor

fouling online in an anaerobic membrane bioreac-tor(AMBR).Short-term running experiments were carried out under different operating conditions to explore feasible ultrasonic parameters.The experimental results indicated that when the crossflow velocity was more than 1.0 m/s,mem-brane fouling could be controlled effectively only by hydro-dynamic methods without ultrasound.When ultrasound was applied,an ultrasonic power range of 60-150 W was suitable for the membrane fouling control in the experimental system.The experimental results showed that the membrane fouling was controlled so well that membrane filtration resistance(ΣR)could stay at 5×10^(11)m^(−1) for more than a week with the crossflow velocity of 0.75 m/s,which equaled the effect of crossflow velocity of more than 1.0 m/s without ultrasound.

A reactor system combining reductive dechlorination with co-metabolic oxidation for complete degradation of tetrachloro-entylene

A laboratory sequential anaerobic aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900 μM (ca. 150 mg/L) of PCE stoichiometrically into cis 1,2 dichloroethylene ( cis DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis DCE by co metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99 % of PCE transformation into cis DCE in the range of influent PCE concentration from 5 μM to 35 μM at hydraulic retention time of 48h. On the other hand, efficient degradation of the resultant cis DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis DCE degradation was obtained when 10 μmol of hydrogen peroxide (H 2O 2) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co metabolic degradation of cis DCE in the aerobic reactor.

Impact of food to microorganism ratio and alcohol ethoxylate dosage on methane production in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor

The effects of food to microorganism （FIM） ratio and alcohol ethoxylate （AE） dosage on the methane production potential were investigated in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor （SAnMBR）. The fate of AE and its acute and/or chronic impact on the anaerobic microbes were also analyzed. The results indicated that AE had an inhibitory effect to methane production potential （lag-time depends on the AE dosage） and the negative effect attenuated subsequently and methane production could recover at FIM ratio of 0.088-0.357. VFA measurement proved that AE was degraded into small molecular organic acids and then converted into methane at lower FIM ratio （FIM 〈 0.158）. After long-term acclimation, anaerobic microbe could cope with the stress of AE by producing more EPS （extracellular polymeric substances） and SMP （soluble microbial products） due to its self-protection behavior and then enhance its tolerance ability. However, the methane production potential was considerably decreased when AE was present in wastewater at a higher FIM ratio of 1.054. Higher AE amount and FIM ratio may destroy the cell structure of microbe, which lead to the decrease of methane production activity of sludge and methane production potential.

An in-situ biochar-enhanced anaerobic membrane bioreactor for swine wastewater treatment under various organic loading rates

A biochar-assisted anaerobic membrane bioreactor(BC-AnMBR)was conducted to evaluate the performance in treating swine wastewater with different organic loading rates(OLR)ranging from 0.38 to 1.13 kg-COD/(m3.d).Results indicated that adding spent coffee grounds biochar(SCG-BC)improved the organic removal efficiency compared to the conventional AnMBR,with an overall COD removal rate of>95.01%.Meanwhile,methane production of up to 0.22 LCH4/gCOD with an improvement of 45.45%was achieved under a high OLR of 1.13 kg-COD/(m3.d).Furthermore,the transmembrane pressure(TMP)in the BC-AnMBR system was stable at 4.5 kPa,and no irreversible membrane fouling occurred within 125 days.Microbial community analysis revealed that the addition of SCG-BC increased the relative abundance of autotrophic methanogenic archaea,particularly Methanosarcina(from 0.11%to 11.16%)and Methanothrix(from 16.34%to 24.05%).More importantly,Desulfobacterota and Firmicutes phylum with direct interspecific electron transfer(DIET)capabilities were also enriched with autotrophic methanogens.Analysis of the electron transfer pathway showed that the concentration of c-type cytochromes increased by 38.60%in the presence of SCGBC,and thus facilitated the establishment of DIET and maintained high activity of the elec-tron transfer system even at high OLR.In short,the BC-AnMBR system performs well under various OLR conditions and is stable in the recovery energy system for swine wastewater.

Concept and application of anaerobic suspended granular sludge bed （SGSB） reactor for wastewater treatment

Bed expansion serves an important function in the design and operation of an upflow anaerobic reactor. An analysis of the flow pattern of expanded granular sludge bed （EGSB） reactors shows that most EGSB reactors do not behave as expanded bed reactors, as is widely perceived. Rather, these reactors behave as fluidized bed reactors based on the classic chemical reactor theory. In this paper, four bed expansion modes, divided as static bed, expanded bed, suspended bed, and fluidized bed, for bioreactors are proposed. A high-rate anaerobic suspended granular sludge bed （SGSB） reactor was then developed. The SGSB reactor is an upflow anaerobic reactor, and its expansion degree can be easily controlled within a range to maintain the suspended status of the sludge bed by controlling upfiow velocity. The results of the full-scale reactor confirmed that the use of SGSB reactors is advantageous. The full-scale SGSB reactor runs stably and achieves high COD removal efficiency （about 90%） at high loading rates （average 40 kg-COD·m^-3·d^-1, maximum to 52 kg·COD·m^-3 ·d^-1） based on the SGSB theory, and its expansion degree is between 22% and 37%.