| Swine wastewater,a high concentration organic wastewater with sulfonamide antibiotics(SMs)and heavy metals,can cause serious harm to ecological environment and human health.The anaerobic process with high volumetric load,low operational energy consumption and energy(methane)recovery is the core unit of swine wastewater treatment.However,the conventional anaerobic process suffers from slow growth of anaerobic microorganisms and sludge loss problem.Using microfiltration(MF)/ultrafiltration(UF)membrane for effective solid-liquid separation,the washout of slow-growth anaerobic microbes,one major problem endangering system performance,can be minimized.However,the widespread adoption of anaerobic membrane bioreactor(AnMBR)is greatly limited by its high operation and maintenance costs,owing to severe membrane fouling.Anaerobic dynamic membrane bioreactor(AnDMBR),where in MF/UF membranes are replaced by inexpensive coarse-pore filtration materials,has emerged as a modified AnMBR.Dynamic membrane(DM),the sludge deposited on the coarse pore filtration material during filtration,can achieve similar solid-liquid separation efficiencies as those of MF/UF membranes.AnDMBR has excellent economic applicability,due to the low price of coarse-pore filtration material and the low filtration resistance of DM.Its excellent process performance has been verified in various wastewater treatment studies,but not reported in the field of swine wastewater treatment.In view of the technical advantages and promising application potential of AnDMBR,its use for swine wastewater treatment has great scientific value and practical significance.The main working mechanisms of AnDMBR are biodegradation and DM retention.Therefore,the key for better AnDMBR performance is to improve the sludge properties and enhance the DM filtration performance.Choosing the appropriate start-up method,regulating HRT parameters and adding activated carbon are the feasible technical measures.AnDMBR was applied for the first time to treat swine wastewater to improve the treatment efficiency and mitigate DM fouling in this study.The treatment efficiency(include COD,NH3-N,TN,TP,SMs,heavy metals,methane production and SMA(specific methanogenic activity))and filtration performance(include turbidity and TMP)variation of AnDMBR were examined.The AnDMBR process performance was analyzed for the effects of different start-up methods,HRT parameters and activated carbon.Meanwhile,the fate of SMs and heavy metals in AnDMBR was analyzed to clarify the distribution pattern and removal mechanism.To reveal the intrinsic mechanisms affecting the biodegradation performance and the fouling process of DM under different conditions.The microbial communities structure(a-diversity index,PCA(principal component analysis),relative abundance of bacterial population)and physicochemical properties(porosity,particle size distribution,apparent morphology,inorganic elements and organic fractions,Zeta potential,RH,etc.)of suspended sludge and DM under different conditions were investigated.The response relationship between mechanism and process performance was established to provide technical support for the engineering application of AnDMBR to swine wastewater treatment.The main research results are as follows:(1)Variations in COD and HRT have different effects on sludge properties in various start-up schemes,affecting the treatment efficiency and filtration characteristics of AnDMBR with significant differences in start-up time and DM fouling.The start-up of AnDMBR is essentially process of sludge domestication by gradually increasing OLR by adjusting COD and HRT.The effect of three schemes on the start-up process of AnDMBR was investigated in this study.The three start-up schemes were as follows:R1:domesticating municipal sludge with high concentration of swine breeding wastewater to increase OLR by shortening HRT;R2:keeping the HRT constant and gradually increasing the influent COD concentration;R3:alternating between increasing COD concentration and shortening HRT.The results showed that start-up time of AnDMBR was directly related to the influent concentration.R1 had the highest influent concentration and the longest start-up time(53 d),followed by R3(43 d)and R2 had the shortest start-up time(37 d).The magnitude of variation of COD and OLR in AnDMBR directly affects the adaptation of anaerobic microorganisms.It determines the removal rate of pollutants such as COD,SMs,and heavy metals by AnDMBR.R3 had the highest removal rate of pollutants,because the OLR at each stage is elevated the least and the anaerobic microorganisms adapt the best.While R1 had the lowest pollutant removal rates because the initial influent COD,heavy metals,and antibiotic concentrations were highest above the microbial tolerance.The pollutant removal rate of R2 was in between R1 and R3.In terms of DM fouling,R2 had the shortest stable operation time(48 d).Because the initial membrane flux(4.0 L/m2·h)was higher and constant than R1 and R3,the deposition rate of suspended sludge to DM was higher than R1 and R3,accelerating the membrane fouling process.While R1 had the longest stable operation time(67 d)because the initial membrane flux was the lowest(0.8 L/m2·h)elevated slowly.R3 had a higher initial membrane flux(2.3 L/m2·h)than R1 but lower than R2,so its stable run time was in between R1 and R2.The convergence of SMs and heavy metal behaviors showed that biodegradation was the main mechanism for the removal of SMs,with some contribution from EPS adsorption.The adsorption contribution of activated sludge for heavy metals Cu2+ and Zn2+was much higher than that of EPS and SMP.(2)A decrease in HRT leads to the reduction of the species and number of bacteria that degrade organic matter,which reduces the pollutant removal efficiency.HRT shortening also leads to denser DM structure and increased membrane fouling.HRT,an important parameter,affects the performance of AnDMBR process for swine wastewater treatment under the condition of constant COD concentration in influent and infinite SRT length.HRT shortening can improve the efficiency of AnDMBR process,but a shorter HRT can reduce the pollutant removal rate and increase the DM fouling.Therefore,it is important to explore the optimal HRT parameters while ensuring the performance of the AnDMBR process.The effect of different HRT(40 h,30 h and 24 h)on the performance of the AnDMBR process for swine wastewater treatment was investigated in this study.The results showed that the removal rate of pollutants such as COD,SMs and methane production did not change when the HRT decreased from 40 h to 30 h.The removal rates of pollutants such as COD,SMs and methane yield decreased significantly at HRT of 24 h.However,the removal rates of heavy metals Cu2+ and In2+ did not change significantly under different HRT conditions.Comparing the bacterial communities structure,it was found that the content of Firmicutes of organic matter degrading and antibiotic degrading Clostridium and Deltaproteobacteria decreased with the HRT shortened.And the organic pollutant(e.g.,COD and SMs)removal rate decreased.Comparison of the archaeal communities structure revealed that the content of archaea involved in various methanogenic pathways decreased with the HRT shortened,such as mixed trophic methanogenic archaea(Methanosarcinia,Methanosarcinae,Methanosarcinae,Methanosarcinae,Methanosarcinae,7th Methanogenic Archaea and Methanobacterium),and acetic acid consuming methanogenic archaea(Methanosarcinae and Methanosarcinae),which were responsible for the decrease in methane production.A decreased in HRT lead to increase of membrane flux,which accelerates the sludge deposition rate and reduces the DM porosity.The increase in membrane fouling and the decrease of the stabilization operation time are attributed to the increase in EPS and metal ions(Ca,Mg,Fe,Al,Cu and Zn)in DM.(3)The addition of activated carbon can enhance the biodegradability and adsorption effect of suspended sludge.It makes the DM sludge cake layer structure more loose and effectively alleviates membrane pollution.Activated carbon has high porosity and large surface area,it can improve sludge properties,enhance dynamic membrane filtration performance and control membrane fouling.This study investigated the effects of powder activated carbon(PAC),granular activated carbon(GAC)and corncob activated carbon(BAC)on the process performance of AnDMBR for swine wastewater treatment.Firstly,the optimal dosages of PAC,GAC and BAC were determined as 4 g/L,1 g/L and 1 g/L based on the results of jar test and dead-end filtration experiment.The pollutant removal efficiency and methane yield of AnDMBR were improved after different types of activated carbon were injected according to the optimal dosage.The COD and SMs removal efficiency and methane production were improved in the following order:P-AnDMBR(with PAC)>B-AnDMBR(with BAC)>G-AnDMBR(with GAC).The heavy metals removal efficiency was in the order of P-AnDMBR>G-AnDMBR>BAnDMBR.Comparing the bacterial communities structure,it was found that the diversity and abundance of bacteria increased after the addition of PAC,GAC and BAC.The phylum Proteobacteria,Firmicutes and Bacteroidetes degrading organic matter and Deltaproteobacteria degrading antibiotics were increased.New bacteria such as Spirochaetota and Verrucomicrobiota,A lphaproteobacteria,Spirochaetia and Campylobacteria were added.Comparing the archaeal communities structure,it was found that the diversity and richness of archaeal microbial communities increased after the addition of PAC,GAC and BAC.Methanosarcinia and Methanosaeta were absolutely dominant in the P-AnDMBR.Methanomicrobia and Methanoregula were absolutely dominant in GAnDMBR.Methanobacteria,Methanosarcina and Methanobacterium were overwhelmingly dominant in B-AnDMBR.The internal reason for the improvement of AnDMBR pollutant removal efficiency and biogas production by adding activated carbon is the change of microbial communities structure.The addition of activated carbon could slow down the membrane fouling process and prolonged the stable operation time,due to decrease of EPS on DM and formed a large pore size,high porosity and compression resistance DM layer.The stable operation time of G-AnDMBR is the longest,because GAC with large particle size and weight has the largest scouring effect on DM and can effectively inhibit the deposition of sludge flocs on DM. |
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