•A concept of AnMBR-PN/A process was proposed for mainstream treatment.•In-situ FA/FNA exposure eliminated Nitrospira while retained Nitosonomas community.••DO limitation prevented switch of the NOB ...community in the mainstream conditions.•The effluent TN of the mainstream PN/A system was lower than 10 mg-N/L.•Enhanced hydrodynamic shear force resulted in sludge settleability deterioration.
In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.
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•A 1670-L mainstream IFAS type PN/A at decreasing temperatures of 25, 20 and 15°C.•The NLR was 0.21–0.24 kg-N/m3/d and the NRE was 65.9–75.4%.•Insufficient treatment capacity of AOB results in ...reduction of nitrogen removal at 15°C.•Candidatus Brocadia and Candidatus Kuenenia were main AnAOB and almost enriched on carriers.•NOB was suppressed by the strategy of intermittent aeration and low DO.
Partial nitritation-anammox (PN/A) is a promising deammonification process to develop energy-neutral wastewater treatment plants. However, the mainstream application of PN/A still faces the challenges of low nitrogen concentration and low temperatures, and has not been studied under a realistic condition of large-scale reactor (kiloliter level), real municipal wastewater (MWW) and seasonal temperatures. In this research, a pilot-scale one-stage PN/A, with integrated fixed-film activated sludge (IFAS) configuration, was operated to treat the real MWW pretreated by anaerobic membrane bioreactor. The removal efficiency of total nitrogen (TN) was 79.4%, 75.7% and 65.9% at 25, 20 and 15°C, corresponding to the effluent TN of 7.3, 9.7 and 12.0 mg/L, respectively. The suppression of ammonium-oxidizing bacteria (AOB) and anammox bacteria (AnAOB) occurred at lower temperatures, and the significant decrease in AOB treatment capacity was the reason for the poorer nitrogen removal at 15°C. Biomass retention and microbial segregation were successfully achieved. Specifically, Candidatus_Brocadia and Candidatus_Kuenenia were main AnAOB genera and mainly enriched on carriers, Nitrosomonas and uncultured f_Chitinophagaceae were main AOB genera and mainly distributed in suspended sludge and retained by sedimentation tank. Moreover, nitrite-oxidizing bacteria (NOB) were sufficiently suppressed by intermittent aeration and low dissolved oxygen, the presence of heterotrophic bacteria upgraded the PN/A to a simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) system, which improved the overall removal of TN and COD. The results of this investigation clearly evidence the strong feasibility of PN/A as a mainstream nitrogen removal process in temperate climates.
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•Mass flows of C and N were redesigned by AnMBR-PN/A.•Removal efficiencies of COD and TN were 90.3%-95.1% and 75.0%-81.7%, respectively.•48.4%-63.1% of C was captured as CH4 and ...26.7%-39.7% of C was captured as sludge.•8.5%-16.1% of N was entrapped by membrane and 45.3%-58.1% of N was removed by PN/A.•AnMBR and PN/A mutually complement each other ensured excellent system performance.
A pilot-scale anaerobic membrane bioreactor (AnMBR) integrated with a one-stage partial nitritation-anammox (PN/A) reactor was operated for the treatment of municipal wastewater (MWW) at seasonal temperatures of 15–25 °C. The removal efficiencies of COD and total nitrogen (TN) were always > 90% and > 75% respectively. The methanogenesis and PN/A were identified as the primary removal pathways of COD and TN, respectively, and were suppressed at low temperatures. With the temperature dropped from 25 °C to 20 °C to 15 °C, the methane-accounted COD decreased from 63.1% to 59.6% to 48.4%, and the PN/A-accounted TN decreased from 58.1% to 51.7% to 45.3%. The AnMBR and PN/A mutually complement each other in this combined process, as the AnMBR removed 8.5%-16.1% of TN by sludge entrainment and the PN/A reactor removed 2.6%-3.4% of COD by denitrification and aerobic oxidation. These results highlighted the strong feasibility of applying the AnMBR-PN/A process to the treatment of MWW in temperate climate.
•5 m3 large-scale AnMBR realized effluent COD < 50 mg L-1 and BOD5 < 10 mg L-1.•COD and BOD5 removal over 90% with biogas recovered by 0.25–0.27 L g−1 removed COD.•An auto-control grille system ...facilitated AnMBR by removing large-size impurities.•60%-64% of influent COD converted to methane and 20%-26% of that converted to MLSS.•Hollow fiber membrane realized an average flux of 0.35 m d-1 at a △TMP of 23.5 kPa.
The aim of this work was to demonstrate the operation of a large pilot-scale submerged anaerobic membrane bioreactor (5.0 m3) for biogas production from municipal wastewater at ambient temperature of 25 °C. To the best of our knowledge, this is the largest one-stage submerged AnMBR that has ever been reported. This AnMBR realized a hydraulic retention time (HRT) of 6 h and a treatment capacity of 20 m3 d-1, obtaining excellent effluent quality with COD removal efficiency over 90% and BOD5 removal over 95%. The biogas yield of the AnMBR was 0.25–0.27 L g−1 removed COD and 0.09–0.10 L L-1 raw wastewater. The methane content of the biogas was at the range of 75%-81%. The COD and nitrogen mass balance were also identified based on long-term operation. The hollow-fiber membrane module realized a flux of 2.75–17.83 LMH. An online backwash chemical cleaning system helped to lower the transmembrane pressure timely.
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•A 5,000 L pilot-scale SAnMBR successfully treated municipal wastewater under seasonal temperatures.•COD removal efficiency was 84.5%-90.7% and effluent COD was < 50 mg/L.•Total ...methane yield was 0.205–0.244 NL/gCOD and 29%-43% of the methane was dissolved.•Microbial products and residual inorganics led to the membrane fouling at low temperature.•The appropriate operating temperature of AnMBR should be ≥ 15 °C.
A 5,000-L anaerobic membrane bioreactor (AnMBR) fed with actual municipal wastewater was employed to study the impact of temperature drops on methanogenic performance and membrane fouling. With temperature dropped from 25 °C to 15 °C, the methane yield decreased from 0.244 to 0.205 NL-CH4/g-CODremoval and the dissolved methane increased from 29% to 43%, resulted in the methanogenic performance reduced by 25%. The membrane rejection offset the deteriorated anaerobic digestion at low temperatures and ensured the stable COD removal efficiency of 84.5%-90.0%. The synergistic effects of the increased microbial products and viscosity and the residual inorganic foulants aggravated the membrane fouling at lower temperatures. As the organic fouling was easily removed by NaClO, the inorganics related to the elements of S, Ca and Fe were the stubborn membrane foulants and required the enhanced acid membrane cleaning. These findings obtained under the quasi-practical condition are expected to promote the practical applications of mainstream AnMBR.
Sludge yield and suspended solid are important factors concerned in the anaerobic treatment of municipal wastewater. In this study, a large pilot-scale anaerobic membrane bioreactor (AnMBR) was ...constructed for effectively treating real municipal wastewater at an ambient temperature of 25 °C. The sludge yield and the degradation of influent suspended solids were evaluated during the long-term operation of the AnMBR. This reactor with 5.0 m3 effective volume is the largest one-stage submerged AnMBR that has ever been used to treat municipal wastewater. During the long-term operation of 217 days, this AnMBR obtained excellent COD and BOD5 removal efficiency over 90%. Stable biogas production was also successfully obtained from treating municipal wastewater. The sludge yield of the AnMBR was approximately 0.19–0.26 g MLSS g−1 COD removed for the treatment of real municipal wastewater. The shortest SRT of the AnMBR was calculated as 29 days for an HRT of 6 h at an empirical MLSS of 10 g L−1. While the influent suspended solid (SS) contained in the municipal wastewater was completely removed by the AnMBR, only 57%–66% of the influent SS was degraded. The rest of influent SS was directly converted to MLSS instead of being degraded. The AnMBR maintained a stable membrane filtration using a hollow-fiber membrane with a total area of 72 m2, realizing a flux of 2.75–17.83 LMH, and the mean transmembrane pressure (TMP) was 0.9–23.5 kPa. An online chemical backwash cleaning system helped to lower the TMP timely using sodium hypochlorite and citric acid when the TMP increased rapidly and reached the rated limit of membrane. This is the first report on demonstrating the successful operation and detailed performance of a large pilot-scale AnMBR applied to the treatment of real municipal wastewater.
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•A large pilot-scale AnMBR with 5 m3 was applied for municipal wastewater at 25 °C.•Stable effluent quality and biogas yield are obtained during long-term operation.•By removing 1 g of COD approximately 0.19–0.26 g MLSS g−1 of sludge was yielded.•Influent SS was 100% removed while only 34%–43% of the SS was degraded by sludge.•The shortest SRT was calculated as 29 days at the HRT of 6 h with MLSS of 10 g L−1.
•A pilot-scale SAnMBR-PN/A plant was successfully applied for real municipal wastewater treatment.•The overall COD and total nitrogen removal efficiencies were 95.1% and 81.7%, respectively.•The ...biogas yield rate was 0.09 NL L−1 of treated wastewater with a methane content of 80%.•Denitrification occurred in PN/A unit, enhancing overall COD and nitrogen removal.
A novel municipal wastewater treatment process towards energy neutrality and reduced carbon emissions was established by combining a submerged anaerobic membrane bioreactor (SAnMBR) with a one-stage partial nitritation-anammox (PN/A), and was demonstrated at pilot-scale at 25 °C. The overall COD and BOD5 removal efficiencies were 95.1% and 96.4%, respectively, with 20.3 mg L−1 COD and 5.2 mg L−1 BOD5 remaining in the final effluent. The total nitrogen (TN) removal efficiency was 81.7%, resulting 7.3 mg L−1 TN was discharged from the system. The biogas yield was 0.222 NL g−1 COD removed with a methane content range of 78–81%. Approximately 90% of influent COD was removed in the SAnMBR, and 70% of influent nitrogen was removed in the PN/A. The denitrification which occurred in the PN/A enhanced overall COD and nitrogen removal. The successful operation of this pilot-scale plant indicates the SAnMBR-PN/A process is suitable for treating real municipal wastewater.
Recently, it was reported that for synthetic low-strength wastewater, the excellent nitrogen removal rate (NRR) accompanied with phosphorus removal could be achieved through the partial ...nitritation/anammox (PNA)-hydroxyapatite (HAP) process. Thus, this research further investigated the performance of the pilot-scale PNA-HAP process treating the effluent of an anaerobic membrane bioreactor (AnMBR) fed with the actual municipal wastewater. The results showed that with the hydraulic retention time of 4.0 h, the influent ammonium concentration ranging from 36.0 to 41.0 mg/L, and the BOD5 ranging from 6.3 to 12.7 mg/L, the average NRR and the nitrogen removal efficiency was 0.13 kg/m3/d and 63.38%, respectively. The specific activity test of sludge confirmed that the PNA process was the main nitrogen metabolism pathway. The effluent nitrate and the BOD5 were almost zero, indicating the existence of denitrification activity in reactor. Given that the oxygenation condition, the heterotrophic organic matter oxidization activity also occurred in reactor. The sludge analysis confirmed the phosphate formation in sludge. Thus, in the reactor, four kinds of biological activities and chemical crystallization occurred harmoniously in sludge. From the mixed liquid volatile suspended solid of 2.4 g/L and the low distribution range of granule size, it was obvious that the sludge had a high dispersity. Based on the well settling ability of sludge during the operation, it was inferred that there was a close bond between biomass and HAP in sludge, which was helpful to enhance the settleability of sludge granule. Besides, the phosphorus-containing sludge was suitable as the fertilizer. In all, this study demonstrated that the PNA-HAP process is an ideal alternative treating the effluent of the AnMBR process in the municipal wastewater treatment.
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•One-stage pilot-scale PNA-HAP process was firstly adopted to treat effluent of AnMBR.•The NRR was 0.13 kg/m3/d with NRE of 63.4%, and few nitrate and BOD5 in effluent.•Four kinds of biological activities and chemical crystallization occurred.•The discharged sludge with high P content was suitable for use as fertilizer.
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•The performance of partial nitritation/anammox process of 15 °C was investigated.•Anammox activity suggested to be the main limitation for the nitrogen removal.•Denitratation process ...occurred with limited influent organic matter condition.•The main functional bacteria were from genus Nitrosomonas and genus Kuenenia.•PNA, denitratation, and the COD oxidization simultaneously occurred.
At ambient temperature condition, the one-stage partial nitritation/anammox (PNA) process has been successfully adopted to treat the filtrate from the mainstream anaerobic membrane bioreactor (AnMBR). However, there is no investigation of the performance of this process at low-temperature condition. In this study, the nitrogen removal performance of a pilot-scale PNA reactor at the temperature of 15 °C for treating the filtrate of a mainstream AnMBR was investigated. The nitrogen removal rate of 0.09 kg/m3/d and the nitrogen removal efficiency of 37.6% were achieved. The anammox reaction was the rate-limiting step of the nitrogen removal. Nitrogen removal was attributed in part to denitrification activity. The microbial community analysis confirmed that the main functional bacteria comprised of genus Nitrosomonas and genus Kuenenia. In sum, this research demonstrated the applicability of PNA process for mainstream AnMBR filtrate treatment to some extent and enriched the related knowledge.
Based on a possibility of the phase separation of methane fermentation connected the two fermenters in series which had different hydraulic retention times, the experiment of the two-phase methane ...fermentation was performed with the substrate of the mixture of swine feces, and swine feces and urine. As the results, it became possible to charge higher loadings of organic matter than that of the former conventional methane fermentation, and digested gas production rate was maintained high as the digested gas yield was increased by 20-30%. It was found that the loading of organic matter (Lvs) of 7.5kg-vs/m3/d was the optimum for the purpose of recovering the energy, and the Lvs of 5.0kg-vs/m3/d was optimum operation condition in case of considering for the quality of digested liquid, such as the ratio of volatile solid removal, volatile acid removal, and NH4+. In addition, each methane gas production rate is 1.596, 1, 447Nm3-CH4/m3/d, respectively.
