Comparison of recirculation configurations for biological nutrient removal in a membrane bioreactor

A 12-L lab-scale membrane bioreactor (MBR), consisting of an anaerobic and anoxic compartment followed by an oxic plate-frame membrane compartment, was evaluated for carbonaceous and nutrient removals by varying the recirculation of mixed liquor and permeate. The hydraulic retention times (HRTs) for the anaerobic, anoxic, and oxic compartments were 2, 2, and 8h, respectively. The solids residence time (SRT) for the oxic compartment was 25 days. Five different recirculation configurations were tested by recirculating mixed liquor and/or permeate recirculation equal to the influent flow rate (identified as 100%) into different locations of the anaerobic and anoxic compartments. Of the five configurations, the configuration with 100% mixed liquor recirculation to the anaerobic compartment and 100% permeate recirculation to the anoxic compartment gave the highest percentage removal with an average 92.3+/-0.5% soluble chemical oxygen demand (sCOD), 75.6+/-0.4% total nitrogen (TN), and 62.4+/-1.3% total phosphorus (TP) removal. When the mixed liquor and permeate recirculation rates were varied for the same configuration, the highest TP removal was obtained for 300% mixed liquor recirculation and 100% permeate recirculation (300%/100%) with a TP removal of 88.1+/-1.3% while the highest TN removal (90.3+/-0.3%) was obtained for 200%/300% recirculation. TN and TP concentrations as low as 4.2+/-0.1 and 1.4+/-0.2mg/L respectively were obtained. Mass loading rates were generally low in the range of 0.11-0.22kgCOD/kgMLSS/d due to high biomass concentrations within the oxic reactor (approx. 8000mg/L). The BioWin model was calibrated against one set of the experimental data and was found to predict the experimental data of effluent TN, TP, and NO(3)(-)-N but over-predicted sCOD and NH(3)-N for various recirculation rates. The anoxic heterotrophic yield for the calibrated model was 0.2kg biomass COD/kg COD utilized while the maximum growth rates were found to be 0.45day(-1) for mu(max-autotroph), 3.2day(-1) for mu(max-heterotroph), and 1.5day(-1) for mu(max-PAO).     

Effect of sludge retention time on inclined plate function,treatment performance and sludge characteristics of inclined plate membrane bioreactors treating municipal wastewater

Two identical bench scale inclined plate membrane bioreactors (ip‐MBRs) were operated for the treatment of real municipal wastewater for 1 year. Sludge retention time (SRT) was varied over the course of operation to investigate the effects on inclined plate function, treatment performance and sludge characteristic. Removal rates of chemical oxygen demand and ammonia over 90% and of total nitrogen (TN) more than 70% were achieved when ip‐MBRs were operated under SRTs between infinite and 40 days while short SRT (20 days) negatively affected TN removal. When the sludge concentration in anoxic tank exceeded 15 g/L, the failure of the inclined plate function was observed, resulting in no difference in sludge concentrations between aerobic and anoxic tanks. To avoid severe effects on inclined plate function and treatment performance, an SRT range of 40–80 days was recommended for ip‐MBRs. Moreover, sludge floc size under prolonged SRT became smaller than that under short SRT due to increased attrition among the sludge floc particles caused by strong aeration needed for keeping a sufficient dissolved oxygen level.     

污泥减量工艺:HA-A/A-MCO的好氧脱氮机制分析

针对污泥减量技术存在对氮、磷去除能力低的问题,开发了一种具有强化脱氮除磷功能并可实现污泥减量化的HA-A/A-MCO工艺。在该工艺取得同步脱氮除磷和污泥减量优异效果的条件下,采用其处理校园生活污水,当进水TN平均为47 mg/L时,出水TN为10.9 mg/L,系统的总脱氮率为76.8%,其中好氧脱氮量占总脱氮量的50%,缺氧脱氮量占26%;HA-A/A-MCO系统存在着在好氧条件下具有反硝化能力的菌属,对好氧脱氮有一定贡献,且DO浓度对其反硝化能力没有抑制作用;好氧池中的DO浓度梯度有利于在污泥絮体内形成缺氧环境,从而促进同步硝化反硝化(SND)的发生,但减小污泥絮体尺寸会削弱絮体内部缺氧区域比例、降低SND的脱氮效率。     

多阴极室反硝化除磷产电装置启动运行研究

多阴极室反硝化除磷产电装置中,将微生物燃料电池引入双污泥反硝化除磷工艺,以厌氧池作为微生物燃料电池的阳极室,以好氧池、二沉池、缺氧池和终沉池分别作为微生物燃料电池的阴极室。以模拟生活污水为处理对象,多阴极室反硝化除磷产电装置经过调控以后进入稳定运行状态,在60 d的测定周期中,对COD、NH4+-N和PO34--P的平均去除率分别为69.88%、62.31%和57.13%,最高去除率分别为80.44%、74.16%和64.86%,厌氧和好氧池、厌氧和二沉池、厌氧和缺氧池、厌氧和终沉池作为4组微生物燃料电池产生的电压和电流平均值分别为0.44、0.40、0.09、0.10 V和0.49、0.45、0.10、0.11 m A,最高电压分别达到了0.55、0.51、0.13、0.12 V。多阴极室反硝化除磷产电装置不仅增强了对生活污水中COD、NH4+-N和PO34--P的去除效果,而且提高了产电性能。     

Phosphorus Removal from Sidestreams by Crystallisation of Magnesium-Ammonium-Phosphate Using Seawater

In recent years, a number of biological-treatment processes have been developed for phosphorus removal, alone or in combination with nitrogen. In anaerobic/oxic and anaerobic/anoxic/oxic processes, it is necessary to lower the concentration of phosphorus in the sidestream from the sludge-disposal processes. To do this, the magnesium-ammonium-phosphate system has been developed in which phosphorus is removed in a side-stream process.
Alternative systems require chemicals such as magnesium chloride as the source of magnesium and sodium hydroxide for pH control, and are economically less viable than that described in this paper in which seawater is substituted for the chemicals.
Dissolved phosphorus removal of over 70% was achieved without pH control by feeding the sidestream which contained 50–111 mg/l dissolved phosphorus and had a pH greater than 7.77, together with a 9–10% flow of seawater into the reactor containing 4–13% of magnesium ammonium phosphate and which provided a retention of 29 mins.     

Biodegradation of the endogenous residue of activated sludge

This study evaluated the potential biodegradability of the endogenous residue in activated sludge subjected to batch digestion under either non-aerated or alternating aerated and non-aerated conditions. Mixed liquor for the tests was generated in a 200 L pilot-scale aerobic membrane bioreactor (MBR) operated at a 5.2 days SRT. The MBR system was fed a soluble and completely biodegradable synthetic influent composed of sodium acetate as the sole carbon source. This influent, which contained no influent unbiodegradable organic or inorganic materials, allowed to generate sludge composed of essentially two fractions: a heterotrophic biomass X_H and an endogenous residue X_E, the nitrifying biomass being negligible (less than 2%). The endogenous decay rate and the active biomass fraction of the MBR sludge were determined in 21-day aerobic digestion batch tests by monitoring the VSS and OUR responses. Fractions of X_H and X_E: 68% and 32% were obtained, respectively, at a 5.2 days SRT. To assess the biodegradability of X_E, two batch digestion units operated at 35 °C were run for 90 days using thickened sludge from the MBR system. In the first unit, anaerobic conditions were maintained while in the second unit, alternating aerated and non-aerated conditions were applied. Data for both units showed apparent partial biodegradation of the endogenous residue. Modeling the batch tests indicated endogenous residue decay rates of 0.005 d⁻¹ and 0.012 d⁻¹ for the anaerobic unit and the alternating aerated and non-aerated conditions, respectively.     

Mechanism of phosphorus removal by SBR submerged biofilm system

The mechanism of phosphorus removal in SBR submerged biofilm system was studied in the research. The DNP and nuclear magnetic resonance methods were employed to verify the mechanism of phosphorus removal by bacteria with the phosphorus release in anaerobic phase and uptake in oxic and anoxic phases. The mathematical models of phosphorus releases in anaerobic phase and phosphorus uptake in oxic phase were deduced and evaluated by comparison between the theoretically calculated values and the test data.     

Simulation of closed double‐sludge retention time anoxic‐oxic process in wastewater treatment: case study for a utility model process

The ‘closed double‐sludge retention time anoxic‐oxic (SRT AO) process’ is a utility model designed by the Shanghai Urban Construction Design and Research Institute. It can quantitatively control the nitrification level by adjusting wastewater distribution and mixed sludge return during wastewater treatment, and can thus considerably reduce construction investment and operation costs. However, mixed sludge return from the sedimentation tank may dilute the concentration of nitrobacteria because the heterotrophic bacteria propagate faster. In this paper, the closed double‐SRT AO process was modelled and simulated based on its application at the Zhuyuan Second Wastewater Treatment Plant (WWTP). The distribution ratio was found to have a significant influence on the nitrobacteria's concentration but does not eliminate the existence of nitrobacteria in the system. Extension of sludge age enhanced the heterotrophic bacteria concentration and to a greater extent the nitrobacteria concentration, thus attenuated the dilution of nitrobacteria. Mixed liquid recycling showed little effect on nitrobacteria concentration. The closed double‐SRT AO process in Zhuyuan Second WWTP had enough capacity for complete nitrification, but the shortage of organic matter in the influent impeded the nitrogen removal.     

Biological oxidation of high strength nitrogenous wastewater

A nitrification study was conducted in continuous flow stirred tank reactors using high strength nitrogenous wastewater (concentrated stream from a urea plant mixed with pharmaceutical wastewater). The reactors were operated at different solids retention times (SRT = 10–62.5 d) and hydraulic retention times (HRT = 1.5–2.1 d). Pharmaceutical wastewater was used as an organic carbon source to maintain a COD/TKN ratio of 1. The nitrification achieved at different SRTs varied from 87 to 99%. The nitrogen balance data show that ammonia assimilation and denitrification accounted for 4–53% of the total nitrogen removed. The yield coefficients and decay coefficients were Y_b = 0.5 (COD basis), k_db = 0.07 d⁻¹ (COD basis) for heterotrophs and Y_n = 0.15 (TKN basis), k_dn = 0.06 d⁻¹ (TKN basis) for nitrifiers respectively.     

Anaerobic/oxic/anoxic granular sludge process as an effective nutrient removal process utilizing denitrifying polyphosphate-accumulating organisms

In a biological nutrient removal (BNR) process, the utilization of denitrifying polyphosphate-accumulating organisms (DNPAOs) has many advantages such as effective use of organic carbon substrates and low sludge production. As a suitable process for the utilization of DNPAOs in BNR, an anaerobic/oxic/anoxic granular sludge (AOAGS) process was proposed in this study. In spite of performing aeration for nitrifying bacteria, the AOAGS process can create anaerobic/anoxic conditions suitable for the cultivation of DNPAOs because anoxic zones exist inside the granular sludge in the oxic phase. Thus, DNPAOs can coexist with nitrifying bacteria in a single reactor. In addition, the usability of DNPAOs in the reactor can be improved by adding the anoxic phase after the oxic phase. These characteristics enable the AOAGS process to attain effective removal of both nitrogen and phosphorus. When acetate-based synthetic wastewater (COD: 600 mg/L, NH4-N: 60 mg/L, PO(4)-P: 10 mg/L) was supplied to a laboratory-scale sequencing batch reactor under the operation of anaerobic/oxic/anoxic cycles, granular sludge with a diameter of 500 microm was successfully formed within 1 month. Although the removal of both nitrogen and phosphorus was almost complete at the end of the oxic phase, a short anoxic period subsequent to the oxic phase was necessary for further removal of nitrogen and phosphorus. As a result, effluent concentrations of NH(4)-N, NO(x)-N and PO(4)-P were always lower than 1 mg/L. It was found that penetration depth of oxygen inside the granular sludge was approximately 100 microm by microsensor measurements. In addition, from the microbiological analysis by fluorescence in situ hybridization, existence depth of polyphosphate-accumulating organisms was further than the maximum oxygen penetration depth. The water quality data, oxygen profiles and microbial community structure demonstrated that DNPAOs inside the granular sludge may be responsible for denitrification in the oxic phase, which enables effective nutrient removal in the AOAGS process.     

Kinetic competition between phosphorus release and denitrification on sludge under anoxic condition

The kinetic behaviors of simultaneous phosphorus release and denitrification on sludge were investigated under anoxic condition. A phosphorus enriched sludge produced from Anaerobic-Anoxic-Oxic (AnAO) process under various SRT (5, 10 and 15 days) operation conditions was carried out in a series of batch tests. Experimental results indicated that the available organic substrate determined the kinetic behaviors of phosphorus release/uptake and denitrification. The simultaneous phosphorus release and denitrification demonstrated a kinetic competition under anoxic conditions in the presence of an available organic substrate. When the substrate was abundant, sludge was under “releasable-phosphorus-limited” condition; phosphorus release rate decreased slightly by nitrate inhibition. However, nitrate significantly inhibited phosphorus release when sludge was under “initial-substrate-limited” condition. Moreover, the sludge's phosphorus contents (as created by different SRT processes) dominated the kinetics of competition between phosphorus release and denitrification. The sludge with a high phosphorus content had a higher phosphorus release rate in accordance with a lower denitrification rate. Additionally, the substrate sequestrated rate markedly increased under the condition of simultaneous phosphorus release and denitrification. Finally, a preliminary metabolism model of denitrifying phosphorus removal bacteria was proposed, and found to be capable of adequately accounting for simultaneous phosphorus release and denitrification under anoxic conditions.     

Modeling simultaneous autotrophic and heterotrophic growth in aerobic granules

A mathematical model has been developed to describe the simultaneous autotrophic and heterotrophic growth in granule-based sequencing batch reactors (SBRs). Experimental results of a laboratory-scale granule-based SBR are used to calibrate and validate the model. The model is able to simulate the reactor performance and gain insight in autotrophic and heterotrophic growth in the granules. With the established model, the fractions of active biomass (autotrophs and heterotrophs) and inert biomass are predicted to be 55.6% and 44.4% of the total mixed liquid volatile suspended solid, respectively, at a solids retention time (SRT) of 20 days. Biomass content increases with increasing SRT, but active biomass ratio decreases. Autotrophs have no significant effect on the total biomass content, although they play an important role in nitrogen removal. Simulation results also demonstrate the key role of the influent substrate and NH(4)(+)-N in governing the composition of heterotrophic and autotrophic biomass in a granule-based SBR. The autotrophs are mainly located on the outer layer of granules, whereas the heterotrophs are present in the center of granules, or on the outer layer of granules.     

Endogenous metabolism of Candidatus Accumulibacter phosphatis under various starvation conditions

The endogenous processes of Candidatus Accumulibacter phosphatis (referred to as Accumulibacter), a known polyphosphate-accumulating organism (PAO) responsible for enhanced biological phosphorus removal systems (EBPR), were characterized during 8-day starvation under anaerobic, anoxic, aerobic and intermittent aerobic–anaerobic conditions. A lab-scale EBPR culture with Accumulibacter representing over 85% of the entire bacterial population as quantified with fluorescence in-situ hybridization was used in the study. Cell decay rates were found to be negligible under anaerobic and anoxic conditions and may be ignored in activated sludge models. The decay rate under aerobic conditions was determined to be 0.03/d at 22 °C, considerably lower than the values commonly used in activated sludge modeling. Polyphosphate and glycogen were utilized simultaneously under anaerobic and anoxic conditions for maintenance energy production, with glycogen being the primary energy source until the glycogen content reached very low levels. Glycogen was used by Accumulibacter as the primary source of energy for maintenance under aerobic conditions in the absence of polyhydroxyalkanoates. However, Accumulibacter did not seem to use polyphosphate for energy production during aerobic starvation, clearly contrasting the anaerobic and particularly the anoxic case. Intermittent aerobic–anaerobic storage resulted in not only negligible cell decay rate, but also slower rates of glycogen and polyphosphate utilization, and may therefore be an effective strategy for long-term storage of EBPR sludge.     

污泥回流比对A_2N反硝化除磷工艺脱氮除磷的影响

以城市生活污水为研究对象,探讨了不同的超越污泥和回流污泥回流比对A2N工艺脱氮除磷的影响.在超越污泥回流比与回流污泥回流比相同且分别为0.3、0.4和0.6的条件下,A2N工艺对COD的平均去除率分别为92.5%、90.3%、91.6%,相应的出水COD为20.3、28.4、25.3 mg/L;对总氮的平均去除率分别为87.1%、90%、84.9%,出水总氮分别为6.75、5.43、6.95mg/L;对磷的平均去除率分别为99.5%、99.6%和99.0%,出水磷浓度分别为0.02、0.02、0.05mg/L.当回流比为0.4时,A2N系统的除污效果最好.研究还发现,超越污泥流量直接决定了未经硝化而直接进入缺氧池的氨氮量,进而影响出水氨氮浓度.因此,在保证缺氧池有足够污泥的前提下,应尽可能减小超越污泥流量,以降低出水氨氮浓度.     

短好氧泥龄下A2/O和BAF联合工艺的脱氮除磷特性

采用小试装置,研究了短好氧污泥龄下A2/O和BAF联合工艺处理低C/N和C/P污水时的脱氮除磷特性.结果表明,通过提高A2/O工艺段的厌氧区有机负荷和缺氧区硝酸盐负荷对反硝化聚磷菌（DPAOs）进行选择和强化后,其在聚磷菌（PAOs）中的比例维持在28%左右,工艺具有部分反硝化除磷能力,能够减少脱氮除磷过程中对碳源的总需求量.但在联合工艺中,好氧除磷仍是主要的除磷方式.在A2/O工艺段内,好氧污泥龄在满足好氧PAOs存活的同时,还必须满足抑制硝化细菌生长的要求,且为了保证工艺对磷的整体去除效果,混合液在好氧区的接触时间须大于30 min.此外,以保证缺氧区出水中含有1～4 mg/L的硝态氮为原则来控制BAF出水的回流量,可达到较好的脱氮除磷效果.该联合工艺结合了活性污泥工艺和生物膜工艺的优点,运行稳定,出水水质优良,不仅适合于新建污水处理厂,也特别适合于不能脱氮除磷污水处理厂的技术改造.     

A2O工艺削减城市污水毒性的能力评估

依次次改变A^2O系统的水力停留时间、泥龄和混合液回流比，并使用发光菌毒性测试法对系统各反应单元的进、出水毒性进行了测试，从而首次从毒减性削角度对A^2O工艺进行了评估，同时对部分工艺运行参数进行了优化选择。试验结果表明：A^2O工艺对城市污水的毒性（以发光菌抑光率表示）有较好的削减能力；在温度为25℃、污泥回流比为100％的情况下，最佳的工艺运行参数为水力停留时间（HRT）=12．5h、泥龄（SRT）=15d、混合液回流比（r）=100％，此时NH3-N、SS、COD的去除率分别达到90．05％、77．17％、80．02％，毒性削减率也达到82．17％，其中厌氧池、缺氧池、好氧池、二沉池各段毒性削减量分别占毒性总削减量的16．29％、7．58％、52．01％、24．12％。     

Evaluation on the microbial interactions of anaerobic ammonium oxidizers and heterotrophs in Anammox biofilm

Anaerobic ammonium oxidation (Anammox) is a cost-effective new process to treat high-strength nitrogenous wastewater. In this work, the microbial interactions of anaerobic ammonium oxidizers and heterotrophs through the exchange of soluble microbial products (SMP) in Anammox biofilm and the affecting factors were evaluated with both experimental and modeling approaches. Fluorescent in situ hybridization (FISH) analysis illustrated that Anammox bacteria and heterotrophs accounted for 77% and 23% of the total bacteria, respectively, even without addition of an external carbon source. Experimental results showed the heterotrophs could grow both on SMP and decay released substrate from the metabolism of the Anammox bacteria. However, heterotrophic growth in Anammox biofilm (23%) was significantly lower than that of nitrifying biofilm (30-50%). The model predictions matched well with the experimental observations of the bacterial distribution, as well as the nitrogenous transformations in batch and continuous experiments. The modeling results showed that low nitrogen surface loading resulted in a lower availability of SMP leading to low heterotrophic growth in Anammox biofilm, but high nitrogen surface loading would lead to relative stable biomass fractions although the absolute heterotrophic growth increased. Meanwhile, increasing biofilm thickness increased heterotrophic growth but has little influence on the relative biomass fractions.     

Evaluation of continuous mesophilic, thermophilic and temperature phased anaerobic digestion of microwaved activated sludge

The effects of microwave (MW) pretreatment, staging and digestion temperature on anaerobic digestion were investigated in a setup of ten reactors. A mesophilic reactor was used as a control. Its performance was compared to single-stage mesophilic and thermophilic reactors treating pretreated and non-pretreated sludge, temperature-phased (TPAD) thermophilic-mesophilic reactors treating pretreated and non-pretreated sludge and thermophilic-thermophilic reactors also treating pretreated and non-pretreated sludge. Four different sludge retention times (SRTs) (20, 15, 10 and 5 d) were tested for all reactors. Two-stage thermo-thermo reactors treating pretreated sludge produced more biogas than all other reactors and removed more volatile solids. Maximum volatile solids (VS) removal was 53.1% at an SRT of 15 d and maximum biogas increase relative to control was 106% at the shortest SRT tested. Both the maximum VS removal and biogas relative increase were measured for a system with thermophilic acidogenic reactor and thermophilic methanogenic reactor. All the two-stage systems treating microwaved sludge produced sludge free of pathogen indicator bacteria, at all tested conditions even at a total system SRT of only 5 d. MW pretreatment and staging reactors allowed the application of very short SRT (5 d) with no significant decrease in performance in terms of VS removal in comparison with the control reactor. MW pretreatment caused the solubilization of organic material in sludge but also allowed more extensive hydrolysis of organic material in downstream reactors. The association of MW pretreatment and thermophilic operation improves dewaterability of digested sludge.     

改良型DE氧化沟工艺的除磷脱氮探讨

四川新都金海污水处理厂采用改良型DE氧化沟工艺,即在DE型氧化沟前加设缺氧池和厌氧池以强化除磷。为防止污泥膨胀,设立了一个生物选择区,而且采用两点进水法(20%的污水进入缺氧区,80%的污水进入生物选择区)。运行结果显示,该工艺运行效果良好,出水水质达到一级排放标准。     

高效初沉发酵池处理城市污水的中试研究

应用生物絮凝沉淀和水解发酵耦合工艺,将传统的初沉池改造为集进水悬浮固体的沉淀分离和沉淀污泥的产酸发酵为一体的高效初沉发酵池,以优化碳源结构,提高后续工艺的污泥活性和脱氮除磷能力。在水力停留时间为0.75 h、悬浮污泥絮体层界面高度不低于高效初沉发酵池有效池深的70%、SRT为4 d的条件下,考察了高效初沉发酵池对进水水质的改善效果。结果表明:高效初沉发酵池对SS的去除率为78%,是普通初沉池的近2倍;出水VSS/SS均值为71.9%,较普通初沉池提高了17.3%;出水C/N和C/P值较进水值分别提高了33%和14%,且明显高于污水厂普通初沉池出水水质。碳源结构的改善提高了后续生物处理工艺的脱氮除磷效果,对TP的去除率稳定在90%～98%。