Suspended biofilm carrier and activated sludge removal of acidic pharmaceuticals

Removal of seven active pharmaceutical substances (ibuprofen, ketoprofen, naproxen, diclofenac, clofibric acid, mefenamic acid, and gemfibrozil) was assessed by batch experiments, with suspended biofilm carriers and activated sludge from several full-scale wastewater treatment plants. A distinct difference between nitrifying activated sludge and suspended biofilm carrier removal of several pharmaceuticals was demonstrated. Biofilm carriers from full-scale nitrifying wastewater treatment plants, demonstrated considerably higher removal rates per unit biomass (i.e. suspended solids for the sludges and attached solids for the carriers) of diclofenac, ketoprofen, gemfibrozil, clofibric acid and mefenamic acid compared to the sludges. Among the target pharmaceuticals, only ibuprofen and naproxen showed similar removal rates per unit biomass for the sludges and biofilm carriers. In contrast to the pharmaceutical removal, the nitrification capacity per unit biomass was lower for the carriers than the sludges, which suggests that neither the nitrite nor the ammonia oxidizing bacteria are primarily responsible for the observed differences in pharmaceutical removal. The low ability of ammonia oxidizing bacteria to degrade or transform the target pharmaceuticals was further demonstrated by the limited pharmaceutical removal in an experiment with continuous nitritation and biofilm carriers from a partial nitritation/anammox sludge liquor treatment process.     

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.     

Total nitrogen removal in a hybrid, membrane-aerated activated sludge process

The hybrid (suspended and attached growth) membrane biofilm process (HMBP) is a novel method to achieve total nitrogen removal from wastewater. Air-filled hollow-fiber membranes are incorporated into an activated sludge tank, and a nitrifying biofilm develops on the membranes, producing nitrite and nitrate. By suppressing bulk aeration, the bulk liquid becomes anoxic, and the nitrate/nitrite can be reduced with influent BOD. The key feature that distinguishes the HMBP from other membrane-aerated processes is that it is hybrid; heterotrophic bacteria are kept mainly in suspension by maintaining low bulk liquid BOD concentrations. We investigated the HMBP's performance under a variety of BOD and ammonium loadings, and determined the dominant mechanisms of nitrogen removal. Suspended solids increased with the BOD loadings, maintaining low bulk liquid BOD concentrations. As a result, nitrification rates were insensitive to the BOD loadings, remaining at 1gNm(-2)day(-1) for BOD loadings ranging from 4 to 17gBODm(-2)day(-1). Nitrification rates decreased during short-term spikes in bulk liquid BOD concentrations. Shortcut nitrogen removal was confirmed using microsensor measurements, showing that nitrite was the dominant form of oxidized nitrogen produced by the biofilm. Fluorescence in situ hybridization (FISH) showed that ammonia oxidizing bacteria (AOB) were dominant throughout the biofilm, while nitrite oxidizing bacteria (NOB) were only present in the deeper regions of the biofilm, where the oxygen concentration was above 2mg/L. Denitrification occurred mainly in the suspended phase, instead of in the biofilm, decreasing the potential for biofouling. When influent BOD concentrations were sufficiently high, full denitrification occurred, with total nitrogen (TN) removal approaching 100%. These results suggest that the process is well-suited for achieving concurrent BOD and TN removal in activated sludge.     

一体化A/O生物膜反应器处理生活污水

根据缺氧 好氧 (Anoxic Oxic ,A O)工艺原理设计了升流式一体化A O生物膜反应器 ,并就反应器对生活污水的处理效果和运行参数进行了试验。结果表明 ,当缺氧区HRT为 5h、好氧区HRT为 3h时对COD的去除率 >80 % (大部分接近 90 % ) ,对SS去除率 >95 % ;维持反应器内适宜的碱度可获得良好而稳定的脱氮效果 ;剩余污泥少 ,无需频繁排泥。     

Comparison of sulfonated and other micropollutants removal in membrane bioreactor and conventional wastewater treatment

Membrane bioreactors (MBRs) were compared with conventional activated sludge systems (CAS) for micropollutant degradation, in laboratory-scale spiking experiments with synthetic and real domestic wastewater. The target micropollutants were polar in nature and represented a broad range in biodegradability. The experimental data indicated that MBR treatment could significantly enhance removal of the micropollutants 1,6- and 2,7-naphthalene disulfonate (NDSA) and benzothiazole-2-sulfonate. 1,5-NDSA, EDTA and diclofenac were not removed in either the MBR or the CAS. The other compounds were equally well degraded in both systems. For 1,3-naphthalene disulfonate, the existence of a minimum threshold level for degradation could be demonstrated. Although MBRs could not always make a difference in the overall removal efficiencies achieved, they showed reduced lag phases for degradation and a stronger memory effect, which implies that they may respond quicker to variable influent concentrations. Finally, micropollutant removal also turned out to be less sensitive to system operational variables.     

Simultaneous P and N removal in a sequencing batch biofilm reactor: insights from reactor- and microscale investigations

A sequencing batch biofilm reactor (SBBR) with well established enhanced biological phosphate removal (EBPR) was subjected to higher ammonium concentrations to stimulate and eventually implement simultaneous nitrification. Changes of activity and populations were investigated by a combination of online monitoring, microsensor measurements and fluorescence in situ hybridisation (FISH) of biofilm sections. Nitrification and nitrifying bacteria were always restricted to the periodically oxic biofilm surface. Both, activity and population size increased significantly with higher ammonium concentrations. Nitrification always showed a delay after the onset of aeration, most likely due to competition for oxygen by coexisting P accumulating and other heterotrophic bacteria during the initial aeration phase. This view is also supported by comparing oxygen penetration and oxygen uptake rates under low and high ammonium conditions. Therefore, simultaneous nitrification and phosphorus removal in a P removing SBBR appears to be only possible with a sufficiently long oxic period to ensure oxygen availability for nitrifiers.     

Fate of beta blockers and psycho-active drugs in conventional wastewater treatment

The removal of beta blockers and psycho-active drugs was investigated in a representative conventional German WWTP by long-term measurement campaigns along different biological treatment processes. The activated sludge treatment with an elevated SRT of 18 d was the only process which led to a significant removal of certain beta blockers and psycho-active drugs. The removal efficiency was below 60% for all compounds except for the natural opium alkaloids codeine and morphine being removed by more than 80%. Primary biological transformation and sorption onto sludge as the main removal mechanisms were examined in lab-scale batch experiments. Sorption onto activated sludge was found to be negligible (<3%). The biological transformation could be described by pseudo-first order kinetics and the transformation constants k_biol were used to predict the removal of beta blockers and psycho-active drugs in an activated sludge unit with a model. For most compounds the removal efficiencies measured on the full-scale WWTP were within the 95% confidence intervals predicted by the model. The results from full-scale measurements and modeling indicate that biological transformation in the nitrification tank together with parameters such as the sludge retention time and the temperature is crucial regarding the biological transformation of beta blockers and psycho-active drugs in conventional WWTPs.     

Development of an innovative vertical submerged membrane bioreactor (VSMBR) for simultaneous removal of organic matter and nutrients

A novel vertical submerged membrane bioreactor (VSMBR) composed of anoxic and oxic zones in one reactor was developed in an attempt to reduce the problems concerning effective removal of pollutants from synthetic wastewater including glucose as a sole carbon source as well as membrane fouling. The optimal volume ratio of anoxic zone/oxic zone was found as 0.6. The desirable internal recycle rate and hydraulic retention time (HRT) for effective nutrient removal were 400% and 8h, respectively. Under these conditions, the average removal efficiencies of total nitrogen (T-N) and total phosphorus (T-P) were 75% and 71%, respectively, at the total chemical oxygen demand (T-COD)/T-N ratio of 10. In addition, the VSMBR showed high specific removal rates of nitrogen and phosphorus while the biomass growth yield from the reactor was about 20% of the conventional activated sludge process.     

Development of a 2-sludge, 3-stage system for nitrogen and phosphorous removal from nutrient-rich wastewater using granular sludge and biofilms

A novel 2-sludge 3-stage process using a combination of granular sludge and biofilm was developed to achieve biological removal of nitrogen and phosphorus from nutrient-rich wastewater. The system consists of a granular sequencing batch reactor (SBR) working under alternating anaerobic/anoxic conditions supplemented with a short aerobic phase and an aerobic biofilm SBR. The wastewater is first fed to the granular SBR reactor, where easily biodegradable carbon sources are taken up primarily by polyphosphate accumulating organisms (PAOs). The supernatant resulting from quick settling of the granular sludge is then fed to the biofilm SBR for nitrification, which produces oxidized nitrogen that is returned to the granular reactor for simultaneous denitrification and phosphorus removal. While maximizing the utilization of organic substrates and reducing operational costs, as do other 2-sludge processes previously reported in literature, the proposed system solves the bottleneck problem of traditional 2-sludge systems, namely high effluent ammonia concentration, due to its high-volume exchange ratios. An ammonia oxidation rate of 32 mg N/Lh was achieved in the biofilm SBR, which produced nitrite as the final product. This nitrite stream was found to cause major inhibition on the anoxic P uptake and also to result in the accumulation of N(2)O. These problems were solved by feeding the nitrite-containing stream continuously to the granular reactor in the anoxic phase. With a nitrogen and phosphorus removal efficiency of 81% and 94%, respectively, the system produces an effluent that is suitable for land irrigation from a wastewater stream containing 270 mg N/L of total nitrogen and 40 mg P/L of total phosphorus.     

采用HYBASTM工艺升级改造传统活性污泥工艺

简要回顾了流动床生物膜（MBBR^TM）工艺开发以来在世界各地的应用,重点介绍了采用MBBR^TM工艺与活性污泥工艺有机结合的流动床生物膜-活性污泥复合工艺（HYBAS^TM）在美国Broomfield市政污水厂的升级改造中取得的除磷脱氮经验和改造效果.     

Effect of sludge fasting/feasting on growth of activated sludge cultures

Reduction of excess sludge in an oxic-settling-anoxic (OSA) activated sludge process might be attributed to a "sludge fasting (insufficient food under an anoxic condition)/feasting (sufficient food under an oxic condition)" treatment. This paper was to examine this explanation by investigating both the sludge fasting/feasting phenomenon and the effect of a fasting/feasting treatment on sludge growth. In this study, five different activated sludge cultures cultivated using synthetic wastewater composed of mainly glucose and other necessary nutrients: (1) an aerobic batch culture, (2) an intermittently aerated batch culture, (3) an anoxic batch culture, (4) a continuous aerobic culture, and (5) an OSA culture, were employed. It was found that only the aerobic batch culture and the aerobic continuous culture are fastable when the oxidation reduction potential (ORP) level is below 100 mV under no-food condition during a 2-h fasting treatment, showing that both the biomass and carbohydrate storage of these two cultures were reduced after the treatment. When the fasted cultures were treated in a feasting environment, an accumulation of carbohydrate storage did not occur, while specific oxygen uptake rates (SOUR) showed a sharp increase. Both the substrate utilization and biomass growth rates were also accelerated. It was therefore confirmed that a sludge feasting did occur after a fasting treatment for the fastable cultures. However, an increase in sludge ATP content was not brought about by the feasting treatment. The sludge fasting/feasting treatment in this paper could not induce a reduction of the observed growth yield (Y(obs)) in all the cultures cultivated with glucose-based synthetic wastewater.     

MBBR和传统活性污泥法组合的BAS工艺

介绍了MBBR移动床生物膜和活性污泥组合工艺（BAS工艺），该工艺可处理进水COD较高或营养物缺乏的污水，占地省、运行稳定、污染物处理效率高、可大幅度降低生物污泥产量和减少出水营养物的排放。     

Effect of nitrite on phosphate uptake by phosphate accumulating organisms

In biological nitrogen removal processes, nitrite can be formed and accumulated through both nitrification and denitrification. Despite the fact that, in practice, biological phosphate removal (BPR) is often combined with biological nitrogen removal, there are only a few publications reporting the effect of nitrite on BPR. In this study, phosphate-accumulating organisms (PAO) were cultivated in an anaerobic-anoxic-aerobic sequencing batch reactor (SBR). The effect of nitrite on the enrichment of the sludge with PAO, the phosphate uptake rates and the sludge respiration was investigated. The results indicate that (1) presence of nitrite inhibits both aerobic and anoxic (denitrifying) phosphate uptake, (2) aerobic phosphate uptake was more affected than anoxic phosphate uptake, (3) presence of nitrite could be one of the factors enhancing the presence of glycogen accumulating organisms (GAO)--competitors to PAO for substrate in the anaerobic phase, and (4) it is required to monitor and control nitrite accumulation in a full-scale wastewater treatment plants.     

Nitrogen control in AO process with recirculation of solubilized excess sludge

In order to establish a sludgeless process with a nitrogen-controlled effluent, batch and continuous experiments in a lab scale anoxic-oxic (AO) process were carried out to investigate the possibility of ozonized sludge (OS) usage as a denitrification energy source. Through ozonation at an ozone dose of 1.2g O(3)/g MLVSS, 63.2% of treated MLVSS was solubilized, 12.7% of COD was lost (probably due to complete oxidation to CO(2)), and soluble COD/TN ratio of OS appeared to be only about 10.78 because ozonation released cellular proteins and other nitrogenous substances. In oxic conditions, incubation of OS supernatant with activated sludge generated nitrate without significant ammonia accumulation, which meant that rapid nitrification occurred following ammonia generation from heterotrophic degradation of nitrogen-bearing cellular substances. In anoxic conditions, externally supplied nitrate was removed at the expense of organic carbons in the OS supernatant. However, ammonia was accumulated as anoxic incubation proceeded probably because of heterotrophic degradation of nitrogenous materials as in oxic conditions. Thus it was appeared that solubilized excess sludge acted as a reducing power for denitrification but also as a nitrogen source. In addition, 24-41% of COD contained in OS supernatant were found to be consumed for denitrification. But the remaining COD was not assimilated further even in the presence of nitrate. It was concluded by a nitrogen balance analysis that the energy source contained in OS was not sufficient to completely reduce the nitrogen that was originated from OS itself to nitrogen gas.     

A simple biofilm model of bacterial competition for attached surface

A simple biofilm model of competition in bacterial growth for an attached surface is developed. Competition for the attached surface is expressed with the crowded and detachment effects. The developed model is verified by comparing simulated results with data obtained in the experiments of batch culture of nitrifier and continuous treatment of actual sewage with biofilm reactor. This model can favorably simulate the growth competition between autotrophic and heterotrophic bacteria for the attached surface. Then some parameters for nitrification process are discussed with this model. It is clarified that the effective removal of organic matter before nitrification tank is required for effective nitrification in the biofilm reactor.     

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。     

Influence of alternating oxic/anoxic conditions on growth of denitrifying bacteria

Denitrifying bacteria that are switched from oxic to anoxic conditions can experience diauxic lag, which is the time required for re-synthesis of nitrate reductase and other denitrifying enzymes. Pseudomonas denitrificans were exposed to alternating oxic/anoxic phases in a continuous flow reactor with either 4-h or 8-h anoxic phase lengths, in comparison to a measured diauxic lag of 9.5 h following steady-state oxic conditions. The P. denitrificans were unable to sustain anoxic growth at either of the anoxic phase lengths tested. Diauxic lag observed after several cycles of alternating oxic/anoxic phases was significantly longer than the diauxic lag measured after steady-state oxic conditions. This may be attributed to increase of cell maintenance energy requirements due to substrate accumulation during anoxic phases and concomitant high specific growth rates during oxic phases.     

Critical operational parameters for zero sludge production in biological wastewater treatment processes combined with sludge disintegration

Mathematical models were developed to elucidate the relationships among process control parameters and the effect of these parameters on the performance of anoxic/oxic biological wastewater processes combined with sludge disintegrators (A/O-SD). The model equations were also applied for analyses of activated sludge processes hybrid with sludge disintegrators (AS-SD). Solubilization ratio of sludge in the sludge disintegrator, alpha, hardly affected sludge reduction efficiencies if the biomass was completely destructed to smaller particulates. On the other hand, conversion efficiency of non-biodegradable particulates to biodegradable particulates, beta, significantly affected sludge reduction efficiencies because beta was directly related to the accumulation of non-biodegradable particulates in bioreactors. When 30% of sludge in the oxic tank was disintegrated everyday and beta was 0.5, sludge reduction was expected to be 78% and 69% for the A/O-SD and AS-SD processes, respectively. Under this condition, the sludge disintegration number (SDN), which is the amount of sludge disintegrated divided by the reduced sludge, was calculated to be around 4. Due to the sludge disintegration, live biomass concentration decreased while other non-biodegradable particulates concentration increased. As a consequence, the real F/M ratio was expected to be much higher than the apparent F/M. The effluent COD was maintained almost constant for the range of sludge disintegration rate considered in this study. Nitrogen removal efficiencies of the A/O-SD process was hardly affected by the sludge disintegration until daily sludge disintegration reaches 40% of sludge in the oxic tank. Above this level of sludge disintegration, autotrophic biomass concentration decreases overly and TKN in the effluent increases abruptly in both the A/O-SD and AS-SD processes. Overall, the trends of sludge reduction and effluent quality according to operation parameters matched well with experimental results found in literatures.     

浙江某工业废水处理厂升级改造运行效果解析

浙江某工业废水处理厂升级改造,采用AAO—MBBR复合生物膜工艺,在未新增建设用地和扩建池容的基础上,日处理量由3×10⁴m³/d提高至6×10⁴m³/d。改造后实际运行出水COD、TP、NH₃-N和TN浓度分别为(37.7±6.61)、(0.09±0.03)、(0.25±0.14)和(5.87±1.54)mg/L,出水水质稳定达到一级A标准。实际监测表明,在好氧MBBR区存在TN去除现象,约占TN总去除量的10.36%。系统内的优势硝化菌属为硝化螺旋菌属Nitrospira,其在悬浮载体生物膜和活性污泥中的相对丰度分别为8.98%和0.92%,悬浮载体的投加使硝化细菌得到有效富集;反硝化菌在生物膜中的占比为7.94%,为悬浮载体同步硝化反硝化(SND)效果的发生提供了微观保证,提高了TN去除率。     

Macroscale and microscale analyses of nitrification and denitrification in biofilms attached on membrane aerated biofilm reactors

A membrane aerated biofilm reactor (MABR), in which O(2) was supplied from the bottom of the biofilm and NH(4)(+) and organic carbon were supplied from the biofilm surface, was operated at different organic carbon loading rates and intra-membrane air pressures to investigate the occurrence of simultaneous chemical oxygen demand (COD) removal, nitrification and denitrification. The spatial distribution of nitrification and denitrification zones in the biofilms was measured with microelectrodes for O(2), NH(4)(+), NO(2)(-), NO(3)(-) and pH. When the MABR was operated at approximately 1.0 g-COD/m(2)/day of COD loading rate, simultaneous COD removal, nitrification and denitrification could be achieved. The COD loading rates and the intra-membrane air pressures applied in this study had no effect on the start-up and the maximum rates of NH(4)(+) oxidation in the MABRs. Microelectrode measurements showed that O(2) was supplied from the bottom of the MABR biofilm and penetrated the whole biofilm. Because the biofilm thickness increased during the operations, an anoxic layer developed in the upper parts of the mature biofilms while an oxic layer was restricted to the deeper parts of the biofilms. The development of the anoxic zones in the biofilms coincided with increase in the denitrification rates. Nitrification occurred in the zones from membrane surface to a point of ca. 60microm. Denitrification mainly occurred just above the nitrification zones. The COD loading rates and the intra-membrane air pressures applied in this study had no effect on location of the nitrification and denitrification zones.