Automatic monitoring of denitrification rates and capacities in activated sludge processes using fluorescence or redox potential

A novel method is described to automatically estimate several key parameters affecting denitrification in activated sludge processes: the nitrate concentration, the denitrification capacity, and the maximum (substrate unlimited) and actual denitrification rates. From these, the concentration of active denitrifying microorganisms and the quality of available organic substrate pool can be estimated. Additionally, a modification of the method allows the determination of the efficacy of various carbon substrates to enhance denitrification, and this can be used to determine optimal dosing rates of an external carbon source. The method is based on measurements of either fluorescence or redox potential (ORP) in an isolated mini-reactor, the Biological Activity Meter (BAM), situated in the anoxic zone of the wastewater treatment plant. Advantages of the method are that it is in situ, operating at the same temperature as in the measured anoxic zone, requires no pumps or pipes for mixed liquor sampling, consumes little or no reagents, and uses measurement signals which are instantaneous and low maintenance, one of which provides a direct measure of biological activity.     

Simultaneous nitrification/denitrification in an aerobic biofilm system

In the biological pretreatment of landfill leachate in Mechemich (Germany) a loss of inorganic nitrogen of up to 90% was observed in the nitrification step (rotating biological contactor) under low DO conditions. Ammonia was removed but only small amounts of nitrate were produced. Nitrite accumulation did not occur. In aerobic batch tests nitrogen loss was confirmed without any addition of organic substrate, even when homogenizing the biofilm mechanically to destroy possible anoxic microzones. N₂ was measured as the gaseous end product of the process. From results presented it can be assumed that a largely autotrophic microorganism population performed this aerobic nitrification/denitrification.     

The root surface as the definitive detail for microbial transformation processes in constructed wetlands--a biofilm characteristic.

It was the goal of the investigations to characterise the biofilm on the plant roots because of the demonstrable major role of these associated bacteria. The essential criteria for the research were to look at the structure of the microbial colonisation (pattern, density) and to determine properties of the rhizoplane biofilm such as thickness and structure. The root material from a hydroponic system, planted with Glyceria maxima and used for nitrogen removal, has been used for the investigations. Several properties of the bacteria became visible due to the application of specific dyes. The evaluation of the samples was performed by scanning confocal laser microscopy (CLSM). It was shown that the microbial colonisation of the root surface of Glyceria maxima was on an unexpected high level and seems to be related mainly to the permeability and therefore to the age of the plant roots. The thickness of the rhizoplane biofilm is remarkably thin; no inactive layers could be observed in contrast to biofilm growing on technical carrier material. Caused by the untypically two-sided supply with nutrients the whole biofilm is in interaction with the surroundings. This indicates the importance of the plant roots for the microbial transformation processes in wetlands and underlines the especialness of the root as carrier for microorganisms.     

Analysis of nitrifying bacterial communities in aerobic biofilm reactors with different DO conditions using molecular techniques

In order to assess the relationship between the dissolved oxygen (DO) concentration and the characteristics of nitrifying bacterial communities in an aerobic biofilm reactor, molecular techniques including denaturing gradient gel electrophoresis (DGGE)/cloning based on PCR targeting 16S rRNA and the amoA gene and fluorescence in situ hybridisation (FISH) were conducted. The D-1, D-2, D-3 and D-4 reactors with different DO concentrations (1, 3, 5 and 7 mg/L, respectively) were set up in the thermostat and acclimated. The optimal DO concentration with stable nitrification efficiency was above 5.0 mg/L. As was shown by the results of DGGE and cloning, the community of ammonia-oxidising bacteria (AOB) and the ratio of Nitrosomonas sp. changed only slightly despite their differing nitrification efficiencies. The results of FISH indicated that higher DO concentrations resulted in an increase in AOB and nitrite-oxidising bacteria (NOB), and a reduction in heterotrophic microorganisms. The INT-dehydrogenase activity (DHA) test demonstrated that the activity of AOB decreased with reductions in the DO concentration. This means that the DO concentration does not influence the community of AOB, but rather the activity of AOB. In the relationship between the attached biomass and the nitrification efficiency, only the active biomass affected the nitrification efficiencies.     

Reproducibility of biofilm processes and the meaning of steady state in biofilm reactors.

The need for reproducing biofilm processes is undisputable - the quality of biofilm research depends on this reproducibility. However, as many biofilm researchers know, long-term biofilm processes are notoriously difficult to reproduce. To avoid problems related to biofilm reproducibility two strategies are used: (1) to study very young biofilms that have accumulated for a few hours to a few days only, and (2) to run biofilm experiments only once. The first approach trades reproducibility for relevance because natural biofilms are usually older, often much older than a few days. This approach can be applied to answer questions relevant to initial events of biofilm formation but not questions relevant to long-term biofilm accumulation. The second approach conceals the problem of biofilm reproducibility. To assure reproducibility of biofilm processes, we methodically followed a procedure for growing biofilms in terms of microbial makeup, media composition, temperature, surface preparation, etc. Despite all this effort the reproducibility of our results for long term growth is unimpressive. Consequently, the question had to be asked: Are biofilm processes reproducible? The experiments described in this paper address this question. Biofilms grown in two identical and identically operated biofilm reactors had comparable structure only until the first sloughing event. After that, biofilms had different patterns of accumulation.     

水解酸化-好氧工艺处理油田废水研究

采用水解酸化-好氧工艺对经过物化预处理的油田废水进行生化处理。结果表明:水解酸化-好氧工艺对经物化处理后的油田废水具有理想的处理效果,好氧段各工况的出水CODCr均能达到国家《石油开发工业水污染物排放标准》(GB3550-83)第一级Ⅰ类标准。该工艺与传统的物理化学法处理流程相比,其工程投资和运行费用也具有较为明显的优势。     

Adsorption and biodegradation of azo dye in biofilm processes.

The removal of a common azo dye, acid orange 7 (AO7), in biofilm systems was investigated in this study. The abiotic and biotic fate of AO7 was examined under a variety of operating conditions: aerobic nitrification, anoxic denitrification and anaerobic digestion. A comparison of the performance between biofilm and activated sludge treatment processes was made. The adsorption of AO7 onto biofilm matrix and activated sludge flocs was found to fit the Langmuir equation. However, there is a significant difference in the adsorption capacities between biofilm and activated sludge. AO7 was recalcitrant in both biofilm and activated sludge systems under aerobic conditions. Under anaerobic conditions, AO7 was readily decolorized. AO7 decolorization was also observed under anoxic conditions. However, the presence of nitrate inhibited AO7 decolorization.     

Removal of organic matter and phosphate using ferrihydrite for reduction of microbial regrowth potential

Dissolved organic matter (DOM) and phosphate in reclaimed water promote microbial growth in distribution systems and deteriorate water quality. In this study, we tested ferrihydrite (Fh) for its potential to remove both DOM and phosphate in order to control bacterial regrowth. Adsorption kinetics on Fh revealed that phosphate has a higher affinity with Fh than has DOM. The removal efficiency of DOM increased at lower pH. Fourier transform infrared spectroscopy (FT-IR) spectra of freeze-dried Fh showed that adsorbed DOM was rich in carboxyl/hydroxyl functional groups, indicating anion exchange at Fh surfaces to be a major mechanism, especially at low pH. Fh preferentially removed DOM greater than 1,000 Da. Specific ultraviolet absorption (SUVA) at 254 nm and DOC results suggest Fh adsorption removes more hydrophilic DOM than the coagulation-sand filtration process. Reduction of bacterial regrowth potential (BRP) by Fh was comparable to that of the coagulation-sand filtration process, which indicated that phosphorus was not the rate-limiting factor of microbial growth.     

Biological nutrient removal in simple dual sludge system with an UMBR (upflow multi-layer bioreactor) and aerobic biofilm reactor.

In this study, a simple dual sludge process was developed for small sewage treatment. It is a hybrid system that consists of upflow multi-layer bioreactor (UMBR) as anaerobic and anoxic reactor with suspended growth microorganisms and post aerobic biofilm reactor with inclined plates. UMBR is a multifunction reactor that acts as primary sedimentation tank, anaerobic reactor, anoxic reactor, and thickener. The sludge blanket in the UMBR is maintained at a constant level by automatic control so that clear water (30 mg-SS/L) can flow into the post aerobic biofilm reactor. It leads to improving performance of the biofilm reactor due to preventing of excess microbial attachment on the media surface and no requirment for a large clarifier caused by low solid loading. The HRT in the UMBR and the aerobic biofilm reactor were about 5.8 h and 6.4 h, respectively. The temperature in the reactor during this study varied from 12.5 degrees C to 28.3 degrees C. The results obtained from this study show that effluent concentrations of TCOD, TBOD, SS, TN, and TP were 29.7 mg/L, 6.0 mg/L, 10.3 mg/L, 12.0 mg/L, and 1.8 mg/L, which corresponded to a removal efficiency of 92.7%, 96.4%, 96.4%, 74.9%, and 76.5%, respectively. The sludge biomass index (SBI) of the excess sludge in the UMBR was about 0.55, which means that the sludge in the UMBR was sufficiently stabilized and may not require further treatment prior to disposal.     

新开河4种水生植物表面附着微生物群落特征

以水生植物金鱼藻、伊乐藻、萍蓬草和菱角为研究对象,利用扫描电镜、荧光显微镜和16S rRNA高通量测序技术,探究不同水生植物表面微生物群落特征。结果表明:沉水植物表面附生藻类密度比浮叶植物的高,且植物表面附生藻类组成与周围水体明显不同;浮叶植物萍蓬草和菱角根部的微生物群落结构与其叶表面的差异较大。4种水生植物表面附着细菌群落优势门类依次为变形菌门、厚壁菌门、绿弯菌门、拟杆菌门、酸杆菌门和疣微菌门,具有水体污染物质净化功能;两种类型水生植物表面附着有大量微生物,且不同植物之间和同种植物不同器官之间的优势种存在一定的差异。     

Modelling the competition of planktonic and sessile aerobic heterotrophs for complementary nutrients in biofilm reactor.

A comprehensive, simplified microbial biofilm model was developed to evaluate the impact of bioreactor operating parameters on changes in microbial population abundance. Biofilm simulations were conducted using three special cases: fully penetrated, internal mass transfer resistance and external mass transfer resistance. The results of model simulations showed that for certain operating conditions, competition for growth limiting nutrients generated oscillations in the abundance of planktonic and sessile microbial populations. These oscillations resulted in the violation of the competitive exclusion principle where the number of microbial populations was greater than the number of growth limiting nutrients. However, the operating conditions which impacted microbial community diversity were different for the three special cases. Comparing the results of model simulations for dispersed-growth, biofilms and bioflocs showed that oscillations and microbial community diversity were a function of competition as well as other key features of the ecosystem. The significance of the current study is that it is the first to examine competition as a mechanism for controlling microbial community diversity in biofilm reactors.     

Coliforms and other microbial indicators occurrence in water and biofilm in full-scale distribution systems.

Biofilm and microbial water quality were studied in four middle size full-scale distribution systems (DS) in France serving 5,000-30,000 inhabitants (maximum residence time 23-160h) through three sampling campaigns over 1 year. Three of these DSs were chosen because of a quite high occurrence of bacterial indicators (i.e. total coliforms), the last DS was considered as a reference. Biofilm was studied on cast iron coupons incubated for more than 1 month in devices continuously fed with water from the DS in conditions imitating those met in DS. The devices were located at different points (4-6) along each DS. The abundance of bacteria in biofilm was estimated by heterotrophic plate counts (HPC) after detachment of the biofilm from the support by sonication. Microbiological water quality was estimated in parallel; analysis of total coliforms, E. coli, enterococci and anaerobic sulphide-reducing bacteria spores (ASRB spores) was carried out in biofilm and water. Over the period of the study, 171 water samples and 57 biofilm samples were collected. Over these 171 waters, 19 (11%) were positive for at least one of the measured indicators while two biofilm samples were positive (3.5%). Significant differences were observed in the levels of contamination between the DSs. High residence time in the DS, low disinfectant residual and high temperature increased the risk of indicator occurrence in the water phase. Due to the low number of biofilm samples positive for bacterial indicators, the data collected in the present study did not allow observation of a direct association between biofilm and water contaminations, even if the occurrence of indicators in water appeared on DSs with the highest density of biofilm (HPC).     

Functional analysis of microbial community in phenol-degrading aerobic granules cultivated in SBR.

Phenol-degrading aerobic granules were cultivated in a sequencing batch reactor with an influent phenol concentration of 500 mg l(-1). Eight strains were isolated from aerobic granules to characterize the functional redundancy of the microbial community in the granules. The specific oxygen utilization kinetics show the eight strains possessed different phenol-degrading activities, with half-saturation constants (Ks) ranging from 0.4 to 70.5 mg phenol l(-1). Two isolates belonging to dominant populations expressed differing functions. The first strain was linked to the function of phenol degradation as this strain has the highest phenol-degrading ability among all isolates, while the second strain was linked to the maintenance of the granule structure because of its strong self-flocculation activity. This study could be used to exploit the granule-based system for treating high-strength wastewaters.     

Dewatering and disinfection of aerobic and anaerobic sludge using an electrokinetic (EK) system

The objectives of the study were to upgrade sewage sludge to Class A Exceptional Quality biosolids (as defined by US EPA) using an electrokinetics dewatering system. The pathogens monitored were Salmonella spp, and fecal coliforms (FC). Ten bench-scale electrokinetic cells were set up for the disinfection of the following sludges: primary, secondary (attached growth culture and suspended culture), and anaerobically digested sludge. A conditioning liquid was also added to five cells. Blower system to aid in dewatering and drying was used in in four EK cells. Sludge characteristics such as water content, volatile solids content, sulfate and chloride ions concentrations, FC and Salmonella spp. before and after the tests were monitored. The highest total solids content (98% TS) was achieved in the cell with the low voltage gradient, in the presence of the conditioner and with the blower system. An average reduction by 50% of volatile solids was observed. The highest, 11 log-reduction of Salmonella spp. was observed in a cell with anaerobically digested sludge. No fecal coliforms were observed in any of the cells after EK treatment.     

Characterization of bacterial biofilm communities in tertiary treatment processes for wastewater reclamation and reuse

The concern with wastewater reuse as a sustainable water resource in urban areas has been growing. For the reclamation and distribution of wastewater, biofilm development deserves careful attention from the point of view of its promotion (e.g. biofiltration) and inhibition (e.g. clogging and hygiene problems). As the first step to control biofilm development, bacterial biofilm communities in tertiary treatment processes were characterized by using molecular biological methods. The result of clone library analysis showed that Nitrospirae-related (nitrite-oxydizing bacteria) and Acidobacteria-related (probably oligotrophic bacteria) groups were dominant. The ratio of the Nitrospirae-related group to the Acidobacteria-related group was associated with ammonia load, whereas other operational conditions (process, media, temperature, salt) did not clearly affect the phylum-level community or the dominant sequence of nitrifying bacteria. The result of real-time PCR also indicated that high ammonia load promotes the proliferation of nitrite- and ammonia-oxidizing bacteria. Regarding water supply systems, some researchers also have suggested the dominance of Nitrospirae- and Acidobacteria-related groups in biofilm formed on water distribution pipes. In tertiary wastewater treatment, therefore, it is concluded that oligotrophic and autotrophic bacteria are the dominant groups in biofilm samples because assimilable organic carbon is too poor to proliferate various heterotrophic bacteria.     

Evaluation of biofilm performance as a protective barrier against biocorrosion using an enzyme electrode

Sulfide is known to be an important factor in microbiologically influenced corrosion (MIC) of metals and concrete deterioration in wastewater treatment structures and sewer pipelines. A sulfide biosensor was used to determine the effectiveness of Escherichia coli DH5 alpha biofilm as a protective barrier against MIC. The biofilm was shown to be effective in protecting surfaces from sulfide and helping to reduce MIC using amperometric measurements. The results also indicated that the growth conditions of E. coli DH5 alpha may have an impact on the performance of the biofilm as a sulfide barrier. The simple method provided in this work enables the comparison of several microbial biofilms and selection of the ones with potential to prevent MIC in a relatively short time.     

Treatment of paper mill effluent using an anaerobic/aerobic hybrid side-stream membrane bioreactor

This paper presents the design and operational performance data of an anaerobic/aerobic hybrid side-stream Membrane Bioreactor (MBR) process for treating paper mill effluent operated over a 6 month period. The paper mill effluent stream was characterized by a chemical oxygen demand (COD) range of between 1,600 and 4,400 mg/L and an average BOD of 2,400 mg/L. Despite large fluctuations in COD feed concentration, stable process performance was achieved. The anaerobic Expanded Granular Sludge Bed (EGSB) pre-treatment step effectively lowered the organic loading by 65 to 85%, thus lowering the MBR COD feed concentration to consistently below 750 mg/L. The overall MBR COD removal was consistent at an average of 96%, regardless of the effluent COD or changes in the hydraulic retention time (HRT) and organic loading rate (OLR). Combining a high-rate anaerobic pre-treatment EGSB with a Modified Ludzack-Ettinger (MLE) MBR process configuration produced a high quality permeate. Preliminary NF and RO results indicated an overall COD removal of around 97 and 98%, respectively.     

淡水湖泊微生物硝化反硝化过程与影响因素研究

简述了参与硝化反硝化过程的微生物类型及其影响因素,指出湖泊中底栖动物提高了沉积物中氨氧化菌的丰度,加快了沉积物和上覆水反硝化过程,同时底栖动物的肠道也是反硝化场所并释放N2O。研究淡水湖泊中硝化反硝化微生物群落结构组成及多样性,阐述硝化反硝化的分子生物学机制,探索底栖动物对参与氮循环微生物群落结构与功能影响。     

A one-stage system with partial nitritation and anammox processes in the moving-bed biofilm reactor.

The ability of bacterial cultures to create biofilm brings a possibility to enhance biological wastewater treatment efficiency. Moreover, the ability of Anammox and Nitrosomonas species to grow within the same biofilm layer enabled a one-stage system for nitrogen removal to be designed. Such a system, with Kaldnes rings as carriers for biofilm growth, was tested in a technical pilot plant scale (2.1 m(3)) at the Himmerfj?rden Waste Water Treatment Plant (WWTP) in the Stockholm region. The system was directly supplied with supernatant originating from dewatering of digested sludge containing high ammonium concentrations. Nearly 1-year of operational data showed that during the partial nitritation/Anammox process, alkalinity was utilised parallel to ammonium removal. The process resulted in a small pH drop, and its relationship with conductivity was found. The nitrogen removal rate for the whole period oscillated around 1.5g N m(-2)d(-1) with a maximum value equal to 1.9 g N m(-2)d(-1). Parallel to the pilot plant experiment, a series of batch tests were run to investigate the influence on removal rates of different dissolved oxygen conditions and addition of nitrite. The highest nitrogen removal rate (5.2g N m(-2)2d(-1)) in batch tests was obtained when the Anammox process was stimulated by the addition of nitrite. In the simultaneous partial nitritation and Anammox process, the partial nitritation was the rate-limiting step.     

Effect of temperature and salinity on the wastewater treatment performance of aerobic submerged fixed bed biofilm reactors.

The influence of temperature (5-35 C) and salinity (up to 20 g/l NaCl) on the wastewater purification process in completely mixed and aerated submerged fixed bed biofilm reactors (SFBBRs) was studied. C- and N-conversion in SFBBRs designed according to the DWA (German Association for Water, Wastewater and Waste) rules for carbon removal was investigated for several months on synthetic wastewater. The DOC degradation rate was even at, according to the DWA, high DOC/BOD loading rates not much affected by temperatures between 5-35 degrees C and salt contents up to 20 g/L NaCl. At these high DOC loadings an appreciable ammonium conversion could also be observed. The ammonium conversion proved to be sensitive to temperature and salinity. At 5 degrees C the ammonium removal rate decreased by a factor of five compared to 25-35 degrees C. Under many operation conditions investigated more than 50% of the converted ammonium was transformed into gaseous nitrogen. The addition of 20 g/L NaCl caused a strong inhibition of the ammonium removal rate over the whole temperature range investigated.