Modelling seasonal dynamics of "Microthrix parvicella".

The filamentous bacteria "Microthrix parvicella" can cause serious bulking and scumming in wastewater treatment plants (WWTPs) all over the world. Decades of research have identified Microthrix as a specialized lipid consumer but could not clarify the processes that allow this organism to successfully compete in activated sludge systems. In this study we developed a model, based on ASM3, that describes the pronounced seasonal variations of Microthrix abundance observed in a full-scale WWTP. We hypothesize that low temperatures reduce the solubility of lipids and inhibit their uptake by non-specialized bacteria. The presented model structure and parameters successfully fit the measured data; however they do not necessarily reflect the only and true selection mechanism for Microthrix. This model is not yet to be used for prediction; it is rather a valuable research tool to coordinate the discussion and plan future research activities in order to identify the relevant selection mechanisms favoring Microthrix in activated sludge systems.     

In situ characterization of substrate uptake by Microthrix parvicella using microautoradiography

Microthrix parvicella is a filamentous microorganism responsible for bulking and foaming problems in many activated sludge treatment plants. The problems have increased with the introduction of nutrient removal in many countries, and presently, there is no reliable control strategy for M. parvicella. Little is known about the physiology of M. parvicella, and conflicting data exist about its preferred organic substrates, and whether it is able to be physiologically active under anaerobic and anoxic conditions. In this study, the ability of M. parvicella to take up various radioactively labeled organic compounds was investigated in situ at three nutrient removal plants using a microautoradiographic technique. Of 12 compounds tested under aerobic conditions only the long chain fatty acids (LCFA), oleic acid and palmitic acid, and to some extent a lipid, trioleic acid, were assimilated. None of the simple substrates such as acetate, propionate, butyrate, glucose, ethanol, glycine and leucine were taken up. Furthermore, the uptake of oleic acid was compared under anaerobic, anoxic and aerobic conditions, and it was demonstrated that in addition to aerobic conditions M. parvicella was also able to take up oleic acid under anaerobic and anoxic conditions. No difference in substrate uptake pattern for M. parvicella was found among the tested activated sludge plants. The results strongly indicate that a better control strategy against M. parvicella must rely on a better understanding of presence and availability of triglycerides and LCFA, and an improved knowledge of the physiology of M. parvicella under anaerobic and anoxic conditions.     

Influence of temperature and sludge loading on activated sludge settling,especially on Microthrix parvicella

During recent years modern full scale wastewater treatment plants with biological nitrification, denitrification and phosphorus removal have had increasing problems with foam formation on the surfaces of aerobic tanks and with bulking activated sludge. The results of a survey in 1995 (Kunst and Knoop, 1996) showed that most often the filamentous bacterium Microthrix parvicella is responsible for these problems. Up to today there is only little knowledge about its selection criteria in activated sludge. Therefore several expenments were done in full scale activated sludge plants and in laboratory systems under defined conditions to investigate the influence of low (< 0.1 kg/(kg·d)) and high (≤ 0.2 kg/(kg·d)) BOD₅-sludge loading rates on the growth and morphology of M. parvicella and the settlement of activated sludge. Furthermore the influence of temperatures of 5°C, 12°C and 20°C on the growth of M. parvicella was investigated. It was shown that M. parvicella grows at low BOD₅-sludge loading rate and low temperature and is the main causative organism of bulking and foaming sludge in nutrient removal plants. On the basis of this investigation it was concluded that the growth of M. parvicella and the settling problems of the activated sludge resulting from excessive growth of this filament will always appear in modern municipal wastewater treatment plants with BOD₅-sludge loading rate ≤ 0.1 kg/(kg·d) especially under low temperature conditions.     

Causes of,and control strategies for,Microthrix parvicella bulking and foaming in nutrient removal activated sludge systems

Bench and pilot scale nutrient removal activated sludge units were used to examine the effect of factors such as temperature, substrate type (easily biodegradable in the form of acetate and slowly biodegradable in the form of oleic acid) on Microthrix parvicella growth. The configurations examined include complete mix with and without selectors (anoxic and anaerobic) and plug flow reactors. The results indicate that low temperatures and substrates in the form of long chain fatty acids favour the growth of M. parvicella. With respect to reactor configuration, a plug flow configuration was shown to be quite effective in controlling the growth of M. parvicella and producing a sludge with good settling characteristics, while the presence of a selector, either anoxic or anaerobic, had no significant effect on the growth of M. parvicella.     

Comparison of microbial activity in anaerobic and microaerobic digesters

Microaerobic alternative of anaerobic digestion offers many advantages especially when sulfide concentration in the digester is high. For better understanding of the microaerobic technology more detailed characterization of biomass activity is needed. Two equal digesters were operated under the same condition except of microaeration in one of them. During long term operation of anaerobic and microaerobic digesters the sludge quality and the biomass activity was monitored. The activity of sulfide oxidizing bacteria of microaerobic biomass was significantly higher in comparison with anaerobic biomass. The activity of sulfate reducing bacteria was comparable. The activity of methanogenic bacteria activity depended on sulfide concentration more than on microaeration. The extent of foaming problems was lower in the microaerobic than in the anaerobic digester.     

Self-heating of anaerobic digesters using energy crops.

With the increasing application of energy crops in agricultural biogas plants and increasing digester volumes, the phenomenon of self-heating in anaerobic digesters appeared in some cases. Until now this development was just known from aerobic systems. To obtain an idea of the thermodynamics inside an anaerobic digester, a detailed analysis of all heat fluxes in a full-scale agricultural biogas plant was carried out. Several experiments were realised to quantify the influences of different internal and external energy sources. To estimate the impact of self-heating in anaerobic systems, data of other full-scale agricultural biogas plants in Austria were collected. Alternatives to the cooling of the digesters are discussed based on individual experiences of several plants. A connection between carbohydrate-rich substrates, especially with high starch contents, and the self-heating could be shown. From the results it can be assumed that the anaerobic digestion of most energy crops is exothermic, which is in contrast to the current thermodynamic belief.     

Syntrophic acetate oxidation in two-phase (acid-methane) anaerobic digesters

The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2-5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, 'Syntrophaceticus schinkii,' and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production/degradation and methane generation observed in the laboratory-scale AP reactor. The model was validated with historical data from the full-scale digesters.     

State estimation for anaerobic digesters using the ADM1

The optimization of full-scale biogas plant operation is of great importance to make biomass a competitive source of renewable energy. The implementation of innovative control and optimization algorithms, such as Nonlinear Model Predictive Control, requires an online estimation of operating states of biogas plants. This state estimation allows for optimal control and operating decisions according to the actual state of a plant. In this paper such a state estimator is developed using a calibrated simulation model of a full-scale biogas plant, which is based on the Anaerobic Digestion Model No.1. The use of advanced pattern recognition methods shows that model states can be predicted from basic online measurements such as biogas production, CH4 and CO2 content in the biogas, pH value and substrate feed volume of known substrates. The machine learning methods used are trained and evaluated using synthetic data created with the biogas plant model simulating over a wide range of possible plant operating regions. Results show that the operating state vector of the modelled anaerobic digestion process can be predicted with an overall accuracy of about 90%. This facilitates the application of state-based optimization and control algorithms on full-scale biogas plants and therefore fosters the production of eco-friendly energy from biomass.     

Lessons learnt from 15 years of ICA in anaerobic digesters.

Anaerobic digestion plants are highly efficient wastewater treatment processes with inherent energy production. Despite these advantages, many industries are still reluctant to use them because of their instability confronted with changes in operating conditions. There is therefore great potential for application of instrumentation, control and automation (ICA) in the field of anaerobic digestion. This paper will discuss the requirements (in terms of on-line sensors needed, modelling efforts and mathematical complexity) but also the advantages and drawbacks of different control strategies that have been applied to AD high rate processes over the last 15 years.     

Autotrophic nitrogen removal from anaerobic supernatant of Florence's WWTP digesters.

In municipal WWTP with anaerobic sludge digestion, 10-20% of total nitrogen load comes from the return supernatant produced by the final sludge dewatering. In recent years a completely autotrophic nitrogen removal process based on Anammox biomass has been tested in a few European countries, in order to treat anaerobic supernatant and to increase the COD/N ratio in municipal wastewater. This work reports the experimental results of the SHARON-ANAMMOX process application to anaerobic supernatant taken from the urban Florentine area wastewater treatment plant (S. Colombano WWTP). A nitritation labscale chemostat (7.4 L) has been started-up seeded with the S. Colombano WWTP nitrifying activated sludge. During the experimental period, nitrite oxidising bacteria wash-out was steadily achieved with a retention time ranging from 1 to 1.5 d at 35 degrees C. The Anammox inoculum sludge was taken from a pilot plant at EAWAG (Zurich). Anammox biomass has been enriched at 33 degrees C with anaerobic supernatant diluted with sodium nitrite solution until reaching a maximum specific nitrogen removal rate of 0.065 kgN kg(-1) VSS d(-1), which was 11 times higher than the one found in inoculum sludge (0.005 kgN kg(-1) VSS d(-1). In a lab-scale SBR reactor (4 L), coupled with nitritation bioreactor, specific nitrogen removal rate (doubling time equal to 26 d at 35 degrees C and at nitrite-limiting condition) reached the value of 0.22 kgN kg(-1) VSS d(-1), which was approximately 44 times larger than the rate measured in the inoculum Anammox sludge.     

Determination of long chain fatty acids in anaerobic digesters using a rapid non-derivatisation GC-FID method

A rapid non-derivatisation gas chromatographic (GC) method for quantification of palmitic, stearic and oleic acids was achieved using a flame ionisation detector and a highly polar capillary column at elevated temperature. These long chain fatty acids (LCFA) can accumulate in anaerobic digesters and a simple extraction method was also developed to permit a more rapid sample turn-around time, facilitating more frequent monitoring. The GC method was satisfactory in terms of peak separation, signal response, reproducibility and linearity range. The extraction method achieved recoveries of 103.8, 127.2 and 84.2% for palmitic, stearic and oleic acid respectively. The method was tested on digestate from mesophilic laboratory-scale digesters fed with source-segregated domestic food waste, and showed good repeatability between replicate samples. It was observed that the concentrations of stearic and palmitic acid in digesters routinely supplemented with trace elements were lower in proportion to the applied lipid loading than those without supplementation.     

Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters.

Anaerobic digestion of concentrated domestic wastewater streams--black or brown water, and solid fraction of kitchen waste is considered as a core technology in a source separation based sanitation concept (DESAR--decentralised sanitation and reuse). A simple anaerobic digester can be implemented for an enhanced primary treatment or, in some situations, as a main treatment. Two reactor configurations were extensively studied; accumulation system (AC) and UASB septic tank at 15, 20 and 25 degrees C. Due to long retention times in an AC reactor, far stabilisation of treated medium can be accomplished with methanisation up to 60%. The AC systems are the most suitable to apply when the volume of waste to be treated is minimal and when a direct reuse of a treated medium in agriculture is possible. Digested effluent contains both liquid and solids. In a UASB septic tank, efficient separation of solids and liquid is accomplished. The total COD removal was above 80% at 25 degrees C. The effluent contains COD and nutrients, mainly in a soluble form. The frequency of excess sludge removal is low and sludge is well stabilised due to a long accumulation time.     

厌氧-生物托盘系统处理生活污水试验研究

针对分散建筑的特点,厌氧-生物托盘系统对生活污水进行了处理试验,分析研究了处理系统污染物的去除效果,COD去除率为90%以上,SS为85%以上,NH3-N为80%以上,TP为80%以上,出水水质各项指标达到中水回用的要求。     

Winery and distillery wastewater treatment by anaerobic digestion.

Anaerobic digestion is widely used for wastewater treatment, especially in the food industries. Generally after the anaerobic treatment there is an aerobic post-treatment in order to return the treated water to nature. Several technologies are applied for winery wastewater treatment. They are using free cells or flocs (anaerobic contact digesters, anaerobic sequencing batch reactors and anaerobic lagoons), anaerobic granules (Upflow Anaerobic Sludge Blanket--UASB), or biofilms on fixed support (anaerobic filter) or on mobile support as with the fluidised bed. Some technologies include two strategies, e.g. a sludge bed with anaerobic filter as in the hybrid digester. With winery wastewaters (as for vinasses from distilleries) the removal yield for anaerobic digestion is very high, up to 90-95% COD removal. The organic loads are between 5 and 15 kgCOD/m3 of digester/day. The biogas production is between 400 and 600 L per kg COD removed with 60 to 70% methane content. For anaerobic and aerobic post-treatment of vinasses in the Cognac region, REVICO company has 99.7% COD removal and the cost is 0.52 Euro/m3 of vinasses.     

Disruption of granules by hydrodynamic force in internal circulation anaerobic reactor.

A process of granule disruption by hydrodynamic force is discussed in this paper. Shear force and attrition among granules originated from hydrodynamic force are the main causes of the disruption. Since it is positively correlated to the attrition force, the shear force is utilized to describe the effect of hydrodynamic force on granule disruption. In the experiment, when increase rate of average shear rate (IRgamma) of the 1st stage is about 0.2 s(-1) x d(-1), the granules are disrupted; while re-granulation could develop when IRgamma is about 0.07 s(-1) x d(-1); even when the shear rate is as high as about 30s(-1), the granulation rate keeps stably at a relatively high level, which shows that granules could bear the high hydrodynamic force only if it increases by low increase rate. The experimental results would be valuable for the operation and controlling of the upflow reactors.     

串联厌氧生物滤池处理城市污水的试验研究

对常温下采用弹性立体填料的厌氧生物滤池和采用砾石填料的厌氧生物滤池串联处理生活污水的适用性、设计运行参数及环境因素的影响进行了研究。结果表明,用污水处理厂二沉池回流污泥对厌氧生物滤池进行接种后,利用污水处理厂钟式沉砂池作为原水,厌氧生物滤池可以在常温（18～25℃）条件下成功启动,有效地去除有机物,并且能承受水质水量波动引起的负荷冲击。除处理出水除氮磷等指标外．其余指标均能达到污水综合排放一级标准。     

曲靖市暴雨洪水特性分析

根据曲靖市的自然地理状况，对全市主要河流按流域分片，结合水文站、雨量站的分布情况，利用实测资料分析片区内暴雨洪水特性，探索暴雨洪水规律，为曲靖市防洪减灾和水资源配置提供科学依据。     

Modeling microbial diversity in anaerobic digestion

The aim of this study is to develop a modeling approach able to handle microbial diversity both in normal and abnormal situations. Normal situations are defined as changing input characteristics that do not imply process imbalance while abnormal situations are illustrated by the presence of toxicant into the reactor. In both cases, modeling is performed by adding a stochastic term on top of a well defined and well structured model such as the IWA Anaerobic Digestion Model No1. Experimental data from a 1 m3 pilot scale anaerobic digester treating wine distillery wastewater are provided to demonstrate the applicability of this approach. Discussion also highlights that monitoring of digesters might receive a renewed consideration in the near future in order to handle explicitly microbial diversity within the control objectives.     

Prion protein: detection in 'spiked' anaerobic sludge and degradation experiments under anaerobic conditions.

The behavior of the transmissible spongiform encephalopathies (TSE) causing agent denominated "prion protein" in anaerobic sludge (biogas reactor) was assessed with incubation tests. A widely applied screening method for BSE in cattle on the basis of the Western blotting protocol was adapted to detect the Proteinase K resistant, scrapie-form prion protein (PrPSC). As PrPsc source homogenized TSE infected brain tissue of animals late in the clinical phase of disease was taken (301V/VM mouse-BSE; bovine BSE and 22A/SV mouse-scrapie). The incubation under mesophilic conditions did not show any significant reduction of the PrPsc titer. Under thermophilic conditions contradictory results were obtained. The reduction time of PrPsc in water was equal to or longer than the PrPsc reduction time in anaerobic sludge. In comparison, with sterilized (121 degrees C, steam pressure) or poisoned (sodium azide, 1% w/v) sludge used as incubation matrix a much shorter time resulted until no prion protein could be detected.