Novel method for enhancing permeate flux of submerged membrane system in two-phase anaerobic reactor

A two-phase anaerobic reactor system with a submerged membrane in the acidogenic reactor was designed for the enhancement of organic acid conversion and methane recovery. A submerged membrane system in a two-phase anaerobic reactor was tested to increase the sludge retention time (SRT) of acidogen and to enhance the solid separation. The pilot plant experiment was performed for piggery wastewater treatment for a year. The membrane material used was mixed esters of cellulose of 0.5 micron pore size. COD removal efficiency was 80% and the methane production showed 0.32 m3/kg COD removed for the submerged membrane system in the anaerobic digester. As the cake resistance of the membrane caused a serious problem, a stainless-steel prefilter and air backwashing methods were applied to minimize the cake resistance effectively. Among the tested prefilters, the 63 microns pore prefilter showed the best performance for reducing cake resistance and a successful long-term operation. By cleaning with alkali first and acidic solutions later, the permeate flux decreased by long-term operation was recovered to 89% of that with a new membrane.     

A survey of municipal anaerobic sludge digesters and diagnostic activity assays

A plant site survey was made of 30 municipal wastewater treatment plants concerning the operational characteristics of their anaerobic sludge digesters. Design information, operating data and analytical data were tabulated. Samples of each sludge were then assayed to determine the residual gas production rate, the maximum potential acetate and propionate utilization rates, the 5 and 30 day biochemical methane potential (BMP₅) (BMP₃₀) and the possible limitation in bioavailability of iron, cobalt or nickel.The average solids content of the raw sludge fed to the digesters was 4. 7%. Eight of the 30 sludges showed stimulation in the gas production rate when iron, cobalt or nickel was supplemented and acetate was unlimiting. Nine of the 30 sludges showed stimulation in the gas production rate when iron, cobalt or nickel was supplemented and propionate was unlimiting.The average BMP₅ was 0. 7 volumes of methane per volume of sludge. The average BMP₃₀ was 1.9 vol CH₄/vol sludge. On average 87% of the biodegradable fraction of the sludge was converted to methane during digestion. The average maximum potential acetate utilization rate (MPAUR) was 0.93 vol CH₄/vol sludge-day. The average maximum potential propionate utilization rate (MPPUR) was 0.18 vol CH₄ /vol sludge-day. The average H₂S in the digester gas was 2200 ppm. The average digester capacity was 0.14 million gallons/million gallons per day (MG/MGD) of raw wastewater. On average the raw sludge pumping rate was 4300 gal per MG of raw wastewater. The average digester gas production was 0.066 vol gas/vol of raw wastewater (8800 ft³ per MG). The average unit gas production rate was 0. 64 volumes of digester gas per volume of digester per day. The average volume of digester gas produced per volume of raw sludge feed was 15. 8 v/v. The average gas production per pound of volatile solids added was 0. 46 m³ kg⁻¹ VS (7. 4 ft³ lb⁻¹ VS). The average gas production per pound of volatile solids destroyed was 0. 94 m³ kg⁻¹ VS (15. 0 ft³ lb⁻¹ VS).     

无接种污泥的厌氧消化系统启动策略研究

以国内最大的污泥厌氧消化系统--上海市白龙港污水处理厂厌氧消化系统的调试启动为依托,研究了两种无污泥接种启动方案的效果.当消化罐内的初始状态为原污泥,且在10 d后以不同投配率投加原污泥时,约需25 d便可实现系统的成功启动,但启动过程中存在酸化的风险,而采用变投配率方式投加污泥可以在一定程度上缓解VFA的积累.当消化罐内的初始状态为清水,且在之后以不同投配率投加原污泥时,用时超过40 d才可成功启动系统,且污泥浓度达到设计值所需的时间较长,不过其酸化风险较小.该研究成果可为白龙港污水处理厂的污泥厌氧消化系统及国内同类工程的启动提供借鉴.     

Optimisation of sludge line management to enhance phosphorus recovery in WWTP

The management of the sludge treatment line can be optimized to reduce uncontrolled phosphorus precipitation in the anaerobic digester and to enhance phosphorus recovery in WWTP. In this paper, four operational strategies, which are based on the handling of the prefermented primary sludge and the secondary sludge from an EBPR process, have been tested in a pilot plant. The separated or mixed sludge thickening, the use of a stirred contact tank and the elutriation of the thickened sludge are the main strategies studied. Both the reduction of phosphorus precipitation in the digester and the supernatant suitability for a struvite crystallization process were assessed in each configuration. The mixed sludge thickening combined with a high flowrate elutriation stream reduced the phosphorus precipitation in the digester by 46%, with respect to the separate sludge thickening configuration (common practice in WWTP). Moreover, in this configuration, 68% of the soluble phosphorus in the system is available for a possible phosphorus recovery process by crystallization (not studied in this work). However, a high Ca/P molar ratio was detected in the resultant supernatant which is pointed out as a problem for the efficiency of struvite crystallization.     

Investigation of the sludge reduction mechanism in the anaerobic side-stream reactor process using several control biological wastewater treatment processes

To investigate the mechanism of sludge reduction in the anaerobic side-stream reactor (SSR) process, activated sludge with five different sludge reduction schemes were studied side-by-side in the laboratory. These are activated sludge with: 1) aerobic SSR, 2) anaerobic SSR, 3) aerobic digester, 4) anaerobic digester, and 5) no sludge wastage. The system with anaerobic SSR (system #2) was the focus of this study and four other systems served as control processes with different functions and purposes. Both mathematical and experimental approaches were made to determine solids retention time (SRT) and sludge yield for the anaerobic SSR process. The results showed that the anaerobic SSR process produced the lowest solids generation, indicating that sludge organic fractions degraded in this system are larger than other systems that possess only aerobic or anaerobic mode. Among three systems that involved long SRT (system #1, #2, and #5), it was only system #2 that showed stable sludge settling and effluent quality, indicating that efficient sludge reduction in this process occurred along with continuous generation of normal sludge flocs. This observation was further supported by batch anaerobic and aerobic digestion data. Batch digestion on sludges collected after 109 days of operation clearly demonstrated that both anaerobically and aerobically digestible materials were removed in activated sludge with anaerobic SSR. In contrast, sludge reduction in the aerobic SSR process or no wastage system was achieved by removal of mainly aerobically digestible materials. All these results led us to conclude that repeating sludge under both feast/fasting and anaerobic/aerobic conditions (i.e., activated sludge with anaerobic SSR) is necessary to achieve the highest biological solids reduction with normal wastewater treatment performance.     

Effect of ultrasound pretreatment in mesophilic and thermophilic anaerobic digestion with emphasis on naphthalene and pyrene removal

In many anaerobic digestion processes for the treatment of the sludge produced in wastewater treatment plants, the hydrolysis of the organic matter has been identified as the rate limiting step. This study is focused on the effect of ultrasonic pretreatment of raw sewage sludge before being fed to the mesophilic and the thermophilic anaerobic digestion. From particle size reduction, COD disintegration degree and biodegradability test, 11,000kJ/kg TS was estimated as the optimal specific energy in ultrasonic pretreatment. Moreover, the use of pretreated sludge improved significantly the COD removal efficiency and biogas production in lab-scale anaerobic digesters when compared with the performance without pretreatment, specially under mesophilic conditions. During ultrasonic pretreatment, the diffusion of polycyclic aromatic hydrocarbons (PAH) compounds to the aqueous phase was stated by a reduction in the pretreated sludge micropollutants content. With sonication, naphthalene was better removed than without this pretreatment, particularly in the mesophilic digester. However, pyrene removal remained at same efficiency level with and without ultrasonic pretreatment.     

The effect of sludge digestion on virus infectivity

The rate of inactivation of coxsackievirus B3 during anaerobic sludge digestion was found to be 2 log units in 24 h at pH 7.0 and 35°C. The rate indicates that virus inactivating factor(s) were produced in the digestion. The virus inactivation was enhanced if the digester sludge was pasteurized at 60°C for 1 h. The reason why digesters at sewage treatment plants do not completely inactivate virus is discussed in terms of the continuous nature of digester operation.     

Anaerobic sewage treatment in a one-stage UASB reactor and a combined UASB-Digester system

The treatment of sewage at 15 degrees C was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-Digester system. The latter consists of a UASB reactor complemented with a digester for mutual sewage treatment and sludge stabilisation. The UASB reactor was operated at a hydraulic retention time of 6h and a controlled temperature of 15 degrees C, the average sewage temperature during wintertime of some Middle East countries. The digester was operated at 35 degrees C. The UASB-Digester system provided significantly (significance level 5%) higher COD removal efficiencies than the one-stage UASB reactor. The achieved removal efficiencies in the UASB-Digester system and the one-stage UASB reactor for total, suspended, colloidal and dissolved COD were 66%, 87%, 44% and 30%, and 44%, 73%, 3% and 5% for both systems, respectively. The stability values of the wasted sludge from the one-stage UASB reactor and the UASB-Digester system were, respectively, 0.47 and 0.36g CH(4)-COD/g COD. Therefore, the anaerobic sewage treatment at low temperature in a UASB-Digester system is promising.     

德国某污水厂浓缩工艺选型案例分析

为了研究最佳的污泥浓缩工艺,德国某污水厂对螺旋式、转鼓式、离心式、带式等7种不同的污泥浓缩机进行了运行性能和费用的对比试验.结果表明,在浓缩机最小处理量为30m3/h、每天24 h连续运行、出泥含固率控制在5%～6%、固体回收率>90%的前提下,某带式浓缩机运行效果好且费用低,是最适合该污水厂的污泥浓缩机;该带式浓缩机的处理量为100 m3/h,药耗约为2.5 g/kgDS,电耗约为0.12 kW·h/m3.     

Preliminary Results of the Anaerobic Biotreatability of the Effluent from the Wet-Air Oxidation of Sewage Sludge

Wet air oxidation and other thermal processes can be used on all sludges, whether they are raw, mixed or digested. The process sterilizes the sludge and gives a considerable reduction in volume. However, apart from the high capital costs which are associated with this technique, one of its principal disadvantages is the high strength of the (effluent) liquor.
This study investigated the feasibility of treating the liquor using an anaerobic digester, which resulted in a good reduction in BOD and a reasonable reduction in COD. The liquor was still strong, but could be returned to the inlet works of a sewage-treatment plant without causing significant organic overloading.     

浓缩时间对污泥浓缩效果、磷释放及去除的影响

针对城市污水厂剩余污泥浓缩过程中浓缩时间对浓缩效果、磷释放及去除的影响进行试验研究。结果表明:对已建有重力浓缩池的城市污水处理厂且污水厂处理能力存有一定富余时,可适当延长浓缩池的污泥浓缩时间,这既可大大提高浓缩池出泥的含固率,又可大部保留污泥中的含磷量,且不会对污水厂除磷产生不良影响。     

厌氧消化设备成套配置问题探讨

总结漳州市污水处理厂11000m3蛋形消化罐污泥中温厌氧消化、沼气利用成套设备配置方案,对设备成套的采购与配置存在问题进行探讨,分析提高成套设备优化配置效益的途径。     

An ASM/ADM model interface for dynamic plant-wide simulation

Mathematical modelling has proven to be very useful in process design, operation and optimisation. A recent trend in WWTP modelling is to include the different subunits in so-called plant-wide models rather than focusing on parts of the entire process. One example of a typical plant-wide model is the coupling of an upstream activated sludge plant (including primary settler, and secondary clarifier) to an anaerobic digester for sludge digestion. One of the key challenges when coupling these processes has been the definition of an interface between the well accepted activated sludge model (ASM1) and anaerobic digestion model (ADM1). Current characterisation and interface models have key limitations, the most critical of which is the over-use of X_c (or lumped complex) variable as a main input to the ADM1. Over-use of X_c does not allow for variation of degradability, carbon oxidation state or nitrogen content. In addition, achieving a target influent pH through the proper definition of the ionic system can be difficult. In this paper, we define an interface and characterisation model that maps degradable components directly to carbohydrates, proteins and lipids (and their soluble analogues), as well as organic acids, rather than using X_c. While this interface has been designed for use with the Benchmark Simulation Model No. 2 (BSM2), it is widely applicable to ADM1 input characterisation in general. We have demonstrated the model both hypothetically (BSM2), and practically on a full-scale anaerobic digester treating sewage sludge.     

青岛麦岛污水处理厂污泥消化及热电联产运行管理经验

污泥厌氧消化/热电联产是一项重要节能工艺技术,对于提高资源和能源利用效率意义重大。完善的管理是保证污泥消化及热电联产系统稳定高效运行的关键环节。麦岛污水处理厂将Multiflo~?Trio初沉污泥与生物滤池剩余污泥进行混合,形成沼气产率较高的混合污泥,并进行中温厌氧消化,所产沼气进入热电联产系统用于发电及沼气锅炉,回收余热作为污泥消化及厂区采暖热源。10余年来,麦岛污水处理厂的污泥消化及热电联产系统实现了安全、稳定、高效的运行,保证了污泥的资源化、减量化、无害化处理及利用。介绍了青岛麦岛污水处理厂污泥厌氧消化及热电联产的运行情况,探讨如何在污泥消化及热电联产间做好运行管理和调控,使之形成良性循环。     

Advanced controlling of anaerobic digestion by means of hierarchical neural networks

In this work several feed-forward back propagation neural networks (FFBP) were trained in order to model, and subsequently control, methane production in anaerobic digesters. To produce data for the training of the neural nets, four anaerobic continuous stirred tank reactors were operated in steady-state conditions at organic loading rates (Br) of about 2 kg m(-3) d(-1) chemical oxygen demand, and disturbed by pulse-like increase of the organic loading rate. For the pulses additional carbon sources like flour, sucrose, 1,2-diethylen glycol or vegetable oil were added to the basic feed, which consisted of surplus and primary sludge of a local waste-water treatment plant, to increase the chemical oxygen demand. Measured parameters were: gas composition, methane production rate, volatile fatty acid concentration, pH, redox potential, volatile suspended solids and chemical oxygen demand of feed and effluent. A hierarchical system of nets was developed and embedded in a decision support system to find out which is the best feeding profile for the next time steps in advance. A 3-3-1 FFBP simulated the pH with a regression coefficient of 0.82. A 9-3-3 FFBP simulated the volatile fatty acid concentration in the sludge with a regression coefficient of 0.86. And a 9-3-2 FFBP simulated the gas production and gas composition with a regression coefficient of 0.90 and 0.80, respectively. A lab-scale anaerobic continuous stirred tank reactor controlled by this tool was able to maintain a methane concentration of about 60% at a rather high gas production rate of between 5 and 5.6 m3 m(-3) d(-1).     

卵形消化池预应力筋摩阻损失及张拉伸长值实测

测试了采用游动锚技术的漳州水处理厂卵形消化池工程预应力钢筋的摩阻损失 ,分析了预应力摩阻损失的组成与计算方法。测得了预应力钢筋的伸长值 ,并与理论计算结果进行了对比。分析表明 ,实测值与理论计算值吻合较好 ;游动锚技术可以用来解决类似工程的相关问题     

Fate of pathogens in thermophilic aerobic sludge digestion

The effect of autoheated aerobic thermophilic digestion on the pathogen content of sewage sludges was studied and compared to that of conventional mesophilic anaerobic digestion. Both systems were full scale, continuously-fed facilities operated in parallel and utilized a feed sludge of thickened primary and waste-activated sludge.The relative populations of viruses, Salmonella sp., total and fecal coliforms, fecal streptococci and parasites found before and after digestion were compared. The full scale mesophilic anaerobic digesters were operated at relatively constant conditions, i.e. digester temperature constant at 35°C, and loading rates constant, etc., while the full scale autoheated aerobic digester was operated under a wide range of loading conditions. At all of the conditions studied, the autoheated digester temperature exceeded 45 C. Virus and Salmonella sp. concentrations in the effluent from the aerobic unit were below detectable limits in 10 of 11 samples and 6 of 6 samples, respectively, whereas the anaerobic digester effluent contained detectable numbers of viruses and Salmonella sp. Bacterial indicator counts and parasite concentrations were less in the autoheated digester effluent than in the effluent from the anaerobic digester. It was concluded that the simple autoheated aerobic digestion process could be used to produce a virtually pathogen-free sludge at a cost comparable to that of conventional, mesophilic anaerobic digestion.     

Clear model fluids to emulate the rheological properties of thickened digested sludge

Optimising flow processes in wastewater treatment plants requires that designers and operators take into account the flow properties of the sludge. Moreover, due to increasingly more stringent conditions on final disposal avenues such as landfill, composting, incineration etc., practitioners need to produce safer sludge in smaller quantities. Anaerobic digestion is a key treatment process for solids treatment and pathogen reduction. Due to the inherent opacity of sludge, it is impossible to visualise the mixing and flow patterns inside an anaerobic digester. Therefore, choosing an appropriate transparent model fluid which can mimic the rheological behaviour of sludge is imperative for visualisation of the hydrodynamic functioning of an anaerobic digester.Digested sludge is a complex material with time dependent non-Newtonian thixotropic characteristics. In steady state, it can be modelled by a basic power-law. However, for short-time processes the Herschel-Bulkley model can be used to model liquid-like properties.The objective of this study was to identify transparent model fluids which will mimic the behaviour of real sludge. A comparison of three model fluids, Carboxymethyl Cellulose (CMC), Carbopol gel and Laponite clay revealed that these fluids could each model certain aspects of sludge behaviour. It is concluded that the rheological behaviour of sludge can be modelled using CMC in steady state flow at high shear rates, Carbopol gel for short-time flow processes and Laponite clay suspension where time dependence is dominant.     

EFFECTIVE DESIGN OF GAS-MIXING SYSTEMS FOR THICK SLUDGE DIGESTION: TWO CASE STUDIES

In the UK and elsewhere, advances in the design of anaerobic mesophilic digesters have resulted in a trend towards the digestion of thicker sludges. This includes a number of new facilities using 'bolt-on' technologies such as thermal hydrolysis, pre-pasteurisation and enzymic hydrolysis. Thermal hydrolysis utilises thickened sludge, and the digester is fed with a high dry-solids content (typically 12%), thereby intensifying the digestion process and reducing reactor volumes. However, there is limited experience in the design of digester mixing systems for such applications. As the trend continues towards advanced digestion technology, more emphasis will be placed on the basic unit process operation of mixing.
This paper describes the design of a gas-mixing system for thick feed sludges for two full-scale plants at Mogden and Aberdeen. Mogden is a refurbishment project and Aberdeen is a newly constructed plant.     

宝钢长材坯料生产污泥处理系统的设计

采用调节池/混凝反应槽/絮凝反应池/污泥浓缩池/带式压滤机工艺处理电炉和连铸机净循环旁滤过滤器反冲洗排泥、连铸浊循环水系统斜板除油沉淀器排泥及VOD浊循环水系统斜板沉淀器排泥等的混合钢铁污泥。该系统自2007年9月初调试正常以来,运行良好,泥饼含固率为30%。