On-line estimation of the dissolved zinc concentration during ZnS precipitation in a continuous stirred tank reactor (CSTR).

In this paper a method is presented to estimate the reaction term of zinc sulphide precipitation and the zinc concentration in a CSTR, using the read-out signal of a sulphide selective electrode. The reaction between zinc and sulphide is described by a non-linear model and therefore classical observer theory cannot be applied directly, as this theory was initially developed for linear systems. However, by linear reparametrization of this non-linear system, the linear observer theory can be applied in an effective way. This is illustrated by a zinc sulphide example using real data.     

Parameter analysis of the IWA Anaerobic Digestion Model No. 1 for the anaerobic digestion of blackwater with kitchen refuse.

The IWA anaerobic digestion model No.1 (ADM1) had been successfully applied to the lab-scale mesophilic blackwater anaerobic digestion (BWAD) plant for cases of only blackwater (BW) feeding and of BW plus kitchen refuse (KR) feeding. In this paper, the simulation results of BW + KR anaerobic digestion are presented and discussed, followed by the analyses and discussion of the critical and important parameters as well as the performance of ADM1 based on these results. The raw BW can contain up to 30% short chain fatty acids (SCFA) which severely impact the performance of the model. The model proved that the disintegration/hydrolysis rate of BW is around 4.5 d(-1), which is about ten times higher than that of KR (Kdis,KR = 0.5 d(-1)). ADM1 is not sensitive to the distribution ratio among carbohydrates, proteins and lipids. For BWAD the C4 metabolism can be integrated in the uptake of LCFA. The uptake delay phenomenon was observed and cannot be simulated by ADM1, but it is tolerable. No unique KI,NH3,ac is found out for all investigated ammonia concentration ranges. Meanwhile, ADM1 is not sensitive to KLa and kp1 so they can easily be set up.     

Implementation of the IWA anaerobic digestion model No.1 (ADM1) for simulating digestion of blackwater from vacuum toilets.

The IWA anaerobic digestion model No.1 (ADM1) is applied to the blackwater anaerobic digestion (BWAD) plant in this work. In order to verify the biochemical kinetics, batch experiments were executed. According to the Monod type kinetics, the maximum uptake rates (km) of butyric acid (HBu), propionic acid (HPr) and acetic acid (HAc) are testified as 18, 14, 13 d(-1), and their half saturation concentrations (Ks) are 110, 120, 160 g COD/m3, respectively. Afterwards, the model was calibrated based on the performance of a laboratory scale BWAD plant (under mesophilic conditions) by three scenario studies, i.e. the reference conditions, different feeding frequencies and high NH4+ concentration. The model successfully simulated three scenarios. The further two virtual scenario studies were achieved based on the calibrated model. First, the performance of BWAD plant was predicted with different hydraulic retention times (HRT); second, the kitchen refuse (KR) was added into the BWAD plant as additional organic loading. The model predicted the perspective of BW plus KR digestion and generated valuable suggestions for the operation of the real BWAD plant.     

Photocatalytic inactivation of Flavobacterium and E. coli in water by a continuous stirred tank reactor (CSTR) fed with suspended/immobilised TiO2 medium

A photocatalytic continuous stirred tank reactor (CSTR) was built at laboratory scale to inactivate two environmental bacteria strains (Flavobacterium and E. coli) in tap water. Several parameters were found to impact reactor efficiency. Bacterial initial concentration is an important factor in inactivation rate. After 30 minutes of irradiation at 10(8)-10(9) CFU mL(-1) starting concentration, a >5 log reduction was achieved while at 10(4)-10(6) CFU mL(-1) only a 2 log reduction was observed. Water hardness and pH have an important influence on the photocatalytic inactivation process. Soft water, with low Ca(+2) and Mg(+2) at low pH approximately 5.3 resulted in increased inactivation of Flavobacterium reaching >6 orders of magnitude reduction. E. coli and Flavobacterium at pH 5 were inactivated by 3 logs more as compared to pH 7 under similar conditions. pH below TiO2 isoelectric point (approximately 5.6) supports better contact between bacteria and anatase particles resulting in superior inactivation. TiO2 powder suspension was compared with immobilised powder in sol-gel coated glass beads in order to exclude the need for particles separation from the treated water. TiO2 suspension was more effective by 3 orders of magnitude when compared to coated glass beads. An interesting observation was found between the two bacterial strains based on their hydrophobicity/hydrophilicity balance. The more hydrophobic Flavobacterium compared to E. coli was inactivated photocatalytically by >3 logs more then E. coli in the first 30 minutes of irradiation interval. The results indicate the importance of the parameters involved in the contact between TiO2 particles and microorganisms that govern the successful inactivation rate in CSTR.     

Anaerobic biodegradability and digestion in accumulation systems for concentrated black water and kitchen organic-wastes.

The feasibility of two accumulation-systems (AC) for anaerobic digestion and storage of concentrated black water with (AC1) or without (AC2) urine + kitchen organic-wastes was investigated. The waste(water) was collected by two vacuum toilet/transport systems. The influent-total COD of the AC2 (53,000 mg/L) was more concentrated by four times than that of the AC1. The suspended COD represented the major part (71-73%) of influent total COD of the two systems. The batch-experiments results showed a high anaerobic biodegradability of the waste(water) (> 85%). The AC systems demonstrated stable performance. There was no inhibition effect of NH4 and VFA concentration decreased in time. Total COD removal of 58% was achieved in both systems, after 105 days at 20 degrees C. Moreover, if only the supernatant in AC1 is withdrawn and the settled sludge stays for the next runs, only 20% of the influent total COD will be in the supernatant. In AC2, 74% of influent ortho-P was removed by precipitation. Therefore, the settled sludge in the AC2 had a high total-P concentration of 1,300 mg/L. The C:N:P ratios of the supernatant and the sludge were 26:13:1 and 35:4.5:1, respectively, in the AC1, and were 28:14:1 and 32:2.4:1, respectively, in AC2.     

搅拌槽内流体力学特性的数值模拟研究

采用FLUENT6.3.26软件求解气液两相流,自由液面的捕捉采用VOF(volume of fluid)法,辅以标准k-ε湍流模型数值求解气液两相流时均方程,使用了半隐式SIMPLE(Semi-Implicit Method for Pressure-Linked Equations)算法求解速度与压力耦合方程组,旨在研究搅拌槽在搅拌过程中流体流动的力学特性,分析比较了不同水深处的水流沿半径方向的径向速度、切向速度及轴向速度的规律,经过研究和分析发现模拟的速度值与实验值吻合良好,为搅拌槽的设计和运行提供了参考。     

Effects of nitrobenzene concentrations and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor and continuously stirred tank reactor system.

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention time (HRT) on the performance of anaerobic baffled reactor (ABR) and aerobic completely stirred tank reactor (CSTR) were studied. In the first step the NB concentration was increased from 30 to 700 mg/L at constant COD and flowrates. Maximum COD removal efficiencies in ABR varied between 88-92% as NB concentrations increased from 30 to 210 mg/L. After this dose, COD removal efficiency decreased to 85 and 79% at NB concentrations of 550 and 700 mg/L, respectively. Removal efficiencies of NB were nearly 100% for all NB concentrations in ABR reactor effluent. In the second step, COD and NB concentrations were kept constant while HRT decreased from 10.38 days to 1 day. As HRT decreased from 10.38 to 2.5 days the COD removal efficiencies in the anaerobic and anaerobic/aerobic reactor effluents were 92-94% and 97-98%, respectively. As HRT decreased from 2.5 days to 1 day COD removal efficiencies in the anaerobic and anaerobic/aerobic reactor effluents decreased to 83 and 95%, respectively. This study showed that HRT is a more important operation parameter than increasing NB concentration in ABR/CSTR sequential reactor system. Although ABR/CSTR system exhibited good COD and NB removal efficiencies, the lower HRTs slightly decreased the removal efficiencies compared to increasing NB concentration.     

Performances of a granular sequencing batch reactor (GSBR).

Aerobic granulation in sequencing batch reactors is widely reported in literature and in particular in SBAR (Sequencing batch airlift reactor) configuration, due to the high localised hydrodynamic shear forces that occur in this type of configuration. The aim of this work was to observe the phenomenon of the aerobic granulation and to confirm the excellent removal efficiencies that can be achieved with this technology. In order to do that, a laboratory-scale plant, inoculated with activated sludge collected from a conventional WWTP, was operated for 64 days: 42 days as a SBAR and 22 days as a SBBC (sequencing batch bubble column). The performances of the pilot plant showed excellent organics removal. COD and BOD removal efficiencies were respectively, 93 and 94%; on the contrary, N-removal efficiency was extremely low (5%-45%/o). The granules dimensions increased during the whole experimentation; change of reactor configuration contributed to further improve this aspect. The experimental work confirmed the essential role of hydraulic settling time in the formation of aerobic granules and in the sludge settleability and the need to find an optimum between granule size and oxygen supply to achieve good N-removal efficiency.     

碧潭观鱼景点真空厕所排污染系统的安装与测试

碧潭观鱼景点真空厕所位于武汉东湖风景区内,排水系统选用了真空排水系统.由于目前国内没有真空排水系统设计、施工、安装及测试的相应规范,结合真空厕所系统工程设计,参考国外相关标准,介绍了该真空厕所的组成及工艺流程;详细阐述了该系统真空便器、各种管道、真空站设备的安装方法和步骤以及系统的测试方法.     

Autogenerative high pressure digestion: anaerobic digestion and biogas upgrading in a single step reactor system

Conventional anaerobic digestion is a widely applied technology to produce biogas from organic wastes and residues. The biogas calorific value depends on the CH, content which generally ranges between 55 and 65%. Biogas upgrading to so-called 'green gas', with natural gas quality, generally proceeds with add-on technologies, applicable only for biogas flows > 100 m3/h. In the concept of autogenerative high pressure digestion (AHPD), methanogenic biomass builds up pressure inside the reactor. Since CO2 has a higher solubility than CH4, it will proportion more to the liquid phase at higher pressures. Therefore, AHPD biogas is characterised by a high CH4 content, reaching equilibrium values between 90 and 95% at a pressure of 3-90 bar. In addition, also H2S and NH3 are theoretically more soluble in the bulk liquid than CO2. Moreover, the water content of the already compressed biogas is calculated to have a dew point <--10 degrees C. Ideally, high-quality biogas can be directly used for electricity and heat generation, or injected in a local natural gas distribution net. In the present study, using sodium acetate as substrate and anaerobic granular sludge as inoculum, batch-fed reactors showed a pressure increase up to 90 bars, the maximum allowable value for our used reactors. However, the specific methanogenic activity (SMA) of the sludge decreased on average by 30% compared to digestion at ambient pressure (1 bar). Other results show no effect of pressure exposure on the SMA assessed under atmospheric conditions. These first results show that the proposed AHPD process is a highly promising technology for anaerobic digestion and biogas upgrading in a single step reactor system.     

搅拌器内转轮半径对气液混合影响的数值模拟研究

研究转轮半径这一因素对搅拌器内气液两相混合流特性的影响,可为搅拌器的设计与优化提供依据。采用RNG k-ε湍流模型结合多参考系法对单叶轮气液搅拌器内的气液混合过程进行了模拟计算。通过模拟计算得到了搅拌器在相同通气率、相同转轮转速、不同转轮半径下的气液流动速度场以及不同方向、不同截面上气含率的分布规律,分析了不同转轮半径对搅拌器内三维流场及气含率分布的影响。模拟结果表明:在通气率不发生改变的情况下,转轮半径大小的改变对搅拌器内的气含率分布的影响较小,而对速度分布有一定的影响。     

Anaerobic digestion as a core technology in sustainable management of organic matter.

In the past decades, anaerobic digestion (AD) has steadily gained importance. However, the technology is not regarded as a top priority in science policy and in industrial development at present. In order for AD to further develop, it is crucial that AD profits from the current fuel issues emerging in the international arena. AD can provide low-cost treatment of sewage and solid domestic wastes, which represents a vast application potential that should be promoted in the developing world. Furthermore, the developments in the last decades in the domain of anaerobic microbiology and technology have generated some interesting niches for the application of AD, such as anaerobic nitrogen removal and the treatment of chlorinated organics. Recently, AD has also generated some serendipities, such as the use of AD in processes for sulphur and calcium removal and the coupling of AD with microbial fuel cells. The international developments in terms of bio-refineries and CO2-emission abatement are of crucial importance with respect to the impetus that AD will receive in the coming decade. There should be little doubt that by placing the focus of AD on the production of green energy and clean nutrients, the future of AD will be assured.     

Anaerobic treatment as a core technology for energy, nutrients and water recovery from source-separated domestic waste(water).

Based on results of pilot scale research with source-separated black water (BW) and grey water (GW), a new sanitation concept is proposed. BW and GW are both treated in a UASB (-septic tank) for recovery of CH4 gas. Kitchen waste is added to the anaerobic BW treatment for doubling the biogas production. Post-treatment of the effluent is providing recovery of phosphorus and removal of remaining COD and nitrogen. The total energy saving of the new sanitation concept amounts to 200 MJ/year in comparison with conventional sanitation, moreover 0.14 kg P/p/year and 90 litres of potential reusable water are produced.     

Organic matter transport and retention in a blackwater stream recovering from flow augmentation and thermal discharge

Organic and inorganic seston, benthic organic matter and woody debris were studied in a blackwater stream/floodplain system recovering from flow augmentation and thermal discharges. The stream had received cooling waters from two nuclear reactors from the mid-1950s to 1968, resulting in flows over 10x greater than normal and temperatures that exceeded 70°C. Channel morphology was markedly altered, woody debris was removed or buried, and floodplain vegetation was destroyed. Fifteen years after termination of cooling water discharges, the stream continued to exhibit many characteristics of a disturbed system. Compared to an undistributed reference stream, the recovering stream had substantially less benthic organic matter, fewer snags and debris dams, and transported more organic and inorganic seston of all size fractions examined. Because of the importance of these biophysical factors in the structural morphology of blackwater streams, it is hypothesized that complete recovery will not be realized until the floodplain forest has matured and large woody debris is contributed to the stream channel.     

Photodegradation of aqueous reactive dye using TiO(2)/zeolite admixtures in a continuous flow reactor

The photocatalytic degradation of an organic dye, i.e. reactive blue 19 (RB19), was studied by employing different TiO(2)/zeolite (TZ) photocatalysts, which have TiO(2)/(TiO(2) + zeolite) weight ratios ranging from 20 to 80%, in a continuous flow system. Three light sources including two UV lights (i.e. λ(max,254 nm) and λ(max,365 nm)) and natural sunlight were used. The results showed that the decoloring rate of RB19 increased as the amount of TiO(2) in the TZ catalyst increased. The photodegradation of RB19 exhibited pseudo-first-order kinetics with respect to the concentration of RB19. Almost 100% of initial RB19 was mineralized under the controlled conditions in this study. And the activities of the prepared photocatalysts were retained after long-term durability experiments. Compared with UV lights (i.e. λ(max,254 nm) and λ(max,365 nm)), the decoloring efficiency of RB19 was significantly increased under natural sunlight illumination, which is likely due to the long-wavelength incident light that photoexcited RB19 and accelerated the degradation rate of RB19 radicals by the UV fraction of sunlight.     

On-site treatment of a motorway service area wastewater using a package sequencing batch reactor (SBR).

A sequencing batch reactor (SBR) treating the effluent of a motorway service station in the south of England situated on a major tourist route was investigated. Wastewater from the kitchens, toilets and washrooms facilities was collected from the areas on each side of the motorway for treatment on-site. The SBR was designed for a population equivalent (p.e.) of 500, assuming an average flow of 100 m3/d, influent biochemical oxygen demand (BOD) of 300 mg/l, and influent suspended solids (SS) of 300 mg/l. Influent monitoring over 8 weeks revealed that the average flow was only 65 m3/d and the average influent BOD and SS were 480 mg/l and 473 mg/l respectively. This corresponded to a high sludge loading rate (F:M) of 0.42 d(-1) which accounted for poor performance. Therefore the cycle times were extended from 6 h to 7 h and effluent BOD improved from 79 to 27 mg/l.     

Difficulties in maintaining long-term partial nitritation of ammonium-rich sludge digester liquids in a moving-bed biofilm reactor (MBBR).

Nitrogen can be eliminated effectively from sludge digester effluents by anaerobic ammonium oxidation (anammox), but 55-60% of the ammonium must first be oxidized to nitrite. Although a continuous flow stirred tank reactor (CSTR) with suspended biomass could be used, its hydraulic dilution rate is limited to 0.8-1 d(-1) (30 degrees C). Higher specific nitrite production rates can be achieved by sludge retention, as shown here for a moving-bed biofilm reactor (MBBR) with Kaldnes carriers on laboratory and pilot scales. The maximum nitrite production rate amounted to 2.7 gNO2-Nm(-2)d(-1) (3 gO2m(-3)d(-1), 30.5 degrees C), thus doubling the dilution rate compared to CSTR operation with suspended biomass for a supernatant with 700 gNH4-Nm(-3). Whenever the available alkalinity was fully consumed, an optimal amount of nitrite was produced. However, a significant amount of nitrate was produced after 11 months of operation, making the effluent unsuitable for anaerobic ammonium oxidation. Because the sludge retention time (SRT) is relatively long in biofilm systems, slow growth of nitrite oxidizers occurs. None of the selection criteria applied - a high ammonium loading rate, high free ammonia or low oxygen concentration - led to selective suppression of nitrite oxidation. A CSTR or SBR with suspended biomass is consequently recommended for full-scale operation.     

Anaerobic digestion of corn ethanol thin stillage in batch and by high-rate down-flow fixed film reactors

Thin stillage (CTS) from a dry-grind corn ethanol plant was evaluated as a carbon source for anaerobic digestion (AD) by batch and high rate semi-continuous down-flow stationary fixed film (DSFF) reactors. Biochemical methane potential (BMP) assays were carried out with CTS concentrations ranging from approximately 2,460-27,172 mg total chemical oxygen demand (TCOD) per litre, achieved by diluting CTS with clean water or a combination of clean water and treated effluent. High TCOD, SCOD and volatile solids (VS) removal efficiencies of 85 ± 2, 94 ± 0 and 82 ± 1% were achieved for CTS diluted with only clean water at an organic concentration of 21,177 mg TCOD per litre, with a methane yield of 0.30 L methane per gram TCOD(removed) at standard temperature and pressure (STP, 0 °C and 1 atmosphere). Batch studies investigating the use of treated effluent for dilution showed promising results. Continuous studies employed two mesophilic DSFF anaerobic digesters treating thin stillage, operated at hydraulic retention times (HRT) of 20, 14.3, 8.7, 6.3, 5 and 4.2 d. Successful digestion was achieved up to an organic loading rate (OLR) of approximately 7.4 g TCOD L(-1)d(-1) at a 5 d HRT with a yield of 2.05 LCH(4) L(-1)d(-1) (at STP) and TCOD and VS removal efficiencies of 89 ± 3 and 85 ± 3%, respectively.     

Anaerobic codigestion of waste activated sludge and OFMSW: the experiences of viareggio and treviso plants (Italy).

The paper presents the results of two full-scale applications of the anaerobic co-digestion process of waste activated sludge together with the organic fraction of municipal solid wastes. The experiences were carried out at Viareggio and Treviso wastewater treatment plants (Italy). In the first plant, 3 tons per day of source sorted OFMSW were co-digested with waste activated sludge, increasing the organic loading rate from 1.0 to 1.2 kgTVS/m3d. This determined a 50% increase in biogas production. At Treviso WWTP, which has been working for 2 years, some 10 tons per day of separately collected OFMSW are treated using a low-energy consumption sorting line, which allows the removal of 99% and 90% of metals and plastics respectively. In these conditions, the biogas yield increased from 3,500 up to 17,500 m3/month. Industrial costs were evaluated less than 50 Euro per ton of organic waste, while the payback time was calculated as two years.     

Monitoring of pH inhibition on microbial activity in a continuous flow reactor by pseudo toxic concentration (C(PT)) concept and time delay model.

The pseudo toxic concentration (C(PT)) concept was introduced as a quantification method to describe pH as an inhibitor concentration. In this research, the applicability of the C(PT) concept model for the detection of pH inhibitions was expanded for a continuous flow activated sludge reactor. A pilot equipped with an inhibition detection system was installed. Inhibitory wastewater was injected for 1 h and the relative activity was calculated by the maximum respiration rate. At the same time, the coefficients for the C(PT) concept model were estimated. At the dynamic conditions, the estimated relative activity by the C(PT) concept model showed time lag compared to the measured one. However, the time lag problem was successfully resolved by introducing a transfer function into the C(PT) concept model. The C(PT) concept model combined with a transfer function (C(PT) + TF model) successfully tracked the variation of the relative activity under dynamic conditions. The C(PT) + TF model could detect 50% inhibition faster than the respirometry based method by approximately 10 min. Moreover, it had additional advantages such as being inexpensive, easy to install and simple to operate. In conclusion, the C(PT) + TF model was an effective and convenient detection method of pH inhibition.