A new instrument for on-line measurement of bicarbonate alkalinity

Alkalinity or buffering in anaerobic digesters may be chiefly attributed to bicarbonate and should be at least 1000 mg CaCO₃/l for successful operation. A simple on-line instrument for the direct determination of bicarbonate concentration, especially for automatic control of anaerobic digesters, is described. The proposed method is based on a continuous measurement of the carbon dioxide flow rate evolved from a stream of sampled solution after saturation with gaseous CO₂ and subsequent acidification with excess acid. This eliminates the need for a pH probe which is subject to fouling.The device was calibrated using sodium bicarbonate solutions (0.01–0.065 M) and the calibration showed an accuracy of ±5%. The device was tested on effluent from anaerobic digesters operating on ice-cream waste supplemented with sodium bicarbonate within a range of 0.02–0.04 mol/l. The results compared favourably with titrimetric measurements, extensively used to determine bicarbonate alkalinity with an accuracy of ±5%. The response of the instrument to variation in alkalinity concentration is sufficiently rapid for most industrial applications.     

污泥嗜热菌好氧消化与传统高温好氧消化的效果对比

在65℃的条件下利用嗜热菌消解城市污水处理厂的剩余污泥，并与传统高温好氧消化的效果进行了对比。结果表明：在有嗜热菌存在的条件下污泥的消化效果更好，对TSS、VSS的去除率分别可达55％和65％，而传统高温好氧消化的仅为40％和50％。嗜热菌好氧消化技术为城市污水处理厂提供了一种新的污泥减量化方法，使得剩余污泥“零排放”成为可能。     

Performance characteristics of the anaerobic baffled reactor

An anaerobic sludge blanket process, termed the anaerobic baffled reactor (ABR), has been developed and shows promise for industrial wastewater treatment. It combines the advantages of high stability and reliability with a high void volume. The risk of clogging and sludge bed expansion with resulting high microbial losses is reduced and there is no need for special gas collection or biological solids separation systems. Organic loadings as high as 36 g COD l^?1day^?1 have been achieved with COD removal rates of more than 24 g COD l^?1 day^?1 and methane production rates exceeding 6 volumes per day per unit volume of reactor. The hypothesis, that the ABR may be adequately modeled as a fixed-film reactor, has been supported. Therefore, a unified approach, based on fundamentals of bacterial kinetics and mass transport, appears useful for modeling this and similar systems. Pilot plant studies are necessary to determine the scaling factors of the system as well as the overall efficiency and costs.     

THE EFFECTS OF IMPROVING SEWAGE SLUDGE DIGESTION

A model was developed and tested to investigate the effects of various parameters on the processing costs of anaerobic digestion. The model was based on empirical data collected from full-scale plants which varied in size from 35,000 to 900,000 population equivalents. (Equivalent to loading rates of 0.5 to 2.7 kg VS/m³/d.) In spite of different operating regimes and conditions of the plants analysed, various relationships were discovered between: sludge quality and volatile solids destruction; sludge quality and biogas yield; and, effluent volatile solids and dewatering. Where correlations existed, these were used to make predictions on operating costs of the digestion and dewatering plant based on sensitivity analysis. The results of the model were used to make recommendations on how to optimise the operation of an anaerobic digestion plant.     

Modelling of two-stage anaerobic digestion using the IWA Anaerobic Digestion Model No. 1 (ADM1)

The aim of the study presented was to implement a process model to simulate the dynamic behaviour of a pilot-scale process for anaerobic two-stage digestion of sewage sludge. The model implemented was initiated to support experimental investigations of the anaerobic two-stage digestion process. The model concept implemented in the simulation software package MATLAB/Simulink is a derivative of the IWA Anaerobic Digestion Model No.1 (ADM1) that has been developed by the IWA task group for mathematical modelling of anaerobic processes. In the present study the original model concept has been adapted and applied to replicate a two-stage digestion process. Testing procedures, including balance checks and 'benchmarking' tests were carried out to verify the accuracy of the implementation. These combined measures ensured a faultless model implementation without numerical inconsistencies. Parameters for both, the thermophilic and the mesophilic process stage, have been estimated successfully using data from lab-scale experiments described in literature. Due to the high number of parameters in the structured model, it was necessary to develop a customised procedure that limited the range of parameters to be estimated. The accuracy of the optimised parameter sets has been assessed against experimental data from pilot-scale experiments. Under these conditions, the model predicted reasonably well the dynamic behaviour of a two-stage digestion process in pilot scale.     

配风方式对垃圾焚烧炉燃烧效率的影响分析

以高水分垃圾(水分为55％)为例，对焚烧炉3项主要热损失(固体不完全燃烧热损失、气体不完全燃烧热损失和排烟热损失)进行了计算，得到了空气温度、空气系数、烟气温度、助燃油量等参数与焚烧炉主要热损失之间的关系。适当的配风方式(即合适的空气温度和空气系数)，可以使焚烧炉内主要热损失减小，从而可以提高焚烧炉的燃烧效率。分析结果还表明，空气温度不是越高越好。     

硫酸盐对抗生素废水厌氧生物处理的影响

采用水解酸化反应器与复合厌氧反应器组合工艺处理高浓度抗生素废水 ,试验结果表明 ,水解酸化反应器最大容积负荷可达 16 .84kgCOD/ (m3·d) ,有效降低了毒性物质的抑制作用 ;复合厌氧反应器最大容积负荷可达 8.5 7kgCOD/ (m3·d) ;系统进水最大SO2 - 4浓度为 132 5mg/L ,COD/SO2 - 4值最低为 3,COD与SO2 - 4的总去除率分别为 75 .5 %和 95 .2 % ,对各种抑制物质和冲击负荷表现出很好的适应性。试验证明 ,水解酸化—厌氧消化工艺可以有效消除SO2 - 4对厌氧处理的影响 ,对于处理高浓度抗生素废水是经济可行的     

Model selection, identification and validation in anaerobic digestion: a review

Anaerobic digestion enables waste (water) treatment and energy production in the form of biogas. The successful implementation of this process has lead to an increasing interest worldwide. However, anaerobic digestion is a complex biological process, where hundreds of microbial populations are involved, and whose start-up and operation are delicate issues. In order to better understand the process dynamics and to optimize the operating conditions, the availability of dynamic models is of paramount importance. Such models have to be inferred from prior knowledge and experimental data collected from real plants. Modeling and parameter identification are vast subjects, offering a realm of approaches and methods, which can be difficult to fully understand by scientists and engineers dedicated to the plant operation and improvements. This review article discusses existing modeling frameworks and methodologies for parameter estimation and model validation in the field of anaerobic digestion processes. The point of view is pragmatic, intentionally focusing on simple but efficient methods.     

Process modeling and analysis of palm oil mill effluent treatment in an up-flow anaerobic sludge fixed film bioreactor using response surface methodology (RSM)

In this study, the interactive effects of feed flow rate (QF) and up-flow velocity (V up) on the performance of an up-flow anaerobic sludge fixed film (UASFF) reactor treating palm oil mill effluent (POME) were investigated. Long-term performance of the UASFF reactor was first examined with raw POME at a hydraulic loading rate (HRT) of 3 d and an influent COD concentration of 44300 mg/l. Extreme reactor instability was observed after 25 d. Raw POME was then chemically pretreated and used as feed. Anaerobic digestion of pretreated POME was modeled and analyzed with two operating variables, i.e. feed flow rate and up-flow velocity. Experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). The region of exploration for digestion of the pretreated POME was taken as the area enclosed by the feed flow rate (1.01, 7.63 l/d) and up-flow velocity (0.2, 3 m/h) boundaries. Twelve dependent parameters were either directly measured or calculated as response. These parameters were total COD (TCOD) removal, soluble COD (SCOD) removal, effluent pH, effluent total volatile fatty acid (TVFA), effluent bicarbonate alkalinity (BA), effluent total suspended solids (TSS), CH4 percentage in biogas, methane yield (Y M), specific methanogenic activity (SMA), food-to-sludge ratio (F/M), sludge height in the UASB portion and solid retention time (SRT). The optimum conditions for POME treatment were found to be 2.45 l/d and 0.75 m/h for QF and V up, respectively (corresponding to HRT of 1.5 d and recycle ratio of 23.4:1). The present study provides valuable information about interrelations of quality and process parameters at different values of the operating variables.     

Occurrence and behaviour of linear alkylbenzenesulphonates, nonylphenol, nonylphenol mono- and nonylphenol diethoxylates in sewage and sewage sludge treatment

The fluxes of linear alkylbenzenesulphonates (LAS), nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) through sewage and sludge treatment of 29 Swiss sewage treatment plants were investigated. Reversed-phase high-performance liquid chromatography (HPLC) was used to determine LAS. Normal-phase HPLC was employed to measure NP, NP1EO and NP2EO which are metabolites of the nonionic surfactants of the nonylphenol polyethoxylate type (NPnEO). Quantitative determinations were performed of raw sewage, primary and secondary effluents and of sewage sludge. Under normal conditions of sewage and sludge treatment, LAS were efficiently removed from the raw wastewater (> 99% w/w) and were partly transferred to the sewage sludge (15–20% w/w). About 50% (molar base) of NPnEO in the sewage were transformed to NP and accumulated in the digested sludge. Large variations existed among different sewage treatment plants. It was estimated that 1.0 g m⁻² y⁻¹ of LAS and 0.3 g m⁻² y⁻¹ of NP are applied with sewage sludge to Swiss soils.