Determination of chemical biodegradation by direct and indirect methods

Summary Degradation of 10 organic chemicals by pre-acclimated microorganisms in BOD dilution water was determined directly by UV spectrophotometry and indirectly by a modified BOD method. Residual chemical concentrations were periodically measured and pseudo-first-order biodegradation rate constants (k ₁) were calculated. Thek ₁ spectrophotometry values ranged from 0.006/h to 0.077/h andk ₁-BOD values from 0.002/h to 0.043/h for 1-methylnaphthalene and indole, respectively. The ratios ofk spectrophotometry to k₁-BOD were between 1.5 for salicylic acid and 3.0 for 1-methylnaphthalene with a mean of 2.7. A significant (=0.001) linear correlation (r ²=0.854,F=46.630) existed between the two sets of rate constants. Results from this study suggest that the modified BOD method may be used to estimate chemical biodegradation rates in synthetic media.     

固定化微生物在生物膜式生化需氧量传感器中的应用现状

生化需氧量(Biochemical oxygen demand,BOD)微生物传感器是一种快速检测水样中有机污染物含量的设备,固定化微生物是其核心部件之一,对其稳定性、响应时间、使用寿命及实际应用范围等性能有着重要影响。生物膜式BOD传感器较其他类型的BOD微生物传感器具有结构简单、灵敏度高、响应时间短等优点,受到广泛的研究和应用。本文主要针对固定化微生物在生物膜式BOD传感器中的应用情况,概述较典型的微生物固定化方式的原理、特点及应用;总结几类应用较多或具有较好前景的载体材料,并讨论载体特性与传感器性能之间的关系;综述微生物在该领域的应用现状;简要介绍生物膜式BOD传感器的实际应用及商业化现状,比较其与另外几种BOD微生物传感器的优缺点;分析生物膜式BOD传感器中固定化微生物现存的一些问题及其发展趋势。     

Monitoring of two-stage anaerobic biodegradation using a BOD biosensor

A previously developed biosensor for fast estimation of short-term biochemical oxygen demand (BOD_st) was used for off-line monitoring of intermediate products from the initial step of an anaerobic process in laboratory scale. Good agreement was generally achieved between the results from the biosensor method and the conventional 5-day test except for samples with high content of organic polymers. During the period of agreement between the measurement principles, good correlation was achieved between the biogas production rate and the organic loading rate. The results from this study demonstrate that BOD_st can be a successful monitoring parameter to achieve a better process control.     

Immobilised activated sludge based biosensor for biochemical oxygen demand measurement

A biochemical oxygen demand (BOD) sensor, based on an immobilised mixed culture of microorganisms in combination with a dissolved oxygen electrode, has been developed for the purpose of on-line monitoring of the biological treatment process for waste and wastewater. The sensor was designed for easy replacement of the biomembrane, thereby making it suitable for short-term use. The drawbacks of activated sludge based sensor, such as short sensor lifetime, were thereby circumvented. The sensor BOD measurements were carried out in the kinetic mode using a flow injection system, resulting in 25 s for one measurement followed by 4–8 min recovery time. Based on the results of normalised sensor responses, the OECD synthetic wastewater was considered to be a more suitable calibration solution in comparison with the GGA solution. Good agreement was achieved between the results of the sensor BOD measurement and those obtained from BOD₅ analysis of a wastewater sample from a food-processing factory. Reproducibility of responses using one sensor was below ±5.6% standard deviation. Reproducibility of responses using different sensors was within acceptable bias limits, viz. ±15% standard deviation.     

Prediction model of DnBP degradation based on BP neural network in AAO system

A laboratory-scale anaerobic-anoxic-oxic (AAO) system was established to investigate the fate of DnBP. A removal kinetic model including sorption and biodegradation was formulated, and kinetic parameters were evaluated with batch experiments under anaerobic, anoxic, oxic conditions. However, it is highly complex and is difficult to confirm the kinetic parameters using conventional mathematical modeling. To correlate the experimental data with available models or some modified empirical equations, an artificial neural network model based on multilayered partial recurrent back propagation (BP) algorithm was applied for the biodegradation of DnBP from the water quality characteristic parameters. Compared to the kinetic model, the performance of the network for modeling DnBP is found to be more impressive. The results showed that the biggest relative error of BP network prediction model was 9.95%, while the kinetic model was 14.52%, which illustrates BP model predicting effluent DnBP more accurately than kinetic model forecasting.     

An integrated physical and biological model for anaerobic lagoons

A computational fluid dynamics (CFD) model that integrates physical and biological processes for anaerobic lagoons is presented. In the model development, turbulence is represented using a transition k-ω model, heat conduction and solar radiation are included in the thermal model, biological oxygen demand (BOD) reduction is characterized by first-order kinetics, and methane yield rate is expressed as a linear function of temperature. A test of the model applicability is conducted in a covered lagoon digester operated under tropical climate conditions. The commercial CFD software, ANSYS-Fluent, is employed to solve the integrated model. The simulation procedures include solving fluid flow and heat transfer, predicting local resident time based on the converged flow fields, and calculating the BOD reduction and methane production. The simulated results show that monthly methane production varies insignificantly, but the time to achieve a 99% BOD reduction in January is much longer than that in July.     

生物传感器快速测定BOD系统的稳定性研究

在前期研究工作的基础上,确定了生物传感器快速测定BOD的实验流程。研究了温度对检测结果的影响,初始BOD浓度与检测时间的关系,并探讨了检测结果的重现性及其线性范围。结果表明：恒温环境可以保持微生物活性的相对稳定,并保证了检测过程的相对稳定,检测结果的最大相对偏差7.7%,满足BOD快速测定的要求;溶液BOD浓度不同,所需的检测时间也不同,BOD浓度越高,所需时间越长。在曝气状态下,可以保证BOD浓度在200mg/l以下的样品在15min以内检测完毕。通过对线性范围的分析,该方法适宜的线性范围可达5－200mg/l。     

Effect of bulk liquid BOD concentration on activity and microbial community structure of a nitrifying,membrane-aerated biofilm

Membrane-aerated biofilms (MABs) are an effective means to achieve nitrification and denitrification of wastewater. In this research, microsensors, fluorescence in situ hybridization (FISH), and modeling were used to assess the impact of bulk liquid biological oxygen demand (BOD) concentrations on the activity and microbial community structure of nitrifying MABs. With 1 g m⁻³ BOD in the bulk liquid, the nitrification rate was 1.3 g N m⁻² day⁻¹, slightly lower than the 1.5 g N m⁻² day⁻¹ reported for no bulk liquid BOD. With bulk liquid BOD concentrations of 3 and 10 g m⁻³, the rates decreased to 1 and 0.4 g N m⁻² day⁻¹, respectively. The percent denitrification increased from 20% to 100% when the BOD increased from 1 to 10 g m⁻³ BOD. FISH results indicated increasing abundance of heterotrophs with increasing bulk liquid BOD, consistent with the increased denitrification rates. Modeling was used to assess the effect of BOD on nitrification rates and to compare an MAB to a conventional biofilm. The model-predicted nitrification rates were consistent with the experimental results. Also, nitrification in the MAB was much less sensitive to BOD inhibition than the conventional biofilm. The MAB achieved concurrent nitrification and denitrification, whereas little denitrification occurred in the conventional biofilm.     

A flow injection analysis system with encapsulated high-density <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> cells for rapid determination of biochemical oxygen demand

The biochemical oxygen demand (BOD) determination was studied using a novel flow injection analysis (FIA) system with encapsulated Saccharomyces cerevisiae cells and an oxygen electrode and was compared with conventional 5-day BOD tests. S. cerevisiae cells were packed in a calcium alginate capsule at a dry cell weight of 250 g/l of capsule core. The level of dissolved oxygen (DO) was reduced due to the enhanced respiratory activity of the microbial cells when the injected nutrient passed through the bioreactor. The decrease in DO (ΔDO) was intensified with the amount of microbial cells packed in the bioreactor. However, the specific ΔDO decreased as the amount of cells loaded in the bioreactor increased. The ΔDO value was dependent on the pH and temperature of the mobile phase and reached its maximum value at 35°C and pH 7–8. Also, ΔDO became larger at longer response times as the flow rate of the mobile phase decreased. The measurement of ΔDO was repeated more than six times consecutively using a 20-ppm standard glucose and glutamic acid solution, which confirmed the reproducibility with a standard deviation of 0.95%. A strong linear correlation between ΔDO and BOD was also observed. The 5-day BOD values of actual water and wastewater samples were in accordance with the BOD values obtained by this FIA method using encapsulated S. cerevisiae cells. Unlike the cell-immobilized bead system, there was no contamination of the bioreactor resulting from any leak of yeast cells from the sensor capsules during BOD measurements.     

Modelling the simultaneous processes occurring during the BOD5 test using synthetic waters as a pattern

Synthetic waters imitating BOD₅ test conditions have been studied to model the progress curves of cell growth, organic matter consumption and oxygen demand. Glucose and glutamic acid were used as organic matter and Bacillus subtilis, Escherichia coli and Pseudomonas putida as microorganisms. The concentrations of all the products were measured simultaneously over time and were fitted to the Logistic and Monod models. Following this, the goodness of fit was analysed. Discrimination between models allowed us to conclude that the Logistic model has acceptable accuracy to describe the kinetic behaviour inside a BOD₅ bottle, while the extra parameter in the Monod model would not be statistically justified. Thus, the logistic parameters were determined under different conditions by non-linear regression and their biological meaning was interpreted.