Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

铁路上海站北广场工程给排水及消防设计特点

铁路上海站北广场是集铁路、轨道交通、长途汽车等为一体的大型交通枢纽。介绍了地面广场和地下空间2个子项的给排水设计,包括给水、污水、雨水和废水系统设计的周边环境情况、设计原则和设备选用等;简单介绍了消火栓系统、自动喷水灭火系统、气体灭火系统和灭火器设置等消防设计内容。最后,重点论述了项目中的设计难点和具体解决方案。     

预制混凝土U型槽在寒区渠道防渗中的应用

阐述了混凝土U型槽的防渗特点和在施工中应注意的问题。     

路基沉降变形机理及发展过程的分析研究

针对高填方路基路堤高度大、自身沉降值大的特点,从地基和路堤自身沉降两个方面探讨了高填方路基的沉降变形机理,对路基沉降的发展过程进行了分析,并得出了一些有益的结论,以供参考。     

UASB/Orbal氧化沟工艺处理垃圾渗滤液

采用UASB/吹脱塔/Orbal氧化沟（投加粉末活性炭）处理垃圾渗滤液,对COD去除率高,脱氮效果明显.一年多的运行实践表明,处理出水水质稳定,各项指标均达到国家排放标准.     

考虑分级开挖的深基坑支护计算

 提出了考虑深基坑变形的一种新的支护结构计算方法——弯杆计算法，在弯杆法的有限元计算中， 通过变换座标的方式考虑上一级开挖的变形，从而达到考虑分级开挖的工况。实例验算表明，该程序能够计算出支护结构变形的变化趋势，并给出了简要的自编计算程序框图。     

灰场原型观测和模拟试验成果及对比分析

本文通过原型观测和室内模拟试验，对灰场的粉煤灰冲填规律进行了分析和探讨.主要内容包括灰水沟槽的位置和断面形状，冲填地形及模拟淤积比降，粉煤灰的群体沉降速度和临界流速.     

渠道防渗衬砌工程的冻害原因分析及防治措施

分析了渠道防渗工程冻害产生的原因，介绍了冻胀的破坏形式，详细阐述了防治衬砌冻害的措施，以提高渠道防渗初砌工程的质量，延长灌区渠道的使用寿命。     

景电二期工程渠道防渗衬砌综述

渠道衬砌结构形式关系其防渗效果及其经济合理性。本文从衬砌材料、结构形式和施工方法进行分析比较，对景电二期工程各级渠道不同的防渗衬砌形式作了介绍，并提出了存在的问题。     

Total RNA concentration as an index of microbial activity and oxygen supply in an oxidation ditch

Total RNA and chromosomal DNA concentrations at a municipal wastewater treatment plant with an oxidation ditch (OD) were monitored for 1.5 years using commercial extraction kits for DNA and RNA. No parameters correlated with the chromosomal DNA concentration. The total RNA concentration exhibited better correlation than the solids retention time and the mixed liquor suspended solids with the removal rate of total organic carbon, and can be regarded as an index of microbial activity. The total RNA concentration varied with a cycle of one year and increased at lower water temperatures in this OD. When diffusion theory was taken into account, it was found that the oxygen dissolution rate increased at lower temperature, and a small change in the oxygen dissolution rate caused a large variation in microbial activity and also affected nitrification and denitrification. The information was insufficient to clarify the various reaction relationships, but total RNA concentration will likely be useful as an index of microbial activity in actual wastewater treatment reactors.