Barter P J
Cawthron Institute, Private Bag 2, 98 Halifax Street East, Nelson, New Zealand.
Water Sci Technol. 2003;48(2):145-51.
The city of Nelson, New Zealand, has a 27 hectare oxidation pond as its primary wastewater treatment facility. Recent changes in the configuration of the pond and installation of a mixer/aerator raised concerns that pond treatment rates and effluent quality may be affected by high internal pond velocities and short retention times. This paper presents the findings of an investigation into wastewater velocity and movement within the pond using qualitative dye dispersion and tracking of small-scale "holey-sock" drogues. Simultaneous deployment of drogues and dye allowed methods to be compared, since small-scale drogues have not commonly been used in wastewater ponds. Dye dispersion was assessed using low-level aerial photography from a tethered helium blimp to track short term movement and mixing, while a datalogger and fluorometer were used to measure pond retention time. Drogue movement was tracked in conjunction with the dye study from a small boat using hand-held GPS. The dye study found that: (i) the first portion of pond influent discharged from the pond after 37.5 hours, substantially quicker than the theoretical pond retention time of 27 days. However, the measured retention time was with a mixer in place and the theoretical time was without a mixer; (ii) the position of the paddle wheel mixer/aerator was not optimally placed for mixing the influent and a quiescent region existed adjacent to the influent point; and (iii) the low-level aerial photography was an effective method of evaluating larger pond systems. The "holey-sock" drogue studies showed that: (i) the drogues accurately followed the movement and velocity of dyed influent within the pond; (ii) wastewater velocity and movement was dominated by the paddle wheel mixer/aerator; and (iii) wind direction had a minor influence on wastewater velocity and movement in areas not directly affected by the paddle wheel mixer/aerator. The study demonstrated that the combined use of dye and drogues was a relatively low-cost and effective means of determining internal pond velocities and movement. Future studies using similar methods will be useful in helping validate computer-modelled movement and velocity.
新西兰尼尔森市有一个27公顷的氧化塘作为其主要的废水处理设施。最近，该氧化塘的结构发生了变化，并安装了搅拌机/曝气器，这引发了人们对氧化塘处理率和出水水质可能受到塘内高流速和短停留时间影响的担忧。本文介绍了一项使用定性染料扩散和跟踪小型“多孔袜”示踪剂来研究氧化塘内废水流速和流动情况的调查结果。同时部署示踪剂和染料可以对方法进行比较，因为小型示踪剂在废水塘中并不常用。使用系留氦气球进行低空航拍来评估染料扩散，以跟踪短期的流动和混合情况，同时使用数据记录器和荧光计来测量氧化塘的停留时间。从一艘小船上使用手持式全球定位系统（GPS）结合染料研究来跟踪示踪剂的移动。染料研究发现：（i）氧化塘进水的第一部分在37.5小时后从塘中排出，比理论停留时间27天快得多。然而，测量的停留时间是在有搅拌机的情况下，而理论时间是在没有搅拌机的情况下；（ii）桨轮搅拌机/曝气器的位置对于混合进水来说放置得并不理想，进水点附近存在一个静止区域；（iii）低空航拍是评估较大氧化塘系统的有效方法。“多孔袜”示踪剂研究表明：（i）示踪剂准确地跟踪了塘内染色进水的移动和流速；（ii）废水流速和流动主要由桨轮搅拌机/曝气器主导；（iii）风向对桨轮搅拌机/曝气器未直接影响区域的废水流速和流动有较小影响。该研究表明，结合使用染料和示踪剂是确定氧化塘内流速和流动的一种相对低成本且有效的方法。未来使用类似方法的研究将有助于验证计算机模拟的移动和流速。
