In the start of a new blog series for WaterFront, Oliver Grievson (manager of the Water Industry Process Automation and Control Group on Linked in) will be looking at the specifics of controlling different elements of the treatment processes that are used everyday in the water industry and how the industry can implement instrumentation, process automation & control to get the best performance out of the treatment works that it runs. This will mainly focus on the wastewater side of the industry as this is where his area of expertise lies.
The first subject area that he will cover over the next four to five weeks is the Activated Sludge Plant.
As a technology in the UK Activated Sludge has been used as a process since it development by Edward Arden & William Lockett in 1914 in their classic paper, “Experiments on the Oxidation of Sewage Without the Aid of Filters” presented at a meeting of the Society of Chemical Industry at the Grand Hotel in Manchester. The process still runs in many of the world’s treatment works in many different forms today but it is more complicated that simple biological filtration and thus has its operational difficulties. It is these difficulties that I will be analyzing over the coming weeks by examining the different parts of the activated sludge process and showing how the correct instrumentation, automation & process control can be used to aid operational staff to get the most out of the process.
So what are the main problems that are encountered in the activated sludge process? Mainly they fall into two categories, the first being the amount of energy that the process consumes on a day to day basis and the second being the quality of the output from the process when things start to go wrong.
Let me explain,
The amount of energy that the activated sludge process consumes is a direct result of how much the process treats which will govern how much bacteria the process holds. The tighter the consent standard, the more that has to be removed and the more bacteria the process has to contain and the more energy it consumes. Is this strictly a “problem?” No, but there are ways of controlling the process to limit the amount of energy that it consumes
The performance of the process is another “problem” so to speak. In practice in the industry solids loss from the process is a common cause for “failure” of the process. Why? The process is usually running at a solids concentration far higher than is optimal and this causes the process to lose solids when it is pushed too far and this is apart from being energy intensive.
Over the next few weeks, on a weekly basis, I am going to examine the different parts of the activated sludge process and suggest ways of installing instrumentation and process control to get the best out of the process. I will not cover advanced methods but simply the basics. The broad categories (subject to addition) that will be covered are:
- MLSS Control & Solids Wastage
- Dissolved Oxygen Control
- Return Activated Sludge Control
- Controlling the Activated Sludge Process for Compliance
Oliver Grievson MSc, MCIWEM, MIEnvSc CEnv CSCi C.WE
LinkedIn Group Manager Water Industry Process Automation & Control