bugs & wastewater bugs

Today I’ve calculated both the weir loading rates and surface overflow loading rates for the secondary clarifiers.

Since I’ve never really explained what these clarifier things are: basically the plant speeds up a process that would happen naturally overtime in the environment. It breaks down organics (aka poop). By the time the large particles are removed during the primary process, the poopwater is treated in a secondary biological process. 

Image result for weir loading rates

From this site

Secondary process:

As the sludge (poopwater) goes into the aeration basin, bugs are at work removing nutrients and breaking down the organic matter. Some bugs require aerobic atmospheres, some anaerobic and some anoxic zones. At this plant the sludge moves through the aeration basin which is designed for specific atmospheres for the bugs to thrive. Then it travels straight into the flocculation basin where it has time to let particles move together to form larger particles (known as floc). Then, on to the secondary clarifier, our heroine of the story, where the large particles have time to settle out.

The rates I’ve been calculating are used to verify that suspended particles have slow enough velocities in the water that they will settle out. In Texas, these rates are regulated by the TCEQ (think Texas EPA). On our project, we’re shortening the weir length (where water is able to spill over into the launder to go on to the next process as seen in the photo above). This re-design is to limit the amount of solids that move on and don’t settle out.

Even though we’ve been hired specifically to improve this process (which is the point of the regulation), we have to show that it still meets code or get a variance to the rule. Thus, all the calculations.

Here is the secondary clarifier at the plant. Just like in the cartoon above, water spills in from two ways into the launder.
A close up of the side weir on one side of the launder. You can see all the little particles that are suspended, unable to settle out, passing over the weir and onto the next process.