04 Streams

The key elements used in PooPyLab for defining streams are:

1)  Splitters

2)  Pipes

3)  Influent

4)  Effluent

5)  WAS (waste activated sludge)

The definitions of the above can be found in the unit_procs/streams.py.

4.1 Splitters

The "splitter" class is chosen as the base for all other stream classes. This is a bit couter-intuitive considering a splitter has three connection points, namely an inlet, a mainstream outlet, and a sidestream outlet. However, it seemed to make the main loop (top level code) cleaner by demanding less frequent probing of whether a process unit has a sidestream.

A splitter can receive flows from multiple sources. However, it can only split the combined inlet flow into two streams, one to the mainstream outlet, and the other the sidestream.

4.2 Pipes

A "pipe" is a "splitter" with a blinded sidestream. Like a splitter, it can have multiple flow sources but only discharges the combined flow to one downstream receiver.

4.3 Influent

An "influent" is a "pipe" without further upstream (i.e. inlet == None). An influent is the flow source of the WWTP.

Currently, an influent only provides a constant flow and a set of constant wastewater constituents. It will offer variable flows and loads output in the future.

A unique function of an influent is that it converts typical wastewater constituent measurements, such as BOD, TSS, VSS, TKN, and NH3-N, into ASM model components (inert COD, readily biodegradable COD, slowly biodegradable COD, slowly biodegradable nitrogen, etc.).

4.4 Effluent

An "effluent" is a "pipe" that is one of the end points of the WWTP's flow (i.e. main outlet == None).

4.5 WAS (Waste Activated Sludge)

WAS is needed to balance out the growth of biomass and maintain the solids inventory in the WWTP. A "WAS" is essentially an "effluent". However, a WAS unit has the funtionality of calculating its own flow based on the solids inventory in the reactors, the solids leaving the WWTP via "effluent", and the target solids retention time (SRT) specified by the user.

What makes the WAS class different from the effluent class is that WAS can be further connected to a downstream process unit such as a sludge thickener or a sludge digester.