# Develop an Excel spreadsheet that solves your mass balance model using Solver (picture of spreads…

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**Question:**

Develop an Excel spreadsheet that solves your mass balance model using *Solver* (picture of spreadsheet and explanation needed). Your model should give the substrate level (in mg BOD/L) and the biomass level (in mg VSS/L) at all key points around the circuit, as well as the required digester volume (in m^^{3}), and the hydraulic and solids retention times (in days).

Solving your model will require you to determine (or set) values for the circuit parameters α, β,. They determine the recycle activated sludge flow rate or RAS (i.e. αQ where Q is the feed flow rate to the circuit) and the wasted activated sludge flow rate or WAS (i.e. βQ). Explain clearly your reasons for the values ofα and β chosen.

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