You are an engineer working on the design of a toilet that converts human waste into methane gas. Only solid human waste enters the toilet and is decomposed (by microorganisms) to produce methane gas and fertilizer. An undesirable by-product of the process is H2S gas, which is removed by a scrubber (it does not exit the toilet). Write an unsteady state mass balance on the H2S gas, human solid waste, and methane.