In this talk, I will present several nonlinear models for microbial dynamics vis-a-vis human and environ- mental health that I formulated and the results I obtained from analyzing them. Firstly, I will present a stoichiometric organic matter decomposition model in a chemostat culture that incorporates the dynam- ics of grazers. This mechanistic biodegradation model leads to reliable and suggestive ecological insights in the preservation and restoration of our fragile ecosystems. Using the model, I answer the following research questions: (i) What mechanisms allow microbes and resources to persist uniformly or go ex- tinct? (ii) How do grazing and dead microbial residues affect decomposition? Secondly, I will talk about a greenhouse gas biogenesis model which I formulated and fitted to oil sands tailings hydrocarbons data to estimate model parameters. This model can be used to (i) predict the volume of greenhouse gasses emitted at any given time in an oil sands tailing pond and an end pit lake, (ii) calculate the time required to produce a given volume of cumulative greenhouse gases from them and (iii) estimate how long it will take for an oil sands tailing pond and an end pit lake to stop emitting greenhouse gases. Lastly, I will present some directly and indirectly transmitted infectious disease models that I designed. The questions I answered using these models include: (i) Why are there irregularities in seasonal patterns of outbreaks amongst different countries? (ii) How can we estimate the transmission function of an infectious disease from a given incidence or prevalence data set? (iii) How can we control the period and intensity of pathogenic disease outbreaks?