Anaerobic digestion (AD) is a natural process whereby microorganisms break down organic material in the absence of oxygen. Biodigesters (sealed tanks where AD occurs) are complex ecological systems where different microorganisms work together to produce biogas (a mixture of methane and carbon dioxide). They are used to produce energy and fertilizers from organic wastes, such as food waste, crop residues, and animal manure. This article describes the use of a simple model biodigester, built from low-cost materials (water bottles), as a way to introduce students to physical and conceptual models while learning about resource recovery, waste management and sustainability. We piloted our curriculum with pre-service teachers at a [US University], in a middle school [US city] and a high school in [Sub-Saharan African city, country]. Students learned about AD, developed research questions, and built a model biodigester as a tool for scientific inquiry. They collected and analyzed data (e.g., daily biogas and methane production), and they interpreted their results to answer their research questions and make recommendations for local biodigester construction. This article provides an overview of the curriculum and how it can be used in science classrooms to engage students in science and engineering practices.