Designing Circular Infrastructure for Large-Scale Dryland Agricultural Expansion: A Project-Status-Adjusted Assessment of Biogas, Biochar, Water and Nutrient Pathways in Algeria

Algeria's expansion of irrigated agriculture in arid and hyper-arid regions can generate crop residues, manure and agri-food by-products relevant to biogas, biomethane, biochar and nutrient recovery. This paper develops a project-status-adjusted framework that separates two questions: what circular-resource outputs are implied by announced development capacity, and what quantities can be supported by current implementation evidence. A six-stage ladder moves from gross theoretical to circularly allocable potential; soil and existing uses are deducted before logistics, and standing protective vegetation is excluded except for unavoidable maintenance residues. The principal announced-capacity envelope comprises the officially documented 153,000-ha combined scale of the Baladna and BF El Djazair parent projects. A separate inclusive sensitivity reaches 154,200 ha by adding a 1,200-ha project reported in secondary sources. To avoid presenting an unknown future crop mix as a forecast, these areas are evaluated only as a standardised wheat-straw-equivalent sensitivity. Its central 153,000-ha case yields 78,506 t yr⁻¹ of logistically recoverable residue and mutually exclusive technical ceilings of 14.80 million m³ CH₄ yr⁻¹ or 24,729 t biochar yr⁻¹. The implementation-based worked example instead uses BF El Djazair's documented 1,600-ha first-wheat-harvest module and yields 821.0 t yr⁻¹, 154,739 m³ CH₄ yr⁻¹ or 258.6 t biochar yr⁻¹ in the corresponding central screens. BF is used for methodological demonstration because public sources identify both its harvested area and crop, not because it is larger or more important than Baladna. All conversion outputs are screening ceilings rather than observed production, additive products, plant designs or contractually bankable supply.