Cow dung valorization via dual-stream separation: An integrated LCA and techno-economic framework for agricultural and algal use

Abstract

Cow dung, often left unmanaged, represents both a nutrient source and an emissions burden. Here we report a decentralized hydraulic process that separates fresh, wet cow dung into two usable streams: a fibrous solid and a nutrient-rich liquid. Pressing removed ∼ 80 % of moisture with fibre recovery of 87 %, yielding materials that supported both plant and algal growth. Fibre application increased the germination energy of Vigna radiata by 47.6 %, while the nutrient powder, obtained through freeze-drying, sustained algal cultures more effectively than synthetic f/2 medium. Life cycle analysis identified freeze-drying as the main environmental hotspot, contributing over half of the system’s climate footprint (∼0.84 kg CO₂-eq per 0.5 kg processed). Scenario modelling showed that solar or hybrid drying could reduce this impact by more than 90 %. A multitask neural network (R2 = 0.79) predicted product yields from raw input, supporting process optimization. Techno-economic evaluation indicated a net loss at bench scale, but break-even and positive returns when deployed in gauśāla settings, where local use and market-linked fibre and nutrient streams offset costs. This dual-stream approach demonstrates that cow dung can be reorganized into structured outputs without secondary effluents. By combining experimental validation, life cycle metrics, and economic modelling, the study provides a realistic pathway for circular bioresource management under decentralized rural conditions.