Optimized waste-free valorization of fish processing by-products: comparative insights into fertilizer production and collagen recovery

This study addresses the inefficient valorization of fish processing waste, a significant challenge in sustainable waste management. Current methods typically focus on either fertilizer production or collagen extraction, lacking integrated approaches that maximize resource recovery. This research develops a dual-purpose strategy for utilizing carp and mackerel residues (bones, skin, head meat) through optimized chemical hydrolysis to produce fertilizers while assessing collagen extraction feasibility. Optimal conditions for alkaline hydrolysis were established at 7.5 % KOH, 80 °C, and a 1:1 solid-to-liquid ratio, while acid hydrolysis required 60 % H 2 SO 4 , 100 °C, and the same ratio. The mutual neutralization of hydrolyzates increased nitrogen content by 1.0 % compared to collagen-extraction methods, enhancing fertilizer efficiency. Short-term plant trials (7 days) demonstrated a 70 % increase in stem growth at low nitrogen doses (20 % of requirements) compared to controls, though long-term effects (30 days) require further evaluation. This study advances waste-free processing by integrating collagen recovery with fertilizer production, aligning with circular economy principles. The proposed method enhances nutrient utilization, reduces environmental impact, and provides an economically viable solution for fish by-product management, contributing to sustainable agricultural applications and clean production technologies. • Zero-waste technology integrates collagen recovery and biostimulant production. • Optimized hydrolysis results in complete collagen denaturation. • Hydrolyzates from both methods exhibit similar biostimulant and fertilizing effects. • Developed approach ensures waste-free fertilizer production and collagen recovery.