Pros and cons of nitrogen replenishment in compost, augmented by natural acidity regulators, agri-buffering adjuvants, and grease trap waste

Nitrogen loss via ammonia volatilisation remains a major limitation in industrial composting, particularly under alkaline conditions with insufficient pH control. In this study, a laboratory-scale in-vessel composting system was established to systematically compare multiple nitrogen regulation strategies, including natural acidity regulators, agri-buffering adjuvants, and grease trap waste (GTW), under identical and controlled conditions. The effects of these additives on nitrogen retention and transformation were evaluated through moisture conservation, pH stability, nitrogen conversion history, total nitrogen content, and elemental evolution during composting. Compared with the untreated control, organic acid–based and phosphate-buffered additives significantly improved nitrogen conservation and process stability. Total nitrogen loss remained below 20% across treatments, while compost pH was stabilised within a narrower range (8.1–9.1) with reduced variability (SD = 0.22). Germination and seedling vigour tests further indicated enhanced compost maturity in selected treatments, with germination rates reaching 100% and seedling vigour index values up to 1300. In contrast, GTW exhibited distinct nitrogen transformation behaviour, revealing trade-offs between nitrogen retention and overall composting performance. This study provides a systematic comparison of nitrogen regulation pathways under identical in-vessel conditions and proposes a holistic framework integrating moisture, pH, nitrogen dynamics, and elemental changes to support informed selection of nitrogen control strategies for industrial composting applications. The industrial Peats Group Ltd. green waste used allowed good composting with all natural additives studied, facilitating the comparative value of this study. • In-vessel composting enabled controlled comparison of nitrogen regulation strategies. • Nitrogen loss remained below 20% under buffered treatments. • Compost pH was stabilised within a narrower range 8.1–9.1 (SD = 0.22) in buffered systems. • Germination and seedling vigour were improved in selected treatments. • Integrated assessment ranked G2 as the best overall treatment, while G6 excelled in C/N evolution.