TITLE:
Development of Phosphate-Enriched Compost Blocks from Spent Coffee Grounds and Cattle Manure Using Calcium Hydroxide as a Sustainable Growing Medium for Chili Seedlings
AUTHORS:
Asmak Afriliana, Sofian Afandi, Muhammad Baharudin Najmi, Elida Novita, Ning Puji, Soni Sisbudi Harsono
KEYWORDS:
Spent Coffee Grounds, Compost Block, Calcium Hydroxide, Phosphate Enrichment, Chili Seedlings, Circular Bioeconomy
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.14 No.9,
September
29,
2026
ABSTRACT: The increasing generation of spent coffee grounds (SCG) from the coffee industry has created significant environmental challenges while simultaneously offering opportunities for resource recovery within a circular economy framework. This study developed phosphate-enriched compost blocks derived from SCG and cattle manure through calcium hydroxide modification and evaluated their suitability as a sustainable growing medium for chili (Capsicum annuum L.) seedlings. Compost was produced using three cattle manure proportions (10%, 20%, and 30%), followed by enrichment with calcium hydroxide and phosphoric acid (H3PO4) before being formed into compost blocks. Compost quality was evaluated through pH, temperature, relative humidity, nitrogen, phosphorus, potassium, organic carbon, and C/N ratio analyses. The agronomic performance of the compost blocks was assessed by measuring seedling height, leaf number, and stem diameter. The results showed that the compost containing 30% cattle manure exhibited the highest composting temperature, the greatest phosphorus (0.15%) and potassium (0.28%) contents, and a C/N ratio within the Indonesian National Standard (SNI 19-7030-2004). Compost blocks prepared from this formulation (K30M) significantly improved chili seedling growth compared with other modified compost treatments, although their performance remained below that of commercial compost. The enhanced plant growth was associated with increased phosphorus availability following calcium hydroxide treatment, which promoted nutrient retention within the compost matrix. These findings demonstrate that phosphate-enriched compost blocks produced from SCG represent a promising environmentally friendly alternative for reducing organic waste while partially replacing conventional nursery media.