Recycling Sprout-Growing Mediums in Urban Areas as Compost and New Growing Mediums

Abstract

Used sprout-growing mediums (SGMs) are nutrient-rich biomass characterised by high lignocellulosic content and low levels of natural biodegradability, producing waste, commonly in urban areas. Accumulation of used SGMs has caused severe environmental pollution in sprout production areas. To reduce waste volume at the source, this study proposed several methods for effectively reusing SGMs in urban areas: producing compost (M1), creating new mediums for growing sprouts (M2), and creating new mediums for growing hydroponic vegetables (M3). First M1, a mixture of used SGM, peanut stalks, urea fertiliser and BIMA microbial product (C: N ratio of 30: 1) was thermophilically composted for 63 d. Then, its chemical and biological properties were analysed. For M2, a mixture of sun-dried used SGM and mung bean sprout husks was crushed and then incubated with the BIMA microbial product for 21 d. For M3, the used SGM was mixed with lime powder and incubated for 7 d before being dried. The products obtained after treating the used SGM demonstrated almost neutral pH reactions (6.37 for M1; 6.31 for M2; 7.52 for M3 - a weakly alkaline reaction). The nutrient content of M1 demonstrated the most organic matter content (OM, 58.44 %), total nitrogen (T-N, 1.77 %), total phosphorus (T-P₂O₅, 1.62 %), and total potassium (T-K₂O, 4.01 %) with a C: N ratio of 15. The M2 medium contained 58.70 % OM, 1.16 % T-N, 0.86 % T-P₂O₅, and 0.98 % T-K₂O, with a C: N ratio of 23. The M3 medium included 72.07 % OM, 0.54 % T-N, 0.55 % T-P₂O₅, and 0.58 % T-K₂O, with a C: N ratio of 63. The heavy metal content (Cu, Zn, Pb, Cd, As) for all products was within the permitted limits. There were no pathogenic microorganisms such as E. coli, Salmonella spp. found in any of the products. Based on the phytotoxicity test, M1 was confirmed to be mature, and M2 could be used to grow sprouts. Lettuce planted in M3 according to the hydroponic method was safe and of good quality. The SGM treatment methods evaluated are accessible and could be applied widely in sprout production locations, especially in urban areas.