Institutional Repository UIN Sunan Kalijaga YogyakartaDINAMIKA POPULASI BAKTERI PADA FERMENTASI CAMPURAN LIMBAH NASI, MOLASES DAN KULIT SINGKONG MENGGUNAKAN METODE FERMENTASI LANGSUNGNIM.:19106040014Nur Hisyam Fu’ad WidodoauthorOrganic wastes such as leftover rice, cassava peels, and molasses have great potential to be processed through fermentation into value-added products. This study aimed to analyze the dynamics of bacterial populations during the fermentation of a mixture of rice waste, molasses, and cassava peels using instant yeast (Saccharomyces cerevisiae) as a starter. The study employed a 4 × 3 factorial completely randomized design (CRD) with substrate variations (A1: 100% rice waste; A2: 100% rice waste + 20% molasses; A3: 80% rice waste + 20% cassava peel + 20% molasses; A4: 70% rice waste + 30% cassava peel + 20% molasses) and fermentation times (24, 48, and 72 hours). Parameters measured included optical density (OD 600) as an indicator of total bacteria, pH, and Total Titratable Acidity (TAT). The results showed that bacterial populations peaked at 24–48 hours of fermentation and decreased dramatically at 72 hours due to limited nutrients and accumulation of organic acids. The highest OD 600 value was obtained in the A4B1 treatment (70% rice + 30% cassava peel + 20% molasses, 24 hours) at 2.143, indicating that this substrate combination was the most optimal for initial bacterial growth. The highest Total Titratable Acidity (TAT) was obtained in the A2B3 treatment (rice + 20% molasses, 72 hours) at 1.008%, proving that the addition of 20% molasses effectively increased organic acid production. The pH decreased from 6 to 4–5 during fermentation, with cassava peel treatments (A3 and A4) showing more stable pH (5) up to 72 hours compared to treatments without cassava peel which reached pH 4. This study concludes that 48 hours of fermentation is optimal for bacterial growth, while 72 hours is optimal for organic acid production. Treatment with molasses addition (A2) is recommended for concentrated organic acid production, while the addition of cassava peels (A3 and A4) is recommended for applications requiring pH stability, such as liquid organic fertilizer or animal feed probiotics.570 Biologi, Ilmu Hayat2026-08-18UIN SUNAN KALIJAGA YOGYAKARTA;FAKULTAS SAINS DAN TEKNOLOGIThesis

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