Integrated Proximate and Contamination Analysis of Tofu Wastewater: A Case Study in Telaga Subdistrict, Gorontalo, Indonesia

Abstract

Tofu wastewater is a major contributor to organic pollution, yet household-scale industries in eastern Indonesia remain understudied. This study integrated proximate and contamination analyses of tofu and its wastewater in Telaga Subdistrict, Gorontalo, Indonesia. Samples were collected weekly for three weeks at three points: upstream (A), downstream (B), and wastewater channel (C). Proximate composition of tofu and wastewater was determined following Indonesian National Standards (SNI) and APHA methods, while contamination parameters (COD, BOD, TSS, ammonia, and pH) were statistically evaluated using one-way ANOVA with Tukey’s test. Results showed that tofu contained 6–7% protein, 1–2% fat, and more than 81% moisture, while wastewater retained residual nutrients, particularly soluble proteins and carbohydrates. Contamination loads at Point C were critical, with COD (7499 mg/L), BOD (864 mg/L), and TSS (147 mg/L) far exceeding national and international thresholds (p < 0.05), whereas ammonia (0.01–0.10 mg/L) and pH (7.2–7.3) remained within acceptable limits. Method validation confirmed analytical reliability (R² ≥ 0.997; %RSD < 10%; recovery 92–105%). This study concludes that even household-scale tofu industries discharge wastewater with pollution loads comparable to larger operations, highlighting urgent needs for low-cost remediation. At the same time, the nutrient residues indicate valorization potential for biogas generation, microbial biomass, and agricultural reuse, providing baseline data to inform local water management policies and circular economy initiatives.