Evaluation of lactic acid produced by fermentation of vegetable waste as a treatment in faecal sludge (Kenya)

The utilization and disposal of fecal sludge pose significant challenges due to harmful microorganisms. Effective sludge treatment methods can reduce pathogens and meet WHO standards for disposal or reuse. In developing countries, treatment options for faecal sludge from On-Site Sanitation facilities are often unavailable, ineffective, or unaffordable. This research evaluated the effectiveness of lactic acid derived from fermented tomato, cabbage, and carrot vegetable wastes as a cost-effective treatment method for faecal sludge from On-Site Sanitation facilities. Equal amounts of fresh tomato, cabbage, and carrot wastes were collected, pre-treated, and lacto-fermented for six days at 37 °C. Daily pH and lactic acid concentration monitoring was done using an electrode pH meter and UV-Vis spectrophotometer. The pH levels decreased from 5.37±0.14, 4.36±0.15, and 5.90±0.05 to 3.20±0.16, 3.30±0.07, and 3.23±0.10 for carrot, tomato, and cabbage waste, respectively, indicating successful fermentation Thin Layer Chromatography confirmed the presence of lactic acid. Cabbage-derived lactic acid was used for faecal sludge treatment since it had higher lactic acid concentrations and a Retention Factor of 0.54, similar to the lactic acid standard. Lactic acid concentrations were 1.61±0.34 mg/ml for carrot, 1.39±0.09 mg/ml for cabbage, and 1.17±0.13 mg/ml for tomato after seven fermentation days. Four reactors were set up with different FS to lactic acid ratios (1:1, 1:0.5, 1:0.35) and a control. Escherichia coli served as the pathogen indicator. Total solids, volatile solids, and odor levels were studied over 16 days. Only the 1:1 reactor eliminated E. coli after four days, with a final plate count of zero cfu/ml, compared to 1.6×10^7, 1.1×10^7, and 1.9×10^3 cfu/ml for the 1:0.5, 1:0.35, and control reactors, respectively. The 1:1 reactor also achieved the highest odour elimination (7.3 TON), followed by the control (25 TON), 1:0.35 (26.6 TON), and 1:0.5 (42.6 TON). These findings suggest that vegetable waste-derived lactic acid can be an effective and affordable faecal sludge treatment method. The optimal 1:1 ratio offers significant pathogen reduction and odour control, presenting a viable solution for faecal sludge management in developing countries. More research should be carried out to establish this method’s scalability in faecal sludge management