Biogas Production from Co-digestion of Cotton Yarn Waste and Human Urine

Aim: To investigate the feasibility of producing biogas from anaerobic co-digestion of cotton yarn wastes (CY) and human urine (HU) using fresh cow dung as the inoculum.

Study Design: Anaerobic co-digestion of CY waste and HU and CY waste alone were done using batch reactors.

Place and Duration of Study: CY were collected from Rivatex Eastern Africa Limited, Eldoret, Kenya while fresh cow manure used as inoculum was collected from a farm at Moi University, Eldoret, Kenya. Human urine sample was collected in a clean sterile container at Moi University hostel, Eldoret, Kenya. The experimental set up and analyses were performed at Chemical and Process Engineering Laboratory, Moi University, Kenya between January 2020 and May 2020.

Methodology: CY, HU and fresh cow dung were subjected to physicochemical analysis. Batch anaerobic co-digestion of CY and HU, and CY alone were carried out under ambient temperature (25 ± 3 ) conditions for 95 days and 37 days, respectively.

Results: The CY contained 90.46% total solids, 77.12% volatile solids and 9.54% moisture content while the corresponding values for HU were 2.9%, 58.5% and 97.1%, respectively. CY had a high carbon to nitrogen ratio. The biogas yield from anaerobic co-digestion was 35.6% more than digestion of CY alone. The highest daily biogas production for co-digestion and digestion of CY alone were 330 mL and 386 mL on day 12 and 21, respectively. The total biogas yield when CY co-digested for 95 days was 10,125 mL which decreased to 6,519 mL without co-digestion after 37 days.

Conclusion: Our results showed that co-digestion produced more biogas than digestion of CY alone. Conclusively, the presence of HU during anaerobic digestion of CY enhanced the biogas production by more than 35.6% demonstrating that HU could be an effective waste for co-digestion of solid wastes such as CY. Further research should focus on monitoring parameters like temperature, buffering capacity and fatty acid levels to ensure optimal efficiency and maximum biogas yield.