Effect of recycling digestate filtrate for cow dung dilution on biogas production

Biogas production in the Sahelian zone faces the problem of water shortage. This is one of the biggest obstacles encountered by projects to substitute firewood by biogas in this areas. The study aims to improve the accessibility of households to biogas in water shortage conditions by recycling the filtrate of the digestate into a new dilution of the substrate for biogas production. Thus, the Cow Dung (CD) digestate from the biogas unit was filtered. Filter with sand and cotton and filter with sand, biochar, and cotton were made. The filtrate obtained was used to make five treatments with CD to feed mini biodigesters (1st generation) of 1 liter each. After a HRT of 30 days, the digestate from the 1st generation was again filtered and reused to dilute five treatment (2nd generation). The biogas production and pH of each treatment repeated three times were evaluated. The results show that the dilution of CD with the filtrate from the 1st generation significantly improves the production of biogas by 47% compared to that of dung diluted with ordinary water. In the 2nd generation, dilution with OW provided the highest production which is 7% more than that obtained from the filtrates without biochar. As the pH is concerned, it varies between 6 and 7.5 when filtrates are used. It was more acidic when OW has been used. It appears that, the same quantity of water can be used three times for substrate dilution. This leads to less water demand for biogas unit running