ISSN: 1659-2751



Anaerobic Biodigestion – an Alternative for the Treatment of Septic Sludge


The study analyzed anaerobic digestion as an alternative for the treatment of septic sludge. In the experimental biodigestor laboratory at EARTH University the effect of biodigestion on the water decontamination process was studied, comparing influents and effluents and considering different retention times. The quality and amount of biogas produced was evaluated regarding a possible marketing of bottled biogas. In the biodigestor laboratory, twelve bags were filled with septic sludge and the bags were closed to induce the anaerobic digestion process. Six of the bags received sludge from an industry located in the region of Guápiles and the other six bags received the sludge from a housing complex near Siquirres. From the six bags of every load, three bags were evaluated with a retention time of 45 days and another three bags with a retention time of 60 days. After each treatment time, the effluent quality (pH, DBO5, DQO, NO3, NH4+, PO43−, ST, and fecal coliformes) was evaluated and the results were compared with the influent results. The biogas was analyzed through CH4 and H2S measurements and the volume of the gas produced was measured during treatment. Between the two different charges of sludge differences were observed, especially in the microbial content; nevertheless most of the evaluated parameters did not differ significantly between the two kinds of sludge. The 60 day retention time showed better results in terms of reduction of fecal coliforms than the 45 day retention time. The other evaluated parameters did not show differences between the retention of 45 and 60 days. Overall, there was a significant reduction of the sludge contamination; however the levels of ST and fecal coliforms failed to comply with the legal requirements after the treatment. The biogas production was very low and the concentration of H2S elevated; therefore, a commercial use of the biogas from raw sludge would not be very profitable.

Key words: biodigestor, biogas, decontamination of water, septic sludge, retention time.

Artículo en español (pdf) (741)