Abstract

MENDEZ-NOVELO, R.I. et al. Anaerobic Digestion of Effluents from Septic Tanks. Ing. invest. y tecnol. [online]. 2012, vol.13, n.3, pp.339-349. ISSN 2594-0732.

In this work, anaerobic digestion was used to treat domestic septic tanks effluents using a UASB reactor. A hydraulic retention time (HRT) of 24 h and a total volume of 24 L were used to design the reactor. A gravel filter in the upper part of the UASB reactor, prior to the effluent discharge, was used as a design modification. Start up methodology was also modified; the reactor was inoculated with and excess of bio-mass, in this case ruminal liquid was used, and it was recycled from half height of the reactor to its lower part at a flow of 4 L/h. Biogas production started after 19 days of inoculation. The reactor was then fed continuously during 71 days, from day 21 to 53 at a HRT of 36 h and at a HRT of 24 h from day 54 up to the day 92. When the continuous feeding started, efficiencies were negative due to the start up strategy, with an excess of inoculums. The system stayed fluctuating up to the day 72, when it was estimated that stability was reached in terms of total and soluble COD efficiencies. Removal of 56% of total COD and 72% of soluble COD were obtained, reaching efuent average concentrations of 166 mg/L of total COD and 62 mg/L of soluble COD.

Keywords : UASB; rumen; septic tanks; start up; anaerobic digestion; wastewater.