Sludge accumulation and methanogenic activity in an anaerobic lagoon

Sludge accumulation and the characteristics of anaerobic digestion in sludg e had been investigated in a primary anaerobic lagoon. Methanogenic potenti al of sludge was evaluated by an anaerobic digestion test which measured th e methane production rate. Sludge was sampled at several points in the lago on to determine spatial variations and with a monthly frequency from the st art-up of the lagoon to observe the development of anaerobic degradation. M aximum amounts of sludge accumulated near the inlet. The mean methane produ ction of sludge was 2.9 ml gVS(-1) d(-1) Sludge near the outlet presented a greater methanogenic activity and a lesser concentration of volatile fatty acids than near the inlet. The different stages of anaerobic degradation w ere spatially separated, acidogenesis near the inlet and methanogenesis nea r the cutlet. This staged distribution seemed to increase Efficiency of ana erobic fermentation compared with septic tanks. Methane release at the surf ace of the lagoon was estimated to be very heterogeneous with a mean of 25 l m(-1) d(-1). The development of performance and sludge characteristics sh owed the rapid beginning of methanogenesis, three months after the start-up of the anaerobic lagoon. Considering the volume of accumulated sludge, it could however be expected that methanogenic activity would further increase .