BACKGROUND: Biological oxidation in biotrickling filters of high H 2 S loads contained in biogas streams still requires further study to reduce elemental sulfur accumulation due to limited gas-liquid oxygen mass transfer inside biotrickling filter beds.Reduction of elemental sulfur accumulation may be improved by regulating the main manipulated variables related to oxygen mass transfer efficiency during biological hydrogen sulfide removal in biotrickling filters. RESULTS: Trickling liquid velocity and co-current flow were selected as the most appropriate manipulated variable and flow pattern configuration compared with manipulating the air supply flow rate and a counter-current flow pattern in order to improve gas-liquid oxygen mass transfer in abiotic conditions. The influence of trickling liquid velocity on the performance of a lab-scale biotrickling filter treating high loads of H 2 S in a biogas mimic and operating in co-current flow at neutral pH and packed with plastic pall rings was investigated.CONCLUSIONS: The effect of trickling liquid velocity modulation between 4.4 and 18.9 m h −1 in biotrickling filter performance was compared with operation without trickling liquid velocity regulation. Velocity regulation resulted in an improvement of 10% in the elimination capacity and, most importantly, a 9% increase in product selectivity to sulfate at a loading rate of 283.8 g S-H 2 S m −3 h −1 . Concentration profiles along the biotrickling filter height evidenced that trickling liquid velocity regulation progressively led to better dissolved oxygen distribution and, thus, enhanced overall biotrickling filter performance.

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To explore the changes in the microbial community structure during the recovery process of an anammox reactor after a temperature shock, the 454-pyrosequencing technique was used. The temperature shock reduced the nitrogen removal rate up to 92% compared to that just before the temperature shock, and it took 70 days to recover a similar nitrogen removal rate to that before the temperature shock (ca. 0.30 g N L(-1) d(-1)). Pyrosequencing results indicated that microbial diversity in the reactor decreased as the reactor progressively recovered from the temperature shock. Anammox bacteria were accounted as 6%, 35% and 46% of total sequence reads in samples taken 13, 45 and 166 days after the temperature shock. These results were in agreement with N-removal performance results and anammox activity measured in the reactor during the recovery process. An anammox specific primer was used to precisely determine the anammox species in the biomass samples.

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