The biogas generated from anaerobic digestion (AD) also includes undesirable by-product such as hydrogen sulfide (H2S), which must be removed before the biogas can be used as a clean energy source. Therefore, it is necessary to find an appropriate strategy to simultaneously enhance the methane yield and reduce H2S production. An efficient strategy-pretreating sludge at pH 10 for 8 d and adjusting the system at neutral pH to produce methane for 20 d-is reported for the synchronous enhancement of methane production and reduction of H2S production during AD. The experimental results showed that the cumulative methane yield was 861.2 +/- 6.1 mL/g volatile solids (VS) of sludge pretreated at pH 10 in semi-continuous stirred anaerobic reactors for 84 d, an increase of 49.6% over the yield in the control. Meanwhile, the cumulative production of H2S was 144.1 x 10(-4) mL/g VS, 54.2% lower than that in the control. (C) 2017 Elsevier Ltd. All rights reserved.