Thermophilic microflora. was seeded into an anaerobic sequencing batch reactor for hydrogen production from palm oil mill effluent and supplemented with nitrogen, phosphor-us and iron sources for biostimulants. The nutrient supplementation increased the hydrogen production yield from 1.6 +/- 0.1 to 2.24 +/- 0.03 mol H-2 mol(-1) hexose and hydrogen production rate from 4.4 +/- 0.38 to 6.1 +/- 0.031 H-2 l(-1) POME d(-1). Pollution reduction also increased as follows: COD removal from 35.5 +/- 9.8 to 62.2 +/- 2.8%, suspended solids removal from 91 +/- 3.8 to 93.6 +/- 1.1% and oil recovery from 75 +/-13 to 80 +/- 1.5%, respectively. The nutrient supplementation strategy increased the bacterial diversity in the reactor and promoted in particular the growth of hydrogen-producing bacteria, e.g. Thermoanaerobacterium thermosaccharolyticum, as assessed by denaturing gradient gel electrophoresis. (C) 2007 Elsevier Inc. All rights reserved.