The studied bacterial strains grew and evolved hydrogen utilizing orange peel as the sole carbon and nitrogen source, as much as their respective controls grown in R€AH media only. Noticeably, orange peel inhibited the uptake hydrogenase (Hup) activity and simultaneously enhanced the cumulative hydrogen evolution levels. The cumulative hydrogen was enhanced as hydrogen oxidation/recycling (through the electron transport chain), that is catalyzed by Hup has been inhibited. Therefore, the role played by orange peel surpassed its intended role as a source of nutrients. Rather, it seems to act as a specific inhibitor of Hup activity. Orange peel, in the literature, is famous for its oils and pharmaceutical components rather than nutritional value. Conversion efficiency of orange peel to hydrogen was not proportional with its reducing sugars content; it has been inhibited by high concentrations most probably due to pharmaceutical compounds in orange peel. The studied strains are purple non-sulfur bacteria (PNS), which have been newly isolated from local sewage water samples at Assiut and Sohag cities (Upper Egypt). Orange peel together with PNS, in this respect, is unique. PNS generally cannot use biowastes for growth, as they do not release exozymes to hydrolyze large molecules (e.g. cellulose, starch or proteins) into absorbable molecules (sugars, organic acids, amino acids, etc.). Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The studied bacterial strains grew and evolved hydrogen utilizing orange peel as the sole carbon and nitrogen source, as much as their respective controls grown in R€AH media only. Noticeably, orange peel inhibited the uptake hydrogenase (Hup) activity and simultaneously enhanced the cumulative hydrogen evolution levels. The cumulative hydrogen was enhanced as hydrogen oxidation/recycling (through the electron transport chain), that is catalyzed by Hup has been inhibited. Therefore, the role played by orange peel surpassed its intended role as a source of nutrients. Rather, it seems to act as a specific inhibitor of Hup activity. Orange peel, in the literature, is famous for its oils and pharmaceutical components rather than nutritional value. Conversion efficiency of orange peel to hydrogen was not proportional with its reducing sugars content; it has been inhibited by high concentrations most probably due to pharmaceutical compounds in orange peel. The studied strains are purple non-sulfur bacteria (PNS), which have been newly isolated from local sewage water samples at Assiut and Sohag cities (Upper Egypt). Orange peel together with PNS, in this respect, is unique. PNS generally cannot use biowastes for growth, as they do not release exozymes to hydrolyze large molecules (e.g. cellulose, starch or proteins) into absorbable molecules (sugars, organic acids, amino acids, etc.). Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Effect of mixed culture bacteria (MCB) addition, initial substrate concentration to inoculum (So/Xo), carbon to nitrogen (C/ N) ratio on the hydrogen production (HP) from organic fraction of municipal solid waste (OFMSW) via dry anaerobic digestion was investigated. The results showed that supplementation of OFMSW with MCB substantially improved hydrogen yield (HY) and HP. HYs were 306.2 ± 33.0, 149.8 ± 16.6, and 155.3 ± 22.9 mlH2/gCODremoved for OFMSW supplemented with MCB, OFMSW, and MCB, respectively. HP at So/Xo ratio of 9.2 gCOD/gVSS was 3.1 times higher than those obtained at So/Xo ratio of 1.7 gCOD/gVSS. The maximum HY of 338.4 ± 18.9 mlH2/gCODremoved was achieved at So/Xo ratio of 9.2 gCOD/gVSS. The HP and HY were substantially increased from 169.7 ± 17.1 to 524.2 ± 34.4 ml and from 163.1 ± 23.6 to 338.4 ± 18.9 mlH2/gCODremoved with increasing the C/N from 16 to 25, respectively. However, HP and HY decreased at C/N ratio exceeding 26.6. The modified Gompertz equation model was highly fitted to the experimental data with correlation coefficient (R2>0.984). The 16S rRNA sequences showed the dominance of Pseudomonas fulva with similarity of 99%. Copyright © 2015 John Wiley & Sons, Ltd.