Rava, Eleonora Maria ElizabethChirwa, Evans M.N.2016-07-042016-05Rava, E & Chirwa, E 2016, 'Effect of carrier fill ratio on biofilm properties and performance of a hybrid fixed-film bioreactor treating coal gasification wastewater for the removal of COD, phenols and ammonia-nitrogen', Water Science and Technology, vol. 73, no. 10, pp. 2461-2467.0273-1223 (print)1996-9732 (online)10.2166/wst.2016.108http://hdl.handle.net/2263/53600The purpose of this study was to determine the effect different biofilm carrier filling ratios would have on biofilm morphology and activity and bacterial diversity in a hybrid fixed-film bioreactor treating high strength coal gasification wastewater (CGWW) for the removal of chemical oxygen demand (COD), phenols and ammonia-nitrogen. Results showed that a carrier fill of 70% formed a ‘compact’ biofilm, a 50% fill formed a ‘rippling’ biofilm and a 30% fill formed a ‘porous’ biofilm. The highest microbial activity was obtained with a 50% carrier fill supporting a relatively thin biofilm. The highest level of biofilm bound metals were aluminium, silicon, calcium and iron in the ‘compact’ biofilm; nitrogen, magnesium, chloride, sodium and potassium in the ‘rippling’ biofilm, and copper in the ‘porous’ biofilm. The bioreactor improved the quality of the CGWW by removing 49% and 78% of the COD and phenols, respectively. However, no significant amount of ammonia-nitrogen was removed since nitrification did not take place due to heterotrophic bacteria out-competing autotrophic nitrifying bacteria in the biofilm. The dominant heterotrophic genera identified for all three carrier filling ratios were Thauera, Pseudaminobacter, Pseudomonas and Diaphorobacter.en© IWA Publishing 2016. The definitive peer-reviewed and edited version of this article is published in Water Science and Technology, vol. 73, no. 10, pp. 2461-2467, 2016. doi: 10.2166/wst.2016.108 and is available at : http://www.iwaponline.com.Anox-kaldnessBiofilmNext-generation sequencingNitrificationPollutantsThaueraCoal gasification wastewater (CGWW)Chemical oxygen demand (COD)Postprint Article