Methane (CH4) is a potent greenhouse gas often emitted in low concentrations from waste sector activities. Biological oxidation techniques have the potential to offer effective methods for the remediation of such emissions. In this study, methods of improving the CH4 oxidation performance of a horizontal flow biofilm reactor (HFBR) technology, operated at low temperatures, were investigated.Three pilot scale HFBRs were operated over three phases (Phases 1, 2 & 3) lasting 310 days in total. The reactors were loaded with 13.2 g CH4/m 3 /hr during each phase and operated at an average temperature of 10 o C.In Phase 1, nutrients were added to the biofilm via a liquid nutrient feed (LNF) comprising water and nutrient mineral salts. Average removals were 4.2, 3.1 and 2.3 g CH4/m 3 /hr for HFBRs 1, 2 and 3 respectively.
Commented [NU1]:In response to Reviewer #1 comment; "Authors must start the abstract with the motivational statement related to the background of study"
Commented [NU2]:In response to Reviewer #2 comment; "Standardize the format of units for performance variables (methane load, methane removal, etc.) through the document included the abstract" units have been standardised as g XX/m 3 /hr In Phase 2 silicone oil was added to the LNF of all three HFBRs. Average removals increased, when compared to Phase 1, by 31%, 79% and 78% for HFBRs 1, 2 and 3 respectively.In Phase 3 a non ionic surfactant (Brij 35) was added to the LNF and silicone oil liquid phase of HFBRs 1 and 2. The operating conditions of HFBR 3 were not changed and it was used as a control. A concentration of 1.0 g Brij 35/L proved most effective in improving reactor performance; with removal rates increasing by 105% and 171% for HFBRs 1 and 2 respectively when compared to Phase 1.These results indicate the potential of liquid phase optimisation for improving mass transfer rates and removal performances in biological reactors treating CH4.