Influence of substrate particle size and detention time on mycelium-colonized sawdust efficiency for removal of faecal bacteria from slaughterhouse wastewater in batch treatment

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Mycofiltration is a recent cost-effective biotechnology that is still under development for wastewater treatment. The use of mycelium-colonised substrate for wastewater treatment in a batch system with delayed residence time and the effect of sawdust particles has not previously been considered. Slaughterhouse wastewater is discharged untreated in many developing countries majorly due to the high cost of existing conventional treatment systems. The effect of sawdust detention time and particle size on the removal efficiency of faecal bacteria from slaughterhouse wastewater by Pleurotus ostreatus mycelium was assessed in the lab using mycelium colonized with sawdust of particle sizes (0.6, 1.18, 2.36 mm and unsorted particle sizes) and under varying detention times (0, 12, 24, 36, 48, 60 and 72 hours) using batch treatment procedure. Hydrogen peroxide produced during mycelium colonisation of the sawdust was also evaluated. Oxidation-reduction potential (ORP) was measured during this study to determine the oxidative capacity in each treatment reactor. The removal efficiency of Escherichia coli ranged from -7.9 – 77.2 % and was the highest for mycofilter with 2.36 mm sawdust particle size at 72 hours detention time (0.7 log removal). Salmonella spp. removal efficiency ranged from 0.66 – 71 % with the highest efficiency recorded in the system with 1.16 mm also at 72 hours (0.4 log removal). Mean hydrogen peroxide concentration ranged from 0.53±0.12 (unsorted inoculated) to 25.18±1.77 mg/l (1.18 mm, 72 hours). ORP values ranged from 5.0±2.2 mV (raw wastewater, 24 hours) to 232±55 mV (unsorted inoculated, 72 hours). The result of this study showed that substrate particle size and detention time have roles to play in the efficiency of mycofilters using batch treatment. The concentration of hydrogen peroxide was also influenced significantly by sawdust particle size. Therefore, there is a need to further study this system in a bid to optimize its ability to remove faecal bacteria from wastewater.