Paper Title
Improve the Efficiency of Productive Biofilm Growth for Better-Harvested Rainwater Quality

Abstract
Harvested rainwater carries bird’s droppings, dust, and sediment from catchment area tostorage. If not well managed, stored rainwater quality can deteriorate. Inside the storage, self-cleaning and regulation of bacterial community are assured by biofilm. However, little research has been done to explore factors influencing the biofilm growth in stored rainwater. Findings from previous studies showed that biofilms are sensitive to environmental factors and bacterial communities. In this present study, the effect of visible light and water depth on biofilm formation were examined. Rainwater was collected in two storages, one exposed to visible light and another stored indoors as dark control. Biofilm formation and viable cells were monitored in each non-partitioned layer in the storage (top, middle, bottom) once a week for 4 weeks. Results showed that rainwater inside the storage exposed to visible light had physical parameters (pH: 6.09 - 7.4, dissolved oxygen:8.21-8.32 mg/L) favorable to biofilm formation compared to the dark control. When exposed to visible light, the number of viable cells in rainwater and in biofilm decreased as water depth increased. When indoors, viable cells in rainwater also decreased with the increase in water depth. However, viable cells incorporated into biofilm was notably highest at the bottom part of the storage. Furthermore, biofilm biomass was also noted to be highest at the bottom layers in both storages exposed and not exposed to visible light. Therefore, biofilm efficiency in improving rainwater quality appears to be better at the bottom part of storage in the dark. Keywords - Biofilm, Stored Rainwater, Visible Light, Water Depth, Biomass.