Intermittent versus continuous operation of biosand filters. Water Research, Feb 2014.
Candice Young-Rojanschi, et al.
Highlights
- Biosand columns were operated either continuously or intermittently.
- Continuous operation of biosand filters is more effective at removing Escherichia coli and MS2.
- E. coli removal occurs during the pause period throughout the filter, up to 20 h.
- Anoxic conditions can occur within the first 10 cm of filter media in intermittenly operated filters.
- Hydraulic conductivity decreased at all media depths over the experimental period.
The biosand filter is a household-scale point-of-use water filtration system based on slow sand filtration, but modified for intermittent operation. Studies on slow sand filters show that intermittent operation reduces filter effectiveness. However, continuous versus intermittent operation of biosand filters has never been compared. Eight 10-cm diameter columns were constructed to represent field biosand filters. Five were operated intermittently with a 24-h residence period, while the remaining three were operated continuously. Continuous operation of the filters resulted in significantly better reduction of Escherichia coli (3.71 log10versus 1.67 log10), bacteriophage MS2 (2.25 log10 versus 0.85 log10), and turbidity (96% versus 87%). Dissolved oxygen levels at 5 and 10 cm of media depth in intermittent filters reached an average of 0 mg/L by 24 h of residence time on day 60 of the experiment. A simple numerical model was developed to describe E. coli removal during ripening from days 0–58 for continuously operated versus intermittent filters. This research confirms that although biosand filters were developed for intermittent operation, the filters perform significantly better when operated continuously. However, both operational modes resulted in a significant reduction of microbial indicators.
