Development of a Passive Filter for Polishing Municipal Lagoon Effluent-Lab and Field Scale Studies

Abstract

The goal of this research is to create and assess a passive system for polishing municipal lagoon effluent. The study's goals include identifying the best media type and hydraulic loading rate for an unsaturated filter, evaluating the hydraulic retention time (HRT) and adsorptive capacity for a saturated filter, and pilot-scale testing of the technology. The experimental variables include unsaturated media, filter depth, loading rate, and Direct Reduced Iron (DRI) adsorptive media HRT. The lab study consisted of a series of column tests with synthetic wastewater, while the field study involved three 1 m3 pilot filters dosed with municipal lagoon effluent. Two sources of coarse sand media in the column study exhibited clogging while a crushed glass media did not under conditions of continuous dosing. A 45-cm layer of crushed glass media at 25 cm/d continuous loading provided optimum treatment for BOD and NH4+. Also, the column study demonstrated that increased hydraulic loading rate at constant organic loading rate increases filter clogging and reduces treatment efficiency. The field study, on the other hand, polishing a low solids and low carbon lagoon effluent with 29 cm/d intermittent dosing found better COD and ammonium reduction with a 45 cm layer of coarse sand compared to crushed glass, and with no signs of clogging. Both lab and field studies found 15 cm of 12.5 mm dia. DRI with 5.7-5.9 hr HRT was effective at phosphorus reduction. A recommended passive filter design to polish municipal lagoon effluent consists of a 45 cm layer of coarse sand and 15 cm of saturated DRI at an intermittent loading rate of 25 cm/d. Crushed glass can be considered as an alternative to coarse sand where intermittent dosing is not viable or high solids or organic loading could contribute to premature filter clogging.