Aerated reed bed system with Forced Bed Aeration (FBA™)
ARM undertook the design and construction of an aerated reed bed system with Forced Bed Aeration (FBA™) for a small community development in Lichfield.
The septic tank effluent from five domestic dwellings in Claypit Lane, plus wash water from local stables and surface runoff, merged into a combined effluent which discharged by gravity through a small filter bed and on into a small receiving watercourse. ARM undertook an asset assessment of the existing filter bed and it was found to be poorly constructed, undersized, hydraulically limited and leaking through its bunding; it was therefore potentially contaminating the surrounding soils and groundwater.
Analysis of water samples identified that the existing filter bed was providing virtually no pollutant removal and sewage fungus was an issue at the outfall location.
The site required a low-cost, treatment solution with minimal footprint and maintenance requirements to prevent pollution of the receiving watercourse and surrounding soils and groundwater.
Following the asset assessment, ARM characterised the wastewater and an appropriate reed bed treatment system was designed to treat a maximum flow rate of 56m3/d, and pollutant concentrations of 140mg/l biochemical oxygen demand (BOD), 23mg/l ammoniacal nitrogen (NH4-N) and 102mg/l total suspended solids (TSS). The design discharge standards for the receiving watercourse were based on typical UK standards of 20mg/l, 30mg/l and 10mg/l for BOD, TSS, NH4-N respectively.
The existing filter was decommissioned and removed and a saturated vertical flow reed bed containing Forced Bed Aeration (FBA™) was installed.
A small blower was required to enhance the oxygen transfer to meet the oxygen demands of the BOD and NH4-N in the influent and minimise the reed bed footprint. The blower is connected to the mains but is operated by solar panels during the summer months.