Wastewater treatment using a vertically moving biofilm system followed by a sand filter

The design and operation of wastewater treatment systems for single houses, farms, hotels, leisure centres, small communities and small businesses are a challenge to wastewater engineers. In this paper, a pilot-scale system comprising a vertically moving biofilm reactor (VMBR) followed by a stratified sand filter was constructed and its performance was evaluated. The vertically moving biofilm reactor was operated as a sequencing batch biofilm reactor (VMSBBR). The results show that the VMSBBR unit efficiently removed 94.8% of the filtered chemical oxygen demand (COD_f) from a synthetic wastewater with the influent COD_f of 1096 ± 425 mg/l, leaving 45 ± 16 mg/l COD_f in the effluent, at an organic loading rate of 0.9 kg COD/m³ day. After the system had been operated for 133 days, the removal efficiency of orthophosphate (PO₄-P) reached 90%. A sand filter polished the effluent from the VMSBBR unit and reduced suspended solids (SS) to 4.4 mg/l and total bacterial by 3 log 10 units. The advantages of the treatment system studied for small wastewater flows include: (1) simple operation and maintenance - sludge was only disposed of once on Day 206 during the 7.5-month study period; clogging, which often happens in other attached-growth biofilm systems, did not take place; (2) efficient removal of COD and phosphorus; and (3) low-energy consumption - the electricity consumption was 4.6 kWh/population equivalent (p.e.) year, or 0.6 kWh/m³ wastewater treated or 0.6 kWh/kg COD removed.