Organic matter and nitrogen removal in a hybrid upflow anaerobic sludge blanket—Moving bed biofilm and rope bed biofilm reactor

• Hybrid UASB-MBBR-RBBR designed for organic matter and nitrogen removal.
• Organic matter removal > 99% and a total nitrogen removal of 89% achieved.
• Major problem of sludge washout in UASB could be eliminated by the use of media.
• Maximum biogas production of 0.61 m3/kg CODremoved achieved.
• Moving rope bed with oxic and anoxic microenvironments favoured nitrogen removal.

A novel hybrid upflow anaerobic sludge blanket—moving bed biofilm reactor followed by rope bed biofilm reactor (UASB-MBBR-RBBR) was designed and operated for about a year to achieve removal of organic matter and nitrogen from sewage. The hybrid reactor could achieve chemical oxygen demand (COD) removal of 99 ± 1% with an effluent COD concentration of around 7 ± 3 mg/L at an organic loading rate (OLR) of 2 kg COD/m3 day and a total nitrogen removal of 89 ± 8% by combination of nitrification-denitrification processes at a nitrogen loading rate of 0.2 kg TN/m3 day. Innovative reactor design with moving rope bed supporting oxic and anoxic microenvironments favoured high nitrogen removal rate. The major problem of sludge washout in UASB reactor could be eliminated by the use of moving media in the UASB-MBBR. A maximum biogas production of 0.61 m3/kg COD removed could be achieved at an OLR of 2 kg COD/m3 day. The hybrid UASB-MBBR-RBBR technology could thus provide an alternative, low maintenance, economical and efficient system for simultaneous carbon and nitrogen removal and energy recovery, which is not otherwise possible using conventional secondary sewage treatment processes.