Biwater Proprietary Limited in South Africa secured a Turnkey Design and Supply Projects for Effluent Treatment for Diageo in the UK at the Ogba Brewery in Nigeria.

Biwater Pty is the main contractor and provider of Process Design (licensed from Paques Technology), M&E Works, Civil Design, Commissioning and Training with Biwater Nigeria LTD acting as the civil Subcontractor and local Project Manager.

The Contract was awarded in July of 2003 and is due for completion early 2005.

Specific design was required to meet the very strict constraints with respect to available space on site, stringent effluent discharge standards and bio-solids production.

The plant consists of buffering, calamity tank, Anaerobic Treatment, Aerobic Treatment, clarification and Sludge Handling. The combined anaerobic/aerobic wastewater treatment plant comprises of Paques BIOPAC IC, and an Activated Sludge technology.

Anaerobic treatment is used to reduce the bulk of the COD by up to 80%, whilst an aerobic polishing step removes the remaining COD fraction.

Anaerobic technology is used up front due to its capacity to handle very high COD/BOD loads in the effluent, while producing a very small amount of sludge. It also requires a very small footprint on site, as the IC Reactor is typically a vertical cylindrical tank, 6,5m in diameter. The reduced power consumption in this process is a further consideration.

Effluent from the recycle tank is pumped into the bottom of the reactor, where it is combined with the internal recirculation line. The mixed effluent percolates through the special granular sludge blanket in the bottom of the reactor and the COD in the effluent is thoroughly mixed with the granular sludge. The COD is broken down into primarily biogas (containing approximately 80% methane and 20% CO2 ) with some new cell growth.

The gas is stripped of in settler modules in the IC Reactor and is utilised for internal recirculation, providing a “free” mixing source for better retention and contact with the sludge, prior to being burnt off to atmosphere or recovered for use on the plant. Due to the quality of the gas produced, a large energy recovery is available to the end user, if required.

The treated effluent overflows from the IC reactor back to the recycle tank and or the aerobic treatment process. At the Ogba site, the overflow from the recycle tank enters the traditional aerobic aeration basin, where the balance of the COD is removed by introducing oxygen into the effluent using vertical mounted aerators.

From the aerobic reactor, the treated effluent is settled in a settling tank, where the majority of the solids are removed for dewatering and the final treated effluent is of a suitable quality for discharge to river.

The sludge from the aerobic processes is treated with Polyelectrolyte and then de-watered using a Solids Technology belt filter press. The dried sludge of approximately 16% dry solids in then removed from site for dumping.

The main project team is situated in the Biwater Pty offices with Biwater Nigeria providing the vital aspect of project management in Nigeria.