Biwater Proprietary Limited in South Africa secured a Turnkey Design and Supply Projects for Effluent Treatment for Diageo in the UK at the Benin 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 at the end of 2003 and is due for completion Mid 2005.

 

The plant consists of buffering, calamity tank, Anaerobic Treatment, Aerobic Treatment, a DAF plant for Clarification and Sludge Handling. The combined anaerobic/aerobic wastewater treatment plant comprises of a Paques BIOPAC IC and a Paques Circox aerobic reactor.

 

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 .

 

The aerobic Circox technology was used at the Benin site, due to extreme space constraints. A Circox reactor typically requires a footprint of only 5m in diameter, compared to the traditional aerobic activated sludge reactor of 2500m³, which would require a foot print of 15 meters by 35 meters.

 

The Circox process also produces far less sludge than the traditional bioreactor .

 

The influent from the brewery is screened and then retained for a period of time in an equalisation/pre-acidification tank. Here the pH of the influent is continuously monitored and corrected while the acidification process takes place. Nutrients can also be dosed at this point to enhance the anaerobic process, should the effluent not contain sufficient nitrates or phosphates .

 

The effluent quality into the treatment works is continuously monitored for pH, temperature and COD loading and if any unacceptable effluent is detected, this is automatically routed to the calamity tank. This effluent is then re-introduced to the process over time .

 

The conditioned wastewater is pumped into the recirculation tank from where the effluent is recirculated through the IC anaerobic reactor. The recycle tank provides an environment for treated effluent from the IC reactor and raw effluent to mix and stabilise for a period of time .

 

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% CO ) 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 Benin site, the overflow from the IC reactor flows into the Circox high rate aerobic reactor where the balance of the COD is removed by introducing oxygen into the effluent via blowers, into a vertical cylindrical vessel. The Circox reactor contains granular sludge enabling a high up-flow velocity and efficient breakdown of the COD with very little sludge pro duction .

 

The treated effluent then flows from the Circox to a Biwater dissolved air floatation (DAF) unit, where the excess solids are removed for dewatering. After the DAF unit, 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 .