Many, many Municipal Wastewater Treatment plants throughout South Africa, are being asked to treat significantly higher flows and organic loads than they were ever designed for. This is leading to inadequate treatment levels and to the discharge into our waterways of partially or untreated effluent, causing extensive environmental degradation, contamination of drinking water sources and possible health hazards from waterborne diseases.
These sophisticated processes could readily meet the new effluent discharge consents and were thus favoured by most South African Waste water treatment consultants.
An Alternative solution worth serious consideration
Faced with significant capacity increased capacity requirements at many of their works, where they have existing but abandoned biofilters, Titanium investigated a
concept that has been used in the UK, USA, Latin America and Europe since the mid ‘80’s, to meet capacity increases combined with more stringent discharge consents, where these old but structurally fairly sound biofilters have been refurbished to provide significant treatment capacity improvements.
This increased treatment capacity is accomplished by removing the existing rock media and support structure, which is then replaced by a much more open support structure and then using structure plastic crossflow biological treatment media, combined with purpose designed and fabricated, speed controllable rotary distributors.
In the case of the Olifantsfontein Wastewater Care Works where, – in what is possibly a 1st for South Africa – this concept is being trialled, virtually no additional energy consumption – apart from the recirculation flow pumps – is used to achieve this significant increase in treatment capacity. This is thanks to the gravity flow regime of the original filter works.
This operation includes:
- Removal and disposal of the existing rotary distributor arms.
- The removal and disposal of the almost 20,000m3 of existing rock media and support structure.
- Refurbishment of the civils structures – both cosmetic and structural.
- Procurement and shipment of the “flat-packed” corrugated sheets that form the BIOdek media.
On-site assembly, of the 19,650m3 of ENEXIO’s BIOdek plastic biofilter media, using a semi-automatic thermal welding technique.
- Procurement and installation of a new simple but very effective support structure.
- Installation of the 19,650m3 ENEXIO BIOdek polypropylene, crossflow, structured, replacement biofilter media, into the six 33.5m diameter x 3.66m deep biofilter shells.
- Design, fabrication, delivery, installation and commissioning of the 6 stainless steel Rotary distributors.
- Excavation and installation of the 39Ml/d diversion pipeline that will in future supply flow to a new primary settlement tank but will in the immediate future divert 16Ml/d to the 6 existing but refurbished Dortmund primary settlement tanks, prior to being fed to the 6 “New” biofilters.
This operation includes the refurbishment of 6 concrete structures, a diversion chamber, a splitter chamber and a flow measurement chamber.
Once completed and commissioned, these six “new” biofilters will each have 3 times the biological and 10 times the hydraulic capacity of the old filters, whilst still being able to provide single digit BOD/COD and TKN levels. This enables a significant proportion of the existing flow to the BNR plant – 16Ml/d – being diverted through the refurbished biofilter stream, thus reducing the biological load onto the BNR module.
After settlement in the Humus Tanks, this fully nitrified, single digit COD/BOD filter effluent, is blended back into the BNR stream for Biological Phosphate and Nitrate removal.
As the biological load to the BNR plant has been significantly lowered by using the biofilters, the effluent standards will, after final settlement and disinfection, be within the discharge consent parameters set by the Environmental Agency for the Olifantsfontein works.