Retrofitting at Hartbeesfontein

Following on from an editorial in the May/June 2013 edition, on the new HYBACS WWTW at Swartruggens, Headstream Water’s commercial director, Julian Moore, talks to Maryke Foulds about two recent HYBACS upgrades that further demonstrate the significant benefits offered by the HYBACS process.

Touching base, close on a year later, it is gratifying to learn that Headstream has recently commissioned its third plant in South Africa, which is a HYBACSretrofit to upgrade the Hartbeesfontein WWTW.

“While we are extremely proud of our first two plants these were greenfield new builds and not an upgrade to an existing plant. The Hartbeesfontein project is an upgrade to an existing plant to double treatment capacity from four Mℓ/d to eight Mℓ/d while also improving treatment performance to enable it to meet nutrient discharge standards,” explains Julian Moore.

“This is very exciting as it demonstrates that the HYBACS process is ideally suited for upgrading conventional activated sludge plants to increase treatment capacity and improve performance. Upgrading existing treatment infrastructure is extremely important in South Africa and it is in this scenario that HYBACS is significantly more competitive than alternative technologies.”

In simple terms the HYBACSprocess works as follows. It is a hybrid BNR activated sludge process where a fixed biomass process is combined with a conventional suspended biomass activated sludge process followed by conventional secondary settlement via a clarifier. It thus lends itself as an ideal retrofit technology for the widely used conventional activated sludge process.

The fixed biomass reactor, which is called a SMART unit and is unique to the HYBACS process, contains a very high concentration of attached biomass and also delivers an oxygen transfer rate significantly higher than that achieved in the suspended biomass reactors. Therefore the SMART units are able to remove a high portion of the incoming COD in a very efficient manner, which when combined with the existing suspended biomass activated sludge reactors enables the plant to deal with a significantly increased load.

“The HYBACS process was initially developed in South Korea in order to address the key challenges they faced due to rapid urbanisation and industrial development around existing plant sites. Thus a significant increase in treatment capacity and an improvement in effluent quality were needed but there was no space in which to expand plants. The key drivers for the development of the HYBACS process was that it needed to retrofit onto existing activated sludge plants and it needed to be able to significantly increase treatment capacity and improve effluent quality within the current plant footprint.” explains Moore. “Additional drivers were cost effectiveness, energy efficiency and the removal of odour, particularly important given that high density accommodation surrounded many of the plant sites in the cities.”

The Hartbeesfontein upgrade was urgently required due to the increased flow into the existing plant combined with the higher loading on the plant from a local abattoir. The upgrade to double treatment capacity to 8Ml/d is being achieved with a HYBACS design that involves the installation of 8 SMARTunits upstream of the existing suspended biomass activated sludge reactors. Additional modifications to the existing plant infrastructure include:

• the conversion of the PSTs to Anaerobic tanks for enhanced biological phosphate removal
• increasing oxygenation capacity in the aerobic reactor with an FBDA system
• the construction of a new clarifier.

“As no increase in the volume of the aeration reactor was required the HYBACS process provided a significant saving for the municipality with respect to reduced civil construction costs. In additional the energy savings that the HYBACS process will deliver, which we estimate to be up to 40% when compared to a conventional eight Mℓ/d plant, will significantly reduce the on going electricity costs for the municipality.”

The plant is currently in its initial commissioning phase with the first six SMART units already installed and operational. The remaining two SMART units will be installed in a second phase in the coming months to take the treatment capacity to eight Mℓ/d.

Another recently completed upgrade project is the upgrade of the Tubli WWTW in the Kingdom of Bahrain completed by Bluewater Bio, the owners of the HYBACS technology. This HYBACS upgrade comprises the conversion of two of the existing 10 aeration lanes and four of the existing 12 clarifiers into a HYBACS plant, by installing 42 SMART units upstream of the aeration lanes. The upgraded HYBACS plant treats 100Ml/d meaning that the two aeration lanes, originally designed for 40 Mℓ/d, now have a 150% uplift in capacity.

“No additional civil construction was required to increase the volume of the aeration lanes and the entire upgrade was achieved within the current plant footprint. The cost of the upgrade was US$20 million, (R220 million) of investment for an increase in treatment capacity of 60 Mℓ/day. That equates to just over R3.6 million per additional Mℓ/day of treatment capacity which demonstrates the exceptional cost effectiveness of HYBACS in an upgrade scenario. Add to that the fact that the electricity consumption of the HYBACS upgrade section of the plant is 40% lower per Mℓ treated than the rest of the plant and one can really appreciate the overall life cycle cost savings delivered” explains Moore.

Results at the HYBACS Tubli WWTW since commissioning have been exceptional, despite the plant receiving a higher influent loading than designed for, with the effluent quality consistently exceeding the effluent standard set: <0.3 mℓ/ℓ ammonia; <10 mg/ℓ TN; <30 mg/ℓ COD; and <15 mg/ℓ TSS. In addition results show a significant improvement in Sludge Settleability with sludge from the HYBACS upgraded portion of the plant flocculating rapidly and settling 40 xs faster than the rest of the plant while operating at a MLSS 3822 mg/ℓ and achieving a SVI 42.9 mℓ/g.

“This is a very significant development for us as it demonstrates the excellent performance of HYBACS on a large scale as the Tubli WWTW is a large plant treating 100 Mℓ/day. The next phase planned is to upgrade the next 40 Mℓ/day of the conventional plant to 100Ml/d so that the total HYBACS portion of the plant is expanded to 200Mℓ/day.”

Headstream Water and Bluewater Bio will be presenting a technical paper and workshop at the upcoming WISA conference in May setting out the results from both the Hartbeesfontein and Tubli WWTWs. “We are confident that when professionals in the industry see these results and the cost efficiencies which are achievable then they will be willing to embrace an innovative solution and recommend the HYBACS process to their clients, particularly in an upgrade scenario, so they can save their clients both Capex and Opex costs.”