Sewage treatment plant that looks like a botanical garden

Integrated Fixed Film Activated Sludge Plants (IFAS) rely on the use of a media on which a biofilm is grown, which results in a compact footprint as a majority of the biomass is fixed to a high surface area as opposed to being suspended.

A recent development of this process by Organica Water has been to combine naturally occurring plants with engineered media. To put it simply, a botanical garden is placed on top of the IFAS reactors, with the plant roots penetrating into the reactors.

The interaction of enzymes and various organic acids from the plant roots to the bio-media creates a diverse biology, leading to increased process stability, less sludge production and lower energy demand when compared to conventional activated sludge plants. And the sewage treatment plant looks like a botanical garden.

Large-scale installations in Europe have been in operation for 10+ years.

1.0 Introduction

Bio-film technology in wastewater treatment has been available since the 1970s, available as moving bed biofilm reactor (MBBR) systems or integrated fixed film activated sludge processes (IFAS). In general the bulk of the developments in this field relates to increased surface area, scouring and bio-film growth.

Generally the media used in either MBBR or IFAS is a non-metallic surface. Both systems provide benefits such as reduced reactor size, high total available biomass inventory, high tolerance against biomass washout during storm events and simultaneous nitrification-denitrification within the biofilm layer.

Organica’s Food Chain Reactor (FCR) combines the use of naturally occurring plants, such as bulrushes, marsh reeds, together with an IFAS-based process. A greenhouse is typically used to house the process, resulting in an aesthetically pleasing treatment system. For warmer climates, a shaded structure is used.

Figure 1: Food Chain Reactor (FCR) — cross-section of the reactor process.

2.0 Discussion

Pilot work for the FCR process was conducted in 2001, and was mostly based on the use of plants, to provide a high surface area for biomass growth. Full-scale wastewater treatment plants were then constructed for 2000 and 5000EP systems, based on sequencing batch process.

Over the next eight years, the process was refined to enable the use of the technology in larger scale wastewater treatment plants, and to improve energy efficiency and with lower biomass yield.

The combined use of the natural plants and engineered media meant that there was no limit on size for the FCR process.

2.1 Reactor configuration

The sequential batch process was then configured to a continuous multistage cascade process. Similar to MLE, an anoxic zone with internal recycle from the last stage was incorporated as part of the nitrogen removal loop.

Figure 2: The multistage Food Chain Reactor (FCR) process.

2.2 Observations from operating sites

The multistage cascade FCR was observed to provide a number of operational benefits. What was found in the pilot scale has been verified in full-scale installations that have been in operation for several years.

Key observations include:

• Independent development of biomass and ecology within each stage
• A significant increase in the diversity of biomass speciation due to the interaction of the natural plants and biomass
• Very high total biomass inventory, due to the biofilm growth
• Very high observed sludge retention time (SRT)
• Reduce Biomass Yield, due to a predatory effect and higher SRT
• A low MLSS in the water phase of 300 mg/L
• Increased alpha factor within the aeration system, due to the lower free MLSS
• Relatively free odour
• No need to return activated sludge (RAS) in process design
   

The lower free MLSS means that the phase separation step post FCR can be designed with a lower loading. Rather than using secondary clarifiers, phase separation can occur in a horizontal disc filter which has a tenth of the footprint as compared to a conventional clarifier.

In addition, the lower MLSS results in a higher diffuser alpha factor, meaning that less air is required to deliver to process oxygen need. This results in a lower energy demand.

Diversity of biomass speciation results in adaptive ecologies forming in each FCR stage. As opposed to 300 to 400 species commonly present in activated sludge plants, the FCR exhibits up to 3000. This diversity creates a very stable process, which is tolerant to shock loads, and in the last stage, the presence of eukaryotes results in the consumption of decayed bacteria.

Operating data from several facilities has demonstrated the robustness of the FCR systems, as well as consistent effluent quality. The discharge quality that can be achieved can be designed to match any conventional activated or MBR process.

The total observed biomass within the FCR system is typically 16,000 mg/L, which is three to four times conventional systems. Although MBR systems exhibit similar high MLSS, the energy demand associated with FCR is significantly less due to simplified secondary clarification phase.

2.3 Aesthetics

The FCR can be housed within a greenhouse structure, or provided with a shading structure. The selection is generally based on minimum temperatures in the winter period. The end result is a wastewater treatment plant that resembles a garden or greenhouse facility, with low odour emissions and a very aesthetically pleasing look.

In some European installations, buffer zones around the treatment plant have been reduced from 350 m to 50 m, freeing up additional land for development and providing a net positive attitude from local communities.

Figure 3: A view of the integrated process.

3.0 Conclusion

The use of bio-film technology provides a number of advantages with regard to footprint and biomass inventory. The combination of natural plants and IFAS results in a process which has been scaled up to full-size treatment facilities, that provides a number of capital and operational cost savings.

The natural plants do not actually treat the wastewater, but provide nutrients, organic acids and enzymes that create a highly diverse biology within the plant roots and IFAS modules. A much denser bio-film is created, when compared to other IFAS systems or MBBR processes.

With an obversed total biomass concentration that is three times conventional systems, a reduced footprint of up to 65% can be achieved. Savings in energy demand and sludge disposal are two other key benefits of the process, particularly over MBR-based systems that exhibit similar space-saving features.

Full-scale installations as large as 80 MLD have demonstrated the technology’s application within the municipal and industrial wastewater field.

The aesthetically pleasing look of the Organica FCR has changed local community attitude towards wastewater treatment, and has provided a place for communities to interact with the process in a very positive way.

As rapid urban growth continues in many cities around the world, this technology has demonstrated its use as a decentralised facility that can be constructed in the middle of a dense urban landscape, to relieve load on existing sewer systems and enable water reclamation in these environments.

Hydroflux Epco is the exclusive Australian representative for Organica Water’s Food Chain Reactor process.