BIOCOS® vs. Conventional Activated Sludge Technology

Today, the traditional biological activated sludge system is widely used for municipal wastewater treatment. World market leaders in the field of wastewater treatment still use this system because of their broad and long-term experience with it. Over the past decades, the system has continuously undergone some minor improvements and has become a major technology especially for large wastewater treatment plants.

Over the years, some new technologies were improved. The goal was to improve various aspects of the traditional activated sludge system. However, until today no system could completely replace or outperform the activated sludge technology. Each one of the new developments has advantages but also disadvantages. Single Batch Reactor (SBR) plants for example are not suitable for large plants and neither are Membrane Bioreactor (MBR) plants. Both are not able to cope with larger hydraulic loads.

Prof. Dr. Ingerle of the University of Innsbruck, Austria was never satisfied with the conventional system and was looking for a truly innovative breakthrough. Step-by-step he considered all known disadvantages of the conventional biological system and developed solutions that would rectify those problems and turn them into advantages of the new technology. Prof. Ingerle did this without looking at specific plant sizes, types or applications but by returning to basic physical and biological principles. The result was a biological combined system (BIOCOS®) unifying the strengths of the conventional activated sludge system and the solutions to its disadvantages. Because of the approach Ingerle took and his solutions, BIOCOS® is not merely a better copy of the traditional activated sludge technology but a quantum leap. The technology won an innovation price in Germany and has been patented.

Since BIOCOS® is in competition with conventional activated sludge treatment plants, we want to point out the differences between the two systems:

Plant construction

• Traditional activated sludge systems have tanks with different geometries. Rectangular aeration tanks and circular sedimentation tanks can not be located directly next to each other. This requires more space, longer piping and makes plant enlargements more difficult.

In addition, the sedimentation basins have conic bottoms, which results in higher demands on a constructor's capabilities and increases construction costs.

Additional pumping stations for sludge movement, final sedimentation tanks and larger aeration tanks further increase overall construction costs.

BIOCOS® tanks on the other hand can be built easily due to their rectangular geometry and flat bottom. All tanks can be placed right next to each other. This reduces the required space as well as overall construction volume. The tanks can be built above or below the ground. They can be completely covered or open. The control building can be integrated with the plant on top of the tanks (to reduce piping) or can be erected as a separate building beside the tanks. Thanks to the rectangular layout of the BIOCOS® tanks, plant enlargement is very simple. Additional basins are merely added directly next to the original tanks.

Plant machinery and plant operation

• Traditional activated sludge systems demand a high level of machinery and technical equipment to be installed. Some of the highlights are scrapers, agitators, floating sludge channels and return sludge pumping station. This high level of machinery requires complex automation and control devices, which make day-to-day operation more difficult and more expensive (e.g. more maintenance). The lack of transparency also has to be compensated by expensive process visualization tools. All those systems and equipments are vulnerable to failure, which may result in higher down times. More machinery and technical equipment is therefore a reason for higher maintenance and spare part costs, higher plant personnel requirements and higher energy consumption. Overall, the number and complexity of technical equipments result in higher costs over the complete life-cycle of the plant from investment over operation to maintenance and repairs.

On the opposite, BIOCOS® has been designed to exploit basic physical and hydraulical principles. For that reason, less machinery and equipment is needed throughout the process. BIOCOS® does not require scrapers, agitators, floating sludge channels, return sludge pumping stations or piping for sludge return. All movement of water and sludge is done using compressed air only.

Less machinery, lower complexity and compact plant layout result in simpler automation and control devices, easier day-to-day handling and lower investment, installation and operating costs.

As a result, down time of BIOCOS® plants is nearly zero. Requirements for and on plant personnel are much lower, there is less maintenance and lower energy consumption. Overall BIOCOS® plants show significant savings in operational costs compared to conventional activated sludge plants.

Purification performance

• Traditional activated sludge plants deliver stable purification results. However, some inherent characteristics of those systems hinder higher purification performance. Dry substance content for example is usually only about 4 mg/l, which results in lower nitrification and pre-denitrification.

Within the clarifier basins of traditional activated sludge plants the process of separating sludge from purified water is only a physical process and does not further contribute to the plant's purification performance by any biochemical processes.

Another common problem occurs because of current and short circuit effects in the secondary clarifier. The sludge-water-mixture from the aeration tanks is continuously fed into the clarifier, while supernatant water is discharged and return-sludge is recycled. All of these processes create complex flow patterns, which influence the sedimentation process and lead to purified water mixing with sludge flocks. Moving scrapers in the clarification tanks even reinforce this effect. Moreover, anaerobic zones on the bottom of the clarifier cause bulking sludge and consequently floating sludge. Additionally, floating sludge often mixes with purified water effluent due to wind waves.

Anoxic sludge in the clarifier tanks is reason for re-dilution of phosphate into purified water and consequently causes over-fertilization and formation of algae in receiving waters.

On the contrary, every part and process-step of a BIOCOS® plant is designed for highest purification performance. The high activated sludge concentration in the aeration basin for example results in a highly efficient simultaneous denitrification. A high ratio of dry substance (4-6mg/l) and undisturbed fast sludge sedimentation guarantee solid free effluent. The high level of dry substance also reinforces the nitrification and acts as buffer for toxic substances.

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