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Most biological treatment systems, particularly sewage treatment systems, are built as over designed continuous activated sludge plants. As a result of increasingly stricter environmental requirements, there is a fast growing interest in the more flexible and more efficient sequencing batch biological purification system, the SBR.

This technology isn’t new. In fact it was already in use in the first half of the 20th century, well before the continuous system gained popularity, because the sequencing batch system just offers a logical and superior treatment process. However, operating a sequencing batch system takes more control effort and was therefore relatively labour intensive as operators were needed for initiating the various process steps. When labour became more expensive, the easier to operate continuous system became the generally accepted standard, although this system was known to be less efficient and to have certain hard to control drawbacks. Today, plant automation is widely available and the batch system is now to be preferred over the continuous system.

The operation of a SBR

The main components of an SBR are:

1. The tank (reactor) in which mixing, purification and settling of activated sludge take place;
2. The waste water supply equipment (usually pumps);
3. The oxygen supply system (for example, air compressors and aeration grid);
4. The control system (for example, PLC-PC or relay panel).

The SBR biological treatment process basically involves a cycle with four distinct phases:

    Fill and treat stage
    waste water is supplied to the tank and the liquid level rises. Air is supplied as required;
    Finishing stage
    the waste water supply is shut off. Air is supplied as required;
    Discharge stage
    the aeration system is switched off. The activated sludge settles and the clear surface layer of treated water is skimmed off. The liquid level falls;
    Rest stage
    the liquid level is low. Air is only supplied in order to maintain endogenous respiration of the activated sludge kept in the tank.

Advantages of an SBR

Batch wise biological waste water treatment has great advantages compared to a continuous system, mainly because the operating and control techniques, which can be used at SBR systems, allow for a far more efficient process performance.

Biological breakdown is a natural process which has several stages and each stage requires its own specific process conditions. In a biological treatment plant, this natural process has to take place in a restricted space, in an effective manner and at minimum cost.
The population of micro-organisms, growing in a biological purification system, depends on the conditions allowed to exist in that system. Through a process of selection, mutation and competition the bio-mass adapts itself to the conditions imposed upon it. In an SBR these conditions can be easily controlled. This also implies that in the SBR we can create the optimal bio-mass properties for each specific type of waste water, while controlling these conditions is relatively simple. This cannot be achieved in continuous systems.

Other advantages of the SBR are:

    No sedimentation basin nor sludge recirculation pumps are needed. The entire process takes place in just one tank;
    No short circuiting occurs as a result of which untreated waste water leaks into the effluent;
    The system is better protected against flow and/or load variations because effluent discharge only takes place once the purification process has been completed;
    The system offers great flexibility in comparison with other activated sludge systems, because filling, processing, discharge and rest stages can be adjusted in a simple and mutually independent manner;
    Sludge management is easy to monitor and control, because the sludge always remains in the reactor and is not re-circulated from the aeration tank to the sedimentation tank or vice versa.

The Pielkenrood Engineering SBR design

The Pielkenrood Engineering SBR design offers you the following additional advantages:

    In our SBR system the periods in which a measurable concentration of oxygen can be observed are very limited;
    Our SBR systems are not operated on the basis of dissolved oxygen concentration, but on the basis of a redox potential signal, which allows for detection of oxygen surplus as well as of oxygen deficiency.

This has considerable consequences:

    The oxygen transfer is optimal, because the reactor is largely operating in a state of a slight oxygen deficiency. The result of this is that during aeration, the oxygen consumption is equal to the maximum rate of oxygen supply. So, the oxygen supply is no more than what is exactly needed, which leads to considerable energy savings;
    Aerobic and anoxic conditions alternate during the process, causing the desired nitrification and de-nitrification to take place virtually simultaneously in just one tank;
    The alternating anoxic and aerobic conditions adapted to the present BOD load stimulate the growth of phosphate reducing bacteria. In a continuous system the risk of anaerobic conditions developing in the sedimentation tank, with the sludge releasing the absorbed phosphate, is difficult to control. As a consequence phosphate will reach the effluent.

Our SBR system is designed to suppress the release of phosphate to the discharged effluent to the maximum possible extent. Our SBR systems are designed to be low load activated sludge units. The sludge load of our SBR systems is comparable with the sludge loads of extended aeration carousels and oxidation ditches.
This results in low sludge growth and consequently only a small amount of surplus sludge needs to be removed. The amount of surplus sludge from the SBR to be discharged can be further reduced by installing an aerobic sludge stabilization/thickening unit and a sludge dewatering system. The result is a considerable reduction in the cost of storing/discharging or incineration of surplus sludge.

Prevention of bulking sludge

Our control philosophy provides you with the opportunity to manipulate BOD load depending on aeration of the bio-mass, so that light filamentous bacteria have little chance to develop and grow. This prevents the forming of poorly settling sludge (bulking sludge) that creates so many problems in other, especially continuous, biological purification plants.


The advantages of the Pielkenrood Engineering SBR summarised:

    We use a simple construction. The whole process takes place in a single tank/reactor;
    Nitrification/de-nitrification and phosphate reduction take place more or less simultaneously and are not dependent on the location in the reactor;
    We offer great flexibility with regard to absorption of flow and/or load variations (peak and shock loads);
    We offer simple as well as more extended possibilities for controlling the conditions and progress of the purification process;
    Energy-saving by optimising the oxygen supply to the bio-mass;
    Low sludge growth due to a low sludge load;
    Well settling sludge produced by discouraging the growth of filamentous bacteria;
    Coupling of energy consumption to BOD/COD removed enables automatic control of sludge inventory and nutrients dosing;
    Integrated toxicity monitoring: abnormal treatment conditions are immediately detected.

The SBR designed by Pielkenrood Engineering combines versatility with simplicity and can be adapted over a wide range for the treatment of ”easy” or ”difficult” biodegradable material on a small or large scale. The natural potential of SBR waste water treatment is now available to you.

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