Sourcebook of Alternative Technologies for Freshwater Augumentation in East and Central Europe


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<Sourcebook of Alternative Technologies for Freshwater Augumentation
in East and Central Europe>

3.10 Activated Sludge Wastewater Treatment

Technical Description

Primary treated sewage effluent is conveyed to an equalizer-aeration tank that is provided with oxygen by deep aerators fed by air blowers forcing air into the pipelines. During aeration, an aerobic microorganism uses the pollutants contained within the wastewater as a nutrient source. From the aeration tank the wastewater flows into a final sedimentation compartment, where the liquid and activated sludge are separated. From this compartment, the purified water is discharged into a receiving waterbody, usually by means of gravity. From the bottom of the settlement tank, a pump recirculates the activated sludge back into the aeration tank. The electrical power required by the technology is about 20.4 kW.

The EGALAIR® system is one example of a specialized activated sludge-based treatment process. It is an Hungarian development, and is a compact, biological sewage water treatment plant based on a method of total oxidation. All of the compartments are included within one, steel construction unit.

Extent of Use

In Hungary, this type of sewage treatment system was built at the Village of Tarpa in 1992, with a daily capacity of 100 m³ of sewage and 30 m³ of sludge from septic tanks (night soil). This capacity is adequate to serve the needs of the 1 500 inhabitants of the village. The treated wastewater is discharged to one of the arms of the Tisza River.

Operation and Maintenance

The operation of this technology requires one mechanical engineer. Additional staff may be required depending on the size of the plant needed to serve a particular community. This technology uses standard wastewater treatment techniques and readily available materials.

Level of Involvement

This technology is implemented at the local community level.

Costs

The cost of a typical activated sludge treatment plant is about $400 000.

Effectiveness of the Technology

This technology can achieve an effluent with a BOD5 concentration of 30 mg O2/dm³, an organic matter content of <50 mg/dm³, a total nitrogen concentration of <30 mg N/dm³, and a total phosphorus concentration of < 5 mg P/dm³.

BIO-CLEAR® Wastewater Treatment System

Another example of activated sludge treatment technology used in Hungary is the BIO-CLEAR® wastewater treatment system. These systems ensure highly efficient biological treatment of wastewater flows in the 50 - 1 000 m³/d range. Depending on the treatment requirements, this treatment system can be a one- or two- staged biological treatment. The one-stage biological treatment method consists of simultaneous oxic (substrate removal, nitrification) and anoxic (denitrification, reduction) zones, while the two-stage treatment includes further mechanical primary sedimentation and high load trickling filtration.

The BIO-CLEAR® technology has four modifications: BC-1 is for domestic wastewater treatment (350-450 g/m³ BOD5) with denitrification and aerobic sludge treatment; BC-2 is for domestic wastewater treatment with denitrification and phosphorus removal; BC-3 is for wastewater with an high organic pollutant load (e.g., agricultural and industrial wastewaters with up to 1 500 g/m³ BOD5) and includes pre-treatment; and, BC-4 is for the same high load wastewater with an higher treatment efficiency.

Suitability

This technology provides treatment of domestic wastewater which is transported to the treatment plant via a piped drainage system or discharged directly into the plant by vacuum-storage trucks. It is ideal for small settlements, institutions (e.g., hospitals, schools, etc.), and holidays resorts, where the capacity of the plant is between 20 and 125 m³/day.

Advantages

This biological reactor is suitable for quantity and quality equalization of domestic wastewater. Detention time is optimised in the reactor for the highest treatment efficiency. The secondary settling tank is loaded at a constant rate, and achieves a treated wastewater that meets Hungarian water quality standards. It is easy to control because the equipment and pipelines are situated on and above ground level. The air-blowers, which are built with a safety operating mechanism, require less operation and maintenance than other technologies. The need for sludge treatment is minimal in this technological process.

Disadvantages

If the plant is not covered, it is sensitive to cold weather. Pipelines may freeze in very cold weather.

Cultural Acceptability

This technology is an accepted and efficient wastewater treatment technology.

Further Development of the Technology

The technology is fully developed.

Information Sources

Petèr Kovac and Dr Kornèlia H. Kocsis, Felsö - Tisza - Vidèki Környezetvèdelmi Felügyelösèg, 4400 Nyiregyhàza, Szèchenyi u.19, Hungary, Tel. (36-42) 310 155, fax: (36-42)310 713.

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