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3.12 Packaged Wastewater Treatment Plants

Technical Description

Small sized wastewater treatment plant technologies have been built as compact units to serve the wastewater treatment needs of small settlements. This technology has many modifications which are typically based upon the activated sludge wastewater treatment process described elsewhere in this document.

Wastewater flows, following screening and settling of particulate, enters the tank unit, which includes a biosorber, a clarifier-regenerator, and a sludge mineralizer. In the biosorber, the wastewater is mixed with activated sludge recycled from the regenerator. At this stage, active adsorption of soluble and suspended solids takes place. The activated sludge, then, is settled in the clarifier and directed to the regenerator. In the regenerator, the sorbed and suspended solids oxidation is completed and the activated sludge recovers its original characteristics. Since the introduction of thin-layer modules, the time required for clarification in these packaged plants is reduced and the sludge is thickened better, which consequently allows the system to maintain a large dose of sludge in the regenerator and the sorber. The excess sludge is discharged into the aerobic mineralizer, where it is stabilized and dewatered in filtration bags under air pressure, with no chemical reagents being used. The dewatered sludge is an excellent fertilizer.

Extent of Use

This type of technology is widely-used, with country-specific modifications and special designs to suit local conditions and effluents, in Latvia, Poland, and Hungary. Typical treatment plants range in capacity from 10 to 1 000 m3/day, and serve populations of between 40 and 5 000 individuals. The plants are meant to treat domestic wastewaters and/or industrial wastewaters of similar composition.

Operation and Maintenance

This technology is easy to start and recovers quickly after temporary stoppages. It is also easy to operate, and does not require constant maintenance and full-time maintenance personnel, chemical reagents, or post-treatment disinfection.

Level of Involvement

This technology is implemented at the local administration level, or through some organized scheme of promotion on a local or country level.

Costs

No cost data are available, but costs may be assumed to be similar to those of conventional activated sludge treatment plants of similar capacity.

Effectiveness of the Technology

This technology can produce an effluent with concentrations of 10 mg/l suspended solids, 8 mg/l BOD5, 4 mg/l ammonium nitrogen, and 1 mg/l phosphate (P2O5).

Suitability

Packaged wastewater treatment facilities are designed for use in small districts, single households, and villages.

Advantages

Activated sludge technologies have a proven track record of reliability, with long-term expenditures for operation and maintenance being within 50% to 150% of the norm, and consistent effluent quality (BOD concentrations ranging from 100 mg/l to 500 mg/l). The plants are relatively odour free, and packaged plant, compared to analogous conventional activated sludge plants, and are 2 to 3 times more compact; have internal sludge disinfection, handling and dewatering processes, and lower construction costs (by 1.5 to 2 times) and equipment costs (by 3 to 4 times); and produce excellent fertilizer as a byproduct.

Disadvantages

Activated sludge technologies are sensitive to overloading and contamination, especially by heavy metals. Packaged plants, in particular, in Eastern Europe are susceptible to theft and vandalism. The technology needs skilled consultants to put it into operation.

Cultural Acceptability

This technology is an efficient wastewater treatment technology well accepted by engineers and society.

Further Development of the Technology

The technology is complete in itself.

Information Sources

Rolands Bebris, Ministry of Environmental Protection and Regional Development, 25 Peldu Str., 1494 Riga, Latvia, Tel. (371-7) 227145, fax: (371-7) 820442, e-mail: BEBRI@VARAM.GOV.LV.

Anna Egle, V/U "Meliorprojects", 11 Novembra Bulvaris 31, LV-1494 Riga, Latvia, Tel. (371-7) 228734.

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