Small sewage treatment plant
Small sewage treatment plants are plants for the purification of wastewater with a rated value of 4 to 50 population equivalents (PE). They are therefore used in single houses, small settlements, restaurants or shelters when wastewater disposal through connection to large, municipal sewage treatment plants is not an option for technical, statutory or financial reasons.
The systems mostly consist of a sedimentation tank (e.g. three-chamber sedimentation tank ) in which the solids and floating fats contained in the wastewater are separated. The wastewater is then cleaned in a biological stage . In principle, the same methods are used as clarification processes as in the large plants:
- Activated sludge process in continuous operation or intermittent SBR
- Various processes with fixed beds ( plant-based sewage treatment plant , trickling filters , submerged fixed bed, sand filter sewage treatment plants , waste water trickling ).
- Non-technical systems, which as a rule manage without technical components (for example plant beds, sewage ponds and soil filter systems - see also plant-based sewage treatment systems )
- Membrane Activation Reactors (MBR)
Mechanical pre-cleaning is sometimes dispensed with in systems based on the activated sludge process .
With regard to the special operational challenges of small wastewater treatment plants such as:
- Self-control by the operator, maintenance by a specialist is required for all small sewage treatment plants with a general building inspection approval (according to the state water law )
- No need for complex measurement and control technology
- Large fluctuations in load must be compensated for by appropriate structural designs (e.g. buffer shaft)
In small wastewater treatment plants, the aim is to use the most robust designs possible. Due to the mechanically simpler structure, processes with fixed beds can be operated stably with less effort than activated sludge processes (fewer mechanical components). Non-technical systems usually require more space than technical systems, but they are easier to control and require less maintenance by the specialist; Often, depending on national regulations, only the sampling has to be carried out by a specialist; the operator can do the mechanical maintenance work himself. Many small sewage treatment plants are monitored using remote maintenance software (e.g. DiWa (digital maintenance protocol for small sewage treatment plants) ).
The discharge of the small sewage treatment plant can be introduced into the receiving water as an open channel. Another possibility is the infiltration into the subsoil, whereby care must be taken to maintain a minimum distance to the groundwater. Difficulties in discharging the treated wastewater can hinder the use of small wastewater treatment plants (no open channels available, water-impermeable subsoil, high groundwater level, risk of waterlogging on slippery slopes). In this case, the treated wastewater can be carried to a suitable point with pipelines, which are possibly cheaper to build than a sewer.
In general, the cleaning performance of small sewage treatment plants is less demanding than that of large plants. This also reflects the operational reality, taking into account the small system size. Nevertheless, in many cases in rural and alpine areas, these procedures are used for reasons of cost. With adequate dimensioning and careful maintenance, compliance with the limit values usually prescribed by the authorities can be expected. This is especially true for the removal of the carbon compounds. Safeguarding a possibly necessary removal of nutrients ( nitrification , denitrification ), sanitization (e.g. by UV treatment) and phosphorus removal ( e.g. by simultaneous precipitation ) requires precautions in the planning and operation of the systems.
In addition to the construction costs, there are ongoing operating costs. The operating costs include energy costs (electricity costs for pumps, compressors and controls), the maintenance of the system, the operationally necessary and officially prescribed controls of the drainage quality and the disposal of the sewage sludge . Models were also developed to organize the operation of the small systems of a municipality together with the municipal sewage treatment plant (maintenance association).
The Education and Demonstration Center for Decentralized Wastewater Treatment offers a manufacturer-independent comparison. V.
The European standard EN 12566 has the status of a German standard. This European Standard specifies requirements, test methods, marking and conformity assessment for small sewage treatment plants up to 50 PE.
Regulations
- DIN EN 12566-1 Small sewage treatment plants for up to 50 PE - Part 1: Factory-made septic tanks (includes Amendment A1: 2003); German version EN 12566-1: 2000 + A1: 2003
- DIN 4261-1 Small sewage treatment plants - Part 1: Systems for wastewater pretreatment
- DIN 4261-2 Small sewage treatment plants - Part 2; Systems with waste water ventilation; Application, dimensioning, execution and testing
- DWA -M 221 Principles for the dimensioning, construction and operation of small wastewater treatment plants with an aerobic biological purification stage
- DWA-A 222 Principles for the dimensioning, construction and operation of small sewage treatment plants with aerobic biological purification levels up to 1,000 population equivalents
Web links
- Technical information base and quality assurance of maintenance on the HP of the DWA (German Association for Water Management, Wastewater and Waste e.V.)