Land-based wastewater treatment plants for more than 50 p.e. Advice on construction, maintenance and emission control

Summary
The project has produced a handbook-style report on land-based wastewater facilities for more than 50 person equivalents (pe), such as landbeds and infiltration facilities. The report presents a proposal for emission control and summarizes recommendations for design, sizing, operation and maintenance.
Municipal land-based sewage treatment plants for more than 50 pe can be a good solution for rural areas.
They are found in several parts of the country, but seem to be slightly more common in southern and central Norrland. The plants are resilient to temporary disturbances.
They have low maintenance and supervision requirements and low
investment costs. The purification of organic matter and contaminants is high and stable. Only phosphorus reduction
is affected by the age of the bed, and it is usually clearly noticeable if the plants do not work by, for example, damming wastewater or smelling bad.
Land-based plants from 2,000 pe and upwards actually have the same requirements as other plants under the EU Wastewater Directive, but today there is no guidance
for emission control of this type of plant. In practical terms, there is a big difference between the possibilities for emission control of, on the one hand, sealed landbeds that have an
outlet pipe, and, on the other hand, infiltration plants and unsealed landbeds that fully or partially infiltrate to the groundwater. For infiltration plants, it is more difficult to define where the plant ends and to take a representative sample of treated wastewater to measure the pollutant content.
The report includes a proposal for discharge monitoring that includes requirements for groundwater measurement and calculation of concentrations/reduction with correction via background parameters/
trace elements (e.g. chloride) for infiltration plants of more than 200 pe. For infiltration plants of 50-200 pe, no requirements for individual monitoring are proposed, but it is nevertheless recommended that the plants are designed so that simple emission assessment can be carried out.

The proposed methodology needs to be developed and evaluated. Among other things, further consideration needs to be given to different calculation methods for in-depth assessment for plants over
200 pe, other methods for emission control (e.g. measurement directly in the plant) and the number of samples to be recommended.
Emission control is needed to be able to check the functioning of land-based plants. The design, dimensioning, monitoring and maintenance of the installations are of great importance for their proper functioning. The report compiles knowledge on
design criteria, care and maintenance requirements, treatment results, soil retention, economic conditions and other critical issues