Sewage treatment plants are primarily and in many cases, exclusively, designed for domestic family homes, not large houses where wastewater treatment systems are underloaded. These are, typically, larger 4 bedroomed houses, with only 2 people living in them.
Almost all sewage treatment plants are only designed to go down to 50% of the size of the plant, meaning that a 6 person plant, needed for a 4 bedroom home, must be used by a minimum of 3 people. This is in order for the bacteria to receive enough 'food' from the sewage per day. They are only tested down to 50% for their EN Certificate, so there is no data available for them for lower percentages, and in many cases, they don't work.
A domestic sewage treatment plant that is connected to a normal house, lived in by enough full-time residents who are responsible for the plant, is the ideal situation for any sewage treatment system. It has a stable flow rate of sewage into the plant and the concentration of pollutants is relatively stable as well.
We manufacture different types of domestic sewage treatment plants, each one designed for different situations to cope with this large home, but few people problem - please see below.