New EC standards published in 2009 led to a surge in onsite wastewater treatment systems reaching the European market. Here we summarize their technical aspects and compare them to known values used in centralized wastewater treatment. The paper deals with two types of processes: attached-growth systems (AGS) on fine media and suspended-growth systems (SGS). Covering 141 technical approvals and 36 manufacturers, we compare onsite design criteria against the centralized wastewater design criteria for each process. The systems use a wide range of materials for bacterial growth, from soil, sand or gravel to zeolite, coconut shavings or rockwool cubes, with a huge range of variation in useful surface, from 0.26 m2/PE for one rockwool cube filter to 5 m2/PE for a (traditional system) vertical sand filter. Some rockwool can handle applied daily surface load of 160 g BOD5/m2. SGS design parameters range from 0.025 to 0.34 kg BOD5 per kg MLVSS/d with hydraulic retention times of 0.28-3.7 d. For clarifier design, water velocity ranges from 0.15 to 1.47 m/h. In the sludge line, sludge storage volume ranges from 0.125 down to just 0.56 m3/PE.
Keywords: Attached growth on fine media; On-site system; Suspended growth; Wastewater treatment systems.
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