Evaluation of small wastewater treatment systems.

Different technologies for the treatment of wastewater from single houses have been evaluated by performing measurements at 14 treatment plants installed at different one-family houses located 35 km south-west of Stockholm. The technologies tested were selected in order to deliver high removal efficiencies with respect to organic matter, nitrogen and phosphorus. They also had to fulfil requirements concerning robustness, nutrient recycling, use of natural resources, economy, user-friendliness and hygiene. The systems can be divided into package plants, urine separating systems, blackwater separating systems and chemical precipitation as a supplement to sand filter beds. All of the systems were able to remove more than 90% of phosphorus and more than 90% of organic matter. Concerning package plants, it is necessary to have reliable dosing equipment and frequent checks to achieve long-term phosphorus removal. The source separation systems require well-informed and motivated users to achieve desirable removal efficiency. Sorting systems seem to be superior with respect to nitrogen removal, even though some of the package plants gave nitrogen removal above 50% during long periods of operation.