Assessment of the Efficiency, Environmental and Economic Effects of Compact Type On-Site Wastewater Treatment Plants—Results from Random Testing

Abstract

This study presents the results of random testing of selected on-site wastewater treatment plants (WWTPs) constructed in Poland in Masovia Voivodship in the years 2011–2016. The vast majority of tested on-site WWTPs were compact (container) type treatment plants, based on low rate activated sludge (AS), sequencing batch reactors (SBR), or a hybrid (activated sludge supported with biological film, AS + BF) method. Compact type plans are becoming more and more popular in single households in Poland, due to the option of co-financing. According to certificates provided by producers and distributors, container on-site wastewater treatment plants are efficient in BOD5 removal, with the expected removal rate being over 80%. The aim of this study was (1) to analyze BOD5 in effluents sampled from randomly selected on-site WWTPs, (2) to evaluate predicted and real environmental effects of the implementation of on-site WWTPs in selected communes within Masovia Voivodship, and (3) to calculate unit environmental and economic effects of container on-site WWTPs in three different technologies. Results of this study show that in most cases, there is a gap between the declared and the real BOD5 removal efficiency. There is also a difference between the performance of different container type technologies. The lowest real environmental effect was obtained for AS technology, and the highest for the hybrid one. The predicted environmental effect has only been almost achieved in the case of hybrid systems. Based on net present value (NPV) benefits, technologies can be set up as follows: AS > SBR > AS + BF, making the AS method the most effective technology from the point of view of the economy.