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.

Green Water from Green Roofs—The Ecological and Economic Effects

“…The assumptions for the NPV analysis are presented in Table 3. The value of the discount rate was adopted from previous studies concerning environmental services [59,60]. The lifespan of GRs was calculated, based on the depreciation rate, specified in Polish law [61].…”

Impact of Uneven Flow Wastewater Distribution on the Technological Efficiency of a Sequencing Batch Reactor

“…The quality of wastewater flowing into individual SBR reactors was significantly differentiated, as shown in Table 2. The nature of the wastewater corresponded to the parameters of municipal wastewater [9,45]. No high concentrations of organic compounds and biogenic compounds were found.…”

“…To date, a number of technological systems have been developed that enable the removal of carbon, nitrogen, and phosphorus compounds from wastewater using this method. These systems, such as Bardenpho, A/O, and A2/O, are known and commonly used most often in large WWTPs [5][6][7][8][9]. Despite their high efficiency, they have a number of conditions that significantly limit the possibilities of their use [10,11].…”

Combination of Microscopic Tests of the Activated Sludge and Effluent Quality for More Efficient On-Site Treatment

“…Oxygen concentrations above 3 mg/L do not contribute to better treatment results, but significantly increase operating costs related to energy consumption [18]. Annual energy use in the analyzed on-site plant was estimated on the assumption of 15/15 cycle [4] for the value of 262.8 kWh/yr (2.8 kWh per m 3 of treated wastewater), followed with unit annual cost of EUR 24.77 per 1 kg of the removed load of BOD 5 and EUR 9.66 per 1 m 3 of treated wastewater [4]. Energy consumption in low-loaded activated sludge plants was lower than reported for sequencing batch reactors (SBR; 365 kWh/yr) [25], the moving bed bioreactor (MBBR, 147 kWh/ca.year), or membrane bioreactors (MBR) which use up to 345 kWh/ca.year [26].…”

“…Treatment efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total solids (TS), nitrogen (N), and phosphorus (P) is a manufacturer's declaration and should be equal to, or higher than the regulations of the country of distribution. The real efficiency of container on-site wastewater treatment systems, however, often deviates from the assumed values [4] and can be a source of contamination of the environment [5][6][7]. The insufficient degree of wastewater treatment in on-site plants was widely reported.…”