Sedimentation devices have been widely implemented to remove suspended solids and attached pollutants from stormwater before entering surface waters. The treatment performance of these best management practices (BMPs) on fine particles is rarely investigated in a standardized way. To overcome this information gap a reliable and standardized testing procedure is formulated.Four devices have been tested on their suspended sediments removal efficiency at different discharges and particle sizes, using the newly developed standardized full scale test method. The observed removal rates of the facilities with a storage volume in the order of 1.5 m3 and settling surface around 1 m2 drop to low removal efficiencies at flow rates of 10 l/s or more. For small sized sediments (up to 63 μm) the removal efficiency is below 50%. The results of the experiments can be used to improve both the design and the dimensions of stormwater treatment devices.
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Urban nature-based solutions (NBSs) are widely implemented to collect, store, and infiltrate stormwater. This study addressed infiltration rate as a measure of the performance of bioretention solutions. Quick scan research was conducted, starting with mapping over 25 locations of implemented green infrastructure in Riga, Latvia. Basic information, such as location, characteristics, as well as photos and videos, has been uploaded to the open-source database ClimateScan. From this, eight bioswales installed in the period 2017–2022 were selected for hydraulic testing, measuring the infiltration capacity of bio-retention solutions. The results show a high temporal and spatial variation of infiltration rate for the bioswales, even those developed with similar designs: 0.1 to 7.7 m/d, mean 2.0 m/d, coefficient of variation 1.0. The infiltration capacity decreased after saturation: a 30% to 58% decrease in infiltration rate after refilling storage volume. The variation in infiltration rate as well as infiltration rate decrease on saturation is similar to other full-scale studies done internationally. The infiltration rate of most bioswales falls within the range specified by international guidelines, all swales empty within 48 h. Most bioswales empty several times within one day, questioning the effectiveness of water retention and water availability for dry periods. The results are of importance for stakeholders involved in the implementation of NBS and will be used to set up Latvian guidelines for design, construction, and maintenance.
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The rain gardens at Bryggen in Bergen, Western Norway, is designed to collect, retain, and infiltrate surface rainfall runoff water, recharge the groundwater, and replenish soil moisture. The hydraulic infiltration capacity of the Sustainable Drainage System (SuDS), here rain gardens, has been tested with small-scale and full-scale infiltration tests. Results show that infiltration capacity meets the requirement and is more than sufficient for infiltration in a cold climate. The results from small-scale test, 245–404 mm/h, shows lower infiltration rates than the full-scale infiltration test, with 510–1600 mm/h. As predicted, an immediate response of the full-scale infiltration test is shown on the groundwater monitoring in the wells located closest to the infiltration point (<30 m), with a ca. 2 days delayed response in the wells further away (75–100 m). Results show that there is sufficient capacity for a larger drainage area to be connected to the infiltration systems. This study contributes to the understanding of the dynamics of infiltration systems such as how a rain garden interacts with local, urban water cycle, both in the hydrological and hydrogeological aspects. The results from this study show that infiltration systems help to protect and preserve the organic rich cultural layers below, as well as help with testing and evaluating of the efficiency, i.e., SuDS may have multiple functions, not only storm water retention. The functionality is tested with water volumes of 40 m3 (600 L/min for 2 h and 10 min), comparable to a flash flood, which give an evaluation of the infiltration capacity of the system.
The application of sensors in water technology is a crucial step to provide broader, more efficient and circular systems. Among the different technologies used in this field, ultrasound-based systems are widely used, basically to generate energy peaks for cell lysis and particle separation. In this work, we propose the adaptation of an ultrasound system to monitor the concentration of solid particles in wastewater treatment plants settlers as well as to indicate sludge level (real time). A similar sensor was developed and tested in another project which operated successfully at solids concentration up to 1% in UASB reactors. Such measurements are nowadays obtained via time-consuming physical (solids) analysis, which can compromise the efficiency of the settlers and the quality of the effluent. The present project proposes an improved version of the sensor, which will combine solids concentration monitoring and sludge level detection. The defined targets have the intention to make a sensor with a much broader range of applications, been suitable not only for UASB reactors but also to settler and aerobic tanks. The project is a cooperation between the Water Technology lectoraat of NHL Stenden University of Applied Sciences, two SME’s - YNOVIO B.V. and Lamp-ion B.V. - and the INCT group (Brazil). If proven feasible, the concept can generate a big business market to the involved Dutch partners as well as favor the automation of WWTP in the Netherlands, Brazil and around the world.
