Particle separation from road runoff by a decentralised lamella system - laboratory tests and experiences in the field

Evaluation and sizing of proprietary sedimentation devices for decentralised stormwater treatment

Suspended solids removal is a key performance measure for proprietary stormwater treatment devices. Various technologies are available, with manufacturers claiming hydrodynamic separators offer performance advantages. However, it is important to assess manufacturers' claims. Accordingly, this study seeks to compare the performance of proprietary devices, by applying dimensional analysis to third-party certification data and experimental data from uncertified devices, and to determine the accuracy of a single parameter estimation (Hazen or Péclet number) of removal efficiency. Statistical analysis indicates that device performance is well described by a single parameter estimation transitioning from Hazen (Nash-Sutcliffe coefficient = 0.81 and root mean square error = 5.1%) at low surface loading rates (SLR) in all technology types (high removal efficiency) to Péclet (Nash-Sutcliffe coefficient = 0.5 to 0.61 and root mean square error = 5.9% to 4.3%) at higher SLR (low removal efficiency) for hydrodynamic separators. This indicates that performance at low SLR is well explained by gravity separation in all technology types, whilst in hydrodynamic separators removal at high SLR is better explained by gravity separation plus advection. Consequently, when high (>80%) removal efficiency is required there is no performance advantage between technology types. However, when low (<50%) removal efficiency is required hydrodynamic separators offer a 33% increase in treatment area.

Simulation and optimization of a lamella settler for cattle feedlot wastewater treatment and nutrients recovery. Experimental validation in the field

Cattle concentrated animal feeding operations (feedlots), whose number has grown considerably in the last years, generate large volumes of wastewaters with a high organic load. The wastewaters are formed by rainfall-runoff of the accumulated manure and may contain hormones and antibiotics, which hampers the use of biological treatments. In this work, the feasibility of continuous separation of the suspended colloidal organic matter and nutrients to clarify the liquid and recover the solid is studied. A flocculation sedimentation system using a decentralized lamella settler is proposed, optimized and further tested in the field. Computational fluid dynamic (CFD) simulation is used to analyze the motion of the liquid and suspended inertial particles representing the formed flocs, for optimizing the settler. The simulations helped in the design of the bench-scale unit tested in the field. The clarified liquid was characterized to analyze its use for fertigation. The proposed treatment allowed excellent removal of organic matter (~98% chemical oxygen demand, and almost complete turbidity) and phosphorus (~95%). Organic nitrogen was partially removed (~70%) and ammonia nitrogen mostly remained in the liquid. Spectral characterization of the clarified liquid suggests that the remaining organic nitrogen is related to soluble protein-like compounds.

Tire wear particles in the aquatic environment - A review on generation, analysis, occurrence, fate and effects

Tire wear particles (TWP), generated from tire material during use on roads have gained increasing attention as part of organic particulate contaminants, such as microplastic, in aquatic environments. The available information on properties and generation of TWP, analytical techniques to determine TWP, emissions, occurrence and behavior and ecotoxicological effects of TWP are reviewed with a focus on surface water as a potential receptor. TWP emissions are traffic related and contribute 5-30% to non-exhaust emissions from traffic. The mass of TWP generated is estimated at 1,327,000 t/a for the European Union, 1,120,000 t/a for the United States and 133,000 t/a for Germany. For Germany, this is equivalent to four times the amount of pesticides used. The mass of TWP ultimately entering the aquatic environment strongly depends on the extent of collection and treatment of road runoff, which is highly variable. For the German highways it is estimated that up to 11,000 t/a of TWP reach surface waters. Data on TWP concentrations in the environment, including surface waters are fragmentary, which is also due to the lack of suitable analytical methods for their determination. Information on TWP properties such as density and size distribution are missing; this hampers assessing the fate of TWP in the aquatic environment. Effects in the aquatic environment may stem from TWP itself or from compounds released from TWP. It is concluded that reliable knowledge on transport mechanism to surface waters, concentrations in surface waters and sediments, effects of aging, environmental half-lives of TWP as well as effects on aquatic organisms are missing. These aspects need to be addressed to allow for the assessment of risk of TWP in an aquatic environment.