Settling Velocity Distribution Research Articles

The role of suspended extracellular polymeric substance (EPS) on equilibrium flocculation of clay minerals in high salinity water

Biophysical cohesive mud, consisting of clay minerals and extracellular polymeric substance (EPS), plays significant role in determining sediments, nutrients and pollutants transport in estuarine and coastal systems. Series of laboratory jar experiments have been conducted aiming at filling the gap of knowledge regarding how biological cohesive EPS affects equilibrium flocculation of EPS-mineral mixtures. Four types of common clay (chlorite, kaolinite, illite and montmorillonite) were chosen due to their abundance in estuarine mud and distinct crystal chemistry and structures. Turbulent shear throughout all the experimental runs were constantly provided at a mean shear parameter of G ≈ 15 s−1 being equivalent to high tidal influenced estuarine turbulent environment. The results reveal that adding EPS increases the equilibrium floc size evidently. The pure mineral flocs show unimodal equilibrium floc size distribution (eFSD) with single peak located at microfloc range (<200 μm) while the EPS-mineral flocs show bimodal eFSD with a secondary peak located in macroflocs range (>200 μm) mostly. Moreover, EPS largely reduces the effective density in EPS-mineral flocs by 1∼2 magnitude. Most importantly, the terminal settling velocity of flocs shows size-dominated in uniform mineral floc cases but density-dominated in EPS-mineral mixture floc cases especially in macroflocs. To model a full floc size or settling velocity distributions in natural environments, furtherly quantification of EPS functions within the large-sized non-fractal mixture floc individually becomes a necessity.

Sedimentation efficiency evaluation of an aquaculture tank through experimental floc characterization and CFD simulation

One of the most important parameters for the proper functioning of an aquaculture tank is water quality. The survival and healthy growth of fish depends on it. The main factors affecting water quality are the remains of food and feces of fish which form cohesive particles called flocs that are kept within the tank or in the modules of the recirculating aquaculture system (RAS). Through the application of non-invasive optical techniques such as particle tracking velocimetry (PTV) it was possible to experimentally characterize the particles from aquaculture tanks obtaining diameters and settling velocity distribution, which allowed estimating the effective density of the flocs. With these parameters, the discrete phase model (DPM) was applied using computational fluid dynamics (CFD) to estimate the position and velocity of the particles within a prototype tank with geometry that promotes hydrodynamics suitable for particles sedimentation while maintaining the conditions for fish growth. Through an experimental validation it was verified that by having a tank with circular geometry, central settler made of concentric cylinders, perimeter gratings and outlet spillway cone, it is possible to achieve an efficiency of 77.91–90% of particles sedimentation not exceeding 1 h in the process. Thus, through computer simulation coupled with experimental validation, it was possible to establish geometric parameters for the design of aquaculture tanks with self-cleaning characteristics under the sustainable scheme of water recirculation and reuse.

WEPP interrill erodibility for clay soils in the crop lands of Northern NSW and Southern Queensland, Australia

Context Water Erosion Prediction Project (WEPP) soil erosion model parameters are rare for cultivated cropping soils in Australia. Aims Measure WEPP interrill erodibility (Ki) for cropping soils. Methods Plots were 50% side-slopes of row-crop furrows. Rainfall was applied for 30 min at 107 mm h−1 under a rainfall simulator, then at higher and lower rainfall intensities for 10 or 6 min. Several of these rainfall sequences were performed with drying between (events). Runoff, sediment concentrations and sediment sizes in runoff and the soil surface after rain and sediment settling velocities were measured. Soils were well-aggregated Vertosols and a Dermosol: clay 31–69%, silt ~20%. Settling velocities and undispersed particle size distributions for rainfall wet soil are provided for a range of soils in Supplemental Data, for use by WEPP users. Key results Runoff during 30 min and 54 mm of rain was 28–44 mm or 50–86% rainfall. Soil losses were 26–61 t ha−1 and sediment concentrations 67–127 g L−1. Infiltration, runoff, sediment concentration and soil losses were sometimes different for soils and events. Gatton and Emerald soils had lower soil losses and Cecilvale, Mywybilla and Narrabri soils had higher soil losses. Conclusions Mean Ki for Emerald and Gatton soils were significantly lower, 2 960 000 and 3 209 600 kg.s m−4, respectively. Ki values were not significantly different for the Cecilvale, Narrabri and Mywybilla soils, 3 900 000 kg.s m−4. Implications WEPP Ki values were like values found for USA cropping on clay soils. Sizes in the soil surface and sediment, and settling velocity distributions, were similar between soils but sediment sizes were finer.

Enhancing bioflocculation in high-rate activated sludge improves effluent quality yet increases sensitivity to surface overflow rate

High-rate activated sludge (HRAS) relies on good bioflocculation and subsequent solid-liquid separation to maximize the capture of organics. However, full-scale applications often suffer from poor and unpredictable effluent suspended solids (ESS). While the biological aspects of bioflocculation are thoroughly investigated, the effects of fines (settling velocity < 0.6 m3/m2/h), shear and surface overflow rate (SOR) are unclear. This work tackled the impact of fines, shear, and SOR on the ESS in absence of settleable influent solids. This was assessed on a full-scale HRAS step-feed (SF) and pilot-scale HRAS contact-stabilization (CS) configuration using batch settling tests, controlled clarifier experiments, and continuous operation of reactors. Fines contributed up to 25% of the ESS in the full-scale SF configuration. ESS decreased up to 30 mg TSS/L when bioflocculation was enhanced with the CS configuration. The feast-famine regime applied in CS promoted the production of high-quality extracellular polymeric substances (EPS). However, this resulted in a narrow and unfavorable settling velocity distribution, with 50% ± 5% of the sludge mass settling between 0.6 and 1.5 m3/m2/h, thus increasing sensitivity towards SOR changes. A low shear environment (20 s−1) before the clarifier for at least one min was enough to ensure the best possible settling velocity distribution, regardless of prior shear conditions. Overall, this paper provides a more complete view on the drivers of ESS in HRAS systems, creating the foundation for the design of effective HRAS clarifiers. Tangible recommendations are given on how to manage fines and establish the optimal settling velocity of the sludge.

Influence of MBBR carrier geometrical properties and biofilm thickness restraint on biofilm properties, effluent particle size distribution, settling velocity distribution, and settling behaviour

The relatively poor settling characteristics of particles produced in moving bed biofilm reactor (MBBR) outline the importance of developing a fundamental understanding of the characterization and settleability of MBBR-produced solids. The influence of carrier geometric properties and different levels of biofilm thickness on biofilm characteristics, solids production, particle size distribution (PSD), and particle settling velocity distribution (PSVD) is evaluated in this study. The analytical ViCAs method is applied to the MBBR effluent to assess the distribution of particle settling velocities. This method is combined with microscopy imaging to relate particle size distribution to settling velocity. Three conventionally loaded MBBR systems are studied at a similar loading rate of 6.0 g/(m2 •day) and with different carrier types. The AnoxK™ K5 carrier, a commonly used carrier, is compared to so-called thickness-restraint carriers, AnoxK™ Z-carriers that are newly designed carriers to limit the biofilm thickness. Moreover, two levels of biofilm thickness, 200 μm and 400 μm, are studied using AnoxK™ Z-200 and Z-400 carriers. Statistical analysis confirms that K5 carriers demonstrated a significantly different biofilm mass, thickness, and density, in addition to distinct trends in PSD and PSVD in comparison with Z-carriers. However, in comparison of thickness-restraint carriers, Z-200 carrier results did not vary significantly compared to the Z-400 carrier. The K5 carriers showed the lowest production of suspended solids (0.7 ± 0.3 g-TSS/day), thickest biofilm (281.1 ± 8.7 µm) and lowest biofilm density (65.0 ± 1.5 kg/m3). The K5 effluent solids also showed enhanced settling behaviour, consisting of larger particles with faster settling velocities.

Advection-diffusion-settling of deep-sea mining sediment plumes. Part 1: Midwater plumes

The evolution of midwater sediment plumes associated with deep-sea mining activities is investigated in the passive-transport phase using a simplified advection–diffusion-settling model. Key metrics that characterize the extent of plumes are defined based on a concentration threshold. Namely, we consider the volume flux of fluid that ever exceeds a concentration threshold, the furthest distance from and maximum depth below the intrusion where the plume exceeds the threshold, and the instantaneous volume of fluid in excess of the threshold. Formulas are derived for the metrics that provide insight into the parameters that most strongly affect the extent of the plume. The model is applied to a reference deep-sea mining scenario around which key parameters are varied. The results provide some sense of scale for deep-sea mining midwater plumes, but more significantly demonstrate the importance of the parameters that influence the evolution of midwater plumes. The model shows that the discharge mass flow rate and the concentration threshold play an equal and opposite role on setting the extent of the plume. Ambient ocean turbulence and the settling velocity distribution of particles play a lesser yet significant role on setting the extent, and can influence different metrics in opposing ways.

Settling velocity distribution of bioflocules generated with different carbon sources during the rearing of the river shrimp Cryphiops caementarius with biofloc technology

Controlling the concentration of bioflocs is one of the main concerns in aquaculture systems with Biofloc Technology (BFT). Biofloc accumulation deteriorates the water quality and can negatively affect the production rates of the farmed river shrimp. This study describes and characterizes the settling velocity distribution of bioflocs generated with the addition of two carbon sources (molasses and chancaca) when applying the BFT for the rearing of the river shrimp Cryphiops caementarius. This study revealed that bioflocs generated with different carbon sources have different settling velocity curves. Regarding the mass fraction settling velocities, there were significant differences (P < 0.05) for mean solids fraction at similar withdrawn times between molasses and chancaca. The average settling velocities for bioflocs were 0.1044 ± 0.1224 cm s−1 for molasses and 0.1131 ± 0.1225 cm s−1 for chancaca. Therefore, a settling device operating with a given overflow rate will more efficiently remove bioflocs generated with chancaca than with molasses. The settling velocity curves obtained in this research contain valuable information to select appropriate devices for bioflocs and suspended solids removal in aquaculture systems with BFT.

The development of a calibration methodology for a realistic primary settling tank (PST) model

The previous models that replicated primary sedimentation units assumed that all the total settleable solids (TSS) components settled at the same velocities. These assumptions resulted in poor predictions of primary sludge characteristics and anaerobic digestion (AD) model. With the accurate knowledge of PS compositions, the settled wastewater that leads to the activated sludge (AS) system can be determined using the principles of material mass balance. The mass balance is achieved by consolidating the known compositions of raw wastewater and primary sludge (PS) hereby allow accurate tracking of elements along the entire WRRF when using the model for design and optimised operation of WRRF systems. In this investigation, the raw wastewater entering the water and resource recovery facility (WRRF) via the PST is comprehensively characterising the TSS. The TSS was categorised into inorganic settleable solids (ISS), biodegradable particulate organics (BPO) and unbiodegradable particulate organics (UPO), each with five settling velocity distribution profiles. The BPO is further defined in terms of its elemental composition and hydrolysis rate kinetic constants to allow for accurate prediction of the AD system performance when linked to the virtual PST. To achieve this, the study introduced the (i) modification of the University of Cape Town Primary Sedimentation Unit (UCTPSU) model of (Polorigni et al., 2021), by the inclusion of hydrolysis and acid fermentation bioprocesses, and (ii) calibration of the UCTPSU model. The calibration was conducted through the (a) performance of a sensitivity analysis on the modified UCTPSU model and (b) the utilisation of the data generated from settleometer and augmented bio-methane potential (ABMP) tests.

Settling velocity and particle size bioengineering parameters gathered from solids generated by wild-caught premature punctuated snake-eels (Ophichthus remiger) reared in a marine prototype recirculating aquaculture system

This research reveals the applied engineering basis for determining the particle size and settling velocity distributions of solids generated while rearing wild-caught premature punctuated snake-eels (Ophichthus remiger) in a prototype recirculating aquacultural system. Settled solids were sampled from the bottom of the rearing tanks, and suspended solids were sampled before filtration within the drum filter and analyzed to characterize their settling velocity and particle size properties. These particle properties are considered bioengineering parameters since they will provide biological information to improve engineering solutions for RAS solids removal processes. The average settling velocity for the settleable solids in the rearing tanks was 2.89 ± 0.02 cm s−1, and the average particle size ranged between 7.32 ± 3.41 and 19.44 ± 8.58 mm. Suspended solids within the drum filters before filtration had an average settling velocity of 0.35 ± 0.11 cm s−1 and it was found that 69.93 % of the particles size was greater than 200 μm, 15.40 % were within the range of 120 μm and 90 μm sizes, and 6.53 % were between 70 μm and 40 μm sizes. The particle physical properties, settling curves, and particle sizes curves obtained from this experience represent valuable information to be used to improve engineering design of solids handling mechanisms, especially in marine land-based systems, and in this case, applied for rearing wild-caught punctuated snake-eels. The present investigation constitutes an advance in the knowledge of applied engineering to the design of a marine aquaculture fattening operation targeted to feed up wild-caught premature punctuated snake-eels to the point of sale or trade.

Normalization of wastewater coagulation-flocculation trials and implications in terms of variability in treatment performance and comparison of commercial coagulants

ABSTRACT Normalizations by TSS or P-PO4 3- initial concentrations are consistent as they are correlated to the Jar-test performances. Jar-tests results are independent of the wastewater quality variations in terms of TSS and P-PO4 3- and independent of the WWTP origin of the water. A notable variability in the TSS results indicates that the pollutant’s initial load has to be taken into account even with normalizations. This variability is lower with normalization by P-PO4 3-, indicating that this is the best indicator to consider. It is possible to determine that the optimal cation dosage is 60 mol Fe3+ / kg P-PO4 3- as it guarantees a residual concentration of 0.7–1.0 mgP/L and a good removal of TSS. Then, six commercially available cationic coagulants were compared, demonstrating a comparable effect at a comparable normalized molar dose, whatever the coagulant on both TSS and P-PO4 3-, as well as on soluble carbon and nitrogen. The differences observed between these types of coagulants in the literature are then probably due to methodological issues. Settling velocity distribution charts were also very similar for the different coagulants. This confirms that the source of cation and the type of cation have no significant effect on physico-chemical settling performances.

Dynamic grit chamber modelling: dealing with particle settling velocity distributions.

Grit chambers are meant to reduce the impact of inorganic particles on equipment and processes downstream. Despite their important role, characterization and modelling studies of these process units are scarce, leading to a lack of knowledge and suboptimal operation. Thus, this study presents the first dynamic model, based on mass balances and particle settling velocity distributions, for use in a water resource recovery facility (WRRF) simulator for design and optimization of grit removal units.

Comparison of modelling approaches to estimate trapping efficiency of sedimentation basins on peatlands used for peat extraction

Peatlands on which there is vacuum peat harvesting must be drained to allow peat extraction. Peat erosion due to mechanical tilling, vacuum harvest and rain can generate large suspended sediment concentrations that must be reduced before reaching the receiving waters. In this study, six sedimentation basins were monitored over one or two ice-free seasons, resulting in seven basin-years time series, to estimate their trapping efficiency. Using these data, two modelling approaches were first applied to predict the seasonal trapping efficiency of the basins, namely the Brown equation and a multilinear regression model (MLR). Secondly, an additional approach based on the hydrodynamic model MOHID was used to compute the trapping efficiency of one of the basins for a single rain event. The Brown equation, used worldwide in agricultural sedimentation ponds, proved to be less efficient in predicting the trapping efficiency of the basins (r = 0.67, p = 0.1, leave-one-out RMSE = 47.2%) than a MLR model using the volume of the basin, the surface of the harvested catchment and the Von Post decomposition degree of the peat as predictors (r = 0.87, p = 0.01, leave-one-out RMSE = 31.6%). The deterministic MOHID model was capable of reproducing high flow suspended sediment concentration at the basin outlet, based on measured settling velocity distribution of the peat through ViCAs protocol, but requires a good description of the settling velocity distribution across multiple hydrological conditions to simulate the suspended sediment concentrations over a full season in order to compute trapping efficiency. The results presented here provide new insights on eroded peat modelling and could lead to better design formulas for basin conception.

Settling velocity and size distribution measurement of anaerobic granular sludge using microscopic image analysis

Settling velocity and size distribution of anaerobic granular sludge samples were studied using microscopic image analysis and settling column experiments. Five granule samples were considered in this study. Three samples were collected at the Top, Middle and Bottom sections of a lab scale upflow anaerobic sludge bed reactor (UASB). Two other granule samples were obtained from industries. This paper aims to establish a method that uses microscopic image analysis and shape factor as a tool to determine the size distribution and settling velocity of anaerobic granules. Image analysis technique was used to calculate the shape factor and equivalent diameter of granules. The equivalent diameter was then used to calculate the theoretical settling velocities based on Allen's formula and estimate size distributions.The results showed that there was a good agreement between the theoretical and experimental mean settling velocity values. Both measured and calculated settling velocities increased with increasing Reynolds number (Re). However, the agreement between measured and calculated values was found to be weaker at higher Re values. Size distribution analyses of the granules have revealed that there was significant difference in the size distribution of granule samples collected at different heights of the lab scale reactor. Overall, granules from the bottom section of the reactor had larger diameter, settling velocity and shape factor than those at the middle and top section granules. Whereas granules collected from the top section exhibited the smallest granular diameter, settling velocity and shape factor.

Sedimentation of Raw Sewage: Investigations For a Pumping Station in Northern Germany under Energy-Efficient Pump Control

Flow control in wastewater pressure pipes can reduce energy consumption but increases the risk of sediment formation due to reduced flow velocity. In this work, the sedimentation behavior of dry and wet weather samples at the inflow of a wastewater pumping station is determined by settling column experiments. Based on the derived characteristic settling velocity (vs) distribution, the impact of energy-efficient flow control on sediment formation in pressure pipes (600 mm diameter) was quantified in comparison to a simple on/off operation. In parallel, the sediment formation for 2 years of pumping operation was monitored indirectly via the friction losses. For the investigated case, settling is strongly influenced by the inflow condition (dry, combined from road runoff). Under combined inflow, the proportion of solids with vs from 0.007 to 1.43 mm/s significantly increases. In energy-efficient mode with smoother operation and shorter switch-off sequences, the sediment formation is significant lower. The mean deposit’s height in energy-efficient control was calculated to 0.137 m, while in on/off operation the mean deposit’s height was 0.174 m. No disadvantages arise over a long period by installing the energy-efficient control. The decreased flow lead under the investigated conditions even to a reduced sediment formation.

Sedimentation Characteristics and Pollutant Content Distribution of Storm Drainage Sediments

To determine the characteristics of precipitation and pollutant content in storm drainage sediments, samples of sediment from building areas (including residential areas), roads, and green spaces in Wuhan were collected and analyzed. The settling velocity results show that particles with high settling velocity weight occupied a larger proportion in the sediment; the settling velocity distribution of sediments in building areas and roads was more stable than that in green spaces; and the proportion of particles with settling velocity over 3.00 cm·s-1 in building areas, roads, and green spaces decreased in turn. The particle size distribution indicated sediment size had a wide variation range, with most particles concentrated in the range 13-628 μm, and that the particle size distribution in sediment from the same land type could differ greatly. Each sample was divided into seven groups according to settling velocity. The contents of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) were tested. The results indicate that pollutant contents in groups containing particles with settling velocity over 3.00 cm·s-1 or below 0.025 cm·s-1 were lower than those in other groups. Most pollutants were concentrated in particles with high settling velocity.The COD concentration declined in green spaces, roads, and building areas, in turn, for most cases. The nitrogen content in the drainage sediment of roads was lower than those in the two other kinds of land, whereas the phosphorus content in the drainage sediment of building areas was higher than those in the two other kinds of land. In the storm drainage sediment, the ratio of COD:TN was between (51-89):1 and that of COD:TP was between (102-186):1.

Numerical solution of a multi-class model for batch settling in water resource recovery facilities

• The numerical solution for several batch settling unit processes in WRRFs is computed. • Multi-class concentration-driven model based on settling velocity distributions used. • Non-linear convection–diffusion equations appear due to the multi-class extension. • IMEX-RK schemes combined with high order shock-capturing technology are applied. In Torfs et al. (2017) a new unified framework to model settling tanks in water resource recovery facilities was proposed providing a set of partial differential equations (PDEs) modelling different settling unit processes in wastewater treatment such as primary and secondary settling tanks (PSTs and SSTs). The extension to a multi-class framework to deal with the distributed properties of the settling particles leads to a system of non-linear hyperbolic-parabolic PDEs whose solutions may contain very sharp transitions. This necessitates the use of a consistent and robust numerical method to obtain well-resolved and reliable approximations to the PDE solutions. The use of implicit–explicit Runge–Kutta (IMEX-RK) schemes, along with the weighted essentially non-oscillatory (WENO) shock-capturing technology for the discretization of the set of equations, is advocated in this work. The versatility of the proposed unified framework is demonstrated through a set of numerical examples for batch settling occurring in both PSTs and SSTs, along with the efficiency and reliability of the numerical scheme.

Acoustic scattering from flocculating suspensions

Acoustic backscatter from sediment suspensions in the marine environment has been limited in application by the lack of understanding of how sound scatters from flocculating particles. To support theoretical development of sound scattering, combined measurements of high frequency acoustic backscatter and particle population characteristics are presented over a range of flocculating suspensions, from natural in-situ muddy suspensions to laboratory controlled pure clay flocs. Field measurements of cohesive suspended sediments were made in the meso-tidal Tamar Estuary, Devon, UK over several tidal cycles during spring tides. Controlled laboratory experiments were conducted using oscillating grid turbulence to suspend kaolin, oxidized, and natural marine sediments sieved below 63 microns. In both field and laboratory cases distributions of floc size and settling velocity were acquired using video techniques (from which effective density was derived) and acoustic backscatter measured over frequencies of 1-4 MHz. Particle measurements were complimented by pumped suspension samples later analyzed for mass and organic content. Measured scattering properties from the various sediments are compared against each other and with predictions from a hybrid elastic-fluid sphere model. Initial results suggest a good agreement with the model for both in-situ field suspensions and oxidized natural sediments from the laboratory.

A storm water basin model using settling velocity distribution

Quantifying processes that affect the fate of particles in storm water basins is a complex but necessary step to predict the effect of various pollutants on receiving waters. A dynamic model for storm water basins taking advantage of the experimental fractionation of particles in different settling velocity classes has been developed to describe the water quality dynamics in the basin. This paper is focused on the calibration of the model using total suspended solids (TSS) time series data and settling velocity distribution data obtained from ViCAs (vitesse de chute en assainissement) tests. Experimental sampling campaigns have been conducted at an actual storm water basin to identify the TSS behaviour under various operational conditions. For one set of experiments, the outlet was always open, and for another, the outlet was kept closed to allow settling before release to the receiving water. The experimental results reveal spatial heterogeneity of the particle concentrations in the basin during the initial phases of water retention for the closed outlet sampling campaign. A calibration procedure is proposed to fit the model to the experimental data. This model was found able to reproduce both open and closed outlet TSS concentration time series with only three particle classes.

Settling regimen transitions quantify solid separation limitations through correlation with floc size and shape

This study monitored three different activated sludge systems from the Blue Plains Advanced Wastewater Plant for a 1 year period to explore the relationship between effluent quality and activated sludge settling and flocculation behavior. Hindered settling rates (ISV) and sludge volume index (SVI) measurements were collected weekly. Novel metrics based on the solids concentration at which the transition between settling regimens occurred were also collected weekly. The transitional metrics were Threshold of Flocculation (TOF), and Limit of Stokesian Settling (LOSS). They marked the transition from discreet to flocculant settling, and from flocculant to hindered settling, respectively. A pilot clarifier and settling column were run and filmed to determine floc morphological properties. SVI was found to lose sensitivity (r < 0.20) when characterizing ISV above a hindered settling rate of 3 m h−1. ISV and LOSS had a strong correlation (r = 0.71), but ISV was subject to change, depending on the solids concentration. Two sludge matrix limitations influencing effluent quality were characterized by transition concentrations; pinpoint floc formation, and loose floc formation. Pinpoint flocs had TOF values above 400 mg TSS L−1; loose floc formation sludge had TOF and LOSS values below 400 mg TSS L−1 and 900 mg TSS L−1, respectively. TOF was found to correlate with the particle size distribution while LOSS correlated to the settling velocity distribution. The use of both TOF and LOSS is a quick and effective way to characterize limitations effecting effluent quality.

Sediment modelling and design optimization for stormwater ponds

Stormwater ponds, including dry ponds, wet ponds and constructed wetlands, have been widely used for sediment removal from stormwater runoff. In this paper, sediment removal mechanisms, modelling approaches and optimization of design for stormwater ponds are reviewed and discussed. The settling velocity for discrete particles is introduced and compared. Settling velocity distribution should be characterized for individual sites for the most cost-effective design of new stormwater ponds. Different methods for estimating trap efficiency of stormwater ponds are then summarized, including empirical models and theoretical models. The sediment transport modelling method is also discussed. Optimization of pond design for improved sediment removal is described, with many key factors taken into account such as residence time, vegetation, wind, turbulence, stratification, inflow and outflow. A high system hydraulic efficiency can be achieved through proper design of the shape of the pond, length-to-width ratio, baffling, depth, and the location of inlets, outlets and vegetation. Finally, various issues associated with typical numerical models for sediment transport in stormwater ponds are discussed. This review paper intends to provide a state-of-the-art of sediment modelling in stormwater ponds and to point the direction for design optimizations.