Real-time control of stormwater detention basins as an adaptation measure in mid-size cities

ABSTRACT

The performance of predictive real-time control (RTC) of outflow from a detention basin, integrating rainfall forecasts in the definition of the control rules, was assessed in terms of peak flow reduction in the receiving water body, improvement of the level of service of the stormwater network downstream and qualitative treatment of runoff. Evaluations were performed using the PCWMM software with rainfall data for a continuous 6-month period and four individual events, in a future climate. As compared to the situation with static control, peak flows at the outfall were reduced by an average of 46% with predictive RTC, and the downstream collector was used up to 22% less during rainfalls. Also, the detention time reached the desired period of 36 h for water quality control, for most of the simulated rainfall events. This demonstrates the usefulness of RTC as an adaption measure to climate change in existing urban areas.     

Design comparison of experimental storm water detention systems treating concentrated road runoff

The aim was to assess the treatment efficiencies of experimental storm water detention (extended storage) systems based on the Atlantis Water Management Limited detention cells receiving concentrated runoff that has been primarily treated by filtration with different inert aggregates. Randomly collected gully pot liquor was used in stead of road runoff. To test for a 'worst case scenario', the experimental system received higher volumes and pollutant concentrations in comparison to real detention systems under real (frequently longer but diluted) runoff events. Gravel (6 and 20 mm), sand (1.5 mm), Ecosoil (inert 2 mm aggregate provided by Atlantis Water Management Limited), block paving and turf were tested in terms of their influence on the water quality. Concentrations of five-day at 20 degrees C ATU biochemical oxygen demand (BOD) in contrast to suspended solids (SS) were frequently reduced to below international secondary wastewater treatment standards. The denitrification process was not completed. This resulted in higher outflow than inflow nitrate-nitrogen concentrations. An analysis of variance indicated that some systems were similar in terms of most of their treatment performance variables including BOD and SS. It follows that there is no advantage in using additional aggregates with high adsorption capacities in the primary treatment stage.     

Biological reactor resistance to inhibition

The phenomenon of complete substrate conversion within biological reactors in the presence of toxic compounds, called the Reactor Resistance to Inhibition (RRI), has been investigated. It was theoretically demonstrated that the RRI value, which means the highest concentration of inhibitor by which complete substrate conversion is possible, depends on liquid detention time. The excess detention time over that required for complete conversion, imply the existence of a “reserve” reaction potential. The value of this “reserve” can be reduced by inhibitor action with no influence on the observed substrate conversion rate. The influence of detention time on biological denitrification in Packed Bed Reactors in the presence of chromium Cr⁶⁺ was investigated. The RRI value for 1 h detention time was 1.5 mg l⁻¹ Cr⁶⁺. For 3 h detention time the RRI value was 22 mg l⁻¹ Cr⁶⁺. The relationship between the RRI value and detention time was linear.     

CFD Simulations of Fire Propagation in Horizontal Cable Trays Using a Pyrolysis Model with Stochastically Determined Geometry

In this paper, a pyrolysis model for a PVC cable is constructed using results from thermogravimetric analysis, microscale combustion calorimeter and cone calorimeter experiments. The pyrolysis model is used to simulate fire propagation in horizontal cable trays. The simulated arrangement corresponds to a cable tray fire experiment from OECD PRISME 2 project. As laying the cables loosely along the horizontal trays is a random process, a novel stochastic method is developed for making the simplified cable tray geometries for the computational fluid dynamics model. In addition, as the simplified cable tray geometry has significantly smaller surface area than a real tray full of cables, the surface area was parametrically adjusted. In contrast to most of the earlier published numerical approaches for simulating cable tray fires, the presented approach does not use empirical correlations for predicting fire propagation and does not require any results from full-scale experiments for calibrating the model. The simulation results are compared to experimental results in terms of heat release rate, mass loss, tray ignition times and lateral flame spread rates. The maximum heat release rate was overpredicted by 8% on average.

     

Improving the performance of stormwater detention basins by real-time control using rainfall forecasts

Dry detention ponds are commonly implemented to mitigate the impacts of urban runoff on receiving water bodies. They currently rely on static control through a fixed limitation of their maximum outflow rate. Real-Time Control (RTC) allows optimizing their performance by manipulation of an outlet valve. This study developed several enhanced RTC scenarios of a dry detention pond located at the outlet of a small urban catchment near Québec City, Canada. The catchment's runoff quantity and TSS concentration were simulated by a SWMM5 model with an improved wash-off formulation. The control procedures rely on rainfall detection, on measures of the pond's water height, and in some of the RTC scenarios on rainfall forecasts. The implemented RTC strategies allow a substantial improvement of the pond's performance - the TSS removal efficiency increases from 46% (current state) to about 90% - while remaining safe and taking a mosquito-breeding risk constraint into account.     

华北地区陆生园林植物去除道路径流 污染物的实证研究

利用植物来削减径流污染物浓度是植物生态修复理 论的主要应用领域之一，其研究多集中在水生植物，对华北地 区城市中大量的陆生植物的研究较少，尤其是对径流污染起重 要源头控制作用的道路绿化植物及其长期修复效果更鲜有研 究，无法满足实际应用需求。与此同时，对生物滞留设施中雨 水径流长期集中入渗所带来的污染风险的研究也不足，对植物 能否起到减缓污染物累积的作用尚不明确。通过盆栽试验分析 了矮生紫薇等11种华北地区道路绿化常用的陆生园林植物对 模拟径流中TN、TP、CODCr的去除效果，以及试验过程中土 壤里TN、TP的积累量的去除率。希望能够对景观设计、环境 工程等领域针对特定目标选择特定植物进行生态修复起到一定 参考。     

Aerobic stabilization of primary and mixed primary-chemical (alum) sludge

This study was conducted to investigate the feasibility of using aerobic digestion as a method for the stabilization of mixed primary-chemical (alum) sludge from a physical-chemical treatment plant. Aerobic digestion was carried out in “continuous” flow (batch fed once a day) laboratory reactors with detention times ranging from 5 to 35 days held at 7, 12, 18 and 25°C.Temperature was found to have a slightly greater influence on the reduction of volatile suspended solids in primary sludge than in mixed primary-chemical sludge. Nitrification took place in the reactors treating both primary and mixed primary-chemical sludge. The high content of aluminum in the mixed primary-chemical sludge did not inhibit the nitrifiers. The oxygen-uptake rate varied between approximately 5 mg O₂ g⁻¹ VSS h⁻¹ and 1 mg O₂ g⁻¹ VSS h⁻¹ depending on the detention time and the reactor temperature. Adenosine triphosphate content per unit volatile suspended solids indicated a low content of active biomass during aerobic digestion.     

Spatio-temporal flood trends & settlement choice in flood-prone areas. A case study of Lubiji micro-catchment,Kampala City

ABSTRACT

This study was conducted to establish the spatio-temporal distribution of flash floods and to learn why people prefer to settle in flood-prone areas of Lubiji micro-catchment in Kampala City. Rainfall data were analysed to ascertain Peak Runoff expected for the given flood event based on Soil Conservation Service Curve Numbers. The micro-catchment was delineated in the Arc GIS 10.0 programme, from the Digital Elevation Model. Feature classes were created to obtain the reach extents and river banks. HEC-RAS model was then used to create flood inundation maps in Arc GIS 10.0 between 1983 and 2014. High magnitude flash floods occurred almost after every three years and the spatial extent varied from 4.4 to 6.8 km². The choice of settlement location in flood-prone areas was influenced by socio-economic ties. The flood hazard maps produced will aid land-use planning, resettlement of the people and setting up a flood forecasting system.     

Survival dynamics of fecal bacteria in ponds in agricultural watersheds of the Piedmont and Coastal Plain of Georgia

Animal agriculture in watersheds produces manure bacteria that may contaminate surface waters and put public health at risk. We measured fecal indicator bacteria (commensal Escherichia coli and fecal enterococci) and manure pathogens (Salmonella and E. coli 0157:H7), and physical-chemical parameters in pond inflow, within pond, pond outflow, and pond sediments in three ponds in agricultural watersheds. Bishop Pond with perennial inflow and outflow is located in the Piedmont, and Ponds A and C with ephemeral inflow and outflow in the Coastal Plain of Georgia. Bromide and chloride tracer experiments at Bishop Pond reflected a residence time much greater than that estimated by two models, and indicated that complete mixing within Bishop Pond was never obtained. The long residence time meant that fecal bacteria were exposed to solar UV-radiation and microbial predation. At Bishop Pond outflow concentrations of fecal indicator bacteria were significantly less than inflow concentrations; such was not observed at Ponds A and C. Both Salmonella and E. coli 0157:H7 were measured when concomitant concentrations of commensal E. coli were below the criterion for surface water impairment indicating problems with the effectiveness of indicator organisms. Bishop Pond improved down stream water quality; whereas, Ponds A and C with ephemeral inflow and outflow and possibly greater nutrient concentrations within the two ponds appeared to be less effective in improving down stream water quality.     

Treatment of stormwater using a detention pond and constructed filters

A stormwater treatment plant, consisting of a detention pond, a constructed filter system and a constructed wetland, has been investigated according to stormwater quality improvement, sediment and heavy metals accumulation and potential toxicity of the stormwater and sediment. The reduction of metal content in the detention pond was on average 26?–?84%. No acute toxicity in the stormwater was detected although heavy metal levels often exceeded guideline values during storm events. Pore water samples of the collected sediments were not toxic but the whole sediment was toxic when assessed with the Microtox^® Solid-phase test. The constructed filter system became clogged due to cementation of the filter substrate.     

Laboratory studies of virus survival during aerobic and anaerobic digestion of sewage sludge

The survival of three enteroviruses (polio 1, coxsackie B3 and echo 1) and a rotavirus (SA-11) was studied under laboratory conditions. The effects of temperature, dissolved oxygen, detention time, sludge source and virus type on virus inactivation were determined. Temperature was the single most important factor influencing the rate of virus inactivation. No significant differences were found for virus inactivation rates at dissolved oxygen levels between 0.9 and 5.8 mg/l. However, the inactivation rate of the viruses under aerobic conditions was found to be significantly greater than the inactivation rate under anaerobic conditions (−0.77log₁₀/day vs −0.33 log₁₀/day). Sludge source, detention time and virus type did not significantly influence the rate of virus inactivation.     

Ultrafast remediation of lead-contaminated water applying sphagnum peat moss by dispersive solid-phase extraction

ABSTRACT

Lead poisoning, correlated to the high blood lead levels among the children of the Gaza Strip, is another severe problem for Palestinians. The paper reports a cost-effective and time-effective remediation by sphagnum moss, which can remove lead from aqueous solution through dispersive solid-phase extraction. The optimum conditions of adsorption such as equilibrium time, pH, adsorbate initial concentration and adsorbent mass were investigated. In conclusion, a cost-effective and ultrafast lead uptake of ~95% was established in 60 s as adsorption-equilibrium contact time. Thus, a design of flow-through remediation unit for lead removal from real-life contaminated water would provide healthy outflow water. Moreover, regeneration and reuse of sphagnum in lead removal is advantageous for less developed economies with a problem of lead pollution in their water.     

Exploring forecast-based management strategies for stormwater detention ponds

Dry detention ponds are commonly implemented to mitigate the impacts of urban runoff on receiving water bodies. They currently rely on static control through a fixed limitation of their maximum outflow rate. This study investigated the performance of several enhanced management strategies for a dry detention pond located at the outlet of a small urban catchment near Québec City, Canada. Among the enhanced scenarios studied are some previously developed real-time control (RTC) strategies, and new operating rules relying on a daily manual adjustment of the outlet gate. Both types of control make use of rainfall forecasts originating from the initial or downscaled Canadian global ensemble prediction system. Different ways of using the forecasts' ensemble spread were considered to take action. The pond performances were investigated considering three different volumetric capacities (including the existing volume). The RTC scenarios are very promising. The value of taking rainfall forecasts into account to prevent pond overflowing is demonstrated. Strategies involving only manual adjustments on a daily basis do not seem helpful.     

Bod removal rates of waste stabilization ponds as a function of loading, retention time, temperature and hydraulic flow pattern

This study evaluates the influence of loading, detention time and temperature on the first order BOD removal coefficient K₁. Numerical values of K₁ are derived from semi-continuous-flow laboratory units of sewage ponds and introduced into the design formula for a multi-stage continuous flow reactor. There was a good correspondence (r = 0.92) between the computed BOD removal rates and the empirical results obtained from three large-scale multi-stage pond systems.     

屋面径流污染物的出流类型与水质特性研究

在对上海城区屋面径流进行监测的基础上,分析了屋面径流中污染物的出流过程,并探讨了其水质特性.通过对污染物出流过程的研究,得到了3种屋面径流污染物的出流类型及出流水质的变化特征和发生的环境条件;污染物出流事件平均浓度(EMC)的对数正态概率分布结果表明,不同污染物的EMC均具有较好的正态分布性;对屋面径流污染物的出流EMC进行统计分析,得到上海城区屋面径流的COD、SS、BOD5、NH3-N、TP、TN的EMC分别为42.6、76.9、15.2、1.61、0.14、4.8 mg/L,其中SS、COD为主要污染物.     

Thermophilic anaerobic digestion of palm oil mill effluent

A laboratory study was carried out using the thermophilic anaerobic process to treat palm oil mill effluent containing 67,000 mg 1⁻¹, COD, 31,800 mg 1⁻¹ suspended solids and a pH of 4.5. Completely mixed reactors were operated to evaluate the effects of feed strength and solids retention times on the system's performance. A range of 5–35 days solids retention time was studied. COD reduction was 72% for the 5-day unit and greater than 90% for units having detention time 15 days or more. pH of all units was self adjusted to 7.4. Gas production was, in general, greater than 0.3 m³ kg⁻¹ volatile solids feed.     

雨水调蓄池的流量演进

流量演进在雨水调蓄池的设计计算和运行模拟中具有重要作用。采用有限差分方法,根据调蓄池的进流过程线确定出它的出流过程线,以此获得调蓄池的洪峰削量、洪峰滞时、最大蓄水量、最大水深、放空时间等水文和水力技术参数。     

Investigation of the impacts of thermal pretreatment on waste activated sludge and development of a pretreatment model

This study investigated the impacts of high pressure thermal hydrolysis (HPTH) pretreatment on the distribution of chemical oxygen demand (COD) species in waste activated sludge (WAS). In the first phase of the project, WAS from a synthetically-fed biological reactor (BR) was fed to an aerobic digester (AD). In the second phase, WAS from the BR was pretreated by HPTH at 150 °C and 3 bars for 30 min prior to being fed to the AD. A range of physical, biochemical and biological properties were regularly measured in each process stream in both phases. The COD of the BR WAS consisted of storage products (X_STO), active heterotrophs (X_H) and endogenous decay products (X_E). Pretreatment did not increase the extent to which the BR WAS was aerobically digested and hence it was concluded that the unbiodegradable COD fraction, i.e. X_E, was unchanged by pretreatment. However, pretreatment did increase the rate of degradation as it converted 36% of X_H to readily biodegradable COD (S_B) and the remaining X_H to slowly biodegradable COD (X_B). Furthermore, X_STO was fully converted to S_B by pretreatment. Although pretreatment did not change the VSS concentration in the downstream aerobic digester, it did decrease the ISS concentration by 46 ± 11%. This reduced the total mass of solids produced by the digester by 21 ± 8%. A COD-based HPTH pretreatment model was developed and calibrated. When this model was integrated into BioWin 3.1^®, it was able to accurately simulate both the steady state performance of the overall system employed in this study as well as dynamic respirometry results.     

Parameter extraction of solar photovoltaic cells and modules using current–voltage characteristics

ABSTRACT

The significance of bio-inspired evolutionary algorithms has attracted many applications for obtaining best solutions to their optimisation problems in the past decades. This paper is about the application of one of these algorithms, namely, quantum particle swarm optimisation algorithm for parameter extraction of solar photovoltaic cells using current–voltage (I–V) characteristics. This algorithm has been used here to extract five parameters, namely, photocurrent, saturation current, series resistance, shunt resistance and ideality factor that influence the I–V relationship of single diode model solar photovoltaic cells. This approach has been validated for a cell and a module. Simulations using Matlab software have shown that the simulated I–V characteristics obtained using the extracted parameters have good agreement with the experimental I–V values. The reason for the interest taken in undertaking this work is to suggest a good and an accurate simulator for solar system designers.