Influence of intermittent wetting and drying conditions on heavy metal removal by stormwater biofilters

Biofiltration is a technology to treat urban stormwater runoff, which conveys pollutants, including heavy metals. However, the variability of metals removal performance in biofiltration systems is as yet unknown. A laboratory study has been conducted with vegetated biofilter mesocosms, partly fitted with a submerged zone at the bottom of the filter combined with a carbon source. The biofilters were dosed with stormwater according to three different dry/wet schemes, to investigate the effect of intermittent wetting and drying conditions on metal removal.Provided that the biofilters received regular stormwater input, metal removal exceeded 95%. The highest metal accumulation occurs in the top layer of the filter media. However, after antecedent drying before a storm event exceeding 3–4 weeks the filters performed significantly worse, although metal removal still remained relatively high. Introducing a submerged zone into the filter improved the performance significantly after extended dry periods. In particular, copper removal in filters equipped with a submerged zone was increased by around 12% (α = 0.05) both during wet and dry periods and for lead the negative effect of drying could completely be eliminated, with consistently low outflow concentrations even after long drying periods.     

Nutrient and sediment removal by stormwater biofilters: a large-scale design optimisation study

A large-scale column study was conducted in Melbourne, Australia, to test the performance of stormwater biofilters for the removal of sediment, nitrogen and phosphorus. The aim of the study was to provide guidance on the optimal design for reliable treatment performance. A variety of factors were tested, using 125 large columns: plant species, filter media, filter depth, filter area and pollutant inflow concentration. The results demonstrate that vegetation selection is critical to performance for nitrogen removal (e.g. Carex appressa and Melaleuca ericifolia performed significantly better than other tested species). Whilst phosphorus removal was consistently very high (typically around 85%), biofilter soil media with added organic matter reduced the phosphorus treatment effectiveness. Biofilters built according to observed 'optimal specifications' can reliably remove both nutrients (up to 70% for nitrogen and 85% for phosphorus) and suspended solids (consistently over 95%). The optimally designed biofilter is at least 2% of its catchment area and possesses a sandy loam filter media, planted with C. appressa or M. ericifolia. Further trials will be required to test a wider range of vegetation, and to examine performance over the longer term. Future work will also examine biofilter effectiveness for treatment of heavy metals and pathogens.     

The effect of nitrate on VOC removal in trickle-bed biofilters

In response to the growing concern over volatile organic compounds (VOCs), biofiltration is becoming an established economical air pollution control technology for removing VOCs from waste air streams. Current research efforts are concentrating on improving control over key parameters that affect the performance of gas phase biofilters. This study utilized diethyl ether as a substrate, nitrate as the sole nutrient nitrogen source within two co-currently operated trickle-bed biofilters, for over 200 days. The two pelletized medium biofilters were operated at a low empty bed contact time of 25 s, inlet gas flow rates of 8.64 m³/day, nutrient liquid flow rates of 1 liter/day, and COD loading rates of 1.8 and 3.6 kg/m³ per day, respectively. Operational parameters including contaminant concentration in the gas phase, nutrient nitrate concentration in the aqueous phase, and the frequency of biomass removal were considered. Special attention was given to the effect and the role of nitrate on VOC removal. Throughout the experiment, nitrate persisted in the liquid effluent and the ether removal efficiencies improved with increasing influent nitrate concentration, which suggest that the nitrate diffusion into the biofilms is rate determining. By increasing the concentration of oxygen in the feed to this biofilter from 21% (ambient air) to 50 and 100%, while maintaining an influent ether concentration of 133 ppmv and a feed nitrate concentration of 67 mg-N/liter, the performance of the biofilter was not significantly affected. These results suggest that nitrogen was rate limiting as a growth nutrient rather than as an electron acceptor for the respiration of ether. The results also indicated that removal of excess biomass is necessary to maintain long-term performance. However, the required frequency of biomass removal depends on operating parameters such as loading.     

颗粒物尺度对滤料过滤性能的影响

介绍了不同学者对滤料过滤机理的研究结果,实验研究了颗粒物尺度对粗、中、高效滤料过滤效率和过滤阻力的影响,对合理选择空调系统过滤材料提出了建议。     

Mesocosm study of enhanced bioretention media in treating nutrient rich stormwater for mixed development area

A well-designed engineered soil for bioretention is important as it ensures that pollutant removal requirements are met. This laboratory study investigated the nutrient removal efficiency of bioretention media enhanced with 10% (by volume) additives from various waste materials (cockle shell, newspaper, printed paper, coconut husk and tyre crumb) and planted with Red Hot Chinese Hibiscus (Hibiscus rosa-sinensis), a common landscape shrub in tropical countries. The results showed that media enhanced with shredded newspaper demonstrated a significant improvement in total nitrogen (TN) removal (80.4%), compared to standard bioretention media (57.5%) without compromising total suspended solids (TSS) and total phosphorus (TP) removal, when dosed with actual runoff. The thick root system and rapid growth rate of the plant was proven to contribute to TN removal. This study concluded that shredded newspaper can be a potential addition to enhance bioretention media performance in treating stormwater, especially nutrient rich runoff from mixed development areas.     

普通快滤池改造为气水反冲洗均质滤料滤池工程实践

针对大连大沙沟净水厂原有普通快滤池过滤周期短、产水量下降、反冲洗效果不佳等问题,进行了技术改造。将原有中阻力陶瓷滤砖配水系统改为Azurfloor整体滤板小阻力长柄滤头配水,煤-砂滤料改为石英砂均质滤料,单一水反冲洗改为气水反冲洗,并完善了滤池的自动控制系统。运行情况表明,改造后滤池出水水质提高,反冲洗效果明显改善,产水量增加了10×104m3/d,运行成本减少且滤站实现了自动化运行,经济效益和社会效益显著。     

Mathematical modelling of hydrogen sulphide emission and removal in aerobic biofilters comprising chemical oxidation

Four different empirical expressions have been compared for estimating the removal of hydrogen sulphide (H₂S) from wastewater by chemical oxidation during its treatment in an aerated biofilter. The relative importance of this removal process is considered in a mass balance proposed by an emission model. Two of the four models investigated were able to predict the mean H₂S removed fraction within a confidence interval of 95% and they demonstrated good agreement with experimental data. Biodegradation and oxidation were the two main removal mechanisms in the biofilter whereas stripping and volatilization made only minor contributions. However they can be of significance when the emission rates are calculated.     

Characteristics of particle removals in a compressible media filter system

The ability to adjust the properties of the filter medium by altering the degree of the medium compression is important because the different porosities in media affect the ideal filter performance according to the properties of influent wastewater. This study therefore focused on the particle size distribution (PSD) of compressible media filter (CMF) effluents depending on the compression ratio (0–30%) and the filter bed depth (Layers 1–5) in order to evaluate the CMF performance. The results showed that the removal efficiency for particles larger than 10 µm was more than 90% while that for particles smaller than 10 µm was less than 85% of removal efficiency. From the power law fit, substantial decreases in the number of large‐sized particles were observed in the PSD. Particle removal efficiencies increased along with the average compression ratio increase. Furthermore, the results demonstrated that each layer in the bed had a different role in the filter performance, and it was found that a filter bed of about 0.45–0.60 m would be needed for the production of the desired effluent quality in this study. The detachment phenomenon was observed in particles larger than 5 µm, especially in 5–15 µm particles.     

Influence of stormwater control measures on water quality at nested sites in a small suburban watershed

ABSTRACT

Stormwater control measures (SCMs) are designed to mitigate the deleterious impacts of urban runoff on the water quality of receiving waters. To assess the cumulative effects of SCMs at the watershed scale, we monitored longitudinal changes in storm discharge and stream water chemistry at high temporal resolution in a suburban headwater stream in Charlotte, NC. SCMs significantly decreased or stabilized instream concentrations of reactive solutes (nitrate, soluble reactive phosphorus, and dissolved organic carbon) relative to the upstream control site. However, SCM outflows minimally influenced concentrations of less reactive solutes (major ions) which increased with urbanization. Additionally, instream concentration variability correlated with antecedent moisture conditions – representative of watershed storage availability – highlighting the role that SCM storage availability plays in the timing of solute delivery to the stream. Our results show that SCMs decrease instream concentrations of biogeochemically reactive solutes but the mitigation potential is temporally dynamic and influenced by antecedent conditions.     

雨水径流携带污染负荷对水体影响的评价方法

分析了城市排水系统规划中对雨水径流所携带污染负荷进行评价的必要性,介绍了在德国ATV规范框架下雨水径流所携带污染负荷对水体影响的评价思路,提出了雨水径流所携带污染负荷对水体的影响以及雨水设施处理效果的量化评价方法。     

Impact of filter media on the performance of full-scale recirculating biofilters for treating multi-residential wastewater

The main objective of this paper was to evaluate the effectiveness of silica sand, crushed glass, peat, and geotextile as a medium in RBFs in the removal for organic matter, nutrients and bacteria from domestic wastewater based on a field-scale study. In particular, this field-scale study was conducted to treat domestic wastewater from a small community of 10 households from the Municipality of Lunenburg, Nova Scotia, Canada. The average influent 5d biochemical oxygen demand (BOD(5)) and total suspended solids (TSS) concentrations into the field filter system were 381+/-64 (mean+/-standard deviation) and 46+/-21 mg/L, respectively. The results showed that crushed glass could be an effective medium in RBFs since the crushed glass filter produced stable effluent BOD(5) and TSS concentrations of less than 20mg/L. Geotextile was found to be another successful alternative filter medium with the effluent BOD(5) and TSS of 18+/-11 and 11+/-7 mg/L, respectively, even though the porosity of geotexitle filter was as high as 0.90. Peat was not able to provide efficient performance due to its poor BOD(5) and NH(4)(+)-N removals. This study measured the water quality variation at different components of the RBFs. The results of this study showed that the recirculation tank was the main facilitator of the denitrification process. In addition, this study found that RBFs could efficiently treat domestic wastewater for BOD(5) removal under the organic loading rates as high as 0.070 kg/m(2)/d.     

混凝土应力状态对碳化深度的影响

为考虑混凝土应力状态对碳化深度的影响,在混凝土碳化深度模型中增加了应力影响系数。利用已有文献的试验数据,进一步研究了应力影响系数随混凝土应力比变化的规律,并分别建立了应力影响系数随混凝土拉、压应力比变化的计算式。将建立的应力影响系数计算式与既有的3组典型计算式进行了对比,结果表明,建立的应力影响系数计算式较合理,具有较高的预测精度。对规范中的应力影响系数计算式进行了评价,结果表明,在混凝土拉应力状态下,应力影响系数取值偏于不安全;相反,在混凝土压应力状态下,取值偏于保守,因此可将文中所提计算式作为规范中应力影响系数的修正式。     

Treatment performance of gravel filter media: implications for design and application of stormwater infiltration systems

Stormwater infiltration systems are widely used to address the flow and water quality impacts of urbanization. However, their pollutant removal performance is uncertain, with respect to varying filter depth, and over time. Seven simulation experiments were conducted on a laboratory-scale gravel infiltration system to test the pollutant removal under a range of water level regimes, including both constant and variable water levels. Gravel filters were found to be very effective for removal of sediment and heavy metals under all water level regimes, even as the system clogged over time. Despite the sediment particle size distribution being much smaller than the filter media pore size, sediment and its associated pollutants were effectively trapped in the top of the gravel filter, even when the water level was allowed to vary. A media depth of 0.5 m was found to achieve adequate pollutant removal. Breakthrough of pollutants may not be of concern, since physical clogging occurred first (thus determining the lifespan of the filter media). However, gravel filters were less effective at nutrient removal, particularly for dissolved nutrients.     

Influence of a stormwater sediment deposit on microbial and biogeochemical processes in infiltration porous media

The purpose of this study was to test the relative influence of organic matter quantity and quality and the pollutant content of a stormwater sediment deposit on mineralization processes, microbial characteristics, and the release of solutes in infiltration sediment systems. In microcosm experiments, two other natural sediment deposits (one low and one rich particulate organic matter deposits) were studied to compare their effects with those of the stormwater deposit. The results showed that the biogeochemical processes (aerobic respiration, denitrification, fermentative processes), the microbial metabolism (enzymatic activities), and the releases of several solutes (NH(4)(+) and DOC) were stimulated in presence of the stormwater deposit and the natural particulate organic matter (POM)-rich deposit because of the quantity of the POM in these deposits. In the stormwater deposit, the high availability of the POM (indicated by its low C/N ratio and its high P content) produced a higher stimulation of the microbial metabolism than in presence of the POM-rich deposit (with a high C/N ratio). Pollutant (hydrocarbon and heavy metal) contents of the stormwater deposit did not have a significant effect on microbial processes. Thus, main effects of the stormwater sedimentary deposit on infiltration system were due to its organic matter characteristics (quantity and quality). Such organic matter characteristics need to be considered in future studies to determine the contamination potential of stormwater management practices.     

负锰滤料去除地下水中锰的影响因素研究

通过锥形瓶静态实验,研究不同参数下负锰滤料对水中锰（Mn2＋）的去除效果.实验表明：滤料粒径为2mm时,Mn2＋的去除率及实际应用效果最佳;随着负锰滤料投加量的增加,Mn2＋的去除率也随之增加;随着溶液pH值的升高,滤料对水中的Mn2＋的去除率也随之增加;若体系中有Fe2＋存在,不利于负锰滤料对Mn2＋的吸附;负锰滤料对Mn2＋吸附等温线更符合Langmuir吸附模型,属于单分子层吸附.     

地下水中天然有机物对生物除铁滤柱的影响研究

采用生物滤柱对地下水进行试验研究,用膜过滤法对其出水进行了分子量分析,考察了生物除铁滤柱对不同分子量区间天然有机物的去除效果。结果表明:有机物分子量大小对出水水质有较大的影响,有机物分子量越大,铁去除率越低,DOC和UV254去除率也越低。生物滤柱对原水中分子量1 kDa的有机物的去除率为82.4%,而对分子量30 kDa的有机物的去除率只有28.5%。     

介质及冻融循环对原位合成高吸水性树脂处理砂浆性能的影响

利用原位合成高吸水性树脂遇水膨胀、无水复原的性能特点,能够很好地解决砂浆(混凝土)微裂缝造成的建筑渗漏问题。试验进一步研究了用原位合成高吸水性树脂处理后砂浆在不同介质条件下的抗渗性及低温条件下的抗冻性。结果表明,碱性条件下,砂浆抗渗能力无明显降低;酸性和盐水条件下砂浆抗渗能力降低明显;用原位合成高吸水性树脂处理的砂浆试件,饱水状态下其抗冻能力较基准砂浆有较大改善。     

冷媒进口温度对管外结冰过程的影响

通过实验研究了冷媒温度对蓄冰槽内水结冰过程中晶胚形成期、孕育期和晶核生长期的影响情况，得到冷媒不同温度下蓄冰槽水温随时间的变化曲线，分析了冷媒温度对晶核形成速率和结冰量的影响，认为-5℃冷媒温度是较合适的制冰温度。     

Retention and removal of pathogenic bacteria in wastewater percolating through porous media: a review

Properly designed biological filters or infiltration systems have the capacity to significantly reduce effluent concentrations of pathogenic microorganisms in wastewater. The retention and elimination of microbial cells in biological wastewater filter systems is influenced by several factors. In this review, these factors are discussed. Immobilization of microbial cells moving through a porous media is influenced by mechanisms such as physical straining as well as adsorption to porous media. The grain size of porous media and bacterial cell size are important factors affecting the straining of bacteria, as are the hydraulic loading rate or the extent of clogging layer development in the filter. Adsorption of cells to the porous media is influenced by the content of organic matter, degree of biofilm development, and electrostatic attraction due to ion strength of the solution or electrostatic charges of cell- and particle surfaces. The rate of inactivation of pathogenic microorganisms, in adsorbed or liquid phases, has been shown to be affected by abiotic and biotic factors such as moisture content, pH, temperature, organic matter, bacterial species, predation, and antagonistic symbiosis between microorganisms in the system.