Godecke-Tobias Blecken

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% (alpha=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.

Long-Term Hydraulic Performance of Porous Asphalt Pavements in Northern Sweden

The effect of clogging on the long-term infiltration capacity and porosity of two 18- and 24-year-old porous asphalts was examined by using replicate double-ring infiltrometer tests and analyzing asphalt core samples. Tests were carried out to see if high pressure washing and vacuum cleaning could restore the hydraulic performance. The infiltration capacity of the porous asphalts decreased substan- tially, primarily due to surficial clogging (0.50 � 0.26 in Lulea, Sweden, and 0.22 � 0.12 in Haparanda, Sweden, compared to initially > 290 mmmin −1 ). In Lulea, washing and vacuum cleaning could partially restore the infiltration capacity (3.48 � 3.00 mmmin −1 ), but in Haparanda, no effect was measured. The porosity was constantly between 16 and 18%. The difference of the long-term behavior and effect of cleaning in Lulea and Haparanda is primarily attributable to different street maintenance, age, and winter maintenance (application of fine gravel and/or sand). Although the infiltration capacity in Lulea was far below initial values, the asphalt still has the capacity to infiltrate an intense design rainfall (100 year average return interval, 15 min duration), underlining that porous asphalt can be a resilient feature also under nonfavorable conditions. DOI: 10.1061/(ASCE)IR.1943-4774.0000569.

Stormwater control measure (SCM) maintenance considerations to ensure designed functionality

Abstract Great investment is made in the design and installation of stormwater control measures (SCMs). Substantial research investment, too, is made to optimise the performance of SCMs. However, once installed, SCMs often suffer from lack of maintenance or even outright neglect. Key maintenance needs for wet ponds, constructed stormwater wetlands, bioretention, infiltration practices, permeable pavement, swales, and rainwater harvesting systems are reviewed with many tasks, such as the cleaning of pre-treatment areas and the preservation of infiltration surfaces, being common maintenance themes among SCMs. Consequences of lacking maintenance are illustrated (mainly insufficient function or failure). Probable reasons for neglect include insufficient communication, unclear responsibilities, lack of knowledge, financial barriers, and decentralised measures. In future designs and research, maintenance (and lack thereof) should be considered. Assessing the performance of SCMs conservatively and including safety factors may prevent consequences of under-maintenance; and requiring regular inspection may help to enforce sufficient maintenance.

The influence of temperature and salt on metal and sediment removal in stormwater biofilters

Stormwater biofilters are used to treat stormwater runoff. In countries with cold winter climates, biofilters are subject to low temperatures which, in some cases, are combined with potentially high salt concentrations from road de-icing, potentially affecting the biofilters performance. Since stormwater biofilters have been developed without consideration of their critical winter use, a laboratory study was carried out to evaluate the performance of stormwater biofilters subjected to low and high temperatures, with and without salt. Both factors and their interaction had a significant effect on outflow concentrations and removal percentages. Salt had a negative impact on outflow concentrations, causing lower removal percentages for (especially dissolved) metals, this impact being most pronounced for Cu and Pb. The unrealistic combination of salt with high temperature seemed to further amplify the negative impacts of salt despite the fact that temperature alone did not cause significant differences in outflow concentrations and removal percentages. Still, biofilters showed the ability to treat stormwater efficiently under the simulated winter conditions; outflow concentrations for total metals as a minimum met the class 4 threshold value defined in the Swedish freshwater quality guidelines, while inflow concentrations clearly exceeded the threshold value for class 5. The relatively coarse filter material (which is recommended to facilitate infiltration during winter) did not seem to exacerbate biofilter performance.

Fat, Oil, and Grease Accumulation in Sewer Systems: Comprehensive Survey of Experiences of Scandinavian Municipalities

AbstractProblems with fat, oil, and grease (FOG) in sewer systems have received relatively little attention, although in the longer term this might imply (inter alia) blockages and sanitary overflows. Therefore, the experiences of Swedish and Norwegian executive water engineers concerning FOG-related issues were assessed using a comprehensive questionnaire that was distributed to all Swedish and Norwegian municipalities (with a response rate of 35% and 25% in Sweden and Norway, respectively). Blockages caused by FOG in sewers and pumping stations were the most prevalent reported problem, followed by increased demand for line flushing. The water engineers singled out city centers as the areas whose sewers had the most severe problems with FOG buildups. Most municipalities mandated the use of grease interceptors (GIs) by businesses, but the maintenance and functional status of these devices were reported to be inadequate. Commonly, water engineers had faith in the functioning of the GI despite the lack of s...

Long-term hydraulic performance of stormwater infiltration systems

Despite the common use of stormwater infiltration systems, there is still only limited data available evaluating the long-term hydraulic function of such systems. The hydraulic performance of twelve stormwater infiltration systems (vegetated and unvegetated concrete grid pavers, unvegetated interlocking concrete pavers and grassed swales) was therefore investigated in field and laboratory environments in Växjö, Sweden. The systems investigated had not been subjected to regular maintenance to sustain infiltration capacity. Due to this, and the fact that, for most systems, an inappropriate joint filling material was used and (at the swales) there was severe compaction, most systems showed a reduced infiltration capacity. Despite this, especially the older vegetated systems, were still capable of infiltrating intense design rainfalls. This study showed the influence of some factors (type and age of the system, the type of joint filling material (grass and macadam) and the distance from the edge of the pavement) on the long-term behaviour of the infiltration capacity. In conclusion, there is a significant risk that existing stormwater infiltration systems are not working adequately in praxis. Proper implementation of construction and regular control by the inspecting authority has to be ensured.

Do salt and low temperature impair metal treatment in stormwater bioretention cells with or without a submerged zone

Although seasonal temperature changes and (road) salt in winter and/or coastal stormwater runoff might interfere with the metal treatment performance of stormwater bioretention cells, no previous study has evaluated the effect of these factors and their interactions under controlled conditions. In this 18week long study 24 well established pilot-scale bioretention columns were employed to evaluate the individual and combined effect(s) of low/high temperature, salt and presence of a submerged zone with an embedded carbon source on metal removal using a three factor, two-level full factorial experimental design. In most instances, the three factors significantly influenced the metal outflow concentrations and thus the treatment performance; the effect of temperature depended on the metal in question, salt had an overall negative effect and the submerged zone with carbon source had an overall positive effect. Despite these statistically significant effects, the discharge water quality was generally markedly improved. However, leaching of dissolved Cu and Pb did occur, mainly from bioretention cells dosed with salt-containing stormwater. The highest concentrations of metals were captured in the top layer of the filter material and were not significantly affected by the three factors studied. Overall, the results confirmed that bioretention provides a functioning stormwater treatment option in areas experiencing winter conditions (road salt, low temperatures) or coastal regions (salt-laden stormwater). However, validation of these results in the field is recommended, especially focusing on dissolved metal removal, which may be critically affected under certain conditions.

Environmental Risk Assessment of Sediments Deposited in Stormwater Treatment Facilities: Trace Metal Fractionation and Its Implication for Sediment Management

To gather further data about metal mobility in accumulated sediments in stormwater treatment facilities, metal mobility in sediments from sedimentation tanks, gully pot sediment traps, and sediment ...

Ecotechnologies for the Treatment of Variable Stormwater and Wastewater Flows

The occurrence of variable stormwater and wastewater flows, mostly precipitation driven, brings with them the challenge of both peak flows and pollutant loads. Wastewater treatment systems can be divided into those that are specifically designed and operated to deal with variable flows, and those that presume more steady-state operation, only coping with peak flows as anomalies for short periods of time. To date, the different types and scales of variability and the impact of this variability on functioning and treatment performance have neither been well characterised nor properly dealt with for the design of suitable treatment systems. In this book, ecotechnologies are defined as processes for the treatment of variable wastewater flows that – harness ecological processes involving microbes, plants, animals, natural soils and media or recycled materials; – have a low reliance on mechanical machinery or external energy sources; and – have a positive impact on the quality and biodiversity of the surrounding environment. K. Tondera (&) Stormwater Research Group, University of the Sunshine Coast, Maroochydore, QLD, Australia e-mail: ktondera@usc.edu.au K. Tondera Institute of Environmental Engineering, RWTH Aachen University, Aachen, Germany C. C. Tanner National Institute of Water and Atmospheric Research, Hamilton, New Zealand e-mail: chris.tanner@niwa.co.nz F. Chazarenc Department of Energy Systems and Environment, Institut Mines Telecom Atlantique, Nantes cedex 3, France e-mail: florent.chazarenc@gmail.com G.-T. Blecken Urban Water Engineering, Luleå University of Technology, Luleå, Sweden e-mail: godble@ltu.se

Emerging Contaminants: Occurrence, Treatment Efficiency and Accumulation Under Varying Flows

Emerging contaminants became a major topic in water treatment when laboratory detection methods for concentrations at a nanogram-scale improved approximately two decades ago. Research on using ecotechnologies to remove emerging contaminants in variable stormwater and wastewater flows has been conducted for more than a decade, but so far, not all removal mechanisms are well understood and only few setups have been investigated. This chapter summarises the current knowledge, focussing on pesticides and emerging contaminants listed on the watch list of the European Union. However, large-scale investigations are still rare and further research will have to be conducted in this field to enable practitioners to provide recommendations for design and maintenance of treatment facilities in the field of ecotechnologies.