Biosculptures™

Problem and Research Objectives

The management of stormwater runoff in densely urbanized areas with substantial impermeable surfaces presents a major design challenge. Large volumes of runoff are generated from extensive impermeable surfaces, yet few locations exist within the urban watershed for its storage and treatment using conventional stormwater best management practices (BMP’s). The large land areas typically required to construct detention basins, and wet and dry ponds prohibit their use in most urban areas. A further limitation of these conventional BMP approaches is their mixed track record in treating the suite of contaminants (i.e., pathogens, metals, nutrients, DOC, etc.) found in urban stormwater. End of pipe solutions, on the other hand, are costly.

A more viable option for urban stormwater management may be a pollution prevention approach whereby runoff is intercepted high in the urban watershed in or on small, underutilized areas and surfaces before it reaches catchbasins and sewers. These urban stormwater “resisters” can then be used to facilitate evapotranspiration and infiltration vis-à-vis vegetation. Our goal is to design these systems to aesthetically improve the urban experience. This is the biosculpture™ concept developed by the designer, Jackie Brookner. The challenge of using such systems in temperate urban climates is to develop a substrate that is both porous, yet has enough structural integrity to withstand disintegration from freeze/thaw cycles, corrosion, sunlight, pH and other chemical interactions. In addition, the substrate would preferably be made from abundant, locally available materials, and must be economical and sustainable in terms of total life cycle analysis from origin to future uses.

The overall goal of the project was to create prototype structures that function ecologically and hydrologically in a stormwater treatment context, but that also aesthetically enhance urban environments.

Methodology

Two studies have been carried out. The first study was carried out by Paul Jawlik with the objective to test numerous materials for suspended solid removal ability. These materials were: Sand 800-1000 μm Grains: Porex Porous Plastic (Fine) 10-20 μm Pores: Porex Porous Plastic (Medium) 20-30 μm Pores; Porex Porous Plastic (Coarse) 90-130 μm Pores; Grodan Rockwool Water Flow – Along Grain; Grodan Rockwool Water Flow – Against Grain; Mirafi Geotextile 1120S;  Volcanic Rock Whole; Volcanic Rock 1000-1500 μm Grains;  The materials were tested for clogging, particulate removal capacity, and hydraulic conductivity with 20 μm particles and where applicable 200 μm particles. The results of this study were given in the technical report submitted last year to WRI. We found that Grodam Rockwool performed best and this material was used for further testing in the second year by M. Ekrem Cakmak a graduate student in the Department of Biological and Environmental Engineering at Cornell University.

In the second study Biosculptures™ were tested for their ability to treat storm water. The biosculpture™ concept was developed by the designer Jackie Brookner. It is envisioned that the Biosculptures™ are placed in urban watersheds in or on small, underutilized areas and surfaces for treating the stormwater before it reaches catchbasins and sewers. These urban stormwater “resisters” can then be used to facilitate evapotranspiration and infiltration vis-à-vis vegetation.

Biosculptures™

Brookner constructed specifically for this project six Biosculptures™ utilizing rockwool in five of them. The properties of the Biosculptures are given in Table-1 . Pictures shown on this page were taken 3 months after the last experiment.

The six sculptures, with different structures and amounts of moss (Table-1), were treated at two different pH levels of simulated rainwater. The ability of the sculptures to remove metals and nutrients from simulated storm water runoff was tested in two separate experimental runs in which the storm water was applied through nozzles on the sculptures. The sculptures were kept moist between rainfall events by applying tap water for one minute each hour using the same nozzles.

During each experimental run sculptures were first flushed with tap water for 20 minutes. This was followed by the application of 114 L of simulated storm water for five hours at a rate of 3.3 cm/h. The experimental run was finished by flushing sculptures for 80 minutes with tap water at the same rate of 3.3 cm/h. The composition of the storm water is given in Table 2. Different amount of acid was added for each of the two experimental runs. In the first experimental run  the sculptures were exposed to simulated storm water with a pH of 2.5 representing the first flush  after snow melt and in the second run at 6.5 representing the summer months  Rainwater was  applied by using large rain-type nozzles (Figure-1).

Samples taken of the water draining from the sculptures were preserved by adding 0.1 ml HNO3 to each 40 ml sample. This resulted in a pH of less than 2 (Standard Methods, 1998) (Section 1060C). The samples were analyzed for Pb, P, Cu, Cd, and Zn with Inductively Coupled Argon Plasma (Thermo Jarrell Ash – ICAP61).

Accomplishments

The amount of moss that covered each Biosculpture was greatly different (Tables 1 and 3, before and after the experiments, respectively). The surface of sculpture #5 was covered with 70 % moss initially, after the experiments at low pH the percentage of moss covering the sculpture decreased to 30-40 %, while the remaining ones had less than 10 % covered (Table 3) after the experiments at low pH.  This was a direct result of the material used in the biosculpture and indirectly of the waste water application. Table 2 shows that the biosculpture #5 had no rockwool used in its construction. This sculpture retained significantly more moss than any of the biosculpture that had rockwool used as part of the design. The poor performance of the biosculptures with rockwool could be attributed to the rockwool providing a path for the water - applied between the experimental runs to keep the structures moist - to drain through the rockwool and as a consequence the moss was exposed to much dryer conditions than the biosculpture without rockwool in which all the water applied could be retained by the moss.

The overall removal rate of the metals and nutrient was the best for biosculpture #5 (Tables 4 and 5). For the pH of 6.5 it removed all of the Zn and Cu, most of the Pb and Ca and 75 % of the P (Table 4). Biosculpture #4 which was covered with approximately 10% (Table 3) had the generally the second highest removal rates (Table 4). The trends were the same for the treatment with the storm water with pH of 2.5 but the overall removal rate was lower with the exception of P of which the removal rate was as expected higher at lower pH (Table 5).  In some especially Zn, the removal case even more of the particular chemical was lost than was applied. The main reason for this is low pH. Influent with low pH (2.5) dissolved the metals already attached to sculptures, which resulted in high metal concentrations in the effluent.
The loss of Pb (expressed a percentage removed from the influent) throughout the experimental period is shown in Figures 2 and 3 as an example for the other elements that showed similiar trends. The removal capacity of biosculptures 4 and 5 is the best for lead at pH=6.5. At pH=2.5 the removal capacity of biosculpture 5 is the best.  Not shown here, but significant is that the moss covering biosculpture 5 was able to bring the pH in the neutral range for the low pH storm water.  The figures of the removal rates of other elements can be found on the left of the page.

Publications
Jawlik, P, 2004, Suspended solid removal from urban stormwater runoff, NSF-REU project report, Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY.

Table-1. Properties and Moss Coverage Percentages of Biosculptures

back to the text

Table-2. Reagents Used and Initial Concentrations of Elements in Simulated Rainwater

back to the text

Table-3. Percentage of Moss Coverage of Biosculptures after Treating with Low pH Storm Water

back to the text

Table-4. Average Percentage Removal Capacity of Biosculptures (pH=6.5)

Table-5. Average Percentage Removal Capacity of Biosculptures (pH=2.5)