Evaluation of Biological Response to Treated Wastewater
Photo 1 Green alga Pseudokirchneriella
Photo 2 Daphnia magna
Photo 3 Zebrafish
The Water Quality Research Team of the PWRI is conducting research to evaluate biological responses to treated wastewater. Biological response evaluation is a type of water quality evaluation based on the response of an aquatic organism to certain stress (i.e., growth inhibition of algae [Photo 1], reduction in the number of neonate of Daphnia magna [Photo 2], or reduction in the hatching rate or survival rate of fish [Photo 3]).
At present, chemicals are generally managed by measuring the concentration of a few hundred individual chemical substances contained in wastewater or estimating their behavior. In reality, the number of those chemicals is much smaller than that of chemical substances we use in our daily lives (about 50,000 kinds). In recent years, worldwide attention has been focused on a biological response evaluation that evaluates water quality based on such biological responses rather than evaluating the toxicity of individual chemical substances. The biological response test has some characteristics. For example, (1) it is capable of evaluating biological impacts by all kinds of chemical substances contained in water, and (2) since it evaluates water quality based on direct impacts on organisms, it helps citizens more realistically see the evaluation results. Tests using biological response are already conducted and used for managing treated water toxicity in some countries other than Japan. The introduction of wastewater management based on biological response is at the stage of consideration also in Japan.
While treated wastewater is one of the major effluents, extremely few research cases in Japan have tested wastewater based on published test methods. Under these circumstances, the Water Quality Research Team is conducting biological response tests on wastewater and collecting various findings and data, including data on biological impacts on test organisms such as alga, Daphnia magna or fish. And it is examining the feasibility of reducing biological impacts by wastewater treatment.
In a wastewater treatment plant employing a conventional activated sludge process, influent (pre-treated wastewater) and treated wastewater were sampled. Then the biological response test was conducted with the above-mentioned test organisms soaked in the sample water. The results showed that the influent inhibited the growth of Pseudokirchneriella (alga), while it was clarified that the treated wastewater had no growth inhibition. Similar results were confirmed for Daphnia magna and zebrafish. These results clearly confirm that the conventional activated sludge process can reduce biological impacts.
If treated wastewater has biological impacts, it is important to clarify the causal substances contained in the treated wastewater that cause biological impacts or the source of those causal substances considering a variety of effluents (chemical substances) flowing into the sewage. The Team is working to study methods of clarifying them and finding solutions to reduce biological impacts of treated wastewater.
(Contact: Water Quality Research Team)
Protection of Steel in Concrete by Surface Coating System
Fig. 1 Rust on reinforcing bars
Fig. 2 Application of resin material
Fig. 3 Image of surface coating
1. Concrete structure
Concrete consists of coarse and fine aggregates that are mixed and hardened with cement and water, and it is suitable for constructing structures. Structures made of concrete are called “concrete structures”. Concrete structures are mainly constructed with concrete and steel (reinforcing bars). A concrete structure consists of a good combination of concrete that is resistant to compression but less resistant to tension, and steel that is resistant to tension. Namely, the concrete and steel compensate for each other’s weaknesses. A large amount of concrete and steel are used in structures. In addition, as the inside of the concrete is highly alkaline, a protective coating is formed on the steel surfaces. This protective coating serves to prevent the steel in the concrete from rusting, and it is an advantage to utilize concrete structures for a long period of use.
2. Corrosion of steel in concrete
A microscopic observation of concrete shows that there are many small pores in concrete. Water, oxygen, chloride ion and so forth permeate gradually into the concrete through those small pores. In reality, this property of concrete can prevent concrete structures from being used for a long time.
For example, salt from the sea can enter a concrete structure that is located near the sea, but it is not desirable. When a certain amount of salt has entered the concrete, it begins to destroy the protective coating of the steel in the concrete. Furthermore, when the protective coating of the steel in the concrete is damaged and there is water and oxygen present, then the steel rust (Fig. 1). As the rusting continues, the cross-section of the steel decreases and it becomes difficult to use the concrete structure safely. In other words, in order to use a concrete structure safely for a long time, it is essential to protect the steel in the concrete.
3. Surface coating system on concrete
In order to protect the steel in the concrete, preventing water and salt from entering the concrete is needed. As one of the ways to protect the steel in the concrete, a surface coating system on concrete is explained (Fig. 2).
Surface coating is like painting a film on the surface that prevents water and salt from penetrating into the concrete (Fig. 3). In reality, a resin material is applied over the surface of the concrete. The resin material coating prevents salt and water from permeating into the concrete due to its barrier property. Since concrete structures are generally used for a long time, the resin material coating also needs to withstand long-time use. It is important to make sure that a resin material can stay effective in order to protect the steel in the concrete for a long time. The Materials and Resources Research Group therefore conducts tests on various kinds of resin materials to confirm whether or not they remain effective for a long period of time.
(Contact: Materials and Resources Research Group)
A Study on a Snowmelt Estimation Method for Road Management
Photo 1 Road slope failure during snowmelt
(May 2012, Nakayama Pass, National Highway 230, Sapporo)
Figure 1 Monthly cases of slope failure on national
highways in Hokkaido (1998-2013)
Figure 2 Relationship between cumulative snowmelt depth
and cumulative temperature (no lower than zero degrees)
It is well-known that heavy rainfalls and earthquakes cause slope failure. In Japan's snowy regions, such as Hokkaido, Tohoku and Hokuriku, slope failure often happens in fine weather during early spring (Photo 1). This is thought to be because snowmelt generates water that infiltrates beneath the ground and makes the ground unstable, similar to what happens during heavy rainfall. Our analysis of the slope failure records of Hokkaido's national highways revealed that nearly 30% of all the slope failures occur in springtime (Figure 1).
To protect pedestrians and vehicles on the street from sudden slope failures and other disasters, national and municipal road administrators take tangible measures for improving roads with tunnels and bridges, as well as on the slopes. On disaster-prone road sections, road administrators take the intangible measures of restricting traffic when the rainfall exceeds the flooding limit. However, there is no flooding limit for excess snowmelt, as it is difficult to estimate the volume of snowmelt water.
Against this backdrop, the Geological Hazards Research Team has been studying methods for estimating the volume of snowmelt water and the topographic and geological conditions of the disaster in the snowmelt season. By combining snowmelt data with existing data on the rainfall flooding limit, it will be possible for us to establish a new flooding limit ap-plicable to snowmelt and to restrict traffic more effectively, thereby avoiding disasters on road slopes.
There are possible methods for estimating the volume of snowmelt water. The easiest method is to calculate the volume from the variation in measured snow depth. (This is called the snow surface lowering method.) This method is intuitive, prone to measurement error and low in resolution. Hence, it cannot forecast future snowmelt. We have instead focused on the degree-hour method, a method that uses a relational equation between temperature (0 degree or higher) and snowmelt water (Figure 2). The degree-hour method allows snowmelt amount to be estimated solely from temperature fluctuations, so it is possible to estimate the snowmelt amount from temperature forecasts. We consider the degree-hour method to be appropriate for estimating the snowmelt amount for road management, as the resolution of the degree-hour method is higher than that of the snow surface lowering method. Meanwhile, the degree-hour method may cause the coefficient of the relational equation to vary by place and year. To address this issue, we will continue on-site surveys and numerical analyses to investigate the method toward modifying coefficients by considering the topographical characteristics of the place.
(Contact: Geological Hazards Research Team, Civil Engineering Research Institute for Cold Region)