Suggested treatments for foul water and when EM is effective
by King Mongkut’s University of Technology Thonburi (KMUTT) and National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency (NSTDA)
Stagnant water becomes putrid when organic matters in the water start to decay. Examples of these organic matters include human waste, municipal waste (from cities) and agricultural biomass (from farm lands). When the natural microbes start decomposing these organic matters, they also use oxygen from the water as part of the process. The process will decrease the amount of oxygen in the water rapidly. Another group of microbes that require little oxygen or none will continue to digest the organic matters under an anaerobic condition (without oxygen). Hydrogen sulfide (rotten egg gas), ammonia or organic acids (sour smelling odor) are by products of this reaction. The exact degradation process depends on the amount of oxygen there is in the water. In general, oxygen in water comes from the photosynthesis of photosynthetic microorganisms, aquatic plants or diffusion of the air above water surface, which depends on the movement of wind or flow. Therefore rigorously moving water will have more oxygen diffusion.
I. For urban areas
During the flooding period, when the water flow speed is high, if there are organic matters collected under the water, the microbes will decompose them using oxygen in the water. The water quality drops as the DO (dissolved oxygen) value decreases while the BOD (biochemical oxygen demand) value will increase. (Note: Good DO is 3 mg/liter or higher while good BOD is < 2 mg/liter.)
Corrective measures:
- Have systematic solid waste and trash collection and management.
- Prevent accumulation of solid waste and trash.
- Add oxygen to wastewater by making waterfalls, creating rapid water movements, using machine to add air to the water, etc.
- Adding microbes or EM during the flood is not recommended as the BOD value is still too low, due to low level of organic matters, for microbes to be effective. In addition, the fast flow of flood water will disperse and dilute microbe concentration.
When water becomes stagnant, less oxygen is transferred into the water. If there is a collection of organic matters, the microbes will start decomposing them therefore further reduce the oxygen. Eventually, the condition becomes anaerobic (DO value < 2 mg/liter). The water color becomes darker, with foul odor. The pH value will drop and bubbles begin to appear. Black sediment will start to float.
Corrective measures:
- Remove solid waste and trash from the stagnant water retention areas and get rid of them appropriately elsewhere.
- Add oxygen to the water using an aerator.
- Add microbes or EM now as long as the water is less than 3 meters deep. (When water is deeper than 3 meters, both oxygen and sun light cannot reach the bottom. In this case, the microbes cannot fully function. Treatment should be done in small area.
II. For agricultural areas
When farm lands are flooded for a long period of time, a large amount of biomass will start to decompose. The process will rapidly reduce the oxygen dissolved in the water. Any water treatment should be conducted only on water that will flow through the communities.
Corrective measures:
- Before this water enters the city areas, add oxygen to the water by making waterfalls, creating rapid water movements, using machine to add air to the water, etc.
- Adding EM now won’t be as effective since the rapid flow of the water will disperse and dilute EM.
- Quickly remove plant matters from the water (and use them as fertilizer later) to reduce the volume of organic matters in flooded water.
- After the water recedes and there will be some flood retentions, adding EM then can be done in specific and small areas.
- When the water is released through canals, these organic matters will cause the canals and water reservoirs to become putrid. Dredging or flushing the canals is recommended. Continue to monitor the water quality by adding air to it until the DO value is back to normal (> 4 mg/liter). (Note: we could use a manmade pond to do this before releasing it into the public water drainage – a Lampakbia principle). The color, odor, temperature, pH value and dissolved oxygen content are water quality indicators that must be monitored.
EM mechanism
There are many types of the microorganisms in nature. Each type has its own specific functions. Effective microorganisms or EM is a product originated in Japan. The concept was based on a group of microbes that can biodegrade organic matters. These microbes are lactic acid bacteria, yeasts and photosynthetic bacteria. One microbe will breakdown a large organic molecule into smaller building blocks or converts them to new molecules which are then digested by the other groups of microbes. The photosynthetic bacteria can use sun light in the process of breaking down these organic compounds. EM has been applied in the areas of agriculture, fisheries and environments where specific microbes are useful in these conditions. That is there are appropriate nutrients for these groups of microbes to grow and to establish a new ecosystem of microbes in the water. An effective biodegradation process is therefore resulted. However EM does not work in all situations. Especially when there is no information on the microbial members of starting cultures or there are not enough microbes, EM is ineffective.
Guidelines for effective use of EM balls
- Use appropriate type, quantity and function of microbes in EM balls. Do not store them too long for their effectiveness.
- EM is microbes in dormant state. In cases where these microbes are starter culture, further preparation must be done before each application to increase the quantity of microbes for the task.
- Use optimum concentration of EM for the treated area to maximize the effectiveness and duration.
- Select optimum depth of water and areas.
- Analyze an area before applying EM. Other techniques such as aeration might be more appropriate than EM. In some areas of water, the microbes in the EM balls cannot grow therefore leave EM balls as extra waste in the water.
- Need quality/quantity control for EM in each area EM to be applied.
- Monitor the water after the EM treatment such as the DO, BOD and pH values.