Preventing Algal Blooms with Nanobubbles and Probiotics

Kyoto moat history

A temple in Kyoto, Japan, with a beautiful moat, had a group of volunteers who maintained it by cleaning and performing regular upkeep. Due to the volunteers' older age, the group stopped most maintenance around 1998. Over the next 20 years, no maintenance was done, and the situation worsened year by year. On the one hand, natural pollution, such as autumn leaves, wasn't removed; on the other hand, excessive, uncontrolled growth of water plants occurred. On the other hand, tourism in Kyoto was on the rise, and more and more litter came into the moat. This led to an uncontrolled situation of bad odor, fish mortality, and opaque water, with the bottom of the moat invisible. In the summer, algal blooms were becoming more and more frequent.

810 meters moat

The Higashi Honganji temple in Kyoto, located nearby the Central Station of Kyoto, was established in 1604. It has a long history and contains one of the tallest wooden structures in the world, it also has burned down a couple of times. Around the temple grounds is a moat of which has a length of 810 meters. As it's a touristic hotspot for both Japanese and international visitors, its important that the water looks clean and doesn't disturb the visitors and neighborhood with bad smell.  The water for the moat is coming from lake Biwa the largest sweet water lake in Japan, the water is transported via an ancient underground water network. When the water is arriving at the Higashi Honganji temple, it's pumped into the moat on the north side of the temple, after which the water slowly travels to the south side of the moat and continues elsewhere.

Nanobubbles & probiotics and cleaning plan

In 2018, Acniti came into contact with the gardener and the temple's management and drew up a plan to bring the moat back to a healthy state. The plan consisted of:

1. Removal of excess natural pollution in spring and autumn, from blossom and leaves
2. Removing excess water from plants once or twice a year, which stops the flow in the moat
3. Putting up signs at the taxi stand to not pollute the water
4. Cooperation with the gardener during maintenance periods, so that no plant debris goes into the water.
5. Putting 2 submersible nanobubble aeration devices with oxygen concentrators
6. A natural probiotic spray program with low intensity application in winter and higher application during spring and summer.

Results

Three months into the project, the results became visible. No more smell and fish mortality, and the water color went from opaque to transparent and clear. Depending on the climate conditions in spring and summer, there is a more intensive cleaning program with longer hours for operating the nanobubble generator. During the summer, at their peak, they run for a max of 13 hours, from 6 PM to 7 AM, always around sunset till sunrise. During the summer daytime, natural oxygen production is sufficient; the problems occur at night, when photosynthesis doesn't produce any oxygen. In the first year, we noticed that DO levels went from 4,5 ppm to 9 ppm. The use of probiotics is more intensive in the summer than in the winter. In Spring and Autumn, the application is 2x a month; during summer, 2 or 3 times; and in the winter, every 8 weeks.

Finally, we got some positive comments from Japanese bloggers who noticed the improvement to the water quality (Japanese only). Especially, this blogger was very surprised by the good water quality. Calling her article:

I was surprised at the feeling of Aquarius in the water of the moat *Higashi Honganji*.