Redrawing the watershed blueprint December 2001 to 2004

Redrawing the watershed blueprint December 2001 to 2004

The Fifth Total Water Quality Regulations shed light on nitrogen and phosphorus as well as the conventional COD. The target watersheds are Tokyo Bay, Ise Bay, and the Seto Inland Sea. The base year is 1999, and the target is 2004. While the objective was to reduce the numerical values, it was also a device to encourage facility renewal and operational optimization across sewage and factories. The regulation was almost a signal to review the way things were done in the field itself.

The main player at the time was biological removal. Nitrogen was removed by connecting nitrification with aerobic and denitrification with anoxic in a rhythmic manner, and efficiency was increased by circular flow and staged aeration. With the introduction of membrane bioreactor, it has become easier to retain bacteria even during low temperatures. In addition, anaerobic ammonia oxidation was beginning to be considered in some areas, and a map for future energy conservation was being drawn.

For phosphorus, the biological phosphorus dephosphorization method is the core of the system, while coagulation and precipitation of iron and aluminum salts, pressurized flotation, and adsorption columns are combined according to the situation. Designs to catch phosphorus released in side streams and relieve the load on the main system were expanded. In crystal recovery, magnesium ammonium phosphate precipitation has entered the practical range, with a high recovery rate and a possible outlet as a fertilizer material.

The regulatory eye is not only looking at the outlet water. The simultaneous requirements were to reduce the amount of sludge generated, to use the recycled water in the community, and to shrink the overall life cycle energy. The water refined by advanced treatment is used for cooling and sprinkling in factories and for maintaining rivers, bringing a double and triple effect to the city's water cycle. Capital investment was expanded, but the question of balancing operating costs and resource conservation was raised.

On the factory side, too, pre-treatment was stepped up for wastewater with a high load of ammonia nitrogen, and a hybrid of chemical and biological treatment was used for complex wastewater containing oil and metals. On-line measurement has become widespread, and operations in which chemical injection and aeration are closely controlled while monitoring DO, ORP, and nitrification/denitrification indices have become common. It is the control logic, not manpower, that follows the fluctuating raw water.

Taking a step back and looking at the historical background, the agreement toward a recycling-oriented society coincided with the limits of patience with eutrophication of the coasts. The field has acquired the touch not only to aim for compliance with the numbers, but also to find a way to come to terms with resource recovery and energy conservation. Nitrogen and phosphorus regulations are not just binding. They spread a common language of technology and operation throughout the watershed to clean water while recovering resources.