On a recent day, a new sewage treatment system started operations at the capital’s Sunamachi Water Reclamation Center in Koto Ward.

The equipment consists of white tanks about 3 to 4 meters high that line the interior of a building. Pipes of various sizes are arranged around them.

Processed sewage water is kept in the tanks from which the solid impurities have been removed. The treated water is characterized by a considerable amount of phosphorus.

Specialized powder fashioned primarily from calcium silicate is added to the water. It is then reportedly dehydrated and dried to recover the phosphorus as calcium phosphate. 

The recovery is part of Tokyo's effort to transform a large portion of the sewage sludge generated in one of the largest cities in the world into vegetable fertilizer.

The aim is reducing Japan’s dependence on imports in securing ingredients for this type of chemical.

FOREIGN RELIANCE CREATING CONCERNS

With almost all those substances coming from outside the nation at present and the surging global prices of fertilizer, a shadow is being cast over the domestic agriculture industry.

Tokyo has embarked on a collaborative initiative with the central government, whereas the capital’s highly urbanized environment may not appear to be suited for extending a helping hand to farmers.

According to the agriculture ministry, ores to extract phosphorus cannot be unearthed in Japan. Consequently, the main ingredient for chemical fertilizer is imported from China, Morocco and elsewhere mainly in the form of ammonium phosphate.

Imported phosphorus covers nearly all the demand in Japan.

However, the global price tag of phosphorus skyrocketed amid not only the war in Ukraine but also the growing need for crops worldwide in 2022.

Trade statistics released by the Finance Ministry show the import price of ammonium phosphate spiked 2.4 times year on year in July that year.

The figure was down temporarily in 2023, but the situation remains unstable.

Hoping to procure phosphorus in a stable manner, Japan is eyeing sewage sludge produced in Tokyo.

The capital, possessing the largest population nationwide, must handle the largest volume of sewage across the country.

Tokyo dealt with 5.66 million cubic meters of sewage, equivalent to more than four Tokyo Domes, on a daily basis in fiscal 2022.

CHANGING NEGATIVE IMAGE OF SEWAGE SLUDGE

To obtain fertilizer’s raw material from the massive amount of sewage sludge, the newly introduced system at the Sunamachi Water Reclamation Center is being tested under a program started by the central government and the Tokyo metropolitan government.

Project costs are estimated at 800 million yen ($5.2 million) for construction and other purposes. The expenses are mostly borne by the central government.

The technology to recover phosphorus from sewage was developed jointly by the Tokyo metropolitan government, leading cement provider Taiheiyo Cement Corp. and major water processing firm Metawater Co.

The center is projected to retrieve 70 tons of calcium phosphate annually for the time being.

The capacity is expected to be raised to 1,400 tons per year through mechanical upgrading at some point. The forecast output is comparable to 0.3 percent of the total ammonium phosphate imported between July 2021 and June 2022.

Tokyo previously said it had been eliminating phosphorus from sewer water since releasing untreated sewage into the ocean can result in a phenomenon known as eutrophication, which makes water bodies overly enriched with nutrients and creates harmful red tides, or algal blooms. 

Recovered phosphorus was not utilized for fertilizer production because rendering it commercially available entails staggering costs.

Though there was a method to compost sewage sludge, fertilizer created that way was “difficult to utilize as Tokyo is home to few agricultural fields,” according to the metropolitan government’s Bureau of Sewerage.

For those reasons, most of the dehydrated sewer sludge was formerly incinerated and buried.

In December, the capital signed a cooperative agreement with the National Federation of Agricultural Cooperative Associations (Zen-Noh), with an eye on the future use of phosphorus derived from sewage sludge.

Tokyo called the joint effort with a nationwide organization for distribution as the first of its kind, while some cases had already been reported in which generated phosphorus was utilized only locally in Kobe and Fukuoka.

The capital said winning over the hearts of the public is important, too, as it is looking to someday cover the treatment costs with sales from the phosphorus.

“We need to shed the conventional negative perception of sewage sludge,” said a Bureau of Sewerage official.

Acknowledging that only a paltry volume of raw material for fertilizer compared to the total is projected to be utilized, Tokyo officials stated that their endeavor still has significance in that other regions can be inspired to follow suit. 

“Having the capital with the largest sewage processing volume actively engaging in it, the initiative is expected to be embraced in a nationwide quest to convert phosphorus from sewage sludge into vegetable fertilizer,” said a Tokyo government representative.

The capital plans to share the recovery techniques tested with other local governments if their effectiveness is confirmed.