６８５：家庭雑排水の利用

いつも開発途上国の水資源だけに目を向けているため、中々先進国の水資源の状況を知る機会が少ない。

偶々、ヨーロッパ環境機構が09年に発行した「ヨーロッパ全域の水資源」という本を見ることがあり大変参考になった。水不足と渇水にどう立ち向かうかというのが主題である。

何回か前に家庭雑排水についての情報を記したが、今回はかんがい用水としての利用について興味深い研究成果が出たので転記してみよう。下記参照。

コンフリクト管理のお勉強からは、ハーバード交渉術の書籍の存在を知ることになった。4冊ほど買うつもりである。南部アフリカからはアフリカ開銀のお兄ちゃんからメールがあった。水省が提案したSIPのTORについてのコメントである。彼もまだ若いしTORに関してのコメントは未熟だ。SIPのあるべき姿をあまり知らないらしい。今は傍観しておこう。SIPの成功例はあるのだが、簡単にアフリカ開銀にはあげない。彼らは主導的になることしか興味が無いので、彼らの得だけのためには協力しない。素人だしね。じっくり攻めていこうとしよう。

Is greywater safe for irrigation?

'Greywater' that is recycled from household washing can be used to irrigate home gardens, according to a new study by Jordanian researchers. The researchers found that treatment units supplied by the Jordanian government produced small quantities of recycled water that could be used to irrigate gardens, whilst meeting national standards for irrigation of trees and many home-grown crops.

Water is scarce across much of Europe, especially where summer temperatures are high, and methods for safely recycling water are increasingly in demand. Last year, the European Environment Agency highlighted the problem of water shortage in Europe and recommended that harvested rainwater and greywater from showers and kitchen sinks could be used for flushing toilets and watering gardens1. In some countries, such practices are already commonplace. In Jordan the government provided over 750 low-income households in 2003 with greywater treatment units to help cope with water shortages.

However, the problem with greywater is that without proper treatment it may retain increased levels of elements that are harmful to the soil and the crops or trees that grow in it. One particular concern is sodium, which in higher concentrations can damage soil permeability and structure, ultimately reducing crop yields.

The researchers monitored sodium levels, as well as levels of other potentially damaging elements, to establish whether water produced by the treatment units and used for irrigation was meeting Jordanian standards. The results may be applicable to areas of Europe suffering from water shortage.

They found that the treated water complied with standards for irrigation of fodder crops and tree crops, including olive trees. However, it did not meet standards for vegetables that must be cooked before eating. For these crops, maximum allowable limits for suspended solids and nitrates are lower, and standards for other water quality indicators are more difficult to meet.

Importantly, sodium levels were within the allowable limits, although the researchers did notice that concentrations of sodium and organic matter increased over time. The leaves and fruits of olive trees were tested and were found to have suffered no ill effects from recycled water. Olive trees are known to be able to tolerate slight increases in salt, which the researchers say makes them suitable for greywater irrigation. Occasional leaching (deliberate flushing) with fresh water may be a way to reduce build up of salts and organic matter in soils irrigated with greywater, according to the researchers.

Source: Al-Hamaideh, H. and Bino, M. (2010). Effect of treated grey water reuse in irrigation on soil and plants. Desalination. 256: 115-119.