Use of wastewater in agriculture

Population growth and rapid urbanization are intensifying pressure on fresh water resources. The lack of quality water and a high level of local water demand is leading to increasing water scarcity and stress and is consequently driving the use of non-conventional waters, such us treated or raw wastewater.

Wastewater use for irrigated agriculture is especially important in urban and periurban areas. Cities are in fact a precious source of water and nutrients for agriculture that have to be properly managed to minimize environmental and health risks. To maximize benefits and minimize risks related to the use of wastewater in irrigation a robust policy and institutional framework needs to be in place. In many countries where wastewater use in agriculture takes place these frameworks are lacking. Responsibilities and jurisdictions among public institutions (health, agriculture, water) have to be clear and coordination mechanisms should be created to come up with comprehensive and effective policies.

Cost effective and appropriate wastewater treatment suited for the end use of wastewater is a fundamental action. But in many developing countries wastewater treatment is not economically feasible in the short term and interim solutions may be needed to protect farmers and public health In these countries the focus should be on prioritizing affordable and easily adoptable risk management strategies. Adopting the multiple-barrier approach (WHO-FAO-UNEP, 2006) can reduce human and crop exposure to toxic compounds and pathogens.

Farmers need to be provided with the specific guidelines to support their productions and to access markets, and proper dissemination and education campaigns need to be designed to facilitate the adoption of such guidelines by farmers. Additionally, policy makers and consumers need to understand the opportunities of water reuse and resource recovery from waste.

Use of saline water in agriculture

Salinized and sodic drainage water and groundwater are often used for irrigation purposes posing agriculture and environmental risks due to soil salinization and water quality degradation downstream.
Even when no overall and complete global quantifications exist, the use of saline or sodic waters is a common practice in many countries such as Bangladesh, China, Egypt, India, Iran, Pakistan, Syria, Spain and the United States, especially to irrigate salt-tolerant plants and trees, but also conventional grains and forage.

When managing salinity it is important to keep in mind that many lands and irrigation areas have varying levels of tolerance to increases in salinity. Therefore salinity must be considered in the context of the particular asset at risk and the value of that asset. To determine the intensity of the measures to apply and the methods to follow salinity risk assessment should be carried out. In areas identified as having a high level of hazard a good salinity monitoring program has to be developed. In addition, actions aiming to prevent further salinization of land and water or to remediate saline or sodic soils have to be implemented. This actions include more efficient irrigated agriculture, effective drainage measures,crop selection or treatment of saline drainage before reuse.
Desalination of salty groundwater and brackish drainage water have risen as one of the options available to cope with the problem of water salinization, in addition it is used for augmenting freshwater resources when seawater is desalinated. Even when there are very interesting prospects with this technology the main constrain for its massive use in agriculture has been so far the high energy consumption rates and associated costs.

Use of arsenic laden waters

Arsenic contamination in groundwater has been reported in more than 20 countries around the world and, in many, shallow groundwater is used for both drinking and irrigation purposes. Natural arsenic in groundwater at concentrations above the drinking water standard of 10 µg/liter is not uncommon, and the realization that water resources can contain insidious toxic concentrations of naturally-occurring chemical constituents, such as arsenic, is fairly recent and increasingly urgent.

First estimates of arsenic toxicity (arsenosis) from drinking water, causing skin lesions and various types of cancers, indicate about 130 million people are impacted. Man-made sources of arsenic, such as mineral extraction and processing wastes, poultry and swine feed additives, pesticides and highly soluble arsenic trioxide stockpiles are also not uncommon and have further caused the contamination of soils and groundwaters. Arsenic accumulation in the food chain (eg arsenic transfer in rice in Asia) is a major concern that has to be tackled globally, and most importantly, the scale of the problem needs to be better quantified.
Finally, it is worth mentioning that management options to prevent and mitigate As-contamination of agricultural land are starting to be developed and successfully tested. For example strategies for management of arsenic that would enable continuing rice production in polluted areas include: (i) growing rice in an aerobic environment where As is adsorbed on oxidized Fe surfaces and is largely unavailable to rice, (ii) switching from As-contaminated shallow groundwater to non-contaminated surface or deep groundwater to avoid further build up of soil As or (iii) identification or development of arsenic tolerant rice varieties, where arsenic uptake is also low.