WASTEWATER REUSE IN AGRICULTURE IN VIETNAM: WATER MANAGEMENT, ENVIRONMENT, AND HUMAN HEALTH ASPECTS

Theme 3: Agriculture, Water and Cities

The survey of wastewater irrigation practices showed that 93% of the cities sampled use wastewater for agriculture or aquaculture or both. The wastewater irrigated areas in most cities is around 1-2% of the total agricultural land around the cities. Extrapolation of these findings to the national level gives a range of 6000 to 9500 hectares as a national figure for wastewater irrigated agriculture.

From prevalence estimates in 29 provinces it was estimated that 33.9 million people in Vietnam are infected with ascaris (prevalence 44.4%), trichuris (prevalence 23.1%) and 21.8 million with hookworm (prevalence 28.6 %). Vegetable cultivation in which night soil is used as fertilizer is a risk factor for hookworm infection especially among adult women.

In general there is a high level of nutrient inputs in both wastewater and non wastewater sites with these inputs being poorly coordinated without consideration of complementarities between different nutrient sources (manure, fertilizer, soil wastewater).

There is a high level of inefficiency and nutrient waste under current farming practices, with significant scope for improvement. Appropriate field level nutrient management would include reducing nitrogen fertilizer inputs, improving synchrony between crop demand and supply, reducing basal application, improving potassium input and increasing hill density.

Nitrogen excess in the wastewater sites results in high Nitrogen contents in the grain and the protein content is likely considerably higher with positive implications for child nutrition and health.

The study brings out a fundamental scientific and management challenge: to develop integrated nutrient management principles and practices specific for wastewater influenced conditions.

The heavy metal contamination study showed that the levels of Zinc, Lead, Nickel, Chromium, Copper and Cadmium are within the Vietnamese guideline values.

53% of samples of stool examined were positive for one or more of the helminth parasites. One important finding was that the study was not able to substantiate an increased risk of helminth infection from exposure to wastewater in agricultural contexts.

Most persons infected with Ascaris and Trichuris came from lower socio-economic groups and households with inadequate sanitary conditions and poor hygiene practices.

A significant difference in the number of people reporting skin disease was observed between the communes where wastewater use was prevalent as compared with lower levels of wastewater use.

From the risk perception and behaviour study it was clear that risk is associated with “bad smell’’ and excreta is seen as “dirty and smelly’ but it is praised for its nutrient value. The concept of cleanliness was linked to “visible” dirt. The nose and mouth were seen as disease entry points. The concept of “invisible” sources of risk was not understood.