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Wastewater- from garbage to greens

In response to industrial wastewater effluents into ecosystems, a consortium of researchers has examined the diverse ways in which wastewater can be treated so as to be reused for irrigation. As a result, the researchers established optimum treatment methods, and also pinpointed the beneficial effects the treated wastewater has had on crops.
Wastewater- from garbage to greens
Firstly, the consortium analysed the different treatment methods and identified the effectiveness of each. Sand filtration was studied as part of tertiary wastewater treatment and removal of heavy metals. It was found that tertiary treatment via sand filtration is more efficient if the sand layer is thicker, and if a low flow (6 l/h) rather than a high flow (9 l/h) is used. Also, the diameter of the sand particles should be smaller than 2000 μm in order to optimise the filtration process. Furthermore, when wastewater is stored in basins so as to be naturally decontaminated, treatment time is shorter if the water is shallow. In fact, in temperatures of 23 to 28 degrees Celsius, it is possible to reduce faecal coliforms by 3 U.log in 3 days if the depth is less than 1.5m, while in a depth of 4m, reduction time is from 7 to 10 days. Then, storage for a period of 2 to 5 months results in the complete eradication of faecal contaminants. On the other hand, if wastewater is stored for more than 2 weeks, the water adopts a stable bacteriological quality similar to that of groundwater.

Interestingly, it was found that algae are extremely effective in fixing heavy metals, and it is this characteristic that could lead to the biological elimination of slight trace mineral components and heavy metals from the wastewater.

Finally, the use of wastewater for irrigation proved to be quite effective. If the climate is temperate, the crops from fields irrigated with wastewaters are more regular than others. It is essential to note that when a controlled irrigation process is used, nitrogen migration and leaching are not affected by wastewater use. Also, the soil is not enriched in nitrogen while the irrigation stimulates plant uptake. Similarly, there are many advantages in using treated wastewater for irrigation in dry climates. The wastewater was used for crops such as citrus trees, eggplants, hot peppers, melons, carrots, cucumbers, and flowers. The consortium concluded that citrus fruits, cucumbers, and hot peppers benefit from the use of treated wastewater instead of clear water whereas melons and flowers met standard criteria. The use of wastewater for these crops leads to the preservation of the environment, as the entrance of wastewater in streams is limited, while crop quality is not harmed.

The use of treated wastewater for the irrigation of greenhouse, forest, and fodder crops is also very advantageous, showing that forests grew and developed faster. In fact, treated wastewater irrigation could lead to reforestation and biomass advances.

Irrigation with treated wastewater has many economic and marketing benefits. Less fertiliser is used, while qualitative and quantitative crop characteristics are better than those resulting from crops irrigated by clear water along with fertilisers. The only drawback to using treated wastewater for irrigation is that it harms crops that are extremely sensitive to hydric stress and salinity. Yet, the use of wastewater for irrigation may prove to be both environmentally and economically beneficial.

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