| dc.description.abstract | As the world’s population has increased, the importance of water sources and wastewater recycling has reached a critical level due to expanding consumption. Concurrently, some available soil is being degraded due to the application of low-quality/polluted water. This has led to water shortages and decreases in usable agricultural lands.
This study investigated the effects of wastewater irrigation on soil, tomato plants, and heavy metal accumulation. The research was carried out from March to June 2021 at Texas A&M University where a hybrid tomato (Solanum lycopersicum, "Better Boy") was grown under greenhouse conditions and irrigated with different wastewater types. These included groundwater (i.e., treated tap water used for control), raw sewage wastewater, and membrane-bioreactor treated wastewater. Different formulations of experimental irrigation waters were prepared by mixing treated and untreated wastewaters at proportions of 25%, 50%, 75%, and 100%. A total of six types of irrigation waters were applied to tomato plants grown in pots. In the greenhouse pots were arranged in a completely randomized fashion with 3 replicates of the 6 irrigation water types. A total of 18 plants were grown to harvest. The effects of irrigation water on soil quality and plant growth were examined. The accumulation and distribution of heavy metals in the soil and plant tissues were also examined.
Total irrigation amounts applied to treatments were 87.25 L. Approximately one-third of the total applied irrigation water was not transpired by the plant. Comparing initial soil conditions to post-experiment conditions, increases in pH, electrical conductivity, nitrogen, phosphorus, and organic matter were observed while decreases were seen in calcium, magnesium, potassium, and sodium. Considering tomato yields, the smallest yields were seen in T₀ (GW), while the highest yields were found in T₁ (MBR) and T₃ (%50 MBR + %50 RWW).
According to the allowable heavy metal limits stipulated by FAO and EPA, 14 elements measured in the applied wastewaters were below acceptable limits. Pre- and post-experiment soil heavy metal concentrations showed decreases in aluminum, beryllium, iron (except T₁), manganese, nickel, and selenium (except T₀). Increases were observed in arsenic, cobalt, chromium, copper, lead, vanadium, and zinc. In plant tissues, the most accumulated heavy metal was aluminum, while the lowest was beryllium. Small amounts of chromium were present, but none was detected in the fruit. Cadmium and selenium were not detected at all. Compared to all other parts of the plant, the fruit showed the smallest heavy metal concentrations, and all were below acceptable levels.
In conclusion, using wastewater for agricultural irrigation of tomatoes may offer a viable alternative to limited freshwater sources because it boosts plant growth and yield through increased fertility (i.e., nitrogen and phosphorus) and the fruit has heavy metal accumulation below acceptable levels for consumption. | |
