Final report, covering period: May 1, 2016 to January 31, 2019 [MERC - M34-011]

The research included lysimeter studies, field and greenhouse experiments, and laboratory determinations. The application of biosolids to the lysimeter experiment did not affect the concentration of the heavy metals in the soil nor their distribution among the different fractions. The main differences were found between the soils. Higher concentration of Cd was observed in the heavy soil, while most of the Cu and that of Pb was found in the RO and OM fractions. In the field experiment the pH values were significantly different in the soil treated with biosolids and TWW. Electrical conductivity (EC) values were lower in soil plots treated with TWW; similarly, the TDS values exhibited the same trends. Nitrate and sulfate levels were quite low in all treatments, whereas, chloride levels were high in all treatments. TWW alone or combined with biosolids application, enhanced the total plant biomass produced as well as fruit weight and plant height. Soil treated with biosolids exhibited lower wetting irrigation zone compared to soil plots that were treated with biosolids. Using the water drop penetration test in a greenhouse experiment it was found that levels of organic materials representing organic fractions in TWW and biosolids, increased the soil hydrophobicity of FW irrigated soils in the order: HA>Dextran>MIX>VA>FW. The rhizosphere bacterial community diversity, was higher compared to the rhizoplane, for all soil types, irrigation treatments and plants. The rhizosphere in soil treatments irrigated with TWW, exhibited a lower resident-active correlation, compared to the FW irrigated soil samples. This lower correlation was not expected since the TWW irrigation adds organic matter and nutrient to the soil, which presumably cause the bacterial community to become more active. This reduction in resident-active correlation could be a response to stress induced by TWW irrigation leading to enhanced salt concentrations and lack of oxygen due to organic matter decomposition. These effects could have acted on both the plant and its microbial population. The bacterial community composition of plants irrigated with TWW was found to differ from the bacterial population of plants irrigated with FW.