Issues concerning soils treated with wastewater: Pedotechnical management with zeolitized tuffs as an option for turning N and P pollutants into potential fertilizers

We studied the effects of amendment with zeolitized tuffs (ZT) in recovering nitrogen and phosphorus as potential plant nutrients in soils treated with wastewater (WW). The surface horizon of two contrasting soils (a sandy, alkaline Entisol, and a sandy-loam, sub-acidic Alfisol), was pedotechnically managed with different ratios of Neapolitan Yellow Tuff (NYT) and a clinoptilolite bearing tuff (ZCL). It was then exposed to repeated treatments with 'dirty' municipal wastewater (DMW). Results showed that the presence of ZTs had several favorable effects. As concerns the aspect connected with the investigation into the supernatant/soil solution, total N and total P decreased sharply in the supernatant as ZT content in soil/zeolite samples increased. Large quantities of nitrate were removed from the solution, most probably via bio-chemical reaction. Investigation of the soil/zeolite samples after twelve consecutive treatment cycles showed that the concentration of the essential plant macronutrients N and P increased as ZT content increased. Overall, the ZTs added directly to the poorly-resilient soils appeared to be a useful amendment in reducing the pollutants load caused by irrigation with untreated wastewater. It also played a positive role in pedotechnique strategies, improving both the natural intrinsic soil resilience and soil functionality.