How treated wastewater used for irrigation, and sewage sludge used as soil amendment affect CO2 emission from soils

Sewage sludge from wastewater treatment plants or farm biosolids can be used as a source of organic matter to improve soil quality. Treated wastewater is due to a water scarcity also used for irrigation. These sources contain a large amount of nutrients, which can enhance conditions for plants’ growth, but also can increase a CO₂ emission from soils. Despite that these soil amendments can have a significant impact on the CO₂ emission from soils, their actual effect on measured values has not been fully revealed. Therefore, the goal of this study was to evaluate the effect of products from the municipal wastewater treatment plant on the CO₂ efflux from soils.  Experiment was carried out directly in the wastewater treatment plant, where nine raised beds were installed, which contained soils taken from topsoil of two soil types Arenosol (two beds) and Cambisol (seven beds). Either maize or a mixture of different vegetables (lettuce, carrot and onion) was grown in these beds. Of the seven beds with the Cambisol, one of the beds containing either maize or vegetables was irrigated with tap water and other pair of beds (maize or vegetables) was irrigated with treated wastewater (i.e., WWTP effluent). In another pair of beds (maize or vegetables), composted sludge from WWTP Three beds containing both types of biosolids were irrigated with tap water. Only vegetables were grown in the beds with the Arenosol, which were irrigated with either tap water or treated wastewater. Climatic data, irrigation doses, drainage water volumes, soil water contents and plant growth were monitored during the experiment. The soil CO₂ efflux was measured in a steel collar (diameter of 11 cm and height of 7.5 cm), which was placed into the surface of each bed one hour prior to the measurement. The net CO₂ efflux (NCER) and the net H₂O efflux were measured using the LCi-SD portable photosynthesis system with a Soil Respiration Chamber. While stabilized and composted sewage sludge considerably increased the CO₂ emission, the effect of treated wastewater or plant was not confirmed.

 

Acknowledgement: Study was supported by the Ministry of Agriculture of the Czech Republic, project "The fate of selected micropollutants, which occur in treated water and sludge from wastewater treatment plants, in soil" (No. QK21020080) and partly also by the European Structural and Investment Funds, projects NutRisk (No. CZ.02.1.01/0.0/0.0/16_019/0000845).