Reclaimed Water Project: Effects of High Na Concentration in Soil and Plant Tissues

Abstract

Clark Water Corporation (CWC) intends to reclaim its treated wastewater (WW) for turf grass irrigation in golf courses and other urban landscapes. CWC’s treated effluent meets the DA (DAO 26) irrigation standard except for sodium which exceed by an average of 17%; creating the need to study the effects of high Na concentration of WW in soils and plant tissues. Soil samples were compiled from 3 sites; 2 from target irrigation sites, P.Balagtas and Korea CC and 1 from the final pond of the Wastewater Treatment Plant’s (WWTP) to replicate long-time irrigated soils. Soils were transferred to experimental plots, planted with foliage and irrigated for 5 months with equal amounts of WW. Results indicate that soils from the target sites are fine grained sandy soils and that WW irrigation have improved their structure and porosity. Calcium and magnesium levels spiked with calcium increasing 60 folds while magnesium levels surging by more than 1000 folds. Soil sodium levels increased by an average of 70% while organic content dropped by an average of 119%. Variances between the former and latter parameters were more prominent with the Korea CC soils. Planted foliage have exhibited tolerance from the high sodium content of irrigation water. Foliage taken from the Korea CC plots generally performed better in the uptake of nutrients as compared to those harvested from P. Balagtas. Disturbingly, all harvested foliage exhibited uptake of arsenic which can be attributed to soil background contamination. Although it cannot be inferred in the experiment, potential problems associated with long-term nutrient build up may arise. Ideally, these effects can be countered by the amount of rainfall and its associated leeching. This anticipation is backed-up by the lack of sodium accumulation from 3rd soil sample taken in proximity of the WWTP final pond.