The Role of Soil Aquifer Treatment (SAT) for Effective Removal of Organic Matter, Trace Organic Compounds and Microorganisms from Secondary Effluents Pre-Treated by Ozone

ABSTRACT

Soil aquifer treatment (SAT) is an effective natural and economically feasible tertiary treatment for wastewater reuse. An innovative hybrid process based on biofiltration, ozonation and short SAT (sSAT, with ~22 days retention time) was demonstrated in a 6 m³/hr pilot system to remove emerging trace organic compounds (TrOCs), organic matter and control Mn²⁺ dissolution in reclaimed water. The biofiltration stage was proposed for nitrification of ammonia as well as removal of dissolved and particulate organic matter (DOM and POM), to enable efficient ozonation of secondary effluents. The pilot system was operated in two modes, where samples were periodically taken from all pilot stages to observe changes in product water quality. At first (Mode 1), biofiltered effluents were infiltrated through sSAT (i.e., no ozonation prior infiltration). During this operation, ammonia, nitrite and phosphate were completely removed, and pathogens were highly reduced. In addition, all measured TrOCs were effectively removed after sSAT, besides the persistent TrOCs Carbamazepine (CBZ) and Iodine-organic contrast media Iopamidol (IPDL). In Mode 2, biofiltered and ozonated (1.0–1.2 mg ozone/mg DOC) effluents were infiltrated through sSAT. In the final reclaimed product, values of DOC, UVA and Mn²⁺ were reduced to 0.8 mg/L, 2.2 L/m, and 29–35 µg/L, respectively. Furthermore, ammonia and nitrite were not detected in the product, and good bacterial quality was obtained. Following 56–75 days of operation at Mode 2, all TrOCs were reduced down to <100 ng/L. The delay in the effect of the pretreatment stages on TrOCs removal by sSAT (>56 days instead of ~22 days) could be explained by their displacement retardation in the upper soil layers of the pilot SAT (0–25 cm). In-depth sampling in the observation well after 111 days at Mode 2 showed homogeneity along the overall perforated section of the well (from −14 to −26 m) with 0.7–0.9 mg/L DOC, 2.1–2.2 1/m UVA and <10 ng/L CBZ. This result proved that the ozonated water completely covered the area around the observation well and positively affected the quality of the reclaimed water.

KEYWORDS:

• Biodegradation
• Biofiltration
• Ozonation
• Reclaimed Water
• Soil Aquifer Treatment
• Trace Organic Compounds
• Vadose

Acknowledgments

We greatly thank the field technicians Vadim Drovitsky and Meir Avraham, and the Process engineers Omer Minis and Tomer Kreitzer from the Shafdan WWTP for their precious help. We would like to thank also Dr. Ido Negev, Dr. Diego Berger, and Dr. Yossi Guttman from Mekorot Hydrology Department; Mario Kummel and Dr. Shai Ezra from Mekorot Water Quality Department for the fruitful discussions and consultancy. Special thanks to Dr. Yossi Manor, Head of the environmental viruses unit in the Central Virology Laboratory, Tel-HaShomer, Ministry of Health, Israel, for his assistant with virus analyses. We thank Dr. Vered Cohen-Yaniv and Aviv Kaplan from the TAU laboratory, Albina Nirnberg and Mekorot Shafdan laboratory team, Liliya Simkhovich and Mekorot Central laboratory team for their analytical support, and Xylem Water Solutions Germany for their cooperation and help.

Funding

This research was supported by the EU FP 7 DEMOWARE project No. 619040.