Combined physical, chemical and biological clogging of managed aquifer recharge and the effect of biofilm on virus transport behavior: A column study

In recent years, treated wastewater has been widely used in managed aquifer recharge sites (MAR) for compensation of groundwater shortage in arid and semi-arid areas. However, the presence of suspended solids, microorganisms and pathogenic agents has led to different problems such as aquifer clogging and groundwater contamination. In this study, the effect of treated wastewater on physical, chemical and biological clogging of sand and limestone-packed columns and subsequently transport behavior of solutes and virus was studied. Transport experiments were performed, using the tracer bromide (Br-) and MS2 bacteriophage, in sand and limestone-packed columns irrigated with treated wastewater at different short and long-term periods (2 and 8 weeks). In addition, some physical, chemical and biological features of columns were measured after irrigation with wastewater. Results revealed that injection of treated wastewater for around 2 weeks not only led to the physical and biological clogging, but also caused a significant increase in MS2 retention in the columns. However, increasing limestone column irrigation to 8 weeks increased solutes and MS2 discharge into the column effluents. This is due to increased saturated hydraulic conductivity caused by the formation of heterogeneities in the columns, as a result of calcium dissolution by microbial activity. From the findings of this research, it can be postulated that long-term application of recycled water in limestone aquifers which causes physical heterogeneities and possible preferential flow paths will endanger groundwater resources with pathogenic contaminations.