Modern Artificial Recharge Plants : Combining chemical flocculation with aquifer recharge

Sammanfattning: Water supply security is increasingly becoming a challenge worldwide. Surface waters, which are often used for drinking water production, have experienced an increase in natural organic matter (NOM) and frequency of algae blooms. Water quantity is also an issue due to increasing populations and potable water demand. As a result, unsustainable extraction of surface and groundwater has led to low water levels and low groundwater tables. Coupled with the uncertainties of climate change, these problems have presented a major challenge for water utilities to secure water supply today and in the future.Managed aquifer recharge (MAR) has the potential to mitigate water shortage, protect water supplies from contamination and remove NOM from surface waters. However, with increasing water demand and NOM content in waters, especially in boreal regions, additional treatment might be necessary. A common way of removing NOM and purifying surface waters is through coagulation and flocculation. This technique is often used in combination with gravity-assisted sedimentation or mechanical filtration, i.e. membrane filtration. Due to the deterioration of surface waters, water utilities have utilized different methods of chemical flocculation prior to artificial recharge. This thesis investigates ways of treating surface water through chemical flocculation combined with disc filters (micro sieves), contact filters and ultrafiltration (UF) membranes. This was achieved through laboratory scale jar tests, pilot-scale and full-scale investigations. Contact filtration, direct precipitation on UF membranes, conventional precipitation with UF membranes and conventional precipitation were the most viable options and could treat surface water to about the same extent (about 70-80 % UVA254nm and 50-60 % TOC removal). As a result, depending on the requirements, such as production capacity, economic and microbial barriers, different options are available for water utilities.Water quality changes during basin infiltration were also investigated. Basin management had a large impact on the bacterial community in the infiltrated water and significant NOM and bacterial community change (2-log removal) occurred after only 50 cm of infiltration. UVA254nm and TOC were removed to a similar extent (about 36 % UVA254nm and 37 % TOC removal), and protein-like components were reduced to a larger extent (33-35 %) than humic-like components (21 %). Depending on the NOM content and composition in the source water, water rich in humic acid would require pre-treatment prior to infiltration.An important part of secure water supply is sustainable source water extraction. The results from these studies could be used by water treatment plants (WTPs) in their investigations to improve MAR.