Pre-Treatment and Post-Treatment of the MP UV/H2O2 Process at Water Treatment Plant Andijk

Requirements of a treatment process for drinking water production from challenged surface water sources shifted over the past decades. The role UV can play in an integrated treatment approach is illustrated by a case study discussing the various research results leading to treatment upgrades at Andijk. The paper describes the feasibility of advanced oxidation based on MP UV/ H2O2 treatment for organic contaminant control and a robust primary disinfection. The impact of conventional surface water treatment based on coagulation, sedimentation, filtration and advanced surface water pre-treatment, based on ion exchange and ceramic microfiltration, on the efficiency and by-product formation is presented. Finally, the role of post-treatment by biologically activated carbon filtration on by-product and toxicity control is evaluated. INTRODUCTION Water treatment plant (wtp) Andijk (The Netherlands) was constructed in 1968 as a conventional surface water treatment plant based on breakpoint chlorination and coagulation sedimentation and filtration (CSF), servicing water from the IJssel Lake as raw water source. Before 1978, the treatment process was upgraded by implementation of granular activated carbon (GAC) filtration (Figure 1). Customer complaints regarding taste and odor were the main cause for this modification. In addition, to further improve the taste and odor of the produced water, postchlorination was replaced with chlorine dioxide dosage. The next retrofit of wtp Andijk was necessary in view of upcoming regulations regarding THMs (Kamp et al, 1997). Furthermore, additional disinfection capacity for protozoa was required. Finally, PWN pursued implementation of a non-selective barrier against organic contaminants because of a shift from non-polar to more polar compounds and from just pesticides to a wide variety of micro-pollutants. Concentrations of organic micro-pollutants such as pesticides, endocrine disruptors and pharmaceuticals as high as 1.0 mg/L have been observed in the raw water source. Storage in reservoirs lowered the maximum concentrations to 0.5 mg/L. Treatment should be capable of lowering this concentration by 80 percent to satisfy the EC standard for pesticides of 0.1 mg/L. As a non-selective barrier, advanced oxidation was pursued. Initially O3/H2O2 treatment was considered (Kruithof et al, 1995). O3/H2O2 treatment (O3/DOC 1.1 g/g, H2O2/O3 2 g/g) proved to be a very robust barrier against organic micro-pollutants. With bromide levels of 300 500 mg/L, IJssel Lake water can be regarded as bromide rich. This high bromide content may cause bromate formation by ozone-based processes (Gunten, von, Hoigné, 1994). In CSF pre-treated IJssel Lake water the bromate formation proved to be very high, especially at low water Figure 1: Treatment process scheme wtp Andijk after implementation of granular activated carbon (GAC) filtration as post-treatment in 1978