Bjørnar Eikebrokk

Comparison of NOM character in selected Australian and Norwegian drinking waters.

Observations from many countries around the world during the past 10-20 years indicate increasing natural organic matter (NOM) concentration levels in water sources, due to issues such as global warming, changes in soil acidification, increased drought severity and more intensive rain events. In addition to the trend towards increasing NOM concentration, the character of NOM can vary with source and time (season). The great seasonal variability and the trend towards elevated NOM concentration levels impose challenges to the water industry and the water treatment facilities in terms of operational optimisation and proper process control. The aim of this investigation was to compare selected raw and conventionally treated drinking water sources from different hemispheres with regard to NOM character which may lead to better understanding of the impact of source water on water treatment. Results from the analyses of selected Norwegian and Australian water samples showed that Norwegian NOM exhibited greater humic nature, indicating a stronger bias of allochthonous versus autochthonous organic origin. Similarly, Norwegian source waters had higher average molecular weights than Australian waters. Following coagulation treatment, the organic character of the recalcitrant NOM in both countries was similar. Differences in organic character of these source waters after treatment were found to be related to treatment practice rather than origin of the source water. The characterisation techniques employed also enabled identification of the coagulation processes which were not necessarily optimised for dissolved organic carbon (DOC) removal. The reactivity with chlorine as well as trihalomethane formation potential (THMFP) of the treated waters showed differences in behaviour between Norwegian and Australian sources that appeared to be related to residual higher molecular weight organic material. By evaluation of changes in specific molecular weight regions and disinfection parameters before and after treatment, correlations were found that relate treatment strategy to chlorine demand and DBP formation.

Design and performance of the BIOFISH water recirculation system

Water is reused in aquaculture due to reasons such as shortages in water quantity and quality, more stringent effluent quality standards, the need for energy conservation, more intensive production regimes and a better overall economy. Conventional water recirculation systems are not, however, widely used in Norway. This is mainly due to the fact that current salmonid production regimes are not able to fully utilize the potentials of recirculation systems, and also because of the rather poor reputation of such systems due to complexities in both design and operation. These facts led to the initiation of a project at SINTEF in 1984 with the main objective being the identification of simple alternatives to the conventional water recirculation systems applied in fish farming. A simple intank water treatment and reuse system, called BIOFISH, was designed. The primary unit of the system is a submerged and aerated upflow biofilter, with nitrification and oxygen transfer as the primary functions. In addition, the biofilter acts as an air lift pump and thereby creates the necessary water circulation flow in the fish tank. Particles are removed with the effluent through a pipe from the tank bottom. The BIOFISH system has been operated for several months; both with rainbow trout and Atlantic salmon smolt. The results show that water consumption, and thereby the amount of effluent water, can be reduced by 90–95% compared to flow through systems. The oxygen concentration in the fish tank was 5 mg/litre or higher, and total ammonianitrogen concentration never exceeded 1 mg NH4+N/litre, even at fish densities as high as 80 kg/m3.

Triple bottom line assessment of raw water treatment: methodology and application to a case study in the municipality of Oppegård in south-eastern Norway

There could be several options a water treatment plant (WTP) can select from, if an improvement in treated water quality (WQ) is desired. This paper outlines a methodology to test a variety of approaches to accomplish pre-set goals as regards WQ, while adopting a triple bottom line approach. This approach, in a nutshell, takes into consideration economic, environmental and social aspects in decision-making. The methodology has been applied to the Stangasen WTP in the town of Oppegård in south-eastern Norway. Among the seven alternative approaches compared were the use, as coagulant, of five different dosages of granulated aluminium sulphate, liquid aluminium sulphate (48%) and liquid ferric chloride (40%). Using the set of weighting factors obtained from experts, it was determined that increasing the dosage of granulated aluminium sulphate by 20% over the current one would be the most sustainable option from a triple bottom line point of view.

Coagulation and Corrosion Control for Soft and Coloured Drinking Water

Soft, acidic, and coloured (humic substances) surface waters with a low turbidity are commonly used for the drinking water supply in Norway. For these waters, coagulation/direct filtration combined with a process for corrosion control is one of the most interesting water treatment alternatives.

RISK AND VULNERABILITY ASSESSMENT ("ROS-ANALYSIS") OF THE BERGEN WATER SUPPLY SYSTEM - A SOURCE TO TAP APPROACH

The paper provides an overview of the application and results of a risk and vulnerability analysis (in Norwegian: ROS-analyse) of Bergens water supply system covering all elements from source to tap (i.e. catchment, source, treatment plant, and distribution). The analysis gives an overview of the risk-picture for the water supply system. The main conclusion is that the flexible and redundant water system of Bergen, where five independent waterworks feed water into the same system, reduces the consequences from many of the undesired events which might happen. This puts Bergen in a unique situation compared to many other water companies in Norway. However, resulting from the analysis, we have identified new possible risk reducing measures for all elements in the water supply system which will improve the safety of the system to an even higher level. Within the project a new procedure for assessing the strength of the hygienic barriers represented by the water treatment step and the disinfection step has been developed. By using large datasets from the SCADA-system, long time-series of water quality data has been aggregated into easy understandable risk measures represented by duration curves. The risk analysis is organised and carried out within a database system, making it easy to update and improve the analysis at later stages.