Torsten Hedberg

Iron corrosion in drinking water distribution systems—The effect of pH, calcium and hydrogen carbonate

The corrosion of iron in synthetic drinking water has been studied through potentiodynamic sweeps and coupon tests. Corrosion rate follows a reversed proportional dependence on the logarithm of the free carbon dioxide content (the sum of protonated carbonic acid and dissolved carbon dioxide). In water with low total carbonate concentrations the addition of calcium ions decreases the corrosion rate. In waters with moderate and high total carbonate content no dependence on the calcium concentration is observed.

Copper corrosion in drinking water distribution systems — the influence of water quality

The copper corrosion in drinking water was studied using potentiodynamic sweeps, coupon tests and field measurements in different Swedish municipalities. The results were compared with equilibrium calculations. It was shown that for the first hours of water stagnation the system is not at equilibrium and the copper content is determined by the corrosion process. In the absence of calcium the corrosion rate increases linearly with the logarithm of the free carbon dioxide content (the sum of protonated carbonic acid and dissolved carbon dioxide). In the presence of calcium both the corrosion rate and the copper concentration in the water increases with the ratio between the free carbon dioxide and the calcium content. Presence of chloride ions in normal drinking water concentrations decreases the corrosion rate.

Removal of Geosmin and MIB by Biofiltration - an Investigation Discriminating Between Adsorption and Biodegradation

Geosmin and 2-methylisoborneol (MIB) are two substances causing earthy/musty odours that are difficult to remove by conventional chemical drinking water treatment. In this study removal of geosmin and MIB by biofiltration of untreated surface water was investigated using granular activated carbon (GAC) and crushed expanded clay (EC) as filter media. Biofiltration through both GAC and EC removed geosmin and MIB present at low (20 ng l−1) concentrations by at least 97 % at an empty bed contact time of 30 minutes and a temperature of 15°C. At lower temperature (6-12°C) and simultaneously lower biomass concentrations, removal efficiency was similar in the GAC but considerably lower in the EC biofilter, pointing to a second mechanism different from biodegradation. Consequently, microbial activity was suppressed with azide to enable discrimination between biodegradation and adsorption. During azide dosage, the GAC biofilters still removed geosmin and MIB nearly unaffectedly. In the EC biofilter, however, removal of both odorants ceased completely. Methylene blue adsorption confirmed that the GAC, even after almost four years of operation receiving surface water, had capacity to remove geosmin and MIB by adsorption. Since odour episodes commonly occur during the warm season when microbiological activity is high, EC constitutes a viable option as carrier medium for direct biological filtration of surface water. The additional GAC adsorption capacity however adds robustness to the removal process.

Copper corrosion in water distribution systems—the influence of natural organic matter (nom) on the solubility of copper corrosion products

The copper corrosion in drinking water distribution systems was investigated by means of field measurements in different Swedish municipalities. The maximum copper content in the water is not reach until after several hours of stagnation. The results are compared with equilibrium calculations. Good correlation between measurements and calculations is achieved if the maximum copper concentration is assumed to be determined by the equilibrium with the meta stable solid cupric hydroxide. However, the correlation is greatly improved when the complexing action of natural organic matter (NOM) is considered in the calculations. The results suggest that NOM is an important factor for the copper concentration in drinking water distribution systems.

Performance of direct biofiltration of surface water for reduction of biodegradable organic matter and biofilm formation potential.

Direct biofiltration of surface water may be considered as pre-treatment for membrane filtration, in order to reduce fouling. The biofiltration process was investigated with regard to biodegradable organic matter and biofilm formation, covering the annual variations under moderately cold climate conditions. Granular activated carbon (GAC) and two types of crushed expanded clay (EC) were compared as filter media. To assess the biological properties of the biofilters, viable biomass and respiratory activity was examined. Biofiltration removed assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) by about 30% and also reduced the bacterial concentration in the water phase. Also, biofilm formation in the treated water was reduced by 80-90% during summer and winter conditions. The reductions in the investigated parameters were similar in the biofilters with GAC and EC. Likewise, a similar amount and development of biomass was found in the GAC and EC biofilters of comparable grain size with a pronounced stratification from top to bottom of the filter bed. The specific respiratory activity of the biofilter biomass was dependent on raw water temperature. Even though slight correlations between BDOC removal and temperature or respiratory activity were observed, AOC and BDOC removals were mainly dependent on the feed water concentrations of these compounds. The results indicate that direct biofiltration of surface water, by reducing AOC, BDOC and biofilm formation in the water, may be an advantageous pre-treatment for membrane filtration processes.

Attitudes to traditional and alternative sustainable sanitary systems

The sanitary system is the most important supply system in a society. A central problem today is the provision of a future urban system which meets the requirements clearly borne out in environmental documents and action plans at local and global levels. The conventional water and wastewater systems have been questioned whether they can be considered as sustainable or not. Other small, decentralized systems have been implemented and a short description of different systems is shown. The attitudes, at different administrative levels in the society, to traditional and alternative sanitary systems are discussed. The general conclusion is that there is a strong driving force and an interest in changing the systems. However, the evaluation of the systems implemented so far shows that it is important to have time for careful and thorough investigations of new but also of existing systems in the light of the criteria for sustainability.

Removal of individual off-flavour compounds in water during artificial groundwater recharge and during treatment by alum coagulation/sand filtration

Abstract The removal of individual off-flavour compounds during artificial groundwater recharge has been compared to the removal of such compounds during conventional alum coagulation/sand filtration. By using an evaluation technique based on gas chromatography with both instrumental and sensory detection (“column sniffing”) it was shown that alum coagulation/sand filtration had no significant effect on any of the off-flavour compounds that could be detected in the raw water samples (geosmin, 2-methylisoborneol, 2-isopropyl-3-methoxypyrazine, 2,4,6-trichloroanisole, 1-octen-3-one, 1-nonen-3-one, dimethyl trisulphide and a number of unidentified muddy or musty odours). During artificial groundwater recharge in sand and gravel ridges, however, the concentrations of all these compounds were substantially reduced, thus proving that artificial groundwater recharge is not only a suitable method for water storage but can also be an effective method for removing muddy and musty odours. The successful use of the column-sniffing technique for evaluating water treatment methods has shown the potential of this technique in resolving some of the present disagreements concerning the effectiveness of different treatment methods for removing tastes and odours from water.

Dissolved Air Flotation: Pretreatment and Comparisons to Sedimentation

Coagulants, flocculation time and mixing intensity were examined in laboratory studies using a synthetic fulvic acid water and three Swedish water supplies. Alum and polyaluminium chlorides (PACs) of various chemistries were effective when used under favorable pretreatment conditions. Alum and PACs had approximately the same optimum dosages for the fulvic acid water when expressed as mg Al added per mg TOC. An exception was the Ca PAC had a lower optimum dose at higher pH. The PACs were effective at flocculation times as low as 5 min while 10 min was needed with alum, especially in cold waters. Dissolved air flotation (DAF) performance improved slightly with increasing flocculation mixing intensity. DAF performed better than settling for aquatic humic or algae type supplies especially with lower flocculation times, and performed better for a river water with turbidity under cold water conditions. Excellent DAF treatment was achieved with Ca, Si, and sulfate PACs.

High Rate Flocculation, Flotation and Filtration in Potable Water Treatment

A study of the optimisation of the process chain of flocculation — flotation — filtration was performed at Lackareback treatment plant in Gothenburg. The Gota River water is a high quality supply of low turbidity and moderate TOC. In winter time the water is generally cold.

Biological Pre-Treatment for Improved Removal of Manganese in Chemical Drinking Water Treatment

Biological pre-treatment was found to enhance the removal of manganese from colored surface waters at two Swedish waterworks, where conventional chemical treatment at times was insufficient. The pilot plant studies also indicated the potential of the bioreactors for removal of odor.