Jörgen Hanaeus

A Swedish overview of selecting hazardous substances as pollution indicators in wastewater

The objective was to outline a process for selecting hazardous substances as pollution indicators that imply a chemical risk for the recycling of wastewater residues on arable land and for wastewater discharge into receiving waters. The reviewed methodologies showed one commonality: grouping of various characteristics that symbolise hazardous properties. From each group, one or several indicator substances were selected to represent the hazardous property of that specific group. The selected set of indicator substances represented the chemical risk characteristics as a whole. One conclusion is that it is difficult to create a comprehensive list of indicator substances for the monitoring of chemical risks in wastewater and residues. Due to the insufficiency of knowledge about the chemical risks from complex systems such as a wastewater system and the methodology for selecting indicator substances, many simplifications have to be accepted. The 100,000 substances present in the technosphere, of which 30,000 are regarded as “everyday” chemicals, may end up in wastewater systems. We have a limited knowledge of many of these substances, thereby providing a weak base for assessing the true chemical risks in wastewater and residues for reuse on arable land. Although the pollution situation will not entirely be understood by measuring the status of only a few substances (important substances may be overlooked), detected substances indicate a specific pollution situation in wastewater or sludge, thus increasing our knowledge about the current concentrations.

Performance of an experimental wastewater treatment high-rate algal pond in subarctic climate.

A pilot-scale experimental high-rate algal pond (HRAP) was investigated in the subarctic mid-Sweden region, at latitude 63 degrees N. During autumn 2002, conditions included temperatures below 10 degrees C and photosynthetic active radiation below 200 microE/m2 x s. Biochemical oxygen demand was reduced by approximately 90% (approximately 40 g/m3), chemical oxygen demand by 65% (approximately 80 g/m3), total phosphorus by 20% (approximately 1 g/m3), and total nitrogen by 46% (approximately 15 g/m3), at a retention time of approximately 2.5 days. During autumn 2003, the performance of the HRAP appeared better with a more dense microalgae culture; however, as a result of poor settling of the microalgae, the reduction was considerably lower. A major difference between the years was the microalgae composition. In 2002, the large green algae Coelastrum dominated with Chlamydomonas, Scenedesmus, Lagerheimia, and the Cryptophyte Rhodomonas. In 2003, there was a total dominance of the very small green algae Chlorella, known to be difficult to settle. In batch growth experiments during spring 2002, doubling times of 4 to 6 days were achieved. The period of temperatures above 10 degrees C and an insolation of more than approximately 270 uE/m2 x s (125 Langleys), which is well-documented as appropriate for HRAP function (Oswald, 1988a, 1988c), were measured to last for 4 to 4.5 months from early May to late September. However, the growth and treatment performance experiments indicated that a longer season may be possible-6.5 to 7 months, at best-from early April to late October.

Seasonal operation of ponds for chemical precipitation of wastewater.

Wastewater precipitation ponds (fellingsdams) are conventional stabilization ponds adapted to cold climate by the use of chemical precipitation to attain sufficient removal efficiency of impurities, primarily phosphorus. The objective with this investigation was to study the influence of an interruption of the dosage of coagulant during summer periods at two fellingsdam systems (Orrviken and Lockne) in the middle of Sweden. The investigation took place over two years characterized by unusual precipitation conditions; 2001 was intense in precipitation whereas summer 2002 represented a dry season. The results showed that there is a potential to utilize the summer biological activity in fellingsdams. At Orrviken the effluent quality measured as organic matter and phosphorus in the effluent was just slightly above the values that were reached by chemical precipitation. At Lockne the performance was lower. The organic matter reduction at Orrviken in the summers of 2001 and 2002 were 71 and 67%, respectively, c...