Evaluation of pre-treatment method of wastewater at MERAB’s waste treatment facility in Rönneholm

In this study the efficiency of a pre-treatment method planned to treat wastewater produced at a waste treatment facility in Ronneholm (Skane, Southern Sweden) was evaluated. At this waste treatment facility, operated by the publicly owned waste recycling company MERAB, a treatment is needed to lower concentrations of potentially environmentally detrimental contents in the wastewater to an extent which would allow discharge into the environment and/or irrigation of a willow plantation as a tertiary treatment. The planned pre-treatment, consisting of an aeration basin and a sedimentation basin which the wastewater shall pass through subsequently, was simulated in the laboratory. Physicochemical properties as well as concentrations of nitrogen, carbon and metals (Al, Co, Cr, Cu, Mn, Ni, Pb and Zn) of the wastewater were measured before, during and after the treatment to assess the effect of the pre-treatment. Concentrations of nitrogen –mainly ammonium nitrogen- and organic and inorganic carbon appeared to decrease during the pre-treatment, with the larger part of decrease occurring during the aeration step. The decreasing concentration of ammonium nitrogen was mainly explained by the activity of nitrifying bacteria, transforming ammonium into nitrates. The fact that the total nitrogen concentrations decreased, too, suggests other processes and sedimentation going on during treatment. Most likely, the decrease of nitrogen was due to denitrification taking place under the anoxic conditions, as well as nitrogen associated with biomass being removed by sedimentation. The consumption of organic carbon by nitrifying and non-nitrifying bacteria and sedimentation are thought to cause the decrease of organic carbon concentration. All measured metal concentrations decreased during aeration and all but manganese concentration decreased further during sedimentation, which was thought to be due to an increasing pH and a concurring decrease in metal solubility. Despite the decrease in concentrations in ammonia- and nitrate-nitrogen, as well as metals, a decrease in toxicity during and after pre-treatment of the waste water was not indicated by results from acute toxicity tests carried out with luminescent bacteria (Vibrio fischeri). Concentrations of ammonium nitrogen, lead and zinc were still too high in comparison to environmental quality standards. The fact that the oxygen concentration took a long time (ca. 35 hours) to increase during aeration indicates that the nitrification process in this experiment had not yet fully been exploited, and that a longer aeration time could further decrease ammonium nitrogen, lead and zinc concentrations. What is more, other studies on the irrigation of short rotation coppice such as willow plantations with wastewater indicate that the water quality of the treated wastewater in this experiment could act as a fertilizer for willow plants. (Less)