The objective of this project was to develop a novel phosphorus removal system using steel slag filters applicable in decentralized applications and to propose design criteria about maintenance needs. Slag exhaustion functions were measured on 2-3 mm, 3-5 mm, 5-10 mm and 16-23 mm slag. Three steel slag columns with particle size of 2-3 mm, 3-5 mm and 5-10 mm were fed with the effluent of an aerated lagoon during 589 days. A barrel reactor test was fed during 365 days with the effluent of an attached growth aerated biological reactor. The o-PO concentration at the effluent of the 2-3 mm and 3-5 mm columns and barrel reactor test was between 0.04 and 0.3 mg P/L. Particulate phosphorus, however, was removed by about 50%. The P-Hydroslag model implemented in PHREEQC was successfully calibrated with data from the column test, and validated with data from the barrel reactor test. The calibrated model was used to simulate long-term operation of a slag barrel reactor with two parallel streams of five replaceable steel slag barrels, with total hydraulic retention time of voids of 15 h. The system longevity was strongly influenced by the influent alkalinity. The simulated longevity was 7 years with an influent alkalinity of 50 mg CaCO/L and 2 years with an influent of 210 mg CaCO/L. The alkalinity of the steel slag filter influent was influenced by the type of aquifer supplying drinking water, the presence of nitrification activity and by the CO concentration in the enriched air of the upstream biological process. Simulated scenarios with partial barrel replacement (e. g. barrels 1 and 2 out of 5 replaced at frequency of 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or 4 years) increased the system longevity up to 14 years while slightly increasing the number of barrels needed.

The main objective of this project was to develop a steel slag filter effluent neutralization process by acidification with CO-enriched air coming from a bioprocess. Sub-objectives were to evaluate the neutralization capacity of different configurations of neutralization units in lab-scale conditions and to propose a design model of steel slag effluent neutralization. Two lab-scale column neutralization units fed with two different types of influent were operated at hydraulic retention time of 10 h. Tested variables were mode of flow (saturated or percolating), type of media (none, gravel, Bionest and AnoxKaldnes K3), type of air (ambient or CO-enriched) and airflow rate. One neutralization field test (saturated and no media, 2000-5000 ppm CO, sequential feeding, hydraulic retention time of 7.8 h) was conducted for 7 days. Lab-scale and field-scale tests resulted in effluent pH of 7.5-9.5 when the aeration rate was sufficiently high. A model was implemented in the PHREEQC software and was based on the carbonate system, CO transfer and calcite precipitation; and was calibrated on ambient air lab tests. The model was validated with CO-enriched air lab and field tests, providing satisfactory validation results over a wide range of CO concentrations. The flow mode had a major impact on CO transfer and hydraulic efficiency, while the type of media had little influence. The flow mode also had a major impact on the calcite surface concentration in the reactor: it was constant in saturated mode and was increasing in percolating mode. Predictions could be made for different steel slag effluent pH and different operation conditions (hydraulic retention time, CO concentration, media and mode of flow). The pH of the steel slag filter effluent and the CO concentration of the enriched air were factors that influenced most the effluent pH of the neutralization process. An increased concentration in CO in the enriched air reduced calcite precipitation and clogging risks. Stoichiometric calculations showed that a typical domestic septic tank effluent with 300 mg/L of biodegradable COD provides enough biological CO for neutralization of a steel slag effluent with pH of 10.5-11.5. A saturated neutralization reactor with no media operated at hydraulic retention time of 10 h and a concentration of 2000 ppm in CO enriched air is recommended for full-scale applications.

A pilot study was performed to evaluate the potential of an inert self-supported immersed fixed film media to upgrade aerated lagoons. Simultaneous organic matter removal and nitrification was assessed under different loading rates and temperatures (near 0 °C) using 12 laboratory-scale reactors operated in parallel. Test results showed that both the temperature and the load have an influence on organic matter effluent concentrations. Effluent quality seemed related to the observed biofilm thickness. Thicker biofilm is believed to have contributed to biomass detachment and increased particulate organic matter concentrations in the effluent. Simultaneous organic removal and nitrification was obtained at loads above 5 g CBOD/m·d. The highest nitrification rate at 0.4 °C was obtained for the smallest load, which showed a nitrification limitation close to freezing point.

An experimental study dedicated to the characterization of the settleability of solids produced in immersed fixed media biofilm reactors has been carried out. The influence of operating temperature (0.1 to 16 °C) and surface organic loading rate (OLR) (0.4 to 10 g of soluble carbonaceous BOD per m of media per day) on settleable solids quantities, particle size distributions (PSD) as well as flocs morphology was evaluated. Results have shown that the OLR has no statistically significant influence on the settleability of the suspended solids. However, the operating temperature was identified as a factor that significantly influences the settling potential. The highest operating temperatures (14-16 °C) were related to the worst settling performances. On the other hand, the best settling performances were observed at intermediate operating temperatures (around 10 °C). The latter conditions were also associated with the largest fractions of large particles (>100 μm) in the effluent. Differences in PSD were found to be well correlated with settling performances. Part of the performance results variability which cannot be explained by differences in PSD can potentially be attributed to differences in flocs morphology (compactness).