Evaluating the effect of seasonal temperature changes on the efficiency of a rhizofiltration system in nitrogen removal from urban runoff.

The study presents an evaluation of nitrogen removal efficiency of a pilot-scale rhizofiltration system in Pretoria, South Africa. The rhizofiltration system was divided into two sections, one side planted with common reeds (Phragmites australis) and the other side was without plants kept as a control. The objective of the study was to evaluate the influence of seasonal temperature on the removal of nitrogen species from the simulated urban runoff using the rhizofiltration system. The final effluent from the filter was collected bimonthly at different sampling points for 10 months after an application time of 5 min and 25 min. Duplicate samples were taken to determine the concentrations of TKN (Total Kjeldahl nitrogen), ammonium, nitrate and chemical oxygen demand (COD) for the raw influent and final effluent from the rhizofiltration system. Temperature and pH were determined on-site. During the monitoring period, there was no significant difference in the inflow concentration of ammonium in colder and warmer months for both planted and control sides. Furthermore, the composition of the feed medium to the rhizofilter was kept the same in both cold and warm season and for both planted and control sides. The removal of ammonium in colder and warmer months was not significant in both systems. At an average temperature increase of 5.2 °C in the warmer months, the ammonium removal efficiency in the planted side increased by 7.5%, while for the control side the removal efficiency increased by 2.4%. The difference in removal was not significant between the averages of effluent ammonium after an application time of 25 min in colder versus warmer months for the planted and control sides of the system. Furthermore, an increased nitrification rate was more evident in the planted than in the control side, which was subsequently denitrified. It was observed that 60.4% of nitrate concentration was potentially removed in the planted side whereas 45.4% was potentially denitrified in the control side. These results suggest positive correlation between nitrate concentration and the potential for denitrification. The nitrate removal efficiency dropped to 32.2% for the planted site and to 26.1% for the control system in colder months. Temperature had an effect on nitrogen removal, since nitrogen removal efficiency decreased in colder months. Complete nitrogen removal could not be achieved under the operating conditions.

Evaluation of the efficiency of selected wastewater treatment processes in removing selected perfluoroalkyl substances (PFASs).

In this study, the efficiencies of selected wastewater treatment plants (WWTPs) to remove selected perfluoroalkyl substances (PFASs) during wastewater treatment processes were evaluated. For this purpose, influent samples from Daspoort, Zeekoegat and Phola WWTPs, were initially screened for the presence of sixteen different PFASs of which only seven were detected. These include: perfluorobutanoic acid (PFBA), perfluoro-n-pentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), perfluorohexane sulfonate (L-PFHxS), and perfluorooctane sulfonate (L-PFOS). To determine the concentrations of these PFASs, wastewater samples were subjected to solid-phase extraction followed by liquid chromatography-tandem mass spectrometry. The results showed that L-PFOS was the dominant compound with the highest concentration of 508 ± 258 ng/L at Daspoort WWTP. Overall, the three WWTPs could not achieve the complete influent-to-effluent removal of the PFASs and the best removals were observed at Zeekoegat WWTP. The removal efficiency of the different unit processes varied from one plant to another and also from each type of PFASs. At Daspoort, the removal efficiency of the primary settling tanks was poor and the highest removal reached 39% for PFHxA. The activated sludge (AS) of this WWTP achieved the highest removal of 84% for the L-PFOS. At Zeekoegat, the AS achieved the highest removal of 94% for the L-PFOS. The anaerobic pond at Phola achieved a higher removal of 80% for the L-PFOS. However, no removal was observed downstream of the biological filter for the same compound. Poor removal efficiency was reported downstream of the wetland at Phola except for the PFOA (16%).

Seasonal variation of nutrient loads in treated wastewater effluents and receiving water bodies in Sedibeng and Soshanguve, South Africa.

The discharge of inadequately treated wastewater effluent presents a major threat to the aquatic environment and public health worldwide. As a water-scarce country, South Africa is facing an alarming situation since most of its wastewater discharges are not meeting the permissible limit. The aim of this study was to assess the physicochemical quality of treated wastewater effluents and their impact on receiving water bodies. During the study period, pH, temperature, free chlorine residue (Cl(-)), dissolved oxygen (DO), nitrate (NO3 (-1)), orthophosphate (PO4 (-3)) and chemical oxygen demand (COD) were measured in order to ascertain whether the selected wastewater systems in Sedibeng and Soshanguve complied with the South African and World Health Organization standards during wet and dry seasons. These parameters were analysed for samples collected from raw wastewater influent, treated wastewater effluent and receiving water bodies. The study was carried out between August 2011 and May 2012, and samples were collected on a weekly basis during both seasons. The physicochemical quality of effluents did not comply with the regulatory limits set by South Africa in terms of pH in Meyerton, Rietgat and Sandspruit (pH 7.6 to 8.1); free chlorine in Sandspruit (0.27 ± 0.05 mg/L); nitrate in Leeuwkuil and Rietgat (2.1 and 3.8 mg/L, respectively) during the wet season; orthophosphate in Meyerton during the wet season and in Sandspruit during the dry season (1.3 mg PO4 (-3) as P/L and 1.1 mg PO4 (-3) as P/L, respectively); and chemical oxygen demand in Rietgat during the dry season and in Sandspruit during the wet season (75.5 and 35 mg/L, respectively). Furthermore, the quality of the receiving water bodies did not comply with the South African standards recommended for pH, chemical oxygen demand and orthophosphate and DO (5 mg/L) in Rietgat during the wet season. The geometric mean of the water quality index values ranged between 32.4 and 36.9 for the effluent samples and between 38.1 and 65.7 for the receiving water bodies. These findings revealed that the receiving water bodies were classified as having "poor" quality status, except Leeuwkuil receiving water body (Vaal River) and Sandspruit upstream (Sandspruit stream). The dry season showed a relatively lower water quality index. This situation might be attributed to the higher amount of organic matter and lower microbial activities in the receiving water bodies. This study suggests that wastewater effluents and receiving water systems should be monitored regularly to ensure best practices with regard to nutrient treatment and discharge of wastewater.

Population Growth and Its Impact on the Design Capacity and Performance of the Wastewater Treatment Plants in Sedibeng and Soshanguve, South Africa.

This study investigated the effects of population growth on the performance of the targeted wastewater treatment plants in Sedibeng District and Soshanguve peri-urban area, South Africa. The impact of population growth was assessed in terms of plant design, operational capacity (flow rate) and other treatment process constraints. Between 2001 and 2007, the number of households connected to the public sewerage service increased by 15.5, 17.2 and 37.8% in Emfuleni, Lesedi and Midvaal Local Municipalities, respectively. Soshanguve revealed a 50% increment in the number of households connected to the sewerage system between 1996 and 2001. Except for Sandspruit (-393.8%), the rate of influent flows received by Meyerton increased by 6.8 ML/day (67.8%) and 4.7 ML/day (46.8%) during the dry and wet seasons, respectively. The flow rate appeared to increase during the wet season by 6.8 ML/day (19.1%) in Leeuwkuil and during the dry season by 0.8 ML/day (3.9%) in Rietgat. Underperformance of the existing wastewater treatment plants suggests that the rapid population growth in urban and peri-urban areas (hydraulic overloading of the wastewater treatment plants) and operational constraints (overflow rate, retention time, oxygen supply capacity of the plants and chlorine contact time) resulted in the production of poor quality effluents in both selected areas. This investigation showed that the inefficiency of Meyerton Wastewater Treatment Plant was attributed to the population growth (higher volumes of wastewater generated) and operational constraints, while the cause of underperformance in the other three treatment plants was clearly technical (operational).