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Landfill leachate is often an important source of emerging organic contaminants including perfluoroalkyl and polyfluoroalkyl substances (PFASs) requiring proper treatment to protect surface water and groundwater resources. This study investigated the occurrence of PFASs in the leachate of a capped landfill site in Singapore and the efficacy of PFASs removal during flow through a constructed wetland (CW) treatment system. The CW treatment system consists of equalization tank, aeration lagoons, sedimentation tank, reed beds and polishing ponds. Target compounds included 11 perfluoroalkyl acids (PFAAs) (7 perfluoroalkyl carboxylic acids (PFCAs) and 4 perfluoroalkane sulfonates (PFSAs)) and 7 PFAA precursors. Although total PFASs concentrations in the leachate varied widely (1269 to 7661 ng/L) over the one-year sampling period, the PFASs composition remained relatively stable with PFCAs consistently being predominant (64.0 ± 3.8%). Perfluorobutane sulfonate (PFBS) concentrations were highly correlated with total PFASs concentrations and could be an indicator for the release of PFASs from this landfill. The release of short-chain PFAAs strongly depended on precipitation whereas concentrations of the other PFASs appeared to be controlled by partitioning. Overall, the CW treatment system removed 61% of total PFASs and 50–96% of individual PFASs. PFAAs were removed most efficiently in the reed bed (42–49%), likely due to the combination of sorption to soils and sediments and plant uptake, whereas most of the PFAA precursors (i.e. 5:3 fluorotelomer carboxylate (5:3 acid), N-substituted perfluorooctane sulfonamides (N-MeFOSAA and N-EtFOSAA)) were removed in the aeration lagoon (>55%) by biodegradation. The sedimentation tank and polishing ponds were relatively inefficient, with only 7% PFASs removal.

Sludge-drying reed beds can be a cost-effective and sustainable solution to surplus activated sludge dewatering and mineralization, especially for small wastewater treatment plants. However, the simplicity as well as low energy and monitoring requirements of this technology are often counterbalanced by frequent operational problems consisting of slow and insufficient dewatering, poor vegetation growth, odor, and overall poor mineralization of the sludge residues. The main reason is that the general rules for facility design and operation are based on empirical experience rather than on the actual and current sludge parameters. In this study a new method for the assessment of activated sludge drainage properties has been applied to determine the reasons behind operational problems faced by the operators of reed bed facility accepting surplus activated sludge from two wastewater treatment plants in Esbjerg, Denmark. The importance of sludge quality monitoring as well as the damaging effect of shear forces, oxygen depletion, and long-distance sludge transportation were demonstrated. Finally, more general guidelines for reed bed facility design and operation are given, based on experimental data from seven full-scale plants.

Lagoon systems generally represent an effective wastewater treatment process for small communities in rural regions. However, sensitive receiving waters promote an increasing need for algal removal and effluent polishing. The study's main objective was to delineate a reed bed process feasible for upgrading lagoon systems. Results are given for two types of small constructed wetlands which have been investigated over a period of several years. The stress is upon the seasonal differences and the effect of dry or wet weather operation. Design, construction and maintenance of the wetlands are described. The reed beds produced high effluent qualities in terms of suspended solids, algae, COD and hygienic aspects. During summer about 50% of influent concentration of chlorophyll and about 60% of suspended matter could be filtered by a subsurface flown constructed wetland. Furthermore, a buffering of pH value and temperature could be observed after the passage of the wetlands.

The present study consists of assessing the efficiency of a macrophyte (Phragmites australis) system in wastewater purification in an arid climate. The experimental system is made up of three beds differing in length (30, 40 and 50 m) and implanted with Phragmites australis. Wastewater inflow through these beds is horizontal with a flow of 10 l.s−1. Retention time varies between 1 and 4 h. The frequency of irrigation is weekly. The studied parameters are: the organic load (COD and TSS), nutrients (total Kjeldhal nitrogen: TKN and total phosphorus: TP) and the parasitical load (helminth eggs). Water, soil and plants are the three components of the experimental system we analyzed. Results reveal that in the output, the decrease in organic load, nutrients and parasitical load is very sharp in the large bed (COD: 62%, TKN: 43%, TP: 14%, helminth eggs: 93%). However, in the small bed (30 m), the decrease is slight (COD: 48%, TKN: 23%, TP: 5%, helminth eggs: 88%). Concerning parasitical load, the study shows that the three beds are effective in eliminating helminth eggs, even with a very short retention time (1–4 h). The quality of the effluent of the reed bed system should be classified within category B according to WHO guidelines (1989) for crops irrigation. Soil sample analysis from entrance to exit shows a decreasing gradient of nitrogen (N), phosphorus (P), organic carbon (Org.C), organic matter (OM) and parasitical helmith eggs. The gradient becomes more significant in the largest bed with decreasing rate, reaching respectively 49%, 44%, 37%, 40% and 100% for TKN, TP, Org.C, OM and helminth eggs. As for the plant material, the composition of major elements (nitrogen and phosphorus) of Phragmites aerial parts shows the same evolution. While the decreasing rate of nitrogen in the leaves reaches 50% in the largest bed, it does not exceed 8% in the smallest bed. Mean aerial productivity of the studied reed beds was estimated at 134 tons dry weight.ha−1. The aerial biomass exported contains only 5–6% of nitrogen and 10–12% of phosphorus with regard to their load at the influent.

The Sludge Treatment Reed Bed (STRB) technology is a cost-efficient and environmentally friendly technology to dewater and mineralize surplus sludge from conventional wastewater treatment systems. Primary and secondary liquid sludge is loaded onto the surface of the bed over several years, where it is dewatered, mineralized and turned into a biosolid with a high dry matter content for use as an organic fertilizer on agricultural land. We analysed the concentrations of five organic micropollutants (galaxolide, tonalide, cashmeran, celestolide and DEHP) and six heavy metals (Pb, Ni, Cu, Cd, Zn and Cr) in the accumulated sludge in a 20-year old STRB in Denmark in order to assess the degradation and fate of these contaminants in a STRB and the relation to sludge composition. The results showed that the deposited sludge was dewatered to reach a dry matter content of 29%, and that up to a third of the organic content of the sludge was mineralized. The concentrations of heavy metals generally increased with depth in the vertical sludge profile due to the dewatering and mineralization of organic matter, but in all cases the concentrations were below the European Union legal limits for agricultural land disposal. The concentrations of fragrances and DEHP ranged from 10 to 9000 ng g−1 dry mass. The attenuation of hydrophobic micropollutants from the top to the bottom layer of the reed bed ranged from 40 to 98%, except for tonalide which increased significantly with sludge depth, and consequently showed an unusual depth distribution of the galaxolide/tonalide ratio. This unexpected pattern may reflect changes imposed by a long storage time and/or different composition of the fresh sludge in the past. The lack of a significant decreasing DEHP concentration with sludge age might indicate that this compound is very persistent in STRBs. In conclusion the STRB was a feasible technology for sludge treatment before its land disposal.

The decomposition processes of organic matter during winter in a 3-year old soil-based constructed reed bed with lateral sub-surface water flow were evaluated by quantifying the in- and efflux of metabolic gases and by considering input-output budgets and relating these to storages within the bed. The total flux of gaseous oxygen into the bed was 5.86 g m−2 day−1 of which 2.08 gm−2day−1 was through the cavities of dead, still standing culms of Phragmites australis. The respiratory oxygen consumption of the roots and rhizomes almost perfectly balanced the oxygen influx through the culms leaving only 0.02 g O2 m−2 day−1 to be released to the surrounding soil. The macrophyte-induced rhizosphere oxygenation was therefore of no quantitative importance for aerobic BOD degradation and microbial nitrification. Organic matter was degraded aerobically by means of oxygen delivered directly from the atmosphere and anaerobically by methanogenic bacteria in the upper layers of the soil. Some nitrogen and phosphorus was retained with sludge deposition on the surface of the bed and in the inlet trench. The constructed reed bed under study did not function according to the theory of the root-zone process. The majority of the wastewater moved along preferred pathways on the surface of the bed because of low soil hydraulic conductivity. Changes in the physical design and the operational practice of constructed reed beds needed to improve and optimize performance efficiency for nutrients are discussed.

This report describes investigations using artificial wetlands which quantitatively assess the role of each of three higher aquatic plant types, Scirpus validus (bulrush), Phragmites communis (common reed) and Typha latifola (cattail), in the removal of nitrogen (via sequential nitrification-denitrification), BOD and TSS from primary municipal wastewaters. During the period August 1983–December 1984, the mean ammonia concentration of 24.7 mg l−1 in the primary wastewater inflow (hydraulic application rate = 4.7 cm day−1) was reduced to mean effluent levels of 1.4 mg l−1 for the bulrush bed, 5.3 mg l−1 for the reed bed and 17.7 mg l−1 for the cattail bed, as compared to a mean value of 22.1 mg l−1 for the unvegetated (control) bed. For all three vegetated beds, the mean effluent ammonia values were significantly below that for the unvegetated bed and for the inflow. The bulrushes and reeds (in that order) proved to be superior at removing ammonia, both with mean effluent levels significantly below that for the cattail bed. The high ammonia-N (and total N) removal efficiencies shown by the bulrush and reed beds are attributed to the ability of these plants to translocate O2 from the shoots to the roots. The oxidized rhizosphere so formed stimulates sequential nitrification-denitrification. Similarly BOD removal efficiencies were highest in the bulrush and reed beds, both with mean effluent BOD levels (5.3 and 22.2 mg l−1, respectively) significantly below that for the unvegetated bed (36.4 mg l−1) and equal to or better than secondary treatment quality (30 mg l−1). Our results demonstrate that higher aquatic plants can indeed play a significant role in secondary and advanced (N removal) wastewater treatment by wetland systems, a role that is completely distinct from that associated with their pollutant uptake capacity.