Anna Pedescoll

Capacity of a horizontal subsurface flow constructed wetland system for the removal of emerging pollutants: an injection experiment.

A continuous injection experiment was implemented in a pilot-scale horizontal subsurface flow constructed wetland system to evaluate the behavior of four pharmaceuticals and personal care products (i.e. ibuprofen, naproxen, diclofenac and tonalide) and a phenolic estrogenic compound (i.e. bisphenol A). The treatment system consisted of an anaerobic reactor as a primary treatment, followed by two 0.65 m² wetlands (B1 and B2) working in parallel and connected to a 1.65 m² wetland (B3) operating in series. Overall removal efficiencies for the selected compounds ranged from 97% to 99%. The response curves of the injected pollutants show that the behavior of these compounds strongly depends on their sorption and biodegradation characteristics. While about 50% of ibuprofen was removed in B1 and B2, 99% was achieved at B3, where the dissolved oxygen concentration was significantly higher (B1-B2=0.5 mg L⁻¹ and B3=5.4 mg L⁻¹). Naproxen and diclofenac were efficiently removed (93%) in B1 and B2, revealing anaerobic degradation as a probable removal mechanism. Moreover, tonalide and bisphenol A were readily removed in the small wetlands (94% and 83%, respectively), where the removal of total suspended solids was 93%. Therefore, given their high hydrophobicity, sorption onto the particulate matter stands for the major removal mechanism. However, the tentative identification of carboxy-bisphenol A as an intermediate degradation product in B3 suggested biodegradation as a relevant bisphenol A removal pathway under aerobic prevailing conditions.

Sludge dewatering and stabilization in drying reed beds: Characterization of three full-scale systems in Catalonia, Spain

Optimization of sludge management can help reducing sludge handling costs in wastewater treatment plants. Sludge drying reed beds appear as a new and alternative technology which has low energy requirements, reduced operating and maintenance costs, and causes little environmental impact. The objective of this work was to evaluate the efficiency of three full-scale drying reed beds in terms of sludge dewatering, stabilization and hygienisation. Samples of influent sludge and sludge accumulated in the reed beds were analysed for pH, Electrical Conductivity, Total Solids (TS), Volatile Solids (VS), Chemical Oxygen Demand, Biochemical Oxygen Demand, nutrients (Total Kjeldahl Nitrogen (TKN) and Total Phosphorus (TP)), heavy metals and faecal bacteria indicators (Escherichiacoli and Salmonella spp.). Lixiviate samples were also collected. There was a systematic increase in the TS concentration from 1-3% in the influent to 20-30% in the beds, which fits in the range obtained with conventional dewatering technologies. Progressive organic matter removal and sludge stabilization in the beds was also observed (VS concentration decreased from 52-67% TS in the influent to 31-49% TS in the beds). Concentration of nutrients of the sludge accumulated in the beds was quite low (TKN 2-7% TS and TP 0.04-0.7% TS), and heavy metals remained below law threshold concentrations. Salmonella spp. was not detected in any of the samples, while E. coli concentration was generally lower than 460MPN/g in the sludge accumulated in the beds. The studied systems demonstrated a good efficiency for sludge dewatering and stabilization in the context of small remote wastewater treatment plants.

Design configurations affecting flow pattern and solids accumulation in horizontal free water and subsurface flow constructed wetlands.

The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.

Evaluation of primary treatment and loading regimes in the removal of pharmaceuticals and personal care products from urban wastewaters by subsurface-flow constructed wetlands

The ability of several mesocosm-scale horizontal subsurface flow (SSF) constructed wetlands (CW) to remove pharmaceuticals and personal care products (PPCPs) from urban wastewater was assessed in the winter and summer of 2008. As CWs are generally used as secondary or tertiary wastewater treatment systems, their efficacy was compared when fed from two different primary treatment systems, a sedimentation tank and an anaerobic hydrolysis upflow sludge bed reactor (HUSB). The influence of plants (Phragmites australis) in the CWs and their feeding regime (continuous flow or batch flow) on PPCP removal were also monitored. One of the CWs was replicated and operated simultaneously in Barcelona and León, Spain, in order to study the effect of environmental conditions on PPCP removal. All systems operated in the open air. The sedimentation tank offered slightly better removal values throughout the experimental period than the HUSB. The presence of P. australis enhanced the removal of salicylic acid, galaxolide, tonalide and methyl dihydrojasmonate, but only in summer (when plants were more active). The use of a batch flow or a continuous flow made very little difference to PPCP removal efficiency. When the two mesocosm replicates were compared, temperature proved to be one of the most determining parameters affecting PPCP elimination, with naproxen, ibuprofen, diclofenac, caffeine, galaxolide, tonalide and methyl dihydrojasmonate being removed in SSF-CWs more efficiently at higher temperatures. In general, the most easily removed PPCPs in planted CWs were caffeine (14 ± 74%–84 ± 7% in winter, 98 ± 1%–99 ± 1% in summer), methyl dihydrojasmonate (28 ± 21%–63 ± 17% in winter, 93 ± 2%–98 ± 1% in summer) and salicylic acid (0%–97 ± 4% in winter, 41 ± 40%–89 ± 9% in summer), followed by naproxen (0%–41 ± 16% in winter, 60 ± 18%–95 ± 4% in summer) and ibuprofen (0%–47 ± 26% in winter, 35 ± 12%–99 ± 1% in summer). Other substances experimented lower removal efficiencies, like ketoprofen (4 ± 27%–27 ± 14% in winter, 0%–37 ± 32% in summer), diclofenac (0%–22 ± 22% in winter, 0%–71 ± 8% in summer), carbamazepine (0%–9 ± 100% in winter, 0%–58 ± 21% in summer), galaxolide (0% in winter, 25 ± 14%–87 ± 5% in summer) and tonalide (0% in winter, 32 ± 12%–76 ± 12% in summer).

Effect of climatic conditions, season and wastewater quality on contaminant removal efficiency of two experimental constructed wetlands in different regions of Spain

The aim of this study was to examine the effects of climate, season and wastewater quality on contaminant removal efficiency of constructed wetlands implemented in Mediterranean and continental-Mediterranean climate region of Spain. To this end, two experimental horizontal subsurface flow constructed wetlands located in Barcelona and León (Spain) were compared. The two constructed wetland systems had the same experimental set-up. Each wetland had a surface area of 2.95 m(2), a water depth of 25 cm and a granular medium of D(60)=7.3 mm, and was planted with Phragmites australis. Both systems were designed in order to operate with a maximum organic loading rate of 6 g(DBO) m(-2) d(-1). Experimental systems operated with a hydraulic loading rate of 28.5 and 98 mm d(-1) in Barcelona and León, respectively. Total suspended solids, biochemical oxygen demand and ammonium mass removal efficiencies followed seasonal trends, with higher values in the summer (97.4% vs. 97.8%; 97.1% vs. 96.2%; 99.9% vs. 88.9%, in Barcelona and León systems, respectively) than in the winter (83.5% vs. 74.4%; 73.2% vs. 60.6%; 19% vs. no net removal for ammonium in Barcelona and León systems, respectively). During the cold season, biochemical oxygen demand and ammonium removal were significantly higher in Barcelona system than in León, as a result of higher temperature and redox potential in Barcelona. During the warm season, statistical differences were observed only for ammonium removal. Results showed that horizontal subsurface flow constructed wetland is a successful technology for both regions considered, even if winter seemed to be a critical period for ammonium removal in continental climate regions.

Reliability and economic feasibility of online monitoring of constructed wetlands performance

AbstractThis study aimed at determining the reliability and feasibility of constructed wetlands (CWs) performance evaluation by online monitoring. Redox potential (EH), turbidity and ammonium (NH4) were continuously monitored for one year by means of online sensors in a pilot plant based on horizontal sub-surface flow constructed wetlands (HSSF CWs). Results were compared with conventional laboratory analyses. Online measures and laboratory analyses showed good agreement for NH4 (r = 0.84, p < 0.01). A significant correlation was also found for: online turbidity vs. Total suspended solids (TSS) (r = 0.85, p < 0.01); online turbidity vs. Biochemical oxygen demand (BOD) (r = 0.88; p < 0.01) and EH vs. BOD (r = −0.62; p < 0.01). Results suggested that in full-scale CWs, continuous monitoring of turbidity, EH and NH4 would help to both daily monitoring and improvement of CWs performance. A general overview about economic aspects suggested that, continuous monitoring of wastewater quality could be technically ...