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This study aimed at determining the treatment performances of a full-scale vertical flow constructed wetlands designed to treat wastewater from a food-processing industry (cookie factory), and to study the influence of the organic loading rate. The full-scale treatment plant was designed with a first vertical stage of 630 m², a second vertical stage of 473 m² equipped with a recirculation system and followed by a final horizontal stage of 440 m². The plant was commissioned in 2011, and was operated at different loading rates during 16 months for the purpose of this study. Treatment performances were determined by 24 hour composite samples. The mean concentration of the raw effluent was 8,548 mg.L-1 chemical oxygen demand (COD), 4,334 mg.L-1 biochemical oxygen demand (BOD5), and 2,069 mg.L-1 suspended solids (SS). Despite low nutrients content with a BOD5/N/P ratio of 100/1.8/0.5, lower than optimum for biological degradation (known as 100/5/1), mean removal performances were very high with 98% for COD, 99% for BOD5 and SS for the two vertical stages. The increasing of the organic load from 50 g.m-2.d-1 COD to 237 g.m-2.d-1 COD (on the first stage) did not affect removal performances. The mean quality of effluent reached French standards (COD<125 mg.L-1, BOD5<25 mg.L-1, SS<35 mg.L-1). [ABSTRACT FROM AUTHOR]

Upgrades to enhance nitrogen removal were tested in a 2 year old pilot vertical flow constructed wetland in spring and summer periods. The effects of a saturated layer and of recirculation were tested in particular. Two pilots (L ¼2 m, W¼ 1.25 m, H ¼ 1.2 m), filled with expanded schist (Mayennite®), were designed with hydraulic saturated layers of 20 and 40 cm at the bottom. Each pilot was fed with raw domestic wastewater under field conditions according to a hydraulic load of 15-38 cm d-1 (i.e. 158-401 g COD (chemical oxygen demand) m-2 d-1) and to recirculation rates ranging from 0% up to 150%. The initial load during the first 2 years of operation resulted in an incomplete mineralized accumulated sludge leading to total suspended solids (TSS), COD and biochemical oxygen demand (BOD5) release. A 40 cm hydraulic saturated layer enabled an increase of 5-10% total nitrogen (TN) removal compared to a 20 cm saturated layer. Recirculation allowed the dilution of raw wastewater and enhanced nitrification in a single stage. A design of 1.8 m² pe-1 (48 cm d-1, 191 g COD m-2 d-1) with a 40 cm saturated layer and 100% recirculation enabled the French standard D4 (35 mg TSS L-1, 125 mg COD L-1, 25 mg BOD5 L-1), nitrogen concentrations below 20 mg TKN (total Kjeldahl nitrogen) L-1 and 50 mg TN L-1, to be met. [ABSTRACT FROM AUTHOR]

The current best option to upgrade constructed wetlands (CWs) for phosphorus (P) retention, in terms of efficiency, cost and simplicity, consists in using media having a strong P affinity. The media can be used either in the planted beds or in a filtration system downstream of the beds. The use of slag filters was shown to be efficient for removing P from wastewater as it represented a slow release source of calcium and hydroxide, favouring the formation of hydroxyapatite. Our study aimed at maximising the P retention capacity of slag filters located at the outlet of CWs since electric arc furnace slag has been shown to inhibit the growth of macrophytes when used in the filtration matrix. Bench-scale columns (Vtot = 6.2 L) filled with various combinations of filter media (slag, granite, limestone) of different sizes (2-5, 5-10, 10-20 mm) were fed on-site during four months with a CW effluent (in mg/L: 30 COD, 30 TSS, 10 Pt). Results showed that the best media combination enabling the maximum o-PO4 retention (more than 80% removal without clogging) consisted in a series of a ternary mix column (slag 5-10 mm, granite 2-5 mm, limestone 5-10 mm) followed by a slag column (slag 5-10 mm). Pilot scale columns (Vtot = 300 L), filled with the best media combination, were installed at the outlet of a 28m² CW. These columns showed more than 75% removal efficiency during one year and were designed to be easily replaced each year. [ABSTRACT FROM AUTHOR]

It is often assumed that planted wastewater treatment systems outperform unplanted ones, mainly because plants stimulate below ground microbial population. Yet, fundamental interactions between plants and associated microorganisms remain only partly understood. The aim of our project was to evaluate microbial density and activity associated to the rhizosphere of three plant species. Experimental set-up, in six replicates, consisted of four 1.8-L microcosms respectively planted in monoculture of Typha angustifolia, Phragmites australis, Phalaris arundinacea and unplanted control. Plants were grown for two months with 25 L m-2 d-1 of secondary effluent (in g m-2 d-1: 1.3 TSS, 7.5 COD, 1.0 TKN). Sampling of substrate, roots and interstitial water was made according to depth (0-10, 10-20 cm). Biofilm was extracted with 500 mL of a buffer solution. Microbial density was directly estimated by flow cytometry and indirectly by protein measurements. Biological activity was determined using respirometry assays, dehydrogenase and enzymatic activity measurements. Our results show that microbial density and activity are higher in the presence of plants, with significantly higher values associated with Phalaris arundinacea. Greater density of aerobic or facultative bacteria was present in planted microcosm, particularly on root surface, suggesting root oxygen release. Microbes were present on substrate and roots as an attached biofilm and abundance was correlated to root surface throughout depth. Plant species root morphology and development seem to be a key factor influencing microbial-plant interaction. [ABSTRACT FROM AUTHOR]

The effect of organic loading, season and plant species on the treatment of fish farm effluent was tested using three-year old mesocosm wetland systems. During one year, nine 1m² mesocosms (horizontal subsurface flow), located in a controlled greenhouse environment, were fed with a reconstituted fish farm effluent containing a high fraction of soluble components (1,600 µS/cm and in mg/L: 230 ± 80 COD, 179 ± 60 sCOD, 100 ± 40 TSS, 37 ± 7 TKN, 14 ± 2 TP). Combinations of three hydraulic loading rates (30, 60 and 90 L.m-2 d-1) and two plant species (Phragmites australis, Typha angustifolia) and an unplanted control were tested for treatment performance and hydraulic behaviour. Loadings higher than 15 g COD m-2 d-1 resulted in a net decrease of hydraulic performances (generation of short circuiting) coupled with low TKN removal. Maximal TKN removal rates (summer: 1.2, winter: 0.6 g.m-2 d-1) were reached in planted units. In all mesocosms, phosphorus was removed during summer (maximal removal rate: 0.3 g TP m-2 d-1) and was released in winter (release rate = ∼ half of summer removal rate). This study confirmed that constructed wetlands are susceptible to clogging when treating anaerobic storage tank supernatant rich in highly biodegradable compounds. Contributions of plants to hydraulic efficiency were mainly observed in summer, associated with high evapotranspiration rates. Both plant species gave a similar removal efficiency for all pollutants. [ABSTRACT FROM AUTHOR]

Tracer studies performed in two aerated facultative lagoons indicate some bypass and an overall hydraulic regime close to completely-mixed. Results were used to calibrate a hydraulic model based on the tanks-in-series approach. The hydraulic model was combined with a simple "death-regeneration" biokinetic model to simulate seasonal nitrification as observed over a three year period. Modifications were made to the hydraulic model to represent the effect of baffle installations to 1) eliminate bypass and 2) impose a plug-flow regime. Simulation results indicate there is some gain to eliminating bypass but that imposing a plug-flow regime would increase biomass washout rates and hinder nitrification. [ABSTRACT FROM AUTHOR]

In France, gravel vertical flow constructed wetlands (gVFCWs) were adapted to treat raw wastewater, which led to important accumulations of matter in filters (organic and mineral). To prevent clogging, large gravel sizes were employed (Ø 2-6 mm). The aim of this paper was to present the influences of matter accumulation on the hydraulic and biological behaviour of the system. A one-year survey of accumulated matter content and potential respiration activities was completed in three gVFCWs (operating for 3, 4 and 8 years). Cores were sampled into filters. Results showed a vertical stratification of accumulated matter and respiration rates. Dry accumulated matter quantities ranged from 20 kg m-2 (3 and 4 years operating) to 80 kg m-2 in the oldest plant (8 years). Potential respiration was larger in the oldest plant (75 g O2m-2 h-1) than in the most recent one (15 g O2m-2 h-1). Accumulated matter seemed to play a role both on the water retention (enhancing initial percolation time by 5 times) and biological profile (enhancing microfauna's diversity). Contrary to what is generally proposed in the literature, accumulated matter in French gVFCWs seemed to provide better treatment efficiency without leading to surface clogging compared to systems using sand. [ABSTRACT FROM AUTHOR]