Effect of trickling filter on carbon and nitrogen removal in vertical flow treatment wetlands: A full-scale investigation.

Vertical Flow Treatment Wetland (VF-TW) systems achieve high efficiencies in terms of carbon related parameters removals from domestic wastewaters. Nitrogen removal is also efficient but optimisations are still needed. This article reports and discusses experimental data collected from 24-h monitoring campaigns of 29 full-scale VF-TWs, having different configurations and operation time up to 13 years. All monitored systems gathered 1 or 2 stage(s) of unsaturated or partially saturated VF-TW. Additionally, some of those included an aerobic biological Tricking Filter (TF) prior to TW stage(s). Results firstly showed that the implementation of a TF improved TSS, COD and BOD5 removal rates in the monitored systems. Regarding nitrogen removal, the association of TF with one stage of partially saturated vertical TW was found to achieve around 79% of nitrification in average and up to 92% in some cases. In the configurations where TF was associated to 2 successive stages of TW, almost all total nitrogen removal by nitrification/denitrification was achieved at the outlet of the first-stage TW. The contribution of the second-stage TW in denitrification was found very low due to limited availability of organic carbon to support heterotrophic denitrification. Specific solutions to enhance the contribution of the second stage in the denitrification process are discussed.

pH and Eh effects on phosphorus fate in constructed wetland's sludge surface deposit.

The objective of the present study was to assess the influence of extreme pH and redox potential (Eh) conditions on phosphorus (P) retention within the surface sludge deposit layer of a vertical flow constructed wetland (VFCW) where phosphorus was captured by FeCl3 injection. Series of 27 successive batch leaching tests were conducted under acidic, alkaline or reductive conditions using a representative sludge sample taken from an 8-year old VFCW plant. Experiments were followed by monitoring the pH and Eh variations and analysing the releases of P and other selected elements into the solutions. The sludge material was also analyzed before and after leaching, using solution (31)P NMR spectroscopy and sequential chemical extractions, in order to evaluate dissolutions of both organic and inorganic P-bearing species and their respective contributions to P release. The correlations between the monitored variables were analyzed and visualized through principal components analyses (PCA). Results showed a very good stability of P retention in the sludge deposit and a relatively good acid-buffering capacity of the sludge, revealing that the risk of accidental P release into the environment would be extremely low during the real plant operation.

Effect of aging on phosphorus speciation in surface deposit of a vertical flow constructed wetland.

This study was conducted to determine phosphorus (P) species captured in a vertical-flow constructed wetland (VFCW) system combining a trickling filter followed by FeCl3 injection for phosphate coagulation. Suspended solids (SS) thus formed accumulated over time at the VFCW surface and transformed into a sludge deposit layer, which was shown to concentrate most of the P captured in the system. In order to investigate the effect of aging on P species, representative SS and sludge samples were taken from a wastewater treatment plant that had been in operation for 8 years and analyzed using P fractionation, solution (31)P NMR spectroscopy, and P and Fe K-edge XANES spectroscopy. A partial mineralization of organic matter was shown by comparing organic carbon contents of SS and sludge materials. Chemical fractionations combined with P and Fe K-edge XANES spectroscopy showed that P was predominantly bound to iron within both samples in the form of ferric phosphate, rather than adsorbed onto ferric oxyhydroxide. Calcium-bound P was more significantly observed in sludge than in SS, suggesting that aging induced the recombination of part of the organic and iron-bound P species into calcium-bound forms, as a possible consequence of the partial mineralization of organic matter.

Mechanical pre-treatment of source-collected municipal biowaste prior to energy recovery by anaerobic digestion.

Pre-treatments are usually necessary to prepare biowaste to anaerobic digestion. The major objectives are (i) to remove undesirable materials such as plastics and metals, which may contaminate the biowaste even if separated source-collection systems are implemented, and (ii) to extract the most readily biodegradable organic fractions from the waste stream. In this study, two wet mechanical pre-treatments, namely air-compressed press and worm screw press, were investigated on urban household biowaste. Two liquid to solid ratios were tested in each pre-treatment. Anaerobic digestion of pre-treated biowaste was studied by measuring their biomethane potentials and by controlled experiments in a continuously stirred-tank reactor with a feed load of 3.5 gVS.L-1.d-1. It was observed that increasing liquid to solid ratio in the pre-treatments allowed to increase the proportion of biodegradable organic matter extracted from the biowaste, up to 949 gCOD.kgTS-1 from household biowaste. The biomethane potentials of pre-treated waste were very high (up 525 LCH4.kgVS-1) and COD (949 gCOD.kg-1TS) from household biowaste. Anaerobic digestion in continuously stirred-tank reactor showed a very strong conversion of COD load (81%) and a high methane production up to 345 LCH4.kgVS-1.

Mechanical pretreatment of municipal biowaste to produce an aqueous slurry dedicated to anaerobic digestion.

The present study investigated a wet mechanical pretreatment to improve methane production by anaerobic digestion from biowaste material by separating a biodegradable aqueous slurry fraction (ASF) from a more recalcitrant particulate fraction (PF). Four source-sorted municipal biowastes were studied, namely household (HBW), supermarket (SBW), restaurant (RBW), and green biowaste (GBW). The treatment consisted in soaking the waste in water and then pressing the slurry through a grid with 3-mm openings to separate the two fractions. Methane production of ASF and PF obtained from the four biowastes were measured using the BMP protocol and compared to the potential of the respective untreated biowaste. Results were very different for GBW as compared to the other three BWs. With GBW, which was the most lignocellulosic of the BW studied, only 17% of the initial methane potential was recovered in the ASF. The extraction was much better on the other biowastes and increased in the following order: HBW (58%) ≃ RBW (57%) < SBW (67%). The ASF from these biowastes exhibited low total solid contents and high BMPs (416, 408, and 423 NLCH4.g-1vs for HBW, RBW, and SBW respectively). The experimental results obtained in this study therefore showed that wet pressing separation was an efficient pretreatment to improve and facilitate methane production by anaerobic digestion of biowaste such as HBW, RBW, and SBW.

French vertical flow treatment wetlands in a subtropical climate: Characterization of the organic deposit layer and comparison with systems in France.

This paper presents an advanced characterization of the organic fraction of the top deposit layer collected in a French vertical flow treatment wetland (first stage) in operation in Brazil (two units with different organic deposit layer accumulation times), and compares the results with those obtained from studies in France. The organic and inorganic constituents of the samples collected were analysed by biological, chemical and thermochemical methods. The unit with the organic deposit with longer accumulation time (almost 10 years) was characterized as a mature one (organic matter - OM: 51.3 and 52.7%, thermal index - RTGA: 0.79 and 0.85, humification index - HI: 0.61 and 1.16, respectively for the depths of 0-5 cm and 5-10 cm). The unit with the deposit organic with less than three years of accumulation also presented characteristics of a mature deposit (OM: 61.2%, RTGA: 0.79, HI: 1.01 for the depth of 0-5 cm), indicating a rapid mineralization of the deposit under the existing subtropical environment. Despite several differences in term of conception, hydraulic and mass loading rates and accumulation rates, the characteristics of the OM of Brazilian deposits were found to be quite similar to the French ones.

Adsorption of heavy metals on to sugar cane bagasse: improvement of adsorption capacities due to anaerobic degradation of the biosorbent.

In this work, anaerobic degradation of sugar cane bagasse was studied with a dual objective: the production of biogas and the improvement of the material's characteristics for its implementation in adsorption processes. The biogas production was determined by means of biomethane potential tests carried out over two months of incubation at 35 degrees C. Biogas and methane cumulative productions were assumed to follow a first-order rate of decay. Theoretical cumulative methane and biogas productions were calculated using Buswell's equation. The anaerobic digestion resulted in a 92% decrease in the leachable organic fraction and a 40% mass loss of bagasse. The average productions of biogas and methane from the whole set of experiments were 293 +/- 6 and 122 +/- 4 mL g(-1) of volatile solids, respectively. The anaerobic incubation of the raw material led to an increase in adsorption capacities towards metal ions, which were multiplied by around 2.0 for Zn2+ and 2.3 for Cd2+.

Monitoring of abiotic degradation of photocrosslinked silicone acrylate coatings: the fate of the photoinitiator.

Photocrosslinked silicone acrylates are used in a variety of applications, such as printing inks, adhesives, or adhesive release liners. Their production requires the use of a photoinitiator. Even if the photoinitiator represents a minor mass in the photocurable formulation (2-10%), it is used in excess and residual amounts may therefore remain in the polymerized products and possibly migrate into the environment during the use of the products and/or at their end-of-life stage. Little is known on the possible degradation of silicone acrylate which may increase the potential release. The present study investigated the release of Darocur 1173, the most commonly used photoinitiator, from silicone matrix and the effect of accelerated photoageing on the extent of the phenomenon. Leaching tests in water were conducted on thin-coated plastic film (release liners) made of a mixture of polypropylene and polyethylene. Results showed that 44% of the Darocur 1173 photoinitiator initially used in silicone formulation was released from silicone matrix in the leaching test. Accelerated photoageing obtained by UV irradiation of the films for up to 200 h was found to favor photoinitiator degradation but also induced a strong and fast oxidation of silicone-coated liners as compared to that of uncoated ones. Graphical abstract.

Leaching behavior of major and trace elements from sludge deposits of a French vertical flow constructed wetland.

Surface sludge deposits were collected from a French Vertical Flow Constructed Wetland (French VFCW) sewage treatment plant. The objectives were to characterize the retention of major elements and trace metals within the sludge deposits particles under regular operating conditions, and the influence of extreme pH conditions on their potential release which may occur in situations when the plant malfunctions or after land application of the dredged sludge. A sequential extraction protocol was first used to assess the distribution of the elements within the sludge deposits. Results showed that most of Cu and Pb were associated to organic matter within the oxidizable fraction. Zn, Ni and Cd were distributed in several fractions, notably bound to Fe-Mn oxides and associated to organic matter. Cr was analyzed mostly in the residual fraction. Aliquot fractions of sludge deposits were also submitted to Acid and Base Neutralization Capacity tests (ANC-BNC) where the samples were suspended into acidic or alkaline aqueous solutions, and the solutions analyzed after 48 h contact time. Results showed a pH-dependent leaching profile for all monitored elements. The role of organic matter was observed for almost all metals. It was particularly dominant for Cu which was leached more extensively under alkaline than acidic conditions. Since Cu is not an amphoteric element, this leaching pattern was attributed to the leaching of organic matter which followed a similar pH-dependent profile than Cu. Spectrometric indices were used to characterize soluble organic compounds. Results showed that complex and humified dissolved organic compounds were mostly released under alkaline conditions.