Energy recovery from food waste and garden and park waste: Anaerobic co-digestion versus hydrothermal treatment and anaerobic co-digestion.

The feasibilities of the anaerobic co-digestion of two of the most relevant biowastes, food waste and garden and park waste, were evaluated and compared with the hydrothermal treatment of each waste and the anaerobic co-digestion of raw biowastes with the process water generated. The effects on the process stability and energy recovery were also analyzed. Anaerobic digestion was the best option for food waste treatment from an energetic point of view, with 81% recovery of the energy stored in the feedstock, while the highest energy recovery from garden and park waste was obtained for the solid fraction generated from hydrothermal treatment (85.5%). In addition, the anaerobic co-digestion of food waste with 5% of the process water generated from garden and park waste showed a similar energy recovery to that of food waste only (∼80%), thus improving the biological stability of the process.

Removal of imidazolium-based ionic liquid by coupling Fenton and biological oxidation.

In this work, we assessed the potential of combining Fenton´s reagent and biological oxidation for removing the imidazolium-based ionic liquid 1-Ethyl-3-methylimidazolium chloride (EmimCl). Fenton-like oxidation was conducted at variable H2O2 doses from 20 to 100% the stoichiometric value as calculated from the theoretical chemical oxygen demand (COD). The stoichiometric H2O2 dose afforded Total Organic Carbon (TOC) conversion and COD removal of 50 and 62%, respectively. Identifying the reaction by-products formed at low hydrogen peroxide doses allowed a plausible pathway for EmimCl oxidation to be proposed. The effluents from Fenton-like oxidation at substoichiometric H2O2 doses were less ecotoxic and more biodegradable than was the parent ionic liquid. The effluent from Fenton-like oxidation with the 60% H2O2 dose (TOC conversion ≅ 41%, COD removal ≅ 31%) was subsequently subjected to an effective biological treatment that allowed complete removal of the starting compound, increased its ecotoxicity to a low-moderate level and rendered it acceptably biodegradable. Biological oxidation was performed in 8-h and 12-h cycles in a sequencing batch reactor. Combining Fenton and biological oxidation of EmimCl afforded TOC conversion and COD removal of around 90%.

Removal of imidazolium- and pyridinium-based ionic liquids by Fenton oxidation.

The oxidation of imidazolium (1-hexyl-3-methylimidazolium chloride, HmimCl) and pyridinium (1-butyl-4-methylpyridinium chloride, BmpyrCl) ionic liquids (ILs) by Fenton's reagent has been studied. Complete conversion was achieved for both ILs using the stoichiometric H2O2 dose at 70 °C, reaching final TOC conversion values around 45 and 55% for HmimCl and BmpyrCl, respectively. The decrease in hydrogen peroxide dose to substoichiometric concentrations (20-80% stoichiometric dose) caused a decrease in TOC conversion and COD removal and the appearance of hydroxylated oxidation by-products. Working at these substoichiometric H2O2 doses allowed the depiction of a possible degradation pathway for the oxidation of both imidazolium and pyridinium ILs. The first step of the oxidation process consisted in the hydroxylation of the ionic liquid by the attack of the ·OH radicals, followed by the ring-opening and the formation of short-chain organic acids, which could be partially oxidized up to CO2 and H2O. At H2O2 doses near stoichiometric values (80%), the resulting effluents showed non-ecotoxic behaviour and more biodegradable character (BOD5/COD ratio around 0.38 and 0.58 for HmimCl and BmpyrCl, respectively) due to the formation of short-chain organic acids. Graphical abstract ᅟ.

Ag-Coated Heterostructures of ZnO-TiO2/Delaminated Montmorillonite as Solar Photocatalysts.

Heterostructures based on ZnO-TiO2/delaminated montmorillonite coated with Ag have been prepared by sol-gel and photoreduction procedures, varying the Ag and ZnO contents. They have been thoroughly characterized by XRD, WDXRF, UV-Vis, and XPS spectroscopies, and N2 adsorption, SEM, and TEM. In all cases, the montmorillonite was effectively delaminated with the formation of TiO2 anatase particles anchored on the clay layer's surface, yielding porous materials with high surface areas. The structural and textural properties of the heterostructures synthesized were unaffected by the ZnO incorporated. The photoreduction led to solids with Ag nanoparticles decorating the surface. These materials were tested as photocatalysts for the degradation of several emerging contaminants with different nitrogen-bearing chemical structures under solar light. The catalysts yielded high rates of disappearance of the starting pollutants and showed quite stable performance upon successive applications.

Assessment of toxicity and biodegradability on activated sludge of priority and emerging pollutants.

Several methods for evaluating the toxicity and biodegradability of hazardous pollutants (chlorinated compounds, chemical additives and pharmaceuticals) have been studied in this work. Different bioassays using representative bacteria of marine and terrestrial ecosystems such as Vibrio fischeri and Pseudomonas putida have been used to assess the ecotoxicity. Activated sludge was used to analyse the effect of those pollutants in a biological reactor of a sewage treatment plant (STP). The results demonstrate that none of the compounds is toxic to activated sludge, except ofloxacin to P. putida. The additives tested can be considered moderately toxic according to the more sensitive V. fischeri assays, whereas the EC50 values of the pharmaceuticals depend on the specific microorganism used in each test. Regarding the biodegradability, respirometric measurements were carried out for fast biodegradability assessment and the Zahn-Wellens test for inherent biodegradability. The evolution of the specific oxygen uptake rate (SOUR) showed that only diethyl phthalate was easily biodegradable and acetylsalicylic acid was partially biodegradable (98% and 65% degradation, respectively). The persistence of dichloromethane, ofloxacin and hidrochlorothiazide was confirmed along the 28 days of the Zahn-Wellens test whereas 1,1,1-trichloroethane showed inherent biodegradability (74% removal). Most of the chlorinated compounds, pharmaceuticals, bisphenol A and ethylenediaminetetraacetic acid were partially degraded in 28 d with total organic carbon (TOC) reduction ranging from 21% to 51%. Sulphamethoxazole showed certain biodegradation (50% removal) with TOC decrease around 31%, which indicates the formation of non-biodegradable by-products.

Degradation of chlorophenoxy herbicides by coupled Fenton and biological oxidation.

A combined treatment for the degradation of the chlorophenoxy herbicides 2,4-D and MCPA in water by means of Fenton and biological oxidation has been studied. The chemical oxidation step was necessary to achieve an efficient removal of these pollutants due to their toxicity and low biodegradability. Aqueous herbicide solutions (180mgL(-1)) were subjected to Fenton oxidation upon different H2O2 doses (from the theoretical stoichiometric amount referred to initial COD to 20% of this value). The toxicity and biodegradability tests of the Fenton effluents suggested that the ones resulting upon treatment with 80% and 60% of stoichiometric H2O2 were the optimal for subsequent biological treatment dealing with 2,4-D and MCPA, respectively. These effluents were treated in a sequencing batch reactor achieving nearly 90% conversion of organic matter measured as COD.

Enhancement of cometabolic biodegradation of 4-chlorophenol induced with phenol and glucose as carbon sources by Comamonas testosteroni.

The biological degradation of phenol and 4-chlorophenol (4-CP) by Comamonas testosteroni CECT 326T has been studied. Phenol and 4-CP were treated alone as a sole carbon and energy source, but only phenol was completely degraded by C. testosteroni. Since the presence of cosubstrates can enhance the toxic compounds removal by pure cultures, phenol and glucose were added as growth substrates for cometabolic transformation of 4-CP. High efficiencies were obtained in all the experiments carried out in presence of both cosubstrates. In spite of the fact that the addition of glucose reduced the lag phase of 4-CP removal, lower phenol concentrations were required to obtain the same degradation efficiencies. The cometabolic transformation of 4-CP was closely related with the extent of phenol removal. The values of the 4-CP/biomass concentration ratio (S/X) obtained for discriminating between complete (S/X ≤ 0.11) and partial 4-CP (S/X ≥ 0.31) transformation showed a narrower range than that reported in the literature. The extent of the cometabolic 4-CP transformation in the presence of phenol could be further enhanced by using glucose as an additional carbon and energy source. However, no significant influence of glucose concentration on 4-CP removal was observed over the concentration range studied.