Our previous work has shown the technical and economic feasibility of the solid substrate anaerobic digestion (DASS) of municipal and non-hazardous industrial solid wastes. However, the anaerobic compost (AnC) quality for direct application as a soil amender or other alternative uses are issues that have received scarce attention. This research aimed at reviewing the advances made by our Group in two areas: anaerobic compost quality determination, and its post-treatment by aerobic composting. A factorial experiment 4×2×2 was run. The factors were feedstock type (4 mixtures of food waste, FW, and lignocellulosic fraction, LG: 100%FW, 67%FW-33%LG, 33%FW-67%LG and 100%LG or FS1, FS2, FS3 and FS4 respectively), temperature (35°C and 55°C), and mass retention time (MRT, 16 and 23 days). The LG fraction consisted of paper mill sludge cake. Anaerobic compost from DASS reactors operated at 23 day/35°C) was fed to lab scale semi-continuous aerobic composters (5 day and 10 day MRT, 35°C and 55°C). The AnC coming from feedstocks with increasing proportion of LG fraction (FS3 and FS4) gave the lowest chemical oxygen demand (COD), biochemical oxygen demand (BOD), volatile organic acids (VOA) and total ammonia nitrogen (TAN) concentrations in the extract and the highest germination indices (GI). The AnC from thermo- digesters showed a lower quality than those from mesophilic reactors (presumably associated to higher contents of VOA and TAN in the extracts), while AnC from digesters at 23 day-MRT had a better quality than those from reactors operated at 16-day-MRT. Overall, AnC generated in reactors fed with FS3 and FS4, at 35°C and 23 day-MRT showed the highest quality. Heavy metal concentrations in all the AnC were lower than the maximum levels indicated in USA and European compost quality standards. However, high total oxygen uptake (UAD), moderate-to-high concentrations of VOA and GIs under 60% indicated that the AnC was not suitable for direct use as a soil improver. Regarding the aerobic post-composting, operation at longer MRT (10 day) and 55°C gave aerobic composts of better quality than those coming from 5 day-MRT composters. Aerobic post-composting caused considerable reductions of TAN, VOA, UAD, immediate oxygen demand rate, and increased compost GI up to approximately 100%.
This work aimed at determining the degree of depuration of a recalcitrant effluent (weak black liquor, WBL) achieved in a series treatment consisting of a first stage methanogenic fluidised bed reactor followed by a second stage aerobic, upflow reactor packed with "biocubes" of Trametes versicolor immobilised onto small cubes of holm oak wood. The mesophilic, lab scale methanogenic fluidised bed reactor contained a microbial consortium immobilised onto granular activated carbon 500 microm average size. The process removed decreasing amounts of organic matter at decreasing hydraulic retention times (HRT), eventually reaching an average of 50% at 0.5 day HRT. Colour and ligninoid removals also decreased with decreasing HRT. Although the methanogenic fluidised bed reactor provided an effective treatment for the degradable organic matter, important concentrations of recalcitrant organic matter and colour still remained in the anaerobic effluent. This anaerobic effluent was fed to the aerobic packed bed reactor. Two HRT were tested in this unit, namely 5 and 2.5 days. The reactor averaged an organic matter removal in the range of 32% COD basis, during an experimental run of 95 days. Colour and ligninoid contents were removed in high percentages (69% and 54%, respectively). There was no significant difference in reactor performance at 5- and 2.5-day HRT. There was a positive correlation between pollutant removal efficiencies and Laccase activity in crude extracts of the reactor liquor. No supplemental soluble carbohydrate was required to sustain the fungus activity and the consistent reactor performance. Overall, the two-stage treatment achieved approximately a 78% removal of the original organic matter of the WBL (COD basis) and ca. 75% of colour and ligninoid contents.
2,4-Dichlorophenoxyacetic acid (2,4-D) is used for commercial herbicides preparation. In Ecatepec, Mexico, there is an industrial plant that manufactures 2,4-D and other herbicides that discharges a low pH, high salinity and 2,4-D rich effluent: a very aggressive and toxic wastewater. This research aimed at acclimating a 2,4-D degrading culture from wild inocula, and implementing and determining the performance of an extractive membrane bioreactor (EMB) for 2,4-D removal from an effluent similar to that industrial wastewater. The experimental work consisted of two phases. In the first phase a mixed, aerobic microbial culture was acclimated to 2,4-D in submerged culture. In the second phase, a lab scale EMB was implemented. The acclimated culture was able to use 2,4-D as the sole source of carbon and energy with an optimum at pH = 8. Gram negative microorganisms predominated in the consortium. The culture growth in 2,4-D followed an Andrews-like substrate inhibition kinetic model with μmax = 0.06 1/h, Ks = 17 mg/L, Ki = 128 mg/L. The hydrophobic membrane had a partition coefficient membrane/water of 131 Laq/Lmembr, which suggested an important adsorption effect/solution in the membrane. The permeability coefficient determined at pH 0, 1 and 4 was practically independent of pH with an average value of 3.2=10-8 m/s. After inoculation, continuous, steady-state experiments were also run at influent 2,4-D concentration of 300 mg/L. The reactor showed 2,4-D unit reductions in the range of 110 to 120 mg 2,4-D/L lumen.h (32 to 34 mg/h.m2) at lumen retention times of 4.1 to 15 min. The unit surface removal rate values in this work compared favourably with literature data for EMB degrading other xenobiotics (for instance, phenol, retention time 353 min, removal rate 94.1 mg/h.m2). Studies are underway to determine 2,4-D removals at longer retention times. Overall, the EMB seems to be an effective configuration for removing 2,4-D while at the same time avoiding the active biomass exposure to the low pH and high salinity concentration of the influent.
The purpose of this work was to evaluate and compare two continuous systems of posttreatment of anaerobically pretreated weak black liquor (WBL). The first system consisted of a packed bed reactor (PBR) with Trametes versicolor (Tv) immobilized on wood cubes of holm oak (biocubes). The second system was a fluidized bed reactor (FBR) with Lentinus edodes (Le) immobilized on wood cubes of holm oak. The reactors operated for 65 days at a hydraulic retention time (HRT) of 5 days, at 28 degrees C, with continuous aeration. Response variables monitored were conventional and specific, unit, net removal efficiency (eta and eta(sun), respectively) of chemical oxygen demand (COD), color, and ligninoids, and enzymatic activities of manganese peroxidase (MnP), lignin peroxidase (LiP), laccase (Lac) and proteases. The PBR showed an average color eta superior to that of the FBR (52.42 +/- 21.78% and 25.34 +/- 14.38% for PBR and FBR, respectively); removals of COD and ligninoids presented a similar pattern to that of color. Lac activity was significantly larger in PBR than in FBR. Activity of MnP in PBR was higher than that of the FBR (0.004 and 0.002 U MnP/mL, respectively). This difference could be ascribed to the different fungi present in each bioreactor. LiP activity was very low in both reactors. Average value of proteases was almost double in the FBR as compared with PBR (0.472 and 0.209 U Proteases/mL, respectively). During the last 2 weeks of operation, biocubes in the FBR experienced a significant loss of the attached Le biomass, probably by attrition. This and higher protease activity in the FBR could explain the lower pollutant removals achieved in the FBR. Overall, PBR with immobilized Tv showed a better performance than the FBR with Le for the posttreatment of the recalcitrant anaerobic effluent. Extended and sustained pollutant removal (65 days) was achieved in the PBR, although more research is needed to evaluate bioreactor performance at shorter hydraulic retention times.
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