Retrofitting a full-scale multistage landfill leachate treatment plant by introducing coagulation/flocculation/sedimentation and ultrafiltration process steps.

Considering that landfilling still remains among the most commonly used methods for the confrontation of solid wastes, effective methods should be applied to treat the leachate generated, due to its recalcitrant nature. In this work, a full-scale system consisting of two SBRs operating in parallel (350 m3 each) and two activated carbon (AC) columns operating in series (3 m3 each) was retrofitted by introducing a coagulation/flocculation/sedimentation (C/F/S) unit of 7.8 m3 and an ultrafiltration (UF) membrane of 100 m2 to effectively treat landfill leachate. The raw leachate was characterized by high COD and NH4+-N concentration, i.e., 3095 ± 706 mg/L and 1054 ± 141 mg/L respectively, a BOD/COD ratio of 0.22, and high concentrations of certain heavy metals. Leachate processing in this retrofitted multistage treatment system resulted in total COD removal efficiency of 89.84%, with biological treatment, C/F, UF, and AC contributing 46.31%, 4.68%, 15.98%, and 22.87% to the overall organic content removal. The retrofitted scheme achieved an overall NH4+-N and TKN removal of 92.03% and 91.75% respectively, attributed mostly to the activity of an effective nitrifying community. Color number (CN) was reduced by 26.96%, 10.29%, 15.94%, and 5.39% after the activated sludge, the C/F, the UF, and the AC adsorption process respectively, corresponding to a 58.91% overall decrease. Regarding heavy metal removal, all elements examined, apart from Ni, i.e., effluent As, Cd, Co, Cr, Cu, Hg, Mg, Mn, and Pb, were below the legislative limits set by the national authorities for restricted or unrestricted irrigation. Lastly, total operating expenses (OPEX) were estimated as equal to 72,687 €/year or 6.64 €/m3.

Evaluation of electrochemical and O3/UV/H2O2 methods at various combinations during treatment of mature landfill leachate.

In this study, electrochemical treatment and application of O3/UV/H2O2 in various combinations were evaluated in respect to their efficiency to depurate mature landfill leachate. Based on preliminary experiments, electrochemical treatment using stainless-steel electrodes at 2 cm gap was performed optimally at 50 mA/cm2 and pH 6, while application of O3 at 120 L/h, UV at 991 J/cm2 and H2O2 concentration of 1 g/L was carried out. Electrochemical treatment and O3/UV/H2O2 under optimal conditions were applied as follows: I) electrochemical treatment, followed by O3/UV/H2O2 and solids precipitation, II) electrochemical treatment, followed by precipitation and then by O3/UV/H2O2 treatment, and III) O3/UV/H2O2, followed by electrochemical treatment. A low performance was observed when O3/UV/H2O2 preceding electrochemical treatment. Solids, TKN and total COD (tCON) removal was primarily achieved through electrocoagulation, whereas color and soluble COD (sCOD) reduction was mainly attributed to electrochemical oxidation. Experimental setup I was the most efficient treatment scheme, resulting in tCOD, sCOD, TKN, TSS, SACUV254nm and color number reduction of 73%, 80%, 76%, 79%, 94% and 98%, respectively. Indeed, O3/UV/H2O2 step could be omitted since its effectiveness was restricted during landfill leachate treatment. In conclusion, electrochemical treatment followed by precipitation could result in effective reduction of nutrients and color.

Isolation, characterization and industrial application of a Cladosporium herbarum fungal strain able to degrade the fungicide imazalil.

Imazalil (IMZ) is an imidazole fungicide commonly used by fruit-packaging plants (FPPs) to control fungal infections during storage. Its application leads to the production of pesticide-contaminated wastewaters, which, according to the European Commission, need to be treated on site. Considering the lack of efficient treatment methods, biodepuration systems inoculated with tailored-made inocula specialized on the removal of such persistent fungicides appear as an appropriate solution. However, nothing is known about the biodegradation of IMZ. We aimed to isolate and characterize microorganisms able to degrade the recalcitrant fungicide IMZ and eventually to test their removal efficiency under near practical bioengineering conditions. Enrichment cultures from a soil receiving regular discharges of effluents from a FPP, led to the isolation of a Cladosporium herbarum strain, which showed no pathogenicity on fruits, a trait essential for its biotechnological exploitation in FPPs. The fungus was able to degrade up to 100 mg L-1 of IMZ. However, its degrading capacity and growth was reduced at increasing IMZ concentrations in a dose-dependent manner, suggesting the involvement of a detoxification rather than an energy-gain mechanism in the dissipation of IMZ. The isolate could tolerate and gradually degrade the fungicides fludioxonil (FLD) and thiabendazole (TBZ), also used in FPPs and expected to coincide alongside IMZ in FPP effluents. The capacity of the isolate to remove IMZ in a practical context was evaluated in a benchtop immobilized-cell bioreactor fed with artificial IMZ-contaminated wastewater (200 mg L-1). The fungal strain established in the reactor, completely dominated the fungal community and effectively removed >96% of IMZ. The bioreactor also supported a diverse bacterial community composed of Sphingomonadales, Burkholderiales and Pseudomonadales. Our study reports the isolation of the first IMZ-degrading microorganism with high efficiency to remove IMZ from agro-industrial effluents under bioengineering conditions.

NH4+-N versus pH and ORP versus NO3--N sensors during online monitoring of an intermittently aerated and fed membrane bioreactor.

Online sensors, which monitor the ammonia oxidation and the dissimilatory nitrate reduction process, can optimize aerobic and anoxic phase duration. The purpose of this study was to comparatively evaluate the effectiveness of online sensors that were in situ-located in an intermittently aerated and fed membrane bioreactor (IAF-MBR) system. Ammonium and nitrate nitrogen sensors equipped with ion-selective electrodes as well as pH and oxidation-reduction potential (ORP) sensors were employed to online monitoring and optimizing of ammonia oxidation and nitrate reduction processes. The "ammonia valley" or pH bending point, which is indicative of ammonia depletion, was effectively and repeatedly detected by measuring the pH profile, while the "nitrate knee" point, which indicates the completion of the denitrification process, was online-detected by obtaining the ORP profile. The "ammonia valley" and "nitrate knee" were detected at pH and ORP values of 6.47 ± 0.02 and - 162 ± 39 mV, respectively. The ORP and pH first derivatives (dORP/dt and dpH/dt) were found to be more suitable than the untransformed ORP and pH values in detecting pH and ORP inflection points and controlling the shift from the anoxic to the aeration phase. Specifically, the ORP and pH bending points were detected at dORP/dt and dpH/dt values of 1.64 ± 0.82 mV min-1 and 0.005 ± 0.001 min-1, respectively. Moreover, the ORP first derivative has appeared earlier than the ORP bending point.

Biochemical and nutritional characterization of the medfly gut symbiont Enterobacter sp. AA26 for its use as probiotics in sterile insect technique applications.

BACKGROUND: Enterobacter sp. AA26 was recently isolated from the midgut of Ceratitis capitata (Wiedemann) and it was shown to have positive effects in rearing efficiency when used as larval probiotics. In this study, biomass production was carried out in bench-scale bioreactors to elucidate the biokinetic properties of Enterobacter sp. AA26 and its nutritional value. RESULTS: Strain AA26 is a psychrotolerant, halotolerant, facultatively anaerobic bacterium with broad pH range for growth (pH 4 to 10.2), which possessed the typical biochemical profile of Enterobacter spp. The specific oxygen uptake rate (SOUR) was calculated as 63.2 ± 1.26 and 121 ± 1.73 mg O2 g- 1 VSS h- 1, with the yield coefficients in acetate and glucose being equal to 0.62 ± 0.03 and 0.67 ± 0.003 g biomass produced/g substrate consumed, respectively. The maximum specific growth rate (µmax) of strain AA26 grown in fill-and-draw bioreactors at 20 °C and 35 °C was 0.035 and 0.069 h- 1, respectively. Strain AA26 grew effectively in agro-industrial wastewaters, i.e. cheese whey wastewater (CWW), as alternative substrate for replacing yeast-based media. Biomass of strain AA26 could provide all the essential amino acids and vitamins for the artificial rearing of C. capitata. Greater intracellular α- and ß-glucosidase activities were observed during growth of strain AA26 in CWW than in yeast-based substrate, although the opposite pattern was observed for the respective extracellular activities (p < 0.01). Low protease activity was exhibited in cells grown in yeast-based medium, while no lipase activities were detected. CONCLUSIONS: The ability of strain AA26 to grow in agro-industrial wastes and to provide all the essential nutrients can minimize the cost of commercial media used for mass rearing and large scale sterile insect technique applications.

Microbiological and physicochemical evaluation of the effluent quality in a membrane bioreactor system to meet the legislative limits for wastewater reuse.

The aim of this study was to assess the efficacy and effluent quality of a pilot-scale intermittently aerated and fed, externally submerged membrane bioreactor (MBRes) treating municipal wastewater. The effluent quality of the MBRes was evaluated regarding system ability to comply with the Greek legislative limits for restricted and unrestricted wastewater reuse. The average permeate flux was 13.9 L m-2 h-1, while the transmembrane pressure remained above the level of -110 mbar. Experimental data showed that biochemical oxygen demand, chemical oxygen demand, total nitrogen, PO43-- P and total suspended solids removal efficiencies were 97.8, 93.1, 89.6, 93.2 and 100%, respectively, whereas turbidity was reduced by 94.1%. Total coliforms and Escherichia coli were fully eliminated by ultrafiltration and disinfection methods, such as chlorination and ultraviolet radiation. In agreement with the Greek legislation (Joint Ministerial Decree 145116/11) and the guidelines recommended for the Mediterranean countries, the disinfected effluent of the MBRes system can be safely reused directly for urban purposes.