Performance evaluation of startup for a yeast membrane bioreactor (MBRy) treating landfill leachate

Landfill leachate treatment using fungi and fungal enzymes: a review

Landfill leachate raises a huge risk to human health and the environment as it contains a high concentration of organic and inorganic contaminants, heavy metals, ammonia, and refractory substances. Among leachate treatment techniques, the biological methods are more environmentally benign and less expensive than the physical-chemical treatment methods. Over the last few years, fungal-based treatment processes have become popular due to their ability to produce powerful oxidative enzymes like peroxidases and laccases. Fungi have shown better removal efficiency in terms of color, ammonia, and COD. However, their use in the treatment of leachate is relatively recent and still needs to be investigated. This review article assesses the potential of fungi and fungal-derived enzymes in treating landfill leachate. The review also compares different enzymes involved in the fungal catabolism of organic pollutants and the enzyme degradation mechanisms. The effect of parameters like pH, temperature, contact time, dosage variation, heavy metals and ammonia are discussed. The paper also explores the reactor configuration used in the fungal treatment and the techniques used to improve leachate treatment efficacy, like pretreatment and fungi immobilisation. Finally, the review summarises the limitations and the future direction of work required to adapt the fungal application for leachate treatment on a large scale.

Technical and economic evaluation of the integration of membrane bioreactor and air-stripping/absorption processes in the treatment of landfill leachate

A membrane bioreactor inoculated with commercial baker's yeast (Saccharomyces cerevisiae) (MBRy) integrated to an air-stripping/absorption (AS/AB) as pre-treatment (aiming ammonia recovery) or a post-treatment (polishment step) was assessed for the landfill leachate treatment. The effect of chemical oxygen demand (COD) and nitrogen (N) ratio (C:N) on the performance of the MBRy was also investigated. At high COD/N ratio, high organic matter removal in terms of COD (71 ± 4%) and ammonia removal (97 ± 3%) was observed. Lower COD/N ratio favored yeast growth in the mixed liquor even under adverse conditions. The results of ammonia removal and recovery, and economic analysis demonstrated that the best way to integrate the AS/BS processes is as pre-treatment of MBRy. The ammonia concentration in the AS/AB process feed was a key factor to achieve the market specification. Although pH and temperature adjustment were adequate to promote ammonia removal/recovery, the AS operation at high temperatures showed the highest ammonia removal rate (99%). Therefore, the integration of AS/AB with MBRy allows obtaining a permeate with a final concentration of 2902 ± 374 mg L^-1 of COD and 9 ± 7.5 mg L^-1 of ammonia. Although it was possible to reach the Brazilian discharge standard for ammonia (20 mg L^-1), it was not possible to reach the standard for COD, where the remaining fraction is recalcitrant organic matter, requiring the integration of a physico-chemical process. It should be noted that the proposed route allowed recovery 7 kg of ammonia per m³ of treated leachate.

Combining yeast MBR, Fenton and nanofiltration for landfill leachate reclamation

This study investigated the best way to combine nanofiltration (NF) and Fenton with membrane bioreactor inoculated with Saccharomyces cerevisiae (MBRy) for the treatment of landfill leachate, aiming at compliance with legislation and water reuse. Firstly, the permeate from MBRy was treated by Fenton process followed by NF (MBRy - Fenton - NF). Another alternative evaluated was the polishment of MBRy permeate by NF and treatment of NF concentrate by Fenton process (MBRy - NF - Fenton_{(concentrate)}). COD removal in the Fenton step was optimized according to central composite design (CCD) and 85.5% removal was obtained at pH = 3, Fe²⁺:H₂O₂ molar ratio = 1:9.81 and C:H₂O₂ molar ratio = 1:1.14. Increased toxicity was observed with the Fenton application (EC₅₀ = 2.45%). The NF showed the best performance treating the MBRy permeate. High permeate flux (8.9 ± 1.6 L h^-1 m^-2) and ion rejection (82 ± 4.2%), and low membrane fouling was observed in this condition. Although both NF permeate presented potential for reuse, the final COD concentration was lower in the MBRy - Fenton effluent (88 mg L^-1). The Fenton application for the NF concentrate was able to remove 87.24% of COD. With a preliminary economic analysis, it was verified that the MBRy - NF - Fenton_{(concentrate)} combination is the most advantageous due to the lower chemical reagent and membrane area requirements. Thus, this route presents itself as an alternative for landfill leachate reclamation.

Evaluation of fouling mechanisms in nanofiltration as a polishing step of yeast MBR-treated landfill leachate

The aim of this study was to evaluate the nanofiltration process as a polishing step of a membrane bioreactor inoculated with commercial baker yeast (Saccharomyces cerevisiae) used to treat sanitary landfill leachate. The contaminants retention and influence of concentration polarization and fouling phenomena on the permeate flux decline (FD) at different operating pressures were analysed. The greatest total flux reductions of 63.57% and 70.83% were observed for the lowest and the highest pressures, respectively, being this reduction attributed mainly to the concentration polarization. Membrane itself and concentration polarization phenomena were the main resistances to the nanofiltration process. Hermia model adjustment to the experimental data revealed that cake formation was the main mechanism that explained the FD at pressures of 8, 10 and 12 bar. At recovery rates above 40%, there was a significant decrease in permeate quality, so this value was chosen as the viable value for the proposed system. Integrated MBR-nanofiltration system led to the high removal of pollutants and made the treated effluent feasible for reuse in the landfill itself.

Leachates and natural organic matter. A review of their biotreatment using fungi

Leachates have different concentrations of organic matter and levels of biodegradability, depending on the age of the landfill and they must be treated using appropriate techniques, such as fungal degradation, in order to protect the environment and water resources. Natural organic matter contains the same type of organic species as old and medium age leachates, but at lower concentrations. The present study compiles and assesses all the available literature on the biotreatment of these compounds, mainly humic acids, by fungi. It was found that the efficiency of the fungal biodegradation of these wastewaters depends on the characteristics and concentration of the organic matter in the leachate, the microorganisms selected and whether they were immobilized or not, the nutrients present in the medium and their concentrations, the experimentation time, the temperature and the pH. The influence of the mode of inoculation has only been studied in natural organic matter, but similar effects are expected in the treatment of the leachates. The interactions between these parameters are complex and the optimal conditions have to be determined by laboratory and pilot testing, employing multivariate statistical techniques and experimental design.