Nitrification in multistage horizontal flow treatment wetlands for landfill leachate treatment

Sequential treatment of young landfill leachate by aeration and UV/US/activated persulfate-hydrogen peroxide: performance, optimization and phytotoxicity evaluation

A comprehensive treatment approach for young leachate landfill (YLL) from Fez City was investigated using an integral system involving aeration as a pretreatment before the binary oxidation process using hydrogen peroxide (HP)/persulfate (PS) as oxidants, in which UV-A irradiation and ultrasonic (US) are used as activators (HP-PS-US-UV-A). The initial treatment by aeration resulted in COD, color, and Abs254 removal efficiencies of 54%, 61%, and 55%, respectively. The efficiency of the AOP was statistically evaluated, and the optimal operating conditions were determined by Box-Behnken design (BBD) to investigate the effects of three operating variables (pH, [S2O82-], and [H2O2]) on three target responses: COD, Abs254, and color removal. The statistical and graphical analyses indicated that the sequential process with aeration as pretreatment and subsequent application of the HP-PS-US-UV-A system achieves cumulative maximum removal of 89% of COD, 99% of color, and 96% of Abs254, under the optimal operating conditions of the H2O2/S2O82-/UV-A/US process as [H2O2] = 500 mg/L, [S2O82-] = 1671 mg/L, and pH = 3. Microbiological analyses showed complete removal of total coliforms, fecal coliforms, and total mesophilic flora using sequential application of AOPs and aeration treatment. Using the bioindicators of Medicago sativa (Alfalfa), namely seed germination and root elongation, the phytotoxicity of both treated and untreated leachate samples was assessed. Results showed a noteworthy phytotoxicity decrease by applying the combined processes. The outcomes were remarkable, not only were exceptionally high pollutant removal rates achieved, but it was also discovered that the treated landfill leachate could meet environmental standards for reuse in industrial processes or even in agriculture. This innovation not only provides a solution for the efficient treatment of young landfill leachate but also opens the door to new applications for landfill leachate reuse on a broad scale, contributing to global sustainability efforts.

Comparative assessment of energy generation from ammonia oxidation by different functional bacterial communities

Bioelectrochemical ammonia oxidation (BEAO) in a microbial fuel cell (MFC) is a recently discovered process that has the potential to reduce energy consumption in wastewater treatment. However, level of energy and limiting factors of this process in different microbial groups are not fully understood. This study comparatively investigated the BEAO in wastewater treatment by MFCs enriched with different functional groups of bacteria (confirmed by 16S rRNA gene sequencing): electroactive bacteria (EAB), ammonia oxidizing bacteria (AOB), and anammox bacteria (AnAOB). Ammonia oxidation rates of 0.066, 0.083 and 0.082 g NH₄⁺-N L^-1 d^-1 were achieved by biofilms enriched with EAB, AOB, and AnAOB, respectively. With influent 444 ± 65 mg NH₄⁺-N d^-1, nitrite accumulation between 84 and 105 mg N d^-1 was observed independently of the biofilm type. The AnAOB-enriched biofilm released electrons at higher potential energy levels (anode potential of 0.253 V vs. SHE) but had high internal resistance (R_int) of 299 Ω, which limits its power density (0.2 W m^-3). For AnAOB enriched biofilm, accumulation of nitrite was a limiting factor for power output by allowing conventional anammox activity without current generation. AOB enriched biofilm had R_int of 18 ± 1 Ω and yielded power density of up to 1.4 W m^-3. The activity of the AOB-enriched biofilm was not dependent on the accumulation of dissolved oxygen and achieved 1.5 fold higher coulombic efficiency when sulfate was not available. The EAB-enriched biofilm adapted to oxidize ammonia without organic carbon, with R_int of 19 ± 1 Ω and achieved the highest power density of 11 W m^-3. Based on lab-scale experiments (scaling-up factors not considered) energy savings of up to 7 % (AnAOB), 44 % (AOB) and 475 % (EAB) (positive energy balance), compared to conventional nitrification, are projected from the applications of BEAO in wastewater treatment plants.

High organic removal of landfill leachate using a continuous flow sequencing batch biofilm reactor (CF-SBBR) with different biocarriers

Landfill leachate contains many pollutants that have a negative effect on the environment when improperly discharged. Thus the treatment of landfill leachate is a crucial issue, especially in the bigger cities in developing countries. In this study, landfill leachate is treated using a continuous flow sequencing biofilm batch reactor (CF-SBBR) with different biocarriers (non-carrier (NC), kaldness ^K1 (K1), mutag biochip 30™ (MB), and sponge polyurethane (SP)). The results show that the best COD, TOC, and NH₄⁺-N removal efficiencies were 79.6 ± 0.8%, 78.1 ± 1.9% and 77.5 ± 3.9% in the MB biocarriers tank with an aeration/mixing ratio of 1.3, a cycle time of 9 h and an organic loading rate (OLR) of 1.74 kgCOD/m³.d. The TN removal efficiencies was decreased when there was an increase in the biocarrier's surface area (NC > K1 > MB > SP). At the highest it was 46.1 ± 6.4%, where the aeration/mixing ratio was 1.3, the cycle time was 9 h, and the OLR was 1.52 kgCOD/m³.d. The higher the surface area of the biocarriers, the greater the anti-shock organic loading capacity of the biocarriers due to the formation of biofilm layers. The microbial communities in the CF-SBBR tanks were abundant with common phylum bacteria as in a conventional activated sludge system. Anammox candidatus bacteria was found to total 0.5%. This study concluded that CF-SBBR is an efficient method to treat landfill leachate.