Nitrification in multistage horizontal flow treatment wetlands for landfill leachate treatment

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.