Masatsugu Mori

Nitrification of ammonium-rich sanitary landfill leachate

The nitrification of ammonium-rich wastewater is considered challenging due to the substrate inhibition particularly in the form of free ammonia (FA) and free nitrous acid (FNA) in ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The feasibility of the nitrifying activated sludge system to completely nitrify synthetic stabilized landfill leachate with N-NH(4)(+) concentration of 1452mg/L was tested in this study. The process started with 0.4kg N-NH(4)(+)/m(3)/day of nitrogen loading rate (NLR) in a fed-batch mode to avoid any accumulation of the FA and FNA in the system followed by increasing the nitrogen loading rate (NLR) gradually. Complete nitrification was achieved with a very high ammonium removal percentage (approximately 100%). The maximum specific and volumetric nitrification rate obtained were 0.49g N-NH(4)(+)/g VSS/day and 3.0kg N-NH(4)(+)/m(3)/day, respectively which were higher than those reported previously for ammonium-rich removal using activated sludge system. The nitrifying sludge exhibited good settling characteristics of up to 36mL/g VSS and a long SRT of more than 53 days which contributed to the success of the nitrification process. The coexistence and syntrophic association of the AOB and NOB was observed by using Fluorescence in situ hybridization (FISH) technique which supported the results on complete nitrification obtained in the system. These findings would be of prominent importance for further treatment of actual sanitary landfill leachate.

Fluorescent in situ hybridization analysis of open lactic acid fermentation of kitchen refuse using rRNA-targeted oligonucleotide probes

Reproducible amounts of lactic acid accumulate in minced kitchen refuse under open conditions with intermittent pH neutralization [Sakai et al., Food Sci. Technol. Res., 6, 140 (2000)]. Here, we showed that such pH-controlled open fermentation of kitchen refuse reproducibly resulted a selective proliferation of a major lactic acid bacterial (LAB) species. In one experiment, the predominant microorganisms isolated during the early phase (6 h) were Gammaproteobacteria. In contrast, those that predominated during the late phase (48 h) were always Lactobacillus plantarum in three independent experiments. To further quantify the microbial community within open lactic acid fermentation, we performed fluorescent in situ hybridization (FISH) analysis targeting 16S (23S) rRNA. We designed two new group-specific DNA probes: LAC722(L) was active for most LAB including the genera Lactobacillus, Pediococcus, Leuconostoc and Weisella, whereas Lplan477 was specific for L. plantarum and its related species. We then optimized sample preparation using lysozyme and hybridization conditions including temperature, as well as the formamide concentration and the salt concentration in the washing buffer. We succeeded in quantification of microorganisms in semi-solid, complex biological materials such as minced kitchen refuse by taking color microphotographs in modified RGB balance on pre-coated slides. FISH analysis of the fermentation of kitchen refuse indicated that control of the pH swing leads to domination by the LAB population in minced kitchen refuse under open conditions. We also confirmed that L. plantarum, which generates lactic acid in high quantities but with low optical activity, became the dominant microorganism in kitchen refuse during the late phase of open fermentation.

Nitrification of high-strength ammonium landfill leachate with microbial community analysis using fluorescence in situ hybridization (FISH)

Nitrification of mature sanitary landfill leachate with high-strength of N-NH4 + (1080—2350 mg L-1) was performed in a 10 L continuous nitrification activated sludge reactor. The nitrification system was acclimatized with synthetic leachate during feed batch operation to avoid substrate inhibition before being fed with actual mature leachate. Successful nitrification was achieved with an approximately complete ammonium removal (99%) and 96% of N-NH4 + conversion to N-NO- 3 . The maximum volumetric and specific nitrification rates obtained were 2.56 kg N-NH4 + m-3 day-1 and 0.23 g N-NH4 + g-1 volatile suspended solid (VSS) day-1, respectively, at hydraulic retention time (HRT) of 12.7 h and solid retention time of 50 days. Incomplete nitrification was encountered when operating at a higher nitrogen loading rate of 3.14 kg N-NH4 + m-3 day-1. The substrate overloading and nitrifiers competition with heterotrophs were believed to trigger the incomplete nitrification. Fluorescence in situ hybridization (FISH) results supported the syntrophic association between the ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria. FISH results also revealed the heterotrophs as the dominant and disintegration of some AOB cell aggregates into single cells which further supported the incomplete nitrification phenomenon.