THE ELEVATED TEMPERATURE AND GAS COMPONENT WITHIN AN OPERATING SEMI-AEROBIC LANDFILL

The semi-aerobic landfill concept, which is based on passive aeration, is the compulsory standard for planning new landfill projects in Japan. The semi-aerobic landfill concept is also applied in several other countries because of its low construction and operating costs. The landfill gas (LFG) component and the LFG temperature are the main indicators of the aerobization of semi-aerobic landfills. Analysis of LFG, its concentration, and its temperature can be easily carried out on-site to evaluate the passive aeration of an operating semi-aerobic landfill. Therefore, this study observed LFG temperatures and LFG components to assess the partial aerobization within an operating semi-aerobic landfill. The observational data revealed that the methane (CH4) gas concentration of most of the main LFG venting pipes (VPs) was below 15%. The aerobic condition happened effectively surrounding the main LFGVP M2 because over the observation period, the ratio of CH4 to CO2 was less than 1.0. The highest gas temperature was above 60°C within the main LFGVP M2, and there was a trend of high temperatures above 40°C for more than 5 years before the temperature declined to 20°C in the most recent observation. The high LFG temperatures were recorded in the winter months due to the buoyancy effect. High temperature and the CH4/CO2 ratio less than 1.0 potentially representing good indicators showed that aerobic decomposition is becoming dominant. The study showed clearly that the aerobic biodegradation performance in this semi-aerobic landfill is extremely good.

Influence of Cowl on the Spatial Distribution of Oxygen in Semi-Aerobic Landfill

To elevate the air flow rate in vent pipes of semi-aerobic landfill, promote oxygen transmit into waste and methane mitigation, a wind-driven cowl was fixed on one of the two semi-aerobic landfills’ vent pipe. With the aim of figuring out the influence of cowl on the spatial distribution of oxygen under different climates, wind speeds were set at 3 m/s, 5 m/s, 7 m/s and 0 m/s sequentially. Oxygen concentrations and temperatures were recorded once a week. Data from experimental results indicated that oxygen concentrations went up along with the height above the bottom of landfill after deducting the oxygen transported by leachate collection pipes. Average oxygen concentrations except the surface layer were 3.5%, 4.2%, 3.8%, 3.0% for S-A with cowl and 2.9%, 3.4%, 3.7%, 3.0% for S-A under the wind speeds of 3 m/s, 5 m/s, 7 m/s, 0 m/s, respectively. Meantime, the aerobic radius in S-A with cowl were 0.84 m, 1.01 m, 0.87 m, 0.62 m and 0.76 m, 0.84 m, 0.87 m, 0.65 m in S-A. The effect of the cowl on oxygen transmission maximized at the wind speed of 5 m/s. It is clearly that wind energy can be better used on enhancing the ventilation in vent pipe and expanding aerobic radius after application of cowl.

Effect of leachate recirculation and aeration on volatile fatty acid concentrations in aerobic and anaerobic landfill leachate

The main aim of this study was to investigate the effect of leachate recirculation and aeration on volatile fatty acid (VFA) concentrations in aerobic and anaerobic landfill leachate samples. In this study, two aerobic (A1, A2) and two anaerobic (AN1, AN2) reactors with (A1, AN1) and without (A2, AN2) leachate recirculation were used in order to determine the change of volatile fatty acids components in landfill leachate. VFA degradation rate was almost 100% in each reactor but the degradation rate show notable differences. In aerobic landfill reactors, total VFA concentrations decreased below 1000 mg L−1 after 120 days of operation and only caproic and acetic acids were determined at this time. The stabilization of the VFA concentrations takes about 350 and 450 days for AN1 and AN2 reactors, respectively. VFA concentrations were higher than that of aerobic reactors because of the acidogenic phase occurred in anaerobic environment. According to the results of VFA components, the stabilization of the waste was achieved after 120 days of operation in aerobic landfills. At this time, anaerobic reactors were in the acidogenic phase which results with the high concentrations of VFA. The results also indicated that leachate recirculation does not affect the degradation rate in aerobic landfills as much as it does in anaerobic landfills