[Short-term monitoring of methane emission regulation from a municipal solid waste landfill].

To understand the regulation and influencing factors of methane emission from landfills in China, rates of methane emission from Hangzhou Tianziling municipal solid waste landfill were measured by static chamber technique. The emission rates ranged from 3.67 to 36.65 mmol x (m2 x h)(-1) on average of the two tested points (No. 1 and No. 2) during 24-hour cycle. The max ratio of emission rates between the two tested points was 625. The difference with the rates of the two tested points could be explained by the depth of the cover soils. Rate of methane emission from each point correlated with atmospheric pressure and water content of landfill cover soils, and the result from stepwise regression was r2 = 0.89 for point No. 1, r2 = 0.76 for point No. 2. Rates of methane emission varied from -0.23 to 0.32 mmol (m2 x h)(-1) on average in 40-day test (points with same depth of cover soils). The low correlation (r2 = 0.15) with atmospheric pressure showed that atmospheric pressure was not the decisive factor. For some time, emission rates correlated with water content or temperature of the landfill cover soils significantly, but not obvious (r2 < 0.4) during the whole monitoring time. When atmospheric pressure was included, the results of stepwise regression were improved significantly, which showed that methane emission rates were influenced by different factors, but the effect of each factor was not the same at a different time.

In situ distributions and characteristics of heavy metals in full-scale landfill layers.

The leachate from methanogenic landfill normally contains low concentrations of heavy metals. Little samples had ever been collected from the full-scale landfill piles owing to technical difficulty for well drilling. We drilled two wells in Hangzhou Tianziling landfill, 20 m and 32 m in depth each, and collected solid samples of waste age of 1-4 years from both wells. The total amounts, the sequentially extracted amounts, and the chemical binding forms of heavy metals of the samples collected at different depths were measured. With the correlation between leachate production amount and the yearly rainfall amount, the leached ratio of the heavy metals were estimated only 0.13%, 1.8%, 0.15%, and 0.19% of Cu, Cd, Pb, and Zn, respectively. The heavy metals amounts in the main compositions of MSW, like glass, food waste, paper, coal cinders, were measured using fresh MSW samples. Afterward, the contents of heavy metals initially landfilled were estimated. A positive correlation was noted between the measured and the estimated initial contents of heavy metals, indicating that the low migration of heavy metals in landfill layers. However, among the metals investigated, Zn has shown better mobility inside landfill layers. Acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were measured for all collected samples with optimal reaction conditions identified to yield nearly perfect sulfide recovery as follows: 100 g wet samples, 80 mL min(-1) N(2) flow rate, reaction time of 150 min. The SEM/AVS ratios ranged 25-45, indicating that the AVS was insufficient to immobilize the SEM. Sequential extraction using six-fraction scheme revealed that the sum of exchangeable and the avid soluble fractions of heavy metals follow: Zn>Cd>Cu, Ni, Pb>Cr. The insoluble fraction of heavy metals in MSW was high, for instance, over 80% for Cr and Pb high insoluble fractions of heavy metals in the landfilled MSW and the sorption capability of the methanogenic landfill layers should be responsible to the low concentrations of heavy metals found in leachate.

Microbiological indication of municipal solid waste landfill non-stabilization.

Accidental collapse resulted from unstable factors is an important technological problem to be solved in sanitary landfill. Microbiological degradation of organic matters in landfilled solid waste are an important unstable factor. A landfill reactor was thus manufactured and installed to examine quantitative and population dynamics of microorganisms during degradation of landfilled solid waste. It was showed that unstable landfill can be reflected and indicated by microbiological features such as rapidly decreased growth amount of microorganisms, no detection of fungi and actinomyces, and changing the dominant population into methanogenic bacteria and Acinotobacter.