The application of enzyme activity measurements to a study of factors affecting protein, starch and cellulose fermentation in domestic refuse

Experimental study on anisotropy of hydraulic conductivity for municipal solid waste

Anisotropy of hydraulic conductivity is an important parameter controlling fluid movement in municipal solid waste (MSW) landfills, while measurements of anisotropy are rare. In this study, a laboratory-scale enhanced reactor was built to create MSW samples with different degrees of degradation. Vertical and horizontal hydraulic conductivities of these samples were measured in a self-designed permeameter to study the effects of compression and degradation on anisotropy of MSW. CT scanning was performed to observe the internal pore-structure of MSW under compression. A prediction model of anisotropy under compression was established. It was found that as degradation time increased from 0 month to 18 months, the dry mass percent of 0D particles increased from 12.3% to 38.8%, while 2D particles content decreased from 78.7% to 47.2%. As vertical stress increased from 50 kPa to 400 kPa, dry unit weight (γ_d) increased from 3.26 kN/m³ to 5.51 kN/m³, anisotropy (A) increased from 1.26 to 5.17. It was because that the size and continuity of pores decreased and the angle of pore arrangement tended to be horizontal as the vertical stress increased. The relation between anisotropy and vertical stress could be well fitted with the prediction model. When degradation time increased from 0 month to 18 months, A decreased linearly from 5.02 to 2.75 due to the decreasing content of 2D particles. Anisotropy also decreased with the decreasing C/L. Compression has much greater influence on waste anisotropy than that of degradation. Anisotropy of MSW at different depths of landfills could be determined based on the trend lines in this study.

The Evaluation System of the Sustainable Development of Municipal Solid Waste Landfills and Its Application

Improving the understanding of the stabilization process is of great significance to guide the sustainable development of municipal solid waste (MSW) landfills. An evaluation system of the stabilization process of MSW landfills has been established. The indices of the evaluation system involve the degradation degree of MSW, the release of landfill gas production potential, and the settlement of landfills. Based on the biochemical-consolidation-solute migration coupled model, an evaluation method of the MSW landfill stabilization process is proposed by combining field tests with numerical simulation. The stabilization process of the Jiangcungou landfill in China is investigated by using the proposed method. The analyzed results show that the stabilization process of high kitchen waste content landfills can be divided into three stages, which is different from the stabilization process of landfills in developed countries. For the Jiangcungou landfill, the ratio of cellulose to lignin in MSW decreases rapidly during the fast degradation stage when obvious settlement occurs. During the slow degradation stage, the hydrolysis rate is slow and settlement develops slowly. When the landfill reaches the stabilization stage, the ratio of cellulose to lignin of MSW changes very slowly; most of the landfill gas potential has been released; the settlement stabilization is completed basically. The change processes of the three evaluation indices are different, of which the degradation stabilization index is the main one. According to the findings above, leachate recirculation is recommended to adjust the degradation environment in the landfill, which can be helpful to avoid acidification at the fast degradation stage. Temporary cover is suggested to improve landfill gas collection efficiency at the beginning of the stable methanogenic stage. The landfill site closure should be operated when the settlement rate is low.

Evolution of saturated hydraulic conductivity with compression and degradation for municipal solid waste

Municipal solid waste (MSW) specimens were created from synthetic fresh MSW degraded in a laboratory scale enhanced degradation reactor. The degree of degradation and saturated hydraulic conductivity k_s were measured to study the effects of compression and degradation on k_s of MSW. The degree of degradation was characterized through the ratio of cellulose content to lignin content (i.e., C/L) and the loss ratio of volatile solid (i.e., DOD). k_s of MSW specimens with different degrees of degradation was measured through triaxial permeameter tests under different confining pressures. It was found that, when the degradation time increased from 0month to 18months, k_s decreased less than 1 order of magnitude for specimens with the same porosity (i.e., n=0.63 or 0.69). However, for specimens with the same degradation time, the decrease of k_s could reach 2 orders of magnitude with n decreasing from 0.8 to 0.6. It indicates that compression has much greater influence on the reduction of k_s than that of degradation. Based on the Kozeny-Carman model and first-order kinetics, a prediction model related to n and C/L (or DOD) of MSW was proposed to analyze the evolution of k_s with compression and biodegradation. The methods to determine the values of model parameters were also proposed.

Microbial characteristics associated with six different organic wastes undergoing anaerobic decomposition in batch vial conditions

In this study, the biodegradation characteristics of six plant-based wastes were compared in anaerobic batch vial systems. The highest gas accumulation and methane (CH4) concentrations (approximately 70%) were observed in samples containing copy paper, newspaper and box paper materials, whereas the lowest were observed in samples containing wood and leaves. In samples containing steamed rice and fruit, the methanogenic activity was inhibited, which resulted in acid accumulation. The high biodegradation activity of newspaper samples was also associated with high adenosine triphosphate levels and dehydrogenase activity. No significant differences were, however, observed in the dehydrogenase activity of the samples. High bioluminescence was observed in samples with high biodegradation activities, indicative of low toxicity.

Nitrogen removal in the bioreactor landfill system with intermittent aeration at the top of landfilled waste

High ammonia concentration of recycled landfill leachate makes it very difficult to treat. In this work, a vertical aerobic/anoxic/anaerobic lab-scale bioreactor landfill system, which was constructed by intermittent aeration at the top of landfilled waste, as a bioreactor for in situ nitrogen removal was investigated during waste stabilization. Intermittent aeration at the top of landfilled waste might stimulate the growth of nitrifying bacteria and denitrifying bacteria in the top and middle layers of waste. The nitrifying bacteria population for the landfill bioreactor with intermittent aeration system reached between 10(6) and 10(8) cells/dry g waste, although it decreased 2 orders of magnitude on day 30, due to the inhibitory effect of the acid environment and high organic matter in the landfilled waste. The denitrifying bacteria population increased by between 4 and 13 orders of magnitude compared with conventional anaerobic landfilled waste layers. Leachate NO(3)(-)-N concentration was very low in both two experimental landfill reactors. After 105 days operation, leachate NH(4)(+)-N and TN concentrations for the landfill reactor with intermittent aeration system dropped to 186 and 289 mg/l, respectively, while they were still kept above 1000 mg/l for the landfill reactor without intermittent aerobic system. In addition, there is an increase in the rate of waste stabilization as well as an increase of 12% in the total waste settlement for the landfill reactor with intermittent aeration system.

Forest products decomposition in municipal solid waste landfills

Cellulose and hemicellulose are present in paper and wood products and are the dominant biodegradable polymers in municipal waste. While their conversion to methane in landfills is well documented, there is little information on the rate and extent of decomposition of individual waste components, particularly under field conditions. Such information is important for the landfill carbon balance as methane is a greenhouse gas that may be recovered and converted to a CO(2)-neutral source of energy, while non-degraded cellulose and hemicellulose are sequestered. This paper presents a critical review of research on the decomposition of cellulosic wastes in landfills and identifies additional work that is needed to quantify the ultimate extent of decomposition of individual waste components. Cellulose to lignin ratios as low as 0.01-0.02 have been measured for well decomposed refuse, with corresponding lignin concentrations of over 80% due to the depletion of cellulose and resulting enrichment of lignin. Only a few studies have even tried to address the decomposition of specific waste components at field-scale. Long-term controlled field experiments with supporting laboratory work will be required to measure the ultimate extent of decomposition of individual waste components.

Cellulolytic activity in leachate during leach-bed anaerobic digestion of municipal solid waste

The degradation of municipal solid waste (MSW) under mesophilic conditions can be enhanced by exchanging leachate between fresh waste and stabilised waste. The optimum point in time when leachate from an anaerobically digesting waste bed can be used to initiate degradation of another waste bed might occur when the leachate of the digesting waste bed is highly active with cellulolytic and methanogenic bacteria. In this study, the cellulolytic activity of the leachate was measured using the cellulose-azure assay. As products of hydrolysis are soluble compounds, the rate of generation of these compounds was estimated based on a soluble chemical oxygen demand (SCOD) balance around the fresh waste bed. It was found that once the readily soluble material present in MSW was washed out there was very little generation of SCOD without the production of methane, indicating that flushing leachate from a stabilised waste bed resulted in a balanced inoculation of the fresh waste bed. With the onset of sustained methanogenesis, the rate of SCOD generation equalled the SCOD released from the digester as methane. The experimental findings also showed that cellulolytic activities of the leachate samples closely followed the trend of SCOD generation. reserved.