Composition and profiles of volatile organic compounds during waste decomposition by the anaerobic bacteria purified from landfill.

Volatile organic compounds (VOCs) become concerned pollutants in landfill gases, and their composition and concentration varied significantly during waste decomposition. Many environmental factors are known to affect VOC emissions, while the effect of indigenous bacteria in wastes on VOC production remains elusive. In this study, a simplified anaerobic degradation experiment, with the single substrate and the purified bacteria from a landfill, was set up to measure the degradation process and the dynamic changes of VOCs. The experiment excluded the abiotic factors for VOC variation. The two isolated bacteria, identified as Sporanaerobacter acetigenes and Clostridium sporogenes, could anaerobically ferment amino acids by Stickland reaction. They produced 51 and 57 species of VOCs in the experiment, respectively. The concentration changes of VOCs over bacterial growth and fermentation were clustered into four types by principal component analysis: three profiles were regular, similar to the variation of nitrate, hydrogen sulfide, and the major fermentation products (carbon dioxide, ammonium, and volatile organic acids), respectively; while one profile was unique to any degradation indicator. The various concentration profiles indicated different origins for VOCs, possibly from the extracellular environment, fermentation, and secondary reactions. The findings provide insights into the understanding of VOC diversity and variability during waste decomposition.

[Community Structure and Succession of Methanogens in Beishenshu Landfill, Beijing].

Methanogens are the key microorganisms for landfill stabilization. RT-PCR and qPCR detecting system were employed to determine the types and abundance of methanogens in 2-15 year-old solid wastes that sampled from Beishenshu Landfill, Beijing. The organic components were almost stable and the pH values were in alkaline range, which indicated that the landfill was in the methanogenic process. Methanobacterials, Methanosaeta, and Methanosarcina were detected, among which Methanosaeta and Methanosarcina are acetoclastic, and Methanobacterials are hydrogenotrophic. As landfill processing, within this time range, although the bacterial abundance was significantly decreased, the amount of methanogens was first increased and then decreased, and finally became stable after being landfilled for 9 years. Methanosarcina was the dominate taxa. Significant correlations were found between the methanogens and the volatile fatty acids, but the correlations between methanogens and larger molecular organic matters were relatively weak or even absent. Taken together, our study revealed that the amount of methanogens were affected by substrates, but hardly influenced by the conversion of large molecules in these wastes landfilled for more than 2 years.

Optimization for municipal solid waste treatment based on energy consumption and contaminant emission.

This paper analyzes the characterization of energy consumption and contaminant emissions from a municipal solid waste (MSW) treatment system that comprises transfer station, landfill site, combustion plant, composting plant, dejecta treatment station, and an integrated MSW treatment plant. The consumed energy and energy medium materials were integrated under comprehensive energy consumption (CEC) for comparison. Among typical MSW disposal methods such as combustion, composting, and landfilling, landfilling has the minimum CEC value. Installing an integrated treatment plant is the recommended MSW management method because of its lower CEC. Furthermore, this method is used to ensure process centralization. In landfill sites, a positive linear correlation was observed between the CEC and contaminant removal ratios when emitted pollutants have a certain weight coefficient. The process should utilize the minimum CEC value of 5.3702 kgce/t MSW and consider energy consumption, energy recovery, MSW components, and the equivalent of carbon dioxide emissions.

Ultrasonic irradiation as pretreatment for the reduction of excess sludge by Fenton-acclimation treatment.

Ultrasonic irradiation as a pretreatment of Fenton-acclimation treatment was investigated to enhance the efficiency of sludge reduction and effectiveness of operating cost. A series of batch experiments were conducted to optimize the reaction conditions for ultrasonic-Fenton treatment. Separate ultrasonic treatment suggested that input power of 0.4 W/mL and ultrasonic time of 10 min were the optimal conditions for sludge disintegration, and the efficiency was reduced with the increase of sludge mixed liquor suspended solids. Separate Fenton treatment revealed that 9 g/L and 40 mg/L were the optimal dosages of H2O2 and Fe(2+) respectively for sludge lysis under pH of 3. Particle distribution (75.49% of the particles distributed between 7.18 and 31.11 µm after Fenton treatment while 93.35% of the particles distributed between 4.62 and 18.50 µm after ultrasonic-Fenton treatment) and chemical oxygen demand (51.89% higher in ultrasonic-Fenton treatment than that in Fenton treatment) demonstrated that combined ultrasonic-Fenton treatment was effective in sludge disintegration compared to separate Fenton treatment. With ultrasound as pretreatment, sludge reduction rate increased from 26.53 to 63.59% with operating cost reduction of 51.46%, indicating ultrasonic irradiation was effective in improving both sludge reduction efficiency and operating cost-effectiveness.

Treatment of anaerobically digested dairy manure in a two-stage biofiltration system.

High concentrations of ammonium and phosphate present a challenge to cost-effective treatment of anaerobically digested dairy manure. This study investigated the efficacy of a two-stage biofiltration system for passive treatment of digested dairy manure. The first stage pebble filters were batch loaded. When the slurry-like digested dairy manure was retained on pebble beds, soluble contaminants were removed before liquid infiltrated over 8-17 days. The pebble filters removed 70% of soluble chemical oxygen demand, 71% of soluble biochemical oxygen demand, 75% of ammonium, and 68% of orthophosphate. Nitrogen removal was attributed to the conventional nitrification - denitrification process and novel nitritation - anammox process. Aerobic ammonium oxidizing and anammox bacteria accounted for 25 and 23% of all bacteria, respectively, in the filtrate of the pebble filters. The longer it took for filtration, the greater the removal efficiency of soluble contaminants. The second stage sand filters had removal efficiencies of 17% for soluble chemical oxygen demand, 45% for soluble biochemical oxygen demand, 43% for ammonium, and 16% for orthophosphate during batch operations at a hydraulic retention time of 7 days. Aerobic ammonium oxidation and anammox were primarily responsible for nitrogen removal in the sand filters. Vegetation made an insignificant difference in treatment performance of the sand filters.