Soil Heavy Metal Pollution Assessment Near the Largest Landfill of China

To assess the extent and potential hazards of heavy metal pollution at Shanghai Laogang Landfill, the largest landfill in China, surface soil samples were collected near the landfill and concentrations of Cu, Zn, Cd, Pb, and Cr were determined. The results revealed that the concentrations of heavy metals, except Pb, were higher in the surface soil near the landfill than in the background soil. Principal component analysis and hierarchical cluster analysis suggested that the enrichment of Cu in soil was probably related to agricultural activities and Cd and Pb to landfill leachates, whereas Zn and Cr concentrations were probably controlled by soil matrix characteristics. The pollution indices (PIs) of the metals were: Cd > Cu > Cr > Zn > Pb. Among the five measured metals, Cd showed the largest toxic response and might cause higher ecological hazards than other metals. The integrated potential eco-risk index (RI) of the five metals ranged from 26.0 to 104.9, suggesting a low-level eco-risk potential. This study indicated the accumulations of Cu, Zn, Cd, Pb, and Cr did not reach high pollution levels, and therefore posed a low eco-risk potential in surface soil near the landfill.     

Effects of copper on expression of methane monooxygenases,trichloroethylene degradation,and community structure in methanotrophic consortia

Copper plays a key role in regulating the expression of enzymes that promote biodegradation of contaminants in methanotrophic consortia (MC). Here, we utilized MC isolated from landfill cover to investigate cometabolic degradation of trichloroethylene (TCE) at nine different copper (Cu²⁺) concentrations. The results demonstrated that an increase in Cu²⁺ concentration from 0 to 15 μM altered the specific first‐order rate constant k_1,TCE, the expression levels of methane monooxygenase (pmoA and mmoX) genes, and the specific activity of soluble methane monooxygenase (sMMO). High efficiency TCE degradation (95%) and the expression levels of methane monooxygenase (MMO) were detected at a Cu²⁺ concentration of 0.03 μM. Notably, sMMO‐specific activity ranged from 74.41 nmol/(mg_cell h) in 15 μM Cu²⁺ to 654.99 nmol/(mg_cell h) in 0.03 μM Cu²⁺, which contrasts with cultures of pure methanotrophs in which sMMO activity is depressed at high Cu²⁺ concentrations, indicating a special regulatory role for Cu²⁺ in MC. The results of MiSeq pyrosequencing indicated that higher Cu²⁺ concentrations stimulated the growth of methanotrophic microorganisms in MC. These findings have important implications for the elucidation of copper‐mediated regulatory mechanisms in MC.     

An influence of methane concentration on the methanotrophic activity of a model landfill cover

Evaluation of kinetic parameters of methane oxidation under various conditions, on the basis of an analysis of the literature and the authors’ own laboratory research, is presented. Variation in methanotrophic activity in the profile of a simulated landfill cover was observed. The greatest activity was found at a depth of 60 cm. A low affinity (1/K_M) and high potential activity (V_max) were observed. V_max values ranged from 0.11 × 10⁻³ to 0.86 × 10⁻³ units. The values of K_M ranged from 0.6 to 2.9% of CH₄ (v/v).     

Parameter and process significance in mechanistic modeling of cellulose hydrolysis

A process-based model relevant to landfill and anaerobic digesters was developed, which included a novel approach to biomass transfer between a cellulose-bound biofilm and biomass in the bulk liquid. Model results highlighted the significance of the bacterial colonization of cellulose particles by attachment through contact in solution. Simulations revealed that both enhanced colonization and cellulose degradation are associated with reduced cellulose particle size, increased biomass populations in solution and increased cellulose-binding ability of the biomass. This suggests that transportation of biomass into the system from elsewhere and/or bacterial inoculation of such systems could enhance degradation significantly. A sensitivity analysis of the system parameters revealed the biological rate and yield properties of the hydrolyzing bacteria are most significant with regard to cellulose degradation in the system.     

Leaching behavior of iron from simulated landfills with different operational modes

The aim of the present study was to investigate the leaching behavior of iron from simulated landfills with different operation modes, with an emphasis on the variation of iron in different oxidation state, ferrous Fe(II) and ferric Fe(III) percentage and the distribution of iron content in different landfill leachate fractions. The leaching behavior and accumulated amounts of iron leached out by leachate from conventional landfill (CL) and leachate recirculated landfill (RL) exhibited decidedly different trends except for the initial 28 days. In addition, the percentage of iron leached from CL and RL accounted 1.00% and 0.14% for the total amount in landfills, respectively. No correlations between iron and selected characteristics in leachate were found were observed in the two simulated landfills. Significant positive correlations between particulate bound iron and Fe(III) were found in the leachates from RL (R² = 0.748) and CL (R² = 0.833).     

Landfill leachate treatment with microbial fuel cells; scale-up through plurality

Three Microbial Fuel Cells (MFCs) were fluidically connected in series, with a single feed-line going into the 1st column through the 2nd column and finally as a single outflow coming from the 3rd column. Provision was also made for re-circulation in a loop (the outflow from the 3rd column becoming the feed-line into the 1st column) in order to extend the hydraulic retention time (HRT) on treatment of landfill leachate. The effect of increasing the electrode surface area was also studied whilst the columns were (fluidically) connected in series. An increase in the electrode surface area from 360 to 1080 cm² increased the power output by 118% for C2, 151% for C3 and 264% for C1. COD and BOD₅ removal efficiencies also increased by 137% for C1, 279% for C2 and 182% for C3 and 63% for C1, 161% for C2 and 159% for C3, respectively. The system when configured into a loop was able to remove 79% of COD and 82% of BOD₅ after 4 days. These high levels of removal efficiency demonstrate the MFC system’s ability to treat leachate with the added benefit of generating energy.     

Long term performance of a constructed wetland for landfill leachate treatment

The constructed wetland (CW) was developed as a pilot integrated system for the capital city's old sanitary landfill site. It consisted of three interconnected beds, two of vertical flow and one of horizontal flow stage. The CW covered 311 m² with an intermittent hydraulic load of 0.5 cm d⁻¹, filled with sand media and planted with reeds and cattails. The performance efficiency of the CW systems was evaluated for 7 years through physical and chemical parameters. Some monitored parameters varied noticeable. The efficiency for COD was 50%, BOD₅ (59%), ammonia nitrogen (51%), nitrate (negative), total phosphorus (P) (53%), sulfates (negative), sulfides (49%), chlorides (35%), and Fe (84%). The average concentrations of suspended solids, COD, BOD₅, nitrate, total P, sulfates, sulfides, and Fe were below limits after treatment. The ratio between N and P showed a limited level of P for biological processes. The performance of the system did not vary significantly with regard to temperature, however, it varied with precipitation. The results showed that the CW system, as a tertiary system or as an independent system, could be a low-cost alternative for the treatment of leachate from old landfill sites.     

Cascade bioreactor with submerged biofilm for aerobic treatment of Tunisian landfill leachate

A bioreactor cascade with a submerged biofilm is proposed to treat young landfill leachate of jbel chakir landfill site south west from capital Tunis, Tunisia. The prototype was run under different organic loading charges varying from 0.6 to 16.3 kg TOC m⁻³ day⁻¹. Without initial pH adjustment total organic carbon (TOC) removal rate varied between 65% and 97%. The total reduction of COD reached 92% at a hydraulic retention time of 36 h. However, the removal of total kjeldahl nitrogen for loading charges of 0.5 kg N m⁻³ day⁻¹ reached 75%. The adjustment of pH to 7.5 improved nitrogen removal to a rate of 85% for loading charge of 1 kg N m⁻³ day⁻¹. The main bacterial groups responsible for a simultaneous removal of organic carbon and nitrogen belonged to Bacillus, Actinomyces, Pseudomonas and Burkholderia genera. These selected isolates showed a great capacity of degradation at different leachate concentrations of total organic carbon.