Characteristics of leachate from refuse transfer stations in rural China

The properties of leachate from refuse transfer stations (RTSs) in rural China were indefinite. In this study, a total of 14 leachate samples from RTSs in nine provinces of China were characterized for their pH, electric conductivity, chromaticity, concentration of organic substances, nitrogen distribution, volatile organic compounds (VOCs), organic phosphorous pesticide, and heavy metals. The structural composition of fluorescent dissolved organic matter (FDOM) was also determined. To evaluate the leachate pollution potential in this study, a leachate pollution index was derived and used. Chromium (Cr) was the most polluting heavy metal present in rural leachate. Ethanol and ethyl acetate were the most frequently detected VOCs at high concentrations. Three-dimensional fluorescence excitation-emission matrix spectra were used to characterize the FDOM. Three components, tryptophan (C₁), tyrosine-like (C₂), and humic acid- and fulvic acid-like (C₃) substances, were identified from all 14 samples. Tryptophan was the major component of FDOM and present in 45.7% of the samples by calculating the fluorescence intensity percentage, on average. Pearson correlations revealed that the fluorescence intensity of C₁ and C₃ was strongly related to soluble chemical oxygen demand and dissolved oxygen carbon, while C₂ had significant positive correlations with ammonia nitrogen and total phosphorus of the solid waste. This study provided detailed data and findings that could serve as a preliminary basis for broadening options for the treatment and management of leachate from rural RTSs in China.

Rural solid waste-characteristics and leachate pollution assessment for different precipitation levels, China

Open dumping adversely affects the environment and remains the most widely used method for waste disposal in many developing rural areas in China. Information regarding the impact of rural solid waste (RSW) on the environment remains limited. The objectives of this study are to investigate the characteristics of RSW and the impact of different precipitation rates, and to evaluate the contamination potential of RSW using a leachate pollution index (LPI). The study showed that leachate concentration was significantly influenced by precipitation rates at the initial precipitation stages. Precipitation rates of 42.00 mm/day appeared to have the largest dilution effects. In contrast, the concentrations of leachate at rainfall rates of 24.00 mm/day and soaking were steady, and no similar trends were observed. The highest amounts of pollutants in leachate were the result of soaking. In the first week of our experiment, the LPI value for each rural area waste sample rapidly increased with rising precipitation rates from soaking to 42.00 mm/day. However, no significant change in LPI was observed thereafter (after 5 weeks) even with increasing precipitation rates. The values of chemical oxygen demand, biochemical oxygen demand, total nitrogen, and NH₃-N in the leachate after 10 weeks were 4.00, 7.34, 1.87, and 2.21 times higher, respectively, than those of the prescribed leachate quality standards in China. The results of our study suggest the following course of action for the three dump sites investigated: in Banqiao, given the size of the population and the size of the waste amount, landfill might be a suitable way for disposing of RSW. In Machen, building a standardized waste collection site would be an economical solution for reducing potential pollution risks. In Jiuduhe, increasing the transportation rate of solid waste might be an effective solution. The results of this study can help to improve the understanding of leachate pollution in Chinese rural areas.

Municipal landfill leachate characteristics and feasibility of retrofitting existing treatment systems with deammonification - A full scale survey

Leachate characteristics, applied technologies and energy demand for leachate treatment were investigated through survey in different states of Germany. Based on statistical analysis of leachate quality data from 2010 to 2015, almost half of the contaminants in raw leachate satisfy direct discharge limits. Decrease in leachate pollution index of current landfills is mainly related to reduction in concentrations of certain heavy metals (Pb, Zn, Cd, Hg) and organics (biological oxygen demand (BOD₅), chemical oxygen demand (COD), and adsorbable organic halogen (AOX)). However, contaminants of concern remain COD, ammonium-nitrogen (NH₄N) and BOD₅ with average concentrations in leachate of about 1850, 640, and 120 mg/L respectively. Concentrations of COD and NH₄N vary seasonally, mainly due to temperature changes; concentrations during the first quarter of the year are mostly below the annual average value. Electrical conductivity (EC) of leachate may be used as a time and cost saving alternative to monitor sudden changes in concentration of these two parameters, due to high correlations of around 0.8 with both COD and NH₄N values which are possibly due to low heavy metal concentrations in leachate. The decreased concentrations of heavy metals and BOD₅ favor the retrofitting of an existing biological reactor (nitrification/denitrification) with the deammonification process and post denitrification, as this lowers average annual operational cost (in terms of energy and external carbon source) and CO₂ emission by €25,850 and 15,855 kg CO_2,eq respectively.

Influence of aeration modes on leachate characteristic of landfills that adopt the aerobic-anaerobic landfill method

As far as the optimal design, operation, and field application of the Aerobic-Anaerobic Landfill Method (AALM) are concerned, it is very important to understand how aeration modes (different combinations of aeration depth and air injection rate) affect the biodegradation of organic carbon and the transformation of nitrogen in landfill solid waste. Pilot-scale lysimeter experiments were carried out under different aeration modes to obtain detailed information regarding the influence of aeration modes on leachate characteristics. Results from these lysimeter experiments revealed that aeration at the bottom layer was the most effective for decomposition of organic carbon when compared with aeration at the surface or middle layers. Moreover, the air injection rate led to different nitrogen transformation patterns, unlike the lesser influence it has on organic carbon decomposition. Effective simultaneous nitrification and denitrification were observed for the aeration mode with a higher air injection rate (=1.0 L/min). On the other hand, the phenomenon of sequenced nitrification and denitrification could be observed when a low air injection rate (=0.5L/min.) was employed. Finally, it is concluded that, for AALM, air injection with a higher air injection rate at the deepest layer near the leachate collection pipe tends to accelerate the stabilization of landfill waste as defined in terms of the enhancement of denitrification as well as organic carbon decomposition.