Nitrogen source recovery from mature leachate via heat extraction technology: An engineering project application

Large pool of ammonia in mature leachate is challenging to treat with a membrane bioreactor system to meet the discharge standard for pollution control of municipal solid waste landfills in China (GB 16889-2008) without external carbon source addition. In this study, an engineering leachate treatment project with a scale of 2,000 m3/d was operated to evaluate the ammonia heat extraction system (AHES), which contains preheat, decomposition, steam-stripping, ammonia recovery, and centrifuge dewatering. The operation results showed that NH3-N concentrations of raw leachate and treated effluent from an ammonia heat extraction system (AHES) were 1,305–2,485 mg/L and 207–541 mg/L, respectively. The ratio of COD/NH3-N increased from 1.40–1.84 to 7.69–28.00. Nitrogen was recovered in the form of NH4HCO3 by the ammonia recovery tower with the introduction of CO2, wherein, the mature leachate can offer 37% CO2 consumption. The unit consumptions of steam and power were 8.0% and 2.66 kWh/m3 respectively, and the total operation cost of AHES was 2.06 USD per cubic leachate. These results confirm that the heat extraction is an efficient and cost-effective technology for the recovery of nitrogen resource from mature leachate.

Wedge method for landfill stability analysis considering temperature increase

The increase in landfill temperature often results in shear strength reduction of both the solid waste and the liner, which leads to slope instability. However, very few landfill slope analysis methods can simultaneously consider the effect of temperature on the shear strength of the waste solid and the liner. In this study, based on the strength parameters of the liner and waste with temperature, a wedge method for translational failure analysis of landfills considering temperature increase was established. The results showed that rising temperatures caused by biochemical degradation at the bottom and middle of the landfill reduced the anti-slide force of back slope more than that of bottom slope. With the leachate level increasing, the effect of temperature rise on landfill stability became obvious. The feasibility of the proposed wedge method was verified by the engineering case study of Xiaping Landfill, Shenzhen, China. This study probably provides important guidance for the design, operation and management of municipal solid waste landfills.

Characterization and pollution potential of leachate from urban landfills during dry and wet periods in arid regions

Leachate originating from municipal solid waste landfills poses a serious contamination threat to public health. The study performed a bio-physicochemical characterization of leachate from two landfills in Oman, i.e., Multaqa landfill leachate (MLL) and Barka landfill leachate (BLL) before and after rainfall. Samples were characterized for ninety-two (92) parameters. Additionally, the leachate pollution index (LPI) was estimated to assess. The study found a high value of the leachate parameters without any rainfall incidents. Pearson correlations (±ve) have to be seen more than 90% in all cases, which is a strong association (r>0.75) for the measured parameters in both MLL and BLL. Rainfall significantly reduced the concentrations of organic contaminants and solids in leachate due to dilution. The study revealed about 18–29% and 14–28% reductions in the LPI sub-index for organic and inorganic contaminants, respectively, after the rainfall. The overall LPI values were higher compared to similar findings from the literature. Such deviations could be attributed to the unsegregated nature of solid wastes, resulting in the formation of contaminants or from the disposal of a high volume of solid wastes in a smaller area. Therefore, the study recommends efficient management strategies of landfills to reduce potential leachate groundwater contamination.

Hydrogeochemical assessment of the sorption properties of heavy metals in the areas of the impact of solid waste landfills on groundwater

Изложены основы методики прогнозирования распространения тяжелых металлов на участках загрязнения подземных вод фильтратом полигонов твердых коммунальных отходов. Выполнен анализ качества фильтрата полигонов твердых коммунальных отходов и применимости статистических и эмпирических оценок коэффициента сорбции тяжелых металлов. Показана ограниченность применимости статистических оценок для анализа распространения высокоминерализованных вод фильтратов. На основе методологии геохимического моделирования разработана модель определения коэффициентов обмена между растворенной и твердой фазами – коэффициентов сорбции. Приведены результаты определения коэффициента сорбции для широкого круга катионов применительно к условиям вытеснения природных вод фильтратом полигонов твердых коммунальных отходов. Разработанная методика может быть использована для оценки влияния полигонов твердых коммунальных отходов на качество подземных вод, для прогнозирования распространения тяжелых металлов в области потенциального влияния отходов, для проведения работ в рамках ОВОС (Оценка воздействия на окружающую среду) и ПМООС (Перечень мероприятий по охране окружающей среды), для разработки систем инженерной защиты подземных вод от загрязнения. Предложенная модель может служить основой для ее дальнейшего развития с учетом процессов образования устойчивых органических комплексов металлов в водах фильтрата и комплексообразования на твердой фазе пород. The fundamentals of the method for predicting the spread of heavy metals in the areas of groundwater pollution by leachate from solid municipal waste landfills are stated. The analysis of the leachate quality of municipal solid waste landfills and the applicability of statistical and empirical estimates of the sorption coefficient of heavy metals is carried out. The limited applicability of statistical estimates for analyzing the distribution of highly mineralized leachate is shown. Based on the method of geochemical simulation, a model has been developed for determining the exchange coefficients between the dissolved and solid phases, i. e. sorption coefficients. The results of determining the sorption coefficient for a wide range of cations are presented with regard to the conditions of natural water displacement by the leachate from solid waste landfills. The developed method can be used to estimate the impact of municipal solid waste landfills on groundwater quality, to predict the spread of heavy metals in the area of potential waste impact, to carry out works within the framework of EIA (Environmental Impact Assessment) and LEPM (List of Environmental Protection Measures), to develop systems for engineering protection of groundwater from pollution. The proposed model can serve as a basis for its further improvement with account of the processes of formation of stable organic metal complexes in leachate and complexation on the hard rocks.