An experimental study on the influence of zeolite on changes of pH and alkalinity in anaerobic treatment of compost leachate

With the increase of urbanization, municipal solid waste has also increased. Therefore, the need for solid waste management is also increasing compared with earlier decades. Composting is a good option for the recycling of solid waste; however, it produces leachate, which requires proper treatment systems to prevent environmental degradation. Due to high chemical oxygen demand (COD) concentrations in compost leachate, anaerobic treatment is the best option for handling the effluent, and an anaerobic baffled reactor (ABR) is one such anaerobic reactor that can be used for its treatment. Because of high ammonia and heavy metal concentrations, as well as the possibility of sludge washout in ABRs, it is important to use proper media, such as zeolite, which can reduce inhibition effects and sludge washout from the reactor. Anaerobic treatment, especially during the methanogenesis phase, is sensitive, and pH and alkalinity are parameters that influence the treatment. Therefore, adjusting these parameters within a normal range is very important to the proper functioning of anaerobic systems. In this study, a pilot‐scale ABR was used, and the last 4 of the 8 ABR compartments were filled with zeolite. The bioreactor was operated at hydraulic retention times (HRT) of 3, 4, and 5 days, with zeolite filling ratios of 10%, 20%, and 30%, and influent COD concentrations of 10,000, 20,000, and 30,000 milligrams per liter (mg/L). In this study, pH value was 6.43 ± 0.1, 6.96 ± 0.3, and 6.96 ± 0.25 at filling ratios of 10%, 20%, and 30%, respectively. According to the results, in all filling ratios, no significant changes were observed in the pH value when the organic loading rate increased and its amount was within a constant range. Influent alkalinity was equal to 2015 ± 510, 2884 ± 505, and 4154 ± 233 milligrams of calcium carbonate per liter (mg CaCO₃/L) at influent COD concentrations of 10,000, 20,000, and 30,000 mg/L, respectively, and in effluent, they were 2536 ± 336, 3379 ± 639, and 4377 ± 325 mg CaCO₃/L, respectively. The amount of alkalinity in the effluent increased compared with the alkalinity in the influent. The results show that the amount of alkalinity in the influent and effluent was similar, and the alkalinity enhancement was lower when the filling ratio was increased from 10% to 20%, and 20% to 30%. Comparisons of the results from zeolite with and without biofilm showed that, in cases of zeolite with biofilm, the amounts of silica and oxygen decreased and the amount of carbon increased, and it showed the formation of biofilm on the surface of zeolite. In addition, the absence of sodium in the zeolite with the biofilm indicated that sodium was exchanged with ammonium ions. According to the results, zeolite can be used in anaerobic reactors as a medium, and it also reduces fluctuations in pH and alkalinity at different organic loading rates, providing a normal range for anaerobic treatment.     

污泥堆肥技术现状及应用中需注意的问题

阐述了堆肥技术背景与基本原理。通过对国内示范项目运行情况的研究分析,提出了堆肥处理处置中应注意的工艺选择、处理规模、通风除臭、自动化与可靠性、减量化与稳定化,以及重金属、POPs、经营风险等问题。分析了堆肥处理处置全过程的经济成本,得出了该技术的参考运行成本;给出了该技术的适用条件和发展趋势。     

Environmental assessment of two home composts with high and low gaseous emissions of the composting process

A Life Cycle Assessment (LCA) of two home composts with low and high gaseous emissions of the composting process is presented. The study focused on the gaseous emissions of the composting process. Gaseous emissions of methane, nitrous oxides, ammonia and volatic organic compounds of the composting process were experimentally measured in field real trials. The results showed that the differences in gaseous emissions between the two home composts were 4.5, 5.8 and 52 for methane, nitrous oxides and ammonia, respectively. Higher emissions of nitrous oxides and methane affected significantly the category of global warming potential, while higher emissions of ammonia affected mainly the categories of acidification potential, eutrophication potential and photochemical oxidation. The differences found in the compost emissions were attributable to the composting production management (quality and composition of waste stream, frequency mixing of waste, humidity and temperature monitoring, among others) as well as weather conditions (temperature and humidity).     

Application of processed organic municipal solid waste on agricultural land – a scenario analysis

Source separation, composting and anaerobic digestion, with associated land application, are increasingly being considered as alternative waste management strategies to landfilling and incineration of municipal solid waste (MSW). Environmental life cycle assessments are a useful tool in political decision-making about waste management strategies. However, due to the diversity of processed organic MSW and the situations in which it can be applied, the environmental impacts of land application are very hard to determine by experimental means. In the current study, we used the agroecosystem model Daisy to simulate a range of different scenarios representing different geographical areas, farm and soil types under Danish conditions and legislation. Generally, the application of processed organic MSW resulted in increased emissions compared with the corresponding standard scenarios, but with large differences between scenarios. Emission coefficients for nitrogen leaching to the groundwater ranged from 0.03 to 0.87, while those for nitrogen lost to surface waters through tile drains ranged from 0 to 0.30. Emission coefficients for N₂O formation ranged from 0.013 to 0.022 and for ammonia volatilization from 0.016 to 0.11. These estimates are within reasonable range of observed values under similar conditions. Furthermore, a sensitivity analysis showed that the estimates were not very sensitive to the mineralization dynamics of the processed organic MSW. The results show that agroecosystem models can be powerful tools to estimate the environmental impacts of land application of processed MSW under different conditions. Despite this, agroecosystem models have only been used to a very limited degree for this purpose.     

Effect of environmental parameters on the degradability of polymer films in laboratory-scale composting reactors

Previous research in our laboratory reported a convenient laboratory-scale composting test method to study the weight loss of polymer films in aerobic thermophilic (53°C) reactors maintained at a 60% moisture content. The laboratory-scale compost reactors contained the following synthetic compost mixture (percentage on dry-weight basis): tree leaves (45.0), shredded paper (16.5), food (6.7), meat (5.8), cow manure (17.5), sawdust (1.9), aluminum and steel shavings (2.4), glass beads (1.3), urea (1.9), and a compost seed (1.0) which is designated Mix-1 in this work. To simplify the laboratory-scale compost weight loss test method and better understand how compost mixture compositions and environmental parameters affect the rate of plastic degradation, a systematic variation of the synthetic mixture composition as well as the moisture content was carried out. Cellulose acetate (CA) with a degree of substitution (DS) value of 1.7 and cellophane films were chosen as test polymer substrates for this work. The extent of CA DS-1.7 and cellophane weight loss as a function of the exposure time remained unchanged when the metal and glass components of the mixture were excluded in Mix-2. Further study showed that large variations in the mixture composition such as the replacement of tree leaves, food, meat, and sawdust with steam-exploded wood and alfalfa (forming Mix-C) could be made with little or no change in the time dependence of CA DS-1.7 film weight loss. In contrast, substituting tree leaves, food, meat, cow manure, and sawdust with steam-exploded wood in combination with either Rabbit Choice (Mix-D) or starch and urea (Mix-E) resulted in a significant time increase (from 7 to 12 days) for the complete disappearance of CA DS-1.7 films. Interestingly, in this work no direct correlation was observed between the C/N ratio (which ranged from 13.9 to 61.4) and the CA DS-1.7 film weight loss. Decreasing moisture contents of the compost Mix-2 from 60 and 50 and 40% resulted in dramatic changes in polymer degradation such that CA DS-1.7 showed an increase in the time period for a complete disappearance of polymer films from 6 to 16 and 30 days, respectively.Guest Editor: Dr. Graham Swift, Rohm & Haas.Paper presented at the Bio/Environmentally Degradable Polymer Society—Second National Meeting, August 19–21, 1993, Chicago, Illinois.     

鸡粪腐解过程中不同溶性腐殖质结合铜的变化

以鸡粪为材料,添加不同比例的铜锌进行腐解试验,研究了腐解过程中不同溶性腐殖质结合态铜(水溶性、氢氧化钠溶性、氢氧化钠-焦磷酸钠混合液溶性)浓度的动态变化、受锌含量的影响及其与有效铜的关系.结果表明,粪肥原样H2O-Cu(水溶性腐殖质结合态铜)占其全铜量的10.97%,在腐解过程中先上升后下降;随着粪肥中添加铜量的增加(1:1、2:1、3:1处理),H2O-Cu占其全铜的比例相应减少了(平均分别占其全铜的比例的7.10%、5.18%和3.74%);H2O-Cu随着腐解时间延长呈增加趋势;在腐解的后期(45、60d),粪肥中锌含量的增加会降低H2O-Cu含量.腐解初期粪肥原样NaOH浸提腐殖质-铜(NaOH-Cu)占其全铜量的70.87%,随腐解进行其比例大幅度下降;NaOH-Cu占其全铜的比例随着加入铜的增大而有所下降,分别为55.59%、46.04%和38.08%,且随着腐解时间延长呈下降趋势;粪肥中锌含量的增加对NaOH-Cu含量变化影响较小.粪肥原样中NaOH-Na4P2O7提取腐殖质结合态铜(NaOH-Na4P2O7-Cu)占其全铜量的24.29%,随腐解过程呈增加趋势,NaOH-Na4P2O7-Cu量随着加入铜量的增加而增加,占其全铜比例的15%～25%;粪肥中锌含量增加对NaOH-Na4P2O7-Cu有促进作用.粪肥添加铜锌后,3种浸提剂提取的可溶性腐殖质结合态铜有55%～80%分配在NaOH的溶液中,10%～30%分配在NaOH-Na4P2O7碱性混合液中,0～10%在水溶液中;随加入铜含量和锌含量的增加,NaOH-Na4P2O7-Cu平均分配比(占3种町浸提性腐殖质-Cu的比例)增加,NaOH-Cu和H2O-Cu的分配比减少.相关性分析结果表明:H2O-Cu、NaOH-Cu和NaOH-Na4P2O7-Cu之间显著正相关,它们与有效铜之间呈显著正相关关系(p<0.01).     

Microbial degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in compost

The microbial degradation of tensile test pieces made of poly(3-hydroxybutyrate) [P(3HB)] or copolymers with 10% [P(3HB-co-10%3HV)] and 20% [P(3HB-co-20%3HV)] 3-hydroxyvaleric acid was studied in small household compost heaps. Degradation was measured through loss of weight (surface erosion) and changes in molecular weight and mechanical strength. It was concluded, on the basis of weight loss and loss of mechanical properties, that P(3HB) and P(3HB-co-3HV) plastics were degraded in compost by the action of microorganisms. No decrease inM _w could be detected during the degradation process. The P(3HB-co-20%3HV) copolymer was degraded much faster than the homopolymer and P(3HB-co-10%3HV). One hundred nine microbial strains capable of degrading the polymersin vitro were isolated from the samples used in the biodegradation studies, as well as from two other composts, and identified. They consisted of 61 Gram-negative bacteria (e.g.,Acidovorax facilis), 10 Gram-positive bacteria (mainlyBacillus megaterium), 35Streptomyces strains, and 3 molds.     

Formation and Emission of N2O and CH4 from Compost Heaps of Organic Household Waster

Composting can be a source of N₂O andCH₄ production. In this investigation, differentcompost heaps of organic household waste weremonitored with the focus on potential formation ofCH₄ and N₂O in the heaps and emission ofthese gases from the heaps. The studied compost heapshad different compost ages, turning intervals andcompost sizes. The analysed compost gases containedbetween 1–3421 L of N₂O-N L^-1 and 0–470 mL of CH₄ L^-1. The emission rates ofN₂O and CH₄ from the compost heaps werebetween 1–1464 mg N₂O m^-2 day^-1 and0–119 000 mg CH₄ m^-2 day^-1. These verylarge differences in compost gas composition andemission indicate the importance of compostmanagement. The results also give an understanding ofwhere in the composting process an increasing emissionof N₂O and CH₄ can occur.     

Refuse treatment options: a case study

Records in public archives were evaluated for the period 1981-1991. Simple surveys of peoples and of technology and physical premises provided insight to gauge the attitudes of a local community in the Melbourne municipality and the Melbourne City Council towards composting of organic waste materials. There is a lag in perception and attitudes between the local community and the local government towards composting of organic refuse as a solid waste treatment option. The simple methodology of the study still made it possible to verify past and present perceptions and attitudes.     

生活垃圾生物处理的研究与展望

综述了国内外生活垃圾生物处理的研究进展和目前生活垃圾微生物研究水平，以及生活垃圾处理发展趋势与新动向，在此基础上提出了生活垃圾处理的建议和展望。