Evaluation of aerated biofilter systems for microbial methane oxidation of poor landfill gas

In the long-term, landfills are producing landfill gas (LFG) with low calorific values. Therefore, the utilization of LFG in combined heat and power plants (CHP) is limited to a certain period of time. A feasible method for LFG treatment is microbial CH(4) oxidation. Different materials were tested in actively aerated lab-scale bio-filter systems with a volume of 0.167 m(3). The required oxygen for the microbial CH(4) oxidation was provided through perforated probes, which distributed ambient air into the filter material. Three air input levels were installed along the height of the filter, each of them adjusted to a particular flow rate. During the tests, stable degradation rates of around 28 g/(m(3) h) in a fine-grained compost material were observed at a CH(4) inlet concentration of 30% over a period of 148 days. Compared with passive (not aerated) tests, the CH(4) oxidation rate increased by a factor of 5.5. Therefore, the enhancement of active aeration on the microbial CH(4) oxidation was confirmed. At a O(2)/CH(4) ratio of 2.5, nearly 100% of the CH(4) load was decomposed. By lowering the ratio from 2.5 to 2, the efficiency fell to values from 88% to 92%. By varying the distribution to the three air input levels, the CH(4) oxidation process was spread more evenly over the filter volume.     

Performance of a passively vented field-scale biofilter for the microbial oxidation of landfill methane

An upflow biofilter system was operated on a passively vented landfill for the treatment of residual landfill methane. Biofilter methane emissions as a basis for determining methane removal rates were assessed by manual and automated chamber measurements, by measuring methane concentrations in the top layer gaseous phase in combination with gas flow rates, and by evaluating the methane load in the reverse gas flow following the change of landfill gas flux direction as governed by the course of barometric pressure. Methane removal rates were very high with maximum values of 80 g h(-1) m(-3). For the observed cases, the limit of biofilter methane oxidation capacity was not reached and absolute removal rates were thus linearly correlated to the amount of methane entering the filter. The analysis of methane loads flowing back from the biofilter following phases of longer, continuous and non-oscillating landfill gas emission, however, revealed that in these situations biofilter performance is restricted by deficient oxygen supply. At the oxygen-restricted capacity limit, removal rates are influenced by temperature (positively), methane influx (negatively) and flow rate (negatively) as a measure for the displacement of oxygen. These situations, however, account for only 12% of all emission phases. The investigated biofilter capacity, as derived from laboratory analyses of methanotrophic activities, is sufficient to oxidise 62% of the methane load emitted annually. Field and laboratory data provide a stable basis for the dimensioning of filters in future applications.     

The effects of aeration rate on generated compost quality, using aerated static pile method

To determine the most appropriate composting process in an active municipal solid waste system, an experiment was carried out using a nested design method with three aeration rates. During each aeration rate, parameters such as temperature, pH, EC, carbon-to-nitrogen ratio, NO(3)-N, nitrogen, potassium and phosphorous were measured and the efficiency of different composting processes was evaluated. The result of this study showed that the lower and medium aeration rates had a significant impact on nitrogen, carbon-to-nitrogen ratio and temperature profile, while higher aeration rates led to higher EC values. Furthermore, the thermophilic phase lasted 13, 9 and 4 weeks for the aeration rates of 0.4, 0.6 and 0.9 L min(-1)kg(-1), respectively. Accordingly, it was concluded that starting at a rate of 0.6 L min(-1)kg(-1) during first 2 months (about 9 weeks) of the process and continuing at a rate of 0.4 L min(-1)kg(-1)until the end of composting process would result in lower energy consumption.     

An enhanced compost temperature sampling framework: Case study of a covered aerated static pile

Spatial and temporal temperature variations exist in a compost pile. This study demonstrates that systematic temperature sampling of a compost pile, as is widely done, tends to underestimate these variations, which in turn may lead to false conclusions about the sanitary condition of the final product. To address these variations, a proper scheme of temperature sampling needs to be used. A comparison of the results from 21 temperature data loggers randomly introduced into a compost pile with those from 20 systematically introduced data loggers showed that the mean, maximum and minimum temperatures in both methods were very similar in their magnitudes. Overall, greater temperature variation was captured using the random method. In addition, 95% of the probes introduced systematically had attained thermophilic sanitation conditions (?55 °C for three consecutive days), as compared to 76% from the group that were randomly introduced. Furthermore, it was found that, from a statistical standpoint, readings from at least 47 randomly introduced temperature loggers are necessary to capture the observed temperature variation. Lastly, the turning of the compost pile was found to increase the chance that any random particle would be exposed to the temperature ?55 °C for three consecutive days. One turning was done during the study, and it increased the probability from 76% to nearly 85%. Using the Markov chain model it was calculated that if five turnings had been implemented on the evaluated technology, the likelihood that every particle would experience the required time–temperature condition would be 98%.     

Oxygen demand for the stabilization of the organic fraction of municipal solid waste in passively aerated bioreactors

Conventional aerobic waste treatment technologies require the use of aeration devices that actively transport air through the stabilized waste mass, which greatly increases operating costs. In addition, improperly operated active aeration systems, may have the adverse effect of cooling the stabilized biomass. Because active aeration can be a limiting factor for the stabilization process, passive aeration can be equally effective and less expensive. Unfortunately, there are few reports documenting the use of passive aeration systems in municipal waste stabilization. There have been doubts raised as to whether a passive aeration system provides enough oxygen to the organic matter mineralization processes. In this paper, the effectiveness of aeration during aerobic stabilization of four different organic fractions of municipal waste in a reactor with an integrated passive ventilation system and leachate recirculation was analyzed. For the study, four fractions separated by a rotary screen were chosen. Despite the high temperatures in the reactor, the air flow rate was below 0.016 m³/h. Using Darcy’s equation, theoretical values of the air flow rate were estimated, depending on the intensity of microbial metabolism and the amount of oxygen required for the oxidation of organic compounds. Calculations showed that the volume of supplied air exceeded the microorganisms demand for oxidation and endogenous activity by 1.7–2.88-fold.     

Effect of compost treatment of sewage sludge on nitrogen behavior in two soils

This work aims to evaluate the effects of compost treatment of digested sewage sludge on nitrogen behavior in two soils, a Spodosol and an Oxisol soil. Digested sewage sludge was composted with sawdust and woodchips, diluting the total nitrogen to one-fourth (dry mass basis) of its original value. Then, sludge and compost were added to the two soils on an equivalent dry weight basis to consider the risk of NO3- -N leaching. Compost treatment of sewage sludge has slowed down the release of mineral-N to half in the Spodosol and to one-third in Oxisol soil. As a result, NO3- -N concentrations in soils incubated with compost were less than half of the amounts found from soils incubated with digested sludge. Estimates were made of the maximum monthly nitrate to leach from the four combinations of soil and sludge treatment. Application of digested sludge, at a higher nitrogen application rate, resulted in a higher nitrate leaching potential than application of the compost product. Soil type also played an important role, with the Oxisol having slightly higher estimated leaching potential than the Spodosol. The higher nitrate release rate in the Oxisol is counterbalanced by its higher field capacity to lessen the expected difference between the two soils.     

Long-term behavior of municipal solid waste landfills

A method is presented to predict the long-term behavior of element concentrations (non-metals and metals) in the leachate of a municipal solid waste (MSW) landfill. It is based on water flux and concentration measurements in leachates over one year, analysis of drilled cores from MSW landfills and leaching experiments with these samples. A mathematical model is developed to predict the further evolution of annual flux-weighted mean element concentrations in leachates after the “intensive reactor phase”, i.e. after the gas production has dropped to a very low level. The results show that the organic components are the most important substances to control until the leachate is compatible with the environment. This state of low emissions, the so-called “final storage quality”, will take many centuries to be achieved in a moderate climate.     

Treatment of methylacetate waste gas using a trickle-bed air biofilter

The trickle-bed air biofilter (TBAB) performance for methylacetate (MA) removal from waste gases was evaluated under different gas flow rates and influent concentrations. In the pseudo-steady-state conditions, the elimination capacity increased but the removal efficiency decreased with the increase of MA loading. More than 95 and 90% removal efficiencies were achieved for influent MA loadings below 390 and 727 g/m3/h, respectively. The TBAB appears to be a very effective treatment process for controlling MA emission under low to high loading conditions, and the effectiveness could be maintained over 190 days of laboratory operation.     

Zero waste management of spent mushroom compost

Journal of Material Cycles and Waste Management - Edible mushroom are grown commercially using lignocellulosic waste by applying a biological process. However after the harvesting season about 70%...     

Home composting versus industrial composting: Influence of composting system on compost quality with focus on compost stability

Stability is one of the most important properties of compost obtained from the organic fraction of municipal solid wastes. This property is essential for the application of compost to land to avoid further field degradation and emissions of odors, among others. In this study, a massive characterization of compost samples from both home producers and industrial facilities is presented. Results are analyzed in terms of chemical and respiration characterizations, the latter representing the stability of the compost. Results are also analyzed in terms of statistical validation. The main conclusion from this work is that home composting, when properly conducted, can achieve excellent levels of stability, whereas industrial compost produced in the studied facilities can also present a high stability, although an important dispersion is found in these composts. The study also highlights the importance of respiration techniques to have a reliable characterization of compost quality, while the chemical characterization does not provide enough information to have a complete picture of a compost sample.     

Evaluation of Solvita compost stability and maturity tests for assessment of quality of end-products from mixed latrine style compost toilets

It is challenging and expensive to monitor and test decentralized composting toilet systems, yet critical to prevent the mismanagement of potentially harmful and pathogenic end-product. Recent studies indicate that mixed latrine composting toilets can be inhibited by high ammonia content, a product of urea hydrolysis. Urine-diverting vermicomposting toilets are better able to accomplish the goals of remote site human waste management by facilitating the consumption of fecal matter by earthworms, which are highly sensitive to ammonia. The reliability of Solvita® compost stability and maturity tests were evaluated as a means of determining feedstock suitability for vermicomposting (ammonia) and end-product stability/completeness (carbon dioxide). A significant linear regression between Solvita® ammonia and free ammonia gas was found. Solvita® ranking of maturity did not correspond to ranking assigned by ammonium:nitrate standards. Solvita® ammonia values 4 and 5 contained ammonia levels below earthworm toxicity limits in 80% and 100% of samples respectively indicative of their use in evaluating feedstock suitability for vermicomposting. Solvita® stability tests did not correlate with carbon dioxide evolution tests nor ranking of stability by the same test, presumably due to in situ inhibition of decomposition and microbial respiration by ammonia which were reported by the Solvita® CO₂ test as having high stability values.     

Chemical and biological characterization of slaughterhouse wastes compost

The chemical and biological properties of compost made from yard trimmings (YT) composted alone or mixed with slaughterhouse wastes (SHW) were evaluated in seven phases. Mixtures were weighed in a 2:1 proportion (YT:SHW) and placed in composting bins (0.91 m2). Temperature was recorded to determine the time (d) needed to reach the first (1HC) and second heat cycles (2HC). Composting characteristics were measured at 0 d, at the peak of the 1HC and 2HC, and at maturation (0, 20, 50 and 70 d). During 1HC, bacterial isolates were cultivated in both treatments and identified using the Biolog System. Chemical composition was statistically analyzed using a 2 (layers of SHW)x7 (composting phases) factorial arrangement of treatments with the ANOVA procedure of SAS. The pH was neutral for YT and ranged from 7.41 to 6.82 for SHW throughout the process. There was a decrease in organic matter (OM) and carbon (C), and a relative increase in nitrogen (N) in both treatments. At 70 d of maturation, C:N values were similar between treatments, but lower (P>0.05) than the initial values. Final N concentration was higher (P>0.05) for the treatment with SHW. Only the SHW treatment exhibited thermophilic temperatures. At the 1HC in both treatments, different populations of bacteria responsible for the breakdown of OM were identified showing an active heterogeneous population. The presence of pathogenic microorganisms was not detected in treatments containing SHW.     

CIELAB color variables as indicators of compost stability

The composting process of different organic wastes both in laboratory and on a large-scale was characterized using CIELAB color variables to evaluate compost stability for the better application in agriculture. The time courses of the CIELAB variables of composting materials were determined directly from the bottom of a glass petri dish filled with dried and ground samples using a Minolta Color Reader (CR-13) calibrated with clean empty petri dishes placed on a white tile. To compare the proposed method with conventional methods, the same materials were also evaluated using commonly used compost stability evaluation indices. Most of the CIELAB variables of a compost made from a mixture of green tea waste and rice bran reached a plateau after 84 days of composting and showed strong relationships with the commonly used compost stability evaluation indices. The time needed for CIELAB variables, especially the L*and b* values, to stabilize at large-scale composting plants of cattle litter, farmyard manure, kitchen garbage and bark compost, were more or less similar to the times of maturation evaluated by the respective compost producers. The CIELAB color variable offers a new, simple, rapid and inexpensive means of evaluating compost stability and its quality prior to agricultural use.     

Application of sewage sludge compost on highway embankments

More and more sewage sludge is being produced in China. Safe and economical methods for sewage sludge disposal should be found considering the increase in sewage treatment. In order to verify the feasibility of sludge disposal on newly built highway embankments, five treatments (0, 15, 30, 60 and 120 tons ha⁻¹) of sewage sludge compost (SSC) were added to a silty-clay embankment soil on the Xi-Huang highway. The results showed that amendment with SSC increased soil available N, available P, organic matter, cation exchange capacity, and water content, and decreased soil bulk density. Application of SSC enhanced ryegrass growth and reduced runoff and soil erosion. Heavy metal losses from sediments in runoff remained constant or decreased relative to the control until a rate of 60 tons ha⁻¹ was exceeded, when heavy metal losses appeared to increase.     

Physical analyses of compost from composting plants in Brazil

Nowadays the composting process has shown itself to be an alternative in the treatment of municipal solid wastes by composting plants. However, although more than 50% of the waste generated by the Brazilian population is composed of matter susceptible to organic composting, this process is, still today, insufficiently developed in Brazil, due to low compost quality and lack of investments in the sector. The objective of this work was to use physical analyses to evaluate the quality of the compost produced at 14 operative composting plants in the Sao Paulo State in Brazil. For this purpose, size distribution and total inert content tests were done. The results were analyzed by grouping the plants according to their productive processes: plants with a rotating drum, plants with shredders or mills, and plants without treatment after the sorting conveyor belt. Compost quality was analyzed considering the limits imposed by the Brazilian Legislation and the European standards for inert contents. The size distribution tests showed the influence of the machinery after the sorting conveyer on the granule sizes as well as the inert content, which contributes to the presence of materials that reduce the quality of the final product.     

Assessment of compost dosage in farmland through ecotoxicological tests

A research project was carried out to evaluate ecotoxicological effects of mature compost addition to agricultural soil, using a battery of ecotoxicological tests. The following species were selected: plant of Lepidium sativum, earthworm Eisenia foetida, aquatic crustacean Daphnia magna and bacteria Vibrio fischeri. The tests were classified as “direct tests” using solid compost samples and “indirect tests” using compost leaching test eluate. The direct bioassays were performed using compost added to artificial soil in concentrations ranging from 2.5 to 100 % (w/w); the indirect ones considered compost eluate, added to a standard solution in the same concentrations used in the direct tests. Both tests aimed at obtaining the ecotoxicological parameters (LC₅₀ and EC₅₀). These values were then utilized to implement the Species Sensitivity Distribution (SSD) analysis and extrapolate the Hazard Concentration (HC), a useful threshold to preserve the biodiversity of agricultural ecosystems. Results indicated an increase in compost toxicity with greater compost concentrations; in particular, for direct tests compost dosage below 10 % showed low toxicity, while for indirect ones the toxicity was higher. Furthermore, SSD analysis showed a Hazardous Concentration (HC₅) for direct bioassays of 3.5 % and for indirect of 14 %.     

生物滴滤塔处理模拟印刷有机废气

选取甲苯、乙酸乙酯为目标污染物模拟印刷有机废气,采用生物滴滤塔对其进行处理。从某污水处理厂曝气池活性污泥中筛选出3株能够高效降解甲苯、乙酸乙酯的优势菌种,经鉴定分别为枯草芽孢杆菌（Bacillus subtilis）、蜡状芽胞杆菌（Bacillus cereus）和嗜麦芽寡养单胞菌（Stenotrophomonas maltophilia）。实验结果表明：增大乙酸乙酯配比对VOCs去除率影响不大,而增大甲苯配比导致VOCs去除率下降明显;在进气VOCs质量浓度为约800 mg/m³（甲苯与乙酸乙酯的体积比1∶1）、气体空床接触时间为300 s、菌液喷淋量为800 L/h、菌液温度为25 ℃的条件下,VOCs去除率可达约99%。生物滴滤塔运行一段时间后,对菌种进行再鉴定,结果与处理前一致。     

Treatment of waste gas containing monomethylamine in a biofilter enriched with Pseudomonas mendocina

Waste gas containing monomethylamine (MMA) was treated in a biofilter packed with compost along with wood chips and enriched with Pseudomonas mendocina. The biofilter could remove MMA to the extent of more than 99% at a loading of 42.36 gm(-3)h(-1) with an empty bed retention time of 12s. At optimal operating conditions, the moisture content in the biofilter was maintained at around 45%. The biodegradative products of MMA were ammonia, nitrite, and nitrate.