Cost Considerations of Municipal Solid Waste Compost: Production versus Market Price

? As more composting facilities come on line across the United States, and a wider spectrum and greater quantity of organic materials are composted, the need to develop a variety of markets for their end products, i.e., compost or mulch, will become ever more critical to the future growth potential for composting and its success. It is often stated that high quality compost will always find a market. However, the economic implications of producing a high quality compost need to be better understood. Publicly and privately operated composting facilities need to compare the costs for building or improving their composting programs to the associated economic returns, i.e., the increased selling price for their product (or, if the product is not sold, the increased avoided cost for what the compost/mulch product is substituted for) and other economic implications.

The scarcity of published information on the costs of producing marketable compost at U.S. municipal solid waste composting (MSW) facilities is largely due to the minimal experience in producing and marketing these composts in this country. In order to improve both facility operation and compost quality, most facilities that have operated for more than one year are making modifications, particularly in the type of feedstock, front-end process, composting process, and final compost processing. A summary of such changes is presented for nine U.S. plants, but little information is available on the costs of these modifications, nor their impact on compost quality. Information is also presented about the European experience with MSW composting, emphasizing the importance of producing better quality compost, and the need to fully account for the added costs associated with producing a higher quality compost.     

Odour Emissions from Composting Plants

In recognition of the reaction that some odours generate, it is understandable that limits for emissions be established for composting plants, especially when there are residential areas nearby. This paper discusses results of an investigation into the environmental effects of odours from a composting facility. Emissions which are generated during delivery, treatment and composting can be avoided by using closed facilities and exhaust air collection systems, as well as by purification of exhaust air through methods such as biofilters. By using a qualified composting system, emissions can be reduced to an acceptable level.     

立式筒仓反应器堆肥技术工艺优化研究

反应器堆肥技术作为一种新型快速堆肥方式逐渐被人们所认可，该技术包括反应器堆肥处理和陈化两个阶段，但反应器堆肥时长和通气方式等工艺参数对堆肥全过程的影响尚不清楚。因此，本研究立足生产中的实际问题，利用12 m³立式堆肥反应器，开展了反应器堆肥工艺优化调控试验，以鸡粪和锯末为原料，分别研究了连续供气和间歇供气（风机开3 min，关7 min）两种供气方式下，反应器处理周期对堆肥有机质降解率、产品含水率、氮素损失和运行成本的影响。研究结果表明：反应器堆肥10 d比2 d的处理物料有机质降解率分别增加60.7%（间歇）和66.2%（连续），产品含水率分别降低41.2%（间歇）和40.7%（连续）。反应器堆肥阶段是物料降解的主要阶段，利用反应器堆肥的时长越长，堆肥产品生产时间越短；但运行成本的增加也对反应器堆肥时长造成了限制，同时增加反应器堆肥时长也会增加堆肥物料的氮素损失，其中连续供气反应器堆肥10 d比2 d氮素损失增加17.5%。连续供气方式可提高堆肥效率，较间歇供气处理堆肥周期平均缩短32.1%，产品全氮含量平均提高7.4%，虽然反应器堆肥阶段每日能耗较间歇供气高20.2%，但堆肥周期的缩短使全程连续供气平均运行成本降低16.5%。其中，连续供气下反应器中处理6 d、8 d和10 d，堆肥产品理化性质无显著差异。综合考虑堆肥效率、产品和经济，本试验建议选择“连续供气方式+反应器内堆肥8 d”处理，既可提高反应器堆肥处理效率，在实际生产中又具有较高的经济效益潜力。     

Economic Analysis of Composting Crab Processing Waste

A study of composting crab processing waste (CPW) was performed to identify a cost-effective alternative to landfilling. If CPW could be economically recycled into a useful value-added product, the waste would not have to go to landfills, and could be sold commercially to the landscaping and nursery industries. Economic models of three systems were constructed and analyses performed using a variety of investment and operating costs. To ensure robust model analysis, several factors of the cost components were varied. The equivalent-uniform-annual-costs were used to compare the alternatives, Ag-Bag, windrowing, and landfilling the waste. Profit analysis was also performed for each of the proposed systems. The average annual cost for the processes of Ag-Bag 1, Ag-Bag 2, and windrowing was $62,903, $73,796, and $53,533 respectively. While none of the methods analyzed were profitable, windrowing results in the smallest loss of $?0.066/kg ($?63.08/ton) for all economic models considered, followed by Ag-Bag 1 with an average loss of $?0.107/kg ($?100.18/ton) and Ag-Bag 2 with an average loss of $?0.117/kg ($?109.80/ton). Although having the least loss, windrowing has drawbacks such as offensive odors. A sensitivity analysis to determine how much additional throughput would have to be utilized to create a profit was performed. This analysis found that the windrow system is the only system capable of ever garnering a profit, with a total throughput exceeding 1,003 tons/year. Under current market conditions, composting CPW by one of the systems described herein is not feasible.     

Field Performance of Bioretention Systems for Runoff Quantity Regulation and Pollutant Removal

Bioretention systems are of immense importance as they serve as small “sponges” for cities, cutting stormwater runoff, removing pollution, and using precipitation resources. However, performance data for these facilities are generally lacking, particularly at the field scale. This study investigated the runoff quantity regulation and pollutant removal performance of bioswale and rain garden systems from 2014 to 2017. A performance assessment of these facilities demonstrated that anti-seepage rain garden, bioswale-A, and bioswale-B effectively retained inflow volumes by the filter media, reducing runoff volumes by 54.08, 98.25, and 77.65%, respectively, on average, with only two events of overflowing. According to the water quality data in 24 rainfall events, the main pollutant indexes for the new city include total nitrogen and chemical oxygen demand, and the median values for their respective effluent event median concentrations were 1.29 and 40.13 mg/L for anti-seepage rain garden and 1.68 and 74.00 mg/L for bioswale-B systems. The mean values of pollutant removal of the three bioretention systems, except for infiltration rain garden, were 39.8–59.73% (median?=?54.32%), 61.06–72.66% (median?=?73.47%), and 76.67%–88.16% (median?=?80.64%). Meanwhile, outflow volume of water was found to be most influenced by inflow volumes for the bioswales and anti-seepage rain garden. Mass removals were higher than concentrations owing to water volume attenuation. Based on the data of monitored pollution loads, this study estimated the annual pollutant load removal as 75.45 and 90.7% for anti-seepage rain garden and bioswale-B according to the percent of monitoring rainfall depth in total annual precipitation. This study also established the target pollutant service life model on the basis of accumulated annual load and media adsorption capacity. The results of this study will contribute to a greater understanding of the treatment performance of bioretention systems, assisting in the design, operation, and maintenance of them.     

海南省琼海市农村生活垃圾产生特征及就地处理实践

以海南省琼海市某村为研究对象,通过运行新建的农村生活垃圾收集处理示范工程,结合入户调查村民的社会经济状况,研究了海南省农村生活垃圾产生特征,并探讨农村生活垃圾就地处理的可行性。结果发现,以实际居住人口计的农村生活垃圾产生率约为0.227 kg.capita^-1d^-1;其物理组分以易腐垃圾为主,占总量的40.4%±6.3%;惰性垃圾占总量的30.8%±6.2%;有毒有害生活垃圾量极少,占总量的0.1%。示范运行结果表明,以混合收集,人工分拣,可堆肥垃圾就地堆肥、惰性垃圾集中处置为特征的农村生活垃圾就地处理技术,减量率达到50%左右,无害化率达到100%,堆肥产品质量符合现行标准要求,具有技术可行性。示范工程的运行成本为304.5元.t^-1,其中,收集239元.t^-1,分拣和堆肥65.5元.t^-1。按户籍人口计,年人均18.7元,仅为村民年纯收入的0.4%;示范工程运行得到村民的支持与欢迎,村民对垃圾收集处理付费支付意愿高达95%,表明实行村民付费解决长期运行费用具有可行性。     

Moisture Relationships in Composting Processes

Moisture is a key environmental factor that affects many aspects of the composting process. Biodegradation kinetics are affected by moisture through changes in oxygen diffusion, water potential and water activity, and microbial growth rates. These relationships are made more complex by the dynamic nature of the composting process, with changes in particle size and structure occurring over time. A deductive model of the effects of moisture on composting kinetics has defined these relationships based on fundamental physical properties and biological mechanisms. This study applies this model to experimental data from a manure and papermill sludge composting system. The results demonstrate that the optimum moisture content for biodegradation can vary widely for different compost mixtures and times in the composting process, ranging from near 50 to over 70% on a wet basis. While there is a significant reduction in biodegradation rate when operating outside the optimum range, the results also suggest opportunities to mitigate this effect through manipulation of substrate density and particle size. This framework for engineering analysis demonstrates the importance and challenges of maintaining optimum moisture content in dynamic composting systems, where biological drying, metabolic water production, and changes in compaction and porosity are all occurring over time.     

Alkaline Amendment for the Enhancement of Compost Degradation for Polylactic Acid Biopolymer Products

This research evaluates the addition of alkaline amendments to enhance the degradation of polylactic acid polymers (PLA) in compost conditions. The use of compostable biopolymers is increasing in part because they are advertised as compostable. However, PLA degrades slowly compared to the organic wastes in compost and even when processed in commercial composting facilities may not fully break down. This results in the accumulation of biopolymers in compost facilities and increased difficulty in identifying and removing contamination from traditional plastics. Alkaline amendments were used to accelerate the degradation of two PLA products in compost conditions. Six flasks containing food scraps, compost inoculant, and an alkaline amendment were set up as bioreactors with half containing clear PLA and the others including opaque PLA. The six bioreactors were incubated for 22 days. The mass loss and final visual inspection, including microscopy, showed increased degradation within the bioreactors containing the alkaline treatments. These results show that the addition of alkaline amendment to composting systems may enable more effective processing of biopolymers, expanding the range and quantity of wastes that can be processes. The enhanced degradation of biopolymers in compost may enable greater diversion rates for institutions and cities by enabling the acceptance of biopolymers and any mixed organics stream which includes biopolymers wastes.     

The Biodegradation and Disintegration of Paper Products in the Composting Environment

The compostability of several paper products was determined according to the standards and criteria of the European standardization committee (CEN). The lignin content of the materials seems to be the main reason for the low biodegradability level achieved in the controlled composting test, which is a biodegradability test based on microbial degradation and measurement of carbon dioxide evolution. Mechanically pulped paper, which contains more lignin and more closely resembles natural wood than chemically bleached paper, generated smaller amounts of carbon dioxide. All the chemically bleached papers generated more than 70% of their organic carbon content as CO₂, while the mechanically pulped unbleached papers in general generated less than 70%. Paper containing mechanical pulp degrades slower because lignin both interferes the biodegradation of cellulose and becomes incorporated in the humus. The test protocol also defines that, even if the biodegradability of paper products is not tested, their disintegration and effect on compost quality have to be determined. In the present study, we also evaluated a number of disintegration test methods in full-scale composting facilities. According to CEN, the disintegration can be studied either in composter bin-scale test equipment or in full-scale composting facilities. In this study, we only present the data from full-scale composting in which several test methods were used to evaluate the degradation of the samples. The disintegration of the paper products in full-scale composting facilities is highly dependent on the method used. The slowest degradation rate was achieved when the samples were composted in nylon bags.     

Treatment of High Ammonium–Nitrogen Wastewater from Composting Facilities by Air Stripping and Catalytic Oxidation

Composting municipal wastewater sludge may generate composting wastewater (acid washer water and tunnel wastewater) with high ammonium–nitrogen (NH₄–N) concentration; this kind of wastewater is usually generated in a rather small daily amount. A procedure of air stripping with catalytic oxidation was developed and tested with pilot-scale and full-scale units for synthetic disposal of the high NH₄–N wastewaters from composting facilities. In air stripping, around 90% NH₄–N removal efficiency was reliably achieved with a maximum of 98%. A model to describe the stripping process efficiency was constructed, which can be used for process optimization. After catalytic oxidation, the concentrations in the outlet gas were acceptable for NH₃, NO_X, NO₂, and N₂O, but the NH₃ and N₂O concentrations limited the feasible loading range. The treatment costs were estimated in detail. The results indicate that air stripping with the catalytic oxidation process can be applied for wastewater treatment in composting facilities.     

墙体材料及其组合对日光温室墙体保温性能的影响

堆肥是由群落结构演替非常迅速的多个微生物群体共同作用而实现固体废物资源化、无害化的动态过程。本文在综合国内外文献资料的基础上,结合本实验室的研究工作,从堆肥过程中微生物群落的演替、有机物降解菌的选育应用、变性梯度凝胶电泳(DGGE)在堆肥微生物研究中的应用等方面介绍了现代堆肥过程中微生物研究的进展及存在问题,并且指出堆肥过程中微生物菌系组成变化复杂和实验手段有限是限制本研究的主要因素,今后应重视利用分子生物学方法进行微生物的研究工作,并根据微生物之间的协同关系有目的地构建降解多种有机废弃物的高效稳定复合菌系,以适应复杂的堆肥环境。     

Mass and Nutrient Losses During the Composting Of Dairy Manure Amended with Sawdust or Straw

Composting has become an increasingly popular manure management method for dairy farmers. However, the design of composting systems for farmers has been hindered by the limited amount of information on the quantities and volumes of compost produced relative to farm size and manure generated, and the impact of amendments on water, dry matter, volume and nitrogen losses during the composting process. Amendment type can affect the free air space, decomposition rate, temperature, C:N ratio and oxygen levels during composting. Amendments also initially increase the amount of material that must be handled. A better understanding of amendment effects should help farmers optimize, and potentially reduce costs associated with composting. In this study, freestall dairy manure (83% moisture) was amended with either hardwood sawdust or straw and composted for 110-155 days in turned windrows in four replicated trials that began on different dates. Initial C:N ratios of the windrows ranged from 25:1 to 50:1 due to variations in the source and N-content of the manure. Results showed that starting windrow volume for straw amended composts was 2.1 to 2.6 times greater than for sawdust amendment. Straw amended composts had low initial bulk densities with high free air space values of 75-93%. This led to lower temperatures and near ambient interstitial oxygen concentrations during composting. While all sawdust-amended composts self-heated to temperatures >55°C within 10 days, maintained these levels for more than 60 days and met EPA and USDA pathogen reduction guidelines, only two of the four straw amended windrows reached 55°C and none met the guidelines. In addition, sawdust amendment resulted in much lower windrow oxygen concentrations (< 5%) during the first 60 days. Both types of compost were stable after 100 days as indicated by CO₂ evolution rates <0.5 mg CO₂-C/g VS/d. Both types of amendments also led to extensive manure volume and weight reductions even after the weight of the added amendments were considered. However, moisture management proved critical in attaining reductions in manure weight during composting. Straw amendment resulted in greater volume decreases than sawdust amendment due to greater changes in bulk density and free air space. Through composting, farmers can reduce the volume and weights of material to be hauled by 50 to 80% based on equivalent nitrogen values of the stabilized compost as compared to unamended, uncomposted dairy manure. The initial total manure nitrogen lost during composting ranged from 7% to 38%. P and K losses were from 14 to 39% and from 1 to 38%, respectively. There was a significant negative correlation between C:N ratio and nitrogen loss (R₂=0.78) and carbon loss (R₂=0.86) during composting. An initial C:N ratio of greater than 40 is recommended to minimize nitrogen loss during dairy manure composting with sawdust or straw amendments.     

A Quantitative Respirometric Method for Monitoring Compost Stability

Compost stability was quantified using dissolved oxygen (D. O.) respirometry during composting of municipal solid waste (MSW) in a pilot-scale system. Changes in stability of samples taken at various times during the composting process were verified with chemical and physical tests. Rates of change of oxygen level in air over a compost sample incubated in a flask at 37°C were converted to a rate of O₂ uptake/(g volatile solids · hour). Oxygen uptake, determined with D. O. respirometry and converted to rates of dry matter loss, was correlated with actual rates, calculated from energy balances observed in the pilot-scale system. The method can be used either as a simple quality control measure or in a more complex way to calculate rates so that efficiency within or among composting facilities can be compared.     

漂浮栽培系统收获植物残体作为番茄育苗基质的应用研究

利用净化猪场废水漂浮栽培系统收获的3种植物残体作为番茄育苗基质的材料，与河沙以不同的比例混合，进行育苗基质筛选。结果表明以美人蕉(Canna indica)残体配制的基质均抑制番茄的生长，番茄在育苗后期全部死亡，而番茄在风车草(Cyperus alternifolius)和香根草(Vetiveria zizanioides)残体配制的基质中均正常生长，其中以风车草残体配制的基质生长较好。香根草的生长相对较差，出现缺氮症状，在使用前应进行适当的堆沤或增加氮肥用量。结果认为风车草和香根草残体作为番茄育苗基质是可行的，而美人蕉残体则有待进一步研究。     

漂浮栽培系统收获植物残体作为番茄育苗基质的应用研究

利用净化猪场废水漂浮栽培系统收获的3种植物残体作为番茄育苗基质的材料,与河沙以不同的比例混合,进行育苗基质筛选。结果表明以美人蕉(C anna ind ica)残体配制的基质均抑制番茄的生长,番茄在育苗后期全部死亡,而番茄在风车草(Cyp erus a ltern if olius)和香根草(V etiver ia z izan ioid es)残体配制的基质中均正常生长,其中以风车草残体配制的基质生长较好。香根草的生长相对较差,出现缺氮症状,在使用前应进行适当的堆沤或增加氮肥用量。结果认为风车草和香根草残体作为番茄育苗基质是可行的,而美人蕉残体则有待进一步研究。     

Using a Biocell to Measure Effect of Compressive Settlement on Free Air Space and Microbial Activity In Windrow Composting

This paper describes the first equipment developed to include compressive loads in a physical model of the composting environment. This new type of composting reactor was named a biological load cell, or biocell for short. Our hypothesis was that the exclusion of compressive settlement in existing physical models may lead to errors if the data is used to design full-scale windrow composting facilities. Municipal biosolids were mixed with three organic amendments (wood chips, straw, and leaves) to yield mixture moisture contents of 55%. Compressive settlement analyses were completed by subjecting the mixtures to loads of 0, 4.3, 8.6, and 12.9 kPa using biocells. The effect of compressive settlement on microbial activity was investigated using the biosolids:leaf mixture under loaded (12.9 kPa) and unloaded conditions. The settlement behavior of all three mixtures was found to fit established soil compaction equations and new equations were developed to represent the vertical free air space (FAS) and bulk density profiles in composting systems. The FAS profiles indicated that existing physical models do not simulate the FAS conditions within a composting matrix and significant differences in microbial activity were observed between loaded and unloaded biocells. The microbial activity differences were attributed to the reduced FAS within the loaded biocells, which, in consequence, lead to lower pore space oxygen concentrations. It proved difficult, however, to simulate the air flow regime within a windrow composting matrix. To further develop the biocells, there is a need to investigate the in-situ stress conditions and natural draft ventilation rates of full-scale windrow systems. While further work is required to perfect the biocells as a physical model of the windrow composting environment, it has demonstrated its potential use for FAS analysis and as a standard bulk density apparatus. Using biocells, it is recommended that FAS curves be developed for a wide range of feedstock recipes. The biocell apparatus could also be developed as a standard bulk density test apparatus. Other important conclusions drawn from the work include: leaves should not be used as a bulking agent; wood chips showed superior bulking properties and are recommended for use in very high (3.7 m) windrows; straw showed intermediate bulking properties and should not be used for high windrows without further investigation; for all materials, compaction occurred rapidly after each incremental load, suggesting that windrow turning will do little to alleviate a low FAS problem associated with an incorrect composting recipe.     

A Comparison of Static Pile and Turned Windrow Methods for Poultry Litter Compost Production

Alternate technologies of compost manufactured from poultry litter (manure) were studied as a means of producing a value-added product for the landscape and nursery industry. Static pile and turned windrow technologies were investigated on a commercial scale with the composting of nearly 300 tons of material. The major difference between the technologies is the amount of energy and labor required. Static pile systems require less energy but more time than windrow turned systems. There was no process advantage found for passively aerated static piles over static piles but costs of passive aeration for pipes and labor were higher than for static piles. Machine turned windrows completed active temperature production within 100 days while portions of both the static and passively aerated piles continued to actively compost past 300 days. Process operational costs and compost quality were similar among the compost methods studied. Production operational cost is driven by the cost of compost ingredients and accounted for 60 to 70% of the cost in the pilot study. Ingredients were poultry litter, wood chips and sawdust. Screened compost was produced at an operational cost of $30 while unscreened compost could be produced for $20 per ton of compost. A production scheme where poultry litter is static pile composted on farms for later transport to regional processing centers appears feasible. This two-part composting procedure will eliminate the transport of raw litter and improve poultry biosecurity. Most likely, a private compost business would provide the expertise, on-farm compost procedures and operate the regional facility.     

Factors Affecting Air Pycnometer Performance For its Use in the Composting Process

Air filled porosity (AFP) is a crucial factor in composting to guarantee aerobic conditions inside the composting matrix. Among the different methods proposed to measure AFP in composting processes, air pycnometry is defined as the most adequate. There is a lack of a standard methodology for air pycnometry utilization for AFP determination in heterogeneous samples as those from composting materials. Air pycnometers currently used for this purpose are custom made instruments operating under different conditions (sample volume, initial pressure, etc.). All factors affecting air pycnometry accuracy in the composting process are related to the proper maintenance and handling of the air pycnometer and the composting sample. In this study, AFP measurements have been performed in more than 50 samples of a wide range of composting materials using two different custom made pycnometers, one of them coupled to a composting reactor allowing in situ AFP measurement. While temperature variation during AFP measurement has been discarded as an error source, the determination of the sample volume has been found to be a significant factor affecting the air filled porosity calculation. Regarding the initial pressure to use, a compromise between accuracy and practicality has to be established for each pycnometer design as AFP values obtained with diverse initial pressures (from 200 to 500 kPa gauge pressure) were found to present no statistical differences. An initial pressure in the range of 300-500 kPa (gauge pressure) is recommended. In conclusion, there is a need for a standard methodology for AFP determination or prediction at industrial scale. A complete procedure for air filled porosity determination by air pycnometry is also presented in this work.     

Physical,Chemical and Biological Processes for Optimizing Decentralized Composting

On-site composting of nonpolluted organic wastes avoids costs and energy for transportation since the volume to be transported can be reduced to about 20% of the original. This paper describes the aerobic processes in a small-scale composting reactor, and evaluates how these processes can be optimized. The optimized composting process has a relatively short turnover time for organic matter; at the same time the temperature of about 60°C decreases the problems with pathogens and weeds in the mature compost. The compost produced has a high nutritional value, with high concentrations of especially nitrogen, potassium and phosphorus, while the contamination by heavy metals and other toxic substances are very low.     

Quantifying the Amount of Yard Trimmings to Be Composted in the United States in 1996

? Based on estimates by the Environmental Protection Agency of the amount of yard trimmings to be generated in coming years, the author calculates that up to 17.1 million tons will be composted in 1996 — the year by which existing state bans on landfill disposal of yard trimmings will all be in effect. Assuming a 50 percent weight reduction through the composting process, up to 8.5 million tons of end product will be generated in 1996. While the estimates provided in this paper are based on assumptions that could be changed by many factors, the calculations do provide springboards for asking questions regarding the composting infrastructure in terms of whas is expected to be in place in terms of educational needs, collection needs, production facilities and effective markets.