Design and application of a pre-composting test step to determine the effect of high fat food wastes on an industrial scale in-vessel composting system

The high fat content in food wastes was suspected to inhibit an industrial in-vessel composting process from reaching the European Union Animal By-Product Regulation (composting temperature >70 °C for 1 h). The aim of this study was to design a test step to guide the mixing ratio of food waste to green waste to meet the regulation. A 15-compartment composting unit was designed to contain the compost mixes. Sausage and cheese wastes were mixed with green waste at 1:1; 1:2; 1:3 and 1:4 ratios by wet weight volume. Only the sausage waste mix ratio of 1:4 gave an average temperature of 70 °C for at least 1 h after 2 days of composting (fat content - 17%; C: N ratio - 8.6). All the cheese waste mixes did not reach 70 °C after 15 days of composting. This study demonstrated that using a simple pre-composting test step could reduce the chances of process failure during industrial composting. Although both sausage and cheese wastes are high in fat, they performed very differently in the composting process. Two linear equations were fitted to model the impact of these wastes on the maximum composting temperature.     

Co-Composting of Soil Heavily Contaminated with Creosote with Cattle Manure and Vegetable Waste for the Bioremediation of Creosote–Contaminated Soil

Mispah form (FAO: Lithosol) soil contaminated with >380 000 mg kg^?1 creosote was co-composted with cattle manure and mixed vegetable waste for 19 months. The soil was mixed with wood chips to improve aeration and then mixed with cattle manure or mixed vegetable waste in a ratio of 4:1. Moisture, temperature, pH, ash content, C:N ratios, and the concentrations of creosote in the compost systems were monitored monthly. The concentrations of selected hydrocarbons in the compost systems were determined at the end of composting. Temperature rose to about 45°C in the cattle manure compost within two months of incubation while temperature in the control and vegetable waste remained below 30°C until the fourth month. Creosote concentration was reduced by 17% in the control and by more than 99% in the cattle manure and vegetable waste compost after composting. The rate of reduction in concentration in the mixed vegetable waste compost was initially lower than in the cattle manure compost. The reduction rate became similar in later months with only small differences towards the end of the composting. The concentrations of selected creosote components were reduced by between 96% and 100% after composting. There was no significant difference in reduction in concentration in both compost systems at p 0.05. Microbial activity correlated with reduction in creosote concentration.     

Development of models for predicting carbon mineralization and associated phytotoxicity in compost-amended soil

Phytotoxicity of compost-amended soil is related to carbon mineralization associated with compost decomposition. The objective of this research was to determine if compost carbon mineralization potential, estimated using compost respiration rate measurements, could be combined with carbon mineralization kinetic models to predict phytotoxicity of compost-amended soil. First-order, second-order, and Monod kinetic models that include compost carbon mineralization potential, compost amendment rate, incubation time, and temperature were developed and compared for their ability to predict carbon mineralization kinetics. Experiments utilized two soil types amended with 0%, 5%, and 50% (v/v) food waste and green waste composts, incubated at 20 degrees C, 25 degrees C, 30 degrees C, 35 degrees C, and 45 degrees C for model development and under a diurnal temperature cycle from 20 degrees C to 30 degrees C for model validation. For most cases, a first-order model had an equivalent or better fit to the data than the other models. Mineralizable carbon estimated using the first-order model was significantly correlated to the probability of phytotoxicity in compost-amended soil.     

Low pH as an inhibiting factor in the transition from mesophilic to thermophilic phase in composting

During composting of household waste, the acidity of the material affects the process during the initial phase of rising temperature. In this study, the effects of temperature (36-46 degrees C) and pH (4.6-9.2) on the respiration rate during the early phase of composting were investigated in two different composts. A respiration method where small compost samples were incubated at constant temperature was used. The respiration rate was strongly reduced at 46 degrees C and pH below 6, compared to composts with a higher pH or lower temperature. The combination of high temperature and low pH is a possible adverse factor in large-scale composting of food waste.     

Rotary drum composting of vegetable waste and tree leaves

High rate composting studies on institutional waste, i.e. vegetable wastes, tree leaves, etc., were conducted on a demonstration-scale (3.5 m³) rotary drum composter by evaluating changes in some physico-chemical and biological parameters. During composting, higher temperature (60–70 °C) at inlet zone and (50–60 °C) at middle zone were achieved which resulted in high degradation in the drum. As a result, all parameters including TOC, C/N ratio, CO₂ evolution and coliforms were decreased significantly within few days of composting. Within a week period, quality compost with total nitrogen (2.6%) and final total phosphorus (6 g/kg) was achieved; but relatively higher final values of fecal coliforms and CO₂ evolution, suggested further maturation. Thus, two conventional composting methods namely windrow (M1) and vermicomposting (M2) tried for maturation of primary stabilized compost. By examining these methods, it was suggested that M2 was found suitable in delivering fine grained, better quality matured compost within 20 days of maturation period.     

Biodegradation of radiolabelled synthetic lignin (14C-DHP) and mechanical pulp in a compost environment

Mineralization of radioactive synthetic lignin (14C-DHP) was studied in a compost environment at 35, 50 and 58 degrees C. Compost samples were successively extracted with water, dioxane and alkali, and the molecular weight distribution of some extracts was determined by gel permeation chromatography (GPC). Biodegradation of lignin-containing spruce groundwood (SGW) and pine sawdust was concurrently determined in controlled composting tests by measuring evolved CO2. The temperatures were the same as in the 14C-DHP mineralization experiment and bleached kraft paper, with a lignin content of 0.2%, was used as a reference. The mineralization of 14C-DHP was relatively high (23-24%) at 35 degrees C and 50 degrees C, although the mixed population of compost obviously lacks the most effective lignin degraders. At 58 degrees C the mineralization of 14C-DHP, as well as the biodegradation of SGW and sawdust, was very low, indicating that the lignin-degrading organisms of compost were inactivated at this temperature. SGW was poorly biodegradable (<40%) in controlled composting tests compared with kraft paper (77-86%) at all temperatures, which means that lignin inhibits the degradation of carbohydrates. During the incubation, water-soluble degradation products, mainly monomers and dimers, and the original 14C-DHP were either mineralized or bound to humic substances. A substantial fraction of 14C-DHP was incorporated into humin or other insolubles.     

Process inhibition due to organic acids in fed-batch composting of food waste – influence of starting culture

Inhibition of the degradation during low pH conditions has been observed in fed-batch composting systems. To analyse this phenomenon, fed-batch composting of food waste with different amounts of starting culture was examined in laboratory reactor experiments. Changes in temperature, carbon dioxide evolution, pH, solids, ash and short chain organic acids were measured. In reactors with a daily feed rate of 24% or less of the starting culture, thermophilic temperatures occurred and the pH and carbon dioxide evolution were high and stable after a starting period of 4–5 days. In reactors with a daily feed rate of 48% or more of the starting culture the composting process failed, as the pH dropped below 6 and remained there and the temperature and carbon dioxide evolution were low. It was concluded that the use of adequate amounts of starting culture consisting of active compost can efficiently prevent low pH conditions and process inhibition in fed-batch composting of food waste.     

Microbial degradation and humification of the lawn care pesticide 2,4-dichlorophenoxyacetic acid during the composting of yard trimmings.

The fate of the widely used lawn care herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) during the composting of yard trimmings consisting of primarily leaves and grass is an important unexplored question. In this study, we determined the extent of 2,4-D mineralization, incorporation into humic matter, volatilization, and sorption during the composting of yard trimmings. Yard trimmings (2:1 [wt/wt] leaves-grass) were amended with 14C-ring-labeled 2,4-D (17 mg/kg of dry weight) and composted in a temperature-controlled laboratory scale compost system. During composting, thermophilic microbes were numerically dominant, reaching a maximum of 2 x 10(11)/g. At the end of composting, 46% of the organic matter (OM) present in the yard trimmings was lost and the compost was stable, with an oxygen uptake rate of 0.09 mg of O2 per g of OM per h, and was well humified (humification index, 0.39). Mineralization of the OM temporally paralleled mineralization of 2,4-D. In the final compost, 47% of the added 2,4-D carbon was mineralized, about 23% was complexed with high-molecular-weight humic acids, and about 20% was not extractable (humin fraction). Less than 1% of the added 14C was present in water expressed from the finished compost, suggesting a low potential for leaching of 2,4-D. Very little volatilization of 2,4-D occurred during composting. It is of interest that our results indicate active mineralization of 2,4-D at composting temperatures of 60 degrees C because microbial 2,4-D degradation at thermophilic temperatures has not been previously documented.     

Growth potential of faecal bacteria in simulated psychrophilic/mesophilic zones during composting of organic waste

Aim: This study investigated the growth potential of Salmonella serotype Typhimurium and faecal indicator organisms in compost materials and the correlation between bacterial growth potential and the physico‐chemical composition of the compost substrate and temperature. Methods and Results: Survival of Salm. Typhimurium, Enterococcus spp. and total coliforms at 14, 24 and 37°C was determined in material of different degrees of maturity collected from composting plants for household waste and manure. All three micro‐organisms showed the potential for growth in the material from active composts (Solvita index 4) but inactivation generally occurred over time in mature compost material (Solvita index 7–8). Conclusions: Salm. Typhimurium had the potential for growth in psychrophilic/mesophilic (P/M) zones of immature compost material and its growth potential correlated negatively with the maturity of the compost and the temperature within the simulated P/M zone. Significance and Impact of the Study: The risk of pathogen regrowth in P/M zones during organic waste composting further emphasizes the importance of good management practices and of avoiding P/M zones in combination with low compost maturity.     

Comparison of characterization and microbial communities in rice straw- and wheat straw-based compost for <Emphasis Type="Italic">Agaricus bisporus</Emphasis> production

Rice straw (RS) is an important raw material for the preparation of Agaricus bisporus compost in China. In this study, the characterization of composting process from RS and wheat straw (WS) was compared for mushroom production. The results showed that the temperature in RS compost increased rapidly compared with WS compost, and the carbon (C)/nitrogen (N) ratio decreased quickly. The microbial changes during the Phase I and Phase II composting process were monitored using denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty acid (PLFA) analysis. Bacteria were the dominant species during the process of composting and the bacterial community structure dramatically changed during heap composting according to the DGGE results. The bacterial community diversity of RS compost was abundant compared with WS compost at stages 4–5, but no distinct difference was observed after the controlled tunnel Phase II process. The total amount of PLFAs of RS compost, as an indicator of microbial biomass, was higher than that of WS. Clustering by DGGE and principal component analysis of the PLFA compositions revealed that there were differences in both the microbial population and community structure between RS- and WS-based composts. Our data indicated that composting of RS resulted in improved degradation and assimilation of breakdown products by A. bisporus, and suggested that the RS compost was effective for sustaining A. bisporus mushroom growth as well as conventional WS compost.     

Composting winery waste: sludges and grape stalks

The composting of winery waste is an alternative to the traditional disposal of residues, and also involves a commitment to reducing the production of waste products. We studied two residues (sludge and grape stalks), mixed in two proportions (1:1 and 1:2 sludge and grape stalks (v/v)), and we also examined the effects of grinding the grape stalks. Our results showed that composting the assayed materials was possible. Best results were obtained in the compost heap in which the residues were mixed in the proportion 1:2, and where the grape stalks had been previously ground. Optimum results required a moisture around 55% and a maximum temperature around 65 degrees C and an oxygen concentration not lower than 5-10%. The resulting compost had a high agronomic value and is particularly suitable for the soils of the vineyards which have a very low organic matter content. The compost can be reintroduced into the production system, thereby closing the residual material cycle.     

Thermal composting of faecal matter as treatment and possible disinfection method--laboratory-scale and pilot-scale studies

When using toilets where the urine and faeces are collected separately for reuse as nutrients in agriculture, the collected matter should be disinfected. One way to do this is by thermal composting. Composting of different material mixes was investigated in a laboratory-scale experiment. This showed that the best mixture for dry thermal composting was a mix of faeces, food waste and amendment. The urine was collected separately by use of urine-diverting toilets. A new method was developed to mathematically evaluate and estimate the safety margins of pathogen inactivation during thermal composting. The method is based upon a mathematical calculation of the number of times total inactivation (at least 12log(10) reduction) of the organisms is achieved. In a pilot-scale experiment, the disinfection of a faeces/food waste mix was performed with a calculated safety margin of more than 37 times the total die-off of Enteroviruses and some 550 times that of Ascaris. Thus, well functioning composting seems to be effective for disinfection of faecal matter. To get a high temperature in all of the material, the reactor has to have sufficient insulation. A major disadvantage is the initial need for handling the raw un-disinfected material. The degradation of the organic matter in the compost was almost 75%, resulting in a small final volume that could safely be recycled.     

Effects of age of cattle,turning technology and compost environment on disappearance of bone from mortality compost

As residual bones in mortality compost negatively impact subsequent tillage, two studies were performed. For the first study, windrows of mature cattle or calves were placed on a base of barley straw and covered with beef manure. Windrows were divided into two sections and turned at 3-month intervals. Approximately 5000 kg of finished compost per windrow was passed through a 6 mm trommel screen, with bones collected and weighed. Bone weight was 0.66% of mature cattle compost and 0.38% of calf compost on a dry matter basis, but did not differ after adjustment for weights of compost ingredients. In a subsequent study, four windrows were constructed containing mortalities, straw and beef manure (STATC) or straw, manure and slaughter waste (STATW). Also, straw, beef manure and slaughter waste was added to an 850 L rolling drum composter (DRUMW). Fresh bovine long-bones from calves were collected, weighed and embedded in the compost. Bones were retrieved and weighed when windrows were turned, or with DRUMW, after 8 weeks. Temperatures achieved followed the order STATW > STATC > DRUMW (p < 0.05). Rate of bone disappearance followed a pattern identical to temperature, with the weight of bones in STATW declining by 53.7% during 7 weeks of composting. For STATC, temperatures were uniform over three composting periods, but bone disappearance was improved (p < 0.05) when compost dry matter was lower (46%), as compared to 58%. Using a ratio of five parts manure to one part mortalities, results of this study demonstrated that residual bone was <1% of cured cattle compost and may be reduced by maintaining a high compost temperature and moisture content.     

双孢蘑菇堆肥中真菌群落多样性分析

以农作物玉米秸和稻草、牛粪为原料,分别设计双孢蘑菇Agaricus bisporus堆肥配方并进行堆肥发酵,研究二者堆肥过程中真菌多样性。在建堆、一次发酵结束和二次发酵结束3个时期分别采集堆肥样品,提取总DNA,以真菌18S rDNA基因通用引物,进行PCR-DGGE扩增和序列分析。累计获得39条特异条带18S rDNA基因信息,分属于真菌14个属、藻类7个属和原生动物3个属。子囊菌是两种配方堆肥过程中的优势菌群,建堆时期的优势类群为Pichia和Wickerhamomyces,一次和二次发酵时期的优势类群为Chaetomium和Lecythophora。多样性指数分析显示,稻草配方微生物多样性大于玉米秸配方;主成分分析（PCA）显示,玉米秸配方一次发酵结束时期与稻草和玉米二次发酵结束时期聚为一类,说明玉米秸配方堆肥提前腐熟。     

Heavy metal contamination of a mixed waste compost: Metal speciation and fate

The aims of this study were to assess changes in heavy metal availability in two contrasting feedstocks during aerobic composting, and the availability of said metals in the finished composts. A high C-to-N ratio mixed biodegradable municipal solid waste (MSW) feedstock was successfully composted on its own and in combination with green waste. Changes in heavy metal speciation throughout the composting process were studied using the modified BCR sequential extraction protocol. It was found that total Cu, Pb and Zn concentrations increased over time due to the progressive mineralization of the compost feedstock. Metals were fractionated differently within the two feedstocks, although only Cu showed significant redistribution (mostly to the oxidisable fraction) over the 5 month composting period. The MSW-derived composts performed comparably with other commercially-available composts in a series of plant growth trials. Plant metal accumulation was not influenced by the heavy metals present in the MSW-derived compost implying that they are not plant available. It is recommended that these relatively low value/quality composts may be used for remediation of acidic heavy metal contaminated sites.     

Composting of lead-contaminated solid waste with inocula of white-rot fungus

The treatment of the simulated lead-contaminated solid waste by composting with white-rot fungus was studied at laboratory scale. The composting system without the inocula of white-rot fungus was prepared as control, and the composting of the uncontaminated solid waste with the inocula of white-rot fungus was carried out as the other control. The results indicated that the solid waste inoculated with white-rot fungus could be successfully processed. The final compost was mature with 70.5% of lead (Pb) in residual fraction and none in exchangeable fraction. Germination index reached 120%. All the results indicated that the bioavailability of Pb in compost was reduced and the potential harm of Pb in compost was alleviated by composting with the inocula of white-rot fungus.     

Determination of degradation of radioactivity and its kinetics in aerobic composting

In this study, the kinetics of disappearance of radioactivity in aerobic composting was investigated. For this purpose, compost materials were prepared by mixing sugar beet wastes, wine factory wastes (grape wastes), straw and biological treatment sludge in different amounts. While alpha-radioactivity was not initially detected in all composting materials, the composting materials had some beta-radioactivity. In the mixtures of sugar beet wastes--straw-biological treatment sludge (1), sugar beet wastes-wine factory wastes (grape wastes)-biological treatment sludge (II) and wine factory wastes (grape wastes)-biological treatment sludge (III), the beta-radioactivity reduced by 82%, 58%, 85% respectively of initial values after 52 d. The beta-radioactivity degradation in the composting process could be represented by first-order kinetics and reaction rate constants of mixtures of I, II and III were k = 0.0693 d(-1) (R2 - 0.84), k = 0.0453 d(-1) (R2 = 0.98), k = 0.0234 d(-1) (R2 = 0.97), respectively.     

翻堆频率对堆肥减量化、腐殖化和稳定化的影响

好氧堆肥是有机固体废弃物处理处置的有效手段之一,堆肥还田也是贫瘠土壤改良的常用措施。但好氧堆肥是一个典型的CO_2等温室气体的释放过程。如何减少堆肥过程中的CO_2释放,强化堆肥的腐殖化过程对于实现有机固体废弃物的低碳化堆肥、提高作为优良土壤改良剂的腐殖质产量具有重要意义。本文选取农林秸秆和餐厨垃圾作为堆肥原料,研究不同翻堆频率对堆肥过程中的物料减量化、腐殖化和稳定化的影响,以期发现一个较低碳的堆肥工艺,并从微生物角度初步探索了其影响机制。研究结果显示,不同的翻堆频率(分别为每2 d、4 d和6 d翻堆一次),堆料的减量化和腐殖化程度有一定差异,翻堆频率为4 d的堆肥工艺物料减量率最高为50.5%,但碳减量率最低为77.4%;而翻堆频率为2 d的堆肥工艺腐殖质产量最高;3种堆肥工艺经62 d堆肥都达到了腐熟程度,翻堆频率为4 d的堆肥工艺腐熟化程度最高。不同的翻堆频率可能通过影响堆肥过程中堆料的温度、含氧量等因素从而改变堆料中活性微生物量、种类和生物酶活性,进而影响堆料的矿化和腐殖化进程。     

Changes in the chemical characteristics of water-extractable organic matter during composting and their influence on compost stability and maturity

Composting is the biochemical transformation of waste organic matter by microorganisms whose metabolism occurs in the water-soluble phase. Therefore, a study of the changes occurring in compost dissolved organic matter can be useful for assessing its stability and maturity. In light of the variety of parameters generally utilized to study composting processes, this work aims at identifying the major chemical processes that occur in solution and their influence on the attainment of stability and maturity with composting time. Compost stability, assessed by means of respirometric analysis which determined oxygen demand as a result of mineralization of the compost's organic matter, and compost maturity evaluated with Lepidium sativum L. seed bioassays, were found to be highly related to the nature and content of water-soluble organic matter. Moreover, fractionation of the water-extractable organic carbon showed that the ratio of hydrophobic to hydrophilic carbon increased to values greater than unity for stabilized compost. These results together with the analysis for non-cellulosic polysaccharides, phenolic compounds and organic nitrogen within the water extracts, confirmed the influence of solubilization, mineralization and organic matter transformation on the quality of the final compost.     

城市污泥强制通风堆肥过程中的生物学和化学变化特征

采用间竭式强制通风堆肥法进行的肥堆体积约4m3,堆肥时间为53d的污泥堆肥试验表明,堆肥的第2天即达高温阶段(≥55℃)并能保持8d,平均最高温度达68℃,局部温度达74℃.粪大肠杆菌由开始时的1.41×105个·g-1降至试验结束时的2.32×101个·g-1.污泥堆肥过程中挥发性固体,总有机C、水溶性有机C、固体有机 C/N比和水溶性有机 C/有机 N比下降明显,而 N、P及重金属含量有所升高.随着堆肥的进程,在前1周堆肥过程中产生的氨氮大幅下降,硝酸盐含量随之升高.相应地,pH在第1周内升高,随后降低.堆肥40d左右,水芹(Lepidiumsativum L.)种子发芽指数即可达 80%.综合堆肥过程中堆温和化学与生物学变化特点,表明污泥堆肥在40d左右基本上接近腐熟,50d后达到完全腐熟.产品外观呈黑褐色,蓬松,无明显异味.